The paper industry is not only a major water user, but also one of the major industries that produce industrial water pollutants. With the increasing shortage of water resources, the strict control of the total discharge of water pollutants, and the release and implementation of the “Water Pollutant Emission Standards for the Pulp and Paper Industry†(B3544-2008), compared with the original standards, the new standards roUr, BCD, SS emissions are reduced by about 50% - 70%. The existing wastewater discharge levels of many papermaking companies are quite different from the new emission standards. Most of the papermaking wastewater that has undergone secondary biochemical treatment cannot meet the emission requirements of the new standard. There is mainly a problem that 0C) Dr>100mg/L is still high in color, so it is necessary to carry out advanced treatment to achieve the standard discharge, even Can be reused. This is of great significance in reducing wastewater discharge, reducing corporate sewage charges, and reducing water consumption.
The advanced treatment of papermaking wastewater is to further treat the secondary biochemical treatment effluent by physical, chemical or biological treatment to remove the dissolved pollutants and suspended solids that the papermaking wastewater does not remove in the secondary treatment, in order to achieve more stringent emission requirements, even Can achieve water reuse.
1 Study on advanced treatment of wastewater
1.1 Physical Chemistry
In the advanced treatment of papermaking wastewater, physical and chemical methods have the advantages of fast treatment and good treatment effect. The commonly used methods include advanced oxidation method, electrochemical method, flocculation precipitation method, membrane separation method and adsorption method.
1.1.1 Advanced oxidation method
Advanced oxidation is a water treatment technology that has emerged in recent years to directly oxidize pollutants in water into inorganic substances such as CO and horse Q or into substances that are easily biodegradable. The OH produced in the advanced oxidation process is a strong oxidizing agent which oxidizes most of the organic matter and the reducing inorganic substance. The advanced oxidation method has the following characteristics: strong oxidizing property, rapid reaction, and reduction of TOO and DOC to improve biodegradability. The technology mainly includes: ozone (Q) oxidation technology, hydrogen peroxide (horse O) oxidation technology, O/HQ oxidation technology, ultraviolet (UV) / H, Q oxidation technology, Q / HO eight JV oxidation technology, titanium dioxide ( TiQ) / UV oxidation technology.
The photocatalytic method can greatly reduce the organic pollutant load of the paperboard production wastewater, and it has the best treatment effect in the closed loop with high CCD content. Under the optimized experimental conditions, the TiQ sol is used to treat the middle-stage wastewater of wastewater in the sunlight, and the color of the wastewater can be effectively removed. The removal rate of OOD is as high as 90%. In addition to the degradation of wastewater under sunlight and fluorescent high-pressure mercury lamps, this photodegradation system also has a certain ability to degrade on cloudy days. In the TC2 photodegradation system with activated carbon fiber (ACF as carrier), the removal rate of wastewater CIXO increases with the surface area of ​​T02/ACF. After 40 minutes, the CCD can be reduced from 215mg/1 to below 100mg/1 and gradually reach equilibrium. However, if the system is recycled, the surface area of ​​the TiQ/ACF is too large, which may lead to an increase in the papermaking waste liquid COEC.
The traditional ozone method can be used for the primary treatment of papermaking wastewater15, which partially oxidizes organic matter, so the removal rate of COD and T:O is relatively low. If ozone is used in combination with the catalyst, complete mineralization of organic matter can be ensured. In particular, CCK and TOC experiments show that the catalytic ozone method is suitable for the tertiary treatment of papermaking wastewater. During the treatment, CCD is linearly related to TOC, and the treatment effect is not affected by the nature of wastewater.
For the removal of organic carbon in waste papermaking wastewater, the light Fmtm rule has a good treatment effect. It is very effective to combine Fentrn and light Fmtrn to treat paper bleaching wastewater. Among the light sources used in the treatment process, the removal effect of sunlight on T3C is better. In this method, temperature plays an important role, a small amount of Q can ensure the progress of the reaction, and the dissolved Fe+ can not exceed 400 mg / L Fmtn method has a good treatment effect, but the price of horse Q is higher. Under the premise of ensuring the treatment effect, if combined with other treatment processes, the cost can be appropriately reduced. In the advanced treatment of papermaking wastewater, if the filling electrode reactor adopts aeration, not only can the corrosion rate of the anode be delayed, but also the water quality can be stabilized.
1.1.2 Electrochemical method
Electrochemical method is a kind of adaptable, high-efficiency, no secondary pollution treatment method. It has various combinations, such as electro-oxidation, electro-precipitation, electrocoagulation, and electricity-Fentaj. When the 1H value is about 8, it is used. Electrochemical treatment of papermaking wastewater, COD and chromaticity removal rate increase with increasing stirring speed, current density, electrolyte concentration and temperature; electrical energy consumption decreases with increasing electrolyte concentration and stirring speed .
The electrocoagulation method can achieve good results in the treatment of oil wastewater, dye wastewater, urban sewage, etc., and the treatment for papermaking black liquor is rarely reported. When the value is 7, the electrolysis time is 50mn, the current density is 14 mA/orf, and the aluminum is used as the electrode, the electrocoagulation treatment of the black liquor can not only obtain better effect and reproducibility, but also moderately reduce the processing cost; In addition, the electrocoagulation process observed in the experiment is consistent with the Langnui and Radkepiausniu isotherms.
In the treatment of wastewater, the combination of catalytic and electrooxidation can play a synergistic role. Under the optimal conditions of current density of 30 mA/on and catalyst dosage of 30 g/L, the CCD can be reduced from 1669 mg/1 to 70 mg/ L丨4-5.
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