Effects of Iron-Loaded Biochar on the Anaerobic Co-Digestion of Food Waste and Sewage Sludge and Elucidating the Mechanism Thereof

Abstract

The inhibition of volatile fatty acid (VFA) production is an important factor affecting biogas (methane) production in the anaerobic co-digestion systems comprising food waste and sewage sludge. In this study, batch experiments were conducted at medium temperature (36 ± 0.5 °C), during which the biogas production index and material–liquid characteristic parameters of the anaerobic digestion systems containing different concentrations of iron-loaded biochar (Fe-BC) were monitored. The cumulative biogas production data were analyzed using a modified Gompertz kinetic model to determine the effect of the Fe-BC on biogas production in the anaerobic co-digestion system. Studies have shown that addition of Fe-BC does not significantly influence the hydrolysis and acidification stages of anaerobic co-digestion, but does have a significant effect on promoting methanogenesis by alleviating the accumulation of VFAs and improving both the buffer capacity of the system and the efficiency of substrate-to-biogas conversion. When the Fe-BC concentration was 16 g·L−1, the cumulative biogas production reached 329.42 mL·g-VS−1, which was 49.7% higher than the blank group, and the lag period was 3.55 d, which was 42% shorter than the blank group. Mechanistic studies have shown that Fe-BC increased the concentration of coenzyme F420 and the conductivity of the digestate in the co-digestion system, which increased the activity of methanogens in the anaerobic digestion system, thereby promoting methanogenesis.