Ammonium enrichment and recovery from synthetic and real industrial wastewater by amine-modified thin film composite forward osmosis membranes

Abstract

In this study, we aimed to recover and enrich NH4+ from real wastewater using forward osmosis (FO). Positively-charged thin film composite (TFC) membranes were developed via chemical grafting with positively-charged polyethyleneimine (PEI). The TFC membrane surface was first activated using 1-ethyl-3-(3-dimethylaminopropyl) carboimide (EDC) and n-hydroxysuccinimide (NHS) to convert the carboxyl groups of polyamide into amine-reactive NHS esters. PEI grafting significantly increased the NH4+ retention in the feed solution. To further improve the NH4+ rejection, quaternization of the amine functional groups of PEI was conducted with iodomethane. Quaternization was found to further increase NH4+ rejection, up to over 98.5%, while maintaining similar water permeability with the PEI-grafted TFC membrane. Fouling control of the pristine and amine-modified TFC membranes were also demonstrated, and the quaternary amine-modified TFC membrane exhibited superior fouling resistance against organic and biological foulants. The amine-modified TFC membranes were evaluated for applicability for dewatering and NH4+ enrichment of real industrial wastewater. NH4+ enrichment using the PEI-grafted membranes was observed following wastewater dewatering, indicating the high NH4+ retention ability of the TFC membranes modified via amine grafting and quaternization. Wastewater dewatering of 90.3 and 92.4% were achieved using TFC-PEI-10 and TFC-qPEI, respectively.