Enhancing nitrogen removal from stormwater through treatment with zeolite carriers

Abstract

This research investigates polyethylene-supported zeolite carriers as an enhancement to current urban stormwater runoff treatment practices. Carriers were deployed in pilot-scale bioretention columns where it was hypothesized that they would sequester ammonium via ion exchange, thereby supporting anammox-driven nitrogen removal. In synthetic stormwater runoff experiments, zeolite and non-zeolite carriers with and without pre-seeding of anammox cultures were tested, along with five hydraulic residence times (HRTs), internal water storage (IWS), and free clinoptilolite zeolite. Total nitrogen (TN) removal was largely unaffected by carrier type, HRT, or the addition of clinoptilolite zeolite, even though ammonium removal was higher with carrier types enhanced with zeolite, pre-seeding, or both, and there was a positive relationship between ammonium removal and HRT. Zeolite seeded carriers from the biofilter columns retained low levels of anammox biomass over 114 days and 22 synthetic storm events, even with relatively low initial biomass concentrations. IWS-enhanced columns significantly improved TN removal compared to biofilter columns without IWS. This study provides information on carrier addition to stormwater runoff biofilters that can inform decisions on full-scale deployment of this treatment enhancement.