r/EPA
United States
Environmental Protection
Agency
West Jackson County,
Mississippi
Constructed Wetland Treatma.
Case History
832
93
005o
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BACKGROUND
The West Jackson County
Constructed Wetland Treatment
System (CWTS) was built in two
phases between 1990 and 1991 to
provide additional effluent treatment
and disposal capacity for the Mississippi
Gulf Coast Regional Wastcwatcr
Authority's (MGCRWA) regional iand
treatment facility. Located north of
Ocean Springs, Mississippi, the West
Jackson County constructed wetlands
consist of three parallel treatment
systems that cover 56 acres.
The iand treatment facility was
originally designed lo treat an annual
average daily flow of l.fi million gallons
per day (mgd). Initially, this capacity
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v\;is siift'ick'nl lo treat the wastewaler
produced within the service area, which
is primarily from household sources.
However, following heavy rainfall
events, hydraulic capacity of the land
treatment facility wa*. exceeded, and
excess flow was bypassed directly into
Costapia Bayou. We!lands were
constructed to increase the site's overall
treatment capacity to 2.6 mgd and to
eliminate this periodic bypass.
.Spray irrigation ix used for
effluent treatment and disposal
at West Jackson Cotmtv
during dry weather.
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A
s designed, the West Jackson
County Natural Land Treatment
^System includes the following
main components:
• a 75-acre lagoon/storage facility
• a 380-acrc land application system
• three constructed wetland treatment
systems, CWTS1, CWTS2, and
CWTS3, with a combined area of
56 acres
• a 0,2-acre post-aeration pond
Waslewater is conveyed to the
regional land treatment facility by a
pressuri/ed force main. Initial treat-
ment is provided as the effluent moves
through the three cells of the lagoon.
which remove grit and settleable solids
and reduce suspended and dissolved
organic materials. The effluent flows by-
gravity to the distribution pump station
where debris is removed by two travel-
ing screens. The effluent is then
pumped to the distribution system.
The partially treated effluent is
applied to crops on two sites: a 245-aere
southern site, located on Mississippi
Sandhill Crane National Wildlife
Refuge lands, and a 170-acre northern
site, located on MGCRWA-owncd land.
Permanent big-gun sprinklers are used
to apply the effluent. Underdrains on
the land treatment fields transfer excess
percolate to wetland ponds on the
Refuge that provide nesting habitat for
the endangered sandhill cranes. These
birds have also benefited from this
project through their use of the spray
fields as feeding habitat.
Alternatively, the effluent can be
pumped to the 22-acre CWTS1 or be
gravity fed to the 34-acre CWTS2 and
CWTS3 sites. CWTS1 consists of two
cells that operate in series. Effluent
from Cell 1A flows over eight adjust-
able weirs into Cell IB. From there,
Cell IB effluent flows into an open
collection ditch where it flows by
gravity to the post-aeration pond
north of CWTS2.
CWTS2 and CWTS3 are two separate,
parallel treatment trains that operate
in series. CWTS2 has three cells and
CWTS3 has two cells. CWTS2 and
CWTS3 are directly downgradient
from the lagoon; therefore, influent
flows by gravity at a constant rate up
to 1.0 mgd. After being measured, the
influent is split between the two treat-
ment trains by a concrete flow splitter.
Approximately 65 percent of the
flow goes to CWTS2, and the rest to
CWTS3, resulting in a uniform loading
per acre to the treatment trains even
though they are different sizes.
After treatment in the three CWTS,
all wetland outflows are combined in
the effluent collection ditch and
conveyed to the post-aeration pond,
which is equipped with two floating
aerators. The post-aeration pond efflu-
ent passes through a Parshall flume for
flow measurement, then through the
outfall pipe where it is discharged into
Costapia Bayou.
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OPERATIONS AND MANAGEMENT
Cattails are the primary
wetland species used for
water quality treatment.
Constructed wetland systems can
orovidc a high level of waste-
water treatment with low opera-
tion and maintenance requirements and
low energy costs. In the West Jackson
County CWTS, wastewater is treated
by the naturally occurring bacteria and
fungi that colonize the sediments on
the bottom of the cells as well as the
stems and leaves of the vegetation
below the water's surface. These
microbes help transform and remove
organic compounds and nutrients that
might otherwise result in pollution of
adjacent surface waters.
The bottoms of the CWTS cells are
slightly sloped for easy draining during
maintenance. Each wetland cell has
three or more "deep zones," which
are 5 feet deep and about 20 feet wide.
The deep zones remain free of rooted
marsh vegetation, allowing them to
redistribute effluent through the system
and provide atmospheric aeration. The
deeper water in these zones furnishes
year-round habitat for aquatic life,
particularly mosquito fish and wetland-
dependent birds such as waterfowl.
Operation of the West Jackson
County CWTS is based on shallow,
overland flow conditions in the first
half of the wetland cells. Water depth
increases to a maximum of about 1 foot
at the downstream end of the cells. This
operational strategy takes advantage
of the fact that higher dissolved oxygen
(DO) occurs in shallow, higher velocity
areas of the wetland cells.
The West Jackson County CWTS was
initially planted with cattail and bulrush
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plants. The CWTS also has been
naturally colonized hy 43 other wetland
plant species, providing a high level of
biological diversity.
