How are the pulp and paper mill effluents treated?
Effluents are treated using mechanical, biological and chemical methods. Most pulp and paper mills have a two-stage effluent treatment plant, consisting of mechanical and biological treatment. Mechanical treatment normally includes screening and primary sedimentation of wastewater to remove solid material such as fibrous sludge (coarse solids, fibers, fillers, coating pigments). Biological treatment utilizes bacteria and microbes to remove dissolved organic compounds and nutrients from the watewater. A few mills carry out additional chemical treatment after the biological stage. This is done mainly to remove any residual phosphorous from the wastewater. Some fine paper mills have such a low organic loading that the treatment of wastewaters can be carried out using only mechanical and chemical treatments. In some cases, part or all of the wastewaters from a mill are piped to municipal effluent treatment plants. Joint treatment with other industrial facilities is also possible.
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