Role and significance of nitrogen and sulfur-doping on algal biochar for regulating methane production

Algal biochar (ABC) was derived from Taihu algal biomass and modified by sulfur (SABC) and nitrogen-doping methods (NABC), the role and significance of two engineered biochars on anaerobic digestion were explored in this study. Results showed that methane production was enhanced by SABC compared to the ABC group since the shortened lag time (67.9 %) and the improved methane yield (12.8 %) were observed. The electron-donating capacity of SABC was increased by 85.7 % after modification. Meanwhile, SABC facilitated the selective enrichment of syntrophic partners like Clostridium and Methanosaeta in the reactors. The enhanced methanogenesis by SABC could be attributed to the improved electron transfer activity and the establishment of interspecies syntrophism relationships. Compared to ABC, the lag time of methanogenesis failed to be shortened (p > 0.05) and the methane yield was reduced by 8.9 % in the presence of NABC. The redox capacity of NABC was not improved after modification, the improved non-selective adsorption and the nitrogenous heterocyclic inhibitors originating from the N-doping process should be responsible for the methanogenic inhibition by NABC. The findings of this study provided a better understanding of biochar modification to enhance methanogenesis, which would be valuable for enhancing anaerobic digestion performance in water pollution control.