hazardous waste management - somaiya vidyavihar. joshi_hazardous... · 2017. 12. 14. · •...

Sem. III ;paper 301; Unit III

Hazardous Waste Management

Dr. Sanjay Joshi

Definition and Classification

• Hazardous waste is defined as the waste which has potential to cause adverse effects on the human health and the health of the ecosystem when improperly treated, stored or disposed of, or otherwise mismanaged

• Hazardous Waste is a "solid waste" which because of its quantity, concentration, or physical, chemical, or infectious characteristics may cause or contribute to an increase in mortality, or an increase in irreversible or incapacitating illness

• A "solid waste" is defined as any discarded material that is abandoned by being disposed of, burned or incinerated, recycled or considered "waste-like." A solid waste can physically be a solid, liquid, semi-solid, or container of gaseous material

Hazardous Waste - legislations

• The principal rules were published in the Gazette of

India, Part-II, Section 3, Sub-section (ii) vide number

S.O. 2265(E), dated the 24" September, 2008 and

• subsequently amended vide :-

• 1. S.O. 1799 (E), dated the 21 July, 2009;

• 2. S.O. 2447 (E), dated the 23 September, 2009;

• 3. S.O. 710 (E), dated the 30 March, 2010; and

• 4. S.O. 1996 (E), dated the 13 August, 2010.

• 5. S,O, 3100(E) dated 14th October, 2013

14-Dec-17

Hazardous Waste-legislations

• Hazardous Wastes (Management & Handling) Rules,

1989 Notified under the Environment(protection) Act,

1986 and were amended In 2000 and again in 2003,

2008 and 2013

• As per these amendments, the rules are now known as

the Hazardous Wastes (Management, Handling and

Transboundary Movement) Amendment Rules, 2013 as

per the Basel Convention (Adopted in March 1989 in

Basel, Switzerland and entered into force in 1992. So far

186 countries have signed the treaty till November,

2016)

14-Dec-17


• Any waste which by reason of any of its

physical, chemical, reactive, toxic, flammable,

explosive or corrosive characteristics causes

danger or is likely to cause danger to health or

environment, whether alone or when in contact

with other wastes or substances, and shall

include wastes listed in Schedules I, II & III of

the Rules


Wastes covered under

Water Act, 1974

Air Act, 1981

MSW Rules, 2000

BMW Rules, 1998

Batteries (M & H) Rules, 2001

Merchant Shipping Act, 1958 (wastes arising from

ships beyond 5 kms of relevant base line)

Are NOT COVERED under HW (M, H & TB M) Rules

Characteristics • Hazardous wastes are generally non-biodegradable and

are persistent in nature

• These can easily enter the food chain resulting in bioaccumulation and biomagnification

• Most of these are highly toxic or lethal even at lower concentrations

• For a material to be categorized as hazardous waste, it must fulfill the following criteria:

i) It should be included in the list provided by the Government agency declaring the material as hazardous

ii) It should possess either or all of the properties like ignitability, corrosivity, reactivity and toxicity

Characteristics and Types

• To ascertain the hazardous nature of the

chemical or any other material in question,

certain assays/tests are performed

• These include toxicity assays,

phytotoxicity studies, genetic activity,

bioaccumulation etc.

• The potential threat to the environment or

human health depends upon the quantity

of the waste and the characteristics of the

waste

Class C 1:

Ignitable Hazardous Waste

• A liquid waste which has a flash point of less than or equal to 600 C as determined by an approved test method (Flash point is the temperature at which a particular organic compound gives off sufficient vapour to ignite in air)

• A non-liquid waste which, under standard conditions, is capable of causing a fire through friction, absorption of moisture or a spontaneous chemical change and when ignited, the waste burns so vigorously and persistently that it creates a hazard

• An ignitable compressed gas or oxidizer

• A simple method of flash point determination is to review the MSDS normally provided with the product

• This category of wastes include Naphtha, epoxy resins, adhesives and oil-based paints etc.

