The Water Quality Analysis And Research On Enhanced Coagulation In Shifo Grit Chamber

This paper mainly described the research status of enhanced coagulation and themolecular weight distribution, analyzed the full-year trend of water quality of the raw waterfrom the conventional water quality data of Shifo Grit Chamber. Meanwhile, compared thePAC, PFS, Ferric chloride, PAFC dosed alone effect on the raw water; Choosing activatedsilicic acid as coagulant, combined with four kinds of coagulant dosing to elect coagulant andcoagulant plus the best investment proportion; Also compared effects that dosiningrespectively the two kinds of permanganate pretreatment agent, activated carbon andpotassium permanganate, on the raw water. By doing this, it can choose the technical andeconomic optimum solution; Further to study the organic molecular weight distribution in theraw water and the removing of organic molecular weight distribution of water woksconventional treatment processes to choose a better water treatment processes.(1) Do a evaluation of the raw water quality by determiningthe annual changes intemperature, turbidity and other24indicators. The status shows that: The water quality ofShifo Grit Chamber is totally good. By fuzzy index evaluation, founding that the8monthswater quality are Grade Ⅰ,3months are Grade Ⅱ, water quality of Februry is much poorerthan other months that belongs to Grade Ⅲ, also in this period, the raw water is lowtemperature and turbidity, all this increasing the water works processing difficulty; Analyingthe organic molecular weight distribution by Ultrafiltration. It found that small molecularweight organic compounds in water and half of the DOC in raw water is organics thatmolecular weight less than1k.(2) When four kinds of coagulants PAC、PFS、FC、PAFC worked individually, FC has thebest treatment effect，followed by PAC, PFS has the worest treatment effect. But the effulentchroma of FC is easily exceed at high dosage. After a comprehensive analysis, PAC is the bestcoagulant worked individually. Activated silicic acid as a coagulant aid combined with fourcoagulants dosing, the effluent water quality has a different improve and the best dosage forPAC、FC、PAFC is13.3mg/L，10mg/L，13.3mg/L when the coagulants dosage are40mg/L.The effluent water quality of PFS combined with activated silicic acid is not significantlyimprove.(3)Four kinds of coagulants and coagulant aid dose together at optimum ratio(PFS dosesalone, the dosage of coagulants are40mg/L), using potassium permanganate and activatedcarbon as pretreatment agent doses before coagulation. The combination of PAC, activatedsilicic acid and is the best combination that has a best effect on raw water than other combinations. So the waterwoks can choose this method to improve the water quality.(4)By measuring each process section of the molecular weight distribution of organicmatter in the effluent water,we found that DOC and UV254for water removal were20%and38%through conventional water treatment processes.In the treatment processes,coagulationand sedimentation can do better than filtration for the removal of organic,disinfection can donothing for this purpose.Sedimentation and filtration plant mainly has effect on removal oforganic substances. But,for the organic molecular weight less than1k,this plant has a limitedeffect; the conventional water treatment process for removal of SUVA is no ideal.All of theseconclusions proved the water treatment process can not effectively reduce the hazard ofdisinfection by-products’generation.(5)When four kinds of coagulants worked individually, the removal of TOC is not idealand all of these coagulant is less than20%;polymeric aluminum-ferric is the best one.Eachkind of coagulant on the matter of every molecular weight organic’s removal isdifferent.Polymeric aluminum mainly for the removal of organic molecular weight greaterthan5K, Polymerization iron on the matter of organic removal, the organic molecular weightless than1k, is better than other coagulants.Ferric chloride can do best for the removal oforganic that molecular weight range from1k to5k and polymeric aluminum-ferric is mainlyused to removal the organic molecular weight range from5k to10k.