Source of Bacteria
Bacteria are tiny organisms occurring naturally in water. Not all types of bacteria are harmful. Many organisms found in water are of no health concern since they do not cause disease. Biological contamination may be separated into two groups: (1) pathogenic (disease causing) and (2) non-pathogenic (not disease causing). Pathogenic bacteria cause illnesses such as typhoid fever, dysentery, gastroenteritis, infectious hepatitis, and cholera. All water supplies should be tested for biological content prior to use and consumption. E.Coli (Escherichia Coli) is the coliform bacterial organism that is looked for when testing the water. This organism is found in the intestines and fecal matter of humans and animals. If E.Coli is found in a water supply along with high nitrate and chloride levels, it usually indicates that waste has contaminated the supply from a septic system or sewage dumping, and has entered by way of runoff, a fractured well casing, or broken lines. If coliform bacteria are present, it is an indication that disease-causing bacteria may also be present. Four or fewer colonies / 100 ml of coliforms, in the absence of high nitrates and chlorides, implies that surface water is entering the water system. If pathogenic bacteria is suspected, a sample of water should be submitted to the Board of Health or US EPA for bacteriological testing and recommendations. The most common non-pathogenic bacteria found in water is iron bacteria. Iron bacteria can be readily identified by the red, feathery floc that forms overnight at the bottom of a sample bottle containing iron and iron bacteria.
Treatment of Bacteria
Bacteria can be treated by microfiltration, reverse osmosis, ultrafiltration, or chemical oxidation and disinfection. Ultraviolet sterilization will also kill bacteria; but turbidity, color, and organic impurities interfere with the transmission of ultraviolet energy and may decrease the disinfection efficiency below levels to insure destruction. Ultraviolet treatment also does not provide residual bactericidal action; therefore, periodic flushing and disinfection must be done. Ultraviolet sterilization is usually followed by 0.2-micron filtration when dealing with high purity water systems. The most common and undisputed method of bacteria destruction is chemical oxidation and disinfection. Ozone injection into a water supply is one form of chemical oxidation and disinfection. A residual of 0.4 mg/i must be established and a retention time of four minutes is required. Chlorine injection is the most widely recognized method of chemical oxidation and disinfection. Chlorine must be fed at 3 to 5 ppm to treat for bacteria and a residual of 0.4 ppm of free chlorine must be maintained for 30 minutes in order to meet US EPA standards. Reverse Osmosis will remove over 99% of the bacteria in a drinking water system.
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