Comparative start-up between mesophilic and thermophilic for acidified palm oil mill effluent treatment

Abstract

Malaysia is one of the largest palm oil producers in the world and its most abundant waste, palm oil mill effluent (POME), can be used as a feedstock to produce methane. Anaerobic digestion is suitable for treating the POME for methane production due to its tolerance to high strength chemical oxygen demand (COD). This work emphasizes the study of conditions during the start-up of anaerobic digestion of acidified POME between thermophilic (55 °C) and mesophilic (37 °C). The pH of the digester was maintained throughout the experiment at 7.3±0.2 in 1000 ml working volume. The study showed that the thermophilic was much faster to stabilize on the 44th days compared with the mesophilic on the 52nd days. Furthermore, the thermophilic also indicates higher biogas production, which was 0.60 l/l/d compared with 0.26 l/l/d of mesophilic. This result can be supported by the COD removal of thermophilic which also higher.

Comparative analysis in the performances of four in‐ground lagoon anaerobic digesters treating palm oil mill effluent (POME)

“…From the data, despite a reduction in COD removal with almost the same feeding amount (4000 m 3 /month), biogas production is seen increasing from September 2020 to October 2020. However, for the case of December 2020–January 2021, further COD reduction occurred at POME feeding of 10 000 m 3 /month, but there was a decrease in biogas production as well as methane yield, which agrees with a report by Hamzah et al 7 Consequently, high COD in the effluent is noticed due to the low consumption of substrate concentration and hence a low methane yield, as shown in the results.…”

“…RR from treated POME is prevalent to maintain the alkalinity of the pH level at 7.0. While specific alkalinity measurements are not carried out in this study, the understanding of the relationship between alkalinity and pH supports the justification for maintaining high alkalinity levels to ensure a desired pH of 7.0 in the system 7 . The preservation of high total alkalinity acts as a pH buffer for the anaerobic digestion system.…”

“…With the presence of pH buffer, it can prevent a notable change in pH and eliminate the remaining volatile fatty acids during the AD. Unstable pH causes the methanogens to not be able to carry out the neutralisation of volatile fatty acids properly in the AD 7 . However, the methanogens favour the pH conditions as they are near the neutral condition.…”

“…This result did not match the study done by Alepu et al, 17 as high HRT will increase biogas production. This could be due to methanogens being incompletely acclimatised to the optimal conditions required for the AD, 7 especially high temperature and low pH, which can be observed from the pre‐treated POME entering the digester in BGP D.…”

“…A mesophilic state is preferred in anaerobic digestion compared to thermophilic states, as the temperature range of 35–37°C is more favourable for various microbial activities that aid in the degradation of organic matter. Thermophilic anaerobic digestion occurs around 55–60°C, requiring additional energy input 7 …”