Nitrogen and Phosphorus Recovery from Wastewater

Use of nitrogen- and phosphorus-based synthetic fertilizers shows an increasing trend, but this has led to large-scale influx of reactive nitrogen in the environment, with serious implications on human health and the environment. On the other hand, phosphorus, a non-renewable resource, faces a serious risk of depletion. Therefore, recovery and reuse of nitrogen and phosphorus is highly desirable. For nitrogen recovery, an ion exchange/adsorption-based process provides concentrated streams of reactive nitrogen. Bioelectrochemical systems efficiently and effectively recover nitrogen as NH3 (g) or (NH4)(2)SO4. Air stripping of ammonia from anaerobic digestate has been reported to recover 70-92 % of nitrogen. Membrane separation provides recovery in the order of 99-100 % with no secondary pollutant in the permeate.With regard to phosphorus (P) removal, physical filtration and membrane processes have the potential to reduce suspended P to trace amounts but provide minimal dissolved P removal. Chemical precipitation can remove 80-99 % P in wastewater streams and recover it in the form of fertilizer (struvite). Acid hydrolysis can convert recovered P into usable phosphoric acid and phosphate fertilizers. Physical-chemical adsorption and ion exchange media can reduce P to trace or non-detect concentrations, with minimal waste production and high reusability. Biological assimilation through constructed wetlands removes both N (83-87 %) and P (70-85 %) from wastewaters, with recovery in the form of fish/animal feeds and biofuel. The paper discusses methods and important results on recovery of nitrogen and phosphorus from wastewater.