Efficient start-up of anaerobic methanogenesis process for kitchen waste biodegradation utilizing polyurethane sponge

The delayed start-up phase of anaerobic digestion (AD) of kitchen waste (KW) seriously affects overall efficiency. The positive impact of organic fillers in anaerobic wastewater treatment has inspired the treatment of oily solid waste. This study compared the impacts of four popular fillers: polypropylene (PP), high-density polyethylene (HDPE), expandable polystyrene (EPS), and polyurethane sponge (PUS) to determine the optimal filler to achieve efficient starting KW-AD. The findings demonstrated that EPS, PP and HDPE reduced cumulative methane production by 43.27 %, 87.64 % and 89.18 %; PP and HDPE increased the concentration of acetate by 42.68 % and 59.90 %, generated start-up failure; the three increased the abundance of Actinobacteriota by more than 15.52 %, which caused sludge foaming. Conversely, PUS shortened the start-up phase of AD by 46.06 %, increased the cumulative methane production by 20.99 %, enhanced the abundances of hydrogen-producing bacteria (Thermotogota) and hydrogenotrophic methanogens (Methanoculleus) in the sludge by 15.73 % and 33.33 %. This suggested that the hydrogenotrophic methanogenesis pathway is significantly augmented. The surface of PUS mainly enriched two electrochemically active bacteria (Thiopseudomonas, 19.76 %; Defluviitoga, 12.71 %) to enhance interspecies electron transfer (IET). Further exploration revealed 2.80 g/g VS was the optimum PUS dosage for the start-up phase of KW-AD; and this threshold should not be lower than 0.93 g/g VS. This research revealed the mechanism by which the filler modulates the microbial community to enhance the degradation of organic matter, while also offering a theoretical reference for the efficient start-up of KW-AD.