SEPARATE PRODUCTION OF HYDROGEN AND METHANE FROM ETHANOL WASTEWATER USING TWO-STAGE UASB SYSTEM

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1 SEPARATE PRODUCTION OF HYDROGEN AND METHANE FROM ETHANOL WASTEWATER USING TWO-STAGE UASB SYSTEM Songphol Jaikeaw a, Sumaeth Chavadej a,b, Malinee Leethochawalit *,c a The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok, Thailand b Center of Excellence on Petrochemical and Materials Technology, Bangkok, Thailand c Innovation Learning Center, Srinakarinwirot University, Bangkok, Thailand Keywords : Hydrogen and Methane production, Ethanol wastewater, A two-stage upflow anaerobic blanket (UASB) system, Mesophillic temperature, Volatile fatty acid ABSTRACT The objective of this study was to determine an optimum COD loading rate for both maximum production of hydrogen and methane from ethanol wastewater using a two-stage upflow anaerobic sludge blanket (UASB) system under mesophilic temperature (37 C) with a constant recycle ratio of 1:1 (final effluent flow rate : feed flow rate). The first hydrogen and the second methane UASB units were operated with working volume of 4 L and 24 L, respectively. The first (hydrogen) UASB unit was controlled at ph 5.5 but the second (methane) UASB unit had no ph control. The system was operated at different COD loading rates from 8 to 20 kg/m 3 d based on total UASB working volume. The results showed that at the optimum COD loading rate of 13 kg/m 3 d, the produced gas from the hydrogen UASB unit provided the hydrogen yield of 1.85 ml/g COD removed (or 0.57 ml/g COD applied) and the SHPR of 7.42 ml H 2 /L R d (or 0.33 ml H 2 /g MLVSS d). The produced gas from the methane UASB unit, mainly contained CH 4 and CO 2 without H 2 which were also consistent with the maximum methane yield of ml/g COD removed (or ml/g COD applied) and the SMPR of ml CH 4 /L R d (or ml CH 4 /g MLVSS d). * sumaeth.c@chula.ac.th INTRODUCTION In the present, the major energy source used around the world is fossil fuels which their quantities are limiting and depleting. In addition, the excessive use of fossil fuels directly results in the release of large amounts of greenhouse gases which cause global warming and acid rain problems (Searmsirimongkol et al., 2011). Therefore, an alternative energy source is considered to replace partially the consumption of fossil fuels and solving the global warming problem. Hydrogen and methane are an interesting alternative energy source with several applications. Methane is almost entirely used for heat and power production. Methane has an energy content on a mass basis of 50 MJ/kg compared to gasoline of 44 MJ/kg. Hydrogen is one alternative fuel substitute for fossil fuels and it will be a fuel of the future. It has a high energy content of 122 MJ/kg, which is 2.75 times greater than hydrocarbon fuels (Pakarinen et al., 2011). The most interesting technique to produce hydrogen and methane is a biological process because it can be operated under ambient conditions (Intanoo et al., 2012). Biological hydrogen production can be attained either via photo or dark fermentation processes. The dark fermentation processes by anaerobic Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 1

