Abstract: It was found difficult to carry out anaerobic treatment of peroxide-containing wastewater. According to the invention, the problem is solved in that the peroxide content of the water is reduced in a catalytic pretreatment step (1), preferably an enzymatic pretreatment step.

Abstract: The invention relates to a method of treating wastewater from the manufacture of peroxide bleached mechanical or chemi-mechanical pulp. The method comprises a hydrolysis step, a methane fermentation steps and an aerobic step. After the hydrolysis and methane fermentation steps, sludge is separated from the wastewater and partially recycled to the hydrolysis step. The redox potential of the outgoing water from the hydrolysis step is continuously measured and controlled to a value between -400 and -260 mV by regulating the amount of sludge recycled or by passing ingoing wastewater directly to the aerobic treating step.

Abstract: At anaerobic treatment of wastewater it was found that resin and fatty acids in the wastewater have a toxic effect on the bacteria culture. According to the invention, this is solved by additions of iron or aluminium and calcium or magnesium.

Abstract: At anaerobic treatment of wastewaters from forestry industries there is the problem, that the wastewaters contain toxically acting complexing agents. According to the invention this problem is solved by the addition of a metal selected from the group iron, calcium, magnesium and aluminum.

Abstract: The invention relates to a method of treating wastewater from closed manufacture of mechanical or chemi-mechanical cellulose pulp, which treatment is carried out in a hydrolysis and acid fermentation step and a methane fermentation step with subsequent sludge separation and recycling of separated sludge.