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Improved Biodegradability of Ligninsulfonic Acid and Wastewater after Ozonation

In this work ozonation in combination with microbiological treatment was employed to remove ligninsulfonic acid and refractory organic substances from the effluent of a paper mill wastewater treatment plant. In laboratory experiments it was shown that ligninsulfonic acid was converted into low-molecular-weight acids, which were biodegradable. At an ozone/DOC ratio of 1.68 a DOC elimination of 22.2 % and a decrease of the UV absorbance of 56.9 % was achieved. For the pilot-scale experiments with the paper mill effluent the DOC elimination and the decrease of the UV absorbance were 46.1 % and 72.2 %. respectively. This was due to the high ozone/DOC ratio of 3.1 applied in these experiments. The high ozone dose did not lead to a significant conversion of the organic substances, but to a complete oxidation of the DOC.