The Development and Demonstration of Small-scale Biogas

Executive Summary Report

Department of Alternative Energy Development and EfficiencyMinistry of Energy

STFE CO., LTD

Prepared by

The Development and Demonstration of Small-scale Biogas Digester using Organic Waste

October 2006

Acknowledgement

Department of Alternative Energy Development and Efficiency (DEDE) has hired STFE Co., Ltd. as a consultant for the development and demonstration of small-scale biogas digester using organic waste. The project comprised the designing and developing of the prototype small-scale biogas digester, the experimentation of organic waste digestion, the fabrication of the 100 fully-developed small-scale biogas digesters as well as the installation and demonstration in many places. All mentioned work has been successful, reaching the project objectives, due to the good cooperation from all parties.

DEDE would like to express its gratitude to Baan Suan Phai Sukkapap Restaurant, Phaholyothin Rd., Phayathai District, Bangkok who kindly gave us permission to install the prototype biogas digester and facilitated us during the whole period of experimentation. The gratitude is also extended to schools under the Office of Education, Bangkok Metropolitan Administration and those which are under the Office of Basic Education Commission; 15th Infantry Regiment, Nakhon Ratchasima; 3rd Armed Forces Development Battalion, Chiang Mai; 6th Infantry Regiment, Suppasitprasong Military Camp, Ubon Ratchathani and Srinet Energy Development Co. Ltd., Maha Sarakham for permitting us to install and demonstrate the use of the biogas digesters.

i

Executive Summary Report Table of Contents

Page

Chapter 1 Introduction 1-1 1.1 Rationale 1-1 1.2 Objectives of the study 1-1 1.3 The project scope 1-1 Chapter 2 The Development of the Small-scale Biogas Digester 2-1

using Organic Waste 2.1 Basic knowledge of biogas production using organic waste 2-1

2.2 The design of biogas digester 2-2 2.3 The fabrication and installation of the prototype biogas digester 2-4 2.4 Improvement for enhancing the efficiency of the biogas digester 2-6 2.5 The experimental result of organic waste digestion 2-11 in the prototype biogas digester 2.6 The performance evaluation of the small-scale biogas digester 2-15 Chapter 3 The Installation of Biogas Digesters in 100 Selected Sites 3-1 and the Digester Use Monitoring 3.1 Selection of biogas digester installation sites 3-1 3.2 The installation of biogas digesters in the 100 selected sites 3-5 3.3 Monitoring result of the use of installed biogas digesters 3-18 Chapter 4 Economic Feasibility Analysis 4-1 4.1 Assumption 4-1 4.2 Analysis result 4-2 Chapter 5 Summary and Suggestions 5-1

5.1 Summary 5-1 5.2 Suggestions 5-2

ii

List of Tables

Page Table 2.5-1 The amount and composition of organic waste at 2-11 Ban Suan Phai Sukkaphap Restaurant Table 2.5-2 The characteristic of the organic waste 2-13 Table 2.5-3 Biogas quality 2-14 Table 2.5-4 The characteristics of digestate and water effluent 2-14 Table 2.5-5 The quality of compost produced from the biogas digester 2-15 Table 2.6-1 Pollutant reduction efficiency of the small-scale biogas digester 2-16 Table 3.1-1 The selection result of biogas-digester installation sites 3-3

iii

List of Figures Page Figure 2.2-1 Process flow diagram of the designed biogas digester 2-5 Figure 2.3-1 The prototype biogas digester after assembled 2-6 Figure 2.4-1 Waste shredder improvement 2-7 Figure 2.4-2 The adjustment of the waste feeding pipe of the digester 2-7 Figure 2.4-3 Changing of the top lid to prevent gas leaking 2-8 Figure 2.4-4 Adding a water level pipe 2-8 Figure 2.4-5 The figure of agitator in the digester 2-9 Figure 2.4-6 Pressure measurement tool changing 2-9 Figure 2.4-7 Metal ladder improvement 2-10 Figure 2.4-8 Installation of biogas storage tank 2-10 Figure 2.4-9 Cooking burner modification 2-11 Figure 2.4-10 Process flow diagram of the prototype biogas digester after improvement 2-12 Figure 3.2-1 The digester installation and operator training in the installations sites 3-5

Executive Summary Report The Development and Demonstration Chapter 1 of Small-scale Biogas Digester using Organic Waste Introduction

Department of Alternative Energy Development and Efficiency, Ministry of Energy

1 - 1

Chapter 1 Introduction

1.1 Rationale The characteristics of municipal solid waste in Thailand changes and differs according to seasons, social and economic condition, and the consumption behaviors of the people in each community/city. Still, generally municipal solid waste is consisted of 3 main components: (1) readily biodegradable organic waste such as food waste, vegetables, fruits, and leaves, making up 40-60% of the municipal solid waste; (2) combustible waste, such as organic waste which degrades slowly namely wood, rubber, leather, and paper; and synthetic organic waste namely plastic and foam, comprising 20-40%; and (3) inert material, such as non-combustible material like gravel, sand, glass, ceramic which comprises another 5-20%. Generally, the disposal of municipal solid waste in Thailand is not in line with the technical procedure. Very little organic waste has been disposed by anaerobic digestion for biogas. Since municipal solid waste is consisted of 3 components as mentioned, organic waste is the main contributor of many environment problems such as odor, leachate, disease transmission as well as methane emission which is the main cause of global warming. Thus if every households/communities separate organic waste and treat it in anaerobic digestion system which effectively treats the main component of the municipal solid waste (organic waste) in environmental sound manner and has compost and biogas as the by-product; the problem of waste disposal will be alleviated. In addition, this disposal method helps reserve energy and environment; and improves living quality of people in the community and society. Department of Alternative Energy Development and Efficiency, hence, would like to have a study and promotion of using organic waste digesters and to fabricate prototype small-scale biogas digesters using organic waste which can be demonstrated in many places across the country. 1.2 Objectives of the study

1) To develop, demonstrate and promote the fabrication and use of small-scale biogas digesters using organic waste

2) To raise the awareness of organic waste separation and increase the understanding of anaerobic digestion process which can produce biogas and compost from organic waste among households/communities/fresh markets, etc. 1.3 The project scope 1) Designing prototype biogas digester using organic waste which has a minimum capacity of 2 cubic meters and can produce biogas for a minimum of 1.2 cubic meters a day, estimating the fabrication cost and making a list of parts and equipments used in fabricating the digester 2) Fabricating a prototype biogas digester and conducting the experiments of organic waste digestion, collecting the data of the experimentation and suggesting the ways to enhance the efficiency of the digester

Executive Summary Report The Development and Demonstration Chapter 1 of Small-scale Biogas Digester using Organic Waste Introduction


1 - 2

3) Fabricating 100 biogas digesters according to the developed prototype 4) Selecting the appropriate 100 biogas-digester installation sites 5) Installing the digesters at the selected sites, start-up, monitoring until the digesters

are stable, compiling an operation and maintenance manual of the digester, and training the staffs responsible for operating the digesters

6) Monitoring the use of the digesters 7) Analyzing the economic feasibility of the project.

