Enhanced Nitrogen Removal and Anammox Bacteria Retention with Zeolite-Coated Membrane in Simulated Mainstream Wastewater

The anammox process has been used for side-stream nitrogen removal. Mainstream anammox is challenging, however, as a result of low ammonium concentrations and retention times that wash out slow-growing anammox bacteria. To overcome these challenges, hollow fiber membranes with zeolite-coated surfaces were prepared to create near-surface microenvironments that mimic attributes of side-stream treatment systems. Results showed that in mainstream-type media, zeolite-coated membranes enhanced the growth of anammox bacteria on the membranes and in the bulk liquid of the reactor compared to reactors containing uncoated control membranes. The zeolite-coated membranes also improved the average total nitrogen (TN) removal to 73 ± 10% compared to 1 ± 49% in the control reactors. Additional experiments containing zeolite particles demonstrated that increasing zeolite mass increased the number of anammox gene copies present and improved TN removal, with effluent TN concentrations decreasing from 51.8 ± 5.9 to 7.78 ± 2.6 mg-N/L (P = 0.00085) as zeolite increased from 0.05 to 1.0 g/reactor, respectively. These results suggest that membranes/surfaces containing a greater quantity of zeolite should further improve retention of anammox bacteria and TN removal. Application of such membranes in an integrated fixed-film activated sludge (IFAS)-type system or membrane-aerated biofilm reactor (MABR) with intermittent aeration and low bulk DO concentrations should facilitate mainstream anammox.