The anaerobic treatment of waste water from the production of peroxide-bleached chemi-thermomechanical pulp was studied. Hydrogen peroxide had to be removed from the waste water before treatment in a methane producing reactor was possible. Peroxide in concentrations up to 200 mg/1 could be removed from the waste water by means of degradation in an acidogenic reactor, the first stage in an anaerobic two-stage process. A system consisting of a prestage and a subsequent acidogenic reactor could successfully remove peroxide in a concentration of 1200 mg/l from the waste water. The prestage was continuously fed with sludge from the acidogenic reactor. The redox potential in the acidogenic stage of a two-stage process proved to be a valuable control parameter when treating waste water containing peroxide. Adaptation of the methanogenic microflora to inhibitory compounds in the waste water was possible. Treatment of the waste water in a pilot plant at low loading rates gave a COD reduction of 50-60% and a methane yield of 0.3 Nm3/kg COD reduced.

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