Executive Summary Report Chapter 2 The Development and Demonstration The Development of the Small-scale Biogas Digester of Small-scale Biogas Digester using Organic Waste using Organic Waste


2 - 1

Chapter 2 The Development of the Small-scale Biogas Digester

using Organic Waste 2.1 Basic knowledge of biogas production using organic waste 2.1.1 Biogas production using organic waste In anaerobic environment, anaerobic microorganisms convert readily biodegradable organic substances to methane (CH4) carbon dioxide (CO2) and water (H2O). This process is called anaerobic digestion. Biogas production using organic waste is anaerobic digestion process which is done in a closed digester which having anaerobic bacteria, digesting the waste, producing biogas and obtaining compost as its final product. 2.1.2 Parameters and process optimization for biogas production

1) Temperature: the rate of anaerobic digestion is greatly increased by

operating in the mesophilic temperature range of 35-40 degrees Celsius and thermophilic temperature range of 50-60 degrees Celsius.

2) pH: in running the biogas production system, pH should be controlled in the

range of 6.6-7.8. The most appropriate pH for the methane producing bacteria is between 7-7.2. 3) Organic loading: must be controlled at an appropriate level since if too

few organic are fed, it is not enough for producing methane and the digester size is unnecessarily too large. Still, if too many organic substances are fed, a volatile fatty acid accumulates, the bacterial processes are inhibited.

4) Retention time: depends on the operating temperature, type, characteristic,

and amount of organic fed into the digester and cost-effective of biogas production. A too short retention time is not enough for the bacteria to produce methane, and it is washed-out of the system too soon. In contrast, if the retention time is too long, there will be too high accumulation of the solid digestate and requiring an unnecessarily large digester. 5) Mixing: this is for mixing the organic substrate fed into the digester to contact the bacteria thoroughly, enhancing the biogas production and decreasing the sedimentation of digested solid at the bottom of the digester and preventing the scum forming at the surface of organic slurry in the digester.



2 - 2

2.1.3 Steps of biogas production from organic waste: Normally there are 3 steps as follows:

1) Front-end treatment is the separation of contrary materials from the organic waste then shredding it in a homogenous size appropriate for the digestion process.

2) Anaerobic digestion is for producing biogas, deodorizating, and stabilizing the waste.

3) Back-end treatment is the treatment of the residue from the digestion process by reducing excess moisture and conditioning it to be appropriate for use as fertilizer. 2.1.4 Utilization of biogas and the digestate from the digestion process

The quantity and quality of biogas from the biogas digestion system depend on types, characteristic, and quality of the treated waste. Moreover, they also depend on digestion environment and operating parameter control. The main components of biogas are methane (CH4) of 50-70% and carbon dioxide (CO2) of 30-50%. Apart from the two main gases are a little content of hydrogen sulfide (H2S), ammonia (NH3), hydrogen (H2) and water (H2O). The heating value of biogas is 21-25 MJ/m3. As for a very small system, the way to utilize the biogas for the full efficiency is to use it with cooking burner. The digestate from the biogas digestion process is an organic matter which microorganisms cannot digest further. Its main component is humus which absorbs water and nutrients for plants well, making soil loose. It also promotes plant roots to uptake water and nutrients better, preventing soil erosion. Thus, it is appropriate to use the digestate from the biogas digestion process as fertilizer. 2.2 The design of biogas digester Points to consider about the design of biogas digester using organic waste are (1) the technical feasibility corresponding to the principle of biogas production using organic waste and in line with the term of references of the study, (2) easy to use, requiring little workload to run and maintain the system and the user able to solve problems and maintain the system himself (3) saving cost by using parts available in the market where users can adapt or fabricate it according to the design by themselves.

2.2.1 Criteria for biogas digester design Type of waste fed into the system : Organic waste which has been separated from

community/household/school

Waste characteristic : 20% total solid (TS) content

90% volatile solid (VS) content of the TS content



2 - 3

Type of the designed digester : Single stage anaerobic digestion

Operating temperature : Ambient temperature

Retention time : Depends on the amount of organic waste fed into the system, but not less than 18 days

Specific gas production : 400-500 liters/kg of VS content (Data from commercial-scale anaerobic digestion system where operating and environmental parameters are controlled)

Biogas characteristic : 60% methane content

Biogas heating value is 6 kWh/m3

Minimum biogas produced : 1.2 m3

Minimum size of digesters : 2.0 m3

2.2.2 Equipment list of the designed biogas digester Most equipment used for the fabrication of the prototype digester are locally sourced and available in the market as follows:

1) Waste shredder is used for shredding organic waste to be particle not larger than 50 mm. It can shred waste not less than 50 kg/hour when running continuously and has a motor of 1 horse power.

2) Biogas digester is used for digesting organic waste and producing biogas. Its capacity is 2.4 m3, retaining organic waste for not less than 18 days and made of Fiber Reinforce Polyester (FRP).

3) Steel ladder is used when feeding organic waste into the digester and when stirring the waste slurry in digester. It is made of rust-proofing steel, 1 meter high.

4) Agitator is used for mixing organic waste in the digester. Its paddle and shaft are made of stainless steel; the shaft is 1.2 meter long.

5) Biogas pipe is an outlet of the produced biogas connected from the biogas digester to the cooking burner. It is made of PVC grade 13.5 with 12.5 mm. diameter.

6) Burner set is used for converting biogas energy to heat energy for cooking.

7) Sand-drying tray is for reducing the moisture content of the digested sludge. There are 2 plastic trays with 60-liter capacity each, filled with gravel and sand about haft of thier capacity.



2 - 4

8) Pressure gauge is used for measuring the pressure of biogas in the digester. Its reading range is between 0-1 bar.

9) Other auxiliary tools are clear plastic pipes, ball valves, rings, screws, bearings, etc. 2.2.3 The operation of the designed biogas digester The operation of the designed biogas digester is shown in figure 2.2-1. It can be summarized as follows

1) Shred the organic waste with waste shredder. Then, add water to adjust the concentration of the feed substrate to make it suitable for digestion

2) Feed the feed substrate through the waste feeding pipe into the digester where the anaerobic digestion takes place and biogas is produced

3) Biogas produced in the digester flows pass through the biogas pipes, to use for cooking

4) Residue from the digestion process is drained from the digester to use as liquid fertilizer or can be dewatered in the sand-drying tray to reduce moisture before use as compost. 2.3 The fabrication and installation of the prototype biogas digester 2.3.1 The prototype digester installation site is provided by Baan Suan Phai Sukkaphap Restaurant, 304 Phaholyothin Rd., Samsennai District, Bangkok where vegetarian food is sold and a campaign of organic waste separation has been promoted among the clients and food vendors. The prototype biogas-digester installation site required an area of 15 m2 (3 x 5 m.). 2.3.2 The fabrication and installation of the prototype biogas digester The prototype digester was a ready-made assembly parts which can be assembled at the site. The assembled prototype biogas digester installed at Baan Suan Phai Sukkaphap Restaurant is showed in figure 2.3-1



2 - 6

Figure 2.3-1 The prototype biogas digester after assembled 2.4 Improvement for enhancing the efficiency of the biogas digester

As for the improvement for enhancing the efficiency of the digester, the following parts and equipments are on focus:

2.4.1 Waste shredder has been improved as follows:

1) Changing the installation method of the waste shredder: According to the design, the waste shredder is directly connected to the digester next to the waste feeding pipe. After having run the machine, we found that the operation and cleaning became complicated. Thus, after the waste shredder has been installed separately, the operation and cleaning are less complicated.

