CONSTRUCTED WETLAND NITROGEN REMOVAL FROM CATTLE
FEEDLOT WASTEWATER
M.E. Ancell, C.B. Fedler, and N.C. Parker
ABSTRACT
A 23-tank, 43 m2, pilot-scale constructed wetland system was loaded daily with
136.2 liters of cattle feedlot wastewater to measure the nitrogen removal effectiveness.
The 23-tanks were separated into six different treatment series, and the effects of four
different total nitrogen (TN) loading rates were investigated with three different series
surface areas and detention times. The four TN loading rates were 11.4, 8.0, 2.3, and 0.5
g TN/day. All four loading rates were tested in treatment series consisting of four tanks.
Additionally, the 2.3 g TN/day loading rate was tested in a series with two tanks and a
series with five tanks.
The removal of nitrogen constituents from wastewater is dominated by
maximizing the permanent removal processes inherent to the nitrogen cycle. Although
the nitrogen cycle is a complex interaction of biological and chemical phenomena,
maximizing its inherent removal processes is attainable in the wetland environment. The
primary facilitator of this nitrogen removal is the root-zone aeration of the predominantly
anaerobic environment surrounding the wetland soil. Given proper amounts of dissolved
oxygen, the microbiota of nitrification can oxidize ammonia to nitrate, and denitrification
can take place in the anaerobic environment, ultimately removing nitrogen from the
wastewater in the form of nitrogen gas. An additional permanent nitrogen removal
pathway in wetlands is defined by the plant uptake of ammonia and/or nitrate. However,
maximizing this removal pathway requires plant harvesting, which can be costly in the
full scale wetland treatment setting and does not always yield an appreciable amount of
nitrogen removal.
Of the series with four tanks, the series loaded with 11.4 g TN/day removed an
average of 54.9 percent of the applied TN; the 8.0 g TN/day series removed 60.8 percent
of the applied TN; the series loaded with 2.3 g TN/day removed an average of 78.0
percent of the a TN applied; and the series loaded with 0.5 g TN/day removed an average
of 33.4 percent of the applied TN. Additionally, the 2.3 g TN/day series with two tanks
removed 44.0 percent of the applied TN, and the 2.3 g TN/day series with five tanks
removed 82.8 percent of the applied TN.
The wetland plants removed 14.9 percent of the applied TN in the 0.5 g TN/day
series. This nitrogen removal in the biomass was the largest of all series tested. The
smallest plant nitrogen removal percentage was observed in the 11.4 g TN/day series
(4.87 percent). Additionally, a model of dry-weight biomass production with increasing
TN loading is presented. The biomass yield as a function of TN loading rate was highly
1
significant (  = 0.010) with an R2 = 0.978.
INTRODUCTION
The passage of the 1987 Water Quality Act Amendments to the CWA established
a new direction in the dispersment of funds for the treatment of wastewater. These
amendments returned the focus of water pollution control back to the states. This
translates into less federal grants for wastewater treatment improvements, and thus, a
greater need for state participation and funding for water quality control. This problem is
magnified by the current need for water quality improvement in the United States. Smith
(1988) outlines many of the water quality problems facing America:
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Treatment works construction needs for small communities (under 10,000 population)
- with the least ability to pay - amount to between $10 and $15 billion nationwide.
Agricultural activities generate large amounts of nonpoint source water pollution and
are causing serious water quality problems in at least 24 states.
Approximately one-third of existing lakes and reservoirs have water quality
impairment from nonpoint source pollution, principally from agricultural activities.
Large treatment needs exist in the industrial sector. For example, acid mine drainage
affects over 11,800 miles of streams in Appalachia alone.
Leachate from landfill disposal of both industrial and municipal solid waste is
affecting water quality.
Industrial toxic chemicals and hazardous waste treatment and disposal have become
major water quality concerns, with high potential costs and uncertain future treatment
requirements and alternatives.
As federal funds for the treatment of wastewater decline, and more pressure is
placed on municipalities and industries to discharge lesser quantities of pollutants, the
need for low-cost and effective wastewater treatment increases (Hammer 1989). One
possible low-cost and effective means of treating wastewater is with the use of
constructed wetlands.
Natural And Constructed Wetlands
Wetlands provide many services and perform many functions for our natural
environment. Wetlands provide fish and wildlife habitat, drinking water supply, ground
water recharge, flood control, protection from erosion, sites for outdoor recreation,
improvement of water quality, nutrient re-cycling, metals removal, point source and
nonpoint source water pollution control, and opportunities for education and research
(Dennison and Berry, 1993; Hammer, 1996). Although all of these functions of natural
wetlands are important to our environment, Hammer (1991) states that the most important
of these wetland functions is water quality improvement. Unfortunately, this function
and the related functions of nutrient recycling, metals removal, and water pollution
2
control are the least understood. Consequently, in order to maximize the effectiveness of
these functions, an analysis of the current knowledge base on this subject is required.
