Study On Advanced Treatment And Reuse Technology Of Printing And Dyeing Wastewater

Printing and dyeing industry has developed rapidly since 90 years of twenty century, as the traditional and preponderant industry of our country, the input and discharge of water have also increased a lot in this industry. Based on statistic, the effluent of printing and dyeing textile was 29 billion meters in 2003 of our country. It means that there was about 1.6 billion m³ printing and dyeing wastewater (PDW) being inpoured to the environment one year, it was 35% of the total industrial wastewater in China. With the development and application of new-style dyes and additives, wastewater treatment has become more and more difficult, although the discharge standard has been hard and fast, water cost has also advanced, the printing and dyeing mills began to search the wastewater reuse to solve the problems of water environmental pollution and the short of water utilization. But now the reuse ratio of PDW is only 7% which is the lowest in all of the industry water utilization in our coutry, and these 7% are main the cooling water. So it is useful and realistically significative to research of the advanced treatment of PDW to reuse.The research object of this research is the reusing treatment of PDW. Based on the investigation and analysis of PDW treatment all over our country, advise the reusing treatment method of hydrolytic acidification-aerobic biochemical process-aerating biological filter- dynamic ceramic membrane filter for the project. In this research, the quality request of reuse water from PDW has been advised and studied for the first time, salt concentration and pH value influence in dyeing process have been analyzed through experiments. To find out the water quality of PDW, and offer the advises for the advanced PDW treatment, the composition of cotton knitting PDW and acrylic textile PDW have been analyzed, and the biodegradability under the aerobic condition of five series dyes including of cationic dyes, reactive dyes, acid dyes, vat dyes and disperse dyes have been studied systematically and vat dyes has also been studies under the facultative condition. Dynamic membrane filtration which was the key technique of PDW advanced treatment in this research has been studied. The conditions of membraning, running and cleaning were optimized through experiments. At last, one knitting printing and dyeing mill has been chosen as the testing base for the pilot research, to validate useful of the treatment method of hydrolytic acidification-aerobic biochemical process-aerating biological filter- dynamic ceramic membrane filter.The results after comprehensive analyses are as following:1. The major treatment method of PDW in our country is biochemical treatment (above 80%), especially, the mass of the treatment method is aerobic biology treatment, and some are combined with chemical treatment. And the surface aeration and catalytic oxidation are the major treatment method of aerobic biology treatment. Due to this result, in this research, biochemical treatment-physical chemical treatment was chosen as the pre-treatment before the advanced PDW treatment. By the secondary hydrolytic acidification and A/B/C thrice catalytic oxidation, adding to physical chemical deposition and biologic filter, COD removal ratio was predicted to 90%, color removal ratio was predicted to 88%. And then the dynamic ceramic membrane was used to remove color, suspended solid and COD ulteriorly to ensure the effluent water meet the need of printing and dyeing process.In this research the reusing water quality of PDW has been discussed at the first time. Compared to the water quality of printing and dyeing, conductance and hypermanganate index were added in the reusing water quality and mensuration of color was changed also. Because the water quality of printing and dyeing was used to assess the water from surface water or ground water, colorimetry of platinum and cobalt was suit to them, but the color of reusing water of PDW from different dyes, the dilute multiple was more suitable for assessing reusing water of PDW. By the dyeing experiments, the results showed that the salt concentration in dyeing water would influence the dyeing effect. As to the dye of reactive violet X-2R which was used in these experiments, when the concentration of sodium sulfate was above 4.0g/L, the staining in fastness to soaping of the dyeing textile was low than 2 class, the dyeing textile couldn't reach the requite. So it is necessary to pay attention to the salt concentration in the reusing water.2. Pollutant components of the typical cotton knitting textile and acrylic knitting textile PDW were analyzed, the results showed that the COD of the effluent were mainly composed of that of the natural organic impurities in the raw cotton, difficult to biodegrade auxiliaries in the bleaching and dyeing while the high level of color was mainly caused by residual dyes in the effluent. The softeners have the greatest contribution to the total COD, about 57.5%. In the effluent of acrylic textile dyeing, the difficult to biodegrade auxiliaries such as oil-stained removing agent, leveling agents and softener were the main contributors to about 70% of the total COD. The level of color of the effluent was mainly caused by residual dyes. So the problem of the color remove from PDW to reuse must be more analyzed.3. Decolor of dyes is always the difficult problem in the PDW treatment. The study on the biodegradability of dyes to solve the decolor problem is one of the keys in PDW reusing treatment. 5 series of dyes, namely 71 dyes, cationic dyes, reactive dyes, acid dyes, vat dyes and disperse dyes were mensurated the aerobic biodegradability by BOD₅/COD. The results showed that cationic dyes owned the best aerobic biodegradability in these five series, and 25% of the cationic dyes which were tested were belonged to easily biodegradable. Compared with cationic dyes, reactive dyes, disperse dyes and acid dyes were main of poorly biodegradable, and vat dyes were almost the hardly biodegradable organics.By the results of the aerobic biodegradability, vat dyes which were the most hardly to biodegrade were chosen to test the facultative condition by active sludge treatment. The results showed that under condition of facultative, the biodegradability of vat dyes was improved. 7 dyes which belonged to hardly biodegradable have changed to poorly biodegradable with the obvious decolor. So when the facultative aerobe treatment combined with the aerobic treatment, the dyes in PDW would be removed effectively.4. The effluent of dynamic ceramic membrane used for the advanced waste treatment in PDW would usually be reused to printing and dyeing process. At first, under the optimum membraning conditions of the kaolin at 6000 screen mesh, cross-flow velocity at 1.0m/s, pressure at 0.20 MPa, concentration of membraning at 0.3g/L and membraning time at 30 min, the aperture of the ceramic membrane could be reduced from 2.0μm to 0.20μm. On the research of operating conditions, the results showed that under the optimum operating conditions of pressure at 0.10 MPa, cross-flow velocity at 1.5m/s, the COD removal ratio could reach 53.7 % and steady permeation flux could be 227L/(m²Â·h). There kinds of washing method were chosen to clean the stained membrane. There were tap water flushing to back flushing to 1 % NaOH washing to 0.5%HCl washing; tap water mixed with air flushing to tap water back flushing to 1%NaOH washing to 1%HNO3 washing; tap water mixed with air flushing to tap water mixed with air back flushing to 1%NaClO washing respectively. By the resume of permeation flux, the third method was the best in these there ones because of the shortest time and the best permeation flux. In order to test the repeatability of the permeation flux, the third washing method was used to clean the membrane repeatedly, the permeation flux were perfect, and after each washing, the renew of permeation flux were all over 98%. Contamination has not cumulated on the membrane, either.5. One typical of cotton knitting printing and dyeing mill was chosen as the base of pilot research. The scale of treatment was 300t/d of rinsing PDW. The treatment technics was secondary hydrolytic acidification and thrice aerobic biochemical process which made the load of sludge was turned from heavy to light and aerating biological filter and dynamic ceramic membrane filter. The reusing rate was 75%. The effluent was reused to practical dyeing process. The results showed that the quality of effluent was steady, invest and running cost was cheap, soaping fastness of dyeing textile was 4 class. It also showed that distributing PDW to light and heavy by water quality could reduce the running cost and prevent the Cumulation of salt in reusing water effective.The above proved that pretreatment by biological and physics chemistry and advanced treatment by dynamic ceramic membrane would be a applied and effective technics for PDW treatment to reuse.