environmental management guideline for the leather tanning & finishing industry

Environmental Management Guidelinefor the Leather Tanning and Finishing Industry

Department of Industrial Works Deutsche Gesellschaft fürTechnische Zusammenarbeit (GTZ) GmbH

Environmental Advisory Assistance for Industry

Environmental Management Guideline

for the Leather Tanning and Finishing Industry

THAILAND

PN 2000.2266.5-001.00

December 1997

IP-Institut für Projektplanung GmbH on behalf of GTZ

Environmental Management Guideline: Leather Tanning and Finishing Industry

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INTRODUCTION The Department of Industrial Works (Ministry of Industry) is implementing the project “Environmental Advisory Assistance for Industry”. This project is executed with support from the German Ministry for Economic Co-operation (BMZ) under the Thai-German Technical Co-operation Programme through the German consulting firm “IP-Institut fuer Projektplanung GmbH” under contract from “Deutsche Gesellschaft fuer Technische Zusammenarbeit – GTZ”. An important activity of the project is the introduction and preparation of industry sector specific environmental management guidelines. The guidelines for the leather tanning and finishing industry are part of this activity and describe alternative methods for utilisation of residues and by-products, waste avoidance and minimisation and give recommendations on how to achieve, in the most cost-effective way, overall environmental management requirements. Sector specific effluent standards from the legal part of the guidelines. These standards can be achieved by implementing the described alternative environmental management methods. The content of the guidelines is the result of teamwork in the “leather tannery” working group. This working group consists of representatives from the Department of Industrial Works, Pollution Control Department, Federation of Thai Industries, Tannery Association of Thailand and the Chulalongkorn University’s Department of Environmental Engineering as well the Environmental Engineers Association of Thailand. The Department of Environmental Engineering has been contracted as consultant for the development of the guidelines. Besides discussion and approval of the guidelines content, the working group also agreed on the effluent standards described for this industrial sector. The project implementing agency, Bureau of Industrial Environmental Technology within the Department of Industrial Works (Ministry of Industry), hopes that the introduced co-operative approach, which led to this guideline, will support both, the industry as well as the environmental control agencies, in applying cost effective environmental management. For further information concerning additional details please feel free to contact the Bureau of Industrial Environmental Technology at the Department of Industrial Works – Ministry of Industry – Bangkok. Bangkok – December 1997 Director Bureau of Industrial Environmental Technology Department of Industrial Works Ministry of Industrial Works


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GLOSSARY eliminate get rid of. solid waste all waste in solid form such as hoof, hair, skin, and sediment residues. rotten egg gas hydrogen sulfide gas. It smells bad like rotten egg and results from

decomposition (reduction) of sulfate in polluted water. This gas is frequently found in tanneries with insufficient wastewater control.

waste unwanted or spent matter which is released into the environment. chromium a heavy metal which is toxic to the nervous system. sulfate a sulfur chemical compound. It may change (reduce) to sulfide. See

“sulfide” and “hydrogen sulfide.” sulfide a sulfur chemical compound. It may change (oxidize) to sulfate, or

lead to the generation of hydrogen sulfide (rotten egg gas) which has bad smell. See “sulfate.”

COD unit to measure pollution of waste water. It includes both organic and

inorganic substances. This value is related to BOD value, and is normally many times higher than BOD. High value indicates high amount of pollution. See “BOD.”

TDS Total Dissolved Solids. It means dissolved substances, mineral, or

mineral salts in water that cannot be filtered by normal filtration but removed by membrane technology.

BOD unit to measure pollution of waste water in the form of organic

substances. High value indicates high amount of pollution. See “COD.”

pollution contamination with waste substances (solid, liquid or gaseous) such

as hair, hoof, animal foot, waste water, lime solution, chromium solution, hydrogen sulfide, ammonia, etc., at a level which causes environmental degradation.

sammying reducing the amount of water contained in anything by pressing,

studding, squeezing or throwing. Sludge soft mud of residue which settles during sedimentation. suspended solids any solid substances (rotten or unrotten) suspended in water, which

settle after a certain period of time. pollutant substance which causes environmental degradation, See “pollution.” VOC Volatile Organic Compound. They are mostly solvents used in

polishing agents and machine cleaners. These substances are highly volatile, and therefore can be easily inhaled and may cause cancer.

ammonia a kind of gas irritating to the nose. In big amount it can cause

inflammation of the respiratory system.


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CONTENT page

SECTION I Effluent and sludge standards for the leather tanning and finishing industry

I Background and description 6 II Effluent standards 8 III Standard for chromium concentration in sludge 9 SECTION II Environmental management guidelines for the Leather

Tanning and Finishing Industry Chapter 1: Introduction 11 Chapter 2: Production Process in Leather Tanning Industry 2.1: Beamhouse Process 14 2.2: Tanning Process 14 2.3: Finishing Process 15 Chapter 3: Sources of Waste 3.1: Raw Hide Preservation 16 3.2: Hide Washing and Soaking 16 3.3: Unhairing and Liming 16 3.4: Fleshing and Splitting 17 3.5: Deliming of Splittings 17 3.6: Pelt Deliming and Bating 18 3.7: Pickling and Chrome Tanning 18 3.8: Sammying and Shaving 19 3.9: Neutralization, Re-tanning, Dyeing and 19 Fat Liquoring for Chrome Tanning 3.10: Vegetable Tanning 20 3.11: Summary of the Properties of Combined Wastewater 22 from Thai Tanning Industry 3.12: Summary of Pollution Load 22 Chapter 4: Method for Minimization of Waste and Wastewater Pollution from Production Process 4.1: Wastewater Pollution Minimization 23 4.1.1: Techniques for Reducing Water Consumption 4.1.2: Reduction of Sulfide in Liming / Unhairing 4.1.3: Recycling of Lime Solution 4.1.4: Deliming by Using Carbon Dioxide (replacement of ammonium salts) 4.1.5: Reduction of Chromium in Effluent a: Chrome High Exhaustion Tanning b: Reusing of Tanning Solution c: Recycling of Chromium d: Substitution of Chromium with other


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chemical tanning agents 4.2: Reduction of Solid Waste Problems 32 4.2.1: Waste from Hide Preservation Step 4.2.2: Waste from Fleshing and Splitting Step 4.2.3: Chrome Shavings 4.2.4: Shavings from Finishing 4.2.5: Solid Waste from Spraying or Lacquering Step 4.2.6: Residue from Wastewater Treatment System Chapter 5: Waste and Wastewater Treatment 5.1: Sulfide Wastewater Treatment from Unhairing Step 38 a: Sulfide Oxidization with Manganese Salt as Catalyst (Air Oxidation) b: Sulfide Oxidization with Hydrogen Peroxide c: Chemical Precipitation with Iron Salt 5.2: Chromium Wastewater Treatment 40 5.3: Combined Wastewater Treatment 42 5.4: Disposal of Chromium Waste 44 a: Chromium Sludge/sediment b: Residue from Combined Wastewater Treatment System c: Chromium containing Solid Waste Chapter 6: Monitoring and Control 6.1: Process Control 45 6.2: End of Pipe Treatment Control 45 6.3: Monitoring and Control by Government Agencies 49 References 50 Appendix A: Reuse of Solid Waste from Leather Tanning Industry 51 Appendix B: Recovery of Protein and Chromium from Chrome Shavings 53 Appendix C: Recycling of Chromium in Leather Tanning Industry 55 Appendix D: Basic Methods for Wastewater Analysis 64


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SECTION I Effluent and Sludge Standards for the Leather Tanning and Finishing Industry I BACKGROUND AND DESCRIPTION

I.1 Former Standard (B.E. 2525)

According to the announcement by the Ministry No. 12 (B.E. 2525) issued in accordance with the Factory Act (B.E. 2512), the standard of effluent for all kinds of factories is as follows: - pH between 5-9 Sulfide not exceeding 1 mg/l Chromium “ 0.5 mg/l SS “ 30 mg/l (normal value used) BOD “ 100 mg/l

I.2 New Effluent Standard for Tanneries Pollution problem becomes more and more serious. Therefore, the governments of many countries throughout the world develop more suitable effluent standards, which are improved continuously. Herein, the effluent standard for monitoring and control of leather tanning and finishing industry in the country has been agreed upon as follows: -

I.2.1 Tanneries grouped in clusters The majority of tanneries in Thailand are located in clusters such as Km-30 group and Km-34 group, Samutprakarn province. Both clusters of tanneries use a central wastewater treatment system – an indication of discharges and waste streams of the central treatment plant is shown in Fig I.1. Wastewater discharged from the beamhouse (area a.) contains toxic sulfide, which besides creating odor problems is also highly toxic and, hence, should be treated (oxidised) separately at its origin in the beamhouse.

For the chromium wastewater from tanning (area b.) of each tannery, if there is no preliminary chromium treatment, there will be the problem of chromium accumulation in the joint wastewater treatment system both in the form of effluent and sludge or sediment.

Wastewater from other parts (area c.) contains mostly organic substances, which can be purified directly in the central treatment system.


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Factory Factory Factory A B C A B C A B C Central wastewater final treatment system effluent Sewer / collection canal

D E sludge / cake Dredging sludge Remark : (a) effluent containing sulfide from beamhouse

(b) chromium containing effluent (c) other effluents

Fig. I.1: Central waste water treatment system - indication of waste streams and discharges In this case, the prescribed effluent standard should be controlled separately at three different positions as recommended in the following Table.

Table I.1: Standard for Joint/Central Wastewater Treatment Parameter beamhouse tanyard central treatment system

pH - - 5.5 – 9.0

Sulfide 2 - 1 mg/l

Chromium - 30 -

Cr. III 0.75 mg/l

Cr. VI 0.25 mg/l

SS - - 50 mg/l

BOD - - 20 mg/l

COD - - 120 mg/l

I.2.2 Single or independent tannery without using joint treatment system The effluent standard for single tanneries for the parameters BOD and COD is changed to 60 mg/l and 400 mg/l respectively. The standard for other parameters, including chromium, has been kept as the same value used for effluent from tannery clusters i.e. central wastewater treatment systems. (See right column in Table 7.1).


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II EFFLUENT STANDARDS 1. pH Apply the existing standard of 5.5-9.0

The existing standard can be followed since it does not require additional investment for compliance by the tanneries and this standard sufficiently protects the environment.

2. Sulfide

Regarding to Development Document for Effluent Limitations, Guidelines for the Leather Tanning and Finishing of U.S. EPA by Anne M. Gorsuch and partners, November, 1982, it has been stated that sulfide could be treated to zero. However, in order to be in accordance with the local condition, it has been fixed to 1 and 2 mg/l respectively. – as compared to the standard in other countries it is between 0.01-300 mg/l . (See Table 5 attached).

3. Chromium

The standard is 0.75 mg/l for Cr.-III – which will be 0.5 mg/l and 0.25 mg/l for Cr.-VI, after 3 years from the date of announcement of these standards. Operational data of the joint wastewater treatment system of tannery complexes at KM 30 and 34 during the period 1991-1992, reveal that good quality effluent can be produced. This is indicated by an average chromium content of 0.7 mg/l, even at the absence of any chromium minimisation / treatment measures by the tanneries. If proper chromium management is introduced and applied by the tanneries, a final effluent quality with a chromium concentration lower than 0.5 mg/l can be achieved. The emission standard for the wastewater discharged from the chromium treatment (or recycle) system at the chrome tanning section has been fixed to 30 mg/l. This standard can be achieved as proven by pilot plant tests. Chromium content standard in solid waste (sludge) from tanneries has been set as max. 1,000 mg/kg of dry weight basis. This standard has been based on experience and data from Germany, which are based on the application of best practical technology (at proper chromium management a standard of 800 mg/kg dry weight basis can be achieved). Information from UNIDO/UNEP suggests that sludge which is used for agricultural purposes should contain a chromium value not exceeding the range 1,000-1,500 mg/kg (dry weight basis).

4. SS

The standard is 50 mg/l which is in accordance with the new standard announced for enforcement by Pollution Control Department and Department of Industrial Works. This standard can be achieved readily, using a properly operated biological treatment system. Data collected from the wastewater treatment system of the tannery complex indicate that this standard has not been achieved in the past. However, this was caused by improper operation as well as overloading of the biological treatment system.


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5. BOD

20 mg/l is used as effluent standard for joint wastewater treatment systems, which are considered as factory category 101 factories and as an industrial estate, which generates high pollution loads and hence has a strong environmental impact.

60 mg/l is used as effluent standard for an individual tannery because it is regarded

as a factory category 29 and has less environmental impact.

At present water pollution produced by the tanneries is very serious. Therefore, control measures must be more drastic and effluent qualities have to be in accordance with the standards announced by the Department of Industrial Works and the Pollution Control Department for enforcement. BOD effluent standards applied for tanneries in other countries are in the range of 5-200 mg/l. If tannery effluent is allowed for discharge into the city sewage system and subsequent treatment in a joint domestic wastewater treatment plant, the applied standard is in the range 150-1,700 mg/l.

