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Public
Education
Wastewater
Treatment Plant Tour
click on images for larger view
North Topeka Wastewater Treatment Plant built
1996
(artist rendition) |
The
North Topeka Wastewater Treatment Plant completed May 1996,
at a cost of 29.3 million dollars, is a state-of-the-art 12
million gallon per day (mgd) Complete Mix Activated Sludge Process
(CMAS). The CMAS process introduces the primary treated (settled)
wastewater in such a way to ensure that incoming wastes are
rapidly and uniformly dispersed throughout the aeration tank.
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| In
so doing the waste is uniformly dispersed to the microorganisms
responsible for the stabilization of the waste. This process
requires much larger basin volume and waste residence time
but allows for the cultivation of the proper microbes (nitrobacter
& nitrosomonas) necessary to oxidize ammonia, which is
toxic to fish, to the nontoxic nitrate thereby protecting
the aquatic habitat of the microorganisms and fish that reside
in the Kansas River.
The
Water Pollution Control Division has taken advantage of the
North Topeka's ability to nitrify by diverting approximately
5.0 mgd of the Oakland Wastewater Treatment Plants typical
flow of 16.0 mgd to the North Topeka Wastewater Treatment
Plant in order to improve the overall quality of Topeka's
wastewater discharge.
The
North Topeka Wastewater Treatment Plant is equipped with odor
control (utilizing both carbon & hypochlorite), nitrification,
disinfection-neutralization, lime stabilization of biosolids,
and a state-of-the-art distributive control system which enables
the wastewater treatment operator to monitor all the plant
processes from a single location. |
(Tour
of North Topeka Wastewater Treatment Plant begins here)
Preliminary
Treatment
Top to bottom view of
bars in the flow channel. |
The
first step in treating the wastewater entering the treatment
plant is to remove the debris (rags, sticks, etc.) and grit
(sand & gravel). This is a two step process. First the debris
is removed using a bar screen. A bar screen is composed of a
series of bars spaced typically 3/4 inches apart in the path
of the wastewater flow for the purpose of straining the wastewater
of debris, which might |
| interfere
with the operation of pumps, valves, and
other equipment in the wastewater treatment process down stream.
This debris (screenings), which has been removed, is then sent
to the landfill for burial. |
Screened material caught on the bar screen is raked up and
dumped into wheelbarrow for burial at landfill.
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The
wastewater then continues on to the next step of the preliminary
treatment, which is the removal of grit. If not removed, the
grit causes accelerated wear and tear on pumps and valves. The
material is removed at the North Topeka Wastewater Treatment
Plant in the cyclone separator. The cyclone separator acts as
a centrifugal separator in which the heavy particles of grit
and inorganic solids are separated by the action of a vortex
and discharged separately |
| from
the lighter (organic) particles and the wastewater. The heavier
material (grit), after settling is removed and sent to the landfill
for burial. |
Primary Treatment
Primary Clarifier with skimmer for oil & grease removal.
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Although
wastewater is typically 99.99 % water and just 0.01% waste material,
the waste material if not removed would have a significant deleterious
affect on our environment. The primary treatment process, which
consists of parallel tanks (clarifiers), enables the separation
of heavy solids (fecal matter) and floating solids (oil &
grease) from the wastewater. The clarifiers are sized to allow
enough |
| quiescent
time (typically 2-4 hours)
so that the fecal matter can settle out and so the oil &
grease can float. The skimmer makes a revolution every half
hour to skim grease and floatables.
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Empty primary clarifier showing solids collector mechanism
in the tank bottom. |
As
the heavier than water fecal matter settles to the bottom of
the clarifier, it is removed from the bottom by scraping the
matter to a centralized hopper where it is collected and pumped
to the solids holding tanks for thickening. The oil & grease
is skimmed off the top, collected in a hopper, and also pumped
to the solids holding tanks for further treatment. Approximately
60 percent of the solid organic material is removed in the |
| primary.
This constitutes about 30 percent of the biodegradable material
in the wastewater. |
Secondary
Treatment
In the
secondary treatment process the majority of pollutants are removed.
This treatment phase utilizes naturally occurring microbes to remove
the remaining waste material, which was not removed by the Primary
Treatment Process. The waste reaching the secondary still contains
about 40-50 percent of the original solids and 70 percent of the
original biodegradable material. To the microbes this material,
which is biodegradable, is food, which can be readily eaten and
digested, in the aerobic environment provided in the process.
3.2 million gallon complete mixed activated sludge aeration
basin. |
The
technical name for the process is Completely Mixed Activated
Sludge (CMAS). The microbes remain in contact with the wastewater
for about 12 hours on average and remove 90 percent of the waste.
As microbes remove the waste from the wastewater, they reproduce,
thereby converting the biodegradable material digested to the
microbial form. Once all the waste has taken on the form of
a microbe, |
| we
simply remove
the microbe from the wastewater, and send the wastewater on
to the next process, discharged separately from the lighter
(organic) particles and the wastewater. The heavier material
(grit), after settling is removed and sent to the landfill for
burial. |
Final clarification basin where the separation of the microbial
mass from the water occurs. |
How
do we simply remove the microbe? Well this is done clarification
process. Just as in the Primary Treatment Process, final clarifiers
serve us in the removal of microbes from the treated wastewater.