Class C 2 Corrosive Hazardous Waste

An aqueous waste with a pH of less than or equal to 2

or greater than or equal to 12.5 is considered to be a corrosive hazardous waste

• It is a liquid and corrodes steel (SAE 1020) at a rate

greater the 6.35 mm per year at a test temperature of

550

• Bureau of Indian Standard 9040 C method for pH

determination and NACE(National Association of Corrosion Engineers) method for establishing

corrosivity towards steel (SAE 020) shall be adopted.

• NaOH, a caustic solution with high pH or HCl with very low pH is often used in many industries to degrease or clean the metal parts before painting and when disposed off after use, these become corrosive in nature.

Reactive Hazardous Waste Class C 3

• It is normally unstable and readily undergoes

violent change without detonating.

• It reacts violently with water or forms potentially

explosive mixtures with water

• When mixed with water, it generates toxic

gases, vapours or fumes in a quantity sufficient

to present a danger to human health or the

environment.

Reactive Hazardous Waste Class C 3

• It is a type of waste which, when exposed to pH

conditions between 2 and 12.5, can generate toxic

gases, vapours or fumes in a quantity sufficient to

present a danger to human health or the environment

• It is capable of detonation or explosive reaction if it is

subjected to a strong initiating source or if heated under

confinement

• It is readily capable of detonation or explosive

decomposition or reaction at standard temperature and

pressure

• It is a forbidden explosive

Class C 4

Toxic Hazardous Waste

A solid waste exhibits the characteristic of toxicity if,

(i) The concentration of the waste constituents listed in

Class A and B (of this schedule-II) are equal to or more

than the permissible limits prescribed therein

(ii) It has been shown through experience or by any

standard reference test- method to pose a hazard to

human health or environment because of its

carcinogenicity, mutagenecity, endocrine disruptivity, acute

toxicity, chronic toxicity, bio-accumulative properties or

persistence in the environment

Class C 4

Toxic Hazardous Waste

• The leachate from the waste shall be extracted as per

US EPA 1311 method for Toxicity Characteristic

Leaching Procedure (TCLP).

• The concentration of the individual constituents shall be

determined as per the manual for characterization and

analysis of hazardous waste published by Central

Pollution Control Board and in case the method is not

covered in the said manual, suitable reference method

may be adopted for measurement

• The hazardous constituents to be analysed in the waste

shall be relevant to the nature of the industry and the

materials used in the process

Listing of the HW

• US EPA and other agencies have

prepared four lists designated with

alphabets F, K, P and U which cover the

waste from generic industrial processes,

specific industrial sectors, unused pure

chemical products and formulations that

are either acutely toxic or toxic

• All regulations related to hazardous

wastes are applicable to these lists

Listing of the HW-US EPA

• F- List: This includes the waste from non-specific sources of generation. It contains the solvents commonly used in degreasing, metal treatment baths and sludges, waste water from metal plating operations and dioxin containing chemicals or their precursors

• Examples include benzene, Carbon tetrachloride, 1,1,1,trichloroethane, toluene, Cresylic acid, Methyle Ethyle Ketone, Mehtylene chloride etc.

• Solvent mixtures or blends containing greater than 10% of one or more of these solvents are also considered as F-listed solvents

Listing of the HW

• K- List: This contains wastes generated by specific

industrial processes like wood preservation pigment

production , petroleum refining , iron and steel

production, pesticide production, explosive

manufacturing etc

• P and U Lists: These lists contain those chemicals that

have crossed their shelf life without being used and need

to be discarded

• These also contain chemicals without particular

specifications, container residues and the residues left after spillage of materials

Listing of the HW

• For example, if a pesticide is not used during its shelf life , it n

• eeds to be disposed off in bulk

• However, P list includes acutely toxic wastes that regulated when the quantity generated or accumulated per month exceeds 1 kg

• The U list includes those chemicals that are regulated when their quantity generated exceeds 25 kg per month

• Pesticide applicators, laboratories, chemical formulators are some examples of the sources of generation of these chemicals

HW Management: Waste Generation

• The most common source of hazardous waste is the industries, although at the community level, outside the industry, some hazardous waste is generated but in very small amounts

• In order to achieve success in waste management methodology, it is necessary to quantify the waste generated at source

• For this, a detailed inventory and measurement study at each potential source of generation needs to be done

