Influence of organic matter and solute concentration on nitrate sorption in batch and diffusion-cell experiments Neelancherry Remya a,1 , Mathava Kumar b,⇑ , S. Mohan a , Rafig Azzam c a Environmental and Water Resources Engineering Division, Department of Civil Engineering, Indian Institute of Technology Madras, Chennai 600 036, India b Institute of Environmental Engineering, National Chiao Tung University, 1001 University Road, Hsinchu 30010, Taiwan c Rheinisch Westfalische Technische Hochschule, Aachen, Germany article info Article history: Received 23 July 2010 Received in revised form 8 December 2010 Accepted 9 December 2010 Available online 22 December 2010 Keywords: Nitrate Adsorption Diffusion-cell test Organic matter Leaching abstract Nitrate sorption potentials of three surface soils (soils-1–3) were evaluated under different solute con- centrations, i.e. 1–100 mg L 1 . Batch and diffusion-cell adsorption experiments were conducted to delin- eate the diffusion property and maximum specific nitrate adsorption capacity (MSNAC) of the soils. Ho’s pseudo-second order model well fitted the batch adsorption kinetics data (R 2 > 0.99). Subsequently, the MSNAC was estimated using Langmuir and Freundlich isotherms; however, the best-fit was obtained with Langmuir isotherm. Interestingly, the batch adsorption experiments over-estimated the MSNAC of the soils compared with the diffusion-cell tests. On the other hand, a proportionate increase in the MSNAC was observed with the increase in soil organic matter content (OM) under the batch and diffu- sion-cell tests. Therefore, increasing the soil OM by the application of natural compost could stop nitrate leaching from agricultural fields and also increase the fertility of soil. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Nitrate, either formed in soils or supplied as fertilizers, is solu- ble in water and subject to leaching. Nitrate concentrations of groundwater resources in many countries increased drastically (Chabani et al., 2006; Jaafari et al., 2004) due to an increasing usage of nitrogenous fertilizers or intensive agriculture, high density housing with unsewered sanitation and irrigation of sewage efflu- ent onto land (McLay et al., 2001). Nitrogen loss from irrigated cropland, particularly from sandy soils, significantly contributes to the nitrate contamination of surface water and groundwater sources (Li, 2003; Shukla et al., 1998). The major concern of nitrate contamination is the associated blue-baby syndrome resulting from the conversion of hemoglobin into methemoglobin, which cannot carry oxygen (Ghosh and Bhat, 1998; Golden and Weinstein, 1998). The ability of soil to adsorb ions from aqueous solution has major consequence on both agricultural issues such as soil fertility and remediation of polluted soil, and health concerns (Bradl, 2004). Several researchers investigated the nitrate transport from non-point source and its concomitant effect, i.e. eutrophication (Davidson et al., 1990; Kinjo and Pratt, 1971; Ndala et al., 2006). The major processes involved in the nitrogen transformation in soil are nitrogen fixation, ammonification, nitrification, immobilization and denitrification. Nitrate retention, either plant/microbial immo- bilization or by sorption onto the hydroxides of iron and alumin- ium has the potential to reduce the leaching of nitrate to the deeper horizons and surface waters. However, the mobility and bioavailability of nitrite in soils are mainly governed by soil prop- erties such as organic matter content (OM), pH, cation-exchange capacity, texture and mineral species especially those constituting the clay fraction (Martinez-Villegas et al., 2004). Nitrogen mineral- ization is controlled primarily by the dynamics of soil OM because the nitrate utilization by denitrifiers is limited by insufficient sup- ply of oxidizable carbon in the unsaturated zone/aquifer (Singh and Sekhon, 1978). The amount of fertilizer nitrogen leaching as nitrate below the root zone and its stability in the unsaturated zone/aquifer are the factors that determine the extent of nitrate pollution of groundwater. The adverse impacts of nitrogen overloading from agricultural fields into sensitive eco-systems are increasingly noticeable in the recent decades. Despite the environmental benefits of limiting the nitrogen release, there is a continuous need to supply organics and nutrients including nitrogen for productivity and fertility (Xu et al., 2010). Therefore, the nitrate leaching is an inevitable con- comitant of the day-to-day agricultural practice. Although several techniques are available for treating the nitrate contaminated water, i.e. reverse osmosis, electro-dialysis, anion-exchange and biological denitrification, source control of nitrate leaching is the 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.12.044 ⇑ Corresponding author. Tel.: +886 35712121/55523; fax: +886 35725958. E-mail address: mathavakumar@gmail.com (M. Kumar). 1 Present address: Institute of Environmental Engineering, National Chiao Tung University, Hsinchu, Taiwan. Bioresource Technology 102 (2011) 5283–5289 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech