Application Of Radiation Technology In Printing And Dyeing Wastewater Treatment

　 1 treatment of printing and dyeing wastewater

(1) color is deep and decolorization is difficult.

In the process of printing and dyeing production, dyestuff The average loss rate is about 20%. Among all kinds of dyes, the dye uptake rate of reactive dyes and sulphur dyes is the lowest, the average dye emission rate is about 30%, and the average discharge rate of acid dyes and direct dyes is above 10%. Therefore, dyeing and printing wastewater has high chromaticity and its decolorization is always the main task of wastewater treatment. The technology of biological activated sludge tank treatment, physicochemical treatment and membrane treatment technology in China has some problems, such as low decolorization efficiency and no recycling of treated and purified water.

(2) COD (chemical oxygen demand) is high and degradation is difficult.

The concentration of COD in printing and dyeing wastewater is very high. This is mainly due to the use of a large number of synthetic dyes in the printing and dyeing process, but also using a large number of dyeing and finishing auxiliaries, such as PVA (polyvinyl alcohol), APEO (alkylphenol polyoxyethylene ether) and ABS (alkylbenzene sulfonate). About 95% of these auxiliaries will remain in waste water, resulting in COD of wastewater up to 2000mg/L and BOD5/COD value of 0.2. 0.3, the biodegradability of wastewater is very poor, [4].

　 Two radiation Mechanism of action

2.1 common sources of radiation

At present, the commonly used radiation sources can be divided into two categories: ray source and instrument source.

The most common source of radiation is 60Co, followed by 1 "CS" and "ship Kr". 60Co radiation generation

R ray has the characteristics of high energy, strong penetrability and long half-life, but because of the fact that Ray source The penetration is strong, so the requirement for safety protection is much higher, and the investment cost in advance is relatively large. The most common instrument source is the electron accelerator, which has the characteristics of high dose rate, good focusing, high energy utilization and easy operation. Among the world's production sources, electron accelerators account for about 70% 1 80%, and 60Co radiation sources only account for 20% to 30%. If the processing capacity is calculated, the electron accelerators will account for about 90%, while 60Co will only account for 10%[6].

　 2.2 radiation degradation mechanism

On the one hand, high energy rays can directly interact with pollutants and cause them to decompose and modify. On the other hand, high-energy rays and accelerating electrons can interact with water to produce a series of free radicals, dissociation, hydrated electrons (e two) and ionic bases. These particles are highly reactive and can be degraded or oxidized by organic pollutants. Under normal circumstances, pure water can react with high-energy rays to produce the following reaction: [7]

H20 -.0H (2.7) +eaq- (2.6) +H` (O.45) +H30+ (2. 6) +H202 (0.7) +H2 (0.45)

Note: the G value in the middle bracket is the energy efficiency of radiation chemistry, which is defined as the number of molecules produced by every 100eV ray energy absorbed.

In these active radicals, eaq- and H belong to reducing ions, and OH and H2O2 are oxidant ions, which play a major role in the degradation of organic compounds. The OH radical has strong electronic affinity, and the redox potential is very high, up to 2.8V. It can react with organic compounds containing aromatic rings or multiple bonds to react with saturated organic compounds. H2O2 can be used as oxidant and reductant.

　　 3 radiation treatment of printing and dyeing wastewater at home and abroad

Using radiation technology to treat wastewater, on the one hand, it will not produce harmful reagents to avoid the two pollution to the environment; on the other hand, it is easy to operate and highly efficient. Therefore, foreign studies began in 70s and 80s twentieth Century, and in 90s factories used radiation technology for wastewater treatment. The following is a brief introduction to the application of radiation technology in printing and dyeing wastewater treatment at home and abroad.

　　 3.1 removal of chromaticity from dyeing wastewater by radiation treatment

The decolorization effect of printing and dyeing wastewater is one of the key indicators to evaluate whether the wastewater treatment method is effective. Because most of the dyestuffs are mainly water, most dyes are soluble in water. Moreover, because of the large mass of dye molecules, most dyes can form hydrophilic colloids in water, making the conventional decolorization of printing and dyeing wastewater very difficult [8]. Radiation treatment is essentially an advanced oxidation process. A large number of OH radicals and H2O2 formed during the radiation process can rapidly oxidize unsaturated groups in dye molecules and destroy their chromogenic groups. {page_break}
 

The study of radiation decolorization of reactive dye aqueous solution shows that radiation treatment can effectively remove the color of dye solution. [9-12]. for low concentration (50mg/L) azo reactive dyes, such as reactive black 5 and reactive red 198, the radiation dose of 1kGy can reach 99% decolorization rate (1 Gy represents 1kg absorbed 1J energy). For high concentration (800mg/L) reactive dyes, such as reactive red M 3BE, active blue XBR and reactive yellow x R aqueous solution, to achieve a significant decolorization effect, the radiation dose needs to be increased. For example, when the decolorization rate of azo red M one 3BE reaches 100%, the absorbed dose is about 27.8kGy[9]; and for the reactive blue XBR of anthraquinones, when the absorbed dose is 25kGy, its decolorization rate can only reach 84%. This indicates that the type of dye plays an important role in decolorization rate. Under low absorption dose (9.2kGy), the decolorization rate of anthraquinone active blue XBR is only 33%, much lower than that of reactive yellow x-R76% with azo structure [10].

