Dynamic sorption of ammonium by sandy soil in fixed bed columns: Evaluation of equilibrium and non-equilibrium transport processes S. Jellali a, * , E. Diamantopoulos b , H. Kallali a , S. Bennaceur a , M. Anane a , N. Jedidi a a Water Research and Technologies Centre (CERTE), Wastewater Treatment and Recycling Laboratory, B.P.273, Soliman 8020, Tunisia b Agricultural University of Athens, Department of Natural Resources Management and Agricultural Engineering, 75 Iera Odos Str,118 55 Athens, Greece article info Article history: Received 16 May 2009 Received in revised form 4 November 2009 Accepted 27 November 2009 Available online 19 January 2010 Keywords: Ammonium Dynamic sorption Breakthrough curves Modeling Hydrus-1D abstract The release of excess nitrogen-containing compounds into groundwater is a major concern in aquifer recharge by the Soil Aquifer Treatment (SAT) process. Ammonium (NH 4 þ ) is one of the most nocive and common nitrogen compounds in wastewaters. In order to assess the risk of wastewater use for aquifer recharge,NH 4 þ adsorption onto Souhil wadi soil sampled from the SAT pilot plant (Nabeul, Tunisia) was studied using laboratory columns experiments. Several experiments were conducted using aqueous synthetic solutions under different aqueous ammonium concentrations and flow rates. Furthermore, a real wastewater solution was used to test the effect of competitive cations contents on NH 4 þ adsorption. Afterwards, the Hydrus-1D model was used in inverse mode to simulate the ammonium transport through the Souhil wadi soil. For the synthetic solutions, the adsorbed ammonium amount varied from 1 to 30.7 mg kg 1 for aqueous ammonium concentrations between 4.9 and 36.4 mg L 1 . The linear isotherm model was found to be the most suitable for describing this adsorption. The flow rate decrease from 45 to 15 mL min 1 induced an increase in the ammonium adsorption capacity by 49%. Indeed, the lesser the flow rate is, the longer the residence time and the higher the exchange between the aqueous solution and soil matrix. The use of wastewater instead of aqueous synthetic solution decreased about 7 times the Souhil wadi adsorption capacity of ammonium because of its relatively high concentrations of competitive ions such as calcium and magnesium. The use of the Hydrus-1D model showed that the chemical non-equilibrium model was the best to simulate the ammonium transport through the laboratory soil columns. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Ammonium is a common subsurface contaminant that may originate from diverse sources. The related contamination could be a result of seepage from landfills, foul sewerage systems and contaminated industrial sites or generated by an induced perco- lation, such as aquifer recharge with pretreated wastewaters and plants fertilizing. Furthermore, ammonium is often considered as a key indicator of leachate contamination arising from landfill sites and Soil Aquifer Treatment (SAT) process. So, it is commonly selected for consideration during the assessment of pollution risks to groundwater. It is a List II substance under both the Ground- water Directive (80/68/EEC) and the Dangerous Substances Directive (76/464/EEC) (Buss et al., 2004). In many regions of Tunisia, treated municipal wastewater reuse for various purposes is a strategic alternative to overcome water shortage. Wastewater is generally reused for agricultural and golf fields irrigation, urban watering and groundwater artificial recharge (Kallali et al., 2005). This process, adopted to increase aquifer-based water supplies, uses underground formations as natural filters to finalize the purification of conventionally treated municipal wastewater prior to reaching the aquifer. It consists in favoring water vertical infiltration in constructed basins through several meters of vadose zone. In typical SAT process, recharge basins are flooded for 3–7 days, and then rested for 4–21 days to allow soil re-aeration and avoid its clogging (Torrens et al., 2009). However, an optimized design and management of SAT basins are needed to insure an efficient complementary purification of the treated wastewater and avoid fresh underground water contami- nation by nitrogen and organic pollution (Jellali et al., 2009). During treated wastewater infiltration in unsaturated subsoil layers, a significant quantity of ammonium is transformed biologically to nitrites and nitrates. However, infiltrating a large quantity of ammonium through low-thickness unsaturated zone raises the groundwater pollution magnitude (Bouwer, 2000; Repert et al., * Corresponding author. Tel.: þ216 79325044; fax: þ216 79325802. E-mail address: salah.jallali@certe.rnrt.tn (S. Jellali). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman 0301-4797/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2009.11.006 Journal of Environmental Management 91 (2010) 897–905