Raw water is contaminated with numerous microorganisms. Microorganisms can include viable bacteria, nonviable bacteria, slime, algae, viruses, and cysts.
Measured bacterial levels in raw water supplies are significantly affected by the enumeration culture media. A heterotrophic plate count, as outlined in Standard Methods for the Examination of Water and Wastewater Section 9215, is used with standard plate count agar (PCA) to determine the total viable bacteria levels in raw water. The literature indicates that only a small fraction of bacteria in Drinking Water are detected by even the most selective culture media.
R2A culture media may show more bacteria values than other media, it requires a much longer incubation time period than PCA. This inhibits the ability to detect a total viable bacteria problem in time. A maximum total viable bacteria Action Limit stated in the General Information Section of the USP is 500 cfu/mL.
There are some critical problems that should be addressed regarding the presence of bacteria and microorganisms in raw water supplies. If the raw water treated with chloramines as the residual disinfectant, it should be recognized that three chloramine compounds will exist. The concentration of each compound is a function of pH and affects the disinfecting properties.
Large microorganisms, such as cysts, require more time for total destruction of cell. To remove complete microorganisms from water multiple chlorination steps can be used in treatment process. Residual disinfectant should not be considered as a source operation for removing either Giardia or Cryptosporidium.
Total Coliform bacteria should be absent in Drinking Water. In raw water collecting, if we collect 40 samples per month, no more than one sample can indicate coliform positive per month. If sample is positive for Total Coliform must be analysed for either Escherichia or fecal coliform. The presence of Fecal Coliform and E. coli indicate that the water is contaminated with human or animal waste containing pathogens. Procedures for determining both total coliforms, fecal coliform and E. coli, are presented by Standard Methods for the Examination of Water and Wastewater Section 9221.
The nature of bacteria present is related to available nutrients. Bacteria are extremely flexible in adapting to environmental conditions. When residual disinfectant is added to a raw water supply, or attempts are made at removing inorganic and organic nutrients, the extremely low nutrient conditions produce a situation where the majority of the bacteria present are classified as gram negative. These bacteria do not retain Gram’s stain in a standard staining method. The presence of objectionable gram negative species of bacteria is a concern for pharmaceutical and related water purification applications, from raw feed water to product water. Gram-negative bacteria, adapting to low nutrient environments, can survive by maximizing the surface area to volume ratio.
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