The wastewater treatment in the modern kraft pulping plant is no longer a problem. However, the situation in the pulp bleaching plant is different. If a new chlorine-free bleaching process has been achieved, the bleaching waste liquid can enter the alkali recovery system as well as the pulp waste liquid. However, if chlorine or chlorine dioxide is also used in the pulp bleaching process, the organic chlorides in the bleaching liquor are treated in addition to the traditional wastewater treatment methods. There are many new technologies for reference, which are briefly described as follows:
1. Ultrafiltration method due to the high content of high-molecular-weight part of the waste liquid, not easily decomposed by microorganisms. Therefore, consider ultrafiltration prior to biological treatment. Ultrafiltration can remove 50%-90% of the organic chloride or AOX in the wastewater from the E section. However, low-molecular-weight chlorophenols are the most toxic components in AOX, and the efficiency of ultrafiltration is very low, but subsequent biological treatment can remove 62%-90% of AOX.
2. Chemical precipitation of iron salts or aluminum salts allows organic chlorides to settle to remove AOX. The use of Polyethyleneiminc also allows the chlorination and alkaline treatment stages to settle down. The AOX removal rate of the chlorination section is 54%-84%. The alkali treatment stage is 50%-73.
3. Oxidation Method 1 Ultrasonic Oxidation During aeration, simultaneous ultrasonic treatment for 1 hour removes low molecular weight chlorinated organic compounds such as monochlorophenol, dichlorophenol, and trichlorophenol ranging from 10% to 60%.
2†Ozone, ultraviolet radiation, and powdered activated carbon are oxidized either individually or in combination. Using activated carbon alone to treat C-stage wastewater, E-stage wastewater, and mixed wastewater, the removal rates of low-molecular-weight TOX were 32.2%--43.7%, 18.7%-78.7%, and 10.2%-53.0%, respectively, and the TOX removal rates were : 82%-86%, 47%-48% and 73%-74%. The range of removal rate is related to the choice of powdered activated carbon used. Oxidation by ultraviolet radiation alone can be called photolysis. The photolysis is mainly the decomposition of C1- by UV under the action of high molecular weight AOX.
3) Oxygen Oxidation E-stage bleaching wastewater can be significantly removed by oxygen oxidation with oxygen. The degradation of chlorine lignin is mainly at the strongest during the initial oxygen treatment, which plays an important role in the removal of TOCL and color quality.
4. Alkaline hydrolysis Alkaline hydrolysis is the reaction of various basic compounds with chlorohydrin. The method of promoting the reduction of AOX in the effluent is due to different or different combinations of the basic compounds. Its ability to reduce AOX in waste liquids is also different, usually with NaOH/Ca(OH)2 or with Na2S, NaOH, and Ca(OH)2 combinations to reduce AOX. In the treatment, the treatment time, temperature, pH value and concentration have an effect on its effect, generally the PH value is certain, the reaction time is long; the reaction time is certain and the PH value is high. The AOX removal rate in the mixture is high.
5. Non-traditional biodegradation waste liquid Non-traditional biodegradation. At present, it is basically a fungus, especially a lignin-decomposing fungus, commonly used in white rot fungi, which can decompose chlorohydrin, but it is necessary to add a carbon source to produce peroxidase, thereby degrading the pH and nutrient of lignin. Oxygen, dissolved oxygen, and contact residence time all affect the effect.
6. Electrolytic treatment The electrolytic treatment method utilizes electrodes of different compositions to conduct electrolysis at different times to obtain the required AOX removal rate. When the AOX removal rate is the highest, it can reach 99% or more. However, this case consumes a lot of energy and is not worth the candle.