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This study was undertaken to determine the effect of ultraviolet (UV) light in combinationwith chlorine based disinfection on the growth of bacteria in a simulated warm climatedistribution system. The focus of this study was to determine the effectiveness of Clsub2/sub,NHsub2/subCl, UV/Clsub2/sub, and UV/NHsub2/subCl in suppressing biofilm growth and coliform occurrencesin drinking water distribution systems through a field-scale study, and to comparetreatment with UV to no UV treatment. Heterotrophic plate counts and coliforms wereused to compare disinfection treatments for bacteria within the systems. In addition,water quality parameters were monitored throughout the experiments. Keller Water Treatment Plant is located in Pinellas County, Florida. Thesource for these experiments was groundwater treated for hydrogen sulphide removal,corrosion control, pH adjustment, and addition of fluoride. The water is disinfected usingfree chlorine followed by addition of ammonia at a ratio of 4.5:1 to producemonochloramine.Annular reactors containing coupons made of PVC material were used to simulatethe distribution system in Pinellas County. Two ARs acted as controls and receivedtreated water containing free chlorine or chloramines. Two more ARs received waterwith either Clsub2/sub or NHsub2/subCl and were additionally treated with UV light. For theseexperiments the water sources were chemically disinfected prior to exposure to UV at a100 mJ/cmsup2/sup dose, whereas in practice, UV disinfection would normally occur prior tochlorination. All non-opaque exposed surfaces of the ARs were covered to reduce thepotential of phototrophic growth in the field systems. The study ran over a seven-monthperiod from April to November, 2005.A general schematic of the annular reactor set-up is presented. Twostreams, one containing monochloramine and one with free chlorine, were the primarysource waters for the model distribution systems. The water collected from each streamwas directed into a separate clearwell. The flow pumped from each of these clearwellswas split to feed both a UV unit and one AR. Each water stream had a separate lowpressure UV lamp (TrojanUV Max Model C) provided by Trojan Technologies. Oncewater streams passed through the UV treatment they were directed towards twoadditional separate clearwells which fed the remaining two ARs. During the study, the ARs were monitored once a week for heterotrophic bacteriacounts (suspended and biofilm), disinfectant residual and coliforms, as well as otherunreported water quality parameters. Bulk samples for HPC bacteria were collected in100mL IDEXX bottles containing 10% w/v sodium thiosulfate to quench disinfectantresidual. The PVC coupons were removed aseptically and placed in sterile 50mL glasscontaining PBS and 0.1% w/v sodium thiosulfate. Both samples were shipped overnightto Dalhousie University laboratory where the attached cells on coupons wereimmediately removed by the scraping method as described by Gagnon and Slawson(1999). The scrapings were vortexed and plated on R2A agar to determine heterotrophicplate counts. New coupons that were treated with ethanol were used to replace those thathad been removed and shipped from each AR. The process for enumeration of HPCbacteria involved a standard spread plate technique as described in Standard Methods forthe Examination of Water and Wastewater (21st edition) on R2A agar (DifcoLaboratories).Coliforms were enumerated using the IDEXX Colilert Quanti-tray system.Commercially available sterile bottles containing sodium thiosulfate were used to collectthe 100-mL samples.Statistical tests were performed and repeated for the various combinations ofdisinfectants. In addition, statistical tests compared the significant differences betweenthe average influent and effluent values for the w

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Edition: Vol. - No. Published: 11/01/2006 Number of Pages: 8File Size: 1 file , 340 KB