Influent from the pretrcatment
lagoon is distributed to the wetland
cells by pipes with 2-inch holes drilled
at 10-foot intervals. This method of
distributing influent begins the flow
through the treatment system and is
critical for effective use of the CWTS
for water quality treatment.
The effluent flows through the cells
for up to 12 days to provide a high
quality effluent. To account for seasonal
changes in the reaction rate of micro-
organisms in the cells., the retention
time is varied by changing water depths.
Because the microorganisms react
more quickly at higher temperatures,
the retenlion time can be decreased
during the summer and still provide
the required contact time for effective
treatment. Conversely, during the
winter's colder temperatures, the
reaction rate of the microorganisms is
lower; therefore, the retention time is
increased by raising water levels. Deep
water zones provide effective redistrib-
ution of water flows along the length of
the wetland cells. Stainless steel outflow
weirs control cell water depth and
promote the flow of effluent through
the treatment system. After it is treated
in the CWTS, effluent is conveyed to
the post-aeration pond, where the flow
rate and water quality are measured
before final discharge.
Post-aeration in essential for
consistent compliance with
the dissolved oxygen permit
limit of 6.0 mg/l.
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PERFORMANCE
Construction of Phase I of the
CWTS began in February 1990.
The earthwork and planting
were completed in July 1990. and
startup and flows to this phase began
in August 1990. Plant cover was fully
established in Phase I by October 1990.
Construction of Phase II began in
June 1990 and was completed about
8 months later. Influent flows to this
phase began in October 1990 and plant-
ing was completed in April 1991. Plant
cover was fully established in Pha<;e II
by June 1991.
Water quality measurements made
since June 1991 following complete
plant establishment indicate that the
West Jackson County constructed
wetlands will effectively reduce BO 1)5
and TSS concentrations to less than
8 mg/L. These reductions occur in
spite of variable BOD5 and TSS
inflow concentrations.
One of the key goals of the West
Jackson County CWTS is ammonia
nitrogen (NH3-N) reduction. Perform-
ance of the CWTS has been variable
to date, with 3 out of 12 months having
outflow NH3-N levels above the limit.
High outflow NH3-N concentrations
have been associated with either high
TKN loadings (over 3 pounds per acre
per day) or with high flows (over 2 mgd).
Operational control of peak flows.
TKN loading, and water level adjust-
ment are currently being used to
optimize this wetland system's nitrogen
removal potential.
West Jackson County
Constructed Wetland Design Criteria
Wetland Design Flow 1.6mgd Areas (acres)
Influent Quality
BOD5 45 mg/L
TN 12. 5 mg/L (167
Effluent Criteria
CWTS1
Ib/d) CWTS 2
BODS 10(13)a mg/L
TSS 30 mg/L
NH3-N 2 mg/L
pH 6-8.5 units
DO 6 mg/L
Feca! 2200 col/100 ml
col if arms
CWTS 3
Cell A
CeliB
Cell A
Cell B
CellC
Ceil A
Cell B
12
10
97
7.8
4.0
9.2
33
IN
TSS
NH3 N
utrogen.
00 Dissolved oxyqen
Water Quality Measurements
Month
1991 June
July
August
September
October
November
December
1992 January
February
March
April
May
BC>; concwTtraui
BODS
In
28
13
23
19
27
-16
39
23
19
19
28
24
Out
TSS
In
9 40
5 41
A 49
2.5 35
4 35
3 36
4 29
4 17
5
12
5 16
4
4.5
18
31
Out
15
15
10
5
4.5
4
7
8
4
5
4
6.5
Nitrogen
TNtn
7.3
4,4
15.2
177
145
13,5
6.9
11 1
145
15,4
12.2
69
NH. Ou!
1 2
1 3
1.0
2.3
3.5
3.9
1.3
1.4
1 6
1.7
1.2
0.05
3 outflow cone?1 •••< .to less than 8
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ANCILLARY BENEFITS
1?
In addition to improving the quality
of the effluent discharged to the
receiving stream, the creation of the
West Jackson County CWTS has
resulted in significant wildlife benefits.
This new wetland habitat provides food
and cover for various types of wetland
dependent vertebrate and invertebrate
life. The aquatic invertebrate popula-
tions throughout the wetlands provide
food for fish and birds.
The 45 wetland plant species identi-
fied to date, combined with open water
zones and shallow edge areas, have
resulted in a diversity of wildlife
habitats and high populations of wild-
life species. Sixty-two bird species were
identified in or around the wetlands
during 1991. About 37 of these species
are considered to be wetland-depen-
dent. Bird populations during the
winter, spring, and fall seasons are
dominated by ducks, sora rails, swamp
sparrows, and wading birds. Summer
bird population studies indicate the
presence of at least 7 nesting bird
species and a total of 30 species in
and around the wetlands.
Winter bird populations
include ducks, rails, sparrow
coots, herons, egrets, and
many other wetland species.
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ACKNOWLEDGEMENTS
Mississippi Gulf Coast
Regional Wastovater Authority
Curt Miller, General Manager
Donald Scharr. Senior Engineer
Linwood Tanner, Chief Operator
Consulting Engineers
Clay Sykes,
CH2M HILL Project Manager
Robert Knight,
CH2M HILL
Project Environmental Scientist
Carl Easton,
CH2M HILL Resident Engineer
U.S. Environmental Protection Agency
Bob Freeman,
Municipal Grants Program,
Region IV
This brochure was prepared by
CH2M HILL for the
U.S. Environmental Protection Agency.
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