Study On Treatment Process Of PVA-bearing Desizing Wastewater

Desizing wastewater, especially containing polyvinyl alcohol(PVA) due to starching, derived from pre-treatment process in textile dyeing and finishing industry, possesses characteristics of complicated composition, high concentration of organic substances and poor biodegradability. In this case, it is very limited for traditional biological treatment technology to deal with desizing wastewater. Meanwhile, discharging of PVA contaminated wastewater into surface water will cause adverse effects to the environment. Therefore, developing an economic and efficient process to pretreat this kind of wastewater before co-treatment with other kinds of printing and dyeing wastewater, has important practical significance in improving treatment efficiency.In consideration of the above and the applicability of different techniques in coping with PVA contaminated wastewater, this present study proposed a combined craft of coagulation-iron chips/Fenton uniting flocculation-SBR to treat PVA contaminated desizing wastewater. Moreover, taking into consideration of economy and technicality, optimum operation parameters of each unit in this craft were studied, with the main contents and conclusions as follows:(1) Single factor experiments were employed to help choose the best coagulant and parameters in pre-treatment process. Results indicated that as to weakly acidic PVA contaminated desizing wastewater, PAC and the coagulation decoloring agent performed better in coagulation. Simultaneously addition of PAC and the coagulation decoloring agent was able to promote coagulation effects. Removal efficiencies of CODCr and PVA reached 37% and 9.3%, respectively.(2) Owing to single factor and orthogonal experiments, influence factors of iron chips/Fenton oxidation and related technological parameters were investigated and optimized, which were than compared with traditional Fenton oxidation process. Results showed that the sort order of influence factors was initial pH > dosage of H2O2 > dosage of iron chips > chemical reaction time. When PVA removing and biodegradability were regarded as the purpose, optimal parameters covered that initial pH was 4.0, dosage of H2O2 was 100 mmol/L, dosage of iron chips was 15 g/L and chemical reaction time was 30 min, respectively. On this occasion, concentration of PVA in effluent was 0.9 mg/L, with removal efficiency reaching 99.9%. CODCr was cut by 23.6%, and biodegradability was significantly improved, with BOD5/CODcr increasing from 0.12 to 0.34. Therefore, iron chips/Fenton process was proved to be better than traditional Fenton process in economical and technical aspects under the same conditions.(3) Influence factors of SBR process were also investigated, and results illustrated that treatment efficiencies could be enhanced dramatically by extending aeration time or adopting multiple A/O operation mode in SBR. When concentrations of PVA and COD in inflow were below 0.56 mg/L and 1375 mg/L, removal efficiencies of PVA and COD could attain 75% and 52% respectively after 12 h-aeration. Continuous aeration for 42 h brought total removal of PVA, and concentration of COD in effluent held firmly below 150 mg/L, with removal efficiencies reaching 100% and 75%. Results demonstrated that when three times-operation mode of SBR was employed to treat effluent from iron chips/Fenton process, removal efficiencies of PVA and COD were increased to 83% and 82% respectively after 12 h- aeration.