Ammonium Removal from Synthetic Stormwater using Clinoptilolite and Hydroaluminosilicate Columns Golnaz Khorsha, Allen P. Davis * ABSTRACT: Ammonium can enter stormwater control mea- sures (SCMs) with the influent, but is also the intermediate product between organic nitrogen and nitrate, and it is important to retain and treat ammonium within the SCM. In this study the use of aluminosilicate aggregates (CA) and clinoptilolite zeolite (ZT) was investigated under SCM (column) conditions. ZT was found to have the highest capacity (0.45 mg NH þ 4 -N/g ZT vis- ` a-vis 0.33 mg NH þ 4 -N/g CA) at 2.5 mg NH 4 - N/L. The presence of Ca 2 þ and K þ was found to reduce the capacity of the media significantly. Increasing the contact time from 10 minutes to 47 minutes enhanced the removal efficiency of the system by 70% for CA and 23% for ZT, respectively. Finally, changes in the influent ammonium concentration resulted in successful removal during concentration increases, but desorption of ammonium for sudden concentration reduc- tion. The use of ZT in media-based SCMs is recommended for ammonium removal. Water Environ. Res., 89, 564 (2017). KEYWORDS: stormwater, nitrogen, ammonium, zeolite, adsorption. doi:10.2175/106143017X14902968254467 Introduction The availability of excess nitrogen in aquatic systems can promote the undesirable overgrowth of algae, leading to depleted oxygen levels and jeopardizing the health of aquatic habitats. The blooming algae and microscopic plants can also reduce the transparency of water and compromise the survival of seagrass habitat (U.S. EPA, 2009). In addition to environ- mental and health problems, the economic losses associated with eutrophication are also significant (Dodds et al., 2008). Urban stormwater runoff has been identified as one of the main sources of eutrophication, with excess nitrogen playing an active role (U.S. EPA, 2009). To address stormwater pollution, many stormwater control measures (SCMs), such as sand filters and bioretention cells are used, and although effective in reducing runoff volume, suspended solids, and heavy metals (Davis et al., 2001, 2006, 2009; Hatt and Fletcher, 2009; Hunt et al., 2006; Sun and Davis, 2007), they have not been highly effective in reducing excess nitrogen (Hatt and Fletcher 2009; Hunt et al., 2006; Li and Davis, 2014; Passport et al., 2009; Rosenzweig et al., 2011). Nitrogen in stormwater has a diverse speciation, often characterized as particulate nitrogen, dissolved organic nitrogen, ammonium, and nitrate (Collins et al., 2009; Duncan, 1999, Kayhanian et al., 2007; Li and Davis, 2014; Taylor et al, 2005; Tiefenthaler et al., 2000). Another influencing factor is the cycling of nitrogen, which results in mineralization of organic nitrogen to ammonium, and nitrification of ammonium. Overall, the fate of nitrogen in SCMs is often associated with poor removal of the incoming nitrogen, and often the export of organic nitrogen and nitrate production (Hatt and Fletcher, 2009; Hunt et al., 2006; Li and Davis, 2014; Passport et al., 2009; Rosenzweig et al., 2011). Implementation of a denitrification zone in bioretention is recommended to enhance nitrate reduction (Davis et al., 2006; Dietz and Clausen, 2005, 2006). While a nitrification/denitrifi- cation system can be beneficial in enhancing the treatment of nitrogen in urban runoff, it should be combined with other chemical and biological processes, such as sorption and/or ion exchange for effective treatment of excess nitrogen. Sorptive/ cation exchange media can be effective in pollutant removal during low temperatures, and shock loads (such as first-flush phenomenon in stormwater runoff), and they require smaller land area as well as lower capital cost for operation compared to biological processes (Booker et al., 1996; Miladinovic and Weatherley, 2008). A proposed design by Khorsha and Davis (2017) for enhancing nitrogen removal involves dividing the SCM into three nitrogen (N) treatment layers as demonstrated in Figure 1. This design will allow for capture of organic nitrogen, allowing it to be mineralized into ammonium in the first zone, with the second zone aiming to capture and hold ammonium Department of Civil and Environmental Engineering, University of Maryland, College Park, MD 20742. * Corresponding author: e-mail: apdavis@umd.edu. 564 WATER ENVIRONMENT RESEARCH  June 2017