Processing of palm oil mill effluent (POME) into food waste digesting microbes: An investigation of acclimatization strategies

Abstract

Anaerobic digestion serves as a feasible and practical technology that converts food waste into biogas. Effective food waste-digesting inoculum must be capable of handling the heterogeneity of organic fractions. Therefore, the preparation of such an inoculum can be challenging. In this work, we explored a new approach to prepare the inoculum from palm oil mill effluent (POME), which is an alternative source of microbial consortium abundantly available in tropical countries, to be a food waste-digesting inoculum. By employing POME as an initial inoculum, our acclimatization was divided into three strategies, which were low, medium, and high-rate acclimatization. The result showed that low acclimatization was a successful strategy to adapt to the consuming behavior of microorganisms inside the anaerobic digestion system. The low acclimatization could provide a methane yield (513.90 mL-CH4/g-volatile solidadded) and a methane production rate (1.02 mL-CH4/g-volatile solidadded.h) higher than those in other reports by up to 12% and 80% for the methane yield and methane production rate, respectively. In addition, we also explored changes in microbial communities throughout the process. Microbial communities significantly shifted from lignocellulose-digesting bacteria to protein, lipid, and carbohydrate-digesting bacteria. Particularly, Papillibacter, Ruminiclostridium, Ruminiclostridium 1, and Ruminococcaceae UCG-010 genera were shifted to Proteiniphilu, Christensenellaceae R-7 group, and W5 genera. Interestingly, the major populations of methane-producing microbes changed from Methanosarcina to Methanosaeta. In low acetate environments, such as those found in stable AD systems, Methanosaeta should outnumber Methanosarcina. The presence of dominating Methanosaeta in the system showed the strategy's stability. The acclimatization strategy developed in this study exhibited promising potential to be used as an alternative method for waste management as well as a sustainable energy source due to its efficient methane gas production using food waste as the substrate.