In addition, it has good decolorization effect on the water soluble acidic [13-16] and direct dye [17] radiation treatment. Gu Jianzhong, Zhu Jinliang and others studied the anthraquinone dye acid blue 40 solution by electron beam radiation. When using 0.3MeV electron accelerator for radiation treatment, with the extension of irradiation time, the color of acid blue 40 solution first decreased rapidly, then gradually stabilized. After 15min, the dye solution had no color; and the larger the dye concentration, the greater the dose needed to achieve complete decolorization. AliVahdat et al. Used 10MeV electron accelerator to decolorizing direct dyes. The results showed that the absorption dose of 50mg, /L's direct black 22 and 9kGy could decolorization completely, and when the dye concentration increased to 100150 and 200mg/L, the decolorization rate decreased to 61.7%, 59.6% and 52.9% respectively.

For the water-soluble disperse dyes, the study of AgustinN.M.Bagyo tame et al has shown that R ray radiation also has an important effect on the sedimentation and decolorization of azo disperse dyes (TR-4G and TBCMS) in aqueous solution. In the oxygen saturated disperse dye solution, when the radiation dose is above 6kGy, the dye solution passes through the radiation and then regulates the pH value by nitric acid. The absorption peak, pH value and total organic carbon of the dye obviously decrease. The authors believe that this is due to the oxidation of disperse dye colloid during the radiation process, and the formation of some organic acids with larger molecular weight. When the nitric acid is added to the solution and the pH value is adjusted to about 1, these organic acid ions become insoluble organic acid molecules and precipitate.

In addition, by studying the UV absorption spectra of dyes before and after radiation, the researchers found that the characteristic absorption peaks of all water-soluble dyes in the visible region were greatly weakened or even disappeared after radiation treatment, and the absorption peaks moved to the shortwave direction. Meanwhile, the pH value of dye solution also decreased. This indicates that the chromogenic groups of dye molecules are destroyed under the radiation of the electron beam, and the acidic substances of small molecules are generated at the same time, which removes the color of dye solution and reduces the pH value of dye solution.

　　 3.2 removal of COD from wastewater by radiation treatment

The removal rate of COD is the most important index of sewage treatment. The larger the COD value, the more serious the pollution of organic matter is. For printing and dyeing wastewater, the COD value can almost represent the amount of oxygen required for the decomposition of all organic matter in waste water, so it is the most widely used indirect indicator of organic pollutants in wastewater. [19] is also the main parameter of waste water discharge in the national standard. According to the discharge standard of water pollutants in the national textile dyeing and finishing industry, the daily average emission concentration of COD should not exceed 100mg/L[20].

In the process of radiation treatment, some of the dye molecules will eventually be oxidized or reduced to inorganic substances, thus removing COD from the wastewater.

The present study found that the COD removal rate of the wastewater is closely related to the absorbed dose and the initial dye concentration by radiation treatment alone. With the absorbed dose

The removal rate of COD increased gradually, while the increase of dye concentration would reduce the COD removal effect. For example, the electron beam radiation of the active dye solution with an initial mass concentration of 57mg/L and 515mg/L was carried out. When the absorbed dose was 0.5kGy, the COD removal rate was 10% and 0%, respectively, and the COD removal rate reached 37% and 13%[21]. when the absorbed dose increased to 108kGy, respectively. The removal efficiency of [9-12,15,21] was 37%.

Compared with irradiation decolorization, the removal rate of COD is much lower than that of decolorization under the same absorbed dose. This is because the dye solution is irradiated by an electron beam, and some chemical bonds of the dye molecules will break or rearrange under the action of active radicals, and the chromophores will be destroyed, so the color of the dye will be removed. However, the destruction of chemical bonds of dye molecules only degrades them into low molecular organic compounds without degrading them into inorganic substances. [10,22]COD reflects all organic matter contents in the system. Therefore, under the same experimental conditions, the removal rate of COD is much smaller than that of decolorization.

At present, adsorption, flocculation, filtration and sedimentation are often used in printing and dyeing wastewater treatment, including biological activated sludge tank treatment, physical chemical treatment and membrane treatment. The first stage treatment is mainly flocculation. The two stage treatment mainly adopts biochemical technology, such as surface aeration, air exposure, contact oxidation, biological turntable and so on. However, there are two pollutions in the process of printing and dyeing wastewater treatment. New advanced oxidation sites in recent years

Such as ultraviolet radiation, Fenton oxidation, photocatalytic oxidation, ozone oxidation and radiation degradation have attracted extensive attention from researchers for their high efficiency and no two pollution. In many high-energy oxidation methods, radiation technology has the characteristics of high efficiency, simple process, good treatment effect and little environmental impact. It is a widely applied wastewater treatment method.

The use of radiation technology to treat wastewater can be traced back to 1960s. In 1956, LoweJr. first used cobalt source to irradiate waste water, and achieved good results. Since then, the research of using radiation to treat wastewater has been deepened. With the rapid development of high energy electron accelerator technology and the industrial application of radiation technology in purifying drinking water and treating wastewater, the great application prospect of radiation technology in sewage treatment is gradually emerging.

According to statistics, the annual water consumption of the domestic dyeing and printing plant accounts for 80% of the total textile industry's water consumption, and the amount of wastewater discharge reaches 6.5 billion tons. Printing and dyeing wastewater has become one of the most difficult to treat industrial wastewater at home and abroad because of its large quantity of water, complex components of organic pollutants, deep color and large variation of water quality.