| ABSTRACT:With the continuous deterioration and increasingly stringent water quality standards for drinking water, coagulation-microfiltration (MF) process becomes aroused extensive attention as a new process of new water treatment technology for it can efficiently remove natural organic matter (NOM) in source water. The optimal coagulation conditions and Al3+/Fe3+ratio of PAFC、PAC and PFC which were prepared by copolymerization method are determined by beaker experiments. Structural characteristics and impact on water quality and structural properties of membrane fouling of PAFC、PAC and PFC coagulation aggregates were studied at different coagulant dosages (0.04,0.08,0.12mmol/L) and Al3+/Fe3+values (8:1,4:1,2:1)in optimal pH5.8. Impact of humic acid removal and membrane fouling were analyzed at different speeds microfiltration (30ml/min,60ml/min) and different membrane pore size (0.22μm,0.15μm) conditions. The conclusions were as follows:(1) With comparison of different flocculation process with natural organic matter-humic raw water, PAFC coagulation mechanism is different from PAC and PFC as PAFC hydrolysis complexes have more and much stronger power of neutralization and adsorption capacity than PAC and PFC, and PAFC has a great advantage in the aspects of humic acid removal and membrane fouling alleviate. Comparison of coagulation effects of PAFC at different Al3+/Fe3+values was made by coagulation sedimentation process with natural organic matter in raw water. Humic acid removal of PAFC8:1in coagulating sedimentation processes is92.38%at optimal dosage range of0.08～0.10mmol/L, is96.97%in coagulation-microfiltration process. The optimal dosage of PAFC4:1、PAFC2:1and PAC is0.08mmol/L, humic acid removal rates were90.9%、90.9%、87.89%, removal rates were95.81%,91.92%,94.98%after microfiltration. The optimal dosage of PFC is0.2mmol/L, humic acid removal rate is89.05%,91.36%by coagulation-microfiltration process.(2)On the basic of research about the combination stability and coagulation effect of coagulant at different Al3+/Fe3+ratio, coagulant dosages (0.04,0.08,0.12mmol/L) of PAFC(Al3+/Fe3+=8:1、4:1、2:1)、PAC were chosen for study on aggregates characteristic law while dosages of PFC were0.12、0.16、0.2mmol/L. Tests showed that coagulation condensation particle size and fractal dimension of PAFC have great significant differences because of different hydrolysis products of at various Al3+/Fe3+. When iron content increases, PAFC aggregates particle size increases, which with small iron content grow slowly. PAFC coagulation under the same conditions with the PAC particle agglomerates similar (208.93-316.22pμm), and the fractal dimension is relatively high (2.72-2.81), especially PAFC8:1have higher fractal dimension than others with minimal impact on membrane fouling. PFC, although has larger aggregates particle size (316～5.49.54μm), fractal dimension (2.6) were less than PAFC.(3) Coagulant type, dosage, microfiltration membrane pore size and the speed of microfiltrationthe have combined effect of coagulation-microfiltration membrane fouling by the process. For PAC and PAFC8:1, slowest decline in flux happens when dosage was0.08mmol/L. For the other two high iron content PAFC coagulant, the optimal dosage is0.12mmol/L. Under the same coagulation conditions, comparing the different microfiltration speeds and different microfiltration membrane pore size on membrane fouling, it is found that, when Al3+/Fe3+=8:1, the faster membrane filtration speed is and the larger pore size of the membrane is, the slower membrane flux decay, membrane has lighter pollution, when Al3+/Fe3+=2:1, the slower membrane filtration speed is and the smaller pore size of the membrane is, membrane has lighter pollution. Taking full account of factors to the practical application of membrane fouling has good instruction significance to membrane fouling control. |
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