lists several examples of these types of
The three biological organisms present in
wastewater are bacteria, viruses, and parasites.
Sewage consists of vast quantities of bacteria,
most of which are harmless to man. However,
pathogenic (disease-causing) organisms such as
typhoid, dysentery, and other intestinal disorders
may be present in wastewater. Tests for total
coliform and fecal coliform nonpathogenic
bacteria are used to indicate the presence of
pathogenic bacteria. Because it is easier to test for
coliforms, fecal coliform testing has been accepted
as the best indicator of fecal contamination. Fecal
coliform counts of 100 million per 100 milliliters
may be found in raw domestic sewage. Detectable
health effects have been found at levels of 2,300
to 2,400 total coliforms per 100 milliliters in
recreational waters. Disinfection, usually chlorina-
tion, is generally used to reduce these pathogens.
Breakdown or malfunctions of chlorination
equipment will probably result in excessive
discharge of pathogenic organisms and can
seriously affect public health.
Bacteria can also be classified according to
their dissolved oxygen requirement. Aerobic
bacteria are bacteria that require dissolved oxygen
to live. Anaerobic bacteria cannot live if dis-
solved oxygen is present. Facultative bacteria can
live with or without dissolved oxygen.
Wastewater often contains viruses that may
produce diseases. Outbreaks of infectious
hepatitis have been traced through water systems
because of wastewater entering the supply.
s e d i m e n t a t i o n , f i l t r a t i o n , a n d
disinfection, if used efficiently, usually provide
acceptable virus removal.
There are also many species of parasites
carried by wastewater. The life cycle of each is
peculiar to the given parasite. Some are dangerous
to man and livestock, particularly during certain
stages of the life cycle. Amoebic dysentery is a
common disease caused by amoebic parasites.
Chlorination, chemical precipitation, sedimenta-
tion, or sand filtration is used to ensure protec-
tion against parasites.
Samples of sewage are taken to find out how
well a treatment plant is working and what
operating changes may need to be made, Some
samples show how much the plant is reducing
pollutants like BOD, solids, and so forth. Raw
sewage entering the plant must be tested as well
as the effluent from the plant and the receiving
stream above and below the discharge point to
determine how well the plant is removing
pollutants. Since wastewater flows often change
a great deal, daily sampling is suggested.
A sample should be taken in a way that will
represent the wastewater being treated. No
matter how good the lab analysis is, if the
sample was not correctly collected, the lab data
will not be correct. With the large changes in
composition and flow rate, getting a represen-
tative sample can be very hard. Careful thought,
planning, and training must be used to develop
and carry out a good sampling program.
Samples may be taken by hand or auto-
matically. Taking samples by hand may be as
simple as tying an open bottle to a pole that can
be lowered into the wastewater. Table 10-7
explains some of the things that should be done
when taking samples by hand. The automatic
samplers may be made by the operator or bought.
A grab sample is a single sample of wastewater
taken over a short span of time, usually less than
15 minutes. This type of sample yields data
about the wastewater at one time and place.
The grab sample should be used where the
wastewater does not change suddenly or change
a great deal. For example, grab samples may be
used to determine pH and temperature. Grab