Ammonia is an indispensable resource for food and pharmaceutical production. While 30% of produced ammonia ends up flowing into urban wastewater treatment plants, the conventional nitrogen (N) management system only transforms valuable ammonia nitrogen (NH3) into inert nitrogen gas (N2). To mitigate current energy-wasting schemes, ammonia recovery technologies have garnered interest as a great alternative for sustainable N-cycle. However, the limitation of ammonia recovery that coerces additional post-treatment (i.e., crystallization) hinders the practical application of the technology in the industry. To this end, we have proposed a novel hybrid system of membrane contactor and antisolvent crystallization that can reduce conventional two-stage processes into a single stage. The liquid-gas membrane contactor that prevents direct contact with wetting-inducing organic solvent (i.e., ethyl alcohol) transfers gaseous ammonia to the binary mixture of organic solvent and aqueous sulfuric acid solution. The transferred ammonia combines with sulfate, simultaneously converting into pristine solid N-fertilizer ((NH4)2SO4, ammonium sulfate). 93.37% of ammonia from wastewater was recovered in ammonium sulfate crystal simultaneously. The recovered crystal represented the homoepitaxy crystalline structure, not the usual orthorhombic structure. The hybrid system also selectively crystallized SO42-, not HSO4- the potential component of valueless byproducts such as letovicite ((NH4)3H(SO4)2) and ammonium bisulfate (NH4HSO4), producing only valuable ammonium sulfate. Likewise, since the organic solvent in the system does not participate in the crystallizing reaction, it can be recycled numerous times with the supply of concentrated sulfuric acid. The novel hybrid system that simultaneously recovers ammonia and crystallizes N-fertilizer may minimize the size and improve the sustainability of the ammonia recovery system, enhancing its feasibility of the ammonia recovery system.

Direct recovery of pristine N-fertilizer crystal from wastewater by combining membrane contactor and antisolvent crystallization

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