6. COD

120 mg/l is as effluent standard for joint wastewater treatment, which is considered as factory category 101 factories and as an industrial estate, which generates high pollution loads and hence has a strong environmental impact.

400 mg/l is used as effluent standard for an individual tannery because it is regarded as a factory category 29 and has less environmental impact. The standard for this parameter (COD) has been developed based on COD / BOD ratio. This ratio has been established for combined tannery wastewater to be in the range of 6-8.

III STANDARD FOR CHROMIUM CONCENTRATION IN SLUDGE In the absence of chromium pre-treatment system, the generated excess sludge (area D) as well as the sludge in the drainage mud (area E)– will contain an excessive amount of chromium. After collecting and analysis of sludge samples from various areas in the tannery complex, it was found that the sludge collected at area d. showed a chromium concentration as high as 8,000-15,000 mg/kg of dry-weight basis. The dried excess sludge from the joint wastewater treatment system showed chromium content in the range of 10,000-17,000 mg/kg of dry-weight basis. This problem can be controlled and managed by the introduction and application of a suitable chromium pre-treatment or recycle system. If the best practical technology is applied in tanneries, the standard for chromium content in sludge can be achieved which is as follows:


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Chromium concentration in sludge from tanneries must not exceed 1,000 mg per kg of sludge (dry-weight basis) Sludge containing less chromium than the above standard is regarded as non-toxic substance, and can be disposed off at a garbage landfill site or used for agricultural purposes. The sludge or sludge cake from the chromium treatment or sedimentation system which contains a high concentration of chromium, if not dissolved and reused, has to be delivered to the Industrial Waste Treatment Service Center for correct treatment and landfill.


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SECTION II ENVIRONMENTAL MANAGEMENT GUIDELINES FOR THE LEATHER TANNING AND FINISHING INDUSTRY CHAPTER 1 INTRODUCTION Environment and pollution problems at present are issues of utmost interest of most countries. The Department of Industrial Works has been conscious of the graveness of industrial pollution problems if protective measures are not established and applied. Therefore, it has considered to move the industrial entrepreneurs to appropriately manage their factory environment so that pollution problems will not grow to an incurable scale. Consequently, the Environmental Advisory Assistance for Industry Project has been set up with technical cooperation from the government of the Federal Republic of Germany (GTZ). This guideline is a part of the project which focuses on the local leather tanning and finishing industry. Objective

The objective of this “Environmental Management Guideline for the Leather Tanning and Finishing Industry” is to provide practical advise and information to the leather tanners for selection and implementation of waste minimization measures (both for solid waste and wastewater), or recycling of waste (directly or indirectly) as well as correct operation of wastewater treatment. By using this guideline, the industrial entrepreneur will understand the importance and possibilities of environmental management in his factory. This in turn will result in improved cooperation with the government agencies responsible for industrial pollution control during actual implementation of pollution abatement and control measures in order to reduce the industrial pollution problem to its minimum. Meanwhile the government officers can use this guideline as a manual for tannery supervision. By introducing this cooperation approach, the public sector aims at reducing the confrontation between the industrial sector and the responsible government agencies. This subsequently will result in improved understanding which will further strengthen the development of the country. Details

This guideline contains both technical data as well as data on management of industrial solid wastes and wastewater from tanneries, beginning from raw materials to the final products. The guideline will cover the following issues:

a) Production Process describing the different steps of each stage of the production process. b) Sources of Waste

presenting basic data on waste generation at different production steps. This will contribute to improved understanding of pollution generation, and will be the basis for planning and implementation of suitable waste management measures.

c) Methods for Pollution, Wastewater, and Solid Waste Minimization in Factories

In order to reduce pollution loads and waste treatment costs, these methods


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comprise minimization of pollution at their source of generation, substitution of chemicals, or waste recycle, etc. In this part, the guideline will present cost-benefit data for Thailand. The scope of data, however, depends on the availability of relevant back-up figures.

d) Wastewater Treatment

Although there are effective measures for pollution and waste minimization, but if pollutants still remain in wastewater, it still has to be treated before it is discharged from the factory into the environment. For the wastewater treatment system there may be separate treatment for different types of wastewater before all wastewater is combined for final treatment.

e) Follow up and Control

It presents a guideline for production process control, control of treatment system, methods as well as frequency of sampling according to purposes, methods of sample analysis and recording of results.

f) Effluent Standard for Tannery Supervision

Tanning industry generates wastewater with unique characteristics, different from other industries. Therefore, the standard of wastewater after treatment should also bee tannery specific. This guideline proposes a standard, which should be applied to the local condition including a standard for the amount of chromium in solid residue.


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CHAPTER 2 PRODUCTION PROCESS LEATHER TANNING AND FINISHING INDUSTRY The leather production process is divided into three main steps namely beamhouse process, tanning process and finishing process as shown in Fig. 2.1. raw hides delivered to tannery soaking liming & unhairing fleshing

Beamhouse splitting Process

deliming, bating pickling vegetable tanning chrome tanning Tanning Process wet blue neutralization sammying shaving Wet fat liquoring & dyeing Finishing re-tanning fat-liquoring, dyeing drying drying Dry crust Finishing finishing and spraying finished leather

Fig. 2.1: Schematic diagram - Leather tanning and finishing process.


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2.1 Beamhouse Process In the beamhouse process, unwanted parts such as hair, skin, hoof, etc. are removed from raw hides. The raw hides are prepared for the subsequent tanning process. There are liming, unhairing with sulfide, fleshing, trimming, deliming and bating. The wastewater from this process is characterized by high alkalinity and contains high concentration of both suspended solids (skin, hair-mud) and oil/grease. In addition, chemicals used in this production step, such as lime, soap, ammonium salts, alkaline, sulfide and bactericide are discharged with the beamhouse wastewater. After the pre-treated hide is split, the top part of the hide, called upper hide or grain, is used for production of finished leather. The lower part is called lower hide or split. 2.2 Tanning Process After hides are cleaned and cut into required sizes, they are tanned. Tanning is to change decomposable raw hide to finished hide which is more stable, not decomposed, and resistant to weather condition and hot water. This is done by chemical reaction between natural tannin, chromium or other chemicals and collagen (protein) in the hides.

Two types of tanning processes are mainly used for the production of leather. They are chrome tanning which uses chromium as tanning agent, and vegetable tanning which uses natural tannin or synthetic substances. Chrome tanning is more popular, because it is faster and cheaper. In addition, the chrome-tanned leather is more resistant to heat and humidity. Prior to tanning, pickling with salt is a necessary step for both processes. Salt, sulfuric acid and formic acid are used in the pickling process. The purpose of pickling is to adjust the pH value to a level which is suitable for the tanning reactions. During the tanning process, specific chemicals (high exhaustion chromium fixing reagents) may be used, in order to increase chromium uptake, and to reduce the residue chromium concentration of the float - wastewater. a) Chrome tanning is carried out in rotating drums with the addition of basic chromium

sulfate (Cr3+

) as tanning agent. Normally about 70% of the chromium added will react with the leather and is

chemically fixed into it. The remaining 30% will be discharged with wastewater. Chromium fixing in leather can be increased by adjusting pH value. Therefore, in chrome tanning sodium carbonate is gradually added in order to adjust pH level to about 4.5.

The leather after the chrome tanning process is called wet blue.

b) Vegetable tanning can be carried out either in rotating wooden tanks or in a series

of concrete tanks. Natural tannin which is used as tanning agent in this process is extracted from quebraco trees, bark of eucalyptus trees, etc. The tanning liquid can be reused. The important step is to remove excess vegetable tanning agent by the addition of oxalic acid. This is important for achieving good final leather quality. The finished leather is heavier than the one from chrome tanning. It is mostly used for making shoe-sole and belts. Its production cost is higher than chrome tanning.

After tanning the leather will be sammied to become dry, trimmed with a trimming machine, and classified according to its quality. Then it is ready for sale or further processing.


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2.3 Finishing Process Re-tanning is usually carried out for wet-blue to improve its quality according to the market requirements. In this step the chemical used may be chromium, tannin or syntan (a synthetic chemical). Leather dyeing may or may not be carried out depending on market demand. The dyeing process itself depends on the type of dye used. Normally formic acid is used for pH adjustment before dyeing. Up-take of dyes on the leather is facilitated at increased temperature. Steam is usually used to heat up the leather and the dyeing liquor. To ensure that the final leather is soft and stable, fat-liquoring is necessary for the tanned leather. It may be carried out simultaneously with re-tanning or dyeing, or it can be carried out separately. After this process, the leather will be taken for spraying, pattern printing, etc., according to the demand of the market.


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CHAPTER 3 SOURCES OF WASTE

Leather tanning is a production process in which animal hides are transformed by using of water, chemicals and mechanical process. Therefore, wastewater from the process will contain a high concentration of pollutants. Moreover, this process also generates solid waste. In this respect, the character of wastewater, the pollution load as well as the amount of solid waste depend on the type of production process including the source of the tanning. The main steps which produce waste are concluded as follows: 3.1 Raw Hide Preservation

Preservation of raw hides is not part of the actual tanning process, but is necessary to preserve raw hides from decomposition. Salt, about 20% of the weight of raw hides, is normally used for pickling of raw hides. In the preservation step, the hides will lose moisture, about equal to the amount of salt added. In addition, bactericides and insecticides are also used for preservation of hides. Therefore, prior to the actual tanning process, the salt must be removed which is normally carried out by shaking of the raw hides. This salt is the first type of solid waste generated by the leather tanning process. If the removed salt is disposed off in an environmentally unsound way it will negatively affect plant growth, aquatic life, and will increase salinity in the water bodies including ground water which may become unfit for drinking purpose or steaming tanks. 3.2 Hide Washing and Soaking During this step hides are rehydrated. Surfactants and alkaline are added for the removal of dirt. The effluent from this process contains BOD, COD, salt, insecticides and bactericides, flesh scraps, hair, skin and dirt (see Fig. 3.1).

Remark: BOD and COD are summary parameters for the characterization of pollution. High values of BOD and COD indicate high water pollution.

Fig. 3.1: Wastewater generation from hide washing and soaking process. 3.3 Unhairing and Liming Liming and unhairing is one of the steps which produce effluent with very high pollution load. Wastewater discharged from this step contains residues of hair, epidermis as well as other dirt accumulated in the hides. The combination of lime (to swell the hides), salt and sodium sulfide (for unhairing) together with bactericides and insecticides accumulated in the hides will be also discharged along with the effluent. The effluent will have high pH, high concentration of BOD, COD, salt, sulfide, insecticides and bactericides, ammonia, alkaline and suspended solids. Solid waste generated are hair-sludge, lime and sludge. Hydrogen sulfide gas (rotten egg gas) is emitted in case insufficient alkaline is added resulting in a pH lower than 9.5.

water, surfactants, washing, soaking BOD, COD, salt, alkaline insecticides, bactericides (waste)


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rotten egg gas water BOD,COD, water, sodium sulfide, lime liming and unhairing salt, ammonia, alkaline, suspended solids hair, lime and sludge Remark: Ammonia gas causes irritation of the respiratory system and results in breathing problems. Hydrogen sulfide gas has very strong smell and is highly toxic. Discharge of suspended solids will reduce the depth of water ways and in addition will create anaerobic conditions due to the decomposition of organic material in the sediment. Hair, lime and sludge will contribute to the clogging of water ways.

Fig. 3.2: Waste from liming and unhairing process. 3.4 Fleshing and Splitting Hide which has been limed/unhaired will be fleshed by a scraping machine. Subsequently the defleshed hide will be split by “splitting machine”. Water buffalo’s skin can be split in upto 3-4 layers. Two of the upper layers will be taken to chrome tanning. Inner or (lower) layer will be delimed before taken to be used further for dog chew production. Main waste generated from this step is fleshings and scraps from the lower part of hides (see Picture 3.3). These hide scraps have dark green color due to the chemical reaction during the step of unhairing and liming. The liquid effluent from this step is small in volume, and has similar composition as the wastewater generated from the liming step but with lower concentration. fleshing and trimming fleshing and hide scraps for reuse water splitting wastewater upper splits tanning dog chew Fig. 3.3: Waste from fleshing and splitting step with potential for reuse 3.5 Deliming of Splittings For deliming of splittings, ammonium chloride is added to reduce leather swelling. Acid is introduced for neutralising purposes, reducing the pH to 7-8. At the same time the splitting is decoloured by using hydrogen peroxide as oxidizing agent. The waste water generated has muddy white color containing BOD, COD, salt, sulfate, ammonium, alkaline, suspended sludge and chloride.