2) Adding auxiliary parts to the waste shredder: the added parts are (1) a funnel for receiving dripping waste liquid from shredded waste (2) waste receiving funnel which is added for safety, relieving the problem of dripping and splattering of the waste. The figures of the waste shredder before and after the improvement showed in figure 2.4-1 2.4.2 Biogas digester The biogas digester has been improved for better efficiency as follows: 1) Adjusting the height of the waste feeding pipe: formerly, the height measured from the bottom edge of the cylinder shape of the digester was 68.0 cm. (working volume of 1,270 liters). It has been adjust to be 95.0 cm. resulting in more working volume of the digester (about 1,800 liters). The adjustment makes the digester able to retain organic waste fed into the digester of 85 kg/day (TS 10%) for 21 days. See figure 2.4-2



2 - 7

(a) Waste shredder (b) A funnel for receiving waste liquid at the bottom before improvement

(C) A waste receiving funnel at the loading tray

Figure 2.4-1 Waste shredder improvement

(A) The level of the ball valve on the feeding pipe (B ) The level of the ball valve on the before adjustment feeding pipe after adjustment

Figure 2.4-2 The adjustment of the waste feeding pipe of the digester



2 - 8

2) Fixing the problem of leaking gas at the lid of the digester: the original design was a 5 mm thick circle fiberglass with the same diameter as the lid. The fiberglass was cushioned with a rubber sheet and fixed to the panel of the digester with 4 screws. It was found that the gas was leaked when the pressure of the digester increasing. Thus, the thickness of the panel has been increased and the lid has been designed like a cap (figure 2.4-3). The number of the screws has also been increased to 8 screws. This helps effectively alleviate the leaking gas problem.

(A) Top lid (before changing) (B) Top lid (after changing)

Figure 2.4-3 Changing of the top lid to prevent gas leaking 3) Adding a water level pipe: A clear plastic pipe has been installed at the side of the digester which shows the level of the slurry in the digester, to have a level control of waste feeding and digestate draining out of the digester. See figure 2.4-4

(A) Before adding a water level pipe (B) After adding a water level pipe

Figure 2.4-4 Adding a water level pipe

4) Changing agitator: since the agitator used initially (figure 2.4-5 A) could not thoroughly mix the organic waste slurry in the digester, they have been changed to 3 level agitator (figure 2.4-5 B). We found that the new agitator can mix the slurry better. The problems of solid sedimentation and pH stratification in the digester have been eased.



2 - 9

(A) Agitator (before changing) (B) Agitator (after changing)

Figure 2.4-5 The figure of agitator in the digester

5) Changing pressure measurement tool: pressure gauge with the reading range of 0-1 bar sometimes could not read the gas pressure since the produced gas was very little. Thus, a manometer has been used. Manometer is simple equipment used to measure gas & liquid and appropriate for measuring pressure with low reading. See figure 2.4-6

(A) Pressure gauge (B) Water manometer (before improvement) (after improvement)

Figure 2.4-6 Pressure measurement tool changing

2.4.3 Metal ladder: initially the ladder was designed 1.0 m. high from the ground which was not high enough for mixing or feeding the waste into the digester. The ladder, hence, has been adjusted to 1.25 m. high for the ease of operation. See figure 2.4-7



2 - 10

(A) Metal ladder (before improvement) (B) Metal ladder (after improvement)

Figure 2.4-7 Metal ladder improvement 2.4.4 Biogas storage tank A biogas storage tank with gas storage capacity of 80 liters, comprising 2 plastic buckets (a 120-liter one is facing down inside the water-filling, 200-liter one) has been installed for more continuously use of the biogas. See figure 2.4-8

Biogas storage tank Figure 2.4-8 Installation of biogas storage tank

2.4.5 Cooking burner Since the cooking burner is conventional type which is designed to use with liquid petroleum gas (LPG), its gas injector cross section and jet openings are expanded for increasing their size to make the burner appropriate for use with biogas. (Figure 2.4-9)



2 - 11

(A) Expanding of gas injector cross section (B) Increasing the size of jet openings Figure 2.4-9 Cooking burner modification The process flow diagram of the prototype biogas digester after improvement see figure 2.4-10 2.5 The experimental result of organic waste digestion in the prototype biogas digester 2.5.1 Components and characteristic of organic waste input The composition and characteristic of organic waste of Ban Suan Phai Sukkaphap Restaurant were analyzed. The samples of organic waste from food preparation of the vendors and customers’ food waste were collected with a standard method. Then they were analyzed for their components: (1) readily biodegradable organic waste such as food waste, vegetable and fruit, and (2) contrary materials. The study result of the amount and components of the organic waste is presented in table 2.5-1. It has been found that contrary materials such as tissue paper, wood sticks, plastic, toothpicks were disposed to waste bin together with organic waste. Thus, the contrary materials must have been sorted out from the organic waste to be fed into the digester. After sorting out the contrary materials, samples of the organic waste were sent to the laboratory to analyze for their characteristic. The result is shown in table 2.5-2. This analysis result represents the characteristic of the organic waste fed into the digester. Table 2.5-1 The amount and composition of organic waste at Ban Suan Phai Sukkaphap Restaurant

1 2 3 1 2 3 1 2 3 1 2 3Organic waste 140.0 149.0 219.7 101.2 90.9 91.7 93.8 92.1 38.46 26.4 22.5 29.1 81.8 85.7 83.3 83.6Contrary materials 14.0 13.5 14.5 87.2 9.1 8.3 6.2 7.9 8.5 4.4 4.5 5.8 18.2 14.3 16.7 16.4Total 154.0 162.5 234.2 188.4 100.0 100.0 100.0 100.0 47.0 30.8 27.0 34.9 100.0 100.0 100.0 100.0

AverageNo.No.Amount (kg.) Percentage

Average

Waste from food preparationComposition Percentage

No. No.

Customer's food wasteAmount (kg.)

AverageAverage

Remark: The analysis of composition and characteristic of organic waste of Ban Suan Phai Sukkaphap Restaurant: 1st time on 23 February 06, 2nd time on 25 April 06, and 3rd time on 7 August 06 by STFE Co., Ltd.



2 - 13

Table 2.5-2 The characteristic of the organic waste Organic waste samples Parameters Unit No. 1 No. 2 No. 3 Average

1. COD mg/l 205,385 143,333 190,840 179,853 2. BOD mg/l 98,583 64,815 88,220 83,873 3. Total Kjeldahl Nitrogen (TKN) mg/l 1,522 3,220 2,534 2,425 4. Total Solid (TS) % (w/w) 11.5 13.7 15.5 13.57 5. Volatile Solid (VS) % of TS 89.6 93.4 92.9 91.97

Remark: Samples collected by STFE Co., Ltd.: 1st time on 25 April 06, 2nd time on 7th August 06, and 3rd time on 16 August 06, analyzed by Pilot Plant Development and Training Institute, King Mongkut's University of Technology, Thonburi.

