Waste cooking oils (WCOs) to biogas nexus: Kinetics, active microbes, and functional enzymes

Abstract

The efficiency of anaerobic digestion (AD) chiefly relies on substrate composition and microbial structure. The lipidic substrates such as waste cooking oils (WCOs) have high biogas potential. The biogas production from WCOs can be increased by active microbes with simultaneous alleviation of environmental contamination. Thus, this study explored the biogas potential of two different WCOs including duck cooking oil (DCO) and fat, oil, and grease (FOG) in AD. The effects on biogas kinetics, oils degradation, microbial community dynamics, and variations in bacterial and archaeal functional enzymes were investigated. The modified Gompertz and logistic growth models showed a curve-fit within a range of 0.98–0.99 R2 value for biogas production in DCO and FOG-loaded reactors. The biogas production was > 5-folds higher in WCOs compared to control. The addition of DCO and FOG showed 76.87 % and 69.76 % of lipid degradation, respectively. The major bacterial enzymes involved in β-oxidation (based on Kyoto Encyclopaedia of Genes and Genomes, KEGG map 00071) of DCO and FOG were acetyl-CoA C-acetyltransferase and enoyl-CoA hydratase. These enzymes correspond to the dominance of Clostridium (>90 %) and might be involved in the formation of biomethane precursors. While the abundance of Methanosphaera (>60 %) and Methanobrevibacter (>30 %) increased the archaeal CoB-CoM reductases and methyltransferase involved in biomethanation. This study demonstrated that the WCOs could be used as potential substrates for biogas production.