Graduate Thesis Or Dissertation
 

Characterization of bacterial populations and turbidity effects in chlorinated drinking water

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/s1784p03b

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  • The present study was conducted as a three part investigation to (i) examine the incidence, distribution and kinds of standard plate count bacteria present in chlorinated and raw water; (ii) study the ecological role and possible health significance of Aeromonas spp. in distribution water, and (iii) evaluate the effects of turbidity at entry points to a distribution system and the resulting drinking water quality related to the 1 and 5 NTU maximum contaminant limits (MCL). To accomplish these goals, nearly 700 standard plate count (SPC) bacteria were isolated from drinking water and untreated surface water and identified according to a scheme developed to permit the rapid, simple classification of microorganisms to genus, species, or group. Actinomycetes and Aeromonas species were the two most common groups of SPC bacteria in chlorinated distribution water. Aeromonas spp. and Enterobacter agglomerans were the two most common groups of (SPC) bacteria in raw water. Identification of bacterial populations before and after contact with chlorine (1-2 mg/1) for 1 h revealed that chlorination selected for gram-positive bacteria. Water that contained high densities of bacteria known to be antagonistic to coliforms had low coliform isolation rates. The membrane filtration technique for enumerating SPC bacteria recovered significantly higher numbers (p <0.001) than the standard pour plate technique. Aeromonas were recovered from over 30% of 132 drinking water samples collected over an 18 month period. Eighty-four percent of the fifteen isolates tested demonstrated a cytotoxic response on Y-1 adrenyl mouse cells. None of the strains were enterotoxigenic in the rabbit ligated ileal loop test nor exhibited pilliation or significant mannose-resistant adhesion to human buccal cells. All Aeromonas strains were identified as A. sobria. All the organisms were resistant to ampicillin and sensitive to chloramphenicol, kanamycin, streptomycin, and tetracycline. Total coliform levels did not correlate with Aeromonas densities in distribution water. Eight-five percent of the time Aeromonas occurred in distribution water when no coliforms were detected by either the membrane filter or MPN techniques. A significant correlation (p <.01) existed between standard plate count levels and Aeromonas. In order to define interrelationships between elevated turbidities and the efficiency of chlorination in drinking water, experiments were performed to measure bacterial survival, chlorine demand and interference with microbiological determinations. Results indicated that disinfection efficiency (log fold decrease in coliform numbers) was negatively correlated with turbidity and was influenced by season, chlorine demand of the samples, and the initial coliform level. Total organic carbon was found to be associated with turbidity and was shown to interfere with maintenance of a free chlorine residual by creating a chlorine demand. Interference by turbidity and other factors with coliform detection could be demonstrated by the recovery of typical coliforms from apparently negative membrane filters. The magnitude of coliform masking in the membrane filter technique was found to increase as the turbidity of the chlorinated samples increased. Coliform densities were underestimated as much as 2.3 logs. Statistical models were developed to predict the impact of turbidity on drinking water quality. The results indicate the need to control turbidity in potable water so as to maintain adequate drinking water quality.
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