2.5.2 Monitoring parameters of biogas digestion 1) pH was between 6.6-7.2. The pH in the start-up period (the first 20 days after running the system) was a bit acidic: 6.6-6.97. After getting in the stable condition, the pH was between 7.0-7.2 which is the most appropriate range for the growth of the methane producing bacteria. 2) Temperature in the day time had an average of 30 degrees Celsius (between 27-32 ◦C) while an average temperature at night was about 27 ◦C (between 26-28 ◦C). Normally, the change of temperature was less than 1 ◦C an hour, except a heavy raining period. 2.5.3 Biogas yield The biogas digestion in a prototype digester using 85 kg of organic waste per day with TS of 10% (8.5 kg/day) and VS of TS of 92% (7.82 kg/day) yielded biogas of 29.18 liter/kg wet weight or 291.8 liter/kgTS. It had specific gas production of 317.14 liter per kgVS. 2.5.4 The analysis result of biogas, digestate, and compost 1) Biogas quality The biogas quality are presented in table 2.5-3



2 - 14

Table 2.5-3 Biogas quality Results

Sample no. Parameters Unit 1 2 3 Average

1. Methane (CH4) % v/v 52.39 54.66 50.59 52.55 2. Carbondioxide (CO2) % v/v 34.06 32.91 38.30 35.09 3. Oxygen (O2) % v/v 1.50 0.67 0.60 0.92 4. Hydrogen (H2) % v/v 8.74 9.16 8.49 8.80 5. Nitrogen (N2) % v/v 3.31 2.60 2.02 2.64

Source: Samples collected by STFE Co., Ltd. 1st time on 11 May 06, 2nd and 3rd times on 11 and 18 August 06 respectively and analyzed by a laboratory of Asian Institute of Technology 2) Characteristics of digestate and water effluent from the biogas digester The analysis result of digestate (digested sludge from the digester) and water effluent discharged from the sand-drying tray is presented in table 2.5-4 Table 2.5-4 The characteristics of digestate and water effluent

Digestate Effluent from sand-drying tray Sample no. Sample no. Parameters Unit

1 2 3 Average 1 2 3 Average

Physical Characteristic

- Black slurry - Yellow water with sediment

-

COD mg/l 7,304 14,284 14,327 11,972 223 120 285 209 BOD mg/l 1,083 2,814 2,190 2,029 96.8 6.9 29.4 44.4 TKN mg/l 970 1,920 1,907 1,599 170 6.3 112 96.1

Source: Samples collected by STFE Co., Ltd. and analyzed by a laboratory of United Analyst Engineering Consultant Co., Ltd., digestate samples collected 1st 2nd and 3rd times on 2nd May, and 7 and 16 August 06 respectively, effluent samples collected 1st 2nd and 3rd times on 19 April, and 9 and 20 August 06 respectively. 3) Compost quality The quality of compost produced from the biogas digester is shown in table 2.5-5



2 - 15

Table 2.5-5 The quality of compost produced from the biogas digester Result Parameter Unit No. 1 No. 2 No. 3 Average

Guideline*

1. Organic Matter %dry weight 31.9 63.7 82.0 59.2 30-60 2. C/N Ratio - 7 6 12 8.3 ≤ 20:1 3. Nitrogen (N) %dry weight 2.6 6.2 4.0 4.3 1 4. P2O5 %dry weight 2.7 2.5 1.1 1.8 1 5. K2O %dry weight 0.5 1.0 1.1 0.9 0.5 6. CaO %dry weight 1.4 - 2.0 1.7 - 7. pH - 6.9 7.1 5.7 6.6 6.0-7.5 8. MgO %dry weight - - 0.2 0.2 - 9. Moisture** % wet weight 7.2 37.0 20.8 21.7 ≤ 35 10. EC dS/m - - 7.4 7.4 - 11.Passing Sieve - - - pass - - 12. Sharp Material - - - no - -

Source: Samples collected by STFE Co., Ltd. compost samples collected 1st 2nd and 3rd times on 23 April, 31 August and 7 September 06 respectively, and analyzed by the Office of Science for Land Development, Department of Land Development, Ministry of Agriculture.

Remark: * Guideline of compost quality introduced by Department of Land Development, Ministry of Agriculture, 1992. ** 1st sample prepared by dewatering on sand-drying tray of 4 days and further sun-dried of 4 days 2nd sample prepared by dewatering on sand-drying tray of 3 days and further sun-dried of 3 days 3rd sample prepared by dewatering on sand-drying tray of 4 days and further sun-dried of 3 days 2.6 The performance evaluation of the small-scale biogas digester 2.6.1 Biogas production The performance on biogas production of the small-scale biogas digester using organic waste can be calculated from the following details:

Organic waste fed into the digester 85.00 kg/day Total solid content (TS Content) 10.00 % 8.50 kg/day Volatile solid content (VS Content) 92.00 %of TS 7.82 kg/day Biogas produced 2,480.00 liter/day Specific gas yield (from the experimentation) 317.14 liter/kgVS Specific gas yield (used in the design) 450.00 liter/kgVS Efficiency of biogas production compared with value used in the design 70.47 %



2 - 16

According to the calculation above, the small-scale biogas digester using organic waste has biogas-production efficiency presented in a form of specific gas yield of 317.14 liter/kgVS. This figure represents 70 % of specific gas yield of commercial MSW anaerobic digester used in the design. The low efficiency are thought to be from not having temperature control of the digester to be in the most appropriate level for operating at mesophilic temperature range (35-37 C◦) and from mixing only twice a day instead of mixing constantly. However, the main contribution to this is assumable from not stirring constantly rather than not controlling the temperature to be steady since according to the study review of GTZ (2003), methane producing bacteria in biogas production system operated in mesophilic temperature range are not inhibited if the temperature change is not over + 1 ◦C/hr., but the temperature record done constantly in 24 hours and many times found that there were very few cases that the temperature change was more than 1 ◦C/hr. Hence, to enhance the biogas production of the digester in the future, the digester should be stirred continuously or mixing equipments should be improved for more convenient use so that the operators can stir the slurry in the digester more times. Still, if electronic equipment for stirring will be installed, energy balance of the system must be considered.