Raw Materials &

Labour

Energy

Industrial Process

Products

Money

Waste heat

Waste water Water

The dirty dozen

• Tanneries

• Textile Dyeing Plants

• Dyestuff Producers

• Metal Working and Electroplating Shops

• Foundries

• Automobile Service Shops and Gas

Stations

• Lead-acid Battery

Manufacturing/Recycling

• Chemical Industries/Laboratories

• Paint Shops

• Printers

• Photographic Processors

• Dry Cleaners

Hazardous waste generators

All industries generate some hazardous waste,

however, the largest quantities come from five

sectors:

• Chemical and pharmaceutical manufacture

• Metals refining

• Petroleum and coal products

• Metal working and fabrication

• Rubber and plastics manufacture

TRP Chapter 2.2 23

Some types of waste associated with different industries

Chemical

manufacturers

Chemical process

wastes

Acids and alkalis

Spent solvents

Reactive wastes

Discarded commercial

chemical products

Construction industry

Paint wastes

Spent solvents

Strong acids and bases

Vehicle maintenance shops

Paint wastes

Used oils

Spent solvents

Acids and alkalis

Furniture and wood

manufacturing and

refinishing

Spent solvents

Paint wastes

Waste generating industries

Large quantity generators:

> 1000kg /month

eg pharmaceutical companies

Medium quantity generators:

100 - 1000kg/month

eg laboratories, printers

Small quantity generators:

<100kg/month

eg dental surgeries,

photographic processors

Small and medium scale industries

In developing economies, these often predominate

• Typically they have:

– low level of technology

– unskilled management

– unspecialised workers

– lack of modernisation

– poor environmental performance

• SMIs may account for one third of the total hazardous

wastes generated

• There are high risks from occupational and

environmental exposure

Some typical household hazardous wastes

• Vehicle maintenance items eg antifreeze, brake fluid

• Cleaning products eg drain cleaners, spot removers, toilet cleaners,

chlorine bleach, oven cleaners

• Cosmetics eg nail polish and remover

• Fire extinguishers

• Pet care products eg Flea collars and sprays

• Garden products eg herbicides, lawn chemicals, pesticides

• Insecticides and insect repellent

• Home care products eg paint and paint stripper, wood stains,

solvents, swimming pool chemicals

• Prescription drugs

Health care wastes

•Diverse mixture of sources and waste types

•doctors’ surgeries

•hospitals

•clinics

•Only a small fraction pose risk - this can be

minimised by:

•Classification of wastes into groups which can be

treated similarly

•Segregation of wastes - non-risk waste should be

disposed of with municipal waste

•Safe storage

•Treatment to reduce the pathogen content of waste

•nursing homes

•dental surgeries

•veterinary practices

Non-industrial waste sources

• Used motor oils

• Used car batteries

• Redundant agricultural pesticides and containers

• Surplus paints and solvents

• Medical and health care wastes

Some examples include:

Table: Community Sources of HW Waste Category Source of Generation

Radioactive Waste Biomedical research facilities, research laboratories in the Universities and colleges, hospitals, nuclear power plants etc.

Toxic Chemicals Battery shops and manufacturing units, Fertilizer and pesticides industries, construction companies, industrial cooling towers, newspaper and photographic solutions, service stations etc

Biological waste Biomedical research facilities, pharmaceutical companies, pathology labs etc

Flammable Waste Petroleum and petrochemical industries, petroleum refining industries, service stations etc

Explosives Dry cleaners, Construction companies, ammunition production factories etc.

Liquid or gaseous waste

Accidental spillage of hazardous liquid on the roads, in or near the water bodies like sea or oceans, or leakage of toxic gas

HW Management

• HW Management has several functional

components as follows:

1. Inventory,

2. Storage and Collection,

3. Transfer and Transport,

4. Processing/ Treatment

5. Disposal

Changing Scenario

Raw Materials

Energy

Water

Industry

Products

Beneficiation Plant

Market

Waste Water

Money

Waste Heat

HW Management: Waste Storage and Collection

• On the basis of the quantity of the waste generated, waste is either stored in small containers or at some special facility

• Normally, when the amount of waste generated from a source in a factory is small, it stored in containers and in limited quantity

• The type of containers to be used for storage will depend upon nature of the waste chemicals to be stored in it

• For example, corrosive acids or caustic solutions are to be stored in fiberglass or glass lined containers

• The containers that are normally used are the large sized drums which are easy to handle during transprtation


• Till disposal for recycling/ treatment/ land filling, HWs are to be

stored onsite in bags/ containers in a covered area.

