PERFORMANCE ANALYSIS OF THREE-STAGE ANAEROBIC REACTORS TREATING TOFU WHEY WASTEWATER FOR BIOGAS PRODUCTION

• Main Author: Wresta, Arini
• Format: Dissertations
• Language: Indonesia
• Subjects: Teknik (Rekayasa, enjinering dan kegiatan berkaitan)
• Online Access: https://digilib.itb.ac.id/gdl/view/72547
• Institution: Institut Teknologi Bandung

Tofu industrial wastewater is one of the liquid wastes that is produced abundantly in Indonesia. Tofu whey, the wastewater generated during the protein coagulation and tofu pressing processes, has a high organic content so it is highly potential for use as a substrate in biogas production. As a protein-rich substrate, tofu whey potentially have a buffering capacity to prevent a decrease in pH during the acidogenesis stage. Several anaerobic WWTPs treating tofu whey into biogas were installed in Indonesia using fixed bed reactors. The use of a multi-stage fixed bed reactor aims to optimize the process by providing suitable conditions for each microbial group that plays a role in the stages of biogas formation in different reactors. However, there is no adequate data on reactor performance yet. This research aims to analyze the performance of a three-stage fixed bed reactor treating tofu whey for biogas production. Performance analysis was started by evaluating the buffering capacity of tofu whey through batch experiments, start-up of continuous experiments in the fixed bed reactors, and then analyzing the performance of three stages fixed bed reactors through semi-continuous experiments. Performance analysis of the fixed bed reactor was carried out by varying the organic loading rate (OLR) or retention time (HRT) after successful start-up. There were five variations of retention time, i.e total HRT of 6.07-14.17 days; 3.75-4.36 days; 2.09-3.54 days; 1.31-1.48 days; and 0.62-1.20 days or total OLR of 0.49-1.32 kg COD/m3/day; 1.58-1.75 kg COD/m3/day; 2.18-2.42 kg COD/m3/day; 2.98-5.54 kg COD/m3/day; and 6.66-9.81 kg COD/m3/day. From the data obtained at various retention times, a simplification of the kinetic model was built so that it can represent the process that occurs in the reactor. The result of batch experiment showed that tofu whey provided a buffer capacity and could maintain pH levels between 6.8 and 8.4 during the process. Biogas production from tofu whey is possibly conducted without any chemical additives, either to increase the pH or as a nutrient source. The specific CH4 production obtained was 284.6 NmL CH4/g VS substrate. A good start-up performance was obtained, with COD removal achieving more than 80% after 90 days. The diversity of bacteria in the reactor on day 73 showed that the utilization of complex proteins and carbohydrates was conducted more in Reactor 1, and the utilization of simple carbohydrates was more in Reactor 2 and 3. The diversity of archaea within the reactor indicated that methanogenesis in Reactor 1 was dominated by hydrogen substrates, and methanogenesis in Reactor 3 utilized hydrogen and acetate as substrates. The reactor showed good performance with COD removal achieving more than 80% at various organic loading rate. Anaerobic microorganisms in the reactor can adapt well to the increased of organic loading rate. Acidogenesis dominated the process in Reactor 1 while methanogenesis dominated in Reactor 2 and 3. The 1 TG? of propionate utilization reaction was close to the equilibrium conditions but did not indicate the possibility of VFA accumulation in the reactor. The propionate concentration could be kept below 0.8 g acetate/L. The COD mass balance confirmed the value of CH4 yield well. Based on previous research, the three stages reactor was successfully operated in a shorter retention time with a higher OLR than a single-stage reactor. The highest CH4 productivity was obtained at an organic load rate of 6.7 kg COD/m3/day (total retention time of 1.1 days), reaching 1.74 Nm3 CH4/m3-day. The simplification of the kinetic model involving two process steps, namely acidogenesis and methanogenesis, represented the conditions in the reactor well. The average relative error obtained was 10.58%. The value of kinetic constants , ma ? , sa K COD Xa Y , VFA Xa Y , CO2 Xa Y , H2 Xa Y , mb ? , sb K , VFA Xb Y , CH4 Xb Y , CO2 Xb Y and ? were 0,83?0,19 day-1, 7,60?1,98 g COD/L, 10,57?2,56 g COD/g, 539,28?213,91 mmol/g, 102,95?44,78 mmol/g, 4,25?1,58 mmol/g, 0,29?0,14 day-1, 36,90?20,55 mmol/L, 207,31?74,45 mmol/g, 109,58?47,76 mmol/g, 39,63?13,80 mmol/g and 0,31?0,06, respectively. The next research opportunity is to observe the formation of biofilm in the reactor. At the same time, validation of the kinetic model can be carried out by confirming the concentration of acidogenic and methanogenic bacteria. Further research development is the implementation of biogas production from tofu whey wastewater on a larger scale with shorter retention time and higher organic loading rate to reduce investment costs and increase biogas productivity.