Pre-treatment of excess sludge with sulfide-containing wastewater for composite electron donor formation to enhance denitrification

Utilizing the fermentation liquor of excess sludge (ES) for the denitrification process represents an effective strategy for the valorization of ES and achieving environmentally friendly denitrification. However, ES fermentation technologies require significant energy or chemical product inputs. The present study proposes a novel method utilizing sulfide-containing wastewater to pretreat ES for generating dissolved organic matter (DOM), with sulfides and DOM collectively forming a composite electron donor (S-ES-DOM). The introduction of S-ES-DOM enables the establishment of integrated autotrophic and heterotrophic denitrification (IAHD) process, achieving 100 % denitrification efficiency. Molecular analysis identified an increase in biodegradable components within S-ES-DOM, which were effectively utilized during the IAHD process. The functional genes associated with nitrate-sulfide-organic carbon metabolism and electron transfer exhibited upregulation. The mixotrophic microbial community enables flexible adoption of multiple metabolic pathways. This strategy simultaneously achieves low-cost ES valorization and low-carbon nitrate/sulfide removal through integrated nitrogen-sulfur-carbon metabolism.