Paper industry

The wastewater from papermaking mainly comes from the two production processes of pulping and papermaking in the papermaking industry. Pulping is the process of separating fibers from plant raw materials, making pulp, and then bleaching it; Paper making is the process of diluting, shaping, pressing, and drying pulp to produce paper.

Both processes discharge a large amount of wastewater. The wastewater generated from pulping is the most severely polluted. The wastewater discharged during pulp washing is black brown in color, known as black water. The concentration of pollutants in black water is high, with BOD reaching 5-40g/L, containing a large amount of fibers, inorganic salts, and pigments. The wastewater discharged from the bleaching process also contains a large amount of acidic and alkaline substances. The wastewater discharged by the paper machine is called white water, which contains a large amount of fibers and fillers and adhesives added during the production process.

The treatment of papermaking industry wastewater should focus on improving the recycling water rate, reducing water consumption and wastewater discharge, and actively exploring various reliable, economical, and fully utilizing useful resources in wastewater treatment methods. For example, flotation can recover fibrous solid substances from white water with a recovery rate of up to 95%, and clarified water can be reused; The combustion method can recover sodium hydroxide, sodium sulfide, sodium sulfate, and other sodium salts combined with organic matter from black water.

Neutralization method to regulate the pH value of wastewater; Coagulation sedimentation or flotation methods can remove suspended solids from wastewater; Chemical precipitation method can decolorize; The biological treatment method can remove BOD and is more effective in treating kraft paper wastewater; The wet oxidation method has been successful in treating sulfite pulp wastewater. In addition, domestic and foreign treatment methods such as reverse osmosis, ultrafiltration, and electrodialysis are also used.

The application of polyacrylamide flocculants in papermaking wastewater treatment and fiber recovery is beneficial for achieving discharge standards. Anionic flocculants are used for air flotation and sedimentation, while cationic flocculants are used for mud pressing.