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The purpose of this study is to experimentally investigate the SAR (Sodium Adsorption Ratio) and TDS (Total Dissolved Solids) reduction in Reverse Osmosis (RO) concentrate using two types of natural zeolites. In order to reduce salinity of wastewater, experiments were carried out by varying the type of zeolite, concentration of zeolite and residence time. The results show that both zeolites can lower the SAR and TDS of wastewater; however, Rhyolitic tuff is more effective than clinoptilolite. It is observed that the concentration of zeolite has not significant effects on wastewater treatment, so, using the lowest level of selected concentration reduces the cost of desalination. In addition, the effect of residence time is negligible. The experimental set up shows that the SAR reduction slop is higher than TDS. Key words: Salinity, RO concentrates, zeolite, irrigation INTRODUCTIONReverse Osmosis (RO) is a well-known membrane technology for treatment of wastewater and production of potable or irrigation water. The main challenge of RO is the concentrated waste produced during the process (Subramani and Jacangelo, 2014). Several materials and technologies are employed for further treatment of reverse osmosis concentrate in order to reduce the rejected volume or treat it to reuse in other applications. Jing et al. (2009) evaluated the cost of the TDS removal by electricity and investigated ion treatment of wastewater produced in polymer-flooding. They revealed that electricity greatly increases the energy consumption; however, the flow rate effects on energy consumption are negligible. Mohammadesmaeili et al. (2010) evaluated the RO concentrate treatment using lime-soda softening process and showed that efficiency of seawater desalination using lime-soda is 80-90%. Nkwonta and Ochieng (2010) designed a pilot plant for wastewater pretreatment using charcoal and gravel. They demonstrated that filters roughness enhances efficiency of pretreatment process for mine water. They also showed that in general, charcoal outperforms gravel. Mrayed et al. (2011) evaluated the effectiveness and flexibility of Nano Filtration (NF) in producing irrigation water from reverse osmosis concentrates. They showed that Poly Acrylic Acid (PAA) increased the ion adsorption capacity of KOCH membrane; however, it did not affect rejected volume of ions by the NF270 element. Al-Rawajfeh et al. (2011) investigated the influences of three layered porous media composed of Tripoli, Pozzolana and Feldspar on seawater pre-treatment. They showed that the composite media has a significant capacity for adsorbing the seawater ions. Ghyselbrecht et al. (2012) investigated the treatment of RO concentrated volume by a combination of an electro dialysis and willow field. They showed that the combination of electrodialysis and willow field is appropriate for treating RO concentrate. Tabatabaei et al. (2012) investigated the clinoptilolite abilities on decreasing chemical and biological index of the compost factory's leachate.

Computational fluid dynamics (CFD) was used to simulate the effect of sparger construction in gas holdup and liquid axial velocity in a shallow bubble column reactor for the air-water system. Model parameters were evaluated in 2-and 3-D simulations by using a two-fluid model and the standard k-e turbulence model. The Eulerian-Eulerian approach was employed to predict the height of column that is affected by the sparger. It was found that increasing the number of orifices in the sparger increases the total gas holdup. Moreover, each orifice causes an increase in the circulation and mixing of liquid in the column. The results of the simulations follow the trends observed in the findings of Dhotre and Joshi [1].