A REVIEW ON BIOGAS PRODUCTION BASED ON CIRCULAR ECONOMY VIA CO-DIGESTION AND IMMOBILIZED SUBSTRATES

Abstract

Organic waste has been discharged into the environment by various industries in a global society. Anaerobic digestion has proven its potential as a waste-to-energy (WTE) technology to produce biogas, which can also replace fossil fuels while accommodating these unwanted wastes. However, there are limitations to anaerobic digestion, such as poor biomethane yield due to limited supply and fluctuations in the composition of the substrates, and an inadequate C/N ratio in the feedstocks. This paper aims to discuss possible methods to overcome the constraints in the process, including co-digestion and immobilization of the substrates via a moving bed biofilm reactor. The parameters discussed in this literature were the following: (1) mode of operation; (2) temperature; (3) type of anaerobic digestion; (4) pre-treatment methods; (5) addition of nutrients; and (6) using plastic carriers. An in-depth study highlighting the role of industries in biogas production toward achieving circularity was also examined. Several studies have shown that co-digestion enhances biogas production more than mono-anaerobic digestion. Notably, using plastic carriers for immobilization can improve the metabolic process due to biofilm formation and serve as a niche for microbial culture. In addition, excessive nutrients can be highly toxic as they can inhibit bacterial activity in the methanogenic phase. This review also presented the techno-economic analysis of utilizing distillery wastewater and press mud from sugarcane industries to produce biogas. Therefore, the findings in this article allow the development of optimization designs for industrial scale based on circular economy to address various organic wastes.