Functional microbial enrichment and chelation-enhanced phosphorus release from marine sediments: Toward sustainable phosphorus management

To improve the efficiency of phosphorus (P) release from marine sediments and contribute to P loop closure, this study proposed a novel strategy combining bio-inoculation with polyphosphate-accumulating organisms (PAOs) and chemical enhancement via chelating agents. Based on prior findings, two-stage experiments were conducted. In Stage 1, anaerobic batch tests assessed the effect of different chelating agents for P release. While citrate showed no promoting effect, the addition of ethylenediaminetetraacetic acid (EDTA) significantly enhanced total P release, reaching 48.5 % within 15 days. In Stage 2, PAO-acclimated sediments were introduced into the system, followed by alternating anaerobic-aerobic fed-batch operation for 7 days, and subsequent EDTA addition with anaerobic incubation for another 6 days. This combined approach achieved a total P release efficiency 83.4 %, with final soluble P concentrations reaching 145.9 mg/L. During this process, PAOs were rapidly enriched, with their relative abundance increasing from 12.9 % to 65.0 %. Metagenomic analysis revealed that EDTA promoted environmental filtering, selectively enriching PAOs (Candidatus Accumulibacter) and thereby reinforcing their specific contributions to P functional genes. The resulting P-rich supernatant was then subjected to precipitation. PHREEQC simulations guided the prediction of optimal precipitation conditions, and laboratory experiments confirmed that most soluble P, especially Fe-bound forms, could be efficiently recovered, with maximum precipitation efficiencies of 98.8 %.