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Ozone Applied in Printing and Dyeing Wastewater Treatment

O3tech 2016-5-20 16:06:54

Ozone Applied in Printing and Dyeing Wastewater Treatment

In an era of rapid development of chemical application, pollution is also very serious. Therefore the State formulates standard which explicitly stipulates that waste water, dirt, etc., can be discharged or recycled only after treatment. So many enterprises built their own sewage treatment plant. As is known to all, sewage treatment is a very complex lock industry consisting of many programs. Some of the COD, BOD, decolorization, toxins, bacteria, virus, impurities in the water need for after many procedures to complete water treatment. Therefore ozone generator is a necessity in the application.

Textile printing and dyeing wastewater is of high quantity, high color, and of complex components. Wastewater contains dyes, pulp, additives, acid, alkali, fiber, impurities and inorganic salts, etc. The amino compounds in the dye structure and the heavy metal elements such as copper, chromium, zinc, arsenic and other heavy metals are toxic. At present, 200 - 0 / 10 of the dye in the dyeing process is discharged into the waste water and seriously polluted the environment. With the development of the dye industry and dyeing and finishing technology, the stability of the dye structure is greatly improved which adds great difficulty to decolorization process. The decolorization of printing and dyeing wastewater has become a big problem to be solved urgently in wastewater treatment at home and abroad. Selection of a simple, economic and effective treatment method has become the focus of the study on the decolorization of dyeing wastewater. Most of the printing and dyeing mills adopt combination of chemical treatment and biochemical treatment methods, but the azo dye prevailing in dyeing wastewater of high stability and high solubility in water. Consequently, it is difficult for degradation and it is hardly to obtain satisfactory results through traditional methods.

Ozone has strong oxidation ability. In nature its oxidation reduction potential ranks second to fluoride, and is commonly used for industrial wastewater disinfection, deodorization and decolorization. As a kind of advanced oxidation technology, it was used for decolorization of dye and dyeing wastewater and removal of refractory organics in recent years.

Ozone produced by ozone generator has strong oxidation ability and can be widely used for various dye types. It can greatly reduce the COD, BOD value and 03 produced in the waste water and excess 03 can rapidly in air and solution decomposition to 02, which will not caused secondary pollution for the environment.

1.The mechanism of ozone oxidation treatment of wastewater

Ozone is a good oxidant. In the treatment of printing and dyeing wastewater, ozone and simple or complex organic react to get some of the same product, these products are very easy to biochemical degradation, and have no obvious toxicity. Ozone can not only oxidize inorganic substances in water, such as CN 1, NH, etc., but also can be difficult to oxidation of biological degradation of organic compounds, such as aromatic compounds, etc.. There are two ways of ozonation: first, the ozone is directly involved in the reaction through the pro nuclear or the pro electric interaction; the two is the reaction of the reactive free radicals (mainly a 0H) and the pollutants through the active free radicals. Ozone can react with many organic or functional groups: C = C, C C, aromatic compounds, heterocyclic compounds, carbon ring compounds, = n n - N, = a s, C, C - N, C - Si, oh, SH, NH, CHO, a n = n a. The effect of ozone destruction and removal of pollutants in wastewater has been studied extensively, and some studies have been carried out on the products of ozonation of organic matter. The research shows that the products of ozonation mainly are one aldehyde, two aldehyde, aldehyde, acid, one acid and two carboxylic acid organic molecules.

 

Oxidation reaction

1.1 to seize the hydrogen atoms, and the chain of carbonyl, aldehyde, ketone, alcohol or acid; aromatic compounds are oxidized to phenol, and then oxidized to acid.

1.2 open double bond, the occurrence of addition reaction:

1.3 Oxygen atoms into the aromatic ring substitution reaction occurred. Ozone is also good oxidative bleaching agent, for water soluble dye wastewater such as active, direct, cationic and acid dyes, the decolorization rate is very high; of disperse dyes it also good decolorization effect; but to the other in a suspended state exists in wastewater reduction, sulfide and coatings, the decolorization effect is poor. The results of Matsui et al showed that the azo dyes were more easily to be oxidized by ozone. The amount of ozone was related to the number of azo groups, such as the direct red 2S and direct black 0.1mol for 2S / 80, the oxygen demand was 1, 130mol / 1, respectively. Ozone oxidation can also be used in combination with other processing technology.

