Implementation of enhanced biological phosphorus recovery for phosphorus mining from eutrophic marine sediments: The optimization of parameters and exploration of microbial responses

To evaluate the feasibility of enriching polyphosphate-accumulating organisms (PAOs) within marine sediment for achieving phosphorus (P) recovery, two sediment-inoculated sequencing batch reactors (SBRs), fed with propionic acid (R1) and glucose (R2), were operated for 119 days. For comparison, two sewage sludge-inoculated reactors (R3 and R4) were also set up. The sediments/sludge fed with 200 mg/L chemical oxygen demand (COD) equivalent propionic acid exhibited satisfactory P release/uptake performance after 56 days of culture. The maximum P release and uptake rates for R1 were 3 mg P/g VSS center dot h(-1) and 2.5 mg P/g VSS center dot h(-1), respectively, while for R3 they were 2.6 mg P/g VSS center dot h(-1) and 5.8 mg P/g VSS center dot h(-1), respectively. Meanwhile, the PAO family (Rhodocyclaceae) in R1 increased from almost 0 % initially to 16.0 % after 42 days. However, the glucose-fed SBRs did not exhibit enhanced biological phosphorus removal (EBPR) performance throughout the operation. As the COD feeding concentration increased to 400 mg/L, the reactors showed EBPR deterioration. Total P in R1 and R3 significantly decreased from 423.7 mg to 307.2 mg and from 368.0 mg to 94.9 mg, respectively. Key intracellular polymer responses indicated that introduction of excessively high COD significantly reduced poly-P content and the anaerobic synthesis of polyhydroxyalkanoate. Microbial analysis suggested that the breakdown of EBPR performance could be attributed to glycogen-accumulating organisms outcompeting PAOs under high carbon feeding conditions. Additionally, PHREEQC simulations confirmed that P-rich supernatant from the anaerobic phase could theoretically be recovered as struvite, with a recovery efficiency of up to 94 %.