Graduate Thesis Or Dissertation
 

Coliform bacteria associated with redwood and drinking water emanating from redwood tanks

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  • Coliform contamination of a rural water system led to a research project investigating the problems surrounding storage of drinking water in redwood tanks. Field studies of redwood tanks presently in use showed development of large coliform populations (notably, Klebsiella and Enterobacter species) soon after tanks were put into use. This was often accompanied by development of a fungal slime layer on wood staves below the water line. The presence of a chlorine residual in some field tanks successfully prevented growth of coliforms and resulted in potable water. Absence of a residual allowed growth of coliform organisms and resulted in water unsafe for human consumption. Studies involving small laboratory sized redwood tanks supported the field observations. Coliforms first develop on the interior staves of a tank, and soon there develops a layer of slime. The coliforms then shed into the water held within a tank unless a suitable chlorine residual is maintained. Investigation of redwood as the source of coliforms revealed large populations present within the wood structure. Total bacterial counts as high as 10⁴/g and coliform counts as high as 10³/g were obtained using a number of different redwood samples. Both Klebsiella and Enterobacter are present in fresh wood samples, but only Enterobacter persists in older samples. Fresh wood samples from a redwood mill in northern California yielded Klebsiella when incubated in a suitable enrichment medium. This consisted of a modified mFC broth (without rosalic acid) and incubation at 37 C. Coliforms are able to survive in redwood due to growth factors present within the wood structure. A complete taxonomic study of all coliform isolates was performed. The results were then compared to those published by Edwards and Ewing (8). A greater percentage of Klebsiella isolates were shown to produce indole and H₂S than clinical isolates. Indo le production has previously been noted for other environmental isolates (2, 4, 6, 9, 14). Specific compounds present in the water soluble extracts of redwood were also examined as possible growth promoting factors for the environmental coliforms. The carbohydrates and cyclitols (approximately 47% of total water soluble extracts) were shown to be widely utilized as growth factors by Klebsiella and Enterobacter isolates. The phenolic compounds (35% of total water soluble extracts) were shown to be inhibitory to all isolates at the concentrations used. The presence of these compounds in the redwood and their subsequent leaching into the tank interior provide a suitable environment for the growth of conforms. The culmination of this study involved the construction and maintenance of a 1000 gallon redwood water system following guidelines observed in the earlier studies. This tank was provided with a calibrated source of chlorine amendments that could be regulated as needed, and provisions for any number of desired retention times. Need for a suitable period of leaching of growth promoting factors and also for periodic sterilization of the tank interior to prevent slime and coliform development were seen. This system has been in operation for over 7 months with no incidents of coliform contamination of the water.
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