2.6.2 Pollutant reduction efficiency Pollutant reduction efficiency of the small-scale biogas digester using organic waste is presented through the removal rate of COD, BOD and total kjeldahl nitrogen (TKN) is illustrated in table 2.6-1 Table 2.6-1 Pollutant reduction efficiency of the small-scale biogas digester

Remark: * The concentration after adjusting the concentration of the organic waste to 10%w/w ** Pollutant reduction efficiency when comparing pollutants of organic waste fed into the digester and pollutants of digested sludge released from the digester *** Pollutant reduction efficiency when comparing pollutants of organic waste fed into the digester and pollutants of effluent discharged from the sand-drying tray The table above shows that the biogas digester has efficiency in reducing COD and BOD at a satisfied level whereas it has relatively low efficiency in reducing TKN. This is considered normal since in the anaerobic digestion system, ammonia (NH3) from protein digestion is in the form of ammonium ion (NH4

+) or bonds with HCO3- to form NH4HCO3

(functioning as the buffer in the system). The NH4HCO3 does not change to N2 until the digestate has been removed out, and this N2 is released to the air. We can observe this from the fact that the effluent has greatly decreasing in TKN concentration. Still, the effluent quality indicates that it is

Parameters (average)

Organic waste fed into the digester*

Digestate

Effluent from sand-drying

tray

Pollutant reduction

efficiency**

Pollutant reduction

efficiency ***

COD (mg/l) 132,541 11,972 209 90.96% 99.84%

BOD (mg/l) 61,809 2,029 44.4 96.71% 99.93%

TKN (mg/l) 1,787 1,599 96.1 10.52% 94.62%



2 - 17

needed further wastewater treatment before discharge to receiving water or needed to be reused such as watering trees, or use it for feed preparation.

2.6.3 Energy production efficiency The biogas digester with organic waste input of 85 kg/day (TS 10%) can produce biogas with 52% methane content of 2.48 m3/day. The energy production efficiency when compared with the energy use can be summarized in the table below: Energy produced from the biogas digester

Biogas produced 2.48 m3/day

Methane content 52 %

Heating value of the biogas 5.2 kWh/m3

Biogas energy 12.90 kWh/day

Energy conversion efficiency of using cooking burner

55.00 %

Heat energy for cooking 7.09 kWh/day

Electricity used in producing biogas

Electricity power needed for waste-shredder

1 Horse power

0.75 kw

Waste shredding time 0.5 hr./day

Electricity used for shredding the waste 0.37 kWh/day

Energy used for biogas production 2.89 % of the biogas energy produced

5.26 % of the heat energy produced

Energy production efficiency 97.11 % when compared with the biogas energy produced

94.74 % when compared with the heat energy produced

2.6.4 A mass flow in the small-scale biogas digester using organic waste

According to the result of the biogas digestion in the small-scale prototype digester and the digester performance evaluation, mass flow in the small-scale biogas digestion system can be summarized as follows:



2 - 18

Organic waste fed into the digester 85.00 kg/day

Determined TS content 10.00 %

8.50 kg/day

TS content in the organic waste 13.57 %

(at Ban Suan Phai Sukkaphap Restaurant)

Required organic waste 62.64 kg/day

TS content in organic waste 8.50 kg/day

VS content 92.00 %TS

7.82 kg/day

Water added for adjusting concentration of organic waste 22.36 kg/day

Total organic waste fed into the digester 85.00 kg/day

TS content 10.00 %

Specific biogas production of the digester 317.14 liter/kgVS

Biogas produced 2,480.00 liters/day

Methane content in the biogas 52.00 %

Heating value of the biogas 0.0052 kWh/liter

Biogas energy produced 12.90 kWh/day

TS content in digestate 6.33 %

Digestate needs to be removed 84.13 kg/day

Determined TS content in compost 55.00 %

Compost produced 9.68 kg/day

Executive Summary Report Chapter 3 The Development and Demonstration The Installation of Biogas Digesters in 100 Selected Sites of Small-scale Biogas Digester using Organic Waste and the Digester Use Monitoring


3 - 1

Chapter 3 The Installation of Biogas Digesters in 100 Selected Sites

and the Digester Use Monitoring

3.1 Selection of biogas digester installation sites

3.1.1 Target sites 100 appropriate sites for installation of 100 biogas digesters were considered from the readiness of the sites in many aspects: quality and quantity of organic waste, staff for operation, utilization of biogas and compost, and other benefits such as making people/youths see the benefit of organic waste separation, having knowledge of biogas production from organic waste, and raising awareness of environment and energy conservation. Accordingly, this will have a good result for waste disposal of the country. According to all aspects considered, the target sites which are most appropriate for installing biogas digesters are schools since they are ready in many aspects: having enough organic waste from school lunch for digestion, having staff for the operation, having an opportunity to make youths see advantages of organic waste separation, raising awareness of environment and energy conservation. In addition, schools also function as a source of the knowledge in biogas digestion for the communities. However, other places which show an interest in joining the project are also considered such as communities, private organizations, universities, schools in upcountry, regiments, and regional center of Department of Alternative Energy Development and Efficiency. 3.1.2 Process in selecting the digester installation sites Process in selecting the digester installation sites can be summarized as follows:



3 - 2

3.1.3 The selection result of biogas-digester installation sites

According to the selection of biogas-digester installation sites through the process mentioned in 3.1.2, organizations/schools which have been selected are presented as follows. Their names are presented in table 3.1-1

Organizations selected as the installation sites (organizations) 1. Schools - Schools under Bangkok Metropolitan Admin. - Schools under OBEC in BKK and perimeter province. - Schools under OBEC in other regions - Private schools - University

40 50 2 1 1

2. Other places - Regiments - Community - Private organization

3 1 1

3. Department of Alternative Energy Development and Efficiency 1 Total 100

279 organizations showing interest in joining the project

150 orders organizations passing the initial selection

Readiness evaluation and initial selection

100 appropriate sites for biogas digester installation

Holding a meeting to give knowledge about biogas digestion and digester use and conducting final evaluation

Sending invitation letters to the target groups of 904 sites and opening for applications for

interested organizations



3 - 3

Table 3.1-1 The selection result of biogas-digester installation sites No. Name Score1 Wichuthit School, Bangkok 99.002 Wat Sri Muang School, Samut Sakorn 90.503 Sri Bunyanon School, Nonta Buri 88.504 Wat Trirattanaram School, Bangkok 88.005 Wat Bangbon School, Bangkok 88.006 Rachananthajan Samsenwitthayalai 2 School, Bangkok 87.507 15th Infantry Regiment, Nakorn Sri Thammarat 87.008 Thai Islamic School, Bangkok 86.509 Wat Prayapla School, Bangkok 86.00

