In Search of the Silver Bullet
The ultimate pathogen destroyer
Our search at Clearwater Solutions began about 5 years ago.
Pathogens were starting to come to the forefront at municipal and state levels
as a pollutant of concern. Tourism was acting as the driving force to start
requiring stormwater permit writers to include a total maximum daily load (TMDL)
for pathogens in impaired water bodies. And our industry was scrambling to try
and find products that would help destroy or limit pathogen bypass in
manufactured stormwater systems.
I mention tourism as the driving
force because, as we all know, tourism equals profit. In this case, the
complaints were coming from people who had vacationed in various locations
around the United States and were getting sick while swimming in our water
playgrounds. High levels of E. coli, streptococcus, and other bacteria
were identified as the cause. The EPA was contacted, state and city water
authorities were put to the task, and pathogen TMDLs were born.
During this time, we received a
patent on our stormwater filter device called the ClearWater BMP. Designed to
fit in sidewalk curb inlets and grated storm drain systems, the multi-chambered
ClearWater BMP is a true filter system. Pollutants of concern can be targeted by
changing out the filter media to fit TMDL needs.
|Testing of the pathogen media|
Because our stormwater filter unit
can be tailored to different TMDL needs, we have had to keep up with many kinds
of filter media and their abilities to remove all sorts of contaminants. These
contaminants range from copper, lead, zinc, oil, and phosphates to the large
family of pathogens. Some examples of media that are used in combating these
pollutants are granulated activated carbon (GAC), zeolites, perlite, and other
proprietary media blends. We have researched and used many of these different
types of media and have come to realize that some of these media work well and
others don’t work at all.
Prior to our hunt to locate an
effective pathogen filter media for the ClearWater BMP, we established a set of
four simple rules that the chosen product would have to adhere to. If the
product passed all of our rules but one, it was rejected! The rules read like
- The filter media must have good
water flow capabilities (15 gallons per minute per square foot).
- The filter media must have a
good shelf life while in our unit (6 months-plus).
- The filter media must not
damage downstream aquatic life (required toxicity tests).
- The filter media must eliminate
a high number of pathogens (85%-plus elimination).
We began by evaluating, and
testing touted pathogen media against our four simple rules.
Some products appeared to have good pathogen elimination
rates but were very unpractical due to the large amount of contact time needed
to achieve those rates. Stormwater is always on the move, so limited contact
time is a must!
Another problem that we ran into
was the fact that some products worked well during the first part of a storm but
became quickly useless. We water-tested a well-touted stormwater bacteria media
that quickly clogged with very fine sediment and slowed the water coming through
the media in the ClearWater BMP to one quarter of its normal capacity. This
pathogen media is lightly molded to fit its surroundings. When sediment was
introduced to the water column, the front of the molded media filter rapidly
clogged. We needed a pathogen media that would allow good flow-through
Toxicity of pathogen-destroying
media to downstream aquatic life was also a big concern of ours. Iodine is a
good example of this. It is very effective at taking care of bacteria, but it
can also be highly toxic to downstream aquatic life if not properly controlled.
|Samples taken during testing|
During our research, we approached
a company called AS Filtration and asked to field-test its pathogen media called
Pathex. We had chanced upon some lab results that showed excellent pathogen
media performance under very good flow rates. Lab tests were showing a 99% plus
elimination rate for incoming colonies of E. coli. This piqued our
interest, and AS Filtration agreed to the tests. During this time, we were just
getting ready to start a round of field testing for the ClearWater BMP for the
City of Los Angeles, CA. Engineers for Los Angeles agreed to the addition of the
Pathex media, and several rounds of testing ensued.
University of California – Los
Angeles doctoral engineering students collected influent and effluent samples to
be sent to Los Angeles’ Hyperion Lab for testing. An independent laboratory also
collected samples to help confirm the data.
As you can imagine, we eagerly
awaited the results. We hoped that the field tests would help to confirm the lab
tests that we had seen. We finally received the call that we had been waiting
for. Seven out of eight tests showed that E. coli elimination rates were
98% or better with excellent continual flow rates and no downstream degradation
of aquatic life. At that point, we realized that this was the
pathogen-destroying media that we had been looking for. It passed our four
simple rules, and now pathogen TMDLs could be properly addressed.
Since that time, both Clearwater
Solutions and AquaShield have signed agreements with AS Filtration to be the
exclusive worldwide distributors for the Pathex media. Pathogen TMDLs are the
bane of stormwater managers, and the more tools that they have to take care of
their problems, the easier it is for them to do their job. Pathex is one quality
tool that can help solve the pathogen TMDL issue.