An integrated process for struvite recovery and nutrient removal from ship domestic sewage

Marine pollution caused by the untreated and substandard discharge of ship domestic sewage has received widespread attention. A novel integrated process for struvite recovery and nutrient removal from ship domestic sewage (SRNR-SDS) based on seawater magnesium source was developed in this study. Removal efficiencies of the total nitrogen (TN) and total phosphorus (TP) for the activated sludge unit in SRNR-SDS process were approximately 67.61% and 41.35%, respectively, under the salinity of 7.85 g/L. The coupling-induced struvite crystallization unit significantly improved the removal efficiency of TN and TP, and the scanning electron microscopy and X-ray diffraction demonstrated that magnesium ammonium phosphate (MAP) crystals were successfully formed on the surface of zeolite. The SRNR-SDS process had an ideal performance for pollutant removal and MAP recovery under the optimal hydraulic retention time of 20 h. The effluent concentrations of COD, NH₄⁺-N, TN and TP in SRNR-SDS process were approximately 34.73 mg/L, 4.31 mg/L, 10.07 mg/L and 0.23 mg/L, respectively, which meet the Chinese and international ship sewage discharge standards. SRNR-SDS process has obvious environmental, social and economic benefits, which could save 6.20%∼57.14% of the operation cost of ship domestic sewage treatment via MAP recovery. The results could provide theoretical and technical support for the development and application of ship sewage treatment process with the functions of pollutant removal and resource recovery.