methane from glucose factory - thailand

Prospects for Biogas Harvesting at Sanguan Wongse Industries Co. Ltd (Thailand)

Report of a Feasibility and Technical Evaluation

20-27 January, 2001

QUALITY RECORD Name Date Revision Prepared By: Tico Cohen 11 February 2001 1 Reviewed By: Dave Donnelly 11 February 2001 1 Authorised By: Revised By: Tico Cohen 12 February 2001 2

Prepared by: Waste Solutions Ltd 1st Floor, John Wickliffe House File No.: 7003/2/53/1 265-269 Princes Street Job No.: 130010 PO Box 997 Date: February, 2000 DUNEDIN Ref: W7003C-67.doc Phone: (03) 477 2375 Fax: (03) 479 2249 E-mail: [email protected]

FTE: Biogas Harvesting at Sanguan Wongse Industries Co. Ltd. FTE 13001/101/1069/1035

Biogas Harvesting at Sanguan Wongse Industries Co. Ltd. Report of a Feasibility and Technical Evaluation

20-27 January 2001

CONTENTS

1 EXECUTIVE SUMMARY 1

2 INTRODUCTION 3 2.1 Background 3 2.2 Prospects for Biogas Harvesting 3 2.3 Feasibility and Technical Evaluation 4 2.4 Purpose of the FTE 4 2.5 Acknowledgements 4

3 FEASIBILITY AND TECHNICAL EVALUATION 5 3.1 Methodology 5

3.1.1 Flow and Temperature Monitoring 5 3.1.2 Wastewater Analysis 5 3.1.3 Vertical Sludge Distribution Profiles 5 3.1.4 Sludge Activity Tests 5

3.2 The Wastewater System 6 3.3 Main Findings of the FTE 8 3.4 Discussion 10 3.5 The Objectives of a Pilot Plant Trial 11 3.6 Recommendations 12

4 TECHNICAL AND SCIENTIFIC RESULTS 13 4.1 Methods 13

4.1.1 Wastewater and Sludge Analysis 13 4.1.2 Flow and Temperature Monitoring 13 4.1.3 Pond Profiles 14 4.1.4 Sludge Activity Tests 14

4.2 Results and Discussion 14 4.2.1 Wastewater Analyses 14 4.2.2 Wastewater Flow 17 4.2.3 Temperature 18 4.2.4 Pond Profiles 18 4.2.5 Sludge Analyses 20 4.2.6 Sludge Activity Tests 21

4.3 The Glucose Factory 22 4.4 Pond Volumes, Sludge Mass, Activity and Projected Gas

Production 23

FTE: Biogas Harvesting at Sanguan Wongse Industries Co. Ltd. FTE 13001/101/1069/1035

5 APPENDIX 24 5.1 Biogas Production from Organic Matter 24 5.2 Photos 24 5.3 Data 29

5.3.1 Wastewater analyses 29 5.3.2 Sludge Analyses 30 5.3.3 Acetate Removal Plots 30

FTE: Biogas Harvesting at Sanguan Wongse Industries Co. Ltd. FTE 13001/101/1069/1035 1

1 EXECUTIVE SUMMARY A Feasibility and Technical Evaluation (FTE) was carried out at Sanguan Wongse Industries Co. Ltd. (SWI), in Khorat, Central Thailand to investigate the potential for biogas harvesting by anaerobic treatment of it’s wastewater. SWI is Thailand’s largest processor of cassava root and discharges in excess of 6,000 m3/day highly concentrated, biodegradable wastewater which is ideally suited for biogas generation. The FTE included a review of the wastewater and the current operation of the existing wastewater system. The purpose of the FTE was to confirm the suitability of the wastewater, the processing conditions at the Factory and the layout of the site for the proposed plant. The review has found that the site is ideally suited for a biogas harvesting plant because of the following factors: • High volumes of highly concentrated wastewater are produced, 24 hours a day,

365 days a year at a virtually constant load. • Near optimal temperatures for anaerobic digestion which eliminates the need for

otherwise costly heating control. • The wastewater contains high levels of starch and glucose which is rapidly

converted into biogas. No interfering substances exist in the wastewater. • SWI is currently spending approximately US$ 1.6 M pa on Heavy Fuel Oil (HFO)

and $ 2.0 M on electricity. Recent dramatic rises in fuel costs provide a strong economic incentive for a biogas harvesting plant with unusually attractive investment rates of return.

• The factory has large areas available for the construction of a biogas plant in close vicinity to the factory and the site is suitable for inexpensive in-pond biogas harvesting technology.

• Projected biogas yield is expected to replace all of the factory’s HFO requirement plus generate an excess for electricity generation to offset a substantial percentage of the factory’s public-grid supplied electricity.

• A biogas plant can conveniently be constructed and commissioned without interference with the current wastewater treatment system and factory operation hence reducing risk.

• A biogas plant will attract saleable greenhouse gas credits, further offsetting the cost of building and operating the plant, and generating additional investment returns.

The main findings of the FTE are: • Virtually the entire load of more than 68 tonnes per day of organic matter is

broken down under vigorous production of biogas in one existing pond. This pond has naturally developed into an anaerobic digester, producing an estimated 8 million m3 of methane per year. This is a conservative estimate as the calculation was based on a below average organic strength of the wastewater at the time of the FTE. Routine, monthly reported analyses over the past two years show waste strength values of up to twice the value found during the FTE. Consequently, the methane yield forecasts would have to be updated accordingly. Based on average BOD5 figures recorded from February 1997 until 7 June 2000 the expected methane yield would be 9 million m³ pa. This is a direct confirmation of the


suitability of the concept of a biogas harvesting plant. Imminent expansion of the factory is expected to further increase overall biogas yield.

• Factory discharge conditions, ambient temperatures, the organic content of the wastewater and the absence of interfering substances confirm that the conditions are ideally suited for a biogas harvesting project.

• Substantial amounts of solids are removed by mechanical means from the wastewater circuit. This material, if not removed from the wastewater, has the potential to generate an additional estimated 5.6 million m3 of biogas per year.

