Optimization of Biogas Production from Kitchen Waste installed at

2018 International Conference on Computing, Power and Communication Technologies (GUCON) Galgotias University, Greater Noida, UP, India. Sep 28-29, 2018

Optimization of Biogas Production from Kitchen Waste installed at College of Science and Technology Tshewang Tenzin1 Sangay Wangdi2 Electrical Engineering Department College of Science and Technology 1 [email protected] 2 [email protected]

Gom Dorji Electrical Engineering Department College of Science and Technology Phuntsholing, Bhutan [email protected]

Prem Kumar Nepal Electrical Engineering Department College of Sciecne and Technology) Phuntsholing, Bhutan [email protected]

Sangay W Tamang3 Langa Tshering4 Electrical Engineering Department College of Science and Technology 3 [email protected] 4 [email protected]

Pravakar Pradhan Electrical Engineering Department College of Science and Technology Phuntsholing, Bhutan [email protected]

Basant Pradhan Science and Humanities Department College of Science and Technology Phuntsholing, Bhutan [email protected]

is Nu. 8,902/- (Ngultrum eight thousand nine hundred and two) per month.

Abstract— This paper presents an overview of the biogas plant and optimization of gas production installed near students’ dining room at College of Science and Technology (CST) located in the Southern foothills of Bhutan. The mixed kitchen waste produced is collected and directly feed to the biogas plant. This research is installed in collaboration with Department of Energy and College of Science and Technology as a pilot project with the aim “Waste-To-Energy Initiatives.” It also aims to replace the use of Liquefied Petroleum Gas (LPG) in students’ mess kitchen. The detail studies of waste production and feasibility studies were carried out before installation of the plant. The maximum biogas production capacity of the plant is 4 m3 per day. As production of gas from the plant depends on type of waste and surrounding temperature, gas yield was not as per the design criteria. To improve the gas production, various methodologies where applied. Keywords— biogas plant, production, maximum capacity, mixed kitchen wastes

In [2] the feasibility study shows that the payback period is within 5 years. The cost of LPG with government’s subsidize rate is Nu.18 per kg whereas for gas produce from biogas plant falls in Nu.10 per kg. In case if the nonsubsidize rate is taken into consideration, the payback period will further reduced by two years. This calculation where done base on the data recorded for two months from the commencement of the plant. The wastes input were given random quantity without grinding the waste and also without taking water and waste ratios. For optimization of the gas production, waste to water ratios, temperature and size of the waste are taken into consideration. The Figure 2, shows an overview of the installed biogas plant.

optimization,

II.

I. INTRODUCTION

A. Collection of waste materials The types of kitchen wastes collected are the mixture of rice, potatoes, cabbages, spinaches, meats, chilies, and daals which contains mostly carbohydrates, proteins and lipids. Experimental studies carried out on a batch digestion reactor on food wastes at the temperature of 37℃ and retention time for 28 days. It is found that the methane gas produced are 0.28, 0.29, 0.47 and 0.48 liters per gram for fresh cabbages, boiled rice, mixed food wastes and cooked meats respectively [3]. Therefore it is understandable that the mixed kitchen food wastes can produce substantial amount of a biogas but not individual food items.

In the year 2014, students’ environment club has segregate types of waste produced by CST residence. The type of waste segregate were degradable, non-degradable, recyclable and non-recyclable waste in collaboration with SUNYA project Aims to zero solid waste. The degradable waste from kitchen were measure and recorded 80 to 120 kg per day in CST campus. The kitchen wastes is non uniform waste consists of rice (maximum), daals, potatoes, chilies and other food ingredients. The biogas plant is designed to operate for mixed kitchen wastes. The overall block diagram of the biogas plant is shown in Figure 1.

B. Biological process of decomposition The organic matters is converted into biogas by a group of microorganisms through a series of metabolic steps, such as hydrolysis, acdification and methanogenesis [4].

Since kitchen wastes were used to produce biogas due to its high organic degradation, calorific value and nutritional value for the microbes, which reduces the dependency on other forms of energy [1]. The 4 m3 production capacity of the biogas plant was commissioned on 16th March 2017. The primary objectives of this research is “Waste-To-Energy Initiatives” and to replace the use of LPG gas. The case study done on total expenditure to buy LPG by CST students’ mess

978-1-5386-4491-1/18/$31.00 ©2018 IEEE

METHODOLOGY

1) Hydrolysis The particulate materials of organic kitchen food wastes is enrich in proteins, carbohydrates and lipids. Bacteria

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Fig. 1. Overall components of Biogas plant in CST

decomposes the long chains of complex proteins, carbohydrates, and lipids into soluble monomers and oligomers such as amino acid, long chain fatty acids, peptides, sugar and glycerol through hydrolysis, also called liquefaction.