• Storage permitted for a period not exceeding 90 days

SPCB may extend the storage period, in case of

i. Small generator, generating HW upto 10 TPA

ii. Recyclers, reprocessors and facility operators upto 6 months of their

annual capacity

iii. Generators who do not have access to any TSDF in the concerned

State

iv. Wastes which need to be specifically stored for development of a

process for its recycling, reuse

14-Dec-17

14-Dec-17

Waste Storage Containers


• The waste thus stored is then transported to the treatment and disposal facility

• The sealed containers are generally loaded manually or by using mechanical equipments onto a truck that has flat floor

• If the collected waste is in liquid state, it is pumped or drained into the collection vehicle

• The type of the transport vehicle depends upon the nature or category of the waste to be transported

Transportation of HW

• Due to unprecedented growth of chemical Industries, the proportion

of hazardous chemicals in total freight traffic is increasing at a rapid

rate

• Of the carriers that carry hazardous goods approximately two-thirds

of them carry flammable petroleum products including Kerosene,

Petrol, LPG, Naphtha etc. The movement of such substances is

more prone to accident than the movement of other goods

• When involved in a road accident , may cause disastrous

consequences like fire, explosion, injuries, in addition to property

loss and environmental pollution

• The safety codes and safety requirements to be followed in

transportation of hazardous materials are laid down in Central Motor Vehicles Rules of 1988


• TAPS ( pipe line )

• PLANE (Air Ways )

• SHIP (Water Transport )

• TRAIN (Rail Transport )

• MOTOR VEHICLE (Road Transport)

37


• Every goods carriage carrying dangerous or hazardous goods shall display a distinct mark of the class label appropriate to the type of dangerous or hazardous goods

• Every package containing dangerous or hazardous goods shall display the distinct class labels appropriate to the type of dangerous or hazardous goods

• In the case of packages containing goods which

represent more than one hazard, such packages shall display distinct labels to indicate the hazards


• Every goods carriage carrying goods of dangerous or hazardous nature shall be fitted with a tachograph, an instrument to record the lapse of running time of the motor vehicle; time speed maintained, acceleration and declaration etc., and a spark arrester

• The class label shall be so positioned that the size of the label is at angle of 45 degrees to the vertical and the size of such label shall not be of less than 25 mm square which may be divided into two portions, the upper half portion being reserved for the pictorial symbol and the lower half for the test.

14-Dec-17

14-Dec-17

HAZARD TYPE COLOUR

Explosive Orange

Flammable Red

Non- flammable Green

Water – reactive Blue

Oxidizing substances Yellow

Toxic/ infectious White

Radio active Half yellow and half white

Corrosive Half white and half black

47

14-Dec-17

14-Dec-17


• The goods carriage must have valid registration to carry the hazardous goods.

• The vehicle is equipped with necessary First-aid, Safety equipments and antidotes as may be necessary.

• The transporter or owner of the goods carriage has full and adequate information about the dangerous or hazardous goods being transported.

• The driver of the goods carriage is trained in handling the dangers posed during transport of such goods.


• Ability to read and write one Indian language and English, and also posses a certificate having successfully passed a course consisting of following syllabus and periodicity connected.

• Period of training 3 days ( for first time)

• Period of training 1 day (for every year)

Syllabus:

• Defensive driving questionnaire – First Day

• Advanced Driving skill and training. – Second Day 1. Discussion 2. Field test training(1 driver at a time)

• Product safety – Third day 1. Product information 2. Emergency Procedure

50

Educational qualification for drivers of goods carriages

carrying dangerous or hazardous goods.

