The Study Of Disinfection Byproducts Formations From Artiifcial Pipewall Biofllms During Chlorination

Pipewall biofilms grown with large population in the city water supply system canprotect pathogenic microorganisms, increase the content of chlorine consumption, acceleratethe speed of the pipe corrosion and reduce the quality of drinking water. Thus manyresearchers at home and abroad are drawn to focus on the pipewall biofilms. Although the aimof chlorine disinfection is to kill water pathogenic bacteria, the contribution of organic carbonby bacteria to disinfection byproducts (DBPs) formations has rarely been studied. Therefore,proving the pipewall biofilms to be the precursor of DBPs during the chlorination hasimportant theoretical significance. Pseudomonas aeruginosa (P.aeruginosa) PAO1, polyvinylchloride (PVC) and galvanized-zinc chips were chosen to form artificial biofilms. The cultureconditions were controlled at25℃, in the stationary in the dark. Swab scraping and ultrasonicprocessing were used to separate the biofilm effectively. Plate count method was used todetermine the viable cell number and as to reflect the biofilm biomass. Pipe chips of maturebiofilms were then used to react with chlorine. Uniform formation conditions (UFC) wereapplied in the chlorine disinfection process. The method of DBP extraction was theliquid-liquid extraction. Finally, the extracts from the organic phase were spiked intoGC-ECD to determine the concentration and species of11kinds of DBPs, includingtrihalomethanes (THMs), haloacetonitrile (HANs), chloral hydrate (CH) and halogenatedketone (HKs). Furthermore, the speciation and formations of DBPs during the chlorination inthe presence of Br-was evaluated. Sterilized saline water was used to simulate the suspendedgrowth of P. aeruginosa to investigate DBPs formations by contrast. Experimental resultsshowed that:Artificial pipwall biofilms and the suspended growth of P. aeruginosa are precursors ofDBPs during the chlorine disinfection process. The major species of DBPs were THMs,trichloroacetonitrile (TCAN) and CH, the major species of THMs was chloroform (TCM).Compared with the suspended growth, attached P. aeruginosa has a high TCAN and CHformation potentials, but low THMs formation potentials. TCAN and CH generationcapacities of galvanized-zinc pipwall biofilms were higher than that of PVC pipewall biofilms. It can be conjectured that galvanized-zinc induce the formation of some kind of protein whichis existed in the biofilm extracellular polymeric substance (EPS). While this kind of proteinhas higher TCAN and CH formation potentials.When adding Br-, THMs and HANs species and the concentration of each componentmade large changes. The formation of TCM reduced with increasing concentration of Br-, andformations of bromodichloromethane (BDCM) and dibromochloromethane (DBCM) firstincreased with the increase of the Br-concentration and then decreased, the formation ofbromine (TBM) increased with increasing concentration of Br-. This mass relationship wasalso found for HANs species. It can be concluded that the strong replace ability of HOBrpromote the conversion of chlorinated products to chlorine-bromine mixed products. Besides,total THMs and HANs yields increased when the concentration of Br-increasing. The resultindicates that not just replace ability, HOBr will also play a strong oxidation capacity in themiddle of the reaction. Hence, the generation capacities of THMs and HANs can be facilitatedwhen the water containing Br-.When reacting with chlorine disinfectant, galvanized-zinc showed higher Br-THMs andN-DBPs generation capacities. And these two kinds of DBPs are thought to be moredangerous for human beings. So the attention should be paid. Therefore, from the perspectiveof DBPs, galvanized-zinc pipes should be controlled to less use. This also provides a newtheoretical basis for the relevant workers in the choice of pipe materials.