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Stormwater Screening Adds
Capacity to Collection Systems
Guest article by Fritz Egger, JWC Environmental
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the rapidly evolving realm of stormwater treatment, city planners
and managers have limited options and a dizzying array of
regulations to deal with. They must somehow get antiquated combined
sewer systems to magically produce more capacity during rain events
and ensure cleaner discharge without overwhelming their local
treatment plant. Moreover, they must purchase and construct new
stormwater treatment systems out of their own municipal budget. It’s
a tall order.
However, there is hope. Environmental
equipment manufactures are rapidly developing innovative machines
that squeeze more treatment capacity out of current collection
systems, while also meeting the EPA’s mandate for cleaner stormwater
Where Things Stand
Combined sewer systems are used in
approximately 772 U.S. cities and collect rainwater runoff, domestic
sewage, and industrial wastewater in the same pipe. Most of the time
combined sewer systems transport flow to a sewage treatment plant
where it is properly treated and then discharged into a water body.
However, during periods of heavy rainfall or snowmelt the wastewater
volume in a combined sewer system can exceed capacity and begin to
strain the pipes and treatment plant. For this reason, combined
sewer systems discharge excess wastewater and stormwater directly
into nearby streams, rivers or other water bodies.
overflows, called combined sewer overflows (CSOs), contain not only
rainwater but also untreated human and industrial waste, toxic
materials, floating debris and trash. They are a major water
pollution concern for local, state and federal regulators. CSOs may
be thought of as a type of urban wet weather discharge, which means
that, like sanitary sewer overflows (SSOs) and stormwater
discharges, they are discharges from a municipality's wastewater
conveyance infrastructure that are caused by precipitation events
such as rainfall or heavy snowmelt.
EPA's CSO Control Policy, published
April 19, 1994, is the national framework for management of CSOs.
The Policy provides guidance on how communities with combined sewer
systems can meet Clean Water Act goals in a flexible and
In early 2004 the agency finalized
its “Draft Policy on Blending”, which aims to establish consistent
national guidelines on the practice of blending that is used by
municipal sewage treatment facilities to manage high flows
associated with storm events. The act of blending is to bypass some
of the wet weather flow from a portion of the plant’s treatment
process and then to blend it with fully treated wastewater prior to
discharge. The final discharge, however, is still subject to normal
discharge requirements and limitations.
How Stormwater Screens Can Help
There is a clear trend towards fine
screening of stormwater prior to discharge. Moreover, primary
treatment is gaining acceptance as an important step before
stormwater is routed for storage, blending or discharge. Excellent
equipment is coming on the market to assist operators in handling
wet weather flows. For example, JWC Environmental’s Storm Monster™ ensures combined stormwater systems operate just as they
should: allowing excess water to pass through preliminary treatment
(screening to 6mm) but trapping pollution, floatables and trash
inside the plant.
The Storm Monster™ is an example
of a high performance band screen designed for installation on the
pre-weir side of a wastewater channel or CSO, and it automatically
activates when flow reaches the top third of the channel. The
Stormsceen’s unique "dog-leg" design increases the hydraulic
capacity of the screen by allowing stormwater to enter through the
bottom and top which improves flow rates by up to 90% over similar
screens. This design nearly doubles the flow of previous stormwater
screens. The "dog-leg" shape also positions the clean-off brush
above the highest waterline so it is never submerged and can operate
Another advantage of the Storm
Monster™ is the advanced panel design. Stainless steel perforated
panels are constructed with 6mm holes on 8mm triangular pitch (51%
open area). Each panel is individually mounted into two endless
conveyor chains forming the screen band. The panels have moving
stainless steel side plates that form a continuous seal against
fixed plastic strips running around the submerged areas to prevent
unscreened material from entering the stormwater overflow.
screen rotates to move solids to the downstream end of the channel
where they are removed by a solid clad cleaning brush. The brush
features an adjustment mechanism and is supported by
self-lubricating bearings. The moving screen technology replaces
previous bar screen designs which used long parallel bars to prevent
solids from passing; however, trash and floatables simply turned
parallel to the bars and would pass into local waterways negating
the benefits and cost of installing a screening system.
Compact design and ease of
installation are also important. The Stormscreen is designed to fit
in tight areas such as wet wells, pumping stations, in front of a
headworks building and elsewhere in the collection system and
requires little, if any, civil work to install. It’s also low
maintenance with the reliable clean-off system and sturdy stainless
There is a second screening option:
removing solids in remote locations. This involves installing a
finescreen, bandscreen or bar screen in pump stations or CSO
discharge locations and handling the wastewater screenings at the
site. A conveyance system and screenings washer compactor is needed
to handle the voluminous amounts of material removed from the
channel, but it can be done.
Screening stormwater is a
cost-effective and proven way to successfully manage wet weather
flows and comply with regional and federal regulations. It also
helps plant managers cut costs by increasing the capacity of their
collection system and better manage the flow entering the treatment
About JWC Environmental
JWC offers a unique line of
all-in-one screening equipment called the Monster Separation Systems™.
It combines the capture efficiency of a high-tech Finescreen Monster™,
or Chain & Rake Monster with the outstanding solids handling
capacity of a Screenings Washer Monster®. For smaller flows (those
up to 60 MGD) the company offers the Auger Monster screen, which is
a combined screen and washer compactor all-in-one.
Contact our author:
Mr. Fritz Egger
Director of Marketing
290 Paularino Ave.
Costa Mesa, CA 92626
Telephone: 949-833-3888 or 800-331-2277
Fax (949) 833-8858
Web site: http://www.jwce.com/
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