Mechanisms of sludge reduction in Nostocoides-driven enhanced biological phosphorus removal process

Nostocoides, a key phosphate-accumulating organism (PAOs), is abundant in wastewater treatment plants (WWTPs); however, the mechanism of sludge reduction in biological phosphorus removal systems under its dominance remains largely unknown. This study employed a lab-scale, exploratory multiparameter approach to examine extracellular polymeric substance (EPS) profiles, intracellular metabolites, microbial community, membrane integrity, and physiological activity to elucidate how Nostocoides-enriched enhanced biological phosphorus removal (EBPR) configurations accomplished sludge reduction. Waste-activated sludge (WAS) was repurposed as fermentation feedstock in the EBPR process. The findings indicate that a 43.23% reduction in sludge was achieved without any preliminary sludge pretreatment. The phosphorus removal rate was 99% without any supplemental carbon, which broke free from the reliance on influent organics that typified conventional EBPR. Illumina-based sequencing indicated that Nostocoides was the dominant bacterial community. Excitation-emission matrix (EEM) spectra showed that aromatic proteins derived from tyrosine and tryptophan, along with soluble microbial by-products embedded in the EPS matrix, were broken down to accelerate sludge disintegration. Flow cytometry was employed to assess membrane integrity along with overall microbial vitality and revealed that microbial cells underwent extensive death and lysis under WAS fermentation conditions, thereby releasing DNA and elevating its concentration in the supernatant, which represent key physiological changes driving sludge disintegration and organic carbon release for nutrient removal in this system. Nostocoides-governed EBPR configuration enables concomitant sludge reduction and nutrient elimination. This preliminary mechanistic exploration within Nostocoides-led EBPR configurations provides exploratory fundamental insights for advancing EBPR technology, with further validation required for practical engineering application.