Sludge composting with self-produced carbon source by phosphate buffer coupled hyperthermophilic pretreatment realizing nitrogen retention

During sludge composting, ammonia emissions is the main pathway of nitrogen loss. In addition to regulating pH, increasing the carbon source is also important for controlling ammonia emissions. Previous studies have focused on additional carbon sources, while this study used phosphate-buffered saline (PBS) and hyperthermophilic pretreatment (HP) to release difficult-to-utilize carbon sources in extracellular polymeric substance (EPS) for composting. The PBS concentration was 0.22 mmol/g total matter (TM), PBS soaking days were 4.74, HP temperature was 149.46 °C, and the soluble chemical oxygen demand (SCOD) was 45.08 g/kg. Compared with the control check, the peak ammonia emission concentration in the pretreated group was reduced by 8.70 % and the total nitrogen loss was reduced by 18.10 %. Changes in EPS, ammonia assimilation activity, and microbial community composition demonstrated that PBS and HP released the carbon source from the sludge, promoted ammonia assimilation, and enriched bacteria related to ammonia assimilation such as Bacillus (16.52 %). HP treatment made Acinetobacter (12.5 %) the dominant genus in the calefactive phase, and the enrichment of Actinobacteriota (27.27 %) promoted the composting maturity. However, total pretreatment reduced the porosity and permeability of the sludge and affected the activity of microorganisms. Considering the cost of energy consumption, partial pretreatment has more practical application prospects.