Paper production is divided into two basic processes: pulping and papermaking. Pulping is the process of dissociating plant fibers into natural or bleached pulps by mechanical, chemical or combined methods. Paper making is the combination of pulp fibers suspended in water and processed to meet various requirements.
The paper industry uses wood, straw, reed and rags as raw materials to separate cellulose and make pulp by high temperature and high pressure cooking. Papermaking wastewater produced by pulping is the most seriously polluted. Wastewater discharged during pulp washing is black-brown, which is called black water. The concentration of pollutants in black water is very high. BOD is as high as 5-40g/L. It contains a lot of fibers, inorganic salts and pigments. The effluent discharged from bleaching process also contains a lot of acid-base substances. Paper-making wastewater discharged from paper machine is called white water, which contains a large number of fibers and fillers and adhesives added in the production process. Papermaking wastewater treatment should focus on improving the recycling water rate, reducing water consumption and wastewater discharge, and actively explore various reliable, economic and wastewater treatment methods that can make full use of the useful resources in wastewater. It can refer to the content of sewage treatment system.