Synergistic effects of biochar and laccase on nitrogen conversation and degradations of two artificial sweeteners during the sewage sludge composting

This study investigates the effects of biochar, laccase, and their combined application on nitrogen transformation, the degradation of sucralose (SUC) and acesulfame (ACE), and the dynamics of bacterial communities during sewage sludge composting. The results indicated that NH3 emissions were reduced by 41.2 %, 17.5%, and 40.8 % in the biochar, laccase, and biochar-laccase treatments, respectively, compared to the control. Meanwhile, N2O emissions decreased significantly by 26.8 % and 16.0 % for the biochar and biochar-laccase treatments, respectively, but increased by 8.1 % for the laccase treatment. Additionally, the biochar, laccase, and biochar-laccase treatments enhanced the degradation of SUC and ACE by 36.6-68.3 % and 49.2-69.8 %, relative to the control, respectively. Network analysis showed that the additive-treatment enhanced the cooperation within bacterial communities, and solidified artificial sweeteners degradation, especially under biochar-laccase application. Phylogenetic investigation of communities by reconstruction of unobserved states further indicated that biochar, laccase, biochar-laccase treatment increased enzymes associated with the degradations of organic matter and artificial sweeteners. In conclusion, it suggested that a combined addition of biochar and laccase was an effectively way to reduce nitrogen loss and promote artificial sweeteners degradations during sewage sludge composting.