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| The
District has for many years maintained an ongoing odor control
program in order to minimize the effect of wastewater odors on the
community. Customer feedback on wastewater odors is an important
part of this program as odors are effected by weather, temperature,
strength of flow, time of day and many other biological, chemical
and environmental factors. Anytime a customer detects a wastewater
odor, they should call the District and
register a
complaint so staff can investigate the
situation. Customers should also check their homes for dry traps in
their internal plumbing and check roof vent stacks for obstructions
as these can contribute to odors entering homes directly. |
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| The
District first began its odor control program in 1990, just four
years after serving its first customers. The most common source of
odor complaints historically has been the District's Meridian
Corridor Lift Station (#2) at the southeast corner of 106th &
Springmill Road. The District has taken the challenge of controlling
wastewater odors seriously and has evaluated a number of different
mechanisms to control odors and be a good neighbor and community
citizen. |
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| There
are numerous products marketed for odor control and many of these
can become quite expensive, either through high up front equipment
costs or through recurring operating costs for chemical additives.
As such, in order to be good financial stewards, the District must
balance costs with benefits continuously. For instance, as part of
the District's plans to upgrade Lift Station #2, solutions are
presently being weighed by the District with its consulting
engineers. Among the options being considered is to enclose the
entire lift station site within an attractive, residential-appearing
structure. This concept was first broached in July 2003 so initial
evaluations of the concept are currently underway. |
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Beginning in 1990, deodorizers and masking agents were used to clean
the lift station wet well walls and a steam cleaning company was
utilized to wash them down. The chemicals were expensive, required
large and frequent applications and was not cost effective for the
results generated. The steam cleaning was not capable of reaching
the majority of the wet well. Today, District staff use owned
equipment to periodically wash down the lift stations. |
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| In 1992,
the District conducted an analysis using ozone generating equipment
from a local manufacturer (Tri Med Environmental Research Co.) at
Lift Station #2. A box fan was used to blow ozone into the station's
wet well but the results were insignificant and the project was
abandoned as ineffective and potentially damaging to concrete and
metal surfaces within the wet well. |
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| By 1994,
the District had progressed to working with a major wastewater
industry supplier to formally analyze potential odor contributors in
the wastewater stream, the most common of which is Hydrogen Sulfide
(H2S) which is a chemical byproduct of decomposing organics in
wastewater. "Grab" samples were taken from targeted areas and it was
determined that H2S was the primary odor agent and the force main
from the Laurelwood Lift Station (District Station #8 located south
of 106th Street off of Ditch Road) was identified as the largest
contributor. |
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| Once
this determination was made, District staff began to research
chemical additives and processes which could prevent or reduce the
generation of H2S as an odor causing agent. In 1996, the District
purchased a Bioxide chemical feed system from US Filter which treats
the Station 8 force main by dosing the wet well with nitrate salts
which are supposed to prevent the formation of H2S. This equipment
(see photos below) is still in place and has been proven to prevent
H2S formation from this source. The one time unit cost and
installation was $8500.00 and requires an annual cost of $4000.00
worth of chemicals. |
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| In 1997,
the District purchased a Flygt Mixer primarily to address the
excessive amount of grease collected at Station 8. District staff
believed this also contributed to the reduction of odor by
introducing air back into the sewage preventing it from going septic
while also suspending solids long enough to be pumped through the
system. The District currently has two of these units, both are at
stations the directly contribute to Lift Station 2. |
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| Again in
1997, the District evaluated another ozone unit for Lift Station 2,
this time in a different configuration where air is drawn from the
wet well and passing it by ozone in the onsite unit to neutralize it
before releasing it into the atmosphere. The District currently has
three such units in service. The following photo depicts the unit at
Lift Station 2. |
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| During
an upgrade in 1998 at Lift Station 1 (behind the Brooks Bend
subdivision near 99th & Keystone), the District added a Purifil air
scrubber unit which draws air through a combination of charcoal and
other medias. In addition, District staff worked with the Brooks
Bend homeowners association to install a row of evergreen trees
around the lift station and along the lake berm in order to provide
a visual screen for the station as well. While complaints about the
station's odor have been eliminated, staff remains unsatisfied with
the unique odor omitted from the unit's media. Annual cost of
replacing the media is $3600.00. The District currently has 2 of
these units (see following photos). |
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| In
continuing its efforts to evaluate a variety of types of equipment
under different lift station conditions, the District purchased a SulfaTreat Drum System for $2500.00 for Lift Station 10 in the
Ashbrook Subdivision in 1998. This unit also draws air through a
charcoal media (see following photo) and is smaller than the Purifil
units. While complaints about the station's odor have been
eliminated, staff remains unsatisfied with the unique odor omitted
from the unit's media. |
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| By 2001,
District staff had also evaluated extending the wet well vents above
ground to incorporate a chamber of chemical deodorizer so that
exhausted air comes into contact with the chemical right before it's
released into the atmosphere. This was marginally effective and
abandoned for more effective means. In 2002, the District added
signage at all lift stations with a phone number and our website
address to encourage feedback from customers and other stakeholders.
In addition, during a 2002 upgrade to Lift Station 2, the District
added a third pump with a mix-flush valve attachment which aids in
odor reduction by keeping the solids suspended so they will not
collect in the wet well and become septic and can be more easily
pumped through the system vs. During that same upgrade, an attempt
was made to further reduce odors by venting the manhole at the head
of the lift station but this arrangement was unsatisfactory and the
unit was re-piped to its original configuration. |