14-Dec-17


• Every consignor shall supply to the owner of the goods carriage full and adequate information about the dangerous or hazardous goods, being transported as to enable such owner and its driver to become aware of the safety rules for transportation of hazardous materials

• To make aware of the risks created by such goods to health or safety

• The owner of the goods carriage shall ensure that the driver holds a driving License as per provisions of Rule 9 of the Central Motor Vehicle Rules

14-Dec-17


• It is the responsibility of the driver to keep all information provided to him in writing in the form TREM CARD (Transport Emergency Card). This is to be kept in the drivers cabin and should be available at all times while hazardous material related to it is being transported

• It is essential for every hazardous material carrier to

display correctly the emergency information panel (EIP) with details and at places as specified under Rule 134 of the Central Motor Vehicles Rules, 1989

• Emergency information panel should be legibly and conspicuously marked in each of the three places specified. So that the emergency information panel faces to each side of the carriage and to its rear and such panel shall contain the following information

14-Dec-17


• The correct technical name of the dangerous or

hazardous goods in letters not less than 50mm high

• The United Nations class number for the dangerous

goods in letters not less than 100mm high

• (UN Numbers are four-digit numbers that identify

hazardous materials in the framework of International

transport. Example: For Flammable Liquids, UN number

is UN1993; for Acrylamide, it is UN 2074)

• The class label of the dangerous or hazardous goods in

the size of not less than 250mm square


• The name and telephone number of the

emergency services to be contacted in the event

of fire or any other accident in letters and

numerals that are not less than 50mm high and

the name and telephone number of the

consignor of the dangerous or hazardous goods

or of some other person from whom expert

information and advice can be obtained

concerning the measures that should be taken in the even of emergency

14-Dec-17

Hazchem Code

• The HAZCHEM code (also called Emergency Action

Code) gives vital information to fire brigade and other

emergency services on the action to be taken to combat

spillage, leakage or fire in an emergency involving a

hazardous substance

• The HAZCHEM code consists of a number from 1 to 4

and any one of the letters, P, R,S, T, W, X, Y, Z followed

at times by the letter E

Number Extinguishing agent

1 Jet

2 Fog

3 Foam

4 Dry Agent 14-Dec-17

Hazchem Code

The letters signify 4 aspects namely,

• Method of controlling spillage a) by diluting

or b) by containing

• Personal protective equipment to be worn

by fire fighters

• Reactive nature of Chemical, and

• Need for evacuation.

14-Dec-17

Hazchem Code

Example 1.

• For motor spirit with UN number 1203, the HAZCHEM

code is 3YE, and this would mean:

3- Use Foam only.

Y- Can be violently (V) reactive or explosive.

Breathing apparatus plus protective gloves to be

used in case of fire. The personal protective

equipment is not a requirement in case of spillage.

Any spillage of the substance should be contained.

E- Consider evacuation as a first priority.

14-Dec-17

14-Dec-17

Hazchem Code

Example 2.

• For ethylene oxide with UN number 1040 and

HAZCHEM code is 2PE and would be decoded as:

2- Use Fog equipment only

P- Can be violently (V) reactive. Full body clothing

with breathing apparatus is necessary. The

substance may be diluted and washed to drain.

E- Consider evacuation as a first priority.

14-Dec-17

14-Dec-17

Alphabets for PPE in Hazchem codes

• P and R : Full Protection

• S: BA (Breathing Apparatus) for Fire only

• T: BA (Breathing Apparatus) for Fire only

• W: Full Protection

• X ,Y and Z: BA (Breathing Apparatus)

14-Dec-17

14-Dec-17

14-Dec-17


• The owner of every goods carriage transporting dangerous or hazardous goods shall ensure to the satisfaction of the consignor that the driver of the goods carriage has received adequate instructions and training to enable him to understand the nature of the goods being transported, by him, the nature of the risks raising out of such goods, precautions he should take while the goods carriage is in motion or stationary and the action he has to in case of any emergency

• The driver of a goods carriage transporting any dangerous or hazardous goods shall, on the occurrence of an accident involving any dangerous or hazardous goods transported by his carriage, report forthwith to the nearest police station and also inform the owner of the goods carriage or the transporter regarding the accident.

