Optimal low-frequency mechanical vibration enhances extracellular polymeric substances-mediated phosphorus removal in...

The biological phosphorus removal (BPR) process relies on frequent phosphorus exchange between functional microorganisms and their surrounding environment. However, limited mass transfer restricts the overall phosphorus removal efficiency. In this study, low-frequency mechanical vibration (LFMV) was introduced into the anaerobic/oxic reactors. The results indicated that LFMV at 40 Hz significantly improved biological phosphorus removal efficiency by approximately 13 %. Assessment of the mass transfer coefficient and sludge characterization collectively demonstrated that optimal LFMV enhanced mass transfer efficiency by >30 %, primarily attributable to alterations in physicochemical properties (e.g., particle size, surface charge, and functional groups). Further analysis of phosphorus distribution and extracellular polymeric substances (EPS) composition suggested that LFMV promoted EPS-mediated phosphorus adsorption and storage by modifying EPS content and composition. Moreover, quantification of metabolism-related biological activities (i.e., specific metabolic rate and metabolic enzyme activities) revealed that optimal LFMV accelerated phosphorus transformation within EPS. In addition, the ³¹P NMR spectra confirmed that polyphosphate in tightly bound EPS increased 2 to 3 percentage points with LFMV treatment. 16S rRNA sequencing results indicated LFMV enriched 14 key genes related to phosphorus metabolism and 4 genes associated with EPS secretion, without significantly altering microbial community structure or the relative abundance of PAOs. These findings collectively indicate that optimal LFMV (i.e., 40 Hz) effectively accelerates phosphorus removal by enhancing EPS-mediated adsorption, storage, and transformation processes. This study provides a promising technical strategy for enhancing the performance of biological phosphorus removal systems.