Gas-Permeable Membranes in Ammonia Recovery from Produced Water: Causes of Fouling and Strategy for Mitigation

Recent studies have demonstrated the feasibility of gas-permeable membrane (GPM) technology in recovering nitrogen fertilizer from produced water (PW), a high-volume waste generated in the oil and gas industry. Since potential for fouling remains a deterrent to wider application of membrane-technologies, this study evaluated the endurance of a tubular GPM reactor in processing raw PW. Despite the complex chemistry of raw PW and the alkaline operating pH, ammoniacal nitrogen (NH3–N) recovery in this GPM reactor remained over 97% with minimal decline of 2% after 150 h, faring well against reported declines of 11.6 ± 4.9%. However, fouling led to a 22% drop in the NH3–N flux as the membrane contact angle dropped from 142° to 79°. Cleaning of the membrane with 0.5 M HCl for 8 h restored it to near-original conditions, raising the contact angle to 121°, which is comparable to literature reports of 84.5 ± 7.9%. Cause of GPM fouling with raw PW was ascribed to its organic and inorganic constituents, as confirmed through inductively coupled plasma optical emission spectrometry, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy analyses. Microscopy images indicated that acid cleaning was able to restore the fibril structure, with only minor distortions of the fibers.