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This production step may be omitted in some tanneries. splittings ammonium chloride + water, BOD, COD, salt, hydrogen peroxide sulfate, ammonium, + deliming of splitting alkaline, suspended sulfuric acid solid, chloride + water for dog chew production Remark: Chloride is compound of salt. If discharged into the water, the water will be brackish and has

only limited usage. Fig. 3.4: Wastewater generation from “deliming of splittings” 3.6 Pelt Deliming and Bating Pelt deliming and bating is used to reduce pH level of the pelt with the addition of ammonium chloride and/or ammonium sulfate. Addition of these chemicals must be sufficient to eliminate the action of lime completely. Enzyme or bate is added to smooth and soften hide tissues. Therefore, wastewater generated from this step will contain BOD, COD, salt, sulfate, ammonium, alkaline, suspended solid, and chloride. Ammonia gas is also emitted at this step. water, BOD, COD, salt, sulfate ammonium chloride/ ammonium, alkaline ammonium sulfate+bate deliming and bating suspended solid, chloride +water ammonia gas Fig. 3.5: Gaseous emissions and wastewater generation from deliming process 3.7 Pickling and Chrome Tanning Pickling is done to adjust pH level of the pelt to the range of 1.4 - 3.0 which is suitable for subsequent chrome tanning. Sodium chloride or sodium sulfate and sulfuric acid are added for the pH adjustment. The pickling takes 1-2 hours. Subsequently, basic chromium sulfate is added as tanning agent, reacting with protein in the hide. Normally 70% of chromium added will remain in the chrome tanned hide. Some tanneries add “tanning aid” during pickling (for high chromium up-take and reduction of chromium concentration in the


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wastewater). Chromium chemical fixation will be more effective if the pH and temperature levels are increased. The wastewater from this step will contain acid, salt, suspended solid, BOD, COD, and chromium. Float residues will contain chromium, and will be discharged along with the effluent. (The concentration of chromium in the effluent is about 2,000-4,000 mg / l). sulfuric acid + formic acid + Feliderm CS pickling (and adding (tanning aid) of tanning aid) water, BOD, COD, salt Diachrome R acid, suspended solids, (basic chromium III sulfate) chrome tanning chromium float residues sodium bicarbonate chrome fixation Remark: Chromium is a heavy metal hazardous to living creatures and dangerous to the nervous system. Fig. 3.6: Wastewater generation from chrome tanning process 3.8 Sammying and Shaving Sammying generates a certain amount of effluent which the composition is similar to the effluent from chrome tanning. Shaving generates ‘chrome shavings’ which is solid waste containing chromium. These shavings create a big problem to the environment and have to be disposed off at a secured landfill site. Disposal at domestic garbage landfills, or by incineration is not recommended. sammying wastewater residues shaving chrome shavings, trimmings (with chromium)

Fig. 3.7: Solid waste and wastewater generation from sammying and shaving.

3.9 Neutralization, Re-tanning, Dyeing and Fat Liquoring for chrome tanned “wet-

blue” Neutralization is to increase the pH level to between 5 and 6 by adding sodium carbonate for the removal of residue chromium and to prepare wet-blue for subsequent re-tanning and dyeing processes. Therefore, chromium is present in the effluent from this step along with suspended solids. Re-tanning is performed simultaneously with fat liquoring. Formic acid, syntans (synthetic tanning agent) and fat liquor are added. The chemicals which are not absorbed by the hides will be discharged along with the effluent in which chromium is also found. See Figure 3.8.


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Wet dyeing is usually applied to chrome tanned hides. It is to dye the entire hide. It is not similar to colour spraying or painting which are usually applied to vegetable tanned hides. Chemicals, dyes, organic acid and hot water is applied for the completion of dyeing. All these substances are to be found in the effluent. Even though this step generates a very small effluent volume, it must be segregated and pre-treated in a sedimentation tank for removal of suspended pigment; the supernatant must be taken to the treatment system for further purification. wet-blue water soaking water, chromium ammonium salt/ BOD,COD, ammonium sodium bicarbonate neutralization suspended solid +water syntans + fat chrome re-tanning and fat liquoring water, acid, chromium

BOD, COD, syntans, fat formic acid acid fixation dyes dyeing water, dyes, fat formic acid acid fixation drying finishing and spraying Fig. 3.8: Wastewater from neutralization, re-tanning, fat liquoring and dyeing. 3.10 Vegetable Tanning Process Vegetable tanning is carried out in rotating wooden tanks, or in a series of concrete tanks, by adding tanning agent extract from eucalyptus bark, quebraco tree, etc. Owing to the high prices of chemicals, vegetable tanning liquid is usually not discharged but re-used. Only vegetable tanning agent is added to the tanning pit. Therefore, there is no negative effect to the environment, since there is no effluent emission. The effluent from the subsequent two-stage washing step creates more problem. Washing of vegetable tanned hides is carried out with the addition of oxalic acid which will be discharged with the effluent along with the surplus vegetable tanning agent (see Figure 3.9). Shavings from vegetable tanning contain no chromium, and can be disposed off as normal garbage. Hence, they do not create any problems to the environment. Coloring of vegetable tanned leather is carried out by painting/spraying colour on the leather surface. It creates only a small effluent volume (see Figure 3.10). This wastewater may be treated with


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plain sedimentation method for removal of suspended solids. Then the supernatant will be discharged to the combined wastewater treatment system of the tannery. sulfuric acid + formic acid pickling tannin from tree barks vegetable tanning acid absorption and oxalic acid + water surplus vegetable water, acid, tannin tanning agent washing drying shaving shavings, trimmings (without chromium) Fig. 3.9: Effluent generation from vegetable tanning process


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fat+dyes+water dyeing/fat liquoring water, dyes, fat drying finishing drying finished leather

Fig. 3.10: Effluent generation from dyeing / fat liquoring of vegetable tanned leather.

3.11 Summary – Average characteristics of combined wastewater generated from

tanneries in Thailand (unit is in mg/l except for pH value) average minimum-maximum pH 8.15 6.67-8.64 BOD 1,535 958-4,200 COD 4,150 2,433-8,100 TKN 394 215-644 SS 2,097 1,027-4361 TS 13,857 9,118-21,881 Cr 77.68 18-204.4 3.12 Summary of Pollution Load Precisely, pollution load from the tanneries will depend on type and amount of chemicals used, but average pollutant emissions will be as follows: Germany Thailand Unit pH 3.5-12 - - COD 90-100 80 kg/ton raw hide BOD 5 28-40 28 kg/ton raw hide Chromium (total) 1.5-3 1.4 kg/ton raw hide Sulfide 5-6 - kg/ton raw hide Heavy sediment (sinkable) 70-100 - kg/ton raw hide Suspended solid - 40 kg/ton raw hide TKN - 7.16 kg/ton raw hide Wastewater 20-30 10-30 m3/ton


23

CHAPTER 4 METHODS FOR MINIMIZATION OF SOLID WASTE AND WATER POLLUTION FROM PRODUCTION PROCESS

Minimisation of solid/liquid waste from the production process is to reduce the amount of waste to be taken for disposal or treatment. Accordingly, pollution load and disposal costs are reduced. Minimisation applies to all media i.e. liquid waste (wastewater), solid waste and gaseous emissions. Cleaner production measures shall be applied as indicated in the diagram below. There are 4 main methods of waste minimization called 4R as follows: 1. Replace. If it is known which chemical or raw material will create a lot of problems, others should be used instead, for instance, aluminum may be used instead of chromium for tanning. 2. Reduce. If it is still needed, its use should be reduced, for instance, using less water to wash the tank. Or it could mean to reduce the waste, for instance, recycling of water or chemicals repeatedly without discharging as waste water, etc. 3. Reuse. Means, i.e. collecting spent chemicals or any material already used, in a tank and use it again. 4. Recycle. Various processes can be used to extract some substances from the waste then use them in the production process again. For instance, chromium extracted from spent liquor from the chrome tanning process can be recycled to the tanning drum. This 4R method can be used in every step of a tannery’s production process and is described in detail below: 4.1 Minimisation of Wastewater Volume and Pollution Load Wastewater volume and pollution load can be reduced by:

- minimising water consumption (which will also reduce the volume of wastewater), - using chemicals effectively, and - reuse/recycle chemicals.


24

Pollution Minimisation Possibilities in the tanning industry Pollution Problem Application of Chemical in Each Main Step Creating Clean Technology Result Step Pollution Problem Effluent with dirt and Using lime and sodium sulfide for Unhairing Reusing of hair Reducing BOD in effluent high value of BOD, unhairing COD, and sulfide Using enzyme for unhairing Reducing sulfide in effluent Effluent with high Using ammonium salt Deliming Changing to use carbon Reducing ammonia in value of ammonia dioxide for deliming effluent Chromium in effluent Using chrome tanning agent Tanning Using chromium fixing aid Reducing chromium in and shaving-residues having chromium oxide effluent Reuse of chromium in Reducing chromium in effluent effluent Using other kind of tanning no chromium in effluent agent without chromium Odor and vapour of Using solvent based colour Finishing Changing to use water Reducing odor and vapour dye solvent based colour of dye solvent


25

4.1.1 Techniques for reducing water consumption The techniques which can be easily applied are: - Use a suitable size of container to reduce the problem of water overflow. - Install flow meters to measure the use of water in every step, and record the daily use

of water. This will help monitor whether there is over-use of water. - Use mechanised system for chemical dosage and water filling. - Use the counter-current system of washing, i.e., use clean water to wash rather clean

leather or piece of work (already washed briefly), then use more dirty water (already used for leather washing) to wash very dirty leather or piece of work. This will save a lot of water.

- Avoid excessive water consumption for washing purposes. - Do not use the system of soaking hides in a tank and allow continuous water overflow.

It should be improved by soaking hide firstly in water for a long time, and using the washwater in that tank repeatedly until it becomes too contaminated and has to be discharged.

- Reuse water (after pre-treatment) in operations which do not require high water quality, for instance, hide soaking, lime mixing, floor cleaning, tank cleaning, etc.

4.1.2 Reduction of sulfide in liming and unhairing Sulfides can generate the emission of “rotten egg” gas which has not only a very bad smell but is dangerous to the respiratory system . It is highly toxic and poses a severe health risk at relatively low concentrations. Therefore, minimisation of sulfide application should be considered. One possibility for the reduction of sulfide application is the use of “enzymes” in the unhairing process. This method will reduce the amount of sulfide required for unhairing and subsequently leads to lower concentration of sulfide in the wastewater as well as a reduced risk of high H2S emissions However, this enzyme unhairing process is slightly costlier than the conventional sulfide unhairing process. 4.1.3 Recycling/reuse of lime solution In the unhairing step hides are soaked in a lime solution, containing sodium sulfide. Hairs will be gradually decomposed in this chemical solution and will form a hair sludge, which also contains non-decomposed hair and hide parts. In normal practice, the spent unhairing solution will be discharged after use. Reuse of the unhairing solution is possible if the hair sludge is removed by fine screening and adding fresh lime and sodium-sulfide to ensure sufficient chemical concentration. This reuse method will reduce sulfide load in the waste water but requires that the hides are thoroughly cleaned in the washing step, thus needing more water in the washing process. The unhairing solution can be reused about 10 times and requires, besides the screening equipment, sufficient storage capacity as well as equipment for the analysis of lime and sulfide in the spent solution. The disadvantage of this method is that the wastewater from this unhairing procedure will contain a higher concentrations of organic substances (indicated by an increased COD value) and in addition has a strong smell.


26

The advantages of this reuse method are: - does not require changes in the production process - easy operation - has no negative effect on the quality of leather

Reuse-method The spent unhairing solution will be pumped from the rotating tank to a fine screen (filter) for separation of the hair sludge. Then, this “filtered” lime solution will be pumped back to the rotating tank (See Fig.4.1), where lime and sodium sulfide is added to the required concentration. This method can be also applied with the paddle tank. This screen (filter) used can be of rotating type made of stainless steel or plastic. Lime solution (recycled) Sodium-sulfide reused Rotating Drum or paddle tank Lime drain Pump Screen Fine Screen

Hair / solids Separation Tank

Fig. 4.1: Lime solution recycle.

Cost Unhairing time requirements are usually one day for cow hides and two days for buffalo hides. Water consumption is about 3 cubic meters per ton of raw hide. Usually, the quantity of hide unhaired each time is 6 tons, therefore, the wastewater generated by each unhairing batch is about 18 cubic meters. The construction costs for a spent solution storage tank including the screens is about 30,000-40,000 Baht . Cost recovery is normally within two years. 4.1.4 Deliming with carbon dioxide (instead of using ammonium salt) After unhairing it is necessary to adjust the hide condition (pH) to make it suitable for the subsequent tanning process. This is achieved by deliming using ammonium salt and diluted sulfuric acid. Therefore, the deliming process generates high ammonia gas emissions, which


27

irritate eyes, nose and lungs, etc. (See Fig 4.5). Ammonia compounds in the wastewater are toxic to fish and have to be treated properly prior to final discharge. Therefore, the amount of ammonium salt used for deliming should be controlled carefully to avoid negative health and environmental impacts.

Alkaline(remaining lime)Ammonia Salt

Ammonia Gas

Fig. 4.2: Emission of ammonium gas in the conventional process of deliming. In order to eliminate both, the discharge of ammonium salt in the effluent as well as ammonia gas emissions in the tannery, the method of carbon dioxide (CO2) deliming can be applied. . The carbon dioxide gas will chemically react with lime and will form “lime stone” (See Fig. 4.6). This method is suitable for split hides with a thickness not exceeding 3 mm. Investment costs for this deliming method is high. Limitations are the longer deliming time requirements and the risk of H2S gas emissions because of lowering of the pH value. Therefore, hydrogen peroxide has to be added to the deliming process to ensure the oxidation of sulfide, avoiding rotten-egg gas odour problems.

