Microbial Contamination in Drinking Water： Occurrence, Mcasurement and Control

的BCASVol.26 No.1 2012Microbial Contamination in Drinking Water:Occurrence, Measurement and ControlYU Xin, LIN Huirong & ZHANG ShenghuaInstitute of Urban Environment, Chinese Academy of Sciences, 1799 Jimei Road, Xiamen 361021 China1. Microbial contamination in drinking waterDrinking water is essential for the health, everyday life the Yangtze River delta area and the Pearl River delta withand social development of human beings. Its importanceShanghai and Guangzhou as their central metropolises,is evident to all the people. Because China now isrespectively.experiencing an unprecedented urbanization progress inThe contaminants in drinking water can be categorizedthe world, its demand for enough and clear drinking waterinto chemical ones and microbial ones. The former includesis expanding every year. Unfortunately, many cities andthe trace level persistent organic pollutants, endocrinetowns in China are suffering from the pollution of sourcedisrupting compounds and mutagenic disinfctionwater, which results in the deterioration of drinking waterbyproducts (DBPs). The microbial contaminants inquality. The so-called“micro-pollution in source water" hasdrinking water discussed in this mini-review includebecome a nationwide problem for the water utilities. Thisthe following: (1) the emerging waterborne pathogensis even serious for the relatively developed areas such asconsisting of bacteria, protozoa and viruses, such as E. coliDr. YU Xin is a professor of environmental engineering at the Institute of UrbanEnvironment, Chinese Academy of Sciences (IUE, CAS). He got his B.S. degreein environmental biology from Nanjing University in 1996, M.S. degree inenvironmental science from the Chengdu Institute of Biology, CAS in 1999, andPh.D. degree in municipal engineering from Tsinghua University in 2003. In2008, he joined IUE and took his current position as a professor. He received anaward from the CAS 100 Talents Program in 2008. He has served as the directorof Xiamen Engineering Research Center for Water Environment and WaterSafety since 2009 and as an editorial board member of Journal of EnvironmentalBiology since 2010.Dr. Yu has published over 70 peer reviewed papers and served as a refereefor over 10 international journals. He is also the inventor or co inventor forover 10 Chinese patents on drinking water related technology. His research interest includes the ollowing (1) Detectionof waterborne pathogens and antibiotic resistance genes using molecular tools; (2)aggregates such as bioflm and activated sludge; and (3) Biological and advanced、中国煤化工E-mail: xyu@iue ac.cn, Tel & fax: +86 592- 6190780YHCNMH G84 Bulletin of the Chinese Academy of SciencesVol.26 No.1 2012 Urban Water & Environmentchallenged the viewpoint that biological processes weren downstream coagulation on DON removal wasgenotoxicologically safe.investigated under different process conditions. DONDr. Yu's group has paid great concern on the formationremoval in coagulation was augmented by the pre-mechanism and remove of DON. A research project .oxidation. Cationic polymer could effectively promotewas conducted in a plant with a production capabilityDON removal and its dosing amount should be appropriate.of 2.50x 10'm' drinking water per day in Pinghu city,Pre-oxidation could convert aromatic nitrogen to aliphaticZhejiang Province, PR China. Except the conventionalnitrogen, with the Zeta potential absolute value ofdrinking water treatment processes including coagulation,particles decreased and high-molecular-weight fractionsedimentation, biofiltration and disinfection, advancedincreased degrading nitrogen enriched compounds inprocesses including biological fluidized bed pretreatment,water. DON removal in coagulation was reduced by thecoagulation, sedimentation, sand filtration, the first stagebiological pretreatment. It was found that biologicalO3-BAC, the second stage O3 _BAC, and disinfection wasfluidization pretreatment could change the compositionused because the source water was severely polluted.of the compounds and generate more nitrogen-enrichedThe DON concentration and other related parameterscompounds. It might be the reason of the lower DONalong the media depth of the biofilter were investigated.removal of biological pretreated water in downstreamDON concentration in biofilter presents a rapidly decreasecoagulation. As a countermeasure, adding cationic polymerat the surface media (0-10cm) of the biofilter, and a slowcould effectively promote removal of DON in coagulation,increase at the deeper media (10- 100cm). At the initialand particularly the promotion of biologically pretreatedstage of the biofiltration, DON was utilized much fasterwater was more obvious (Zhang, et al, 2011, 2012).than SMPs generation, leading to a dramatic reduction ofDON removal by using Alpillared bentonite adsorptionDON concentration. However, with the decrease of thewas also studied. The method based on pillared bentonitelevel and biodegradability of the substrates, the SMPsadsorption is proved to be effective in removing DON andbegan to accumulate along the deeper media depth, as wellrelated substances. The maximum adsorption capacities ofas the BAPs became predominant in SMPs, resulting in thethe bentonites vary from 7.11 to 7.61 mg/g. Kinetic studiesfinally substantial increase of DON concentration. EEMshow that the adsorption of DON on the bentonites can beresults confirmed the nitrogen-enriched aromatic protein-described by the pseudo-second-order kinetic model, andlike fractions of SMPs contributed to the increase of DONthe intra-particle diffusion controls the limiting rate. PHconcentration in biofilter.is found to be the key parameter affecting DON removal.A comprehensive investigation was made in this studyAcidic conditions are favored while alkaline conditionson the variation of DON during a whole backwashing cycleare impeded. Furthermore, it is found that the adsorptionof the biofilration for drinking water treatment. In such acapacity of the pillared bentonites depends on the ratio ofcycle, the normalized DON concentration (emue/Cimuwen)OH /AI+ during the pillaring process. Three dimensionalwas decreased from 0.98 to 0.90 in the first 1.5 h, and thenexcitation- emission matrix (EEM) is also applied to assessgradually increased to about 1.5 in the following 