10 Wat Jorakae Yai School, Samut Prakran 85.5011 Bang Chuak Nang School (Phoonbumphen Anusorn), Bangkok 85.5012 Wat Bangpla School, Samut Sakorn 84.5013 Wat Chansamosorn School, Bangkok 84.5014 Wat Lanbun School, Bangkok 83.5015 Wat Madua School, Nonta Buri 83.0016 Srinet Energy Development Co.,Ltd., Maha Sarakham 83.0017 Phranakhon Rajabhat University, Bangkok 83.0018 Wat Nangsaw School, Samut Sakorn 82.5019 Chumchon Wat Buakawkaesorn School (Woraphonganukul), Pathum Thani 82.5020 Bangkaw Prachasarn School, Samut Prakran 82.5021 Satri Samutprakarn School, Samut Prakran 81.5022 Wat Samngam School, Bangkok 81.5023 Princess Chulabhorn's College School, Buriram 81.5024 Wat Rajbamrung (Ngamsiriwittayakarn), Bangkok 81.5025 Prayamonthatrajasriphijit School, Bangkok 80.5026 Khlong Nongyai School, Bangkok 80.0027 Wat Bangnoi School (Jamprachanukul), Samut Songkham 80.0028 Princess Chulabhorn's College School, Pathum Thani 79.5029 Wat Bangkudeethong School, Pathum Thani 79.0030 Chumchon Wat Rajbamrung School, Samut Prakran 79.0031 Wat Donwai School, Nakorn Pathom 78.5032 Chanhunbamphen School, Bangkok 78.5033 Khlong Kaja School (Phongsombhatbamrung), Bangkok 78.0034 Wat Matchantikaram School, Bangkok 77.5035 Bangbo Witthayakom School, Samut Prakran 77.5036 Lamkhaek Mosque School, Bangkok 77.5037 Bannaisri School, Bangkok 77.0038 Laembuawitthaya School, Nakorn Pathom 77.0039 Banbuamon School (Chareonraj U-Thit), Bangkok 76.5040 Khlong Bangwaek (Mon Jarasingha), Bangkok 76.5041 Wat Bhothong School, Bangkok 76.5042 Panyaworakhun School, Bangkok 76.5043 Wat Puranawas School, Bangkok 76.0044 Assumption College School Thonburi, Bangkok 75.0045 Seanghiranwitthaya School, Bangkok 74.5046 Princess Sirindhorn's College School, Nakorn Pathom 74.5047 Nonthaburi Pitthayakhom, Nontha Buri 74.0048 Wat Rajkosa School, Bangkok 74.0049 Suksawas Kindergarten, Samut Prakran 74.0050 Wat kamphlang School (Reanlommananukul), Bangkok 74.00



3 - 4

Table 3.1-1 The selection result of biogas-digester installation sites (continued) No. Name Score51 Wat Thienthawai School, Prathum Thani 73.5052 Wat Maklua School (Kanchanalakwitthaya), Nakorn Pathom 73.5053 Wat Rajadhivas School, Bangkok 73.5054 Sathasamut School, Samut Songkham 73.0055 Sriwareenoi School, Samut Prakran 73.0056 Triamudomsuksa Nomklao, Bangkok 72.5057 Khlong Songpheenong School, Samut Prakran 72.5058 Wat Chaimongkhol, Bangkok 72.5059 Thepsirin Khlong 13, Pathum Thani 72.0060 Kaeha Thungsonghong Witthaya School 2, Bangkok 71.0061 Wat Aiyikaram School, Pathum Thani 70.5062 Wat Bangkhunthiennok School, Bangkok 70.0063 Wat Talingchan School, Bangkok 70.0064 Wat Thaphud School, Nakorn Pathom 69.5065 Bang Khaenua School (Chan Chamnong Chongsuan-Oi), Bangkok 68.5066 Wat Maphrawtear School, Bangkok 68.5067 Wat Thongsuttharam School, Bangkok 68.5068 Chalermprakeat Somdejphrasrinakarindra School, Srisaket 68.0069 Khlong Jan Mosque School, Bangkok 68.0070 Wat Udomrangsri (Por Petiwanupatham), Bangkok 68.0071 3rd Development Battalion, Chiang Mai 68.0072 Kaeha Bangphlee School, Samut Prakran 67.0073 Wat Nang School, Bangkok 66.5074 Chumchon Wat Phichitpityaram School, Pathum Thani 66.5075 Chumchon Lertphinijphithayakhom School, Pathum Thani 66.0076 Phunbamphen Community, Bangkok 66.0077 Prathom Thanbin Kamphangsean School, Nakorn Pathom 65.0078 Nawamintharachinuthit Suankularbwitthayalai School, Samut Prakran 64.5079 Wat Jetrew School (Sakhonkijkosol), Samut Sakorn 64.5080 Amphawan Witthayalai School, Samut Songkham 64.5081 Triamudomsuksa Phatthanakarn School, Samut Prakran 64.5082 Nakdee Anusorn School, Samut Prakran 63.5083 Wat Klathumsuapla School, Bangkok 63.0084 Wat Saseemum School, Nakorn Patom 63.0085 Thanasit Anusorn School, Samut Prakran 63.0086 Wat Praduthammathipat School, Bangkok 62.5087 Wat Sai School (Thavornprommanukul), Bangkok 62.0088 Wat Phailorm School, Nakorn Patom 62.0089 Wat Bangsakaenai School, Bangkok 62.0090 Sangkaprachanusorn School, Bangkok 61.5091 Phaholyothin School, Bangkok 60.5092 Kajornsubamrung School, Phathum Thani 60.5093 Wat Muong School, Bangkok 60.5094 Wat Prasert Sudhavas School, Bangkok 59.5095 Huamaknoi Mosque School, Bangkok 59.0096 Triamudomsuksa Nomklao, Nonthaburi 58.5097 6th Infantry Regiment, Ubon Ratchathani 55.0098 Khlong Makhamtet School, Bangkok 54.5099 Wat Phonmanee School, Bangkok 54.00

100 Department of Alternative Energy Development and Efficiency, Bangkok -



3 - 5

3.2 The installation of biogas digesters in the 100 selected sites The installation of biogas in the 100 selected sites has 3 steps: 1) A survey of the sites and giving suggestions about sites preparation to the selected organizations before installation. The operation was from 7 July 2006 to 1 September 2006 2) An installation of biogas digesters at the 100 selected sites. The operation was from 21 July 2006 to 9 October 2006. 3) Start-up the biogas digester and training the operators about process and how to operate the biogas digesters, handing the operation and maintenance manuals and publicizing posters to the organizations. This step was done on the installation day.

The digester installation and training to the operators in the 100 selected sites are presented in figure 3.2-1. Installation day: 21 July 2006

Installation day: 24 July 2006

Figure 3.2-1 The digester installation and operator training in the installation sites

Wat Praduthammathipat School Wat Matchantikaram School

Huamaknoi Mosque School Khlong Kaja (Phongsombhatbamrung ) School



3 - 6

Wat Chaimongkhol School

Installation day: 25 July 2006 Installation day: 26 July 2006 Installation day: 27 July 2006 Installation day: 28 July 2006

Triamudomsuksa Nomklao School

Khlong Jan Mosque School

Wat Thongsuttharam School

Wichuthit School

Wat Chansamosorn School

Nonthaburi Pitthayakhom School

Sri Bunyanon School

Figure 3.2-1 The digester installation and operator training in the installation sites (continued)



3 - 7

Banbuamon School (Chareonraj U-Thit)

Installation day: 31 July 2006 Handing in to the organizations in upcountry: 1 August 2006 Installation day: 2 August 2006 Installation day: 4 August 2006

Kaeha Thungsonghong Witthaya 2 School Wat Trirattanaram School

Panyaworakhun School

Wat Madua School

Triamudomsuksa Nomklao Nonthaburi School




3 - 8

Sangkaprachanusorn School


Installation day: 7 August 2006

Wat Prayapla School Wat Lanbun School

Installation day: 8 August 2006 Installation day: 9 August 2006 Installation day: 10 August 2006

Wat Rajkosa School

Phranakhon Rajabhat University

Rachananthajan Samsenwitthayalai 2 School

Chanhunbamphen School

Wat Rajadhivas School



3 - 9


Installation day: 15 August 2006 Installation day: 16 August 2006 Installation day: 17 August 2006 Installation day: 21 August 2006