• An estimated 750 tonnes of highly active bacteria are present in the anaerobic digester pond, which is more than sufficient to seed a new plant. The availability of sufficient biological material will result in fast startup time of a new plant, quickly achieving full load conditions, thus returning biogas shortly after startup.

• The effluent of a glucose plant at the factory contains high levels of soluble organic matter and, if added to the main waste stream, is expected to generate an additional 0.5 million m3 of methane per year.

• The construction of a new plant is recommended, rather than upgrading the existing anaerobic digester pond for reasons of distance to the factory, and reasons of flexibility, reliability and cost savings associated with the construction of a new plant.

• Proceeding to the next phase of the Project is recommended which entails the construction and erection of a pilot plant at the site. The pilot plant is expected to provide valuable engineering data, confirm expected biogas yields from wastewater and suspended solids, provide operational data, lead to project cost savings and reduce overall risk of the project.


2 INTRODUCTION

2.1 Background Sanguan Wongse Industries Co. Ltd. (SWI), in Khorat, Central Thailand. SWI is Thailand’s’ largest processor of cassava root at 2,200 tonnes per day, increasing to 2,900 tpd in the near future. The factory produces 550 tonnes of native tapioca starch per day (increasing to 700 tpd) modified tapioca starch and glucose syrups as its main products. The factory currently discharges more than 6,000 m3 of concentrated wastewater per day with soluble and particulate organic matter as its main constituents. The wastewater flow is expected to increase to more than 7,000 m3 in the future.

2.2 Prospects for Biogas Harvesting The particular conditions at SWI make the site an ideal candidate for the generation of energy-rich biogas from anaerobic digestion of the organic constituents of the waste. All of the usual parameters on the checklist of the biogas project developer stack up in favourable terms: • High volumes of highly concentrated wastewater are produced, 24 hours a day,

365 days a year, thus maximising the utilisation rate of an installed biogas system. • Ambient temperatures are nearly optimal for anaerobic digestion, so no heating is

required. • Starch and sugars (the main constituents of the wastewater) are ideal substrates for

biogas production, with low levels of interfering compounds such as sulfide and ammonia.

• SWI is currently spending approximately US$ 1.6 M pa on Heavy Fuel Oil (HFO) and $ 2.0 M on electricity. From January 1999 until January 2000 the cost of HFO increased from 3.7 to more than 7.5 Baht per litre. With a doubling in energy costs within one year SWI experienced lower profit margins in a competitive market.

• The factory has large areas available for the construction of a biogas plant in close vicinity of the factory.

• The availability of land area means that inexpensive in-pond technology can be utilised, in contrast to UASB or expanded bed high-rate anaerobic reactors which are expensive and were primarily developed to save foot print area.

• Projected biogas yield is expected to replace all of the factory’s HFO requirement plus generate an excess for electricity generation to offset a substantial percentage of the factory’s public-grid supplied electricity.

• The returns on biogas production and the cost of the biogas plant are expected to result in unusually attractive investment rates of return.

• A biogas plant can conveniently be constructed and commissioned without interference with the current wastewater treatment system and factory operation hence reducing risk.

• The wastewater is currently discharged to a large lagoon system, where the organic matter is broken down naturally by anaerobic processes. Biogas escapes to the atmosphere in excess of 10 million m3 methane (a greenhouse gas at least nine times more potent than carbon dioxide) per year. Harvesting of this biogas will replace the use of mineral fuel and will attract saleable greenhouse gas credits,


further offsetting the cost of building and operating the plant, and generating additional investment returns.

2.3 Feasibility and Technical Evaluation The implementation of a biogas harvesting plant at SWI is planned to proceed in four stages: 1. Feasibility & Technical Evaluation (FTE) site evaluation. 2. Pilot testing phase. 3. Design, build and commissioning phase. 4. Establishment of a Project Operating Company (POC). Engineering personnel from Clean Energy Development Company (Thailand) Ltd., the Project Developer and Project Manager, and from Waste Solutions Ltd, the Project Design Engineer, have conducted an FTE site evaluation. Engineering personnel, lead by WSL’s Dr Tico Cohen visited the site during the week of 20-27 January 2001.

2.4 Purpose of the FTE The purpose of the FTE phase was to assess the overall technical feasibility of the Project. To be more specific, the FTE included the following tasks: 1. An investigation into the suitability of the wastewater for biogas generation. 2. An assessment of the current mode of operation of the waste treatment system,

identification of existing anaerobic processes and evaluation of the characteristics in terms of treatment efficiency, biogas production and other factors.

3. An assessment of the layout and operation of the current wastewater system with an eye on possible (re-)utilisation of parts of the existing system and the availability of active biomass (bacteria) to start a full scale plant.

4. An assessment of factory management practices with respect to the current handling of the wastewater.

5. An assessment of the current site layout and identification of a suitable site for a future plant.

6. Identification of eventual areas of risk and recommendations for steps to be taken in the planning process.

This report is subdivided into two main sections: Chapter 3 discusses the findings of the FTE in general terms, Chapter 4 focuses on the technical and scientific aspects. An Appendix is added, containing photos, analytical laboratory results and scientific evaluation of sludge activity.

2.5 Acknowledgements We thank Sanguan Wongse Industries for their hospitality and the excellent assistance from factory staff with the FTE site tests.


3 FEASIBILITY AND TECHNICAL EVALUATION In this Chapter the general methodology and results of the FTE are discussed in general terms. The reader is referred to Chapter 4 for a more detailed technical and scientific discussion.

3.1 Methodology The FTE included a number of tests and other investigations involving the wastewater, the performance of the current treatment system and factors related to the factory operation and the site layout.

3.1.1 Flow and Temperature Monitoring In order to establish the flow of wastewater from the factory, and, more importantly variations and peak flow of wastewater, a recording flowmeter was installed in a channel which conveyed the entire wastewater stream to the wastewater ponds. In addition to the flow rate of the wastewater, the temperature of the wastewater was recorded as well.

