Impact Of Ozonation On Disinfection By-products Formation From Chlorination Of Algal Organic Matter

Algal bloom is a serious problem for drinking water supplies.The released massive algal organic matter(AOM)has become an important precursor of disinfection by-products(DBPs)during chlorination process.As a strong oxidant,ozone can quickly react with DBP precursors thus affecting the generation of DBPs in the subsequent chlorine disinfection process.However,the studies on the impact of ozonation on the formation of DBPs during chlorination of AOM were limited.In this study,Microcystic aeruginosa was chosen as the target pollutant to investigate the effects of ozonation on the properties of AOM and microcystin-LR(MC-LR),the formation and speciation of DBPs during subsequent chlorination disinfection.Ozonation did not change the level of total organic carbon(TOC)and specific UV absorbance(SUVA)of AOM solution.Part of organic nitrogen in AOM degraded into NH4+.EEM analysis shows that AOM contained aromatic protein,chlorophyll-a,phycocyanin and the humic acid,all of which were degraded by ozonation.At an ozone dose of 4mg/L,the content of humic acid declined more than 99%,while the aromatic protein,chlorophyll-a and phycocyanin was 76.2%.In chlorination of AOM,THMs,HKs,TCNM and HANs were generated.Generally,ozonation enhanced the formation of total DBPs in subsequent chlorination.High pH favored the formation of total DBPs.The formation of TCNM was not affected by pH in chlorination,but increased in ozonation-chlorination.Ozone doses had different effects on DBPs.In 24 h chlorination,the formation of TCM,DCAN,and BCAN increased with increasing ozone doses.The formation of 1,1-DCP and1,1,1-TCP had increasing and then decreasing trends with increasing ozone doses,and their maximum formation levels were obtained at an ozone dose of 2 mg/L.In the mixed soultion of AOM and NOM,AOM and NOM competely reacted with oxidants.Increasing the portion of NOM enhanced the formation of total DBPs,but decreased the formation of HANs.With the presence of bromide,increasing the portion of NOM enhanced the formation of brominated DBPs.MC-LR degraded fast and part of the organic nitrogen in MC-LR transformed to NO3-in chlorinaiton and ozonation-chlorination.The conversion ratio of organic nitrogen to NO3-in ozonation-chlorination reached 56.7%.MC-LR generated THMs,HKs and HANs in chlorination,and TCM was the major DBPs.DBPs from MC-LR formed fast in 10 min,and reached stable levels at 24 h.Ozonation can reduce the formation of THMs,but it can not control the formation of 1,1,1-TCP,1,1-DCP and DCAN in subsequent chlorination of MC-LR.