Environmental Engineering Reference
In-Depth Information
are fixed, and only certain points in the system can be monitored. In addi-
tion, the number of monitoring locations required to capture the physical,
chemical, and biological complexity of a system can be prohibitive. The use
of portable sensors can overcome this problem of monitoring many points
in the system. Portable sensors can be used to analyze grab samples at any
point in the system but have the disadvantage that they provide measure-
ments only at one point in time.
Sensors for Monitoring Chemical, Biological,
and Radiological Contamination
Toxicity tests measure water toxicity by monitoring adverse biological effects
on test organisms. Toxicity tests have traditionally been used to monitor
wastewater effluent streams for National Pollutant Discharge Elimination
System (NPDES) permit compliance or to test water samples for toxicity;
however, this technology can also be used to monitor drinking-water dis-
tribution systems or other water/wastewater streams for toxicity. Currently,
several types of biosensors and toxicity tests are being adapted for use in the
water/wastewater security field. The keys to using biomonitoring or biosen-
sors for drinking water or other water/wastewater asset security are rapid
response and the ability to use the monitor at critical locations in the sys-
tem, such as in water distribution systems downstream of pump stations
or prior to the biological process in a wastewater treatment plant. Several
different organisms can be used to monitor for toxicity (including bacteria,
invertebrates, and fish), but bacteria-based biosensors are ideal for use as
early-warning screening tools for drinking water security because bacteria
usually respond to toxins in a matter of minutes. In contrast to methods using
bacteria, toxicity screening methods that use higher level organisms such as
fish may require several days to produce a measurable result. Bacteria-based
biosensors have recently been incorporated into portable instruments, mak-
ing rapid response and field testing more practical. These portable meters
detect decreases in biological activity (e.g., decreases in bacterial lumines-
cence), which are highly correlated with increased levels of toxicity. At the
present time, few utilities are using biologically based toxicity monitors to
monitor water/wastewater assets for toxicity, and very few products are now
commercially available. Several new approaches to the rapid monitoring of
microorganisms for security purposes (e.g., microbial source tracking) have
been identified; however, most of these methods are still in the research and
development phase.
Arsenic Measurement Systems
Arsenic is an inorganic toxin that occurs naturally in soils. It can enter water
supplies from many sources, including erosion of natural deposits, run-
off from orchards, runoff from glass and electronics production wastes, or
