Ammonium recovery and concentration from synthetic wastewater using a poly(4-methyl-1-pentene) (PMP) liquid–liquid membrane contactor: Flux performance and mass transport characterization

Abstract

Hollow fiber membrane contactors are a promising technology for the removal and recovery of ammonia from liquid effluents. However, a better understanding of the process engineering (e.g. mass transport of ammonia over water) and performance optimization is required. In this study, the performance of a hollow fibre liquid–liquid membrane contactor (HF-LLMC), incorporating a new polymer chemistry (i.e., poly (4-methyl-1-pentene (PMP) and an asymmetric fibre structure, for the recovery and concentration of ammonium from synthetic aqueous solutions, was investigated. The influence of the feed and acid flow rates was evaluated experimentally by determining the overall mass transfer coefficient (kov), the ammonium recovery as a function of time and the acid consumption. In addition, the experimental results were fitted to a mathematical model to determine the membrane permeabilities to ammonia (PNH3) and water (Pw) and identify the mass transfer resistance regime. The highest kov values experimentally obtained were in the range of 3·10–3 to 3.51·10–3 m/h with corresponding ammonia recovery rates of 94 and 96.2% after 10 h, operating at a feed and acid flow rates of 180 L h−1 and 500 L h−1, respectively, which are in the upper range of the HF-LLMC literature. The overall results of this study were not only the upper range of the HF-LLMC ammonia recovery literature but a much-lower water transport was confirmed indirectly by the concentration factor (CF) values obtained experimentally. The remarkable selectivity of the membrane towards ammonia over water (i.e., PNH3 = 87–180 L m–2h−1 bar−1 and Pw = 1.2–1.4·10–3 L m−2 h−1 bar−1 at NTP conditions) is attributed to the asymmetrical membrane structure and the polymer chemistry (i.e., PMP). The proven high ammonia selectivity of the HF-LLMC makes it a promising technology for the recovery and concentration of ammonium from urban (e.g. wastewaters) and industrial (e.g. soda ash and fertilizers production) diluted streams.