Treatment of bleaching wastewater by the hottest w

2022-08-14
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The application of white rot fungi in papermaking bleaching wastewater is reviewed. The research status of degradation and decolorization of lignin and organic chlorides at home and abroad is described, and its mechanism is analyzed and discussed

key words: white rot; Bleaching wastewater; Organic chloride

at this stage, the problem of wastewater pollution in China's paper industry is still very serious. With the strictness of environmental regulations, it is of great practical significance to further study and find new methods and ways to effectively treat papermaking wastewater pollution, and to carry out more effective external treatment of wastewater

papermaking bleaching wastewater contains a large number of toxic organic chlorides that are difficult to biodegrade. More than 200 kinds of organic chlorides have been identified only in the wastewater discharged from sulfate bleaching pulp workshop. It is difficult to treat organic chlorides in Papermaking Wastewater by conventional biological and physicochemical methods. Recent studies have shown that white rot fungi can degrade pollutants that other microorganisms cannot or are difficult to degrade, especially some pollutants with aromatic ring structure and greater toxicity. The special degradation mechanism of white rot fungus determines that its degradation has the characteristics and advantages of broad-spectrum, high efficiency, low consumption and strong applicability. It is not affected by the solubility of pollutants and the toxicity of wastewater, and has low requirements for pollutant concentration and thorough degradation

1 pollution control methods of bleaching wastewater

to reduce the absorbable organic halide (AOX), COD, BOD, chromaticity and toxicity in bleaching wastewater, so as to meet the wastewater discharge standards set by the government, the factory must take different treatment measures

traditional bleaching wastewater treatment methods have no obvious effect on the elimination and decolorization of toxic substances in bleaching wastewater due to high treatment costs or the special properties of bleaching wastewater, and have certain limitations in practical application. Unconventional biodegradation is a promising solution. The biodegradability of wood materials by self rot fungi in nature provides material source conditions for biocatalysts, enzymes and microorganisms. Therefore, screening white rot fungi and enzymes that can efficiently degrade lignin to control the environmental pollution of bleaching wastewater has become one of the recent research hotspots

2 white rot fungus

white rot fungus (white rot fungus) is classified as Basidiomycota in biology. It rots on trees or wood, causing light colored spongy clumps in the shape of bags, sheets or rings. It can produce a large number of extracellular peroxidase enzymes in the lignin cell cavity, such as lignin, etc.

2.1 mechanism of white rot fungus degrading organochlorine compounds

organochlorine compounds in papermaking wastewater are mainly chlorinated aromatic compounds. Structurally, it refers to the products of aromatic hydrocarbons and their derivatives after one or more chlorine atoms are replaced by hydrogen atoms. It is precisely because the introduction of hydrogen atoms that the aromatic structure changes, The biodegradability of chlorinated aromatic compounds is much lower than that of aromatic hydrocarbons. The key of degradation is dechlorination. White rot fungus has a unique living enzyme system that can degrade lignin. The main components of this enzyme system are bound to the cell wall or secreted outside the cell; They have their own division of labor, but they work together. The carbon center free radical produced by this living enzyme system can destroy the ring structure of the compound, and has a strong biodegradation effect on the organochlorine compounds in the paper industry wastewater. It is found that the catalytic ability of laccase in white rot fungus lignin degrading enzyme system is better than that of lignin peroxidase, and its reaction process is as follows:

laccases+02= compound I

compound i+ah= compound II +a ·

compound II +ah=laecases+a ·

the effect of lignin enzyme system on matrix depends on the structure of chemical substances, matrix concentration, pH of reaction, enzyme activity, length of induction period and temperature. The substitution position and number of chlorine atoms in chlorophenols have an important influence on their degradation

