Papermaking wastewater mainly comes from two production processes of pulp making and paper copying in papermaking industry.
Pulping is the separation of fibers from plant materials into pulp, which is then bleached.
Copying paper is to dilute, shape, press and dry the pulp into paper.
Both processes discharge large amounts of waste water.
The wastewater from pulping is the most polluted.
When washing the slurry, the waste water is dark brown, called black water. The concentration of pollutants in black water is high, and the BOD is as high as 5-40g /L, which contains a lot of fiber, inorganic salt and pigment.
The waste water from bleaching process also contains a lot of acid and alkali substances.
The waste water discharged by the copying machine, called white water, contains a lot of fiber and filler and glue added in the production process.
Disposal of wastewater from papermaking industry should concentrate on improving circulation water use ratio, reduce water consumption and wastewater emissions, at the same time should also actively explore a variety of reliable, economic, and can make full use of useful resources in wastewater treatment.
For example, floatation method can recover fibrous solid substances in white water with a recovery rate of up to 95%.
The combustion method can recover sodium hydroxide, sodium sulfide, sodium sulfate and other sodium salt combined with organic matter from black water.
The pH value of wastewater was adjusted by neutralization method.
Coagulation precipitation or flotation can remove suspended solids from wastewater.
Decolorization by chemical precipitation;
BOD can be removed by biological treatment, which is more effective for kraft waste water.
The treatment of sulfite pulp wastewater by wet oxidation is successful.
In addition, reverse osmosis, over - filtration, electrodialysis and other treatment methods are also adopted at home and abroad.