Liqu

id C

O2

Heating Coil

CO2 Gas

Hide Soaking/Deliming Tank

Fig. 4.3: Carbon dioxide gas deliming system.

4.1.5 Reduction of chromium in effluent Prior to the chrome tanning process, the delimed hides are pickled with sulfuric acid for pH adjustment. Subsequently the tanning agent, basic chromium (III) sulfate with a chromium content of 26 % (as Cr

2O

3) is added. The amount of chromium required for tanning is in the

range of 8-10 % of hide weight. Time required for chrome tanning carried out in wooden drums, is about 8-10 hours.


28

Chromium will chemically react with the carboxyl group of the protein in the hides. The fixed chromium makes the hides stable and gives the necessary strength. However, the hides will absorb only 65-70% of the chromium added. Therefore, chromium will remain in the spent chrome tanning liquid, which is normally discharged as waste water. The overall discharge of chromium from a typical tannery is shown below - 20% remaining in the effluent from chrome tanning, can be reused/recycled - 2% in the liquid remaining in the tanned hide layer - 8% in the effluent from sammying (sammying float) - 3-5% in the shavings, hide tissues and scraps. - 2-7% in the re-tanning liquid. The volume of waste water generated by the chrome tanning process (residue float) is about one cubicmeter per ton of raw hide. The residue float has an average chromium content of about 3 g./ l. (or 3,000 mg/l) if the conventional (standard) chrome tanning process is applied. The concentration of organic substances and suspended solids in this wastewater is relatively low. Therefore, methods for residue float utilisation and/or chrome discharge minimisation should be introduced and applied . The following three methods for chromium discharge minimisation have been proven and are applied successfully: a) High-exhaustion chrome tanning process At present so-called “tanning aids” or “chromium absorption aids” are used in the high exhaustion chrome tanning process. By using these agents, which improve the chromium uptake, the total amount of chromium required for tanning can be reduced. This subsequently results in reduced chromium content in the residue float (wastewater). One brandname of these tanning aids is Feliderm CS. A comparison of tanning chemicals required in the standard tanning process and the high exhaustion process is shown below: weight of hides soaked with lime 1,000 kgs. without tanning aid using tanning aid chromium used = 8%x1,000 = 80 kgs. chromium used = 5 % x 1,000 = 50 kgs. (remark: reducing chromium from 8% to 5%) chromium price=80 kgsx25=2,000 B chromium price=50 kgsx25=1,250 B Feliderm CS price =10 kg x 100 B Total of chromium & tanning aid =2,250 B (chromium in effluent = 3,700 mg/l) (chromium in effluent = 1,300 mg/ l) Fig. 4.4: Comparison between standard and high-exhaustion chrome tanning process

(using Feliderm-CS) The above diagram indicates that the chromium content in the effluent from the high exhaustion chrome tanning process is only 1,300 mg Cr/l) as compared to 3,700 mg/l from the standard chrome tanning process. However, the reduced chromium concentration is still by far too high for direct discharge and has to be further reduced by proper treatment, by chemical precipitation and sedimentation. Moreover, the application of a complex organic compound like the tanning aids has shown to make chromium precipitation and sedimentation more difficult. In addition, the application of tanning aids requires good process control to achieve satisfactory leather quality.


29

b) tanning solution reuse After tanning a high concentration of chromium still remains in the “residue float” . If this liquid is collected and refurbished with fresh tanning agent (basic chromium sulfate) the residue float can be reused for tanning purposes. This will lead to reduced chromium load discharged from the tannery. However, the residue float must be correctly analyzed for its remaining chromium content as well as salt content and concentration of organic substances. The residue float has to be discharged whenever the content of salt and organic substances reaches a pre-determined maximum concentration. Usually, the residue float can be reused for a period of up to 3-4 months. c) Recycling of chromium Chromium recycling is carried out by separating chromium from the residue float by means of chemical precipitation using Magnesium oxide (MgO). The chromium hydroxide sludge is separated from the solution by sedimentation and dissolved in sulfuric acid for subsequent use as tanning agent. A schematic diagram of the chromium recycling process is shown in Fig. 4.5 and 4.6. This method has a proven high chromium recovery efficiency, is simple in its operation & maintenance and has no negative effect on the leather quality. The chromium removal efficiency by this process is more than 90%, resulting in tremendously reduced chromium load from a tannery.


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ChromeTanning Drum

Spent chromeliquor (residue

float)

Precipitation Tank

Dissolution

Sedimentation

Chrome solution(high chromeconcentration)

Alkaline - MgO- dosage

Sulfuric Acid

ChromeRecycled chrome

solution

Supernatant (Chromereduction 90%)

discharge to furthertreatment

Fig. 4.5: Schematic flow-diagram of chromium recycle process used in leather

tanning industries


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Fig. 4.6: Leather Tanning – Chrome recycle system Using “quick methods” for the analysis of chromium in the “residue float” the required amount of MgO-solution/suspension can be determined by using the following table: the value of chromium readable (g / l) 1 1.5 2 2.5 3 the volume of MgO to be added ( l ) 100 150 190 240 290 Remarks : 1) residue float volume = three cubic meters

2) 10% MgO solution, prepared by using MgO 30 kgs./300 liters of water the solution must be prepared 1day beforehand and must be stirred all the time during working period.

Further details of the chrome recycling method, including the cost-benefit analysis, can be seen in Appendix C of the guidelines It can be concluded that at an investment cost in the range of 300,000-500,000 Baht (depending on the size of tannery) and if the high-exhaustion tanning process (tanning aid Feliderm-CS) is not used, the payback period of the chrome recycling system is around 2-3 years. However, if the high exhaustion chrome tanning process is used, the chrome recycling system will not cover costs, which is mainly resulting from the comparatively low chromium concentration in the high-exhaustion “residue float”.


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Table 4.1 indicates the amount of chromium which can be recycled (indicated as chrome tanning agent “Diachrome R”) at different volumes and concentrations of the recycled chrome solution. Table 4.1: Volume of chromium recycle in the form of tanning agent (Diachrome R) in kilograms.

Chrome solution (liter)

Chrome conc. (gram / liter)

300

350

400

450

500

550

600

650

700

750

800

15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0

18 24 30 36 42 48 54 60 66 72

21 28 35 42 49 56 63 70 77 84

24 32 40 48 56 64 72 80 88 96

27 36 45 54 63 72 81 90 99

108

30 40 50 60 70 80 90

100 110 120

33 44 55 66 77 88 99

110 121 132

36 48 60 72 84 96

108 120 132 144

39 52 65 78 91

104 117 130 143 156

42 56 70 84 98

112 126 140 154 168

45 60 75 90

105 120 135 150 165 180

48 64 80 96

112 128 144 160 176 192

d) replacing chromium with other chemical tanning agents Aluminum, zirconium, titanium and ferrous salts (II) can be used as replacement for chromium as leather tanning chemical. But the leather which is tanned using these chemicals has a lower quality than chrome-tanned leather both in terms of softness and thickness. In addition, chrome tanned leather has higher resistance to heat, indicating that leather tanned with other chemicals (replacing chromium) may not be suitable for the shoe industry. The advantage of this chrome-free tanning process is the absence of chrome shavings. Shavings from this process, therefore, can be either taken to a domestic landfill site for disposal, or can be reused for the production of leather board or fertiliser or roof tiles. 4.2 Minimisation of Solid Waste Solid waste herein means residue of animal skin, hooves, horns, pieces of bones, small pieces of hide, dry sludge from wastewater treatment system, etc. 4.2.1 Solid waste from hide preservation After cutting the hides from the animals they must be preserved in order to prevent decomposition. Normally, the raw hides delivered to the tanneries are preserved by pickling with salt. This salt is removed before the beamhouse process by manually shaking the hides. The collected salt is sometimes disposed off at unsecured landfill sites. This procedure can create problems to the environment because salt makes the soil unsuitable for agricultural purposes. In addition, salt may be dissolved by rainwater and absorbed into the soil and water which may destroy plants and aquatic flora and fauna. If the tannery is situated near to the sea, this problem may be not as serious because of the already brackish water and salty soil in that area.


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Solid waste from this production step, apart from salt, are excrements from animals, blood, hair and small pieces of hide. Methods of solid waste minimisation at this step are:- a) chilling of raw hides (hide preservation)

storing raw hides at low temperature to prevent decomposition (cooling can be done by using dry ice and/or liquid carbon dioxide)

- preservation method is rather expensive, special transportation system and insulated container is required.

- suitable for tanneries situated next to an agricultural sensitive area. b) separation and collection of salt for reuse - salt reuse method is as follows: collect salt mix with saturated salt solution crystallization of purified salt for reuse

- the problem is to find the place where this clean salt can be reused. Salt has to be transported to the slaughterhouse for preservation of hides.

- This salt reuse system is mainly used in India.

Another possible area of reuse is within the tannery in the production areas of hide soaking, pickling and preservation of splittings.

c) production management If hide preservation is not required in the first place, this solid waste (salt) problem will be eliminated altogether. This can be achieved through the introduction of an effective production planning and management system, including good cooperation between the slaughterhouse and the tannery. This system has to assure that the raw hides are transported to the tannery and processed in the beamhouse within 24 hours after collection in the slaughterhouse. 4.2.2 Solid waste from fleshing and splitting activities The solid waste generated by fleshing and splitting activities consists of small pieces of unusable hide scraps and animal foot or hoof scraps. This solid waste has a commercial value and can be used for production of dog chew, glue, gelatin incl. medical capsule and sausage skin, etc. In addition, this solid waste can be used for the extraction of fat, which is used as raw material for the production of cosmetics or soap. Details of the utilization of this waste in other production will be shown in Fig. 4.7 and Table 4.2 as well as in Appendix A.


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Raw hide Limed hides fleshings & other solids upper split lower split pelt fish feed split deliming gelatin and/or lime soaking gelatin glue production deliming dog toy / dog chew chrome tanning wet blue “dry” blue after shaving shavings & trimmings retan & fat liqu. solid waste cushion polishing of leather board manuf. Aluminum

utensils Fig. 4.7 Schematic diagram: Flow of raw material, products and by-products of the different hide

processing steps


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Table 4.2: Solid waste minimization in the leather tanning industry. Step Waste Method of utilisation/treatment Other countries Local at present 1. Pre-tanning process Fleshing trimmings, fleshings with lime collagen, fat fish food, fertilizer protein food Splitting lower hide with lime collagen, gelatin dog chew, upper hide sausage skin, gelatin and glue dog chew 2. Tanning process Chrome tanning Shaving shavings with chromium glue, noise filter burying, disposal gelatin, animal food, fertilizer, absorbing- products, leather board Vegetable tanning hide scraps fertilizer, leather sheet, disposal, low cost leather absorbing products, leather board 3. Ornamentation hide scraps with chromium and low cost leather sale, disposal dyes 4.2.3 Chrome shavings At present, chrome shavings along with unusable hide scraps and cuttings are generally disposed off along with domestic garbage and/or are burned in the open. However, because of its high environmental impact this method of solid waste disposal should be abolished urgently .If the chrome shavings are disposed off at an unsecured landfill, chrome salts which can be washed off from the shaving can contaminate groundwater resources. Incineration (burning) of chrome shavings will transform (oxidise) the chrome(3) compounds into chrome(6) compounds which are highly toxic and carcinogenic. These hide scraps can be reused for the extracting protein and the recovery of chromium which can be reused in the tannery. Protein can be recovered by this method through digestion of the chrome shavings in a strong alkaline solution. Subsequently, the residue from the alkaline extraction will be digested in sulfuric acid for the recovery of chrome. The recovered chrome-sulfate can be recycled to the tanning process. The extracted protein can be used in the glue production industry or for animal feed purposes. The final residues (after chromium extraction) have fertiliser value and can be reused for gardening purposes. A schematic flow diagram of the chrome shaving utilisation process is shown in Fig. 4.8. Additional details of this reuse method can be found in Appendix B. The Asian Institute of Technology (AIT) has demonstrated and evaluated (including cost-benefit analysis) the above chrome shaving utilisation system at a tannery with a production


36

capacity of 100 hides per day. This pilot project indicated that the operation and maintenance costs of the chrome shavings reuse system are about 252,000 Baht/year, resulting in a payback period in the range of 5-7 years. The payback period depends on the size of the tannery as well as on the price of the by-products, such as protein (animal feed stuff) or glue. Another reuse method for chrome shaving is the production of leather board which can be used for the production of a variety of goods i.e. noise insulation materials, inner-shoe layers, dividers in bags as well as for the production of shoe-heels or low cost leather products (low quality handbags, book-cover, tool-box. A schematic flow diagram of the leather board production process is shown in Fig. 4.9. 4.2.4 Shavings and other solid waste from the finishing section Large size scraps from the ornamentation process can be sold for the production of low cost leather goods. Smaller size scraps are of value for the furniture industry where they are used as lining material. Furthermore, the small scraps are used in the production of kitchenware, particularly for the polishing of aluminium. Buffing dust from the leather finishing section must be collected properly and disposed off at the landfill site of the Industrial Waste Treatment Service Center. Because of the chromium content in the tanned leather, incineration of these leather shavings and solid waste is banned. Incineration of this solid waste will transform (oxidise) the chrome(3) compounds to the more toxic and carcinogenic chrome(6) compounds, creating a serious health and environmental risk. shavings alkaline digestion with alkaline dissolution of protein animal food, gelatin residue sulfuric acid chromium extraction chromium solution used in tanning residue organic fertilizer

Fig. 4.8: Protein and chromium extraction from shavings.


