Water & Wastewater Asia July/August 2020

34 FOCUS
In addition to measuring ATP, adenosine
monophosphate (AMP) can also be
measured using the same technology. The
ratio of ATP to AMP can be used to assess
the dormancy of the population. If most
exists as ATP, it’s an indication of a healthy,
growing population. If the amount of AMP
is higher, it’s an indication of dormancy
and that the population may be stressed
but not necessarily killed.
Of various microbiological testing techniques, ATP testing forms the
base of the pyramid as a daily monitoring tool
ATP
ATP testing is at the frontline of microbial
control and can be applied to almost
anywhere within the system. Test kits are
available to test all sample types: fluids,
solids, or surfaces so that both planktonic
and sessile microbiological populations
can be assessed. ATP provides nonspecific
results for the concentration of
the total microbial community in units of
ATP per mL, g or surface area. Equipment
is portable and easy to use in the field,
so that samples can be tested as soon
as they are collected so the population
is measured accurately. Versatility to
perform testing in the field prevents
sample degradation during shipping which
is a concern when testing is not available
at or near the sampling point. It also
reduces the time between measurement
and corrective action, if needed. While the
susceptibility of samples to change during
shipping depends on the composition
of the microbial community, oxygen
conditions, and nutrient supply, it is
preferred to test sooner rather than later in
every case.
act as a forewarning to alert operators
to an increase in microbes, either due to
their introduction from outside the system,
or from a decreased biocide efficacy. In
the case that ATP testing indicates the
presence of a larger population compared
to the baseline, more advanced techniques
(such as qPCR) can be deployed to
determine the identity of the increased
population to determine if they represent
a MIC risk.
qPCR
qPCR is a molecular microbiological
method that is used to identify and
quantify specific DNA (or RNA) sequences
from microorganisms. A specific probe and
primer set must first be developed to allow
the measurement of the desired DNA. This
requires knowledge of the unique genetic
structure of the targeted organism(s).
Many DNA sequences are available in
publicly compiled databases that can be
used to design qPCR probes.
qPCR testing can be performed in under
two hours, which gives unprecedented
rapid access to data that otherwise
ATP testing can be performed in less than
five minutes per sample, and as such is an
easy way to monitor the effectiveness of
a biocide program to ensure microbes are
kept in check. ATP should be used daily or
a few times weekly as this quick test will
While microbiologically influenced corrosion (MIC) is not a unique form of corrosion, it is unique in
that microorganisms are ubiquitous in almost all of the systems which are concerned with MIC, which
can make risk mitigation difficult.
Photo credit: Andrew Martin
July / August 2020 • waterwastewaterasia.com