Study On Surface Water Treatment By Ultrafiltration

With the continuous development of society, the micro-pollution of drinkingwater has become increasingly prominent. On the one hand, the pollution of surfacewater is more and more serious; on the other hand, conventional treatment processcan not meet the increasing water quality standard for drinking water. Therefore, inorder to resolve all kings of contradictions about drinking water treatment, thetraditional water treatment technologies should be transformed or seek a new kind ofdrinking water treatment technology.Ultrafiltration membrane (UF) technology has attract a lot of attention as a newkind of water treatment technology, which not only has a lower actuating pressure,but also has a good removal efficiency for the colloids, the particles and the microbesin water. The paper inspects the treatment efficiency and running conditions of threekinds of different ultrafiltration membrane combined processes to Northeast surfacewater, and these three kinds of combined processes are direct ultrafiltration system,coagulation/UF system, coagulation/sediment/UF system, and the paper inspectsthe the removal efficiency of coagulation/sediment/UF system to halogenacetonitriles (HANs) and halogen acetonitrile precursor. The main findings andconclusions are as follows:(1)The removal rate of direct ultrafiltration system to turbidity, CODMnandUV254are96.42%,28.61%and9.47%, and the turbidity of treated water which isless than0.2NTU is very stable, and the quality of treated water meets the demandsof the national life drinking water quality standard; but removal efficiency of systemto organic matter is lower; by studying the influence of different back flushingconditions to transmembrane pressure (TMP) of ultrafiltration membrane find thatback flushing intensity, back flushing time and back flushing frequency do not muchaffect to the growth trend and growth rate of total transmembrane pressure.(2)The removal rate of coagulation/UF system to turbidity, CODMnand UV254 are96.67%,54.72%and29.11%, significantly higher than the removal rate of directultrafiltration system to organic matter; with the dosage of coagulant increased from0mg/l to25mg/l, the removal rate of system to turbidity increases from97.94%to98.00%, and the removal rate of system to CODMnincreases from26.71%to58.14%,and the removal rate of system to UV254increases from7.55%to41.18%, therefore,when the dosage of coagulant increases, the removal rate of system to turbidity haslittle change, but the removal rate of system to CODMnand UV254is graduallyincreased.(3)The removal rate of coagulation/sediment/UF system to turbidity, CODMnand UV254are96.89%,54.73%and30.14%; with the increase of run time, treatmenteffect of system has little change, transmembrane pressure of ultrafiltrationmembrane is gradually rise and then slowly rise, finally, rapidly rising, and viceversa specific flux; with the filtration flux increased from90L/(m2·h) to110L/(m2·h),the removal rate of system to turbidity and CODMnare95.62%and48.24%, but theremoval rate of system to UV254increases from2.63%to12.94%.(4)In the research of coagulation/sediment/UF system removes halogenacetonitriles and halogen acetonitrile precursor find that the concentration of fourkinds of HANs in the treated water of conventional process and system from large tosmall order is trichloroacetonitrile, dichloroacetonitrile, bromochloroacetonitrile,dibromoacetonitrile, and dibromoacetonitrile is not detected in all of the watersamples, therefore, dibromoacetonitrile is difficult to exist in the drinking watertreatment process;trichloroacetonitrile is detected in the raw water samples, whichindicates that the organic matter in raw water becomes trichloroacetonitrile after pre-oxidization, the concentration of dichloroacetonitrile in coagulation water rises from0μg/l to1.25μg/l, which indicates that PAC can react with organic matter in water toform dichloroacetonitrile; the concentration of trichloroacetonitrile, dichloroacetoni-trile and bromochloroacetonitrile have a certain degree of growth in disinfectionwater, by comparing the treated water of raw water/coagulation/sediment/UFsystem and conventional process find that the concentration of haloacetonitriles in system is less than the conventional process, therefore, the removal rate of system tohaloacetonitriles is superior to conventional process; with the operation of the system,the concentration of trichloroacetonitrile and dichloroacetonitrile is decreasing overthe time; under different filtration flux conditions, the downtrend of haloacetonitrilesis consistent.