Modification of a plant-scale semi-centralized wastewater treatment system to enhance nitrogen and phosphorus removal from black water

Abstract

Owing to the low ratio of chemical oxygen demand to total nitrogen (SCOD/TN), effective removal of nutrient pollutants from black water is difficult. In this study, to enhance nitrogen and phosphorus removal from such wastewater, a series of operational modification strategies was investigated and applied to a plant-scale semi-centralized system used for black water treatment. The results showed that 21 mg Fe3+/L was the optimal dosage for the chemical-enhanced pretreatment process, achieving average removal efficiencies of 51.1 and 74.1% for organics and phosphorus, respectively, with a slight enhancement in nitrogen removal by 2.3%. However, nitrogen and phosphorus removal could be further enhanced to 88 and 96%, by the addition of carbon sources in the post-anoxic zone of the reversed anaerobic–anoxic–aerobic process. Contrastingly, neither the addition of carbon sources in the pre-anoxic zone nor the prolongation of the time for pre-denitrification could significantly improve the nitrogen and phosphorus removal efficiencies. Furthermore, reducing the aeration intensity promoted simultaneous nitrification and denitrification in aerobic reactors, thereby making it a potential energy-saving method for system operation. HIGHLIGHTS A series of modified operations was employed in a plant-scale semi-centralized system to improve N and P removal from black water.; 21 mg Fe3+/L was the optimal dosage for TP removal by chemical-enhanced primary treatment.; Reducing aeration intensity was a potential energy-saving method for a reversed A2O system.; Carbon source added into the post-anoxic zone was more effective than in the pre-anoxic zone.;

Keywords

• black water
• chemical-enhanced pretreatment
• dosing of carbon source
• nitrogen and phosphorus transformation
• reversed a2o process