Objectives The sulfur transformation and the release of volatile sulfide during sewage sludge composting process were studied under different ventilation conditions. This study was conducted to provide a reference for the retention of higher sulfur content in the compost and the control of malodorous substances.

Methods A composting experiment was conducted for 15 days in a composting device with automatic ventilating system. The frequency of the blower was set into 10, 13, and 16 Hz to achieve low, medium, and strong ventilation treatments, respectively. In all the three ventilation treatments, the sewage sludge and sawdust were mixed in 3∶1 (wet weight), and the ventilation was set to an interval of 20 minutes every 1 minute. Multi-point mixed samples were collected, and the emission of volatile sulfides was determined in the beginning and in days 1, 2, 3, 5, 7, 9, 11, 13, and 15 of the composting process.

Results The peak concentration of H₂S decreased by about 50% while the cumulative release increased by 45.4% in the strong ventilation treatment. The cumulative release of methyl sulfide increased by 398%, and the peak concentration increased by 490.8% in strong ventilation treatment. In strong ventilation treatment, the cumulative release of CS₂ decreased by 57.8%, and the peak concentration decreased by 77%, compared to the low ventilation treatment. The concentrations of available sulfur in the final product increased by 19.5%, 19.1% and 36.1% under low, medium, and strong ventilation, respectively, as compared with that before composting.

Conclusions In the process of composting, strong ventilation intensity reduced the peak concentration of H₂S, but increases the cumulative release of H₂S. Strong ventilation also promotes the release of methyl sulfide, and increases the peak concentration and cumulative release of methyl sulfide. Thus, it can be concluded that strong ventilation helps to increase the available sulfur content in sewage sludge compost.