2 bacteria offer a more promising approach for hydrogen production as compared to the photo fermentation processes because the dark fermentation does not require light supply and waste stream transparency. In addition, it gives a higher and more stable hydrogen production rate (Searmsirimongkol et al., 2011). Anaerobic digestion consisted of four main steps of hydrolysis, acidogenesis, acetogenesis and methanogenesis. For the hydrolytic step, insoluble organic compounds are broken down by external enzymes to yield water-soluble organic compounds of sugars, amino acids and fatty acids. The water-soluble organic compounds are then consumed by acidogenic bacteria to produce organic acids, hydrogen, carbon dioxide and alcohols in the acidogenic step. For the acetogenic step, all high molecular weight organic acids are further converted to acetic acid, hydrogen, and carbon dioxide. For the final step of methanogenesis, both acetic acid and hydrogen produced are converted to methane by methanogenic bacteria (Gomez et al., 2011). The objective of this study was to determine an optimum COD loading rate for both maximum production of hydrogen and methane from ethanol wastewater using a two-stage upflow anaerobic sludge blanket (UASB) system under mesophilic operation (37 C). EXPERIMENTAL A. Seed sludge and Ethanol wastewater preparation Seed sludge and ethanol wastewater were supplied by Sapthip Co.,Ltd., Thailand. The ethanol wastewater without the fermentation residue was kept at below 4 C before being used in this research. The characteristics of ethanol wastewater had a chemical oxygen demand (COD) value about 60,000 mg/l and a COD to nitrogen to phosphorous ratio of 100:1:0.9, indicating that the wastewater contains sufficient amounts of both nutrients (N and P) for anaerobic decomposition for biogas production (the theoretical ratio of COD: N: P = 100:1:0.4, (Intanoo et al., 2012). B. The Two-Stage UASB set up and operation The two-stage upflow anaerobic sludge blanket (UASB) reactors used in this study were constructed from borosilicate glass with a 4-L and 24-L working volume for hydrogen and methane UASB units, respectively. The system was operated at mesophillic temperature (37 C) with a recycle ratio of 1:1 (feed flow rate: effluent flow rate). The ph in the hydrogen UASB unit was controlled at 5.5 by using ph controller while the ph of methane UASB unit was not controlled. The ethanol wastewater was fed to the bottom of the hydrogen UASB unit by a peristaltic pump and the effluent from the hydrogen UASB unit was directly pumped into methane UASB unit. The final effluent from the methane UASB unit was fed back into the bottom of the hydrogen UASB reactor with the recycle ratio of 1:1 (effluent flow rate: feed flow rate). The schematic of the studied two stage upflow anaerobic sludge blanket (UASB) unit is shown in Figure 1. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 2

3 Fig. 1 Schematic of two stage upflow anaerobic sludge blanket (UASB) units. C. Measurements and analytical methods The gas production rate of each UASB unit was measured by using a wet gas meter (Ritter, TGO5/5). The gas composition was analysed by a gas chromatograph (GC, PerkineElmer, Auto System) equipped with a thermal conductivity detector (TCD) and a packed column (HSN6-60/80, 7 x 1/8 SULFINERT and MS13X4-09SF2 40/60 IN 9 x 1/8 ). The effluent sample from the hydrogen and methane tanks were analysed for volatile fatty acids (VFA), chemical oxygen demand (COD), and volatile suspended solids (VSS). The total amount of volatile fatty acids (VFA) was determined by High-Performance Liquid Chromatography (HPLC, Shimadzu, with a RI detector (UFLC)). The COD values in the feed and effluent samples were determined by the dichromate method using a COD digester and absorbance measurement by a spectrophotometer (HACH, DRB200). The volatile suspended solids (VSS) represented the microbial washout from the system and the mixed liquor volatile suspended solids (MLVSS) in the reactor were measured according to the standard methods (Eaton et al., 2005). Organic nitrogen was analysed by the diazotization and cadmium reduction method and inorganic nitrogens were analysed by the salicylate method with the TNT persulfate digestion (Eaton et al., 2005). The total phosphorous in the feed and effluent samples was determined by the molybdovanadate method with acid persulfate digestion (Hach Company). RESULTS AND DISCUSSION A. The overall process performance The overall process performance of the two-stage UASB system as a function of COD loading rate is shown in Figure 3. The total gas production rate increased steadily with Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 3

