Enhancing biomethanation performance through co-digestion of diverse organic wastes: a comprehensive study on substrate optimization, inoculum selection, and microbial community analysis

Abstract A blend of organic municipal solid waste, slaughterhouse waste, faecal sludge, and landfill leachate opted as substrates in different mix ratios to formulate a pertinent mixture for biomethanation. Individual substrates were characterized and the mix ratio was optimized with the help of the response surface methodology tool to a value of 1:1:1:1 (against a C/N ratio of 28 ± 0.769 and VFA of 2500 ± 10.53) to improve the overall performance. The optimized blend (C/N ratio: 28.6, volatile fatty acids: 2538 mg/L) was characterized for physicochemical, biological, and microbial properties and subjected to anaerobic digestion in lab-scale reactors of 1000 ml capacity with and without the addition of inoculum. The gas yield of individual substrates and blends was ascertained separately. The observed cumulative gas yield over 21 days from the non-inoculated substrates varied between 133 to 2035 ml. While the addition of external inoculation at a 5% rate (w/w) against the substrate, uplifted the minimum and maximum cumulative gas yield values to 203 ml and 3394 ml. The inoculum procured from the Defence Research and Development Organisation (DRDO) was screened beforehand considering factors such as maximizing VFA production and consumption rate, gas yield, and quality of digestate. A similar outcome related to gas yield and digestate quality was observed for the equivalent blend. The cumulative gas yield value increased from 2627 ml to 4284 ml over 21 days post-application of a similar dosage of DRDO inoculum. Analysis of the 16S rRNA gene revealed that the predominant bacterial population belonged to the Firmicutes phylum, with the majority falling within the orders Clostridiales and Lactobacillales. Ultimately, the study advocates the potential of the aforementioned blend for anaerobic co-digestion to enhance the gas yield and digestate quality.