III.

GAS PRODUCTION BEFORE OPTIMIZATION OF THE WASTES FEEDINGS

Previously, the mixed kitchen wastes are directly fed to the reactors without maintaining the solid wastes to water ratios. The temperature inside the methanation tank is also not taken into consideration. The Table I and Figure 3 shows an average weekly data of gas production from the biogas plant recorded on October 2017. TABLE I. GAS PRODUCTION AT AMBIENT TEMPERATURE Weeks

Waste quantity (kg)

Gas production (m3)

Week 1

80

0.768

Week 2

96

0.85

Week 3

112

0.879

Week 4

128

0.8

Fig. 2. Overview of installed Biogas plant

2) Acidification The bacteria which produces acid that converts the organic food wastes into acetic acid, carbon dioxide, hydrogen and these bacteria are developed in the anaerobic closed acdification reactor. Dissolved oxygen or bounded oxygen are used to produce acetic acid, carbon dioxide and oxygen [5]. Thus, these bacteria helps in creating an anaerobic condition which is necessary for microganisms to produce methane gas and also they reduce those compound having low molecular weights into organic acids, amino acids, alcohols carbon dioxide, hydrogen sulphide, and trace of methane [6]. 3) Methanogenesis The compounds having low molecular weights are decomposed by methane producing bacteria and it uses hydrogen, acetic acid and carbon dioxide to produce methane and carbon dioxide. The hydrogen pressure contained in the system must be limited and if the partial pressure of hydrogen increases, then it leads to accumulation of volatile fatty acids and also decrease in pH. This leads to failure of the methanogenesis process and also anaerobic digestion process in the system. Methane producing microorganisms are obligate anaerobes and very sensitive to environmental changes but hydrogen utilizing methanogens have been found to be more resistant to environmental changes. The terminal fermentation products in the acidogenesis phase affects loading efficiency and running stability [4]. It affects the concentration of sugar in water if the ratios are not proportional.

Fig. 3. Gas production versus input (wastes)

The maximum gas of 0.879 m3 is produced on 3rd week, when the average wastes feedings is 112 kg. IV.

OPTIMIZATION OF BIOGAS PLANT

To increase the gas production in existing Biogas plant, there are five factors which are strictly monitored throughout the entire three months. The data are being collected in daily basis after six days of retention time. A. Temperature monitoring The most and common types of reactor used based on the economic consideration is the mesophilic system. It has a

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fell in the gas production. This is mainly due to the fact that the improper digestion in the reactor at the end of six days. And also, living bacteria in the second phase (i.e. methanation tank) are unable to consume all the leachate in a day. Thus, the pump speed at leachate feeding side must increase and this affects the gas production.

temperature ranges from 25℃ to 45℃ whereas for thermophilic system, the temperature ranges from 45℃ to 60℃ [7]. In order to track the temperature at minimum deviation, the electric heater is introduced inside the methanation room. For the input of food wastes 155 kg, water of 196 liters is added. For this experimental testing, input ratio is not maintained but rise and fall of temperature is recorded. The average ambient temperature is 24℃ in winter and 29℃ in summer. By using heater, the temperature is maintained at around 31℃ to 36℃ at deviation of ± 3℃. However it is observed that Gas production is improving with the rising of temperature as shown in the Figure 4.

Fig. 5. Gas Production versus Input (Grind) at different Ratios

D. Ungrind wastes at different ratios Similarly, Figure 6 shows for the ungrind wastes feeding to acidification reactor and it ranges from 96 kg to 112 kg. The input ratio is maintained as shown in the graph. When input of wastes is 112 kg with water 168 liters at ratio 1:1.5, gives 2.15 m3 which is the optimum gas production for the ungrind wastes. The decline of gas production is due to the fact that firstly, improper decomposition of wastes in the reactor, and leachate consumption by living bacteria exceeds a day which affects next fresh leachate. Therefore, pump speed has to increase for timely consumption of leachate which affects the gas production.