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shavings

milling leather scraps in a pulverizer

crushing and mixing leather scraps with chemicals

passing mixture through “vacuum” machine to produce sheet

smoothing leather sheet with calendering machine

pressing with hydraulic press

leather board

Fig. 4.9: Production of leather-board from shavings. 4.2.5 Solid waste from colouring and lacquering process It is prohibited to dispose off solid waste from this production step, consisting of solvents and colour/paint residues, at garbage landfill sites. Many of the solvents used in the tanneries are not only highly inflammable but toxic and carcinogenic. If this solid waste is incinerated, the temperature used has to be not lower than 600 C. 4.2.6 Residue from wastewater treatment system At present, the wastewater treatment systems applied in tanneries in Thailand purify the combined tannery wastewater, consisting of wastewater from the tanyard (containing chromium) mixed with wastewater from the beamhouse and other discharges (containing mostly organic substances). As a result, the generated excess sludge from the combined wastewater treatment system contains high concentrations of chromium and has to be disposed off as hazardous waste. The most suitable method to ensure that the excess sludge from the wastewater treatment system is “chrome free” and can be used either for agricultural purposes or is allowed for disposal at a domestic waste landfill, is to separate as much as possible chrome containing wastewater from the overall wastewater. Chrome containing wastewater has to be treated separately for either recovery/recycle of chromium or removal of chromium (treatment) by chemical precipitation and save disposal of the chromium sludge. The pre-treated “chrome fee” wastewater from the tanyard subsequently can be combined with other wastewater streams for further biological treatment. Further details of the chrome treatment system are given in Chapter-5.


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CHAPTER 5 WASTEWATER AND SOLID WASTE TREATMENT Tanneries in general will discharge wastewater from the various production areas into a single collection drain, leading to the wastewater treatment system. However, because of the type and amount of chemicals applied in the different production steps, as well as because of the different reactions taking place in the various productions steps, the composition/characteristics of wastewater generated in each production step, shows big variances, as shown in Chapter 3 of the guidelines. Therefore, separate treatment (or pre-treatment) of wastewater generated at the different production steps should be considered, which could reduce overall wastewater treatment costs for a tannery.. The main process steps at which wastewater should be pre-treated prior to mixing with other wastewater streams are the unhairing process in the beamhouse and the chrome tanning process in the tanyard. 5.1 Sulfide wastewater pre-treatment from the unhairing step Unhairing is a production step in which a very high pollution load is generated. About nine cubic meters of wastewater per ton of raw hides (9 m3/ton) are generated, having the following characteristics:- Pollutants Concentration Unit BOD 13,000 - 50,000 mg/l pH 12 - 13 - sulfide 500 - 1,400 mg/l The high content of sulfide in this waste water is of particular concern. Sulfide treatment systems applied both in Europe and USA are oxidization and chemical precipitation/sedimentation. These treatment methods are described as follows:

a) Sulfide Oxidation with Manganese Salt as Catalyst (Air Oxidation) Sulfide containing waste water (spent unhairing liquor) is collected in a suitable tank. A predetermined amount of Manganese (Mn

2+) salt is added and the tank content is aerated by

introducing air by means of a blower-diffuser system. Sulfide will be oxidized/transformed into thiosulfate, sulfite and sulfate ( which are more inert than sulfide). Details of system design and operation are shown in Fig. 5.1 and Table 5.1 respectively Pressure air Manganese salt solution Wastewater Collection P Oxidation treated effluent Sulfide Screen Sump Tank for further purification

Fig. 5.1: Sulfide Oxidation Treatment Process.


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Table 5.1: Design and Operation of Sulfide Oxidation. % of Plant Flow Treated Catalyst Mn

++ Batch Oxidation Time Aeration Equipment

Type mg/l (hour) HP/1000ft3 KW/1000m

3

100 MnSO4 31 3-10 1.5 (40) 40 MnSO4 9.1 4 - (-) 40 MnSO4 55 7 4.2 (110) 15 MnSO4 91 8 1.8 (47) 25 MnSO4 302 8 1.3 (34) 40 MnSO4 51 8 3.8, 5.2 (100, 137) 100 MnCl2 0.3 24 1.5 (40) 100 MnSO4 79 960 0.14 (4) 40 MnSO4 - 2-3 1.5 (40) * batch means the total period of time required for complete chemical reaction - tank emptying - tank filling and chemical addition etc.. Indicating that this is not a continuous process. In general, this waste water contains sulfide with a concentration in the range of 1,200- 1,400 mg/l which can be treated by the introduction of air at the ratio of 1 m3 air/minute/m3 of waste water or 20 m3/hour/m2 (m2 of water surface area) at a tank depth of not less than 4-6 meters. Pressurized air is supplied for a period of 6-12 hours and Manganese sulfate is added in the range of 50 and 100 g per m3 of waste water - both, mechanical surface aerators as well as submersible aerators can be used for the supply of air. The collection tank must be equipped with a bottom scraper for the collection and removal of sediments. During the introduction of air, hydrogen sulfide gas (rotten egg gas) and ammonia gas will escape from the tank causing odor problems. The correct method is to cover the tank and withdraw the contaminated air, by means of an exhaust fan, to a biofilter purification system - the air disposal rate should be 1.5 m

3/hour per m

2 of water surface area.

Remarks :

1) - If pH is lower than 8, there will be the problem of hydrogen sulfide gas (bad smell, can lead to death at a concentration of 2,000 ppm)

- If pH is higher than 10, there will be the problem of generation of ammonia gas - pH should be managed in the range 9-10

2) - sulfide concentration in the treated effluent can be lower than two (2) mg/l.

b) Oxidation of Sulfide with Hydrogen Peroxide (H2O2) This method is used successfully to oxidize sulfide in tannery wastewater. Investment costs for construction of the chemical reaction tank and purchase of chemical dosing equipment are low, however the cost of Hydrogen peroxide is rather high. Therefore, this method is suitable for small tanneries with little effluent from Unhairing activities (for instance discharging Unhairing liquor 1-2 times a week). In this oxidation method, the effluent is collected in the chemical reaction tank, pH of the liquid is adjusted to below 8, followed by the addition of Hydrogen peroxide. At a pH value below 8.0, sulfide will be oxidized to sulfur. If the pH is higher than 8, sulfide will be oxidized into sulfate. However, oxidation to sulfate requires 3 times more Hydrogen peroxide than oxidation to sulfur. Therefore, it is important for economic reasons to adjust the pH of the waste water below 8 before adding the peroxide solution.


40

About 200 mg/l of Hydrogen peroxide is required to reduce sulfides from an initial concentration in the range of 100-300 mg/l to less than one (1) mg/l in the treated effluent.

c) Chemical Precipitation with Iron Salt Precipitation of sulfide with iron salts is another effective method of reducing sulfide concentration. There might be incidental removal of other pollutants in this process too, i.e. suspended solids and BOD. The iron salts may be available at a low price from the steel industry - using their spent pickling liquor (acid). However, this method has disadvantages, i.e. bad smell, effluents with very black color, high chemical requirements, and a rather high cost for Ferrous-sulfate (in case spent acid from the steel industry is not available and the chemical has to be purchased). In addition, this process generates a voluminous sludge which has to be taken for further treatment. Since this sludge is not suitable for agricultural purposes the treatment and disposal costs are quite high. 5.2 Chromium Wastewater Treatment The treatment method used for the purification of wastewater from chrome tanning, sammying of wet-blue, re-tanning and dyeing is chemical precipitation of chromium with alkaline solution (such as lime) and discharge of the supernatant for further biological treatment. A tank similar to the one which has been designed for recycling of chromium can be used (see item 4.1.5c). The alkaline used for chromium treatment does not have to be MgO (which is much more expensive than other alkaline chemicals – in particular CaO) since the created chromium hydroxide sludge is not taken for reuse in the tanning process. The most suitable chemicals for chromium treatment are lime (CaO), Sodium Carbonate (Na2CO3) and caustic soda (NaOH). To achieve rapid sedimentation of the precipitated chromium-hydroxide sludge (adding lime solution until a pH of about 8.5 is achieved) either Anionic Polyelectrolytes or Ferric chloride can be added. The chromium removal efficiency by this physico-chemical treatment system is more than 98%. The effective amount the sedimentation aids (Ferric chloride and/or polyelectrolyte) has to be established in Jar tests. The settled chromium-hydroxide sludge should be dewatered either by means of a filer press or at a drying bed. The dried sludge cake should be properly packed, signed and sent to the Industrial Waste Treatment Service Center for further treatment and final disposal. The supernatant from either the chromium treatment system or the chromium recycling system still has a high concentration of organic substances and has to be sent to the biological wastewater treatment system for further purification. (see Fig. 5.3 and Item 5.3 for a description of the overall wastewater treatment system). However, it has to be emphasised that the volume of hazardous sludge (chrome containing) produced from this chrome treatment step is much less compared with the volume of sludge generated by a combined wastewater treatment system without a pre-treatment system for chrome containing waste streams. In addition, if chrome pre-treatment systems are installed, the excess sludge generated from the joint wastewater treatment system will contain very low chromium concentrations and, hence, can be used as fertilizer or disposed off at a domestic landfill site. This excess sludge then is not classified as hazardous waste anymore. Therefore, the costs which have to be paid to the Industrial Waste Treatment Service Center for special treatment of sludge with excessive chromium concentrations can be reduced substantially. The hazardous waste related costs are then only for transportation and treatment of sludge produced by the chrome tanning wastewater pre-treatment system to/at the Industrial Waste Treatment Service Center. It is estimated that about 0.12-0.25 ton of sludge/ton of raw hides are generated by the chrome treatment system. The total chrome-sludge disposal cost thereby depend on the distance the sludge has to be transported i.e. from the tannery to the


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Service Center (see Table 5.2).

Wastewater from wastewater from wastewater Chrome tanning drum sammying machine from retanning wastewater

Equalization tank \\\\ (SCREEN) Lime (CaO) Ferric-chloride Reaction and Chrome supernatant polyelectrolyte Sedimentation Tank discharged to the combined sewer chrome sludge for further treatment filtrate sludge drying bed or filter press dry sludge cake (to be sent to the industrial waste

treatment service center) Fig. 5.2: Chromium Wastewater Treatment System - Chemical Precipitation.

Table 5.2: Treatment and disposal cost for excess sludge from leather tanning industry wastewater treatment system.

solid waste treatment 400 Baht/ton transportation (loading) 250 Baht/ton transportation from tannery to the Center 2.50 Baht/ton-km transportation of waste from the Center for landfill in Ratchaburi 190 Baht/ton landfill 250 Baht/ton Remark: The above price is adjusted on 25 September 1996.

For tanneries in the Samutprakarn province, the total service cost is about 1,500 Baht per ton. (This price may be changed according to investment condition).

-------------------------------------------------------------------------------------------------------------- * Volume of chrome effluent ........................ about 0.5-0.75 m3/ton of raw hides Volume of chromium sludge ..................... about 0.2-0.3 m3/m3 effluent

or about 0.1-0.2 m3/ton of raw hides or about 0.12-0.24 ton/ton of raw hides


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5.3 Combined Wastewater Treatment The treatment system applied in the leather tanning industry normally emphasizes on the removal of organic substances (BOD), sulfide and chromium. A schematic diagram of the treatment process is shown in Fig.5.3, indicating chromium wastewater segregation and separate chromium treatment. Subsequently, the pre-treated effluent from this precipitation/sedimentation process will be combined with the wastewater from unhairing step and with overall tannery wastewater to be discharged into the pump sump from where it will be transferred for further biological treatment. The first step of the biological treatment is an anaerobic system (no mechanical aeration equipment and hence no electricity consumption at this step). In this process bacteria which do not require oxygen will digest organic compounds in the wastewater and purifying the same. However, treatment efficiency of the anaerobic system is not sufficient to allow discharge of the effluent to a water body. Therefore, the pre-treated effluent from the anaerobic treatment is further purified in an aerobic system. This method is characterized by the requirement of oxygen for biological oxidation. Oxygen is supplied by mechanical aeration systems resulting in high electricity cost. At this treatment step, another kind of bacteria (aerobic) will further digest organic compounds of the wastewater until it is clean enough for discharge into a public water source.

