Study On Treating Printing And Dyeing Wastewater With Flocculation-Ultrafiltration

Texitile printing and dyeing industry is one of industrial segments which consume a large amount of water and meanwhile produce plenty of effluent water. Printing and dyeing wastewater has the characteristics of high COD, high chroma and changeful pH. If the wastewater discharges without any disposal or not disposing to standard rate,it would destroy water body and ecosystem.After consulting the both foreign and domestic information about printing and dyeing wasterwater treatment,we chose chemical flocculation-ultrafilter to treat and recycl the wasterwater.Therefore,disposal of wasterwater can reduce environmental pollution and relieve water shortage.For chemical flocculation progress, a series of flocculant/coagulant,such as polymeric aluminum chloride(PAC), aluminum sulfate, ferric sulfate, ferric chloride and polyacrylamide(PAM) treated disperse red, direct red, reactive bright red mixed dyes simulation wastewater.Factors influencing chroma and COD removal were studied,including the consumption of flocculant,pH value,the time and speed of stirring,depositing time etc.The flocculant mechanism was also investigated.The study shows that aluminum salts are better than ferric salts.Aluminum sulfate has a best decolorization result towards disperse red and mixed dyes simulation wastewater with pH value 5～7.Polymeric aluminum chloride(PAC) is the best flocculant to direct red and reactive bright red simulation wastewater with pH value 4～6.The more dose of flocculant,the better flocculant result.However when dose increased to a certain level,fouling was higher instead.Adding PAM was helping to remove COD and chroma. The other factors were studied. Depositing time is 50min.In mixing progress, rotational speed is 500 r/min,the time is 30s, (G|-) value is 834.5, (G|-) T value is 25035;in flocculation progress rotational speed is 60r/min,the time is 15min。(G|-) value is 18.3, (G|-) T value is 16474。For chemical flocculation-ultrafilter progress,the same flocculant treated four dyes simulation wastewater. The study shows that for chemical flocculation progress aluminum salts are better than ferric salts.But the filtrate show that both aluminum salts and ferric salts have good effect.For disperse red simulation wastewater, ferric sulfate is the best flocculant.For direct red simulation wastewater,PAC, ferric sulfate and ferric chloride have the same effect. Aluminum sulfate and ferric chloride have the same result to reactive bright red simulation wastewater. Aluminum sulfate and PAC are same to mixed dyes simulation wastewater.According to the use of the filtrate,the dose of PAC can be 2g/L or 2.5g/L。The filtrate can be used as industrial cooling water or fountain water.For the UF progress,the service pressure should be limitted below 0.07MPa.The chemical washing method is soaking for 20min and direction flushing for 10min with NaOH solution pH value 9.Hydraulic conversely flushing period is 60min, chemical washing period is 300min...