Removal of ammonium from greywater using natural zeolite Nurul Widiastuti a, ⁎, Hongwei Wu a,b , Ha Ming Ang b , Dongke Zhang c a Curtin Centre for Advanced Energy Science and Engineering Curtin University of Technology, GPO Box U1987, WA 6845, Australia b Department of Chemical Engineering, Curtin University of Technology, GPO Box U1987, WA 6845, Australia c Centre for Energy (M473), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia abstract article info Article history: Received 21 August 2010 Received in revised form 21 February 2011 Accepted 9 March 2011 Keywords: Ammonium removal Natural zeolite Adsorption Kinetics Thermodynamics Desorption This paper focuses on the effectiveness of removing ammonium ion and the theoretical aspects of adsorption including adsorption isotherm, kinetics and thermodynamics as well as desorption–regeneration studies. Results have demonstrated that natural zeolite shows good performance with up to 97% for ammonium removal depending on contact time, zeolite loading, initial ammonium concentration and pH. The adsorption kinetics is best approximated by the pseudo-second-order model, whereas the adsorption isotherm results indicated that Freundlich model provides the best fit for the equilibrium data. Furthermore, with regard to thermodynamic parameters, it was found that Gibbs free energy change or adsorption energy (ΔG°), -19.52 kJ/mol at 25 °C, -20.45 kJ/mol at 35 °C and -22.91 kJ/mol at 45 °C is negative indicating the spontaneous nature of the adsorption process, whereas the enthalpy change (ΔH°), 30.96 kJ/mol is positive indicating endothermic adsorption process. The entropy change (ΔS°), 0.169 kJ/(mol K) at 25 °C is also positive indicating increasing randomness at the solid-solution interface during adsorption. In addition, the desorption–regeneration studies demonstrated that desorption of ammonium on the zeolite is sufficiently high using NaCl solutions. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Greywater is wastewater originated from bathroom and laundry in households. Ammonium is one of the significant greywater contam- inants that is found in bathrooms because of urine [12], in kitchen from the use of ammonium salts as acidity regulators, thickeners and stabilisers [24] and in laundry wastewater due to the use of cationic surfactants such as quartenary ammonium salts, dialkyldimethylam- monium chlorides, distearyldimethylammonium chloride and alkyl- dimethylbenzylammonium chlorides in fabric softeners and laundry disinfectant agents [2,15,18]. Although ammonium is a very important nutrient for algae, the excessive presence of ammonium in water streams and effluent causes eutrophication of estuaries, rivers, lakes and coastal seas [25] as well as corrosion/biological fouling problems in industrial water system [11] due to the growth of algae blooms. On the other hand, with the increasing issue of water reuse, ammonium is one of grey water contaminants that need to be removed due to health concerns especially for bathroom wastewater and swimming pool wastewater reuse. Existing methods of ammonium removal are biological nitrification– denitrification, air-stripping and ion-exchange [7]. Among the various methods, ion-exchange is more competitive over air-stripping and biological methods due to little influence at low temperature. Moreover, ion-exchange takes up relatively little space particularly its relative simplicity of application and operation [7] as well as environmentally friendly [10]. Ion-exchange, therefore, seems to be an attractive method especially when low cost materials are used [27]. Natural zeolites are an abundant cation exchange material that is economically feasible for water and wastewater treatment. They have high selectivity toward water contaminants such as heavy metals reached up to 1800 mg/g [28] and ammonium ion reached up to 90% [26]. In addition, natural zeolites have advantages over other cation exchange materials such as organic resins [26] because they provide low-cost treatment, exhibit excellent selectivity at low temperatures, release non-toxic exchangeable cations (K + , Na + , Ca 2+ and Mg 2+ ) to the environment [19], compact size in relatively little space and simply operation as well as easy maintenance of the full-scale ap- plications [6,7]. Natural zeolites, therefore, gained significant interest over the last two decades especially with regard to eliminating or at least reducing water pollution problems. Natural zeolites are composed of three dimensional frameworks of aluminosilicate tetrahedral where the aluminum and silicon structure atoms are bound by covalent bonds over common oxygen atoms to form interconnected cages and channels [10]. Each aluminum (Al 3+ ) atom substitution for silicon (Si 4+ ) in the zeolite framework gen- erates one negative charge on the framework. The greater the alu- minum atom substitution, the higher the negative charge of zeolite [23]. The negative charge within the pores is balanced by positively Desalination 277 (2011) 15–23 ⁎ Corresponding author at: Current address: Department of Chemistry, Institut Teknologi Sepuluh Nopember (ITS), Kampus ITS Sukolilo, Surabaya 60111, Indonesia. Tel.: +62 87861137535, +62 315992090; fax: +62 5928314. E-mail address: nurul.widiastuti@chem.its.ac.id (N. Widiastuti). 0011-9164/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2011.03.030 Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal