Wet oxidation of concentrated wastewaters of paper mills for water cycle closing

Experimental research into wet oxidation of concentrated wastewaters from paper mills was undertaken. Evaporation and membrane concentrates from paper mills were selected as experimental objects. The aim of the wet oxidation of the paper mill concentrates was to reduce the concentration of organics and to improve biodegradability of the concentrates. The effect of temperature, pH and the influence of homogeneous and heterogeneous catalysts on the rate of the wet oxidation process was studied. The experiments were carried out in stainless steel batch reactor at temperatures from 130 to 200°C and at pH 2, 5 and 10. The partial pressure of oxygen was maintained at 1 MPa for all experiments. The results showed COD and TOC removal increases of 50 to 80% at temperatures from 160 to 200°C. The best results with respect to the improvement of biodegradability were, however, observed under milder conditions. By the use of both homogeneous and heterogeneous catalysts, a biodegradability of 60 to 78% was achieved with wet oxidation at 150°C. Operational cost estimation for the wet oxidation process was also done and showed that the cost of wet oxidation of concentrated water by air is less expensive than an oxygen-based process.