Papermaking wastewater mainly comes from two production processes of pulp and paper making and photocopy paper. Pulping is to separate the fibers in plant raw materials into pulp, and then carry out bleaching; paper copying is to dilute, shape, press, dry and make pulp.
Both methods produce a lot of waste water. Pulping produces the most serious wastewater pollution. In the washing process, the waste water discharged is black and brown, which is called black water. The concentration of pollutants in black water is very high, BOD is as high as 5-40g / L, which contains a lot of fibers, inorganic salts and pigments. The waste water from bleaching process also contains a lot of acid and alkali substances. The waste water discharged from the paper machine is called white water, and a large number of fibers, fillers and gels are added in the production process.
In the treatment of papermaking wastewater, we should pay attention to improving the rotation rate, reducing water consumption and wastewater discharge, actively explore reliable, economic and effective treatment methods, and make full use of the useful resources in the wastewater. For example, the method of flotation can recover the fibrous solid matter in white water, the recovery rate can reach 95%, and the clarified water can be reused. Sodium hydroxide, sodium sulfide, sodium sulfate and other sodium salts combined with organic compounds can be recovered by combustion.
The pH value of wastewater was adjusted by neutralization method. The suspended solids in wastewater can be removed by coagulation sedimentation or flotation. Chemical precipitation can decolorize; biological treatment can remove biochemical oxygen demand, and the treatment effect of kraft paper wastewater is better. The treatment of sulfite pulp wastewater by wet oxidation method has achieved good results. In addition, reverse osmosis, ultrafiltration and electrodialysis are also used at home and abroad.
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