3.1.2 Wastewater Analysis The initial treatment of the wastewater occurs in a series of five ponds, before it is pumped up a hill on its way to an extensive series of facultative aerobic ponds. The wastewater flowing into, and from each of the initial five ponds was sampled and analysed for various parameters (including but not limited to) COD, BOD5, Suspended Solids (SS) and Volatile Suspended Solids (VSS). The intention of the sampling and analysis was to establish the current performance of the first five existing ponds. This would provide further information on how the organic matter in the wastewater breaks down and how quickly, and if, and where the bacteria are located that are responsible for the initial stages of the current treatment process.

3.1.3 Vertical Sludge Distribution Profiles Using a small dinghy vertical profiles of suspended solids were measured at different locations on the ponds. A special probe was used to establish the vertical distribution of sludge. In addition, the pH and the temperature of the water in the ponds were measured. The measurement of the depth of the ponds, together with the vertical distribution of the sludge would allow an estimate to be made of the active volume of the ponds, and the quantities of sludge in the ponds.

3.1.4 Sludge Activity Tests It was useful to not only assess how much sludge was available in the ponds, but also what the capability of the sludge samples was to convert COD into biogas. Sludge was pumped from several areas in Ponds 4 and 5 (See Layout Map of the Sanguan Wongse Industries Khorat facility, Figure 1) close to the perimeter of the ponds. A 5 m long suction hose was tied to a pole and pushed into the sludge layer


near the bottom of the pond. (Figure APP-2) Sludge samples were collected into sealed bottles fitted with a rubber serum cap. The bacteria in the bottles were ‘fed’ with acetic acid (an important intermediate in the production of biogas, Figure APP-1) and the gas production in the bottles was measured with a pressure gauge. (Figure APP-3). Some gas samples were collected for analysis at WSL’s NZ laboratory by releasing the gas into a gas tight syringe.

3.2 The Wastewater System Wastewater passes through a rotary screen system (Figure APP-4) prior to discharge. The samples of the main factory effluent (FE samples) have been collected downstream of this screen (Figure APP-5). Downstream of the sample point of the factory effluent, two static screens remove fine particles from the effluent (Figure APP-6), after which the water flows to the ponding system. A plan view of the first five ponds of the wastewater system is shown in Figure 1, along with positions of wastewater sampling points, vertical profiles and sludge sampling points. Ponds 1 and 2 were full with sludge and the dotted lines indicate ‘flow channels’ of the wastewater over the surface of the sludge. The dotted lines in Pond 3 indicate a more or less solidified ‘dyke’ which partitioned the pond into two areas.


FIGURE 1 Layout of the wastewater system (first 5 ponds). Numbers in rectangles refer to

wastewater sampling points; numbers in triangles show approximate positions of the vertical sludge profiles and numbers in circles show approximate sludge sampling

positions.


Factory wastewater entered the system at Pond 1, flowed by gravity into Pond 2, and from thereon into Pond 4. The effluent of Pond 4 flowed via multiple conduits into Pond 5 and then into Pond 6 from where the water is pumped up the hill. At the time of the site visit the main flow from the factory was about 260 m3 per hour (see below). The wastewater from the Glucose Factory, which represents a small flow of about 15 m3 /hour (advised by the owner of SWI) flows into Pond 3 and from there into Pond 5, bypassing Pond 4.

3.3 Main Findings of the FTE The results of the FTE lead to a number of important findings, which are discussed below • Only one pond is active. Only Pond 4 appears to be active in the anaerobic

breakdown of organic matter. The pond achieves a high degree of removal of a BOD5 load of more than 60 tonnes plus approx 8 tonnes of SS per day. This would lead to an estimated annual gas production of 8 million m3 of methane. It is important to note that this figure is based on a BOD5 analysis at the inlet of Pond 4 of 9,750mg/l at the time of sampling during the FTE. This value is below the average recorded from February 1997 until June 2000 (monthly reported routine analysis). BOD values were nearly 11,000 on average, with peak values as high as 20,000mg/l. Consequently, expected biogas yield forecasts would have to be upgraded to 9 million m³ pa for an expected BOD5 average of 11,000 mg/l. The tests have shown that Ponds 1,2, 5 and 6 are full with sedimented sludge and do not contribute to biological waste treatment of any significance. Ponds 1 and 2 have turned acidic, which inhibits the growth of methane bacteria. The wastewater from the factory flows through both ponds over the sedimented sludge layer which reaches to the surface of the ponds (Figure APP-8). Pond 4 is effectively a large anaerobic digester with gas visually escaping from the surface of the pond (Figure APP-9). The high gas production in the pond has a strong mixing effect and keeps the sludge in the pond in suspension. This prevents sludge particles settling to the bottom and silting up of the pond (as has happened with the other ponds). Organic constituents of the waste such as soluble COD and BOD5 are effectively removed. The effluent of Pond 4 is effectively stabilised and has little residual BOD5 and suspended solids


The low levels of residual BOD5 in the effluent of Pond 4 imply that in the downstream ponds hardly any biological activity occurs. The lack of gas production eliminates the turbulence and sludge particles settle out. Ponds 5 and 6 are also full with sedimented sludge.

• Suspended solids are mechanically removed from the wastewater and provide an opportunity for additional biogas recovery. Significant quantities of suspended solids are removed from the wastewater transportation system, in particular through removal by the static screens and by sedimentation in Ponds 1 and 2. Biogas recovery, predicted in previous reports, was partly based on the breakdown of suspended solids (small particles of beets and root systems). It appears that between the factory outfall and the entry point into Pond 4 substantial reduction takes place of the suspended solids concentration. An important contribution towards removal of suspended solids is the static screens, and to a minor extent solids are also removed by sedimentation in Ponds 1 and 2. Modification of the existing wastewater transport system and adjustment or elimination of systems that are removing most of the suspended solids in the waste stream will provide an opportunity to achieve targeted methane production yields as outlined in previous reports. As a result, the methane yield is expected to increase from the current 8 million m3 to 13.6 million m3, thus representing a potential increase of 70%. Modification of the transport and solids handling system shall be one of the focal points of future pilot plant operations.

