| With the latest version of "Standards for drinking water quality" full implementation and the cost reduction of ultrafiltration(UF) membrane, ultrafiltration technology has been more and more applied in our old water plant renovation and new water plant construction. Coagulation process has become the most widely membrane pretreatment in ultrafiltration,because of its effective virtue, low cost and easy handling. Previous studies indicated that the shortened process of microflocculation- ultrafiltration could save occupied area and reduce the investment, and also had advantage of the pollutants removal and controlling membrane fouling compared with other forms of technology portfolio. Polyacrylamides(PAMs) was often used as an organic polymer coagulant in conventional water treatment process for low temperature and low turbidity water or high turbidity water, and its excellent coagulantion efficency has been proven in practice and also been applied in water treatment. Based on these two aspects of practical applications, this subject applied polyacrylamide to microflocculation – ultrafiltration combined process, to study the treatment efficacy and the evolution mechanism of ultrafiltration membrane fouling through the combination of macro and micro characterizations so as to propose the controlling theory to apply PAMs to the microflocculation – ultrafiltration process.The paper applied four kinds of polyacrylamide and inorganic coagulant aluminium polychlorid(PAC) in microflocculation – ultrafiltration process, and studied the effect of the coagulant aid types(polyacrylamide NPAM500: molecular weight 50 million; polyacrylamide NPAM1000: molecular weight 100 million; polyacrylamide APAM1000: molecular weight 100 million; polyacrylamide APAM2000: molecular weight 200 million) and coagulant dosages(0.1 mg/L, 0.2 mg/L, 0.3 mg/L, 0.4 mg/L, 0.6 mg/L, 0.8 mg/L and 1.0mg/L) on the efficiency of the ultrafiltration process. And the results showed that the four kinds of polyacrylamide improved the efficiency of the ultrafiltration process, effectively enhanced the removal rate of turbidity and humic acid.With increasing dosage of PAMs, water quality has been improved, the removal rate of turbidity w as higher than 99%, and effluent turbidity was kept less than 0.1NTU, besides, humic acid removal rate was increased by 30%, meanwhile, PAMs retention rate was almost 100%, and p H remained between 6.8 and 7.5 in filtered effluent.Based on different types of the coagulants and dosages, using macroscopic flux decay curve and microscopic changes on the surface of ultrafiltration membrane before and after contaminated(AFM, SEM, contact angle, FTIR) as characterization methods, we studied the effect of polyacrylamide(PAMs) on membrane fouling evolution in microflocculation- ultrafiltration process. The results showed that polyacrylamide added could improve the membrane surface hydrophily and change contaminated layer structure. The coagulant dosage of NPAM500 0.3 mg/L, NPAM1000 0.2 mg/L, APAM1000 0.1 mg/L, APAM2000 0.1 mg/L could alleviate membrane fouling, but increasing dosage could result in the aggravation of membrane fouling. Based on this research, we studied the ultrafiltration membrane cleaning of PAMs 0mg/L, NPAM1000 0.2mg/L, APAM1000 0.1 mg/L after cleaning the fouled membrane flux recovery rate(FR) were 19.17%, 20.17%, 19.69%, coagulant dosing didn’t enhance cleaning difficulty.Based on the research foundation that dosing appropriate polyacrylamide could alleviate membrane fouling, this paper further investigated the effect of PAMs on the removal rate of emerging contaminants(antipyrine, ANT). The results suggested that organic polymer flocculant changed the contaminated layer structure, providing antipyrine(ANT) additional adsorption sites and penetration resistance, so as to obviously improve the removal rate of antipyrine(ANT) in proper dosages of PAMs. |
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