Operational data obtained from the combined wastewater treatment system of the tannery cluster at km 30 Samutprakarn indicate average electricity costs of about 420,000 Baht/month - total operating cost i.e. including personnel cost, chemical cost, etc. are reported as 900,000 Baht/month equal to a total wastewater treatment cost of about 3 Baht/cubic meter (excluding costs for chemicals, personnel, water analysis, equipment maintenance, etc.)


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Fig. 5.3: Combined Wastewater Treatment System of Tannery Industry.


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5.4 Disposal of Chromium Containing Solid Waste

a) Sludge from Chromium Treatment System

Dewatered sludge from the chrome treatment (precipitation) system contains high concentrations of chromium; exceeding the standard prescribed for landfill or agricultural use. (See Table 5.3). Therefore, this sludge is considered as hazardous waste and must be treated at the Industrial Waste Treatment Center – the treatment/disposal costs are shown in Table 5.2 above.

Table 5.3: Recommended standards for Chromium (III) concentration in

soil and sludge for agricultural use (by UNIDO/UNEP) concentration in soil, mg/kg dry soil 150-200 concentration in sludge, mg/kg dry sludge 1000-1500 total metal added in agricultural area 300-600 (a), (c) amount added in agricultural area per year (kg/hector/year) 45 (b), (c)

Remark: (a) for the soil with background concentration of 50 mg/kg, the increase of

concentration is allowed to be 100-200 mg/kg, at 25 cm depth and soil density of 1.20.

(b) total metal accumulation in a period of 100 years must not exceed 450 kg/hectare

(c) total increased value must not exceed the concentration standard in the soil.

b) Excess sludge from combined/joint biological wastewater treatment system After segregation and separate treatment of chromium wastewater, the combined wastewater will contain only minimal chromium concentrations. Therefore, the excess sludge produced in the combined/joint biological treatment system will contain a chromium content not exceeding 800 mg/kg dry solids (experience from Germany). This sludge can be either disposed off at a domestic landfill site, or used for agricultural purposes. The disposal costs for this type of solid waste consist mainly of the transportation cost to the landfill site (or to the agricultural area) and landfill costs which are much lower than treatment cost for hazardous waste landfills.

c) Solid waste containing chromium Chromium containing solid waste, such as chrome shavings, (if these chrome shavings are reused) has to be sent for treatment and landfill at the Industrial Waste Treatment Center in Ratchaburi province. Incineration is prohibited because it will result in the creation of highly toxic and carcinogenic Cr(+6) compounds. Hence, transferring solid waste pollution problems into air pollution problems.


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CHAPTER 6 MONITORING AND CONTROL

In order to minimise the environmental impact from tanneries it is necessary to introduce suitable measures for pollution related to both the production process and the wastewater treatment system, including proper operation and supervision. To achieve this in both, individual tanneries and tannery the environmental management guidelines for the leather tanning and finishing industry must be applied. Moreover, the tanners should cooperate closely with government officers, responsible for supervision, follow up and control of pollution control measures at the production process and the wastewater treatment system. This regular co-operation will result in continuous improvement of the environmental management system at the tanneries and will correct any operational problems and deficiencies. 6.1 Process Control Tanners should pay special attention to the following issues: - Good house keeping - Development of production process, applying clean technology or less polluting technology - Improvement of control and supervision of the different production steps in order to ensure proper operation of the different equipment and avoid the discharge of pollutants to the environment

- Introduce wastewater segregation, especially separating the wastewater stream from the chrome tanning section from other wastewater

-Chromium recycle system should be installed in case of the tannery without application of chromium absorption agent (Feliderm-CS). However, when

Chromium absorption agent is applied, it is necessary to install and operate a chromium pre-treatment system to remove chromium to the prescribed level of 30 mg/l.

- Measure and control the volume of water and chemicals applied in each production step, keep records of consumption ratios in relation to the amount of hides processed

- train operators and workers in the safe handling of chemicals and cleanliness of the tannery

- Install signboard to show the name of chemicals used in the production process and their potential danger. Introduce proper storage of chemicals.

6.2 End of Pipe Treatment Control Correct collection of samples from end-of-pipe wastewater treatment systems is required to avoid the generation of wrong information concerning operation, efficiency and compliance of the final effluent quality with the prescribe standards. A correct and quick estimation of the treatment efficiency will depend on the following factors:- 6.2.1 Method of sample collection

There are basically two main methods of sample collection, namely, grab sample and composite sample. The advantage of the first method of grab sampling is that its easy and convenient but the disadvantage is that the data obtained may not be representative of the actual situation since the grab sample could have been taken accidentally during either very good or very poor operation / discharge conditions. The composite sample is the combination of many different samples taken at predetermined intervals, probably every 2 hours. This method is more accurate but it takes much more time and efforts than the first method.

Details of both methods of sample collection can be found in the Chapter “Method of


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Water Sample Collection for Analysis” in the book (in Thai language) “Wastewater Analysis Manual” printed by Environmental Engineering Association of Thailand, which is sold in the book centers of universities.

For tanneries in Thailand, sample collection should be carried out as per the local

requirements and conditions as follows: - a) Sulfide treatment system Wastewater: collecting grab sample from the collection tank every time before air or chemicals are introduced. Effluent: collecting grab sample from the stocking tank every time after treatment. b) Chromium precipitation system Wastewater : collecting grab sample from the reaction tank before adding chemicals. c) Chromium recycle system Wastewater : similar to b) Chromium solution: collecting grab sample after dissolving with acid. d) Joint/combined wastewater treatment system of tannery group Wastewater : composite sample once a week. Effluent : composite sample once a week. e) Wastewater treatment system of single or independent tannery Wastewater : grab sample once a month. Effluent : grab sample once a month. d) Sludge or solid waste - Excess sludge from wastewater treatment plant collect sample every time of draining analyse for chromium every time the sludge is sent to the Industrial Waster Treatment Service Center. - Dry sludge from wastewater treatment system without chromium pre-treatment: analyse for chromium every time the sludge is sent to the Center,

with chromium pre-treatment or recycle collect sample and analyse for chromium once a week in case of a joint

wastewater treatment system for a tannery group. and once a month for the wastewater treatment system of a single

tannery. 6.2.2 Method of Sample Analysis The sample collected must be delivered to the laboratory for analysis as quick as possible, otherwise the result will be incorrect. Standard methods of sample analysis have to be used, for instance, 1. Standard Method for the Examination of Water and Wastewater printed by American Public Health Association, American Water Work Association, Water Pollution Control Federation. 2. Wastewater Analysis Manual printed by the Environmental Engineering Association of Thailand. 3. Standard of Sample Analysis of International Standard Organization such as ISO 5184 (about BOD), ISO 9174 (about total Chromium), ISO 10523 (about pH), ISO 10530 (about dissolved Sulfide). For the tanneries in a cluster, it could be economically worthwhile they create their

common laboratory facilities with sufficient equipment and personnel (analysts). The parameters to be analysed include pH, TDS, Sulfide, SS, BOD and COD. More difficult and complex analysis i.e. analysis of chromium should be done in specialised laboratories such as


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Chulalongkorn University, Mahidol University or at commercial laboratories. A list of registered laboratories is available at the Department of Industrial Works – Ministry of Industry.

For a single or independent tannery, they should carried out only analysis of parameters

for which only inexpensive and simple equipment is required. Equipment should be available for the analysis of pH, TDS, Sulfide, and Chromium (simple field-type analysis method).

The standard method of wastewater analysis for tanneries is as follows:- pH using pH meter TDS using conductivity meter for a rough indication of the TDS value Sulfide using color comparison method or titration SS using glass fiber paper filter, and a balance with four decimal points BOD using azide modification method COD using the potassium dichromate digestion method Chromium - in case of field measurements, see Appendix E. if effluent standard compliance has to be verified, Atomic Absorption

Spectrophotometry method is required Samples should be given only to a reliable laboratory, to ensure quality analysis and reliable results.

TKN using Kjeldahl method 6.2.3 Recording of operational data Wastewater treatment system operation results should be grouped into three areas as follows: - a. Daily operation log-sheet: is the most detailed information collection/recording system. The plant supervisor may record important events every 1 or 2 hours. The following information should be recorded: - - energy used - chemicals used - wastewater treatment efficiency - operating conditions of treatment unit and important equipment b. Daily Operation Report The data are taken from operation log-sheet compiled as a daily average data in a daily operation report. c. Monthly Operation Report is the compilation of the daily reports. This report will be submitted to the responsible pollution control officers as compliance document. Concerning the result of wastewater treatment system operation, the report should include - general data - results of chromium treatment - results of joint (biological) treatment system operation - sludge treatment and disposal Main parameters to be included in the Monitoring Checklist are shown in the checklist sample in Table 6.1 below.


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Table 6.1: Main parameters to be included in the Monitoring Checklist. Process Parameter Unit Chrome tanning wastewater treatment - effluent/flow rate m3/day - chromium in effluent mg/l - used chemical such as kg/day - magnesium oxide(for chromium recycle) or lime (for chromium treatment) - Ferric Chloride - Polyelectrolyte (PE) - conc. of chromium in supernatant mg/l after sedimentation with alkaline - sediment kg/day - conc. of chromium in sediment g/kg weight of dry solids Joint/combinedwastewater treatment system Equalization tank - wastewater flow rate m3/day - BOD mg/l - SS mg/l - Chromium (Cr.) mg/l - Sulfide (H2S) mg/l - pH - volume of sludge removed from the m3/month pond - conc. of chromium in the sludge g/kg weight of dry sludge - treatment method for this sludge - Aeration tank - wastewater flow rate m3/hour - MLVSS or MLSS g/m3 - dissolved oxygen mg/l - sludge volume index (SVI) ml/g - energy consumption kW/day Final clarifier / sedimentation tank - return sludge rate m3/hour - quality of final effluent BOD mg/l Cr. mg/l COD mg/l TKN mg/l O/G mg/l SS mg/l Excess sludge volume m3/day dry solids content g/kg chromium conc. in dry sludge g/kg


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6.3 Monitoring and Control by Government Officers The government officer responsible for pollution control in tanneries should have good knowledge and understanding of the different production processes involved as well as the environmental management guidelines. He should have particular knowledge about environmental management systems in tanneries, especially concerning waste minimisation and pollution control measures. Monitoring should be focused on the main issues as follows: -

- Working conditions of tanneries in general, it should have systematic environmental management.

- methods of pollution minimization in the production process, including development of waste reuse or further treatment.

- Checking the efficiency of wastewater treatment system. - Considering the analysis reports and sample collection from the monthly report of the

tannery. - Tannery inspection should be carried out 4-5 times annually, depending on the

overall credibility (towards environmental management and compliance) of the tannery’s operation.


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References Thai 1. Thongchai Pansawad and Orathai Chawalpharit 1992. Wastewater Survey from Leather

Tanning Industry, Bangkok, study report submitted to the Industrial Works Department, Ministry of Industry, in the Project of Chromium Recycle from Industrial Effluent

2. Thongchai Pansawad and Orathai Chawalpharit 1993, Study on Pay-Back of Chromium

Recycle from Leather Tanning Effluent with Pilot Plant, Bangkok, study report submitted to the Industrial Works Department, Ministry of Industry, in the Project of Chromium Recycle from Industrial Effluent

English 1. ‘Clean Technology and Environmental Auditing’ World Leather, Shoe Trade Publishing UK

ltd., 1991. 2. Kumar, M. 1992. ‘Potential of Converting Tannery Solid Wastes into Glue and other

Utilizable By-Products’. Seminar on the Profitability of Clean Technology in the Leather Tanning Industries 20-21 Oct 1992, Samutprakarn, Thailand.

3. Meyhoefer, B. 1992. ‘Treatment of Wastewater in the Leather Tanning Industry.’ Seminar on

the Profitability of Clean Technology in the Leather Tanning Industries. 20-21 Oct 1992, Samutprakarn, Thailand.

4. ‘Reducing the Oxygen Demand : On Overview of Hair Shaving Technique’, World Leather,

Tanning and the Environment, Aug 1993. 5. Skrypski - Mantele and Bridle, T.R., ‘Environmentally Sound Disposal of tannery Sludge’,

Water Res., Vol 29, Nol4, pp 1033-1039, 1995. 6. ‘Tannery Waste Minimization : An Overview of Some Process to Minimize Tannery Waste’,

World Leather, Shoe Trade Publishing, April/May 1992. 6. The British Leather Confederation 1992. ‘Minimizing Tannery Waste.’ World Leather, Shoe

Trade Publishing, April/May 1992. 7. Toward Greener Tannages : An Overview of Substitution of Chrome Tannage. World

Leather. Shoe Trade Publishing UK Ltd., 1991. 8. Ullrich, W. Activity Report Environmental Management Guideline for Tanneries. Stuttgart, 39

pp., 1992. 10. Zhuang, Y. ‘Profitability of Protein Recovery from Leather Shavings with High Level

Chromium Content’ Seminar on the Profitability of Clean Technology in the Leather Tanning Industries. 20-21 Oct 1992, Samutprakarn, Thailand.