• Conditions are conducive to anaerobic digestion. Conditions of flow, temperature and the very low levels of potentially toxic substances are conducive towards successful implementation of a stable process. Flow at the time of the FTE averaged 260 m3/hour, with fluctuations between approximately 170 and 340 m3 per hour. These fluctuations are well within the boundaries of safe and reliable process operation. The temperature of the wastewater at the point of discharge is about 3 oC above ambient temperature. During its course through the pond system the water gradually cools down to ambient temperatures of about 30 oC, which is near optimal for anaerobic digestion. During the monitoring period no evidence was found of hot discharges which could potentially lead to overheating. The maximum levels of ammonia recorded in the system were 117 mg/l, a very low and safe level for operation of an anaerobic process. Sulfide was not measured but according to the owner very little sulfuric acid (a main source of sulfide production in anaerobic systems) was used in the process. Moreover, possible high iron levels in adhered soil would see any sulfide


production precipitated as insoluble iron sulfide. Low levels of sulfide in the biogas are conducive to reducing odour problems and extending the life cycle of biogas driven generator sets and boilers.

• Highly active biomass is present in Pond 4. Pond 4 contains an estimated 750 tonnes (as VSS) of highly active anaerobic sludge which would be suitable and more than sufficient to start up a new plant. As an example, a new plant for the processing of 7,200 m3 wastewater with a total COD load of 132 tonnes per day would require 265 tonnes VSS to achieve full load at startup, which is equivalent to 35% of the sludge in Pond 4. This requirement for startup sludge can be further reduced by gradual startup procedures. The bacteria in Pond 4 are highly active and it is estimated that at the current load conditions the bacteria only use about 12% of their potential methanogenic activity. Pond 5 is filled with sedimented sludge from Pond 4. It would be suitable for starting up an anaerobic treatment plant but its characteristics and potential activity are inferior to the sludge in Pond 4.

• Effluent of Glucose Factory. The effluent from the glucose factory represents a low flow of about 360 m3/d, but it appears highly concentrated and is expected to be easily degraded in an anaerobic system, adding an estimated 0.5 million m3 pa to the potential biogas yield. The effluent of the glucose factory was at the time of sample collection highly acidic (pH 1). The glucose effluent runs through Pond 3, and not much evidence was found of any appreciable biological activity in the pond.

Note that these conclusions reflect the situation encountered at the time of the FTE, which covered a short monitoring period and care must be taken with generalisation of the results.

3.4 Discussion The site conditions, the composition and other characteristics of the wastewater appeared ideal for the proposed biogas harvesting project. The strongest evidence was presented by the fact that Pond 4 was already an active anaerobic digester. However attractive it would appear to just cover Pond 4 and collect the biogas, this would not be advisable for a number of reasons: • Pond 4 is shallow, has a large surface area and covering of the pond would be

costly. The pond is at considerable distance from the factory and reticulation of gas and electricity would be expensive as well.

• Several large areas (at least hundred rai) are available near the factory for the construction of a new plant. Short distances mean reduced reticulation costs and minimising losses of BOD5 and suspended matter, and minimising the risks of odour generation.

• A newly designed plant can be optimised towards the objectives of the project. New design-build plants often offer more flexibility (and therefore cost savings)


than upgrades to existing systems. For instance, a new plant could be built 8-10 m deep, which improves mixing characteristics and minimises costs of a cover.

• A new plant can be built in parallel with the existing system and can be started up without any interference with the operation of the current system.

Despite the positive outlook for a biogas harvesting project at SWI, the use of a pilot plant is strongly recommended. The objectives of a pilot plant phase are outlined in the next section.

3.5 The Objectives of a Pilot Plant Trial In general, the use of a pilot plant enables the collection of valuable data which assist with an economical design, and minimises any associated risks. While there is a cost involved with a pilot scheme, it is common that savings made on full scale project development arising from economical design or increased plant safety, concluded as a result of pilot plant operations, more than offset the costs and operation of a pilot plant. The objectives of a pilot plant trial at SWI are the following: 1. Test process configurations which minimise Hydraulic Residence Time without

compromising the safety of the plant. Shorter HRT reduces the volume of the plant and thus construction costs. But how far can the volume be reduced without introducing new risk of biomass losses caused by washout? Providing an answer to this question is one of the main objectives of the trial.

2. Collect important biokinetic and other process design information. The pilot plant will permit the collection of important process information regarding mixing conditions, biomass activity and growth, plant stability and so on under realistic conditions. The information will be primarily used for process design, but also will add to the know-how of the newly formed POC with a view on plant operation and maintenance.

3. Opportunity for trialling alternative process configurations. The pilot plant will be designed with maximum flexibility and will allow side by side evaluation of two parallel process configurations, including Anaerobic Hybrid Baffled Process, Anaerobic Contact Process and UASB Process.

4. Optimise gas production from fine suspended solids. In accordance with the findings of this study it is of great importance to investigate opportunities for maximising biogas recovery from suspended matter and investigate its digestibility. Optimisation of this nature is very hard, if not impossible to conduct in a laboratory.

5. Establish achievable gas recovery for contractual purposes. As a full-scale plant will be built under a BOT contractual arrangement between the new POC company and the owner of SWI, promising the delivery of a certain gas volume, it is important to establish what levels of methane production are achievable without risk of over-commitment.

6. Increase know-how and experience with operational characteristics of a cassava operated anaerobic wastewater treatment process prior to the commissioning of the full scale plant. This will further reduce operational risk and also will anticipate possible operational problems on full scale.


7. A pilot plant is a suitable demo site for further proliferation of biogas technology in Thailand and in the cassava industry in particular. The owner of SWI is the Chairman of the khorat Association of Cassava Processors and it is expected that this project will lead to extensive project replication within the industry in Thailand.