 

2. Influencing factors

Ozone dissolved in water, there will be the following two responses: one is direct oxidation, it is relatively slow and has obvious selectivity of the reaction; another is in the carboxyl group in water, hydrogen peroxide, organic matter, humus and high concentration of hydroxide induced by self decomposition into carboxyl radical, indirect oxidation of organic compounds, microorganisms, or ammonia. After a reaction very fast, and there is no selectivity, but also can be oxidized into bicarbonate and carbonate bicarbonate. One kind of reaction is more intense and the oxidation ability is stronger after these two kinds of reactions. Due to the fact that the hydroxyl and organic matter can be induced by ozone self decomposition into carboxyl radical, so under low pH values conditions it is conducive to direct ozone oxidation reaction, and under high pH and high organic matter content conditions it is conducive to the carboxyl radicals indirect oxidation reaction. he decomposition rate of ozone is largely determined by the pH value, temperature, UV value, concentration of ozone and other available removal in water. Ozone concentration, temperature and contact time: generally speaking, ozone of hydrophilic dyes direct dyes, acid dyes, basic dyes, Reactive Dyes Decolorization speed is fast and the effect is good, therefore, to achieve the expectation of a dye removal efficiency, we must increase ozone dosage. The oxidation ability of ozone also depends on the ozonation rate. The higher the temperature, the faster the oxidation rate, and it need less oxidation time. At room temperature, the oxidation time of 30rain is sufficient to remove the dye of L / 3-4mmol in water 50%.

 

3. Coagulation treatment

Study on Lin.S.H shows that for wastewater containing low concentration of dye printing and dyeing, ozonation can effectively remove color and turbidity of the water. However, with medium and high concentration of dye printing and dyeing wastewater, application of ozonation n PAC flocculation processing can enhance the ozone treatment. Combined use of ozone and flocculation process can increase the removal rate to 70%, and reduce the cost of chemical reagents in addition to 30%.Processing German Ochtrup water factory, printing and dyeing wastewater by ozonation treatment 12min, dye COD value decreased 60% to 80% of AOX decreased by 60%, polyvinyl alcohol concentration reduced by 50%, so that not previously by biodegradable material to be part of the oxidation and to facilitate the next step of biological treatment.

 

4.  Adsorption of activated carbon

Activated carbon is the most commonly used adsorbent due to good adsorption properties and stable chemical properties. The activated carbon adsorption method was applied to the advanced treatment of the wastewater after ozonation. However, due to difficulty of the operation of activated carbon regeneration system and high cost of operation of the device, the application is limited.

 

5. Prospects of wastewater ozonation

Ozone treatment technology development can be illustrated from two aspects: the first is ozone as a pre - or post processing, combination with other processing methods, such as flocculation, air floatation, biochemical; the second is development of ozone treatment unit itself, such as photocatalysis, metal catalyzed oxidation.

 

6. Conclusions

6.1 Ozone is a strong oxidizing agent which can react with most organic substances and microbes in wastewater. Ozone can also remove organic compounds that cannot be biologically degradated, such as aromatic compounds and other pollutants and reduce the COD, BOD value and plays the role of decolorization, deodorization, sterilization.

6.2 Under alkaline conditions, the effect of ozone on the decolorization of wastewater was good, with the increase of the initial pH value, the decolorization rate increased significantly. Ozone dosage, contact time, temperature, light, and catalyst etc. have great impact on the oxidation reaction and the decolorization rate.

6.3 Ozonation can improve the biodegradability of dyeing and printing wastewater. Ozone as pretreatment or post-treatment of printing and dyeing wastewater, when used with other treatment methods, it is considered to have best effect.

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