A Pilot Study On Integrated Process Of Ultrafiltration Membrane For Luan River Water Treatment

In recent years, with the deterioration of water environment and the standard ofdrinking water improved, the limitations of conventional technology become apparent,Upgrading and improving the traditional is imperative. Ultrafiltration membranetechnology as a key technology of the third generation water purification technologyhas been widely concerned. This research, based on submerged membrane ultrafiltration,combing with the upgrading treatment technology of Tianjin Yangliuqing Water Plant,using the pilot system, has made a deeply study on ultrafiltration membrane integratedtechnique. The main results and conclusions are as follows:（1） The membrane effluent turbidity is irrelevant to the type and dosage ofcoagulants. After pretreatment with different coagulants, the membrane effluentturbidity is about0.075NTU, and there have been the certain similarity for the effluentorganics removal efficiency and the effect on membrane pollution control, that is, PAClis optimal, the FeCl₃is second, and AS is worst. The pretreatment efficiency of PAClfor different characteristic organics is better than FeCl3and AS, especially in the way ofeliminating the hydrophilic and small molecular weight organics. With the applicationof both orthogonal test and weighing scoring method, consideration of the three factorsof effluent quality,△TMP and water production rate, the optimal operating parametersof membrane system obtained: Membrane flux18L/m²·h, the filter cycle90min,5cycleperiod for one emptying time, backwash flow rate3.6m³/h, backwash time60s, gasflushing flows3.2m³/h.（2） With the application of projection pursuit clustering analysis method, thesource water has been classified into three water quality periods: low temperatureperiod （from December to March of the next year）, high algae period （from June to September） and normal period （from April to May and from October to November）.Dissolved organics are mainly composed by strong hydrophobic and hydrophilicorganics in different water quality periods, and among which, the organics of molecularweight <500Da occupies the highest proportion. Through investigation of the pollutantsremoval efficiency of membrane integrated system in different water quality periods,the results show the turbidity of the membrane effluent can be maintained less than0.1NTU, particulate matter is less than10/mL, the removal rate of CODMnis about45%,and the removal rate of UV254and DOC are around25%, and all of the bacteria and thealgae in the water can be almost removed entirely; the membrane integrated systemperforms better in the removal of hydrophobic and large molecular weight organicscontained in raw water, but poorly of hydrophilic and small molecular weight organics.（3） In low temperature period, the precipitation of dissolved gas from water is themain factor affecting the stability of the membrane system. Controlling initial and upperlimit TMP can make membrane system stable operation in short period, which mayincrease the cost and difficulty of system operation, however. The integrated applicationof gas-water separation and self-control technologies can effectively collect anddischarge water bubbles, and ensures the stable operation of the membrane system. Thepre-chlorination in high algae period will cause the hydrophobic organics and lowmolecular weight organic content to increase in coagulation effluent, which will notonly reduce the system organic removal efficiency but also exacerbate the membranepollution; However, the biomanipulation pretreatment process can effectively reducethe algae content in raw water. The average content of algae in effluent counts2773million/L, decreased by42.9%. It can reduce the impact of algae on the membranesystem and guarantee the stable operation of the membrane system, without side effectson membrane effluent quality.（4） Aiming at contaminated ultrafiltration membrane, after investigation of theEFM cleaning mode in different water quality periods,the study shows: in normal andlow temperature periods, citric acid is mainly used, with intermittent use of sodiumhypochlorite, and in high algae period, the cleaning way is opposite. Through SEM andEDS analysis of contaminated membrane surface in special water quality periods, theconclusion has been drawn that the membrane fouling in different water quality periodsis caused by basically the same material elements. The only difference between them isthat the membrane fouling in low temperature period is mainly caused by inorganicmatters, while the membrane fouling in high algae period is caused by organic matters.After component analysis of eluent by means of atomic absorption spectrophotometry and GC/MS analysis methods, the results show that the inorganic pollution tomembrane surface is mainly caused by the deposited ferric salt on the membranesurface, and that the organic pollutants are mainly consist of small molecular weightunsaturated hydrophobic aromatic compounds.（5） With the integrated application of both actual project and pilot test, bycomparing with the pollutant removal efficiency and economy between the conventionalprocess, the pressured membrane process, and the submerged membrane process, theresearch shows that in terms of the pollutant removal efficiency, the pressuredmembrane process performs slightly better than the submerged membrane process, butwithout significant difference. The both are superior to the conventional process. Theremoval rates of turbidity and CODMnof the two membrane processes respectively riseby about4%and6%than the conventional process, and the residual ferric in membraneeffluent is <0.05mg/L. The disposable water production rates of different processes areall above85%. In terms of operating cost, the conventional process is economical,saving by32.2%and21.6%compared with the pressured membrane process and thesubmerged membrane process. Combining with other influence factors, a analytichierarchy model has been established. Considering of “cost” and “benefit”, the eventualconclusion obtained that the weight value of the conventional technology, pressuredmembrane technology and submerged membrane technology is separately（0.2518,0.3318,0.4164）. By the principle of “the more weight value, the moreadvantages”, it’s believed that the submerged membrane technology is more suitable forYangLiuQing Water Plant production and operation than the two others.