HW Management: Processing and Treatment

• After collection and storage, the waste is generally

processed before actual treatment options are actually

used mainly for the recovery of certain elements

• Processing of the waste involves separation, volume

reduction, detoxification, storage etc.

• This involves 16 different types of physical processes

such as aeration, Ammonia stripping, dialysis,

flocculation, reverse osmosis etc, 8 different types of

chemical processes such as ion exchange, solvent

extraction, neutralisation, oxidation, precipitation etc and

thermal as well as biological processes

14-Dec-17

Operation/Process Function/Activity Category Form

Physical Treatment

Aeration SE 1,2,3,4 L

Ammonia Stripping VR, SE 1,2,3,4 L

Carbon Sorption VR,SE 1,3,4,5 L,G

Centrifugation VR,SE

1,2,3,4,5 L

Dialysis VR,SE

1,2,3,4 L

Distillation VR,SE

1,2,3,4,5 L

Electrodialysis VR,SE

1,2,3,4,6 L

Encapsulation ST 1,2,3,4,6 L,S

14-Dec-17

Operation/Process Function/Activity Category Form

Physical Treatment

Evaporation VR ,SE 1,2,5 L

Filtration VR, SE 1,2,3,4,5 L, G

Flocculation/Settling VR,SE 1, 2,3,4,5 L

Flotation SE

1,2,3,4 L

Reverse Osmosis VR,SE

1,2,4,6 L

Sedimentation VR,SE

1,2,3,4,5 L

Thickening SE

1,2,3,4 L

Vapour Scrubbing VR, SE 1,2,3,4 L,

14-Dec-17

Operation/Process

Function/Activity

Category

Form

Chemical Treatment

Calcination VR 1,2,5 L

Ion Exchange VR, SE, DE 1,2,3,4,5 L

Neutralization DE 1, 2,3,4 L

Oxidation DE

1,2,3,4 L

Precipitation VR,SE

1,2,3,4,5 L

Reduction DE

1,2 L

Solvent Extraction SE

1,2,3,4,5 L

Sorption VR, SE 1,2,3,4 L

14-Dec-17

Operation/Process

Function/Activity

Category

Form

Thermal Treatment

Incineration VR ,DE 3,5,6,7,8 S,L,G

Pyrolysis VR, DE 3,4,6 S,L,G

Biological Treatment

Activated Sludges DE

3 L

Aerated Lagoons DE

3 L

Anaerobic Digestion/Filters DE

3 L

Trickling Filters DE

3 L

Stabilization Pond DE 3 L

14-Dec-17

Operation/Process

Function/Activity

Category

Form

Deep Well Injection DI 1,2,3,4,5,6,7

L

Detonation DI 6,8 S,L,G

Engineered Storage DI 1-8 S,L,G

Land Burial DI 1-8 S,L,G

Ocean Dumping DI

1,2,3,4,7,8 S,L,G

Legend to Tables

Abbreviations Numbers

• VR= Volume Reduction 1= IC- HM

• Se= Separation 2= IC+ HM

• De= Detoxification 3= OC-HM

• St= Storage 4= OC+HM

• Di= Disposal 5= Radiological

• L= Liquid 6= Biological

• S= Solid 7= Flammable

• G= Gas 8= Explosive

14-Dec-17


• After processing, the waste is subjected to various treatment operations

• There are several options available for treatment, however, depending upon the nature and composition of waste, suitable and appropriate option should be selected

• The treatment options involve physical and chemical method, Thermal method and Biological methods etc.


Physico-Chemical Methods

Most of the hazardous waste is treated by these methods. These include:

• Filtration and Separation

• Chemical Precipitation

• Oxidation-Reduction

• Solidification and Stabilization

• Evaporation, and

• Ozonation


Filtration and Separation

• This is a method of separating solid particles from a liquid using a porous medium by applying various forces such as pressure gradient, gravitational pool, centrifugal force, vaccum etc. There are following two methods of filtration namely, Clarification and Dewatering



Clarification

• Suspended solid particles from a liquid with less than 100 ppm concentration are removed from the liquid waste by depth filtration and cross-flow filtration

• The suspended solids are concentrated in a reject stream while clear aqueous effluent is processed further and is then discharged into drainage



