Sustainable Nutrient Recovery Through Integrating Electricity-Assisted Membrane Processes

Abstract

The rising use of mineral-based fertilizer and water for agricultural operations to feed a growing population has polluted water bodies and depleted resources. In addition, nutrient contamination has caused eutrophication and wastewater concerns that conventional wastewater treatment cannot solve. Thus, meeting new water treatment regulations and procuring more value-added products from these procedures is crucial. Conductive ultrafiltration membranes precipitate and extract struvite, an ecologically good fertilizer, from synthetic livestock effluent. This technique produces solid fertilizer and irrigation-quality water. Since the recovery process relies on electrochemical hydrolysis and local pH modulation along the membrane surface, pH correction does not need chemical additions. The system was tested using cow effluent with up to 1,000 mg/L of nitrogen and phosphorus. Analytical tests showed that the precipitates were struvite and that up to 65% of the phosphorus and nitrogen were removed in the first 30 minutes of electrochemical filtration. Low membrane fouling and flux drop made the recovery technique successful. A mathematical model of N, P, and Mg ions in an external electric field explained the fouling and precipitation tests. Thus, precipitation happens near the membrane but not on it. This reduces surface fouling. Forward osmosis was used to make struvite with less energy. A voltage near the FO membrane enabled magnesium to migrate opposite into the feed chamber, where it reacted with ammonium and phosphate in the feed solution to form struvite. Electrical charging increased struvite recovery by 77% and water recovery by 39%. Ion migration may have reduced dilutive and concentrative polarization on the draw and feed sides of the FO membrane, causing the rise. High external voltage, draw concentration, and draw pH made water recovery and struvite precipitation simpler. This study suggests that reverse salt flow might improve FO systems' nutrition and water recovery. These devices were combined with microbial electrolytic cells to generate electricity and prevent biofouling. FO treatment was investigated using vacuum membrane distillation for sustainability and zero discharge. Constant draw solution reconcentration yields more steady flux values than the typical lowering flux. The research will increase knowledge of treatment system synergy in water reclamation and nutrient recovery. It also identifies possible obstacles to development.