A Study On The Effects Of Pre-ozonation On Enhanced Coagulation

Disinfection By-Products (DBPs) have become a great challenge to the safety ofdrinking water, among various methods to remove precursor of DBPs, EnhancedCoagulation was considered the best available technology, pre-ozonation also employedto control the DBPs. But the effects of pre-ozonation on enhanced coagulation have beennot yet drawn a uniform conclusion. In this paper PDA (Photometric DispersionAnalyzer), apparent molecular weight distribution and fractionation of organic matterstechnique were adopted to study the Effects of Pre-ozonation on Enhanced Coagulationsystematically. The mechanism of pre-ozonation on coagulation was also primarilyexplored.The study results show pre-ozonation has a notable influence on coagulation ofpolyaluminum chloride (PACl) with various B (OH/Al ratio). The removal of turbidityand the formation of flocs related to the Alb of PACl. The more Alb quantity, the moreturbidity removed. But the removal of dissolved organic matter (DOC) by coagulationwith different dosage of ozone has no great change. On the contrary, the increase ofozone dosage hinders the removal of turbidity and the formation of flocs.Apparent molecular weight distribution experiment results show pre-ozonationtransfer large molecular weight organic matters to small molecular weight organicmatters, the organic matters with molecular weight ranged from 1 to 10k Daltonincreased significantly. The pre-ozonation with ozone dosage 1.1mg/L promoted theremoval of large molecular weight organic matter by coagulation, when the ozone dosageincreased to 4.4 mg/L, the pre-ozonation hinder the removal of organic matter withmolecular weight ranged from 10 to 30k Dalton.Judged from the results of fractionation, great influence was made by ozone, whichincreased fraction of more hydrophobic neutral organic matters. The sequence of removalefficiency of DOC from high to low by coagulation without pre-ozonation washydrophobic neutral fraction, hydrophobic base fraction, hydrophobic acid fraction,XAD-4 fraction, hydrophilic fraction. After pre-ozonation and coagulation with ozonedosage 1.1mg/L, hydrophobic neutral fraction was removed greatly, the removalefficiency was about 95%. With ozone dosage increased to 4.4mg/L, the removal ofhydrophobic acid fraction, XAD-4 fraction and hydrophilic fraction was all improved,but the removal of hydrophobic-base fraction and hydrophobic-neutral fraction have nochange.