Scientists first realized the advantages of having wetlands in the water
environment when in the 1960's and 1970's the EPA began monitoring the water quality
characteristics of natural wetlands that received wastewater discharges. It seemed that
natural wetlands had been used as wastewater discharge sites for as long as sewage has
been collected (for more than 100 years in some locations). It was not until the 1960's
that these wetlands were monitored for their water quality characteristics and the water
purification potential of these wetlands was finally realized (Kadlec and Knight, 1995).
Hammer (1994) states that constructed wetlands are formerly terrestrial
environments that have been modified to create a system of undrained soils and wetland
emergent and submergent vegetation whose primary purpose is the removal of
contaminants or pollutants from wastewater. The processes in and the functions of
natural wetlands define the water purification of constructed wetlands. Additionally, if
constructed wetlands are designed properly, they serve to maximize the water purification
potential of natural wetlands.
There are two primary types of constructed wetlands, free water surface (FWS)
constructed wetlands, and subsurface flow (SF) constructed wetlands. Influent water in
free water surface constructed wetlands flows over and largely above the surface of the
soil and through the emergent stems and leaves of wetland vegetation. Water depth in
FWS wetlands can range from 2 cm to 0.8 m or more, depending on the use and location
of the wetland. Typically, FWS wetland depths are approximately 0.3 m (Reed et al.,
1995). Water of subsurface flow (SF) wetlands passes entirely through the soil substrate,
leaving no visible surface water flow. Typically, the soil substrate in SF wetlands is 0.3
to 0.6 m deep and made up of various sizes of gravel, crushed rock, and soil (Reed et al.,
1995).
Although there are only a few SF wetlands in the U.S., European municipal
systems frequently employ soil-based SF wetlands. Many operational SF systems have
experienced serious substrate clogging, and therefore SF constructed wetlands are not
recommended for any wastewater treatment greater than tertiary polishing of effluents
with low nitrogen loading. Additionally, SF systems are not reliable treatment techniques
for effective nitrogen removal (Hammer, 1994).
Constructed wetlands accomplish water quality improvement or purification
through a variety of physical, chemical, and biological processes. Some of these
processes are independent, and others depend upon the products of a previous process to
facilitate pollutant removal. Wetland vegetation serves four purposes: (1) obstruction of
wastewater flow, which reduces flow velocity and allows for particulate settling, (2)
creation and maintenance of a thin-film bioreactor on the surface area of live and
decomposing plant material, (3) transportation of oxygen from the atmosphere to the
3
largely anaerobic environment beneath the surface of the water, and (4) assimilation of
wastewater nutrients and carbonaceous material. Because many organic and nitrogen
compounds enter wetlands through wastewater absorbed to particulate matter, as flow
velocity decreases these particles settle to the bottom of the wetland, providing additional
surface area and nutrients to microbial biota. Additionally, as nutrients accumulate in the
wetland environment, wetland plants grow more rapidly, produce more surface area for
microbial growth, and provide more oxygen to their root structure and the attached
microbiota. The result is a constructed wetland environment with excess nutrients and
carbonaceous material, abundant microbial life, and aerobic and anaerobic sites for
corresponding microbial-mediated pollutant removal.
Constructed Wetlands For Wastewater Treatment
Worldwide, there are approximately 1000 managed FWS wetland systems in
operation for various purposes, and at least half of these systems are in the U.S. (Reed et
al., 1995). Constructed wetlands have been used to adequately treat many different types
of wastewater, including: (1) municipal wastewater, (2) acid mine drainage wastewater,
(3) industrial wastewater, and (4) agricultural wastewater (Hammer, 1988; Kadlec and
Knight, 1995; Reed et al., 1995; WPCF, 1990). Constructed wetlands for agricultural
wastewater treatment for both nonpoint and single discharge pollution have been
investigated extensively (Baldwin and Davenport, 1994; Brenton, 1994; Bankson, 1994;
Campbell, 1995; Cathcart et al., 1994; Dennison and Berry, 1993; DuBowy and Reaves,
1994; Godfrey et al., 1985; Hammer, 1997; Hammer, 1994; Hammer, 1988; Healy and
McCloud, 1994; Holmes et al., 1994; Hubbard et al., 1994; Hunt et al., 1994; Jann, 1994;
Kadlec and Knight, 1995; Kent, 1994; MacMaster et al., 1994; McCaskey et al., 1994;
Moshiri, 1993; Reaves et al., 1994; Reed et al., 1995; Sikora, 1994; Skarda et al., 1994;
Toor and Eddleman, 1994; Tanner, 1995; WPCF, 1990).
