ABSTRACT
Ammonia (NH3) is a harmful pollutant for the environment that is present in urban wastewaters. For that reason, urban wastewater treatment plants (WWTP) have double ecological challenges: (i) reduce ammonia excess in the ecosystem because it generates eutrophication phenomenon, and (ii) valorize ammonia in a circular economy scheme. From this point of view, ion-exchange processes, such as zeolites, can be used in WWTPs to reduce ammonia content (up to 1 mg/L). However, this process is limited by the desorption step, since NaOH or a mixture of NaCl/NaOH solutions are used to regenerate zeolites, obtaining an effluent composed by higher ammonia concentration (1-3 NH3g/L in 1-2 g NaOH/L) than contained in the urban wastewater. Therefore, hollow fiber (HF) liquid-liquid membrane contactors (LLMCs) are proposed as a novel and environmentally friendly technology for ammonia recovery. Two liquid phases are in contact with a HF hydrophobic membrane and species are only transported by diffusion phenomena. Thus, wastewater effluent, containing NH3(g), reacts with an acid stripping solution (nitric, sulfuric and phosphoric acids) producing ammonium salts (NH4NO3, (NH4)2SO4and (NH4)2(HPO4), respectively) in closed-loop configuration up to 10–15%. Therefore, ammonium salts can be used as liquid fertilizers in agriculture industry. Overall, HF-LLMCs is an innovative membrane technology that allows to recover more than 95% of ammonia from urban wastewater for its subsequent use as ammonium salts for liquid fertilizer production.