3.6 Recommendations The outcome of the FTE Phase investigation and analysis leads to two main recommendations: 1. Proceed with the next stage of the Project; the construction of a pilot plant

followed by site testing. 2. Conduct trials into increasing suspended solids levels in the waste stream and

establish its biodegradability and associated gas yield. If necessary, extend the investigations into methods for size reduction (e.g. maceration) prior to anaerobic digestion. It is recommended that some of this work be done in co-operation with SWI.


4 TECHNICAL AND SCIENTIFIC RESULTS In the following sections the technical details of the investigations are documented as a reference for the more general discussion in the previous Chapter.

4.1 Methods

4.1.1 Wastewater and Sludge Analysis While it was intended that the raw wastewater from the factory would be sampled on a continuous basis for several days using an automatic sampler we did not succeed in obtaining an automatic sampler during the FTE visit. Therefore three samples were collected from the main factory effluent on three consecutive days. All samples were collected as grab samples. The following data were recorded at the time of sampling: temperature, pH (using a Hanna Instruments portable pH/temperature meter), turbidity (using a Zuellig Cosmos SS/turbidity analyser) and ammonia (using a Merck Nessler Ammonia colorimetric quick test). All wastewater and sludge samples were stored in sealed sample bottles and kept refrigerated until analysis. Wastewater samples were analysed for mixed COD, filtered COD, BOD5, Suspended Solids, Volatile Suspended Solids, Total Kjeldahl Nitrogen (TKN) and Ammonia-Nitrogen. All sludge samples were analysed for Suspended Solids, Volatile Suspended Solids and Total Kjeldahl Nitrogen (TKN). All analyses were carried out by San E.68 Lab Company Ltd in Bangkok according to Standard Methods for Examination of Water and Wastewater (AWWA, APHA and WEF).

4.1.2 Flow and Temperature Monitoring Flow and temperature were recorded using a StarFlow Ultrasonic Area Velocity Flowmeter. The flowmeter sensor was mounted on a base plate and suspended horizontally in a flow channel, 1.57 m wide, 4.03 m long and about 3.5 m deep. The sensor was located at a depth of about 1.5 m below the surface. The flow inlet and outlet into the channel were located near the surface of the water. It is assumed that the water column below the sensor was stagnant and contained settled solids. The sensor head was placed well above the bottom of the channel to avoid solids covering the transmitter and receiver. A picture of the sensor is shown in Figure APP-7 shows a picture of the sensor head at the time of removal. Flow and temperature data were continuously sampled and averaged every 15 minutes. Data were periodically unloaded from the sensor using a laptop computer.


4.1.3 Pond Profiles Vertical sludge profiles in the ponds were made using a Zuellig Cosmos Suspended Solids Analyser. All readings were recorded in Direct Units and later calibrated against a suspended solids sample of known composition. Any readings exceeding approximately 3% Suspended Solids returned a ++++ saturation signal and was therefore not recorded.

4.1.4 Sludge Activity Tests 50 ml sludge samples were put into 120 ml serum bottles. The headspace of each bottle was flushed with nitrogen gas and then sealed. The bottles were stored at ambient temperature (30-35 oC) and monitored for gas production at regular intervals.

4.1.4.1 Gas Production Measurement Gas production pressure was monitored using a hypodermic needle pierced through the rubber seal at the serum bottle, connected to a proprietary electronic pressure gauge. Sufficient quantities of gas were released into a proprietary ‘condometric analyser’, a condom suspended in a measuring cylinder filled with water. Gas would blow up the condom and volume was measured by positive displacement.

4.1.4.2 Gas Composition Analysis Some gas samples were collected in sealed syringes and taken to New Zealand for gas analysis. Methane and carbon dioxide content were measured by gas chromatography.

4.1.4.3 Sludge Activity Tests The sludge samples were taken to Bangkok and incubated at ambient temperature (32.5 – 41.7 oC) and incubated with 2.5 and 5 mmol sodium acetate solution (2.5 mmol per ml), injected using a 1 ml syringe. Gas production was recorded at regular intervals. Gas production was plotted against time and corrected for methane content after analyses. Plots were made for calculated acetate utilisation against time and were checked for substrate-independent kinetics by attaining similar initial rates in 2.5 and 5 mmol incubations of the same sample. All checked incubations appeared to follow substrate-independent kinetics.

4.2 Results and Discussion

4.2.1 Wastewater Analyses Changes in the composition of the wastewater during its course from the factory outfall (FE) to Pond 6 are shown in Figures 2 and 3 respectively. Figure 2 shows that there is a strong reduction of CODm, SS and VSS from the factory outfall (FE) to the inlet of the ponding system (IN). The reduction of CODm is associated with the removal of suspended solids because the soluble COD and BOD5 are constant.


FIGURE 2

Changes in mixed COD (CODm), soluble COD (CODf), BOD5, SS and VSS from the discharge point at the factory until the outlet of Pond 5.

The main point of removal of suspended matter between the factory outfall (FE) and the entry point to the pond system are the static screens (Fig. APP-6). As projected biogas production for the future plant is partly based on gas recovery from suspended solids, the removal of solids by the static screens represent a significant reduction of the suspended solids load. In addition, further significant removal of suspended solids occur in Ponds 1 and 2 through sedimentation. On the day of sampling the total annual methane production would have been about 8 million m3 instead of the projected 13,6 million m3. This target is still achievable by returning the solids to the main waste stream and prevention of removal by sedimentation. Adding suspended solids back to the waste stream, and the opportunity for increased biogas recovery will be one of the focal points of investigation during the second phase of the project. Figure 2 also shows that virtual complete removal of soluble COD and BOD5 takes place in Pond 4, beyond which little further removal takes place. Figure 3 shows the breakdown of organic nitrogenous compounds (TKN) and the formation of ammonia, as well as the pH. The low pH at IN, 1E and 2E and the rise of pH in 4E is consistent with a strong acidification in the first two ponds, followed by removal of VFA, soluble COD and BOD5 in Pond 4. The further removal of ammonia in 5E and 6E is unexplained.