Three main attributes of wetlands define their water purification potential:
wetland hydrology, wetland soils, and wetland plants (Hammer, 1988; Kadlec and
Knight, 1995; Reed et al., 1995). These three attributes in turn define the environment
inside a wetland that facilitates microbial growth and nitrogen pollutant removal.
In the wetland environment, water is found in excess. This excess water presents a
plant stress because it inhibits the diffusion of gases to and from plant roots (oxygen
diffusion is about 10,000 times slower in water than in air) and because the presence of
oxygen-demanding constituents in the water tend to lower the amount of dissolved
oxygen (DO) available to supply root metabolism (Whitlow and Harris, 1979). Wetland
plants, namely the vascular plants called hydrophytes (plants that thrive in the presence of
excess water), have adapted to the flooded conditions found in wetlands through the
development of various plant tissues and transport mechanisms necessary for growth in
this hostile environment. Lenticels are small openings on the above water portions of
wetland plants that provide an entry point for atmospheric oxygen that is then transported
by an aeranchymous tissue network to and from the roots through the vascular tissues of
4
the plant that are above water and in contact with the atmosphere (Armstrong, 1978;
Jackson and Drew, 1984; Zimmerman, 1988). Lenticel surface area may be increased
through plant growth, plant height increases, or the formation of swollen buttresses in
trees and woody herbs and in cypress knees. Another adaptation to flooding shared by
many hydrophytes is the growth of adventitious roots from flooded stem tissue. These
roots can potentially extract DO and plant nutrients from water, where gases and nutrients
may be more available than in the anaerobic soil zone (Kozlowski, 1984).
Oxygen transport into the root zone of wetland plants has been measured and
found to be at various levels: 2.08 g of O2/m2 of wetland/day (Brix and Schierup, 1990)
and between 5 and 12 g O2/m2/day (Armstrong et al., 1990) for Phragmites australis
grown in gravel beds; and between 5 and 45 g O2/m2/day (Boon, 1985; Lawson, 1985),
depending on plant density and oxygen stress levels in the root zone (Kadlec and Knight,
1995; Reed et al., 1995). Sometimes this oxygen transport seems to be great enough to
only offset root metabolism, and therefore not result in additional aeration of the
surrounding soil and sediment (Brix, 1990). These aerobic microsites around the roots
and rhizomes of wetland plants can serve to initialize removal of wastewater nitrogen
constituents in wetlands. Therefore, wetland plants can support aerobic bacteria that
under appropriate conditions achieve pollutant removal (Reed et al., 1995).
Nitrogen Cycle In Wetlands
The nitrogen cycle is a very complex environmental interaction that defines the
extent and fate of the nitrogen element in our environment. This cycle in a wetland
includes six basic chemical transformations of nitrogen: 1) biological nitrogen fixation, 2)
ammonification, 3) ammonia volatilization, 4) nitrification, 5) denitrification, and 6)
biological assimilation. In a wetland, the magnitude of these transformations is directly
related to wetland hydrology, wetland soil, wetland plants, temperature, pH, and
dissolved oxygen content in the wetland water column.
Elemental nitrogen has an atomic weight of 14.01 g/mol with five electrons in its
outer shell of atomic structure. Three electrons of this outer shell are available to form
nitrogen-based compounds. These compounds occur in nature with varying stability and
have oxidation states ranging from +5 to -3. Many organic and inorganic nitrogen
compounds are essential for biological life. The most important inorganic forms of
nitrogen are ammonia (NH3), nitrite (NO2-), nitrate (NO3-), nitrous oxide (N2O), and
dissolved elemental nitrogen or dinitrogen gas (N2). Typically, inorganic forms of
nitrogen are expressed in terms of elemental nitrogen with the terminology of nitratenitrogen (NO3- -N) or ammonia-nitrogen (NH3-N), for example. Organic nitrogen
compounds include urea, amino acids, amines, purines, and pyrimidines. An
understanding of each of these nitrogen compounds is essential to analysis of the nitrogen
cycle.
5
Nitrate-nitrogen is the most highly oxidized form of nitrogen found in wetlands.
Nitrate-nitrogen’s high oxidation state (+5) and overall negative charge dictate its
existence and persistence in water. The resulting chemical nature of nitrate-nitrogen is
chemically stable, highly mobile, and highly soluble in water. Nitrate-nitrogen’s high
mobility and water solubility are a result of the negative charge (-1) of the compound.