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Appendix A Reuse of Solid Waste from Leather Tanning Industry Solid waste consists of small pieces of animal hides, hooves, horns, bones, shaving and splittings including fleshing sludge and dried excess sludge from the waste water treatment system. Raw hides are transferred into several products and by-products after passing through the different process steps of a leather tannery, including the utilisation of hide residues.. In Thailand hide residues such as, fleshings, splitting and trimmings are use for the production of fish feed, dog chew, gelatin, glue and fertiliser. Most widely used methods of utilisation of hide residues are described as follows:

a) Limed trimmings and fleshings

Trimmings, ear scraps and fleshings after cleaning and can be sold for the production of gelatin (to make jelly or medicine capsule). Some part of the trimmings is sun dried and sold as fertilizer. Some tanneries sell trimmings and fleshings (at Baht 200 per ton) to fish and/or shrimp farms where they are used (after cleaning and further processing for the removal of sulfide) as fish feed. After the removal of lime and sulfide the trimmings and fleshings.can be further processed into animal feed which has a higher value. Cleaned trimmings can also be sun-dried and subsequently cut into smaller pieces and sold as soil conditioner and/or fertiliser.

b) Limed splittings

Most tanneries will further process (deliming, bleaching, sun-drying) good quality splittings with uniform thickness and large size) which sell for about 30-40 Baht/kg. For the production of glue, gelatin or dog chew. A schematic flow diagram of the dog-chew production process is shown in figure A-1.


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limed splittings

forming / pressing

drying

cutting

sun-drying

deliming

packing

addition of ingredients (starch,glucose, gelatin, color etc.)

Fig. A.1: Production of dog chew from “splittings”


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Appendix B Recovery of Protein and Chromium from Chrome Shavings Chrome shavings are regarded as hazardous waste due to their chromium content which is in the range of 1-8% of dry weight. Because of their chromium content, these shavings should not be disposed off at a domestic garbage landfill site or used as directly as fertilizer. There is a certain risk that the chromium may be washed off from the shavings and reaches ground soil water, which could lead to severe health risks. In other countries, several methods have been studied to take recover protein and chromium from these shavings (Zhuang, Y.*, 1992). The recovered chromium can be reused in the leather tanning process. The recovered protein can be used for the production of glue, gelatin or as animal feed. The final residues, after protein and chromium extraction, can be used as organic fertilizer for gardening purposes. The research on this subject in Thailand has been carried out by the Asian Institute of Technology (AIT) both at laboratory scale and at pilot scale in a small size tannery. In the applied recovery process, the chrome shavings are firstly boiled under constant stirring in a calcium hydroxide solution. In this alkaline boil, protein is dissolved but chromium is precipitated as chrome sludge. The alkaline boil mixture is subsequently filtered in a vacuum filter system. The filtrate will be neutralized with sulfuric acid, resulting in precipitation of protein, which after separation, can be directly used for the production of glue, gelatine or animal feed. The filter residue, consisting of chromium sludge, will be dissolved in sulfuric acid for the extraction of chromium. Subsequently sodium carbonate is added to the clear chromium solution for precipitation of chromium hydroxide which, after sedimentation is dissolved in sulfuric acid to obtain chromium sulfate which can be reused as tanning agent. The final residues from this reuse process still contain some protein and traces of chromium and can be sold as Nitrogen organic fertilizer for gardening purpose. Because of the remaining chromium content, this fertiliser should not be applied on vegetable or grain plantations, but should be used only for flower growing purposes. The laboratory study results conclude that the protein recovery rate of this method is in the range of 60 – 70%. - at a lime dosage in the range of 0.1 –0.3 kg per kg of shavings, a reaction temperature of about 100 oC and a reaction time of 2.5 hours. The optimum operation conditions of protein and chromium recycle process is as follows:- Time for protein dissolution = 2.5 hours Temperature for protein dissolution = 100.C Lime (CaO) dosage = 0.15 kg./kg. shavings Water = 6.0-10.0 l./k g. of shavings

(required water volume depending on moisture content in the shavings)

Time for chromium extraction = 4 hours Suitable temperature = room temperature Concentration of sulfuric acid = 1:4 (acid : water) Source : Zhuang, Y., ‘Profitability of Protein Recovery from Leather Shavings with High

Level Chromium Content’, Seminar on the Profitability of Clean Technology in the Leather Tanning Industries., 20-21 October 1992, Samutprakarn, Thailand.


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The pilot plant study results for recovery of protein and chromium recovery at a small tannery (production capacity of 100 hides/day and shavings of 130 kg/day) indicate that the payback period will be at least 5 years. This payback period is possible if the equipment and operation/maintenance costs are 170,000 Baht and 252,000 Baht/annum respectively. Table B.1: Value of production growth from shaving (yield per one ton) Item Yield Unit Price Value of total kg/ton (Baht/kg) production (Baht)

1) Chromium in the form of 10 20 (80% of 200 chromium sulfate market price or in the form of chromium sulfate salt 2) Protein used as fish feed 268 14* 6,968*** (50%protein) Option 1. (26**) 3) Protein used in glue production -268 -8,040 Option 2. 4) Residues remained in the form 78 8.5 (50% of 663 of Nitrogen organic fertilizer for market price uneatable vegetable Total (Option 1.): 7,831 Total (Option 2.): 8,903 Remarks: * Unit price of fish food with protein 50% = 16 Baht/kg. Herein, the price of protein is 80% or the price of fish food. ** Net income of animal feed with protein content of 50% or 16 Baht/kg protein recovered. *** Total value = 268 kg X 29 Baht/kg. Table B.2: Cost/benefit assessment for shavings reuse system Item Option 1* Option 1* Option 2** Option 2** Baht/annum Baht/annum Baht/annum Baht/annum Interest 7% Interest 10% Interest 7% Interest 10% Income, per annum 347217 347217 347217 347217 Payment, per annum***: Operation and maintenance cost 252690 252690 252690 252690 Term of payment 3 years 64,780 68,370 64,780 68,370 Term of payment 3 years 41,487 44,853 41,487 44,853 Term of payment 3 years 31,625 34,925 31,625 34,925 Profit**** Term of payment 3 years 12,061 15,651 29,747 26,157 Term of payment 3 years 11,232 7,866 53,040 49,674 Term of payment 3 years 21,094 17,794 62,902 59,602 Remarks: * Option 1 = chromium + protein + fertilizer ** Option 2 = chromium + glue + fertilizer *** Calculated from the above equation **** Benefit = Income - Payment


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Appendix C Recycling of Chromium in Leather Tanning Industry The demonstration project results on chromium recycle from tanning wastewater implemented by the Department of Environmental Engineering, Chulalongkorn University (1993) indicate that precipitation of chromium with MgO (Magnesium-oxide) is the most suitable recycling technology for leather tanneries in Thailand. Average chromium recycle efficiency is between 65 and 76 %. The introduced chromium recycle system is easy in operation and control and it has been found that the recycled chromium does not have any negative effects on the final leather quality. Chromium recycling from “residue float” of the standard chrome tanning process The demonstrated chromium recycling process has a payback period in the range of 3-7 years, depending on the equipment costs and the applicable interest rates charges by the financing institutions. The cost-benefit analysis has been based on cost figures from the pilot/demonstration project which may be on the higher side, because of the “technological sophistication” of the pilot plant. Several tanneries reportedly constructed copies of the chromium recycling plant by their own mechanical shops at much lower costs, thereby improving the overall economic feasibility and profitability of the chromium recycling system. Chromium recycling from “residue float” of the high exhaustion chrome tanning process Chromium recycling from “residue float” of a high-exhaustion chrome tanning process (using chrome absorption enhancement additives) has been found to be economically not attractive. This is mainly the result of the lower chromium residue concentration in the “float” which is at an average of 1,541 mg/l (compared with a residue chromium concentration in the standard tanning “float” of about 3,000 – 4,000 mg/l). The chromium recycle pilot plant project has also analysed the possible accumulation of impurities in the recycled chrome liquor and its effects on the leather quality. This long-term study included the analysis of impurities such as total organic nitrogen, oil and fat, chloride, iron and alkalinity. It has been found that these impurities have not been accumulated to a risky level. Therefore the recycled chrome liquor does not have any negative effect on the final leather quality which has been confirmed by a German leather technology expert, advising the project personnel. Cost benefit analysis of the chromium recycle system- Based on the results of the chromium recycle pilot plant project the economic analysis, at a required capital investment of 1,310,483 Baht and applicable interest rates of 10% and 15.5%, is as follows:- 1. Effluent without chromium absorption agent a) Investment capital 1,310,483 Baht with interest rate 10% The interest rate gives a net present (zero) value of 17.43%. It means within 5 years, the ratio of turnover exceeding from the standard interest is 7.43 (can pay back in the period of 5 years). Details have been shown in Table C. 1. b) Investment capital 1,310,483 Baht with interest rate of 15.5%. The interest rate gives a net present (zero) value of 17.78%. It means within 7 years, the ratio of turnover exceeding from the standard interest is 2.28% (can pay back in the period of 7


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years). Details have been shown in Table C. 2. For this pilot plant operation using effluent without chromium absorption agent, it has been found that the break-even could be within 5-7 years or a profit of 2.28%-7.43% depending on the interest rate. However, if the recycling plant is simplified (no sludge dewatering system, only one reaction/sedimentation/dissolution tank) resulting in reduced equipment cost, the initial investment capital required is only 903,648 Baht. Therefore, break-even is achieved within 3 years. Using the interest rate of 10% the ratio of turnover exceeding from the standard interest is 16.38% or the profit of 16.38 (Table C. 3). Calculating at an interest rate of 15.5%, the interest rate making the net present (zero) value to 19.07%. This means within 3 years the ratio of turnover exceeding from the standard interest is 3.57% or the profit of 3.57% (Table C. 4). Therefore, it is concluded that for the case of “residue float” without chromium absorption agent the recycle system can be applied economically at a profit rate in the range of 2.28 - 16.38%, reaching break-even within 3-7 years depending on the required equipment/capital costs and the interest rate of financial institutes. If the tanneries can lower the equipment costs further, the break-even period will be reduced resulting in higher profits.

2. Effluent with chromium absorption agent It has been found out that chromium recycle from the “residue float” with chromium absorption agent is economically not feasible. This is the result of the low quantity of chromium available for recycle. The result of economic analysis is shown in Table C. 5.. However, although the method of chromium recycle for this type of “residue float” is not economically attractive, the environmental impact from the presently uncontrolled chrome waste disposal practice is extraordinary high resulting in high social costs. To solve this environmental problem the recycling of chromium even from this type of “residue float” appears pleasing, also considering the relative low investment costs required.


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Table C. 1 Economic analysis with investment capital of 1,310,483 Baht with interest rate of 10% Economic analysis of the pilot plant Case study : Sedimentation with magnesium oxide for the effluent without chromium absorption agent Ratio of leather tanning: 3,228 tons of raw hide/annum Quantity of chrome tanning substance(BCS): 98.4 tons/annum Investment capital of pilot plant 1,310,483 Baht Annual operation cost : - Maintenance 57,640 Baht - Chemicals 98,903 Baht - Electricity 8,522 Baht - Water 323 Baht - Labor 51,688 Baht Total annual operation cost : 217,076 Baht Interest (10% of capital) 131,048 Baht Total annual cost : 348,124 Baht Annual income : - Value of chrome tanning substance in the form of recycled chrome tanning substance 15.78 tons @ 21,000 Baht/ton 331,380 Baht - Saving the use of Feliderm 12.3 tons @ 98,000 Baht/ton 1,205,400 Baht - Reducing the use of chrome tanning substance in tanning process 36.9 tons @ 21,000 Baht/ton (774,900)Baht Total annual income: 761,880 Baht Net Profit : 413,756 Baht Analysis on Investment Payback of Pilot Plant Option 1 : Interest Rate 10% interest rate 0.15 interest rate 0.2 interest rate 0.1743 ___________________________________________________________________ Year Net Reduction rate Present Reduction rate Present Reduction rate Present currency comparing comparing comparing value value value __________________________________________________________________________________________________ 0 1,310,483 1 413,756 0.86956521 359,788 0.83333333 344,797 0.85157114 352,343 2 413,756 0.75614366 312,859 0.69444444 287,331 0.72517342 300,045 3 413,756 0.65751623 272,051 0.57870370 239,442 0.61753676 255,510 4 413,756 0.57175324 236,566 0.48225308 199,535 0.52587649 217,585 5 413,756 0.49717673 205,710 0.40187757 166,279 0.44782124 185,289 ___________________________ ___________ _____________ Total 1,386,974 Total 1,237,384 Total 1,310,770 ___________________________________________________________________________________________________ Ratio = Total Present Value = 1.06 0.94 1.00 Initial Investment ____________________________________________________________________________________________


