United States	Office of Water
Environmental Protection	EPA 820-F-20-002
Agency	June 2020
KANSAS: HIGH-QUALITY WATER FROM SMALL POTWS
Operators draw on outside help—and deploy their own expertise
At many publicly owned treatment works (POTWs) across
the United States, staffs have made low-cost modifications
and operational changes to reduce effluent nutrient
discharges. EPA's National Study of Nutrient Removal and
Secondary Technologies investigates similar optimization
efforts, and this fact sheet, one product of that study,
describes some specific successes at the Clay Center and
Concordia, Kansas POTWs.
In their optimization work, the Clay Center and Concordia
operators drew on free, hands-on, onsite technical help
from the Kansas Rural Water Association (KRWA) and the
Kansas Department of Health and Environment (KDHE).
The Clay Center and Concordia staffs actively engaged
with this assistance, reducing nutrient discharges and
showing that investment in staff training coupled with
operational changes provides nutrient load removal
benefits.
Neither Concordia nor Clay Center POTW was originally
designed to remove nutrients. But their 2015 National
Pollutant Discharge Elimination System (NPDES) permits
required them to modify operations to achieve one of two
annual average effluent nutrient goals for total nitrogen
(TN) and total phosphorus (TP):
» TN 10 mg/L and TP 1.0 mg/L
» TN 8.0 mg/L and TP 1.5 mg/L
These conditions were similar for many POTWs across
Kansas.
Clay Center POTW
The Clay Center POTW has a design capacity flow of 0.715
million gallons per day (MGD) and an average daily flow
of 0.34 MGD. The plant includes preliminary treatment, a
primary clarifier, an oxidation ditch, a secondary clarifier,
and UV disinfection. The oxidation ditch has two rotors,
one each on the east and west ends, as well as dissolved
oxygen (DO) sensors at both ends. All process control is
manual.
Clay Center staff (left to right): Ron Richardson, Ed Hedberg,
Raymond LaVisse, Kent Hess ting
Operators began by installing new rotors with variable-
speed drives to experiment with aeration cycling. They
added a baffle to the west side of the ditch, creating an
anoxic zone for denitrification (nitrogen removal) followed
by an anaerobic zone for biological phosphorus removal.
To enhance phosphorus removal, they added fine bubble
diffusers just before the secondary clarifier: this gave
polyphosphate-accumulating organisms (PAOs) enough
oxygen to retain TP throughout clarification. When they
added a second baffle following the first, TP effluent
concentrations dipped below 1 mg/L at first (though
that performance did not last). Polyaluminum chloride
is added for emergency polishing. The Clay Center plant
now surpasses both TN permit goals. Meanwhile, monthly
energy costs at the plant have decreased from $5,600
before optimization to $2,500 afterward.
Clay Center staff studied nutrient removal and took
meticulous daily notes as they made these changes,
making it much easier to assess their impacts.
National Study of Nutrient Removal and Secondary Technologies
Nutrient removal through optimizing plant operations

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Clay Center POTW Monitoring Data
Concordia POTW Monitoring Data

Effluent TN
Concentration
(mg/L as N)
Effluent TP
Concentration
(mg/L as P)
Pre-optimization
Average
(June 2014-
November 2016)
16.32
3.46
Post-optimization
Average
(December 2016-
February 2020)
3.24
1.63*
Percent Removal
80%
53%

Effluent TN
Concentration
(mg/L as N)
Effluent TP
Concentration
(mg/L as P)
Pre-optimization
Average
(March 2014-
March 2015)
16.21
3.58
Post-optimization
Average
(April 2015-
April 2017)
1.37
1.70*
Percent Removal
92%
53%
"While this cumulative average is above the TP goal, annual
average TP concentrations decreased post-optimization and are
now consistently below 1,5 mg/L.
Concordia POTW
The Concordia POTW has a design capacity flow of 1.35
MGD and an average dally flow of 0.4 MGD. The plant
includes preliminary treatment, an Orbal® ditch system
with three concentric ditches, two secondary clarifiers,
and UV disinfection. The outermost and middle ditches
are operated identically while the innermost ditch is not
used. Two blowers aerate the ditch system in summer, one
in winter. The outermost ditch has an oxidation-reduction
potential (ORP) probe. All process control is manual.
Concordia staff (left to right): Brian Peterson, Paul McGuire, Tom
Strecker
*Vv'hile this cumulative average is above the TP goal, annual
average TP concentrations decreased post-optimization and are
now consistently below 1.5 mg/L.
Concordia staff began experimenting with aeration cycling
using a timer to promote nitrification/denitrification and
biological phosphorus removal. They found great success
with cycles of 60 min on/60 min off, producing monthly
effluent TN concentrations typically less than 1 mg/L. They
next tried controlling aeration cycling with ORP setpoints
but could not get the same effluent quality. So, they went
back to timed control, using ORP readings to adjust the
length of the aeration cycles. Seasonally, operators add
polyaluminum chloride for supplemental phosphorus
precipitation when warmer temperatures impede
biological removal. Monitoring data show the Concordia
plant has surpassed the TN permit goals.
Optimization Opportunities and Benefits
Optimizing existing treatment systems
can effectively reduce nutrient discharges
from POTWs. Local training, support from FfSGt¦
regulatory agencies, onsite consulting, and,
most importantly, operator ingenuity and
enthusiasm enabled these Kansas POTW operators to
make the most of existing equipment and reach their
nutrient goals. For Clay Center, optimizing also saved
energy costs, showing optimization can produce
additional benefits beyond improved surface water
quality.
Acknowledgements
Aii nutrient monitoring data were collected from EPA's integrated Compliance and Information System-National Pollutant Discharge Elimination
System (ICIS-NPDES). Energy savings are from internal plant records. Tom Styles and Gerald Grant supported KDHE and KRWA in improving
nutrient discharges at POTWs in Kansas.

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