Evaluating analytical methods for the characterization of lipids, proteins and carbohydrates in organic substrates for anaerobic co-digestion

- Lipid-rich substrates yielded higher biogas.
- Protein and carbohydrate-rich substrates had faster biogas production rates.
- In terms of biogas yield, FOG is more desirable co-substrate for WAS than foodwaste.
- In this study, C/N ratio did not have an impact on the co-digestion process.

This study provides insights into the characterization of lipids, proteins and carbohydrate content in substrates for codigestion, and evaluates their effects on biogas yield. Among the analytical methods evaluated, the Bligh and Dyer, Hach Total Nitrogen and the Anthrone method were found to be most suitable for lipids, proteins and carbohydrates analysis, respectively. The co-digestibility of ten co-substrate mixes prepared using various volume-to-volume ratios of foodwaste (FW), fats, oils and grease (FOG), and waste activated sludge (WAS) were tested using biomethane potential assays. The three main substrates were mono-digested as well. WAS mono-digestion yielded the lowest methane yield of 118 mL CH4/g VS, while a 50:50 mix of WAS and FOG, containing 85% lipid and 15% protein produced the highest methane yield of 1040 mL CH4/g VS. In general, lipid-rich samples yielded more biogas than samples rich in proteins and carbohydrates. However, samples rich in proteins and carbohydrates had faster biogas production rates.