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Table C. 2 Economic analysis with investment capital of 1,310,483 with interest rate of 15.5% Economic analysis of pilot plant Case study : Sedimentation with magnesium oxide for the effluent without chromium absorption agent Ratio of leather tanning: 3,228 tons of raw hide/annum Quantity of chrome tanning substance (BCS) 98.4 tons/annum Investment capital of pilot plant 1,310,483 Baht Annual operation cost: - maintenance 57,640 Baht - chemicals 98,903 Baht - electricity 8,522 Baht - water 323 Baht - labor 51,688 Baht Total annual operation cost : 217,076 Baht Interest (15.5% of capital) 203,125 Baht Total annual cost : 420,201 Baht Annual income : - value of chrome tanning substance in the form of recycled chrome tanning substance 15.78 tons @ 21,000 Baht/ton 331,380 Baht - saving the use of Feliderm 12.3 tons @ 98,000 Baht/ton 1,205,400 Baht - reducing the use of chrome tanning substance in tanning process 36.9 tons @ 21,000 Baht/ton (774,900)Baht Total annual income : 761,880 Baht Net Profit : 341,679 Baht Analysis on Investment Turnover of Pilot Option 2 : Interest Rate 15.5% interest rate 0.15 interest rate 0.2 interest rate 0.1778 ________________________________________________________________________________________________________ Year Net Reduction rate Present Reduction rate Present Reduction rate Present currency comparing comparing comparing value value value ____________________________________________________________________________________________________ 0 1,310,483 1 341,679 0.86956521 297,112 0.83333333 284,733 0.84904058 290,099 2 341,679 0.75614366 258,358 0.69444444 237,277 0.72086991 246,306 3 341,679 0.65751623 224,659 0.57870370 197,731 0.61204781 209,124 4 341,679 0.57175324 195,356 0.48225308 164,776 0.51965343 177,555 5 341,679 0.49717673 169,875 0.40187757 137,313 0.44120685 150,751 6 341,679 0.43232759 147,717 0.33489797 114,428 0.37460252 127,994 7 341,679 0.37593703 128,450 0.27908164 95,356 0.31805274 108,672 ____________________________ ___________ ___________ Total 1,421,528 Total 1,231,613 Total 1,310,501 ________________________________________________________________________________________________________ Ratio = Total present value 1.08 0.94 1.00 Initial investment ___________________________________________________________________________________________


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Table C. 3 Economic analysis with investment capita of 903,648 Baht with interest rate of 10% Economic analysis of pilot plant Case study : Sedimentation with magnesium oxide for the effluent without chromium absorption agent Ratio of leather tanning: 3,228 tons of raw hide/annum Quantity of chrome tanning substance (BCS) 98.4 tons/annum Investment capital of pilot plant 903,648 Baht Annual operation cost : - maintenance 41,487 Baht - chemicals 98,903 Baht - electricity 6,643 Baht - water 323 Baht - labor 51,688 Baht Total annual operation cost : 199,044 Baht Interest (10% of capital) 90,365 Baht Total annual cost: 289,409 Baht Annual income : -value of chrome tanning substance in the form of recycled chrome tanning substance 15.78 tons @ 21,000 Baht/ton 331,380 Baht - saving the use of Feliderm 12.3 tons @ 98,000 Baht/ton 1,205,400 Baht - reducing the use of chrome tanning substance in tanning process 36.9 tons @ 21,000 Baht/ton (774,900)Baht Total annual income : 761,880 Baht Net Profit : 472,471 Baht Analysis on investment turnover of pilot plant Option 3 : Interest rate 10% interest rate 0.15 interest rate 0.1 interest rate 0.2638 _______________________________________________________________________________________________________ Year Net Reduction rate Present Reduction rate Present Reduction rate Present currency comparing comparing comparing value value value _______________________________________________________________________________________________________

0 903,648 1 472,471 0.86956521 410,844 0.90909090 429,519 0.79126444 373,850 2 472,471 0.75614366 357,256 0.82644628 390,472 0.62609941 295,814 3 472,471 0.65751623 310,657 0.75131480 354,974 0.49541020 234,067 ___________________________ _____________ ____________ Total 1,078,758 Total 1,174,965 Total 903,730 _______________________________________________________________________________________________________ Ratio = Total present value = 1.19 1.30 1.00 Initial investment ___________________________________________________________________________________________


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Table C. 4 Economic analysis with investment capital of 903,648 Baht with interest rate of 15.5% Economic analysis of pilot plant Case study : Sedimentation with magnesium oxide for the effluent without chromium absorption agent Ratio of leather tanning : 3,228 tons of raw hide/annum Quantity of chrome tanning substance (BCS) 98.4 tons/annum Investment capital of pilot plant 903,648 Baht Annual operation cost : - maintenance 41,487 Baht - chemicals 98,903 Baht - electricity 6,643 Baht - water 323 Baht - labor 51,688 Baht Total annual operation cost : 199,044 Baht Interest (15.5% of capital) 140,065 Baht Total annual cost : 339,109 Baht Annual income : - value of chrome tanning substance in the form of recycled chrome tanning substance 15.78 tons @ 21,000 Baht/ton 331,380 Baht - saving the use of Feliderm substance 12.3 tons @ 98,000 Baht/ton 1,205,400 Baht - reducing the use of chrome tanning substance in tanning process 36.9 tons @ 21,000 Baht/ton (774,900)Baht Total annual income : 761,880 Baht Net profit : 442,771 Baht Analysis on investment turnover of pilot plant Option 4 : Interest rate 15.5% interest rate 0.15 interest rate 0.11 interest rate 0.1907 ______________________________________________________________________________________________________ Year Net Reduction rate Present Reduction rate Present Reduction rate Present currency comparing comparing comparing value value value ___________________________________________________________________________________________ 0 903,648 1 422,771 0.86956521 367,627 0.90090090 380,875 0.83984210 355,061 2 422,771 0.75614366 319,676 0.81162243 343,130 0.70533476 298,195 3 422,771 0.65751623 277,979 0.73119138 309,127 0.59236984 250,437 _________________________ __________ ____________ Total 965,281 Total 1,033,132 Total 903,693 ___________________________________________________________________________________________ Ratio = Total present value 1.07 1.14 1.00 Initial investment


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Table C. 5 Economic analysis with investment capital of 1,310,483 Baht with interest rate of 10% Economic analysis of pilot plant Cast study : Sedimentation with magnesium oxide for the effluent with chromium absorption agent Ratio of leather tanning : 3,228 tons of raw hide/annum Quantity of chrome tanning substance (BCS) 61.5 tons/annum Investment capital of pilot plant 1,310,483 Baht Annual operation cost : - maintenance 57,640 Baht - chemicals 60,600 Baht - electricity 8,522 Baht - water 323 Baht - labor 51,688 Baht Total annual operation cost : 178,773 Baht Interest (10% of capital) 131,048 Baht Total annual cost : 309,821 Baht Annual income : - value of chrome tanning substance in the form of recycled chrome tanning substance 3.81 tons @ 21,000 Baht/ton 80,010 Baht Net Loss : 229,811 Baht


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Table C. 6 Economic analysis with investment capital of 500,000 Baht with interest rate of 10% Economic analysis of pilot plant Case Study : Sedimentation with magnesium oxide for the effluent without chromium absorption agent Ratio of leather tanning : 3,228 tons of raw hide/annum Quantity of chrome tanning substance (BCS) 98.4 tons/annum Investment capital of pilot plant 500,000 Baht Annual operation cost : - maintenance 41,487 Baht - chemicals 98,903 Baht - electricity 6,643 Baht - water 323 Baht - labor 51,688 Baht Total annual operation cost : 199,044 Baht Interest (10% of capital) 50,000 Baht Total annual cost : 249,044 Baht Annual income : - value of chrome tanning substance in the form of recycled chrome tanning substance 15.78 tons @ 21,000 Baht/ton 331,380 Baht - saving the use of Feliderm 12.3 tons @ 98,000 Baht/ton 1,205,400 Baht - reducing the use of chrome tanning substance in tanning process 36.9 tons @ 21,000 Baht/ton (774,900)Baht Total annual income 761,880 Baht Net Profit : 512,836 Baht Analysis on investment turnover of pilot plant Option 1 : Interest rate 10% Interest rate 0.15 Interest rate 0.1 Interest rate 0.648 _________________________________________________________________________________________________ Year Net Reduction rate Present Reduction rate Present Reduction rate Present currency comparing comparing comparing value value value __________________________________________________________________________________________________ 0 500,000 1 512,836 0.86956521 445,944 0.90909090 466,215 0.60679611 311,187 2 512,836 0.75614366 387,778 0.82644628 423,831 0.36820152 188,827 ____________________________ ____________ ______________ Total 833,722 Total 890,046 Total 500,014 __________________________________________________________________________________________________ Ratio = Total present value 1.67 1.78 1.00 Initial investment _______________________________________________________________________________________


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Table C. 7 Economic analysis with investment capital of 500,000 Baht with interest rate of 15% Economic analysis of pilot plant Case study : Sedimentation with magnesium oxide for the effluent without chromium absorption agent Ratio of leather tanning : 3,228 tons of raw hide/annum Quantity of chrome tanning substance (BCS) 98.4 tons/annum Investment capital of pilot plant : 500,000 Baht Annual operation cost : - maintenance 41,487 Baht - chemicals 98,903 Baht - electricity 6,643 Baht - water 323 Baht - labor 51,688 Baht Total annual operation cost : 199,044 Baht Interest (15% of capital) 75,000 Baht Total annual cost : 274,044 Baht Annual income : - value of chrome tanning substance in the form of recycled chrome tanning substance 15.78 tons @ 21,000 Baht/ton 331,380 Baht - saving the use of Feliderm 12.3 tons @ 98,000 Baht/ton 1,205,400 Baht - reducing the use of chrome tanning substance in tanning process 36.9 tons @ 21,000 Baht/ton (774,900)Baht Total annual income : 761,880 Baht Net Profit : 487,836 Baht Analysis on investment turnover of pilot plant Option 2 : Interest rate 15% Interest rate 0.15 Interest rate= 0.1 Interest rate 0.589 _______________________________________________________________________________________________________ Year Net Reduction rate Present Reduction rate Present Reduction rate Present currency comparing comparing comparing value value value _______________________________________________________________________________________________________ 0 500,000 1 487,836 0.86956521 424,205 0.90909090 443,487 0.62932662 307,008 2 487,836 0.75614366 368,874 0.82644628 403,170 0.39605199 193,208 ______________________________ _____________ _____________ Total 793,079 Total 846,658 Total 500,217 ______________________________________________________________________________________________________ Ratio = Total present value 1.59 1.69 1.00 Initial investment ___________________________________________________________________________________________


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Appendix D Wastewater Analysis Methods Special analytical publications should be used as reference for analytical procedures of more complex parameters. The following is a description of simple analytical methods to be used on-site at the tanneries. 1. pH measurement Use fine-graded pH paper, tip it into the water sample, resulting in color change on the pH paper as per the pH value. This colour is then compared with standard color paper (attached to the pH paper box), indicating the pH value of the water sample. Or use pH meter, clean the measuring head with soft paper tissue, then put the probe into water sample, stir slightly and wait until the digital/analog indicator stabilises. Stabilisation of the readout may take up to 2-3 minutes. Read pH value from the meter. Then rinse the measuring probe with clean water, dry it and keep the probe head in the distilled water. 2. TDS measurement Use the same method as pH measurement but with a conductivity meter. Adjust the value to be TDS according to the operating manual. 3. Chromium field analytical method 3.1 Chemicals required - EDTA 0.1 M. (2 litres) - KCr(SO4)2 * 12H2O 100 grams 3.2 Equipment required - 2 calibrated glass bottles with stopper, size 1,000 ml - measuring pipettes, volume 1 ml, 10 m (2 each) - 2 pipettes 10 ml - 2 measuring cylinders 25 ml - 50 test tubes - electric stove - 5 beakers of 250 ml - 5 beakers of 400 ml - 5 glass bottles of 1 litre - 10 glass plastic bottles of 1 litre 3.3 Standard solution - Stock solution : Dissolve 59.134 grams of KCr(SO4)2 * 12H2O in 800 ml of distilled water, fill the calibrated glass bottle to exactly 1000 ml volume. This solution has a chromium concentration of 9.00 grams as Cr2O3/litre. - Standard solution : Dilute the stock solution as shown in Table 1 below


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Table 1. Standard solution dilution No. Stock solution, ml Volume of distilled water, ml Concentration as g Cr2O3/l 1 1 8 1 2 2 7 2 3 3 6 3 4 5 4 5 5 7 2 7 6 9 0 9 Pipette 1 ml of the stock solution with each concentration into a test tube, add 20.00 mg of EDTA solution, boil for 10 minutes. The content of the test tubes will develop different levels of purple colour – indicating the amount of Cr present. Cool to room temperature. These solutions are reference solutions for subsequent colour comparison.. 3.4 Test method - collect 1 liter of wastewater sample - pipette 1 ml of wastewater into test tube - add EDTA solution of 20.00 mg - boil for 20 minutes, purple colour develops - cool to room temperature

- compare the color with the standard solution and estimate the concentration as grams of Cr2O3 per litre.

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environmental management guideline for the leather tanning & finishing industry

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