Study on the effects of high-load induced EPS accumulation and Thiothrix introduction on the performance and...

This study focuses on optimizing the efficiency of the biological phosphorus removal process, with the core objective of simultaneously enhancing the upper limit of phosphorus release in the anaerobic phase and the phosphorus uptake capacity in the aerobic phase. To this end, an independent enhanced biological phosphorus removal (EBPR) system was established, and the accumulation of extracellular polymeric substances (EPS) was induced by increasing the influent COD load to investigate its role and mechanisms in a high-phosphorus environment. The results indicate that the release process of intracellular phosphorus from polyphosphate-accumulating organisms (PAOs) into the aqueous phase is driven by the concentration gradient formed between the phosphorus content in EPS (P_EPS) and the phosphorus concentration in the aqueous phase (P_Water). The EPS accumulation induced by high COD load enriches phosphorus in the aqueous phase through adsorption, thereby increasing the P_EPS level, which significantly raises the anaerobic phosphorus release equilibrium limit of the system. At the microbial community level, the high influent COD promoted significant proliferation of Thiothrix in the sludge, suppressed the relative abundance of glycogen-accumulating organisms (GAOs), enhancing the competitive advantage of PAOs for carbon sources in the anaerobic phase. Meanwhile, Thiothrix exhibited significant polyhydroxyalkanoates (PHA) synthesis capability, and its metabolic activity promoted the accumulation of PHA in the sludge, providing an additional energy source for the aerobic phosphorus uptake process. This further optimized the aerobic effluent PO₄^3--P from originally below 0.3 mg/L to stably below 0.1 mg/L. This study provides a novel strategy for synchronously enhancing the phosphorus removal performance of the system.