Ammonia removal using thermally induced phase separation PVDF hollow fibre membrane contactors

Abstract

Hollow fibre membrane contactors (HFMCs) are a promising new technology for ammonia recovery but are limited by the mass transfer efficiency as well as their chemical resistance and physical strength. Thermally Induced Phase Separation (TIPS) Polyvinylidene Fluoride (PVDF) membranes offer a new HFMC option for ammonia recovery due to their superior removal performance and physicochemical properties. In this study, two chemically robust TIPS PVDF HFMCs were synthesized and evaluated for the recovery of ammonia from wastewater. The HFMCs displayed an uncompromised high tensile strength of up to 19.12 ± 0.93 MPa under a long-term chemical exposure against acids, alkalis, and oxidants over 60 days of immersion. The HFMCs had a high air permeance flux of up to 1.67 ± 0.26 mol/m2/s. The crystalline structure of the TIPS PVDF membranes affected the hydrophobicity of the membranes more than pore size. Optimisation of ammonia removal was achieved by the Taguchi method for design of experiments using five operational parameters namely pH, temperature, ammonia solution velocity, concentration, and air sparging rate. Empirical evidence showed that the TIPS PVDF HFMCs achieved the highest ammonia removal of greater than 99% and a mass transfer coefficient (Kov) of up to 4.53 × 10-5 m/s. Comparatively, the Kov and flux of both TIPS PVDF membranes in this study are up to one order higher than those previously reported and could even be higher with further improvements to operating conditions. Air sparging is for the first time used in HFMCs to improve ammonia removal and is known to simultaneously reduce membrane fouling.