Re-circulation of Fe/persulfate regulated sludge fermentation products for sewage treatment: Focus on pollutant removal efficiency, microbial community and metabolic activity

Persulfate (PS)-based technologies have been demonstrated as efficient methods for enhancing the performance of waste activated sludge (WAS) anaerobic fermentation. Except for volatile fatty acids (VFAs), however, some exogenous substances would be also released during this process, which might affect its application as a carbon source for sewage treatment. To fill this knowledge gap, the feasibility of sludge fermentation liquid regulated by Fe/persulfate (PS) (PS-FL) as a carbon source for sewage treatment was investigated in this study. Results indicated that PS-FL exhibits distinct effects on the pollutants removal compared with commercial sodium acetate. It facilitates PO43--P removal but slightly inhibited COD removal & denitrification, and sludge settleability was also decreased. The mechanistic analysis demonstrated that PS-FL could stimulate the enrichment of phosphorus-accumulating bacteria (i.e. Candidatus Accumulibacter) and the enhancement of their metabolic activities (i.e. PKK), thereby enhancing the biological PO43--P removal. Moreover, Fe ions in PS-FL could combine with PO43--P to form a precipitate and thus further contributed to PO43--P removal. Conversely, the sulfate reduction process induced by SO42- in PS-FL inhibits denitrification by reducing the abundance of denitrifying bacteria (i.e. Dechloromonas) and metabolic activities (i.e. narG). Additionally, PS-FL also decreased the abundance of flocculation bacteria (i.e. Flavobacterium) and down-regulated the expression of functional genes responsible for COD removal, by which it exhibited certain negative effects on COD removal and sludge settleability. Overall, this work demonstrated that PS-FL can re-circulation as a carbon source for sewage treatment, which provides a new approach to recovering valuable carbon sources from WAS.