Wastewaters of the wood processing into groundwood are characterized by increased concentrations of organic contaminants (oils, resin acid, lignin (polymeric phenols), lignin salts (sulphonates, phenoxides), tannins, triglycerides, waxes, free long-chained fatty acids and other). Organic compounds which appear as colour come from extracted lignin, tannins and resin acids. Wood processing effluents are often resistant to degradation using biological methods, and are not removed effectively by conventional physicochemical treatment methods, such as coagulation/flocculation, sedimentation, filtration and ozonation. For processing of those effluents it is often necessary to link different methods of purification, and one of the alternative methods is sorption. In this work the removal of organic pollutants was tested from effluent of the production of mechanically milled groundwood by using sorption to clinoptilolite tuff and to samples of tuff which were modified using the solutions of cationic surfactant- hexadecyltrimethylammonium bromide (HDTMA-Br) of different concentrations. The sorption processes of hexadecyltrimethylammonium bromide were researched on the clinoptilolite tuff from Turkey (Aegean Region Turkey, Bigadic), which contains more than 70 % of clinoptilolite, and in smaller mass fraction quartz and opal-CT are present. The tested effluent has the following characteristics: chemical oxygen demand (COD): 13200 mg dm-3, total organic carbon (TOC): 3010 mg dm-3, biochemical oxygen demand (BOD5): 470 mg dm-3, colour: 681 Pt Co, turbidity: 799 NTU, pH 4.8. All testing was done without the adjustment of pH. The conventional process of pre-processing of effluent by coagulation with aluminum chloride hexahydrate (AlCl3·6H2O) was tested and the application ofHDTMA-modified clinoptilolite tuff with the intention of further decrease in organic burden of wastewater. In the Fig. 1A the results of the HDTMA uptake onto clinoptilolite tuff are shown, and in Fig. 1B the pertaining zeta potentials of the samples are shown. HDTMA cations were essentially quantitatively taken up by the clinoptilolite tuff up to loading level of L = 0.204 mmol g-1-(Fig. 1A). The results of the zeta potential measurements show that the negative surface charge changed to positive after modification with surfactant solutions (Fig. 1B). HDTMA cations form a stable organophilic coating on the clinoptilolite surface, and above surfactant loading level of 0.110 mmol g-1(isoelectric point), a second layer of HDTMA+ cations reverses the surface charge into positive. The optimal mass concentration of coagulant AlCl3·6H2O for the tested wastewater is γ = 0.8 g dm-1(Figs. 2A and 2B). Zeta potential of the solution above sediment received by coagulation with AlCl3·6H2O of mass concentration γ= 0.8 g dm-3 is ζ= -3.92 mV. The efficiency of removing the turbidity (Table 1) and COD is η = 67 % (from 799 to 263 NTU) and 54% (from 13 200 to 6 040 mg dm-3). The efficiency of removing solved organic carbon and colour is significantlylesser: 22.7% (from 3010 to 2322 mg dm-3) and η = 33.0 % (from 681 to 457 Pt Co). By processing the solutions received after coagulation with AlCl3·6H2O of mass concentration of 0.8 g dm-3, with natural tuff and organo-zeolites whose loading are: 0.074; 0.123; 0.164 and 0.204 mmol g-1 HDTMA, TOC was decreased from γ=2322 mg dm-3 to the following: γ=2042, 1976, 1945, 1907 and 1821 mg dm-3 and was sorbed: q = 28.0; 34.6; 37.7; 41.5; and 50.1 mg g-1 TOC (Fig. 3A). Using the sample of organo-zeolite with loading of 0.204 mmol g-1 HDTMA, the efficiency of removing the organic carbon was improved from η= 22.7 % to 40.0 %. The efficiency of discolouring the tested solutions also increases with the change of the surface charge of organo-zeolites from negative to positive(Fig. 3B). The efficiency of removing the colour by using the natural tuff was improved from η= 33.0 % to η = 40.0 %, and by using the organo-zeolite with loading of L = 0.204 mmol g-1 HDTMA to η= 76.3 %. In order for the biodegradation of the processes effluents to be tested, the rations of BOD5/COD are predetermined (Figs. 4A and 4B). According to literature data, the good value of biodegradation is the ratio of BOD5/COD higher than 0.5. The tested effluent was characterized as having particularly poor biodegradation. After processing the effluent with coagulation and organo-zeolite (0.204 mmol g-1 HDTMA), the biodegradation has not shown significant improvement. It could be concluded that HDTMA-modified clinoptilolite tuff can be used for discolouring and purification of the examined wastewater in one part of wastewater treatment which combines and some other physicochemical and/or biological purification methods.