Effects of compound bacterial agent on gaseous emissions and compost maturity during sewage sludge composting

The study aimed to provide an efficient compound bacterial consortium (CBC) containing three thermotolerant sulfide-oxidizing bacteria (SOB) strains to elucidate the effects of bacterial inoculation on odor emissions and maturity of sewage sludge composting. Compared to the single strain, the CBC exhibited more efficient sulfide oxidation capacities and enhanced enzymatic thermostability with the optimal temperature range of 40–50 °C. After inoculating the CBC agent into the 32 L reactors for 22 d composting, the cumulative H₂S, NH₃, and NO odor emissions of the inoculated group were reduced by 48.9%, 19.4%, and 57.8%, respectively, compared with the control group. The reduced sulfur was oxidized to sulfate with the action of the SOB to avoid H₂S emissions, and the pH decrease process also facilitated the reduction of NH₃ and NO emissions. Additionally, the increase of sulfate and germination index (GI) suggested that the CBC agent promoted sulfur conservation and compost maturity. Redundancy analysis indicated the close correlations of O₂, temperature, and pH on odor emissions; the partial least squares path modeling demonstrated both direct and indirect (by reducing odor emissions) positive impacts of bacterial inoculation on sulfate production. The results implied an effective strategy of CBC agent inoculating into SS composting to control odor release and accelerate the composting process.