1 air float
Air flotation is a common method in white water treatment. The substances in white water are short fibers, fillers, colloidal substances and dissolved substances,
After adjustment, it is mixed with dissolved air water after pressure reduction in the air flotation tank. After the air flotation operation is completed, the clean water enters the clean water tank for paper machine reuse, and short fiber enters the pulp tank for paper machine reuse. Air flotation method has been widely used in paper enterprises in China. Mudanjiang Hengfeng Paper Group uses air flotation method to separate fiber, filler and water, and gets a satisfactory effect. The treated water is reused.
Shandong Linqing Yinhe Paper Group used super effective shallow air flotation technology to recover the white water of paper machine, with SS removal rate reaching 94%, COD reduced to below 200mg/l, and the effluent was clear and transparent, and the treatment cost was only 0.18 yuan / m3.
2 flocculation
Flocculation method has also been applied in the white water treatment of paper making. Its principle has been introduced and is no longer described. Zhang Guanghua and others have achieved satisfactory results in the treatment of white water by starch cationic modified flocculant. Liu Quanxiao and others have carried out experiments on the flocculation effect of peo/pfr dual flocculation system, anion polyacrylamide and cationic polyacrylamide on white water of papermaking. The results show that peo/pfr dual flocculation system has a good flocculation effect. The removal rate of COD was 98% and the operation method of hBD-1 flocculant was simple, the period was short and the treatment result was stable.
3 filtration method
There are two common methods used in white water treatment: vacuum filtration and microfiltration. Vacuum filtration has the characteristics of fast filtration, large processing capacity, stable process, small land occupation, less infrastructure cost and low operating cost. The treated white water can be directly used in papermaking process. In recent years, some large-scale paper enterprises in China have vigorously promoted the vacuum filter for white water treatment, which greatly improves the treatment and recycling of white water.
The filter medium used in microfiltration is stainless steel mesh or chemical fiber mesh. The size of the filter aperture can be randomly selected according to the different types and concentrations of waste water of users, and the minimum pore size equivalent can be less than 20um. The advantages of the utility model are simple technology, less land occupation and less investment, high filtration capacity, high efficiency, low operating cost and extremely simple operation. Wenzhou type wax paper factory adopts microfiltration method to treat white water of paper making, recover fiber, and reuse the treated white water. The microfilter can bring economic benefits of 260000 yuan per year.
4 membrane separation
Membrane separation technology can remove metal ions and dissolved inorganic salt from white water of papermaking completely, which is one of the effective measures to achieve the goal of zero emission of paper. The results of membrane separation method for white water treatment showed that the removal rates of TOC and COD reached 78% - 96%, 88% - 94%, respectively, while the decrease rate of conductivity was 95% - 97%. However, the membrane separation method has little capacity and high cost, and it is still in the laboratory research stage in the field of white water treatment of paper making, and it is still a long way to go from the actual production.