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

FE avg IN 1E 2E 4E 5E 6ESample location

mg/

l

CODmCODfBOD5SSVSS


FIGURE 3

Changes in TKN, ammonia and pH from the discharge point at the factory until the outlet of Pond 5.

FIGURE 4

Relative changes of composition of the wastewater in the distribution system from Factory to Plant inlet (IN), Pond 4 (4E) and Pond (5E)

The results shown in Figures 2 and 3 are summarised in Figure 4, which shows the relative contributions of the wastewater circuit before the pond inlet, Pond 4 and Pond 5. Strong removal of mainly SS and VSS (and the particulate fraction of CODm) occurs in the wastewater circuit, with the removal of BOD5, soluble COD and the remainder of the mixed COD in Pond 4. Beyond pond 4 there is little further activity.

0

50

100

150

200

250

300

350

400

450

500

FE avg IN 1E 2E 4E 5E 6ESample location

mg/

l

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

pH

TKNNH4+pH (direct)

-20%

0%

20%

40%

60%

80%

100%

IN 4E 5E

Sample location

Rem

oval

%

CODmCODfBOD5SSVSS


FIGURE 5

Wastewater flow profile. After about 5 pm on 24/1 the wastewater flow characteristics changed as a result of maintenance work in the factory.

4.2.2 Wastewater Flow The flow profile was recorded in two periods; a short period of about 2 hours on the 23rd of January 2001 and a longer period on the 24th (Figure 5). However, during the second period maintenance work in the factory reduced the average flow, and it is apparent from Figure 5 that a major disruption occurred as well. Average flow

(m3/hr) Total flow (m3/day)

Period 1 (23/1/01) 261.9 6,287 Period 2 (24/1/01, until factory disruption) 260.3 6,247

TABLE 1 Summary of flow data on 23 and 24 January

Figure 5 shows, that apart from the disruption, the flow appears to be reasonably constant with fluctuations between 170 and 330 m3/hr. A summary of average and total daily flows is shown in Table 1.

0

100

200

300

400

500

600

700

1/23/019:36

1/23/0114:24

1/23/0119:12

1/24/010:00

1/24/014:48

1/24/019:36

1/24/0114:24

1/24/0119:12

1/25/010:00

1/25/014:48

1/25/019:36

1/25/0114:24

Flow

(m3/

hr)


4.2.3 Temperature The temperature profile is shown in Figure 6.

FIGURE 6

Wastewater temperature profile. After about 5 pm on 24/1 the wastewater flow characteristics changed as a result of maintenance work in the factory.

The temperature fluctuates between 32.5 and 34.0 oC and is therefore slightly above ambient temperature of about 30 oC. This is also reflected by temperatures recorded in the ponds (Table 2), which shows that the FE, IN and 1E samples were about 3 degrees above the temperature in the remainder of the system.

FE IN 1E 3E1 4E 5E 6E Temperature (oC) 32.9 33.5 33.5 29.1 30.9 30.5 30.8

TABLE 2

Temperatures recorded in the wastewater system The temperatures in the ponds are close to optimal for methane bacteria and no overheating problems are expected.

4.2.4 Pond Profiles Pond profiles were measured on locations shown in Figure 1. The results are shown in Table 3.

32

32.5

33

33.5

34

34.5

35

1/23/01 12:00 1/24/01 0:00 1/24/01 12:00 1/25/01 0:00 1/25/01 12:00

Tem

pera

ture

(oC

)


Sludge Profile Pond 1 Solid sludge to less than 0.5 m below water surface Pond 2 Solid sludge to less than 0.5 m below water surface Pond 3 About 2 m until solid sludge layer or bottom, profile shown in Figure 7 Pond 4 About 3 m until solid sludge layer or bottom, profile shown in Figure 8 Pond 5 About 1 m until solid sludge layer Pond 6 About 0.5 m until solid sludge layer

TABLE 3

Summary of sludge profiles Pond 1 and 2. Full with sedimented solids. The acidic wastewater from the factory inhibits biological activity, leading to compaction of the solids. Factory effluent runs in ‘channels’ over the surface of the sludge (Figure APP-8). Pond 3. only receives wastewater from the glucose factory, which is only a small flow of approx. 15 m3/hr. The flow passes through a ‘channel’ (Profiles 1 and 2). The remainder of the pond (Profiles 3 and 4) have very low concentrations of suspended solids down to a depth of about 1.5-2.5 m. Pond 4. This pond is highly active and nearly all of the BOD5 and soluble COD is removed to biogas. Biogas production is evident from active gas bubbles ‘erupting’ on the surface of the pond (Figure APP-9). The high rate of gas production in Pond 4 keeps the pond mixed and prevents the sludge from settling to the bottom. With the exception of Profile 1 which was very close to the inlet channel from Pond 2, carrying strong acidic wastewater, all other profiles show good mixing and sludge density of up to 2.5 %. Pond 5 and 6. Both ponds are full with sludge, which originates from Pond 4. As the organic matter is predominantly removed in Pond 4, little biogas activity remains in Ponds 5 and 6 and sludge settles out, forming a dense sludge layer.


FIGURE 7

Vertical sludge profiles in Pond 3

FIGURE 8

Vertical sludge profiles in Pond 4.

4.2.5 Sludge Analyses Sludge samples could only be collected from the perimeter of the ponds (stretching about 5 m from the shoreline), as the pump and attachments were too heavy to carry into a dinghy. It is important to note that the sludge near the edge of the pond may not be as active as the material throughout the pond and therefore may not be truly representative for the activity in the bulk of the ponds. Sludge samples were used for activity tests (refer to next paragraph) and analysed for SS, VSS and TKN. TKN represents nitrogen, which is largely associated with bacterial protein. Highly active sludge with pure bacterial content would typically show 10-12% TKN on the basis of VSS.

