Effect of exogenous CaO addition on HS production from waste activated sludge and its influence mechanism.

Hydrogen sulfide (HS) production from waste activated sludge (WAS) is the main reason for odor emission during anaerobic fermentation system. CaO has been reported to effectively improve the resources recovery of WAS, but its potential effect on HS production in anaerobic fermentation process remains unrecognized. In present study, it was found that the addition of 60 mg/g VSS CaO greatly inhibited HS production and the maximum yield of HS was 60.1 ± 1.8% lower than the control. Mechanism investigation demonstrated that CaO destroyed sludge structure and increased the release of intracellular organic matter with hydrogen bonding networks destroying, but had a mild effect on the transformation of sulfur containing organic matters and inorganic sulfate reduction. Additionally, the enhancement in H and S consumption by alkaline condition and metal ions release was another reason for the inhibition of HS production in CaO addition reactors. Furthermore, microbial analysis showed that CaO addition importantly reduced the hydrolysis microorganism, particularly denitrification hydrolytic bacterias (e.g., unclassified_f_Chitinophagaceae and Dechloromonas), sulfate reducing bacterias (SRBs) (e.g., unclassified_c_Deltaproteobacteria and Desulfosarcina) and genes (e.g., PepD, cysN/D, CysH/C and Sir) involved in organic sulfur hydrolysis and sulfate reduction. Results from this study provides theoretical insights into the practical applications of CaO.