Comparative evaluation of biochar, pelelith, and garbage enzyme on nitrogenase and nitrogen-fixing bacteria during the composting of sewage sludge

Abstract This study investigated the effects of garbage enzyme (GE), pelelith (PL), and biochar (BC) on nitrogen (N) conservation, nitrogenase (Nase) and N-fixing bacteria during the composting of sewage sludge. Results showed that the addition of GE, PL, and BC reduced NH3 emissions by 40.9%, 29.3%, and 67.4%, and increased the NO3-N contents of the end compost by 161.4, 88.2, and 105.8% relative to control, respectively, thus increasing the TN content. Three additives improved Nase, cellulase, and fluorescein diacetate hydrolase (FDA) activities and the abundances of nifH gene, and the largest increase was BC, followed by PL and GE. In addition, the additives also markedly influenced the succession of N-fixing bacteria, and significantly increased the abundance of Proteobacteria during the whole process. The BC and PL additions strengthened the sensitivity of N-fixing bacteria to environmental variables, and FDA, TN, moisture content, and NO3-N significantly affected the N-fixing bacteria at genus level.