0.00 0.50 1.00 1.50 2.00 2.50

0

0.5

1

1.5

2

2.5

Pond

dep

th

%SS

Profile 1Profile 2Profile 3Profile 4

0 0.5 1 1.5 2 2.5 3 3.5 4

0

0.5

1

1.5

2

2.5

3

Pond

dep

th

%SS

Profile 1Profile 2Profile 3Profile 4Profile 6


The results of the sludge analyses are shown in Table APP-2 in the Appendix. Average values for VSS/SS and TKN/VSS ratios are shown in Table 4. Pond 4 Pond 5 Average VSS/SS 59.1% 52.6% Average TKN/VSS 9.0% 6.7%

TABLE 4

Sludge analysis summary The biomass in Pond 4 has a higher organic matter content and a much higher nitrogen content than the sludge in Pond 5. This indicates that the sludge in Pond 4 contains more bacterial material in comparison with the sludge in Pond 5.

4.2.6 Sludge Activity Tests After collection of the sludge samples, 50 ml of each sample was transferred into sealed serum bottles and the gas production was monitored for about a day. Duplicate samples were collected from each sample point. Very little gas was produced (less than 20 ml per bottle) indicating that either the sludge was collected from a non-active zone or that very little residual substrate (feed) was available in the samples. The next day, each of the samples was incubated with sodium acetate in 2.5 and 5 mmol concentrations. In most samples gas production started almost immediately. Two gas samples were collected and analysed in NZ with the following results: 4L1b 86.4% and 4L2b 76.0% methane. An average of 81.2 % methane has been used for the calculations. The principle of the sludge activity tests is the following: If the bacteria have little feed, they become less efficient and the rate of gas production goes down. If the level of feed is increased, the rate of gas production goes up and increases to a maximum. This is the maximum rate of conversion and indicates the potential activity of the sludge. The incubations were done with high levels of feed, but at two different concentrations; if the rate of gas production at the lower concentration is the same as at the higher concentration it indicates that the maximum rate of gas production has been reached. Plots of acetate consumption rates for 5 mmol and 2.5 mmol incubations were similar (Figure APP-10), indicating that the feed levels were saturated and the bacteria produced methane at ‘maximum speed’. The trials showing a decline in gas production near the end of the test period also show calculated acetate levels close to zero, indicating that assumptions about gas composition were correct or close to the real value. The results of the activity tests have been summarised in Table 5. The first line of the table displays the capability of the sludge in Ponds 4 and 5 to produce methane. A tonne of VSS would produce 200-250 m3 methane per day. Sample 4L5 appears to be an outlier, which is not surprising because the sample was collected very close to the


outlet of Pond 2 (Figure 1). It is possible that the bacteria in this sample have been ‘hit’ by the acidic wastewater entering Pond 4 at that point. The sludge samples collected in Pond 5 are also active but to a much lesser extent. The lower activity of Pond 5 sludge samples is consistent with the findings discussed in the previous paragraph, where it was shown that samples from Pond 5 seemed to contain less protein (bacteria). Units 4L1 4L2 4L3 4L4 4L5 5L1 5L2 5L3Total specific methane production rate1

m3/tonne VSS/d 251 273 262 191 29 82 168 64

Density kg VSS/m3 36 34 30 34 23 25 33 35 Max Productivity Volume methane

per volume per day9.0 9.2 7.8 6.4 0.7 2.1 5.6 2.2

TABLE 5

Results of sludge activity tests. 1Assuming that 70% of the produced methane originates from acetic acid intermediates

The next line in Table 5 lists the concentration of sludge in the samples, which, after combination with the rates listed in the first line will give a volumetric production value. For instance for 4L1 it is predicted that one m3 of pond volume would produce up to 9 m3 of methane per day. This is a high rate and is comparable with what could be achieved in a UASB reactor. Summarising Table 5, the average maximum methane production rate for Pond 4 would be 244 m3/tonne VSS per day (excluding outlier 5L5), and 105 m3/tonne VSS per day for Pond 5. The maximum sludge activity would be 0.7 g COD per g VSS per day for Pond 4 and 0.3 g COD per g VSS per day for Pond 5. Again, the value for Pond 4 is considered a high rate, and the value for Pond 5 could be considered as moderate, but not insignificant.

4.3 The Glucose Factory Analysis of the wastewater from the Glucose Factory indicated that the waste is strong. The flow is about 360 m3/d, and the methane potential from this waste stream would amount to approximately 1,300 m3/d (Table 6).

Flow 360 m3/d BOD5 11 kg/m3 Total load 3,960 kg/d Methane potential 1,316 m3/d

TABLE 6

Methane production potential from Glucose Factory Effluent


4.4 Pond Volumes, Sludge Mass, Activity and Projected Gas Production

The findings discussed in the above sections have highlighted that Pond 4 is practically achieving full removal of the entire BOD5 load. The sludge in this pond is highly active and would be ideal for startup of a new plant. The main characteristics of the wastewater flow of the factory and the role of (the sludge in) Pond 4 are summarised in Table 7. Pond 4 contains about 766 tonnes of active sludge. As an example, a new plant for the processing of 7,200 m3 wastewater with a total COD load of 132 tonnes per day would require 265 tonnes VSS to achieve full load at startup, which is equivalent to 35% of the sludge in Pond 4. Estimated current biogas production originates predominantly from soluble COD (or BOD5) from the main factory. Small contributions are made by the suspended solids and the effluent from the glucose factory.

Pond volume 52,131 m3 VSS 766 tonnes Daily flow main factory 6,240 m3/d Estimated daily flow Glucose Factory 360 m3/d Total daily flow 6,600 m3 BOD5 load to pond 60,840 kg/d Solids load to pond 7,800 kg VSS Methane production from BOD5 20,229 m3/d Methane production from VSS 1,911 m3/d Methane production from glucose plant 1,317 m3/d Total methane productivity 23,457 m3/d Total annual methane production 8,561,805 m3 Potential methane production 187,345 m3/d Actual/maximal methane potential 12%

TABLE 7

Summary data, assuming using sludge from Pond 4 in a future plant The two lines at the bottom show that the sludge in Pond 4 has the capacity to produce up to 187,000 m3 of methane per day, therefore only 12% of its capacity is actually utilised.


