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

Experimental research into wet oxidation of concentrated wastewaters from p aper 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 temperat ure, pH and the influence of homogeneous and heterogeneous catalysts on the rare of the wet oxidation process was studied. The experiments were carrie d out in stainless steel batch reactor at temperatures from 130 to 200 degr ees 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 increa ses of 50 to 80% at temperatures from 160 to 200 degrees C. The best result s with respect to the improvement of biodegradability were, however, observ ed under milder conditions. By the use of both homogeneous and heterogeneou s catalysts, a biodegradability of 60 to 78% was achieved with wet oxidatio n at 150 degrees C. Operational cost estimation for the wet oxidation proce ss was also done and showed that the cost of wet oxidation of concentrated water by air is less expensive than an oxygen-based process. (C) 2000 Elsev ier Science Ltd. All rights reserved.