Evaluating and modeling biogas production from municipal fat, oil, and grease and synthetic kitchen waste in anaerobic co-digestions

► Biogas from anaerobic co-digestion of kitchen waste (KW) and FOG was evaluated. ► KW and FOG enhanced CH4 production at estimated ideal S/I ratios of 1.20 and 0.46. ► Linear and modified Gomertz non-linear regressions combined to describe co-digestion. ► Models indicated that co-substrate addition can shorten lag phase of co-digestion. ► Evaluated S/I ratios and estimated parameters can support large scale operations. The feasibility of using synthetic kitchen waste (KW) and fat, oil, and grease (FOG) as co-substrates in the anaerobic digestion of waste activated sludge (WAS) was investigated using two series of biochemical methane potential (BMP) tests. Ranges of ideal substrate to inoculum (S/I) ratio were determined for the FOG (0.25–0.75) and KW (0.80–1.26) as single substrates in the first experiment. The second experiment, which estimated the methane production performances of FOG and KW as co-substrates for WAS co-digestion, was conducted based on the optimal parameters selected from the results of the first experiment. Results indicated that co-digestions with FOG and KW enhanced methane production from 117±2.02mL/gTVS (with only WAS) to 418±13.7mL/gTVS and 324±4.11mL/gTVS, respectively. FOG exhibited more biogas production than KW as co-substrate. Non-linear regression results showed that co-substrate addition shortened the lag phases of organic biodegradation from 81.8 (with only WAS) to 28.3h with FOG and 3.90h with KW.