Dewatering

• This process of filtration is generally used for the slurries

containing about 1% to 30% solids by weight

• It involves concentrating the solid particles from aqueous

medium by cake filtration

• This can be used for neutralization of strong acids with

lime or limestone or for precipitation of dissolved heavy

metals such as carbonates or sulphides followed by

settling and thickening of the resulting precipitated solids

as slurry

• The slurry thus formed can be further dewatered and

discharged


Chemical Precipitation

• In this method, the soluble substance is converted into an insoluble form either by chemical reaction or by change in chemical composition of the solvent to be treated

• Due to this, the solubility of the substance in it gets diminished

• Precipitated solids can then be removed by settling or other methods

• This method has wider application in removal of toxic metals from aqueous waste by converting them into an insoluble form

• Thus, the waste containing arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel thallium, zinc etc can be treated by this method


• Precipitation is used in hazardous waste treatment

primarily for the removal of heavy metal ions from water

as shown for the chemical precipitatiopn of cadmium:

Cd2+ (aq) + HS- → CdS (s) + H+ (aq)

• The most widely used means of precipitation metal ions

is by the formation of hydroxides such as chromium (III)

hydroxide:

Cr3+ + 3 OH- → Cr(OH)3

14-Dec-17


• The source of hydroxide ions, OH-, is a base (alkali),

such as lime (Ca(OH)2, sodium hydroxide (NaOH), or

sodium carbonate (Na2CO3).

• Sulfide precipitation is very effective means of

treatment, because the solubility of some heavy metal

sulfides is extremely low. Sources of sulfide ions include

sodium sulfide, Na2S, sodium hydrosulfide (NaHS),

hydrogen sulfide (H2S), and iron (II) sulfide.

14-Dec-17


• Some metals can be precipitated from solution in the

elemental metal form by the action of a reducing agent

(e.g. sodium borohydride, NaBH4)

• Metal ions can be converted to the elemental form and

removed from solution by reaction with more active

metal by a process called cementation – the reduction of

toxic cadmium with relatively harmless zinc:

Cd2+ + Zn → Cd + Zn2+

14-Dec-17


Oxidation-Reduction Method

• In this method, the oxidation state of one reactant is raised while that of the other reactant is lowered by the removal or addition of the electrons respectively in the ionic or atomic or molecular form

• This is generally accomplished by using oxidising agents such as sodium or calcium hypochlorite, hydrogen peroxide, potassium permanganate, ozone etc.

• Chemicals like sulphur dioxide, sodium borohydride etc are used as the reducing agents


• These reactions are generally used in the treatment of many organic wastes such as phenols, pesticides and sulphur containing compounds

• These are also used in treatment of metal containing wastes, sulphides, cyanides, chromium etc.

• Reducing agents are generally used to treat wastes containing hexavalent chromium, mercury, organometallic compounds, and chelated metals

• The Oxidation-Reduction method is more suitable for treating the wastes at lower concentration

Examples of Redox Reactions

• Oxidation of organics

(CH2O) + (O) → CO2 + H2O

organic matter

• Oxidation of inorganics

Cyanide: 2CN- + 5 OCl- + H2O → N2 + 2HCO3- + 5Cl-

Iron (II): 4 Fe2+ + O2 + 10 H2O → 4 Fe(OH)3 + 8H+

• Reduction of inorganics

Chromate 2CrO42- + 3 SO2 + 4H+ → Cr2(SO4)3 + 2H2O

Permanganate MnO4- + 3Fe2+ + 7 H2O → MnO2(s) + 3

Fe(OH)3 (s) + 5 H+

14-Dec-17


Solidification and Stabilization (S/S)

• These processes are mainly employed to reduce the

mobility of the waste compounds under treatment

• Due to this, the waste then becomes acceptable under

prevailing land disposal requirements

• These processes are designed to improve handling the

waste and also to improve their physical characteristics

• These processes also result in decreased surface area

across which pollutants can transfer or leach, limit the solubility or detoxify the hazardous components

14-Dec-17


The processes involved are described briefly:

