Optimization On Advanced Drinking Water Treatment Process Of Biological Activated Cabon-ultrafiltration

The advanced drinking water treatment process with biological activated cabon-ultrafiltration(BAC-UF)as the main treatment unit was investigated.The performance of the BAC-UF process and ozone-biological activated cabon(O3-BAC)in application was compared.The contribution and target pollutants of ozone and ultrafiltration to the performance of the process was compared.The effects of chemical cleaning agents onthe aging PVDF hollow fibet ultrafiltration membrane.Existence of large particles in membrane effluent was also researched.The results showed:Ultrafiltration membrane can control the water particles effectively.The average particles of effluent from BAC-UF process and O3-BAC process were 19/mL and 67/mL,respectively.Ultrafiltration decreases the particle count and microorganism in BAC effluent significantly.Ozonation improved the removal of ultra violet absorbence at UV254.Ozonation can also remove part of antibiotics,but when the ozone dosing is low,the effect is not obvious.The growth of alge and Actinobacillus in the BAC may cause the increase of tastes and odors.The microbial community structure in the BAC of O3-BAC process is more complex,which is beneficial to the removal of pollutant.Ultrafiltration membrane and ozone can't remove 2-MIB.The polyvinylidenefluoride(PVDF)ultrafiltration membrane was aged with sodium hydroxide(NaOH),sodium carbonate(Na2CO3),sodium hypochlorite(NaClO),hydrochloric acid(HCl)and citric acid(H3Cit),and the aging effects happens at the beginning of the soak.The average membrane pore size and the number of membrane pores increased after membranes exposed to cleaning agents.The total organic carbon rejection efficiencies(TOC)decreased.The pure water flux increased.After exposed to NaOH for 75 days,the TOC decreased 21%and the flux increased 62%.The tensile strength and ultimate elongation reduced along with the increased aging time.After exposed to NaOH for 75 days,the tensile strength decreased 11%.The contact angle of membrane surface increased.After exposed to NaClO for 75 days,the contact angle of membrane surface increased 12.8°.The dehydrofluorination occurred during the aging process,whice was indicated by the increased pead intensity of C=O and C=C.The chemical composition and structure of the membrane were changed by the chemical cleaning agents and this caused the reduction of membrane hydrophilicity.The effects of acide cleaning agent on PVDF membranes are not obvious.Alginic acid coused much more serious membrane fouling than humic acid.The humic acid is unfolded and soft in high pH condition,and can pass through the ultrafiltration membrane easily.This causes the reduced DOC rejection efficiency,increased the particle count of membrane effluent and decreased trans-membrane pressure.But in acidic condition,the humic acid is folded and hard and more humic acid was rejected compared to high pH condition.The mechanism of the large humic acid occurred in membrane effluent is that the soft humic changes its shape under the pressure of water,and then it can pass through the small membrane pore with the activity of "peristalsis" or destroyed by membranes under pressure and form small size particles.The humic acid that passed through the membrane can gather together when there is a core.Humic acid is the appropriate surrogate to simulate the mechanism of large particle existed in membrane effluent.The humic characteristic of the organic matter in BAC effluent decreases because most of the organic matter is carbohydrates and protein.New surrogate should be used to investigate the mechanism.