The Detection of Organic Pollution by
Automated COD
A. H. MOLOF, Associate Professor of Civil Engineering
New York University
University Heights
New York, New York
N. S. ZALEIKO, Staff Consultant
Technicon Co.
Chauncey, New York
A rapid automated analytical test which can indicate the strength of a process
stream is the goal of operating people in every field including water pollution.
The strength of a waste water, whether sewage, industrial waste or a combination
of both, can usually be indicated by its total organic content.
The total organic content in a waste water has been determined by manual
analysis principally from the biological (BOD) and chemical (COD) viewpoints.
There are, of course, specific tests for organic chemicals, i.e., phenols and ABS;
however, they are not of the total organic type to be considered here.
The use of the biological test, biochemical oxygen demand (BOD), has been
the primary method used to determine the strength of a waste water whether it be
domestic sewage, industrial waste, or river water. However, there are inherent
disadvantages to the BOD test, i. e., time delay of five days, biological seed
variability, chemical effects through toxicity, and the possible need to acclimate
the seed. In order to attempt to overcome these disadvantages, the chemical oxygen demand (COD) test which requires a time of a few hrs has been used (1) as a
supplement to the BOD test and (2) as an individual test per se. However useful the
COD is as a guide, it does not completely replace the BOD in supplying biological
information to pollution authorities since the COD is based on chemical oxidation
while the BOD is based on biological oxidation.
The Standard Methods (1) COD procedure based on the work of Moore, Kroner
and Ruchhoft (2) uses a mixture of sulfuric acid and potassium dichromate as the
basic chemical oxidant. The use of this chemical oxidation to determine the
level of organic pollutants and its application to the various fields of pollution,
i. e., waste water and river water, has been described on numerous occasions (2, 3,
4,5, 6, 7). Specifically, the COD test has been used for industrial waste treatment
plant control as well as industrial process loss detection and control. The COD
test has provided a method for detecting toxic conditions and the presence of biologically resistant organic materials. In conjunction with BOD, the COD can indicate the degree of biological stability of a stream and, in many cases, be used
to predict the BOD. It should be noted that the COD is a measurement of the total
organic content and does not solely indicate the carbon content of the sample.
It is the objective of this paper to describe the results of the work started in
late 1961 by the authors in converting the manual COD as outlined in Standard
Methods to an automated chemical test. It is the authors' belief that this work
will enable the use of the COD test to be extended even further by providing a
continuous, automated analysis for continuous pollution testing, monitoring, and
control.
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