**4. Conclusion**

A comparison of the efficiency of NOM removal from native groundwater and the same water with addition of sodium hypochlorite as oxidizing agent showed that at smaller SFR values up to 50 BV/h, the process was more effective in the presence of the oxidant. However, at the SFR values that were up to ten times higher compared to the maximum values given in the manufacturer's declaration, the NOM removal was more efficient in the absence of the oxidant. Namely, the NOM level in the effluent originated from the native groundwater was below MTC of 2 mg O2/L at a SFR value that was 9.2 times higher, whereas under the oxidative conditions this was observed at the SFR that was by 6 times higher than the declared maximum SFR value. The arsenic removal to the level below the MTC of 0.01 mg/L was more efficient in the presence of the oxidant and shorter SFR compared to the minimum and at 10 times higher SFR values compared to the maximum value of SFR declared by the resin manufacturer. In the absence of the oxidant, only native As(V) was removed, and the process was essentially less effective because of the competition with sulfate ions. It was shown that at small BV values, of up to 700, the removal of NOM and arsenic is more efficient in the presence of the oxidant, whereas in the major part of the working cycle, the efficiency of their removal is higher from non-chlorinated water. The values obtained for the resin adsorption capacity for NOM from non-chlorinated water are by about 15 times higher than the corresponding value given in the specification of the resin manufacturer. New approach to the determination of resin sorption capacity, through definition of specific adsorption capacity, at pseudo-equilibrium showed that investigated resin posses very high affinity to NOM. Occurrence of NOM desorption, measured as COD, was observed in the treatment of non-chlorinated water, as well as by measuring the adsorbed TOC in the case of both chlorinated and non-chlorinated water. Desorption of arsenic from the resin surface was observed only in the case of treatment of chlorinated water. Namely, when the results for the optimum SFR are obtained for a pilot plant system for concrete groundwater of distinct physicochemical characteristics, it is simple to design a unique ion-exchange water treatment system of any capacity.

The obtained results make a sound basis for designing an appropriate plant for the removal of NOM from groundwater of the region of the town of Zrenjanin. The tested resin can also be used in the process of pretreatment of the same water, since it allows the removal of about 50% of the naturally occurring arsenic.
