水中细菌来源与处理
Source
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
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.