Fig. 4. Gas production versus temperature

B. Early Optimization technique Though the biogas plant has maximum capacity of gas production of 4 m3, it is never producing to its rated capacity. In [4], various technique has adopted to increase the gas production like mixing of kitchen wastes with cow dung, solid wastes and water ratio, maintaining different temperature and also observed the grind and ungrind wastes gas production. In each cases, gas production is different for different quantities of the input wastes. Similarly, various combinations are also adopted in CST biogas plant and recorded the gas production against each methods. TABLE II. GAS PRODUCTION AT DIFFERENT RATIOS Maximum Biogas Production(m3) from different waste input Sl. No

Waste Input (kg)

1

Ungrind Waste Input to Water Ratio

Grind Waste Input to Water Ratio

1:1

1:1.5

1:2

1:1

1:1.5

1:2

96

1.95

1.7

1.57

1.6

2.25

1.91

2

112

1.56

2.152

1.97

2.34

2.47

2.3

3

128

1.95

1.89

1.5

1.52

2.17

1.78 Fig. 6. Gas Production versus Input (Ungrind) at different ratios

The Table II shows the gas production for various method wastes to the reactor.

E. Grind and ungrind wastes feeding at 1:1 wastes to water ratio. The wastes ranges from 64 kg to 160 kg were feed in acidification reactor by maintaining the same acidification reactor temperature at 32°C. The Figure 7 shows the gas production data plotted against volume of waste input. From the Figure 7 at 112 kg wastes input of grind wastes it produces maximum gas of 2.344 m3 of gas per day with the lowest 0.91 m3 for ungrind wastes at 64 kg of wastes input.

C. Grind wastes at different ratios For the grind wastes, restricting to the design capacity different input ratios are maintained. The input ranges from 96 kg to 128 kg at different wastes to water ratio as given in the graph. The input of 112 kg at ratio 1:1.5 has maximum gas production of 2.47 m3 per day. A linear line depicts that the substantial amount of gas is generated when average feeding is 112 kg and when feeding is 128 kg, observed the

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TABLE III. LEACHATE CONSUMED AT VARIOUS PUMP SPEED Pump speed (Psi) 38 40 45 50 55 60

Leachate consumed per hour 3.75 Liters 4.25 liters 6.25 liters 8.5 liters 9.0 liters 10 liters

Total leachate consumed 90 102 150 204 216 240

Less gas is produced because at high pump speed, pressure is high in the methanation tank and living bacteria is unable to feed on leachate effectively. Due to this, useful leachate is pushed outside to atmosphere through effluent pipe. So there is gas losses to atmosphere. Therefore, pump speed must 3.1 to 3.45 bar. At these pump speed, leachate will be consumed on time. And also gas is producing readily.

Fig. 7. Gas production for different input (grind & ungrind) waste with waste to water ratios 1:1

V. GAS PRODUCTION FLOW RATE Gas production rate in biogas plant is not linearly increasing as per the simulation done in research paper. It is because gas molecules can be highly compressed and it requires large amount of gas molecule as volume increases and tries to attain the saturation point. The Figure 9 shows the biogas production rate for 208 liters of leachate in 28 hours from feeding time at pump speed 3.10 bar.

This optimization technique concludes that the wastes input in the biogas plant should be grinded. The fact for this is, anaerobic bacteria finds easier to digest the wastes for smaller food particles or in other words, smaller particles are easier to digest. F. Pressure Regulation at Effluent Tank Initially, height of the effluent tank is 0.4 m from the base. Applying Bernoulli's theorem on steady, column of water in the tank pressure exert to effluent outlet is found to be 1.0522 bar. This pressure is not sufficient to withstand gas volume about 2.5 m3 and there is gas leakage from effluent outlet pipe. To avoid the gas leakage height of the tank is raised to 0.7 m, additional pressure of 0.0394 bar. The new height of tank can exert 1.0916 bar withstanding the maximum gas capacity about 3.8m3.

Fig. 9. Gas production versus time taken (hours)

VI.

RESULT & DISCUSSION

The experimental work and subsequent data collection was done for three months on the Biogas plant, preinstalled at CST, near students’ dining hall. The system was studied thoroughly and design capacity of the plant is for minimum of 20 kg to 120 kg. For that existing and preinstalled Biogas plant, the exclusive experimental research was based on the optimization of biogas production. Under optimization, wastes sizing and wastes to water ratio, temperature regulation and pumped regulation were strictly maintained.

Fig. 8. Current height of the effluent tank is 70 cm withstanding the gas capacity of 3.28m3 at Gas holder

G. Pump Speed regulation The observations are made on variations of pump speed and corresponding time period and leachate consumptions. The range of fresh leachate collected over the leachate collection tank is 150 to 175 liters at the end of a day. This data are based on maintained ratio such that wastes to water ratio at 1:1.5. When pump is less than 40 Psi, the leachate consumption is below 102 liters whereby leachate is not consumed completely by methanagenesis bacteria on time and that hampers the collection of next fresh leachate. If the pump speed was above 55 to 60 Psi, the leachate is completely consumed by the bacteria before 24 hours, before next fresh leachate is ready. And also found that less production of methane gas as indicated by gas holder where methane gas is collected and it is shown in the table III.

