Treatment of ionic rare earth smelting wastewater by a membrane bioreactor based on aerobic granular sludge

Organic wastewater from rare earth smelting is a high-concentration acid with great harmfulness and complex water quality. The main pollutants include organic matter, ammonia nitrogen, suspended matter, inorganic salts, and heavy metals, so it is of great significance to study how to effectively treat organic wastewater from rare earth smelting to protect water and soil. A sequential batch membrane bioreactor (SBR-MBR) was constructed, combining with aerobic granular sludge (AGS) to form an aerobic granular sludge membrane bioreactor (AGS-MBR). On this basis, the effect of different C/N ratios (the ratio of total contents of carbon to nitrogen in organic matter C/N) on the AGS-MBR treatment process was studied. The results show that when C/N is 10, the aerobic granular sludge has the best stability, with the removal rates of COD, NH₄⁺-N, TN and TP at 99.0%, 96.7%, 79.3% and 91.1%, respectively. The decrease in influent C/N has little influence on the removal of COD by AGS-MBR but has a great effect on the form of effluent N and TP. When C/N≤7, part of the aerobic granular sludge disintegrates, and the effluent TN and TP concentrations meet the requirements of Grade A discharge standard GB 18918—2002(2006) in the Pollutant Discharge Standard for Urban Sewage Treatment Plants, which provides a theoretical basis for further research on the treatment of organic wastewater from rare earth smelting with lower C/N ratios.