4 increasing COD loading rate from 8 to 13 kg/m 3 d and then decreased with further increasing COD loading rate to 20 kg/m 3 d. The total COD removal increased with increasing COD loading rate and reached a maximum value of 86% at a COD loading rate of 20 kg/m 3 d which much higher than another related work (Intanoo et al., 2014). The increase in COD loading rate resulted from an increase in organic compounds available for microbial degradation, leading to increasing COD removal (Intanoo et al., 2015). As shown in Figure 2b, the composition of produced gas mainly contains methane and carbon dioxide with a very small amount of hydrogen (less than 5%).Both methane production rate and methane yields slightly increased with increasing COD loading rate from 8 to 13 kg/m 3 d and then decreased with increasing COD loading rate. Additionally, the maximum of both hydrogen production rate of 4 L/d and hydrogen yield of ml/g COD removed were found at a COD loading rate of 17 kg/m 3 d. From the results, the COD loading rate of 13 kg/m 3 d, which reasonably provided both maximum total gas production rate and methane yields with relatively high total COD removal, was considered to be an optimum COD loading rate for methane production from ethanol wastewater. The total VFA and the microbial concentration in term of mixed liquor volatile suspended solid (MLVSS) in both H 2 and CH 4 UASB units as a function of COD loading rate are shown in Figure 3. The total VFA concentration of both hydrogen and methane UASB units increased with increasing COD loading rate from 8 to17 kg/m 3 d then decreased with increased COD loading rate to 20 kg/m 3 d due to the toxicity of VFA accumulation. The highest VFA concentration in hydrogen UASB unit was found at the COD loading rate of 17 kg/m 3 d which corresponded to the maximum hydrogen production rate and hydrogen yield. However, the maximum methane production rate and methane yield were found at COD loading rate 13 kg/m 3 d (fig.2). It can be concluded that the inhibition levels of VFA to hydrogen and methane producing bacteria under were around 11,000 and 800 mg/l as acetic acid, respectively which is good agreement with our previous work (Intanoo et al., 2015). The MLVSS in the second hydrogen UASB units increased with increasing COD loading rates from 8 to 17 kg/m 3 d and then decreased with further increased COD loading rate. The highest MLVSS of 29,000 mg/l in methane UASB units was found at a COD loading rate of 13 kg/m 3 d which corresponded to the maximum methane production rate and methane yield. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 4

5 Fig. 2 Effects of COD loading rate on overall gas production rate and (a) overall COD removal, (b) H 2, CO 2 and CH 4 production rate, (c) CH 4 yield, and (d) H 2 yield at ph 5.5 and 37 C. Fig. 3 (a) Total VFA concentration and (b) Microbial concentration in term of MLVSS in both H 2 and CH 4 UASB units as a function of COD loading rate at ph 5.5 and 37 C. Figure 4 depicts the VFA compositions of the ethanol wastewater and effluents of the hydrogen and methane USAB unit as a function of COD loading rate including acetic acid, butyric acid, propionic acid, and valeric acid. The hydrogen UASB unit exhibited the Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 5

6 highest composition of VFAs as compared to the feed of ethanol wastewater and the second methane UASB unit. These results can be explained by the reaction pathways of hydrogen UASB unit (Equations 1-4) (Saady et al., 2013; Intanoo et al., 2015). CH 3 CH 2 COOH + 2H 2 O CH 3 COOH + 3H 2 + CO 2 (1) Propionic acid CH 3 CH 2 CH 2 COOH + 2H 2 O 2CH 3 COOH + 2H 2 (2) Butyric acid CH 3 CH 2 COOH + 2CO 2 + 6H 2 CH 3 (CH 2 ) 3 COOH + 4H 2 O (3) Propionic acid Valeric acid CH 3 CH 2 COOH + CH 3 COOH + H 2 CH 3 (CH 2 ) 3 COOH + 2H 2 O (4) Propionic acid Valeric acid In addition, the ethanol wastewater consists of glucose, ethanol and lactic acid which were not found in hydrogen and methane UASB units. These results can be explained that glucose, ethanol, and lactic acid were consumed by both methane-producing bacteria in methane UASB unit and hydrogen-producing bacteria in hydrogen UASB unit, as shown in equations 5-10 (Saady et al., 2013): C 6 H 12 O 6 + 2H 2 O 2CH 3 COOH + 4H 2 + 2CO 2 (5) Glucose CH 3 CH 2 OH + H 2 O CH 3 COOH + 2H 2 (6) Ethanol C 6 H 12 O 6 + 2H 2 2CH 3 CH 2 COOH + 2H 2 O (7) Glucose Propionic acid CH 3 CHOHCOOH + 2H 2 O CH 3 COOH + 2H 2 (8) Lactic acid 4H 2 + CO 2 CH 4 + 2H 2 O (9) CH 3 COOH CH 4 + CO 2 (10) Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 6

