Study On Major Disinfection By-products Formation By Representative Microorganisms In Drinking Water During Chlorination

Microorganisms were ubiquitous in natural water.Escherichia coli and most Staphylococcus aureus are known as waterborne microbial pathogens and representative microorganisms,could contaminate the global water intended for drinking.According to the 2003 third forum for the exchange of information,due to water contamination by bacteria and other viruses,resulting in an average of at least 500 people worldwide died of related diseases every year.For a primary goal to protect human health from contact with pathogenic organisms of water including those causing cholera,polio,typhoid,hepatitis,and a number of other bacterial,viral,and parasitic diseases,disinfection is a necessary process.A concomitant fact concerns disinfecting chemical's reaction with the natural organic matter(NOM),algae cells,bacteria and other microorganisms,yielding by-products(DBPs).Even though disinfection target is to reduce the microbial risk,it however exposes consumers to the dangerous action of DBPs.NOM is usually considered as a conventional and main precursors of DBPs.Bacteria exhibited higher potential for N-DBPs(HANs and TCNM)formation in comparison with dissolved organic matter during chlorination.Compared to carbonaceous disinfection byproducts(C-DBPs),nitrogenous disinfection by-products(N-DBPs)was more toxic in CHO cells.But the research about whether bacteria could produce DBPs,especially HNMs formation,was still fewer.It is quite necessary to investigate the factors influencing DBPs,especially HNMs formation of bacteria upon chlorination in detail.Therefore,this study researched the formation of DBPs during the chlorination of Escherichia coli and Staphylococcus aureus and the formation influencing factors.The results showed that during the chlorination,all Escherichia coli and Staphylococcus aureus could produce DBPs including chloroform(TCM),dichloroacetic acid(DCAA),trichloroacetic acid(TCAA),dichloroacetone(1,1-DCP),trichloroacetone(1,1,1-TCP),dichloroacetonitrile(DCAN),trichloroacetonitrile(TCAN)and chloropicrin(TCNM).Increased chlorination dosage made the concentration of TCM,1,1,1-TCP,TCNM,DCAA and TCAA increasing,DCAN and TCAN concentrations increased first and then decreased,and 1,1-DCP concentrations decreased.Prolonged reaction time made the concentration of TCM,TCNM,DCAA and TCAA increasing,DCAN?TCAN?1,1-DCP and 1,1,1-TCP concentrations increased first and then decreased.During the chlorination of Escherichia coli and Staphylococcus aureus,different pH affected the DBPs formation greatly.TCM content increased slowly by raising the pH,but 1,1,1-TCP and TCNM decreased evidently.TCAA and 1,1-DCP concentrations increased first and then decreased with rising of pH.When the precursor was Escherichia coli,DCAN andTCAN reached maxima at a pH of 6,and then decreased instead as pH elevated.Escherichia coli after disinfection brought the DCAA content decreased continuously with pH.When the precursor was Staphylococcus aureus,DCAN and TCAN reached maxima at a pH of 7,and then decreased instead as pH elevated.Staphylococcus aureus after disinfection brought the DCAA concentrations increased first and then decreased.Different concentrations of bacteria also influenced the formation of these DBPs.The total organic carbon(TOC)concentrations was changed from 1mg/L to 4mg/L.TCM?TCNM?DCAA and TCAA concentrations were increasing with increased TOC concentrations,but such relationship was not found with 1,1,1-TCP and DCAN.When the precursor was Escherichia coli,1,1-DCP and TCAN was not found to be intimately associated with the TOC concentrations.When the precursor was Escherichia coli,1,1-DCP and TCAN concentrations were increasing with increased TOC concentrations.It is hypothesized that the differences in cell walls between gram(+)and gram(-)bacteria may have accounted for the differences in DBPs formation pattern between the cultures.Though many factors could contribute to this behavior,it is conjectured that glycine and teichoic acid may have played an important role in the differences of the DBPs formation between the two bacterial suspensions.