dilution water. This figure is multiplied by the dilution factor and the final result is the
BOD of the wastewater.
(2) Evaluation of BOD. The BOD has proven to be the best single test for
measuring the progressive and overall efficiency of wastewater treatment processes
and for indicating the probable effect of the plant effluent upon the receiving body of
water. The major disadvantages of the test are the length of time necessary for
obtaining values plus the fact that the results cannot immediately be translated into
control procedures. The test is relatively complicated, but in the hands of the skilled
operator meaningful results are obtained.
d. Dissolved Oxygen. The dissolved oxygen determination is made to
ascertain the quantity of atmospheric oxygen, which is dissolved in the given sample of
water or wastewater. It is also the major analytical step in the BOD determination. In
collecting a sample for this test, extreme care must be exercised in order to avoid the
entertainment or absorption of any oxygen from the air. The temperature of the
wastewater sample should also be recorded to the nearest degree Celsius. The test
should be carried out immediately after collection of the sample.
e. pH. The pH test measures the acidity or alkalinity of wastewater and is useful
in indicating whether it is fresh or septic during the collection system or during any other
wastewater treatment process. The test is performed by using certain dyes or
indicators which exhibit color changes at different levels of hydrogen ion concentration.
If the sample to be tested is colored, electrometric instruments are used to make the
f. Chlorine Demand. The chlorine demand test of a wastewater is made to
determine the chlorine required to be added to the wastewater to produce a trace
chlorine residual. The chlorine demand is determined by adding a sufficient quantity of
a standard chlorine solution to a sample of wastewater until a yellow color is developed
with the addition of orthotolidine solution. This amount is called the immediate chlorine
g. Residual Chlorine. Residual chlorine can be determined by the old orthotol
iodine test or the newer N, N-diethyl-p-phenylenediamine (DPD) test. The orthotolidine
test can be used until new equipment is acquired. When new equipment is acquired,
the DPD test equipment should be used. Both tests consist of adding a small quantity
of the appropriate reagent to the wastewater and comparing the resulting color with the
correct color standard. Each test is used to measure the chlorine residual in the plant
effluent; however, the DPD method is preferred.
a. General. Wastewater samples are collected by plant operating personnel for
regular, periodic laboratory tests to assist in proper plant operation and control. Army
Medical Department personnel collect samples for the purpose of conducting
investigations and surveys.