2.2 research and application

at present, the most research on the treatment of papermaking wastewater is laccase degradation. Laccase can oxidize phenols to produce macromolecular black insoluble quinone derivatives, and reduce the adsorbable organic chloride (AOX) in kraft paper bleaching wastewater. Many toxic polychlorinated phenols and guaiacol are partially dechlorinated, except 2-chlorophenol and 4-chlorophenol. J. Dec and j.m.bollay studied the detoxification of chlorophenols by two laccases, rhizoctoniaplaticola and Trametes versicolor rill543. When 2,4-dichlorophenol is used as the matrix, the two laccases can catalyze chlorophenols to produce oligomers with an average relative molecular weight of about 800. The insoluble precipitates produced by polymerization can be removed by sedimentation and filtration, so that substituted phenols with a concentration of up to l600mg/l can be removed. During the polymerization process, 20% of the chloride ions enter the solution, but the removal rate of chlorophenol decreases with the increase of the number of substituted chlorine atoms and relative molecular weight

3 research progress of white rot fungi in bleaching wastewater treatment

3.1 white rot fungi directly treat bleaching wastewater

using the living enzyme system of white rot fungi, the organic chlorides in bleaching wastewater are transformed into inorganic chlorine, co:h:o and bacteria itself, so as to destroy and eliminate the organization and structure of chromophores, and achieve the purpose of removing organic chlorides, COD, BOD and chromaticity u4jl. The mycor process invented by Zhang Houmin et al. Fixes white rot fungi on the RBC (rotating biological contactor) biological turntable to treat bleaching wastewater. 70% AOX can be removed after 2 days of hydraulic retention time, 50% toci can be removed after 1 day of hydraulic retention time, 49% TOCl with high relative molecular weight can be removed within 1 day, 62% toci with low relative molecular weight can be removed within 2 days after treating the wastewater in the alkali extraction section, The decolorization rate is more than 80%. If in mycortoci, 60-80% chromaticity and 50% cod, white rot fungus tfichocherma. print is fixed on RCB to treat Wood Pulp CEH bleaching wastewater. After treatment for 3 days, the decolorization rate reaches 85%. The mycopor process developed by Messner et al. Fixed white rot fungus p.rysosporiumbkm/f-1767 on the porous foam carrier of the trickling filter, with a residence time of 6~12 h, and its decolorization rate, AOX removal rate and COD removal rate can reach 87%, 80% and 40% respectively. Eaton, Chans and k-phthalein decolorize 60% of the wastewater in El section with p.chrysosprium for 4 days. Adding carbon source to the culture medium is very important for the decolorization process, while using membrane reactor can decolorize 80%. Fukuzumi et al. Studied the decolorization of kraft pulp black liquor to light yellow liquid Ⅲ J with tinctoria sp. The degradation rate of Dichlorophenol can be as high as 96% after continuous treatment. Livernoche

et al. Found that the decolorization rate of coriohs version color embedded in sodium alginate for 3 days was as high as 80%, while without embedding treatment, the decolorization rate was only 60%, and showed that the bacteria reused under air conditions could decolorize repeatedly and effectively than under anaerobic conditions. Ph=5.0 decolorizes faster than ph=7.0, and the pH range conducive to mycelium growth is different from that conducive to mycelium decolorization. Sammaiah pallerla et al. Studied the decolorization and dechlorination of sulfate pulp bleaching wastewater by using polyurethane fixed t.ver-colo in a fluidized bed reactor system. Intermittent treatment decolorized 72% every day. The removal rate of AOX was 52%. The initial decolorization is mainly by polyurethane adsorption, and the decolorization is mainly caused by the degradation of wastewater components by embedded bacteria after adsorption saturation. Continuous processing. The hydraulic retention time is 24 h, the decolorization rate is (69 ± 5)%, the AOX removal rate is (53 ± 5)%, and the longest continuous treatment time is 32 days; The decolorization rate of calcium alginate embedding continuous treatment is (75 ± 4)% in the process of ordinary use, the AOX removal rate is (59 ± 6)% and the longest continuous treatment time is 22 days. The highest decolorization rate can reach 9600 Cu/LBD by polyurethane embedding. Seon holet et et al screened and isolated ks-62, izu.154. Ks-62 was incubated for 3 and 7 days, and the decolorization rates were 66% and 80% respectively. Izu-154 decolorized 78% and 89% respectively in 1 and 2 days. Wang Shuangfei et al. Treated Reed Pulp CEH three-stage bleaching mixed wastewater with p.chrysos.porium bkmif-1767 adsorption fixation method (with cinder as filler). After two months of continuous operation, the treatment effect was stable, with COD removal rate of 65%-68%, BOD5 removal rate of 89%-92%, toci removal rate of 58%-62%, The subsequent use of lime water coagulation sedimentation can meet the national discharge standard. Lin Lu et al. Found that white rot fungus can effectively eliminate the toxicity of wastewater, and the treatment effect is related to the treatment method. Adsorption immobilized white rot fungus continuous treatment>pva immobilized white rot fungus intermittent treatment>pva immobilized white rot fungus static culture> free white rot fungus static culture