8 h. Finally,the effect of adsorption on the removal of different DONit remained stable until the end of this hour cycle. Thisfractions, and the results show that the tyrosine-like fractionsclearly 3-stage profile of DON could be explained by threeare easier to be adsorbed (Gu, et al, 2010, 2011).aspects as follows: (1) the impact of the backwashing on thebiomass and the microbial activity; (2) the release of soluble3.3 Formation mechanism and control of bioflms inmicrobial products (SMPs) during the biofiltration; (3) thedrinking water pipelinescompetition between heterotrophic bacteria and nitrifyingA biofilm is an assemblage of microbial cells thatbacteria. Al1 the facts supported that more DON wasusually accumulate at a solid-liquid interface and aregenerated during later part of the backwashing cycle. Theencased in a matrix of highly hydrated extracellularsignificance of the conclusion is that the shorter backwashingpolymeric substances (EPS). Biofilm-dwelling cells haveintervals between backwashing for the drinking watera high tolerance由角性化二host defenses,bioflter should further decrease the DON concentration inand are attributa: health threats.efluent of biofilter (Liu, et al, 2012).Bacterial biofilTYHCNMHGofindustrialThe effect of pre-oxidation and biological pretreatmentproblems associated with corrosion and biofouling.Blletin of the Chinese Academy of Sciences 89图BCASVol.26 No.1 2012Drinking water distribution systems (DWDS) oftenits structure is similar to the AHLs.2(5H)-furanone hasface the problem of microbial contamination mainly duealready been proved to be a competitor for AHLs in someto biofilm formation. The presence of biofilms in DWDSstudies. Results showed that there were no significantcan deteriorate the water quality of the distributed water,differences for biomass with addition of 100 nM of MXdevelop the bio-corrosion of the pipe as well as contributeand 2(5H)-furanone, respectively. The discrepancy of QSto offensive odors. In order to control these bioflms, it isinhibitory effect of 2(5H)-furanone may be attributed to thenecessary to better understand the mechanisms for bioflmdifferences in species considered and the inhibition reportedformation in DWDS. Quorum sensing (QS) systems havepreviously may be species-specific. The fact of MX may bebeen proved to play a prominent role in the regulation ofexplained that biofilms in drinking water environments aremicrobial biofilm formation, and inhibition of QS systemsnot inhibited by the chlorination disinfection byproducts,may be a promising approach in controlling biofilms inthough it is structure analogues of furanone.DWDS.In conclusion, AHLs play a certain role in biofilmIn its study, isolates from drinking water environments,formation for some of the drinking water environmentalincluding source water, biofilters, and finished waterbacteria. It also indicates that QS may have importantwere taken into account by Dr. Yu's group. To address theeffects on bioflm formation in DWDS and should thereforehypothesis that AHLs play a role in mediating biofilmshelp in developing strategies based on QS inhibitionfor the drinking water environment bacteria, each isolateprinciple. Nevertheless, potential QS inhibitors, MX andwas incubated in the presence and absence of four types2(5H)-furanone, infuenced biofilm formation negligibly inof AHLs with final concentrations from 0.1 to 100 nMthis study. For further work, more QS inhibitors and moreduring the biofilm formation period and then the biofilmcomplex multiple-species system should be applied forbiomass amount was measured. As the results showed, themore drinking water bacteria (Zhang, et al, 2011).biofilm biomass did not appear to increase with increasingFurthermore, Dr. Yu and his colleagues addressedAHLs in some cases. However, for some strains, thethe effect of pipe materials, nutrients and temperature onsupplementation of AHLs had promoted biofilm formation,biofilm formation in simulated drinking water distributionand there were clear dose-effect correlations between AHLssystem using the annular reactors. When bioflm formationlevels and biomass in certain ranges. About 1/4 of the totalon four different pipe material coupons were compared,strains had this positive response to the addition of AHLs,the biomass was in the sequence of casting iron > copper >suggesting that the biofilm development of a significantPVC > aluminum, the microbial growth rate was as (castingnumber of strains in the drinking water environments wasiron, copper)> PVC > aluminum; PVC was the ideal piperegulated by QS. For strains that had QS signals and werematerial for drinking water distribution system; A varietyaffected by the additional AHLs, it gave the direct evidenceof nutrient elements influenced the biofilm formation, andthat AHL have impacts on the biofilm biomass, and itphosphorus played the greatest role; Temperature betweenimplied that AHL -mediated QS regulate biofilm formation20°C and 30°C was preferable for the growth of biofilm andfor these drinking water environmental bacteria. For stainshigher or lower than this range could inhibit the biofilmthat did not have QS signals but were also affected by thegrowth; The impact of lower temperature seemed moreadditional AHLs, a possible mechanism may be that thesesubstantial.bacteria encoded a putative AHL receptor, but not an AHLMicrobial process is the key step in wastewatersynthase, and with the addition of external synthetic AHLs,treatment, during which the bio-available or bio-adsorbableAHL-mediated biofilm formation was triggered.organic and inorganic pollutants are degraded or removed.In view of the role of QS in biofilm formation, theActivated sludge process, where the aerobic bioflocdisruption of the QS systems of microbes seems to be(ABF) acts as the biocatalyst, is most widely applied fora promising method for controlling biofilm formation.wastewater processing. So we also pay great attention onThe isolates were taken into account to test the biofilmthe variations of both bacterial community and extracellularinhibition of MX and 2(5H)-furanone. MX, a series ofpolymers in a中国煤化工chlorination disinfection byproducts which naturally occursTo invesYHc N MH G increase of cellin drinking water pipelines, is a furanone compound, andhydrophobicity trom aerobic b1otloc (ABF) and granular90_ Bulletin of the Chinese Academy of Sciences.中国煤化工YHCNMH G