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Coagulation/flocculation,which can remove particles,colloids and some membrane surface adsorbing organic matters from the feed water to decease membrane fouling,become a conventional and beneficial pretreatment for membrane process.In this study FeCl3 was chosen as coagulant,while two kinds of flocculate aids,polyacrylamide(PAM)and Kuriverter EP-301(EP),were compared for organic matters removal from secondary effluent of municipal wastewater plant.EP achieved a better performance than PAM in terms of Membrane Filtration Factor(MFF).Optimal dosage for PAM is 30mg-Fe/L FeCl3 and 1mg/L PAM,at which MFF is 2.13,while MFF is 1.47 when 30mg-Fe/L FeCl3 and 1mg/L EP were injected.Optimal dosage for EP is 50mg-Fe/L FeCl3 and 2mg/L EP,at which MFF is 1.05.Moreover,EP flocculation is more efficiently than PAM flocculation in terms of removal of suspended solid(SS),turbidity,dissolved organic carbon(DOC).However,EP and PAM showed similar capability for removal of DOM with UV254 absorbance.It is inferred that EP could remove larger amount of DOM with non-aromatic structures than PAM.Hydrophobic acids(HOA)and hydrophilic acids(HIA)fractions were the major parts of DOM in the secondary effluent,occupying 55%and 21%of total DOC in the secondary effluent tested.HOA fraction was significantly decreased by coagulation/flocculation compared with other fractions.The removal of HOA fraction by 30mg-Fe/L FeCl3 and 1mg/L PAM or EP were 46.6%and 56.8%,respectively.PAM and EP used in this study are both cationic flocculant aids.The molecular weight(MW)of PAM was 105-106 and charge density of PAM was 30%,while EP has larger MW(>107)and similar CD(30%).Larger MW made EP more effective than PAM in DOM removal,especially for HOA fraction,in terms of polymer bridging mechanism.Moreover,EP has a three-dimensional molecular structure,which made the integration more tightly,enhanced the charge neutralization between EP molecular and the flocs or DOM in water and then achieved a better performance in DOM removal than PAM.