| Numerous water plants are facing the upgrade under the dual pressures of the increasingly serious water pollution and strict hygiene standards for drinking water. Under the current background, most of conventional and advanced treatment processes try to increase drug delivery types and dosage or to extend the technological process to enhance the effect of water treatment. However, dosing more agents will definitely bring hazard risk to water quality, and with the increasing dosage and kinds of reagents, the greater negative effect and the safety risk will arise; the use of an extended process is limited by space and capital cost. So it is incompatible for being widely used. Ultrafiltration(UF) has excellent separation efficiency. It can guarantee water quality under the condition of fewer dosages of water treatment chemical or even zero dosage. It has broad application prospects in water plant reconstruction, expansion and new construction. However, membrane fouling problem has always been an obstacle in the applications of UF. To solve these problems, this paper carried out UF application experiment under low reagent, low flux and short process for treating slightly polluted water. In addition, evaluation of direct ultrafiltration water plant also was introduced in the thesis.Firstly, the step-flux method combined with pre-compression was utilized for evaluating raw water, micro-flocculation water and settled waters’ UF threshold flux. Comparing contamination rate of three kind of water, we found micro-flocculation causes more serious contamination than raw water, and after coagulation-precipitation, the fouling rate is significantly reduced. The first threshold flux of raw water, micro-flocculation water and water after coagulation and precipitation are 8L/(m2·h), 8L/(m2·h) and 11L/(m2·h) respectively, and the second threshold flux are 20 L/(m2·h), 26 L/(m2·h) and 26 L/(m2·h) respectively. By comparison of raw water ultrafiltration in different flux for a long period of time, we found that high flux not only caused a great increase of pollution rate, but also an increase of the pollution irreversibility.Then, direct UF, micro-flocculation UF and coagulation-sedimentation UF pilot study shows that although the process was shorted those three kinds of short processes UF can still effectively remove contaminants in the water and output high quality water. Comparing water quality, we’ll find the longer process, the better removal of organic matter and ammonia nitrogen. Nonetheless nitrite nitrogen removal found no significant difference, and both ammonia and nitrite nitrogen removal affected by backwashing significantly. Reduction of dosage, micro-flocculation UF removal changed little, and coagulation-sedimentation UF’s removal marked decline which comes to the same level with the micro-flocculation UF. On membrane fouling, membrane pollution has been effectively controlled under low flux running. Direct UF membrane found mild fouling under low flux, but membrane fouling growth significantly owing to the storm caused an increase in organic matter in water. In contract, micro-flocculation UF was more stable, halved dosage makes no significant effect. In coagulation-precipitation UF, dosing reduction affected the efficiency of sedimentation and worsened water quality of membrane effluent. So membrane fouling increased strikingly compares to normal dosing with changing flux, and irreversible pollution appeared. Comparison of three short processes UF technology, we found micro-flocculation UF combined with low flux can yield high quality water stability.Finally, a short process UF water plant was studied both in the purification efficiency and operation. Timian UF waterworks operation study showed that UF running under low flux and no agent mode greatly simplified the waterworks equipment and operation and reduced the operation maintenance difficulty and cost. Using a combination of ultrafiltration and disinfection can ensure the chemical and biological safety of drinking water and guarantee the security and stability of rural water supply effectively. Membrane fouling development analysis showed that high raw water turbidity will aggravate membrane fouling and overall pollution is relatively slow owing to low flux running. Fluorescence analysis of raw water, UF effluent, concentration of membrane pool and backwashing water showed that the amino acid tryptophan protein prefers to cause reversible contamination and humic-acid organic matter is more likely to cause irreversible pollution. |
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