Treatment options for nanofiltration and reverse osmosis concentrates from municipal wastewater treatment: A review

Conventionally treated municipal wastewaters create environmental challenges due to eutrophication of effluent receiving waters and significant concentrations of micropollutants and other harmful impurities. To enhance purification, different tertiary membrane filtration technologies are utilized. The concentrate produced in membrane filtration is a voluminous waste stream, which further treatment is challenging. Also the valuable components in the concentrate remain typically unutilized. This review identifies potential treatment strategies for membrane concentrates originating from municipal wastewater treatment and evaluates approaches for value component recovery and waste minimization. Various technologies were examined as possible options for advanced concentrate treatment. Study concluded that electrodialysis processes or shear enhanced nanofiltration or reverse osmosis could be promising approaches to concentrate the valuable components, mainly nutrients, in concentrate. Few technologies were seen potential for value component recovery. These included ammonium recovery or struvite recovery with electrodialysis combined with crystallization or with struvite crystallization as well as calcium phosphate recovery with EPR process or with combined process of electrodialysis and crystallization. The concentrate recirculation back to the biological treatment can be enabled by concentrate oxidation which increases biodegradability. Combining these unit processes appropriately, an efficient strategy of membrane concentrate management can be implemented and even zero wastewater discharge achieved.