42    ATP TOXICITY TEST IN ACTIVATED SLUDGE SYSTEMS
PR. Senthilnathan, Senior Environmental Engineer
Merck & Company
Elkston, Virginia 22827
J. J. Ganczarczyk, Professor
Department of Civil Engineering
University of Toronto
Toronto, Ontario, M5S 1A4, Canada
INTRODUCTION
The microbial population in activated sludge plants are vulnerable to toxic substances in the
influent. Particularly, the municipal sewage treatment plants experience sometimes unexpected upsets
due to toxins discharged by industries. In order to prevent such upsets, toxicity screening tests of
industrial discharges are recommended.
Among various methods available for the short term toxicity screening, adenosine triphosphate
(ATP) assay has gained a broad popularity. At present, many commercial testing equipment and
protocols are available to measure the level of ATP in activated sludge. Generally, the short term
toxicity screening test is carried out as follows: the suspected influent is added to a sample of the
activated sludge and aerated while another sample of the activated sludge is aerated under endogenous
conditions as a control. At selected time intervals (e.g. 30, 60 and 120 minutes), the level of ATP in the
test and control activated sludge is determined. A substantial decrease in ATP level is considered to
indicate the toxicity of the tested wastewater.
However, some precautions are necessary for a correct application of this method. This paper
identifies some measures which have to be considered to avoid wrong conclusions.
BACKGROUND
Toxicity testing methods using microorganisms has an excellent potential in predicting the toxicity
of wastewaters. Various methods for this purpose are described elsewhere.',2 Among various methods, respirometry, ATP measurement, and dehydrogenase activity measurement (for e.g. by 2, 3, 5-
triphenyl tetrazolium chloride [TTC]) are broadly used for measuring the toxicity of wastewaters to
activated sludge.
Several investigators reported ATP measurement as a useful tool for measuring viable biomass
concentration1"20 applied the ATP measurement for predicting toxicity to activated sludge. For toxic
substances causing uncoupling of oxidative phosphorylation, ATP measurement was more sensitive
than respirometry in predicting the toxicity.21
Adenosine triphosphate (ATP), a universal constituent of living cells, plays an important role in
bacterial metabolism. It is also known as the "universal energy currency". Hydrolysis of ATP to ADP
(adenosine diphosphate) yields about 7 kcal/mol of ATP. ATP decomposes rapidly upon cell death.
ATP is usually measured by a bioluminescent enzymatic reaction as shown below.
Mg+ +
Luciferin + Luciferase + ATP > Luciferin-Luciferase-AMP + Pyrophosphate
♦ o2
Luciferin-Luciferase-AMP >Oxyluciferin + Luciferase + AMP+ C02 + Light
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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