5 APPENDIX

5.1 Biogas Production from Organic Matter To put the investigations into context it is useful to briefly discuss the mechanism of anaerobic conversion of organic matter into biogas. The process proceeds roughly in three steps (Figure APP-1).

FIGURE APP-1

Anaerobic degradation of organic matter. During the first phase of the process, organic matter is ‘dissolved’ under the influence of enzymes into soluble products, such as sugars. Fermentation processes convert the soluble products in Volatile Fatty Acids (VFA), a mixture of organic acids which tend to reduce the pH. During the next phase a different group of bacteria which forms a symbiosis with methane bacteria convert some of VFA into acetic acids, carbon dioxide and hydrogen gas. The final step is the conversion of these products into biogas by methane bacteria.

Organic matterOrganic matter

Volatile Fatty AcidsVolatile Fatty Acids

BiogasBiogas

Acetic Acid,carbon dioxidehydrogen gas

Acetic Acid,carbon dioxidehydrogen gas

Hydrolysis

Acidogenesis

Acetogenesis

Methanogenesis

Fermentative

bacteria

Symbiotic

bacteria

Methane

bacteria


5.2 Photos

FIGURE APP-2 Collection of sludge samples from the ponds

FIGURE APP-3 Hotel room laboratory, showing sludge activity tests in progress.


FIGURE APP-4 Rotary screen before the factory discharge point (FE)

FIGURE APP-5 Factory Effluent (FE) sample location


FIGURE APP-6 Static screens remove fine particles from main factory wastewater

FIGURE APP-7 Main drain flow channel and area velocity flow sensor head (at the time of removal)


FIGURE APP-8 Flow channel on top of Pond 1.

FIGURE APP-9 Gas bubbles on the surface of Pond 4.


5.3 Data

5.3.1 Wastewater analyses

Location Factory Factory Factory Inlet Glucose factory

Inlet Pond 3

Outlet Pond 1

Outlet Pond 2

Outlet Pond 3

Inlet Pond 5

Outlet Pond 4

Outlet Pond 5

Outlet Pond 6

SAMPLE NR FE1 FE2 FE3 IN GLF GE 1E 2E 3E2 3E1 4E 5E 6E DATE 23-Jan 24-Jan 25-Jan 23-Jan 23-Jan 23-Jan 23-Jan 23-Jan 23-Jan 24-Jan 24-Jan 23-Jan 23-Jan TIME 17:00 9:15 8:40 17:20 16:45 17:15 17:30 11:40 9:45 9:15 9:30 12:30 18:15 pH (direct) 6.04 - 6.10 4.51 1.07 6.64 4.38 3.92 7.30 7.15 6.92 6.98 7.43 CODm 36,000 30,000 30,000 13,800 20,000 2,050 13,250 18,000 7,500 600 1,300 1,200 650 CODf 11,000 8,333 11,625 8,250 15,750 100 9,600 12,750 50 70 180 100 120 BOD5 7,250 6,250 9,250 7,500 11,000 41 6,500 9,750 16 33 75 22 49 SS 24,800 20,900 16,150 4,030 807 2,290 3,475 1,420 18,200 433 387 855 545 VSS 23,700 20,100 14,500 3,567 613 1,220 3,000 1,250 7,700 273 303 495 325 TKN 433 315 496 323 210 189 307 234 783 233 197 197 95 NH4+ 35 72 43 31 34 89 27 36 76 19 117 42 15 Turbidity 812 - 196 1,844 279 141 1,005 1,871 32 129 116 112 160 Temperature 33.4 - 32.3 33.5 45.6 30.4 33.5 - 29.0 29.1 30.9 30.5 30.8

TABLE APP-1

Results of wastewater analyses


5.3.2 Sludge Analyses Location Pond 4 Pond 4 Pond 4 Pond 4 Pond 4 Pond 5 Pond 5 Pond 5 SAMPLE NR 4L1 4L2 4L3 4L4 4L5 5L1 5L2 5L3 SS 62,800 55,600 51,400 57,200 37,200 48,400 60,400 69,000 VSS 36,000 33,600 29,800 33,600 22,800 25,200 33,200 35,000 TKN 3,719 3,088 2,647 2,962 1,796 2,017 1,639 2,490 VSS/SS 57% 60% 58% 59% 61% 52% 55% 51% TKN/VSS 10.3% 9.2% 8.9% 8.8% 7.9% 8.0% 4.9% 7.1%

TABLE APP-2 Results of sludge analyses

5.3.3 Acetate Removal Plots

-1

0

1

2

3

4

5

6

0 5 10 15 20

Time (hours)

Ace

tate

(mm

ol)

4L1a

4L1b

-1

0

1

2

3

4

5

6

0 5 10 15 20Time (hours)

Ace

tate

(mm

ol)

4L2a

4L2b

-1

0

1

2

3

4

5

6

0 5 10 15 20Time (hours)

Ace

tate

(mm

ol)

4L3a

4L3b

-1

0

1

2

3

4

5

6

0 5 10 15 20

Time (hours)

Ace

tate

(mm

ol)

4L4a

4L4b


FIGURE APP-10

Sludge activity tests; Acetate removal plots

0

1

2

3

4

5

6

0 5 10 15 20Time (hours)

Ace

tate

(mm

ol)

4L5a

4L5b

0

1

2

3

4

5

6

0 5 10 15 20Time (hours)

Ace

tate

(mm

ol)

5L1b

-1

0

1

2

3

4

5

6

0 5 10 15 20

Time (hours)

Ace

tate

(mm

ol)

5L2a

5L2b

0

1

2

3

4

5

6

0 5 10 15 20Time (hours)

Ace

tate

(mm

ol)

5L3a

5L3b

methane from glucose factory - thailand

Documents