Biochar addition to mitigate oil inhibition in anaerobic digestion of food wastewater: Microbial insights from biochemical methane potential tests

The high oil content in food wastewater often limits the process of anaerobic digestion by suppressing microbial activity and growth, both essential for organic conversion and consequently methane production. The objective of this study was to optimize biochar dosage for enhancing anaerobic digestion of food wastewater. Thus, the synthetic food wastewater containing 4 g/L of sodium oleate (oleate-Na) and an initial organic concentration of 5000 mg/L COD was used. Results show that methane production was severely suppressed during the anaerobic digestion of food wastewater with the addition of oleate-Na, reducing cumulative methane yield by 36.61 %. The inhibitory effect was mitigated with biochar addition, particularly at 5 g/L, which facilitated oleate-Na biodegradation to increase the cumulative methane production by 196.50 %. Sludge characterization and microbial analysis indicated that adding 5 g/L of biochar significantly enhanced biomass growth and selectively enriched functional bacteria, such as Thermotogae and Bacteroidetes, along with archaea like Methanoculleus and Methanosarcina, promoting hydrogenotrophic methanogenesis for methane production. Nevertheless, this benefit was reduced when biochar addition was increased from 5 g/L to 8 g/L, likely due to its excessive adsorption of compounds, like volatile fatty acids, to limit further methanogenesis.