Wat Klathumsuapla School

Wat Aiyikaram School

Chumchon Wat Phichitpityaram School

Wat Bangkudeethong School

Wat Thienthawai School

Chumchon Lertphinijphithayakhom School Kajornsubamrung School

Wat Jorakae Yai School



3 - 10



Installation day: 28 August 2006

Chumchon Wat Buakawkeasorn School

(Woraphonganukul)

Princess Chulabhorn's College School

Prathum Thani

Wat Saseemum School

Thepsirin Khlong Sibsam

Prathum Thani School

Khlong Makhamtet School

Wat Phonmanee School

Bangkaw Prachasarn School Wat Sriwareenoi School



3 - 11



Wat Rajbamrung School (Ngamsiriwittayakarn)

Wat Talingchan School

Panyaworakhun School

Bang Khaenua School (Chan Chamnong Chongsuan-Oi)

Khlong Nongyai School Bang Chuak Nang School

(Phoonbumphen Anusorn)



3 - 12

Wat Nang School

Wat Udomrangsri (Por Petiwanupatham) School

Phunbamphen Community

Wat Maphrawtear School

Wat Muong School


Installation day: 4 September 2006 Installation day: 5 September 2006

Installation day: 6 September 2006 Installation day: 7 September 2006

Assumption Thonburi School

Wat Bangbon School

Bannaisri School



3 - 13


Installation day: 11 September 2006 Installation day: 12 September 2006 Installation day: 13 September 2006 Installation day: 14 September 2006

Wat kamphang School (Reanlommananukul)

Prayamonthatrajasriphijit School

Wat Sai School (Thavornprommanukul)

Wat Bangkhunthiennok School

Khlong Bangwaek School (Mon Jarasingha)

Wat Bhothong School

Wat Bangsakaenai School

Wat Prasert Sudhavas School



3 - 14



Wat Puranawas School

Wat Maklua School (Kanchanalakwitthaya)

Prathom Thanbin Kamphangsan School

Wat Saseemum School

Kaeha Bangphlee School

Thanasit Anusorn School

Laembuawitthaya School

Wat Jetrew School (Sakhonkijkosol)



3 - 15



Wat Donwai School

Wat Thaphud School

Princess Sirindhorn's College School

Wat Phailorm School

Satri Samutprakarn School

Nakdee Anusorn School

Chumchon Wat Rajbamrung School

Nawamintharachinuthit Suankularbwitthayalai School



3 - 16


Installation day: 28 September 2006 Installation day: 29 September 2006 Installation day: 2 October 2006 Installation day: 3 October 2006

Bangbo Witthayakom School

Nawamintharachinuthit

Triamudomsuksa Pattanakan

Wat Bangpla School

Sathasamut School

Suksawas Kindergarten

Khlong Songpheenong School

Wat Sri Muang School

Wat Nangsaw School



3 - 17


Installation day: 4 October 2006 Installation day: 5 October 2006 Installation day: 6 October 2006 Installation day: 9 October 2006

Wat Bangnoi School (Jamprachanukul)

Sanghiranwitthaya School

Lamkhaek Mosque School

Thailand Islamic’s collage School

Department of Alternative Energy

Development and Efficiency

Ampawan Witayalai School



3 - 18

3.3 Monitoring result of the use of installed biogas digesters

3.3.1 Methods of monitoring the use of installed biogas digesters

Methods of monitoring are as follows: 1) Compiling a record sheet for the organizations/schools which are the

installation sites to record the use of the digesters and send the filled record sheet every 2 weeks

2) Monitoring through telephone by monitoring the use of the digesters in every sites from the 3rd day after installation every weeks. Suggestions about operations/trouble shooting are given as appropriate

3) Establishing a Call Center (tel. 02-2730037 ext. Technical Department of STFE Co., Ltd.) for Q&A about the use of the biogas digesters. Staffs who know well about the digesters are on duty from Mon-Fri 8.30 AM-5.30 PM.

4) Sending staffs to solve problems when finding that organizations/schools where the digesters have been installed have problems concerning their use and cannot fix it by themselves.

3.3.2 Monitoring result

We found that the majority of the installation sites are successful or likely to successful in using the digesters (can produce biogas and start to use it). However, some sites still have problems/obstacles in the operation. They can be summarized as follows:

1) Users or operators of some organizations/schools still do not fully understand how to use and operate the biogas digester. Some organizations/schools have changed their staff responsible for operating the digester so that the new staff do not fully understand the system since they have not been trained or transferred knowledge from the old staff. 2) The decision of joining the project and having the digesters installed in some sites has been made by only the management of those sites whereas the operating staff are not ready or willing to do the work, not caring of the work much. 3) The management/coordinate of some organizations/schools do not support/cooperate in operating the biogas digester. As a result, so much responsibility or work falls on only one particular person that he/she gets discouraged when facing obstacles. 4) Some schools do not have budget to purchase tool used with the biogas digesters (pH meter). They, thus, cannot run the system when pH meter damages.



3 - 19

5) Operating staff have other works to do so they do not use the digesters, and since it is a voluntary work, some organizations/schools do not see the importance of the use of the digesters much. 6) Due to the budget limitation, the biogas digesters need for improvement for more convenient use, requiring less workload and staff, preventing the users from getting discouraged.

Executive Summary Report The Development and Demonstration Chapter 4 of Small-scale Biogas Digester using Organic Waste Economic Feasibility Analysis


4 - 1

Chapter 4 Economic Feasibility Analysis

4.1 Assumption 4.1.1 General assumption

1) The time required for fabrication and installation of biogas digesters in

the 100 sites is 3 months. 2) The system lasts at least 5 years. The digesters are operated 300

days/year to produce biogas. 3) All 100 digesters are used appropriately with the full efficiency. The

operator feed 85 kg organic waste with 10% TS content into the digester a day. 4) Discount rate is 10%. 5) Average inflation rate is 5% a year.

4.1.2 Expenses are:

1) Fabrication, transportation, and digester installation cost are in the following details:

Cost per 1 set Cost per 100 setsDetails (Baht) (Baht)

Digester fabrication - Waste shredding machine 4,400 440,000- Biogas digester 14,000 1,400,000- Steel ladder 3,600 360,000- Agitating equipment 1,500 150,000- Biogas storage tank 1,500 150,000- Cooking burner and safety valve 1,000 100,000- Sand-drying trays 450 45,000- Pipes, connectors, and valves 750 75,000- Additional accessories such as clear plastic pipes, rings, and screws 2,000 200,000Transportation cost (Bangkok and perimeters) 3,000 300,000Inoculums transportation cost 250 25,000Installation cost 5,000 500,000Sub total 37,450 3,745,000Value added tax (VAT) 2,622 262,150Total 40,072 4,007,150



4 - 2

2) Operation and maintenance expenses

To operate and maintain the digester, the following expenses arise:

expenses per 1 set expenses per 100 set (baht/year) (baht/year)

Operation expenses- Labor wage for running the system 10,350 1,035,000 - Electricity charge 450 45,000 - Tap water charge 360 36,000 Sum of operation expenses 11,160 1,116,000 Annual maintenance expense 584 58,400 Equipment/part replacement (just in 3rd year) 3,200 320,000

Details

4.1.3 Income Income from the small-scale biogas digester using organic waste is calculated from expenses that can be saved from utilization of the digester.