7 Fig.4 Volatile fatty acid composition in ethanol wastewater, H 2 and CH 4 UASB units: (a) acetic acid; (b) butyric acid; (c) propionic acid; (d) valeric acid at different COD loading rate. CONCLUSIONS Separate production of hydrogen and methane from ethanol wastewater using using twostage UASB system under mesophilic operation and a controlled ph of 5.5 was investigated. The optimum COD loading rate of 13 kg/m 3 d (based on total working volume) provided the maximum gas production performance of both methane production rate and methane yield. The produced gas from the hydrogen UASB unit gave the hydrogen yield of 1.85 ml/g COD removed (or 0.57 ml/g COD applied). The methane UASB unit mainly contained CH 4 and CO 2 without H 2 which was consistent with the maximum methane yield of ml/g COD removed (or ml/g COD applied). In addition, this system had the highest the COD removal of 86% which much higher than typical UASB systems. ACKNOWLEDGEMENTS The authors would like to thank The Thailand Research Fund (the TRF Senior Research Scholar grant (RTA578008)) for partially financial support. The Petroleum and Petrochemical College and Center of Excellence on Petrochemical and Materials Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 7

8 Technology, Chulalongkorn University, Thailand, are also acknowledged. In addition, the authors would like to thank Sapthip Lopburi Co., Ltd., Thailand, for providing the seed sludge and ethanol wastewater used in this research. REFERENCES Eaton, A.D., Clesceri, L.S., Rice, E.W. and Greenberg, A.E. (2005). Standard methods for the examination of water and wastewater. Washington, DC: American Public Health Association (APHA), American Water Works Association (AWWA) & Water Environment Federation (WEF). Gomez, R.R. (2011) Licentiate thesis project. Department of Chemical Engineering and Technology. School of Chemical Science and Engineering. Royal Institute of Technology (KTH). 12 p. Intanoo, P., Chaimongkol, P., and Chavadej, S. (2015). Hydrogen and methane production from cassava wastewater using two-stage upflow anaerobic sludge blanket reactors (UASB) with an emphasis on maximum hydrogen production. Hydrogen Energy, 41, Intanoo, P., Malakul, P., Chavadej, S., and Rangsunvigit, P. (2014). Optimization of separate hydrogen and methane production from cassava wastewater using two-stage upflow anaerobic sludge blanket reactor (UASB) system under thermophilic operation. Bioresource Technology, 173, Intanoo, P., Namprohm, W., Bandhit, T., Chavadej, J., and Chavadej, S. (2012). Hydrogen production from alcohol wastewater by an anaerobic sequencing batch reactor under thermophilic operation: Nitrogen and phosphorous uptakes and transformation. Hydrogen energy, 37, Pakarinen, O. (2011). Methane and Hydrogen production from Crop Biomass through Anaerobic Digestion. Biological and Environmental science, 229, Saady, N. (2013). Homoacetogenesis during hydrogen production by mixed cultures dark fermentation: Unresolved challenge. Hydrogen energy, 38, Searmsirimongkol, P., Leethochawalit, M., and Chavadej, S. (2011). Hydrogen production from alcohol distillery wastewater containing high potassium and sulfate using an anaerobic sequencing batch reactor. Hydrogen energy, 36, Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 8