The mixture of wastewater and microbes is sent on to the secondary
clarifiers where the mixture is given 2-4 hours of quiescent
settling time. The microbes, having a mass greater than water
settle to the bottom of the clarifier. |
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A portion of these microbes is sent to the solids holding tanks
for removal from the system, and the remaining microbes are
returned to the head of the secondary treatment system where
they begin the eating and digestion of the incoming waste all
over again. |
Certified Wastewater Treatment Plant Operator performing a
process measurement. |
The
key to a well-operated system is balancing the daily microbial
population with the incoming waste material. Balancing the microbial
population is done by the wastewater treatment plant operator
by controlling the number of microbes in the system. The operator
as part of the daily testing measures the bacterial population
by running a gravimetric test called the suspended solids test.
This test yields an |
| approximation
of the bacterial population in inventory. Excess bacteria are
sent to the solids thickening process prior to land application.
The wastewater leaving the secondary clarifiers, with already
90 percent of the original pollutants removed, continues on
to the Disinfection process. |
Disinfection/Neutralization
Prior
to discharge to the Kansas River, the treated wastewater from the
North Topeka Wastewater Treatment Plant is disinfected. Disinfection
is the selective destruction of disease-causing organisms as opposed
to sterilization, which is the destruction of all organisms. In
wastewater there are three categories of human enteric organisms
of greatest importance as they are capable of producing disease.
These are the bacteria, viruses, and amoebic cysts. Disease caused
by water borne bacteria includes typhoid, cholera, paratyphoid,
and bacillary dysentery; diseases caused by waterborne viruses,
which include poliomyelitis and infectious hepatitis. Because the
treated wastewater will be discharged to the Kansas River where
it again enters the water use cycle, it is disinfected to ensure
its safe reuse.
Serpentine Channels to reduce short circuiting and ensure
good chlorine contact with the bacteria (disinfection). A
minimum of 30 minutes contact time is built in.
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Chlorine
is the disinfectant of choice used at the North Topeka Wastewater
Treatment Plant. Chlorine is the most commonly used chemical
for the destruction of pathogenic and other harmful organisms,
that might endanger human health, found in wastewater. Chlorine
forms in water hypochlorous acid, Hypochlorite ion, & chloramines.
All these products are toxic to the harmful organisms mentioned
above that survive the wastewater treatment process. Although
chlorine is a potent oxidant, |
| which
results in good destruction of harmful bacteria, it also can
react with organic compounds found in wastewater to form toxic
compounds. Many of these toxic organic compounds can have
long-term adverse effects on the sensitive biota of the Kansas
River and impair other uses of the river.
De-chlorination
with a strong reducing agent such as Sulfur Dioxide minimizes
toxicity. De-chlorination removes the total combined chlorine
residual that exists after chlorination before the treated
wastewater is released to the Kansas River thereby reducing
the toxic effects those compounds would have had.
Sulfur
Dioxide reacts with chlorine and its various compounds to
yield fairly innocuous products such as chlorides, sulfates,
and in some cases small amounts of ammonia. These reactions
are almost instantaneous and complete in a well-mixed environment.
The chlorine residual as well as the sulfur dioxide dosage
is monitored by operators daily. |
Outfall/Discharge
The wastewater flowing over a discharge weir and
being naturally aerated. |
After
Disinfection / Neutralization the disinfected wastewater (effluent)
leaves the North Topeka Wastewater Treatment Plant and makes
its way to the Kansas River. As the effluent leaves the plant
it pours over a weir which acts like a waterfall to create a
natural aeration which will add to its dissolved oxygen content.
Dissolved oxygen is necessary for fish and aerobic biota in
order to survive. Just as oxygen in the air is important to
|
| us,
so too is oxygen in the water to the aquatic life that lives
there. |
Diversion structure which funnels discharge to the Kansas
River. |
After
aeration, the effluent makes its way down a channel to a small
drainage ditch where it is directed via the concrete structure,
pictured at left, through the dike to the Kansas River. The
concrete structure serves to control bank erosion and increase
the velocity of the effluent entering the Kansas River facilitating
good mixing with the Kansas River flow. |
The three flood pumps for pumping wastewater over the dike
when the Kansas River is in flood stage. |
In
the event that the Kansas River level rises above flood stage,
the effluent could not be discharged through the dike as the
floodgates would be closed. Although this does not happen very
often, it does occur as it did in 1993. In that event the effluent
from the North Topeka Wastewater Treatment Plant can be pumped
over the dike via a system of pumps on the plant site.
Not only are these pumps sized large enough to pump all the
wastewater the plant is |
|
designed to treat (approx. 12 million gallons per day), but
they also are sized large enough to pump all the storm-water
that will drain from the area. |
©Copyright
2002-2003
Kansas Water Environment Association
All rights reserved.
Problems with the site?
Last
Updated
March 4, 2003
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930
NE Hilltop Drive
Topeka, KS 66617
Tel: (785) 357-4780
Fax: (785) 357-4725
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Upcoming Events |
Fall
Workshop
KWEA & AWWA Joint Workshop will be held October 28 & 29, 2003
in Hutchinson, Kansas.
Spring Conference
The 2003 KWEA Annual Spring Conference will be held April
7-10 in Topeka, Kansas at the Capital Plaza Hotel.
WEF Conferences
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Board
Meetings |
Executive
Board
The next executive board meeting is scheduled for February
21, 2003 at the Topeka Capitol Plaza Hotel in Topeka,
KS.
Meeting
Minutes
Minutes from the November 15, 2002 executive board meeting
are now available. |
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