Ammonia recovery from source-separated hydrolyzed urine via a dual-membrane distillation in-series process

This study presents a dual membrane distillation (MD) in-series process to recover ammonia from sourceseparated hydrolyzed urine. The first MD stage separates and recovers ammonia from the hydrolyzed urine using an acid solution, while the second MD stage helps dewater the acid solution with captured ammonia and maintain its solution pH. The feed temperature and pH were optimized for operational conditions. The specific ammonia transfer (SAT) value was evaluated to obtain comparative results. While the water fluxes of both the single and dual-MD in-series set up systems were similar, the dual-MD in-series module showed higher SAT values and ammonia fluxes. At pH = 6, the ammonia flux values were minimal, but at pH = 13.2, they significantly increased to over 180 g/m2 h for the dual-MD in-series setup, which was approximately twice as much as the single MD setup (about 100 g/m2 h). In addition, the ammonium concentration in dual-MD in-series setup rose to over 200 mg/L at pH around 9, which is twice higher than that of a single MD setup. The results demonstrated that during the experiment, the dual-MD in-series configuration could help maintain the acid collector pH around 3 while for a single setup it continuously increased and reached to over 8 after 4 h. This innovative design not only preserves the desired pH range but also minimizes the amount of acid consumed, making it a promising approach in advancing nutrient recovery from human urine.