3.2 lignin degrading enzymes treat bleaching wastewater

lip, MNP, tyrosinase, phenol oxidase (laccase) and other enzymes can reduce waste liquid pollution and waste liquid toxicity. The mechanism of enzyme treatment of organic chlorides is to form free radicals through enzyme reaction, and then free radicals polymerize to form polymer compound precipitation and remove it. However, there are not many people who directly use enzymes to treat papermaking wastewater. Freddick studied the decolorization of up and MnP in bleaching wastewater, and showed that MNP was more important than lip in the decolorization process. In the degradation of synthetic lignin, lip plays a major role, while map plays a smaller role. The decolorization rate of white rot fungus directly growing in the medium of CEH Bleaching Wastewater of eucalyptus kraft pulp is greater than that of enzyme treatment. The highest decolorization effect of enzyme treatment is lip, which is only 29.8%, and the worst decolorization effect is lactase, which is only 20.1%. Compared with that, the decolorization rate of enzyme is faster. There is still much room for the development of peroxidase and laccase non-ferrous materials, which can significantly eliminate the toxicity of Eucalyptus Kraft Pulp CEH bleaching wastewater. There is no delay period for the elimination of the toxicity of bacteria to the wastewater. In terms of the elimination of toxicity by different enzymes, lip> MNP> laccase

the main factors affecting the efficiency of organic chloride enzyme treatment include the type and concentration of pollutants, the type and concentration of enzymes, pH, flocculants and adsorbents, and the synergistic effect between pollutants. The research shows that the number of chlorine atoms forming Petrochemical exchanges is from 2 to 5, and the removal rate of chlorophenols decreases. The treatment effect of 4-chlorophenol and tyrosinase is the best

compared with general methods, the treatment of organic chlorides in Papermaking Wastewater by enzyme has the advantages of high catalytic efficiency, mild reaction conditions and low requirements for reaction conditions and reaction equipment. However, the problems to be solved in the enzymatic treatment of bleaching wastewater mainly include reducing the cost of oxidase, maintaining the activity of enzyme in the reaction process, increasing the scope of enzymatic treatment of wastewater containing a variety of organic chlorides, and further improving the utilization and efficiency of enzymatic treatment of organic chlorides. If the enzyme is immobilized, the treatment efficiency can be improved. After the reaction, the immobilized enzyme can be recycled by simple methods such as filtration or centrifugation to reduce the cost of enzyme preparation

3.3 white rot fungus is used to remove colored substances in papermaking wastewater. Papermaking wastewater contains modified lignin, chlorinated lignin or its degradation products such as chlorophenols, chloroguaiacol and chlorocatechols, carboxylic acids, oligomeric derivatives, etc., which are the main substances that constitute the color of wastewater. The color of papermaking wastewater depends on the molecular structure of chromogenic substances. Generally speaking, the longer the molecular structure * * * * yoke chain of wastewater compounds, the darker the color; The benzene ring increases and the color deepens; The relative molecular weight increases, especially the number of conjugated double bonds increases, and the color deepens. The decolorization of coloring wastewater is to destroy the chromogenic groups in papermaking wastewater. Decolorization of papermaking wastewater with white rot fungi is to use the special enzyme system produced by white rot fungi to catalyze the oxidation-reduction chromogenic substance molecules, destroy their unsaturated conjugation bonds, and metabolize some degradation products into the bacteria itself, so as to

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