Integrated in-situ electrochemical-membrane process for ammonia valorization and sustainable water reuse

Conventional wastewater treatment often overlooks the potential to recover resources, leading to chemical-intensive and less sustainable operations. This study demonstrates an integrated electrochemical-membrane process that directly valorizes unrejected ammonia into monochloramine-a well-known disinfectant-produced in-situ during water reuse. An electrolyzer generated hypochlorite (OCl⁻) in the draw solution, which reacted with residual ammonia to form monochloramine that acts as a mild oxidant at the membrane interface. Lab- and pilot-scale forward osmosis experiments with real municipal wastewater validated this approach: optimal monochloramine production with 25 mg L⁻¹ NaOCl enhanced water flux, minimized reverse solute flux, and stabilized performance over extended operation. The presence of monochloramine reduced both organic and biological fouling, as shown by decreased contact angle and sustained hydrophilicity of the membrane surface. Comparative analysis revealed that monochloramine outperformed dichloramine and chloramine-free conditions in sustaining flux. This performance advantage is attributed to monochloramine's superior chemical stability, which ensures prolonged biofouling mitigation, contrasting with the rapid decay and oxidative aggressiveness of dichloramine that can compromise membrane integrity. The system could maintain stable pH (6.5-7.5) and effective chloramine levels without excessive chemical consumption due to balanced oxidation of NH₄⁺. By transforming waste ammonia into a functional cleaning and disinfecting agent, this process can provide a pathway for circular nitrogen use, reduces reliance on external chemicals, extends membrane lifetime, and lowers operational costs. Together, these outcomes advance sustainable wastewater reuse and offer a practical, resource-efficient solution for greener water management.