The condition optimization and mechanism of aerobic phosphorus removal by marine bacterium Shewanella sp

Excessive release of phosphorus (P) from wastewater into water systems is a significant environmental problem. Aerobic P removal, a new P removal pathway, was investigated. P removal primary mechanisms of marine bacteria Shewanella sp. CF8-6 (S. sp. CF8-6) were studied by batch tests and characterization analysis. The strain showed wide environmental adaptability (temperature 5.0–35.0 °C, dissolved oxygen (DO) 5.2–8.6 mg/L, pH 5.8–9.6, salinity 0.0–10.0%, P concentration 1.1–11.7 mg/L and COD/N (C/N) 7–13) and a relatively high P removal performance under strict aerobic conditions. The optimum conditions of P removal by S. sp. CF8-6 was: temperature 25.0 °C, DO 7.83 mg/L, pH 7.2, salinity 5.0%, P concentration 11.74 mg/L and C/N 13. The higher P removal rate was associated with better biomass growth of S. sp. CF8-6 in general, but the strategy of biomass-independent P removal was also indicated. Only a small percentage (20.0%) of removed P contributed by bacterial growth and intracellular metabolism, while a considerable part (up to 60%) was reserved in extracellular polymeric substances (EPS) in the form of extracellular phospholipid nanoparticles. The scanning electron microscope-energy dispersive spectrometer (SEM-EDS) results indicated the element in the accumulation nanoparticles was carbon, oxygen, sodium and P. The 31P nuclear magnetic resonance (NMR) analysis illustrated that orthophosphate monoester was the only intracellular P species, while both orthophosphate monoester and diesters existed extracellularly. Batch treatment of actual wastewater showed S. sp. CF8-6 had application potential in saline wastewater treatment. This study introduced a new pathway of P accumulation and removal. Application of marine bacteria S. sp. CF8-6 provided us an alternative method for P removal, especially in saline wastewater.