The main technical objective in reducing the discharges to water is to implement technology to maintain a desired level of priority pollutants. Several investigations indicate that the priority pollutants may be found in the chlorinated material discharged from the bleach plant.

Based on this assumption the state of art of production and abatement technology will be reviewed. Oxygen bleaching is in most cases the most efficient first step to reduce the discharge of chlorinated material. With appropriate process design and control the discharge of chlorinated material will be 3-4 kg/tonne (as TOC1).

If lower discharge levels are aimed at, the chlorination stage can be modified by applying lower chlorine charge alone or in combination with chlorine dioxide addition. The present Swedish environmental requirements of about 2 kg TOC1/tonne necessitate such measures. Careful process optimization is necessary to avoid changes in product quality. Modified cooking can be one way to create the extra flexibility necessary to maintain top quality.

To reduce the discharge levels further, new process technology has to be introduced. The Prenox process, membrane filtration of effluents, partial or complete recycle of bleach effluents, will be discussed and also external treatment methods.

Forest industry wastewater, chlorinated material, process modification, oxygen bleaching, PRENOX, recycle of effluents, prolonged cooking, low multiple chlorination, chlorine dioxide
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