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Rapid detection of chemical contamination in the distribution system is essential in protectingpublic health, and using water quality surrogates to signal a contamination event offers theadvantage of detecting a large number of chemicals. The concern over using surrogateparameters is whether they offer the ability to detect contaminants at concentrations low enoughto prevent serious illness. The best candidates for water quality surrogates are generally thoughtto be chlorine residual and total organic carbon (TOC), with conductivity, pH and turbidity being less sensitive to manychemical contaminants. All of these surrogate measurements have been in direct response to thechemical contaminant itself. This paper describes research on how the indigenous biofilm in thepresence of toxic chemicals may provide an effective, indirect surrogate response with eitherturbidity or UV254. Rotating annular bioreactors and pipe loops were used to quantify the effectthat the biofilm has on the turbidity and UV254 measurements. The hypothesis is that, if toxicchemicals are added to the distribution system, the biofilm would die and slough off to an extentthat would change the UV254 absorbance and light scattering of the water so that relativelyinexpensive monitors could detect the event. In previously documented work, three reactorswith 20 PVC coupons in each were used to acclimate the biofilm for at least six weeks. Thenumber of biofilm cells on each coupon was enumerated using automated fluorescencemicroscopy. The coupons were submersed into beakers with four potential chemicalcontaminants: aldicarb, cyanide, arsenate and fluoroacetate. The concentration of thecontaminants was less than 1 mg/L, a concentration that was shown to be feasible to achieve in adistribution system in previous research. The turbidity was measured after 1, 8 and 48 minutesto determine the response time of the biofilm to the chemicals. In all cases, the turbiditysignificantly increased after one minute and in most cases continued to increase at the longertimes. The batch data indicate that turbidity may be a useful surrogate monitor for chemicalcontamination due to die-off of the indigenous biofilms. Biofilm sloughoff and increasedturbidity response occurred in the present study in which a commonly used turbidity monitor anda simple, inexpensive turbidity sensor monitored a simulated distribution system inoculated withfive common industrial chemical contaminants. This paper details the results of the pipe loop studyat the conference and describes the inexpensive turbidity monitor that has been developed. Includes 14 references, figures.

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Edition: Vol. - No. Published: 11/01/2006 Number of Pages: 18File Size: 1 file , 690 KB