How to treat papermaking wastewater?

The core idea of zero wastewater discharge technology is that the sum of raw material moisture and papermaking production water consumption should be equal to the sum of sludge, sieve residue moisture, finished paper moisture and evaporation water, when the wastewater discharge is zero. At present, the paper industry has achieved zero discharge of wastewater in Holland, Japan, Europe and other countries, and the core of zero discharge process of papermaking wastewater is to realize the recycling of wastewater.

The whole wastewater zero discharge process system can be divided into two parts: pretreatment part and membrane system reuse part. The purpose of pretreatment is to remove part of COD, reduce hardness, turbidity, SS and other indicators. The reuse part of membrane system is the core part of the whole zero discharge process system, which can separate and remove all kinds of organic matter, suspended solids and other impurities to meet the requirements of reuse.

Common processing methods:

1. Ultrafiltration membrane method

Ultrafiltration membrane method is to apply pressure on one side of the membrane filter to separate suspended solids, macromolecular organics, microorganisms and micro fibers from wastewater, so as to achieve the purpose of water purification.

2. Reverse osmosis

In the treatment of papermaking wastewater, the reverse osmosis method can remove a large amount of salt accumulated in the recycled wastewater, and effectively improve the quality of recycled water. In practical application, through two-stage reverse osmosis or ion exchange process, this reverse osmosis process has the function of concentration for papermaking wastewater, which can improve the concentration of papermaking wastewater and retain the effective components.

3. Electrodialysis membrane process

As the wastewater from papermaking contains a variety of complex organic impurities, which seriously pollutes the membrane, it is necessary to clean the membrane frequently. In the treatment of papermaking wastewater, electrodialysis membrane method can be used to recover alkali from papermaking wastewater in time, effectively extract xylose from wastewater, desalting organic matter in papermaking wastewater and removing salt from recycled materials.

4. Ceramic membrane filtration

In the process of papermaking wastewater treatment, the ceramic membrane recycling technology is adopted. The ceramic membrane has the advantages of easy cleaning and regeneration, long service life, uniform pore size, good mechanical strength and rigidity, corrosion resistance, acid and alkali resistance, organic solvent resistance, high temperature resistance and so on. The sedimentation tank temperature of papermaking wastewater is about 80 ℃. In order to ensure the smooth progress of the subsequent process, the cooling tower spray method can be used, In the process of reducing the treatment temperature of papermaking wastewater, there is a rise of hot gas, which will pollute the natural environment. By using ceramic membrane to filter papermaking wastewater, thermal energy can be reused, and the amount of steam can be reduced in wastewater treatment, which has higher economic benefits.