The kitchen food wastes was collected and resized to 0.1 to 1.0 mm and fed to the reactor subsequently with different water ratio. Unlike this, kitchen wastes was collected and feed to the reactor directly without sizing but at maintained wastes to water ratio. The feeding ranges from 64 kg to 160 kg with waste to water ratio 1:1, 1:1.5 and 1:2 for both grind and ungrind wastes. Amongst all at different feeding ratio, wastes to water ratio of 1:1.5 gives the optimum gas production for both grind and ungrind wastes when input to the reactor was 112 kg. For grind kitchen wastes, optimum

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gas production was 2.47 m3 and 2.15 m3 was the optimum gas production for ungrind wastes. Although, the designed and installed plant capacity of gas production was 4 m3 as the maximum capacity at every end of day but it was not achieved as yet. This is because of the nature of the system location and its surrounding temperature.

ACKNOWLEDGMENT This Research would not have been successful without support from the faculties of Electrical Engineering Department, College of Science and Technology for providing field to conduct experimental research on Biogas Plant located near student mess.

VII. RECOMMENDATION

REFERENCES

For the highest gas production as per research work and the experimental data done on mixed kitchen food wastes in CST is grind waste with 112 kg at wastes to water ratio of 1:1.5. For this set of input parameters, the pump speed for leachate feeding to methanation tank where methane gas produced should be in the range of 45 to 50 Psi, maintaining the average temperature about 35 ℃ with deviation ±3℃.

[1]

S. A. Iqbal, S. Rahaman, M. Rahman and A. Yousuf, "Anaerobic Digestion of Kitchen waste to produce biogas," in 10th International Conference on Mechanical Engineering,ICME 2013, 2014. [2] College of Science and Technology,Institute for GNH Studies, Department of Renewable Energy, "Waste To Energy Initiative, Harnessing Biogas from Biodegradable Mixed Kitchen Waste," DRE, Thimphu, 2017. [3] Chen, . R. . T. Romano and R. Zhang, "Anaerobic digestion of food wastes for biogas production," in Department of Biological and Agricultural Engineering, USA, December 2010. [4] Maile, E. Muzenda and C. Mbohwa, "Optimization of Biogas Production through Anaerobic Digestion of Fruit and Vegetable Waste," in 7th International Conference on Biology, Environment and Chemistry, Johannesburg, 2016. [5] S.Yimer and O.P. Sahu, "Biogas as Resources of Energy," International Letters of Natural Sciences Vol 9, pp. 1-14, Feb 2014. [6] V. Suyog, "Biogas Production from Kitchen Waste," Rourkela, 20102011. [7] L. Kardos , A. Juhasz, G. Palko, J. Olah, K. Barkacs And G. Zaray, "Comperison Of Mesophilic And Thermoliphilic Anaerobic Fermented Sewage Sludge Based On Chemical And Biochemical Tests," Corvinus University Of Budapest, Hungary, 7th Octomber 2011. [8] Aasim, R. Li, M. Feroz, W. Muhammat, Salahuddin and M. Muhammad, "Preditive Modeling of Biogas Production from Anaerobic Digestions of Mixed Kitchen Waste at Mesophilic Temperature," International Journal of Waste Resources , 06 June 2016. [9] L. Bonten, K. Zwart, R. Rietra, R. Postma and H. d. M.J.G, BioSlurry as Fertilizer, Wageningen, April 2014. [10] East Bay Municipal Utility District, "Anaerobic Digestion of Food Waste”," U.S. ENVIRONMENTAL PROTECTION AGENCY REGION 9, March 2008.

VIII. FUTURE SCOPE In order to meet the requiring maximum capacity of installed Biogas plant, wastes circulating system needs to improve for better decomposition of organic materials. Not manual but it should be operated automatically. Besides, temperature inside the methanation room needs to maintain without using the heater. IX.

CONCLUSION

The major problems associated with the installed Biogas Plant in CST are like temperature monitoring, gas leakage at effluent tank, wastes resizing, pumped speed regulation and also unidentified input wastes to water ratios. The different wastes to water input ratios are applied for both grind and ungrind food wastes. Observations are made for all the implemented methods to compare the gas production in which grind food wastes at wastes to water ratio of 1:1.5 gives the maximum methane gas production of 2.47 m3 per day, provided the temperature in methanation room is maintained at 35°C with slight deviation of ±3°C . Therefore, it is found that the main factor behind gas production is temperature and it must be regulated, not less than 32°C for optimum methane production.

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