Porous Polyethylene-Supported Zeolite Carriers for Improved Wastewater Deammonification

Abstract

Wastewater treatment is increasingly important as anthropogenic activities continue to stress our water systems. Ammonium is one of the most common pollutants in wastewater streams and is typically oxidized to nitrate during treatment, which still results in the discharge of reactive nitrogen to the environment. Anaerobic ammonium oxidation (anammox) can completely remove reactive nitrogen, forming dinitrogen, and also decreases the cost of ammonium removal compared to conventional activated sludge wastewater treatment systems. Anammox faces challenges in mainstream implementation, however, as a result of the slow growth rates of anammox bacteria, narrow ideal growth conditions, and competition with other taxa. Addition of zeolite, such as faujasite, into low ammonium waste streams improves ammonium removal and locally concentrates ammonium ions, which in turn can improve the proliferation of anammox bacteria. Here, we report the development of a scalable approach to plastic carriers for potential use in mainstream anammox reactors that combines the processability of thermoplastics and the ammonium sequestration ability of zeolites. Carriers were prepared by melt-blending polyethylene (PE), microparticulate zeolite 13X (Z13X, a faujasite), and a sacrificial poly(ethylene oxide) (PEO) template. Removal of the PEO template by solvent etching in water exposed a percolating pore network within the PE support structure and the particulate zeolite trapped within the exterior. A pore size in the range of 10–25 μm was typical, with zeolite loadings as high as 45% by mass in the final product. The hybrid inorganic–polymer carriers were highly effective in sequestering ammonium, capable of removing >75% of ammonium from a 45 mg/L TAN (total ammonium nitrogen) aqueous environment in 24 h at less than 1% mass loading of carriers as compared to solution mass. Ammonium removal by ion exchange was confirmed by spectrophotometric methods and by energy-dispersive X-ray spectroscopy, and the kinetics of ammonium sequestration were determined to be zeroth-order with respect to ammonium and first-order with respect to zeolite. The materials described in this article are expected to find utility in future bioreactor development.