| In this study,a set of effective treatment process was explored based on the characteristics of water-borne paint waste liquor,which combined coagulation-flocculation,membrane treatment and biological treatment.The effect of FeSO4,PAC and PFS on the treatment of water-borne paint waste liquor was investigated by response surface methodology(RSM).The optimal treatment conditions of coagulants were optimized according to the response surface model.Fitting models were evaluated by analysis of variance(ANOVA).The results showed that the paint is the main contributor of the high suspend solid and COD of the waste liquor.And the suspend solids can be removed by the coagulants,which the removal efficiency is more than 99%.The COD decreased from 6.52×105 mg/L to 1.73×105 mg/L with the PFS dosage of 2.43 g/L at pH 5.71,which obtained the maximum removal efficiency of 73.4%,PAC showed lowest efficiency on COD removal,while COD can be further reduced by Fe3+.The ANOVA showed that the response surface model performed good fitting degree,which can reflect the coagulation-flocculation process and is feasible approach for actual prediction.The economic cost of the coagulants showed that PFS performed the best removal effect,and FeSO4 is of the most economical coagulant,and PAC required the highest cost.The effluent of the supernatant of coagulation sedimentation was treated by nanofiltration and reverse osmosis,the COD was reduced from 1.75×105 mg/L to about 1.10×104 mg/L,and the removal rate was 93.7%.The removal of COD by nanofiltration was 25%-31%.The removal rate of COD by RO was between 85%and 93%.Through the analysis of membrane flux,the performance of tubular nanofiltration membrane and vibrating nanofiltration membrane were compared and indicated that the treatment performance and durability of the membrane were better than that of the tubular membrane.The particle size distribution of coagulation sedimentation effluent,nanofiltration effluent and reverse osmosis effluent were characterized by particle size analysis.The results showed that the particle size distribution of coagulation sedimentation effluent was wide and the distribution range of each particle size was relatively average.In the process of membrane,the median diameter of the solute molecules in each stage is gradually reduced,and the range of particle size is gradually narrowed.The nanofiltration process has obvious effect on the removal of macromolecules with size of 4 ?m or more.However,the size of solute is mainly below 2.48 ?m after reverse osmosis process,which is mainly small molecule,which is important for subsequent biochemical treatment.The results of scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS)indicated that the pigment was the main factor causing the pollution of nanofiltration membrane and the resin molecules was the main cause of RO membrane blocking.The effluent of the aqueous paint with COD of 7000?8000 mg/L was treated by anaerobic-aerobic process after membrane process.The results showed that UASB could reduce COD to 1100 mg/L,and the removal rate was 84%?86%.The effluent COD was 300?400 mg/L after aerobic contact oxidation,which the removal rate reached 94%-96%.The effluent COD reached the tertiary discharge standard of urban sewage,and could be discharged directly after the treatment by the inner circulating UASB-aerobic contact oxidation process.The waste liquor after membrane process showed good biodegradability,and the treatment is effective on the high concentration water-borne paint waste liquor. |
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