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CONFERENCE PROCEEDING
Enhancing the methane production from biogas effluent of palm oil mill using microbial electrolysis cell
Phatnarin Buakhao1*, Nu-Aime Baniahmad1, Rattana Jariyaboon2, Prawit Kongjan2
1Demonstration School Prince of Songkla University, Pattani Campus
2 Faculty of Science and Technology, Prince of Songkla University, Pattani campus
*Corresponding author: [email protected]
ABSTRACT
The palm oil industry is a very important in a Southern Thailand’s economy but during processing of oil palm process, it produce too much wastewater (Palm oil mill effluent; POME). Many factories use POME as substrate in biogas production as a treatment for the effluent, but the effluent after treating by biogas processing still have high chemical oxygen demand (COD). Therefore, the wastewater with a high COD value is suggested to treated with microbial electrolysis cell or MEC, a process that uses electrical energy from an external energy source to catalyse internal biological reactions. MEC increases the efficiency of the removal of organic matter by microorganisms and can continue to produce biogas.
This research aims to study the effect of feeding electricity into the MEC system for treating the synthetic wastewater on biomethane production efficiency based on analysis of results obtained by feeding 0.7, 1.0, and 1.3 V currents into 2 serum bottles with electrodes and 3 serum bottles without electrodes for 23 days. The result exhibited that methane production using MEC with applying 0.7 V give an 8.50% higher daily cumulative CH4 production than control set and methane production using MEC with applying 1.0 and 1.3 V give 0.76% and 2.56% lower daily cumulative CH4 production than control set. It can be concluded that by applying 0.7 V to MEC could enhance the methane production.
Keywords: microbial electrolysis cell; anaerobic digestion; Methane bioproduction; Electrical energy input
INTRODUCTION
As we all know, the palm oil extraction industry is critical to the economy of southern Thailand.
However, during the extraction process, excessive wastewater known as Palm oil mill effluent (POME) is produced. POME has a high organic content and can be used as a co-treatment substrate in biogas production, but the effluent from biogas production using POME still has a high chemical oxygen demand, and further treatment methods such as aerobic digestion, a factorial pond, and a polishing pond have a high cost due to constant air feeding and additional costs in excess sludge removal. So, in this study, we use a microbial electrolysis cell, or MEC, to treat the synthetic effluent from biogas generation using POME (a mixture of sucrose and BA medium), which is a technique that employs electrical energy from an external energy source to accelerate internal biological reactions. MEC improves the effectiveness of microorganisms' removal of organic matter, allowing them to continue producing biogas.
METHODOLOGY
Attaching the electrodes into the MEC serum bottles
There are 2 types of serum bottles, which are 500 mL serum bottle with electrodes and serum bottle without electrodes. The electrodes that were used in this experiment were 2x5 centimeter Titanium mesh as a cathode and Carbon cloth as an anode. The naked wires were used to hold both electrode parallelly and inserted into the middle of rubber
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septum tightly capped with aluminum cap the distance between the electrodes was approximately 1.5 cm as shown in Figure 1.
Figure 5. MEC configuration for biomethane production (a) diagram and (b) the MEC used in the experiment
Preparing of fermentation liquid
Firstly, the culture medium, BA medium, the suitable medium for anaerobic microorganisms were prepared followed the composition presenting in Table 1.
Table 1. The composition of the BA medium at a total volume of 1 L (Tan et al., 2018)
210 mL of inoculum, 90 mL of BA medium, and 3 g of sucrose in total of 300 mL working volume were used for the anaerobic digestion of the synthetic wastewater.
Afterward, all the serum bottles were closed with rubber septum and covered with an aluminium cap to prevent any leakage. After that, the headspace was purged with nitrogen gas for 3 minutes to make an anaerobic condition in the system.
Methane production
All the serum bottles were kept at room temperature. Gas samples were taken daily for analyzing the gas component by Gas chromatography-thermal conductivity detector (GC-TCD) and for measuring the gas volume by the water displacement method. For the MEC serum bottles, the electricity at 0.7 V was applied at day 3 After 23 days of the experiment were stopped and started again with another electricity load of 1.3 V and 1.0 V.
RESULTS AND DISCUSSION
Figure 2 shows the cumulative CH4 production of the control set without electrode compared to the MEC (with electrodes) with different electricity applied. The 0.7 V
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MEC serum bottle had 8.5% higher cumulative CH4 production than a control serum bottles at statistical significance of 95% confident interval. At the first 3 day of experiment the attached electrodes serum bottle set also produced a bit higher methane production than the bottle without electrode. This is because the electrodes used are Titanium mesh which can be acted as a natural catalyst to accelerate the biochemical reactions inside the bottles. Furthermore, an attached electrode serum bottle has 7.5%
higher methane concentration than a control set as presented in Figure 3
(a) (b)
(c)
Figure 2. Cumulative CH4 production of the control set without electrode compared to the MEC (with electrodes) with electricity applied at: (a) 0.7 V (b), 1.0 V, and (c) 1.3 V
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(a) (b)
(c)
Figure 3. CH4 content in the biogas produced from the control set without electrode compared to the MEC (with electrodes) with electricity applied at: (a) 0.7 V (b), 1.0 V, and (c) 1.3 V
In contrast, the 1.3 V and 1.0 V electricity applied serum bottles had 2.56% and 1.2%
respectively lower daily cumulative CH4 production than a control serum bottles because over-voltages impair the cell membrane of biogas-producing cells and slow their metabolism (Ding et al., 2018), and will reduce the amount of methane produced.
Methane concentrations obtained from MEC 1.3 V and 1.0 V were also less than those from the control at 6.92% and 3.78%, respectively, as shown in Figure 3.
CONCLUSION
Attaching the metal electrode allows for faster reactions. Biogas production with MEC at 0.7 V has daily cumulative CH4 production better than control set at 8.50% and methane concentration over control set at 7.50%. While, Biogas production with MEC at 1.0 V and 1.3 V has daily cumulative CH4 production and methane concentrations less than control set.
ACKNOWLEDGEMENT
This project was supported by Science Classroom in University Affiliated School (SCiUS) under Prince of Songkhla University, Pattani Campus and Demonstration School Prince of Songkhla University. The funding of SCiUS is provided by Ministry of Higher Education, Science, Research and Innovation.
REFERENCES
Ding, A., Yang, Y., Sun, G., & Wu, D. (2016). Impact of applied voltage on methane generation and microbial activities in an anaerobic microbial electrolysis cell (MEC). Chemical Engineering Journal, 283, 260–265. https://doi.org/10.1016/j.cej.2015.07.054
Tan, K. A., Morad, N., Norli, I, Lalung, J., & Wan Omar, W. M. (2018). Post-treatment of palm oil mill effluent (POME) using freshwater green microalgae. Malaysian Journal of Microbiology.
https://doi.org/10.21161/mjm.1113918
