Effect of inoculum type and organic load on methane recovery from lipid-rich confectionery wastewater

The recovery of biofuels from lipid-rich industrial waste streams offers a sustainable strategy to renewable energy production and wastewater management. In this context, the present study investigates confectionery wastewater as a substrate for biomethane production through biochemical methane potential tests under different organic loads, focusing on the influence of inoculum type, i.e., urban wastewater digestate (DWW) and anaerobic granular sludge (AnGS), initial organic matter concentration, and inoculum-to-substrate ratio. Methane production was fitted using the modified Gompertz and first-order kinetic models, while long-chain fatty acid (LCFA) degradation was assessed to evaluate possible inhibitory effects. Kinetic modelling revealed that the modified Gompertz model best describes methane production with DWW, whereas first-order kinetics more accurately represent the behaviour observed with AnGS. DWW performed better at low initial organic matter concentration, achieving 264.8 ± 21.6 mL CH₄/g tCODinf. Conversely, AnGS showed higher tolerance to high organic loads, reaching 313.5 ± 4.3 mL CH₄/g tCODinf and up to 96% LCFA degradation. These findings demonstrate that AnGS is a suitable inoculum for efficiently converting confectionery wastewater into methane, limiting LCFA inhibition and supporting the valorisation of high-strength, seasonally variable industrial wastewater.