Effect of rice husk and palm tree-based biochar addition on the anaerobic digestion of food waste/sludge

[Display omitted] •Biochar influence anaerobic digestion of food waste/sludge at mesophilic temperature.•Biochar dosage increased specific methane yield while not influencing biogas yield.•Increasing biochar dosage improved reduction capacity of tVFA and NH4+-N. This study explored the impact of different types of biochar on the anaerobic digestion (AD) of food waste and sludge and the biochar-enhanced mesophilic AD of food waste for methane production. A particular focus was placed on the process and underlying mechanisms. Rice husk biochar (RHB550) and palm tree biochar (PTB400) were loaded at levels of 5, 10, and 15 g/L. The results showed that 5 g/L of RHB550 led to an increase in methane yields of 455.83 ± 17.9 mL/gVSadd compared to the control yield of 333.32 ± 14.9 mL/gVSadd. The addition of an adequate amount of biochar improved the cumulative methane yield, whereas excessive amounts inhibited the AD process. RHB550 biochar improved the process stability, which was favourable for syntrophic volatile fatty acid (VFA) oxidation, and consequently increased the cumulative methane yield by up to 36.75 ± 2.9%. Earlier stagnation was also shown to be caused by the elimination of VFAs and ammoniacal-nitrogen and the degradation of chemical oxygen demand (COD). Increasing the concentrations of RHB550 biochar enabled significant improvement in methane yield by increasing the pH and COD removal, which could be a useful strategy in AD to further increase the organic loading rate.