• Solidification: In this process, the compounds or

certain materials are added to the waste to make it

more solid and practically immobile. In this, chemical

bonding or reactions may or may not take place

• Stabilization: In this, certain chemicals are added

which will specifically react with the waste to convert it

into a chemically stable form or convert a toxic

compound into a new, non-toxic compound

• Chemical Fixation: In this, basically, a toxic

compound is converted into non-toxic one. However,

the process does not involve chemical bonding as

such 14-Dec-17

HW Management: Processing and

Treatment

• Encapsulation: Toxic particles or waste components are

completely coated with some chemical compound having

binding or additive properties. When individual particles

are thus enclosed, it is micro-encapsulation and when an

aggregation of particles is thus enclosed, it is called

macro-encapsulation

• In general, S/S methods are used for treating the wastes

having chemical properties which are suitable for land

filling

• The most important application of this process is the

solidification of metal containing wastes

• Lower permeability, lower leaching rate etc make the

wastes acceptable for landfills 14-Dec-17


Evaporation

• Evaporation is another important physical treatment process which

involves conversion of a hazardous waste liquid from a solution or

slurry into a vapour

• Evaporation systems require the transfer of sufficient heat from

heating medium to process fluid to vaporize the volatile solvents

• It is commonly used to decrease the quantity of the material before

final treatment

• It is also useful in concentrating the products before incineration

when no other treatment methods are feasible. For example,

compounds like trinitrotoluene (TNT) is to be incinerated after it is

made concentrated

• Evaporation is the most suitable and appropriate method for such

reactions

14-Dec-17


Ozonation

• Ozone is one of the unstable and strongly oxidizing

agents known so far

• It is used as a substitute for conventional oxidizing

agents such as chlorine, hydrogen peroxide, potassium

permanganate etc.

• Ozone along with UV radiations provide excellent

medium for detoxification of industrial organic wastes

containing aromatic and Aliphatic polychlorinated

compounds and ketones, alcohols etc

14-Dec-17

HW Management, Processing and Treatment: Thermal Treatment

Incineration

• It is a chemical reaction in which, carbon, hydrogen and other

elements in the waste mix with oxygen in the combustion zone

thereby generating heat

• In most of the incinerators, the “Combustion Zone” has a

temperature range of 900-11000C to ensure complete combustion,

complete elimination of odours etc

• Incinerators are designed to maximize the burning of the waste

while minimizing emissions by balancing the oxygen (air), as well as

the time, temperature and turbulence

• Complete incineration of solid wastes produces virtually an inert

residue with larger reduction in the volume. The residue is subjected

to landfill

14-Dec-17

HW Management, Processing and Treatment: Thermal Treatment

• The purpose of incineration is to burn solid wastes to

reduce their volume to about one –tenth, without

producing offensive gases and ash

• Depending upon the composition of the waste, there is

almost 90% reduction of volume of the waste

• Also the average weight of the solid waste is almost

reduced by 70-75%

• The ash thus produced is considerably inert mainly due

to the oxidation of the organic components of the waste

stream

• Because of this, the problems associated with landfill

management are significantly reduced

14-Dec-17

Hazardous Waste Thermal Treatment: Pyrolysis

• It is the chemical decomposition or change brought

about by heating in the absence of oxygen

• In this process, solid and liquid carbonaceous materials

are converted into gaseous components and the solid

residue containing carbon and ash

• In the first step, which is endothermic, the wastes are

heated in pyrolyser or heating chamber and separated

into two components namely volatile and non-volatile

products like char and ash at the temperature ranging

between 425 t0 7600C

• Volatile components are then burned in fume incinerator

under controlled conditions

14-Dec-17

Pyrolysis

• Pyrolysis is specifically used for treating the waste made

up of sludge that is either too viscous, too abrasive or is

too much inconsistent

• It is also useful for treating the plastics, high-residue

material such as high ash liquids and sludge etc

• Materials containing salts and metals, which melt and

volatise at normal incineration temperature

• Waste containing salts and metals which melt and

volatize at normal incineration temperature are also

suitable for treatment by pyrolysis

14-Dec-17

14-Dec-17

hazardous waste management - somaiya vidyavihar. joshi_hazardous... · 2017. 12. 14. · •...

Documents