Income per 1 set Income per 100 set(baht/year) (baht/year)

- Money saved from no buying LPG for cooking 6,321 632,091 - Money saved from no buying compost 8,550 855,000 - Money saved for local government organizations from 12,750 1,275,000 having no collecting, trasporting and disposing organic wasteTotal income 27,621 2,762,091

Details

4.2 Analysis result The analysis result for the whole period of the project which is divided into 2 cases as follows: Case 1: considering only profits arising from the produce of the biogas digesters: biogas used for cooking and compost. (1) Internal Rate of Return: IRR cannot be calculated, showing that the project is not feasible for investment. (2) Net Present Value: NPV is -2,925,733 baht which is lower than the breakeven point of 0. (3) Payback period: no payback period in the life cycle of the digesters. (4) Benefit/Cost: B/C Ratio is 0.27 which is lower than the breakeven point of 1.



4 - 3

Case 2: considering profits arising from the produce of the biogas digesters: biogas used for cooking, compost and benefit from saving money for local administrative organizations from collecting, transporting and disposing waste. (1) Internal Rate of Return: IRR is 30.35% which is higher than the discount rate of 10%; the project is highly feasible for investment. (2) Net Present Value: NPV is 2,366,725 baht which is higher than the breakeven point of 0. (3) Payback period is around 2.5 years, a relatively short period, low investment risk. (4) Benefit/Cost: B/C Ratio is 1.59 which are higher than the breakeven point of 1. According to the economic analysis in 2 cases above, it can be summarized that the project is not feasible for investment if considering only the benefits from the produces of the biogas digesters. In contrast, the project has highly financial rationale for investment if looking at the overall picture by considering the benefits from the produces of the biogas digesters along with the expense being saved for local administrative organizations from collecting, transporting and disposing waste in environmental-sound manner. Thus, the biogas production and use of small-scale biogas digesters should be supported by the government, local administrative organizations or related organizations so that the project prevails and has a large-scale benefit in environmental and energy conservation of the country.

Executive Summary Report The Development and Demonstration Chapter 5 of Small-scale Biogas Digester using Organic Waste Summary and Suggestions


5 - 1

Chapter 5 Summary and Suggestions

5.1 Summary 5.1.1 The small-scale biogas digester using organic waste developed are comprised the following equipments and parts: (1) a digester with capacity of 2.4 m3 made of Fiber Reinforce Polyester (FRP) (2) a waste shredder (3) a steel ladder (4) biogas pipes (5) a biogas storage tank (6) a manometer (7) an agitator (8) a cooking burner set, and (9) a sand-drying tray set. 5.1.2 The experimental result of organic-waste digestion in the prototype digester is summarized below: 1) The maximum organic-waste input for the digester is 85 kg/day (10% TS content and 92%VS content of the TS content). The biogas yield is 2.48 m3/day. This figure represents specific gas production of 317.14 liter/kg of volatile solid and yields compost of 9 kg/day (with 45% moisture content) 2) Biogas produced from the organic waste digestion consists of methane (CH4) 52.53%, carbon dioxide (CO2) 35.09% and other gases: oxygen (O2) 0.92%, hydrogen (H2) 8.80% and nitrogen (N2) 2.64%. 3) Compost obtained from organic waste digestion has 59.2% organic content. C/N ratio is 8.3. It has nutrients for plants: nitrogen 4.3%, 1.8% available-to-plant phosphorus (P2O5), 0.9% available-to-plant potassium (K2O), 1.7% calcium (CaO), and 0.2% magnesium, and the average pH is 6.6. 4) The biogas digester uses electricity energy for 2.89% of the biogas energy the digester produced, and equals to 5.26% of heat energy obtained from converting biogas to heat by using cooking burner. 5) The digester has pollutant reduction efficiency in removing COD, BOD and TKN of 90.96%, 96.71%, and 10.52% respectively when comparing the pollutant load in the organic waste fed into the digester and the pollutant load in the digestate removed from the digester. The figure is 99.84%, 99.93% and 94.62% respectively when comparing the pollutant load in the organic waste fed into the digester and the pollutant in the effluent discharged from the sand-drying tray. 5.1.3 The 100 sites selected for installing biogas digesters are composed of 93 schools; 40 under Bangkok Metropolitan Administration (BMA), 52 under the Office of Basic Education Commission, and 1 private school; and other 7 places; 1 university, 3 regiments of Royal Thai Army, 1 community, 1 private organization, and the Department of Alternative Energy Development and Efficiency (DEDE).

Executive Summary Report The Development and Demonstration Chapter 5 of Small-scale Biogas Digester using Organic Waste Summary and Suggestions


5 - 2

5.1.4 The installation of biogas digesters in the 100 sites had been done from 24 July 2006 to 9 October 2006. The process included the installation of the digesters, operator training, giving operation and maintenance manuals and publicizing posters for using in activities of the organizations/schools. 5.1.5 The monitoring result of the digester use shows that the majority of the installation sites are successful or likely to successful in using the digesters. Some sites, however, have problems and difficulties in using them. This results from the lack of understanding in running the system due to a staff change/the lack of support from the management and cooperation from colleagues/the operating staff lacking of willingness and care for doing the work/the lack of budget for purchasing additional equipment (pH meter)/ the organizations where the digesters are installed not concern about the importance of running the digester system because they not paying anything for the installation/the digesters is needed for improvement to decrease the workload of the operating staff. 5.2 Suggestions 5.2.1 Since the small-scale biogas digesters using organic waste have both benefits; an alternative energy and helping dispose Municipal Solids Waste environmental-friendly, production and use of biogas digesters should be supported by the government, local administrative organizations or related organizations so that their production and use prevail across the country. 5.2.2 A follow-up, consulting service and problem solving concerning the use of the digesters for the 100 sites should be conducted continuously. In addition, reward should be set for each organization who use the digester at full efficiency. An improvement of the digesters should be done for the organizations which effectively run the system so that the need of its use can be met and the system can run at its full efficiency. 5.2.3 Conferences and trainings should be held to give knowledge on biogas production from organic waste to such organizations as schools, local administrative organizations, and communities across the country to develop understanding and make people at a large scale see advantages of biogas production from organic waste. 5.2.3 The 100 sets of biogas digester installed in the 100 sites are considered as a prototype which needs improvement and adjustment for more convenient use and higher efficiency.

Energy Research and Development Office Department of Alternative Energy Development and Efficiency Ministry of Energy 17 Rama 1 Rd. Pathumwan Bangkok 10330 Tel 0-2211-853, 0-2223-0021-9 ext 1205 Fax 0-2225-2548 www.dede.go.th

STFE CO., LTD 17th Floor., S.P. Bldg, 388 Phaholyothin, Bangkok 10400 Tel 0-2273-0037 Fax 0-2273-0735 www.stfe.co.th

Documents

The Development and Demonstration of Small-scale Biogas