Application of the hottest membrane separation tec

Application of membrane separation technology in special paper wastewater treatment

special paper consumes a lot of water per ton of paper, and it is difficult to reuse reclaimed water. The process of Fiber Filter Ultrafiltration activated carbon reverse osmosis is used for treatment, and the reuse rate of reclaimed water reaches 80%. The production of paper machine and the quality of paper products are not affected

according to GB regulations, the paper-making enterprise has a drainage capacity of 20t per ton of paper, and the white water recycling rate needs to reach 88% based on the sizing mass fraction of 0.6%. The commonly used separation membranes in the paper industry mainly include: microfiltration (MF), 0.1-1 μ m. It is mainly used to separate suspended solids and bacteria, and can be used as the pretreatment unit of membrane treatment. Sand filtration should be arranged before microfiltration to eliminate the blockage of microfiltration membrane holes by fine fibers and colloidal substances in wastewater; Ultrafiltration (UF), 0.01-0.1 μ M (or mm is 2 × 103——300 × 103), which is mainly used to separate macromolecular organics, colloidal substances, coagulates, bacteria, etc., and can be directly used for the treatment of paper machine white water; Nanofiltration (NF), with mm of 150-1000, is mainly used to separate small molecule organics, dye molecules, cations with large relative molecular weight, etc., and can be used for water softening; Reverse osmosis (RO) is mainly used to intercept na+, cl- and other monovalent ions, and is mainly used at the end of white water recycling cycle to reduce the conductivity of recycled water

current situation

after collection, flocculation and radial flow sedimentation, the pH of sewage is 6-9, CODcr ≤ 80mg/l, TSS mass concentration ≤ 20mg/l, turbidity ≤ 30ntu, conductivity ≤ 350 μ S/cm, meeting the emission limit of water pollutants specified in GB. However, due to the special requirements of special paper products, the water consumption per unit product is large, and some paper products can produce up to 100t of white water per ton. The conventional water treatment process is difficult to meet the recycling demand and can not meet the water consumption requirements. If the test piece of recycling technology needs to be tested for the second time, it has become a key problem for the technical transformation and transformation development of special paper enterprises

through the membrane treatment process, the key indicators such as cod, conductivity, TSS content of recycled water are reduced, so as to realize the replacement of recycled white water for some clean water while being used in the fatigue test of composite rolls. See Table 1 for the indicators of inlet and outlet water of membrane treatment

membrane treatment process design

the white water treatment process of special paper adopts the process combination of fiber filtration ultrafiltration activated carbon security filtration reverse osmosis. After the raw water is collected, flocculated and treated by radial flow sedimentation, the pollutants such as fine fibers and inorganic fillers in the sewage are greatly reduced. Setting fiber filter can further remove pollutants such as suspended particles, colloids and bacterial macromolecules, so as to ensure the normal operation of subsequent ultrafiltration membranes; Ultrafiltration membrane mainly removes suspended particles, colloids, organic matter and other pollutants, reduces the turbidity, COD and other indicators of sewage, and removes possible bacterial macromolecules to ensure the quality of membrane treated effluent; The activated carbon filter is used to remove microorganisms, free chlorine, and some colloids and organics to ensure the normal operation of the reverse osmosis membrane; The security filter is used to prevent damage to the surface of high-pressure pump and reverse osmosis membrane caused by broken particles that may leak from the pretreatment device in front of the reverse osmosis device; Reverse osmosis membrane is mainly used to remove inorganic salt pollutants and reduce the conductivity of sewage

commissioning and operation results

adopt the development concept of unitization, modularization and standardization

make statistics on the data steadily promoted from point to area in the second week of commissioning and operation. The distribution of system pollutant removal rate is shown in Figure 1

the COD and conductivity of the effluent from the stable operation of the system are shown in Figure 2

according to figure 2, the conductivity of reverse osmosis effluent is ≤ 100 μ S/cm, cod ≤ 20mg/l, suspended solids SS cannot be detected, and the quality of effluent meets the requirements of treatment design. It can be reused in the pulp grinding, flow conveying and paper machine department, reducing the discharge of waste water per ton of paper and the consumption of clean water

conclusion

according to the characteristics of large water consumption per ton of special paper and high difficulty of reclaimed water reuse, the fiber filter ultrafiltration activated carbon reverse osmosis process is adopted, and the effluent quality takes into account the dual requirements of conductivity and COD, achieving the expected goal of system design. Effluent turbidity ≤ 0.5 NTU, conductivity ≤ 100 μ S/cm, total suspended solids not detected, cod ≤ 20mg/l, normal operation cost 2.62 yuan/cubic meter. The effluent quality meets the needs of special paper production, and the reuse rate of reclaimed water reaches 80%. The paper machine production and the quality of paper products are not affected