Characteristics of Papermaking Wastewater
Papermaking wastewater has high COD and suspended solids(SS) content. Meanwhile, the chroma is serious. COD is usually composed of insoluble COD and soluble COD. Usually, insoluble COD accounts for most of the total COD composition. When SS in wastewater is removed, most of the insoluble COD is removed at the same time.
Adding polyacrylamide by air flotation or precipitation method can remove most of the SS, while removing most of the insoluble COD and partially soluble COD and BOD.
Precautions for Adding Polyacrylamide
- Dissolution temperature. A certain temperature is required for dissolution to speed up the dissolution rate. However, if the temperature is too high, the molecular chain of the polymer will be broken and the use effect will be reduced. The most suitable dissolution temperature is below 60℃.
- Stirring conditions. Excessive stirring will break the molecular chain, thereby reducing the use effect. Low-speed paddles should be used for mixing. High-speed centrifugal pumps should also be avoided during transportation, and piston pumps or diaphragm pumps are more suitable.
- Disperse and feed materials evenly. The key link in the dissolution of polyacrylamide is the uniform dispersion of the feed. After starting the mixer, it is best to use a mechanical vibrating screen for feeding to avoid the production of “large clumps” and “fish-eye” insoluble particles, so that the polyacrylamide can be fully dissolved and the effect can be exerted.
- Avoid connecting with iron. In the dissolution stirring and conveying dosing system, it is best to use plastic, enamel, aluminum, stainless steel and other materials.
- Choose the right model of the product. Due to the different raw materials and sewage treatment processes used in the papermaking process, the water quality is very different. When purchasing polyacrylamide, sewage or sludge should be provided for selection tests.