Study On Combined Membrane Process For Drinking Water Treatment

Presently the water resource suited for drinking water treatment plants has been contaminated slightly by organic matter.The traditional drinking water treatment processes could not remove the organic chemicals to adequate low levels sometimes.With increasing attention to the potable water security, the combined membrane process has became one of water treatment research issues. The process of coagulation-hollow fiber ultrafiltration (C-HFUF) integrated with powder activated carbon to treat micro-polluted water is studied in this dissertation. In this experiment, the operation condition, the removal efficiency, the fouling characteristics and cleaning method were studied and analyzed.The coagulant effect on the filtration performance and the effluent of combined membrane reactor was discussed under different aluminium sulfate dosage. Results indicated that membrane fouling could be prevented greatly by adding chemicals. However, overmany coagulants would not efficiently improve the filtration performance increasingly.By changing the amount of PAC, the influence of PAC on the integrated process performance and effluent quality was studied. It was shown that the UV254 removal rate would rise after adding PAC and the rates could increase with more PAC. Furthermore, turbidity was always kept less than 0.4NTU under different PAC dose.The reactor performance under different operation conditions was evaluated based on orthogonal test and built appraise method. It was indicated that the values of synthetic index would be relatively small under two operating conditions: coagulant 0mg/L, PAC 400mg/L, rate of the operation to stop time 15/3, aeration 0.10nvVh or coagulant 1mg/L, PAC 300mg/L, the operation to stop time 15/3, aeration 0.25m~3/h. Moreover the standard deviation of the latter was smaller.In other words, its effluent quality would be more steady.Under the optimal operating mode the removal effect of C-HFUF and the ultramembrane filtration behavior as well as the membrane fouling and cleaning were studied. It was displayed that the effluent turbidity was kept less than 0.4NTU at alltimes when that of influent fluctuated from 8.6NTU to 60NTU. The removal rates of UV254 and TOC were respectively about 60% and 40% after the PAC rapid adsorption. When the influent NH3-N was 1.22mg/L, the NH3-N removal rate was up to 60% and the NH3-N of effluent was lower than 0.5mg/L. While PAC had been saturated, the C-HFUF process could still remove materials such as GSM and MIB effectively and the removal rates were higher than 85% and 70% respectively. Based on the membrane filtration behavior analyzing, the membrane fouling course included rapid and slow stages. Four kinds of membrane contamination models were adopted to each stage of the membrane filtration. There is no apparent difference among the fitting results got by using four different membrane contamination models. For stage one and three, the results indicated that all the models may fit simultaneously. But for stage two, possibly because the total resistance did not change during the period, none of the four models fitted this stage well.Furthermore, the cleaning experiment showed that the fouling was mainly caused by the small molecule organic s. Alkali wash was an effective way to clean them.