The Research Of Quorum Quenching Bacteria’s Influence On Water Quality, Biofilm Forming And Microbial Diversity In The Circulating Cooling Water System

In the circulating cooling water system, large population of microorganisms willcause corrosion, fouling, biofouling and other hazards. Bacterial quorum sensing systemis closely related to the whole process of bacterial biofilm formation and can regulatethe factors that influence biofilm structure at different levels. Thus quorum quenchingtechnique has been regarded as a way to inhibit microbial contamination on differentmembrane surfaces.In the research scanning electron microscopy and TGGE were used to study theinfluence of quorum quenching bacteria on the film-forming ability and diversity ofmicroorganisms in the circulating cooling water system. While the static couponcorrosion experiment was taken to study the influence of the addition of quorumquenching bacteria on the water quality parameters of the circulating cooling watersystem and on the corrosion rate of the coupon.Six bacterial strains were isolated from the circulating cooling water system, threeof them were screened out as Gram-negative bacterias with high film-forming abilityand the ability to produce AHLs. The strains were identified to be Serratia sp,Alcaligenes sp, Flavobacterium cucumis respectively. One strain with low film-formingability and the ability to degrade AHLs was screened out and identified to be Bacillusthuringiensi.When the quorum quenching product concentration was10%the inhibitoryeffects on the three AHLs producing strains were the best and can reach to41.4%,34.3%,58.7%respectively, while the inhibitory effects on the number of planktonic bacteriaof the three AHLs producing strains were all less than20%. Optical microphotographand SEM photograph showed that the bacterial density of the three AHLs producingstrains reduced significantly and the porosity of the biofilm increased accordingly as theconcentration of quorum quenching product increased.The pH, alkalinity, calcium and hardness in the Experimental group reactor withaddition of quorum quenching product increased greater over time than that in Controlgroup reactor, while the chloride, total iron and total heterotrophic bacteria are on thecontrary, the coupon corrosion rate in the Experimental group reactor is37%lower thanthat in the Control group reactor. Gray relational analysis indicated hat the corrosion of coupon in the Control group reactor was mainly impacted by pH, alkalinity, hardnessand Ca2+, while the corrosion of coupon in the Experimental group reactor was mainlyimpacted by pH, Ca2+, Cl－and alkalinity.According to TGGE patterns UPGMA cluster analysis, samples of Water andcoupons in the Experimental group reactor belong to the same group, while blank watersample and samples of Water and coupons in the Controll group reactor belong toanother. Shannon-wiener index of both reactors had an increasing trend.Shannon-wiener index of water samples of the Experimental group reactor were lowerthan the Control group reactor. The Shannon-wiener index of coupons were lower thanthat of water samples.These results suggest that the quorum quenching products inhibit the biofilmformation of the three AHLs producing strains mainly through interfering thequorum-sensing system of them. The quorum quenching bacteria can reduce themicrobial diversity in the reactor and the corrosion rate of the coupon.