Because soil particles are generally negatively charged as well, nitrate-nitrogen has no
affinity for these particles and thus is not bound by the soil. Therefore, nitrate-nitrogen
would persist in the wetland environment were it not for two processes for nitratenitrogen removal, denitrification and plant uptake. Detrimental effects arise from excess
levels of nitrate-nitrogen. The first of these effects is termed eutrophication, which
becomes a problem in surface waters with high nitrate-nitrogen concentrations. The overabundance of nitrate allows plants an unlimited supply of nitrogen, resulting in
uncontrolled growth of algae and other plant species. Nitrate-nitrogen and subsequently
nitrite-nitrogen are of further importance in water quality control because they are toxic to
infants (they result in a potentially fatal disease known as methylglobanemia) when
present in drinking water supplies of polluted surface or ground water (Kadlec and
Knight, 1995). As a consequence of nitrate-nitrogen’s chemical nature and detrimental
environmental effects, the removal of this compound from wetlands is important, and
design procedures for its removal are necessary.
A number of important processes that serve to transport and translocate
nitrogenous compounds without transforming them exist in wetlands. These processes
include: 1) particulate settling and re-suspension, 2) diffusion of dissolved nitrogen
compounds, 3) plant uptake and translocation, 4) litterfall, 5) sorption of soluble nitrogen
substrates, 6) seed release, and 7) organism migrations (Kadlec and Knight, 1995).
Although these processes do not significantly reduce nitrogen compound concentrations,
the nitrogen cycle would exhaust itself without their aid.
Nitrification
Nitrification is the principal transformation pathway for the reduction of
ammonia-nitrogen concentrations in wetlands. Nitrification involves a two-step
microbial process that ultimately converts ammonia-nitrogen to nitrate-nitrogen via
oxidation. The rate of nitrification is directly dependent upon DO concentration. If DO
concentrations remain above 0.3 mg/L (Reddy and Patrick, 1984), two bacteria genera,
Nitrosomonas and Nitrobacter, are able to oxidize ammonia (NH4+) to nitrate (NO3-).
The overall nitrification process can be summarized by a single equation:
NH4+ + 2.0 O2  NO3- + 2 H+ + H2O
As defined here, approximately 4.6 mg of O2 is required to oxidize a mg of ammonianitrogen to nitrate-nitrogen (Kadlec and Knight, 1995).
6
(1)
Denitrification
If not for denitrification, the biogeochemical processes that cause nitrogen fixation
would ultimately deplete the atmosphere of nitrogen gas. Denitrification is an energyrequiring process that reduces nitrate or nitrite-nitrogen (NOx-N) to nitrogen gas, nitrous
oxide, or nitric oxide. A stepwise reaction summary of denitrification is as follows
(Tchobanoglous, 1991):
NO3-  NO2-  NO  N2O  N2
(2)
Denitrification is an essential and complementary process to heterotrophic metabolism in
soil and aquatic environments when dissolved or free oxygen is absent. Aerobic
respiration is an energy deriving mechanism that utilizes oxygen as the final electron
acceptor in the most energetically positive step of respiration, the electron transport chain.
In denitrification, an enzyme called nitrate reductase allows certain genera of bacteria to
use the tightly bound oxygen atoms in nitrate and nitrite molecules as the final electron
acceptors, in the absence of free oxygen (Kadlec and Knight, 1995).
Nitrate-nitrogen can also be reduced in wetlands through plant uptake. However,
nitrate uptake by wetland plants is presumed to be less favored than ammonium uptake.
Subsequently, nitrate-nitrogen loss in wetlands is often attributed to denitrification.
However, other known and studied candidate mechanisms for nitrate loss in wetlands
include assimilation by plants, assimilation by microbiota, and dissimilatory reduction to
ammonium nitrogen (Kadlec and Knight, 1995).
Total nitrogen (TN) is the sum of all water soluble nitrogen constituents: nitratenitrogen, ammonia-nitrogen, and organic nitrogen. The removal or persistence of each of
these nitrogen species is dependent upon each of the nitrogen cycle components.
Therefore design models for the removal of TN in wetlands must recognize these nitrogen
flux processes and integrate them into an overall wetland nitrogen removal scenario.
Plant Harvesting for Nitrogen Removal
Plant productivity is directly related to the amount of nutrients available. As
nutrient levels increase in a wetland, a maximum growth rate is achieved in the plants. At
higher levels of nutrient concentrations, plant growth tends to level off in a range of
nutrient supply that produces optimal plant growth. However, at even higher nutrient
concentrations, phytotoxic responses are observed and plant die-off ensues.
Plant productivity in wetlands with increasing nutrient concentration has been
noted as another possible means of nitrogen removal. The nutrient removal potential of
wetland plant species in wetland treatment systems was monitored and recorded by
Reddy and DeBusk (1987). Reddy and DeBusk (1987) report that treatment wetland
cattails (Typha spp.) can produce a yearly growth of between 8,000 and 61,000 kg/ha,
with a yearly nitrogen uptake of 600 to 2630 kg/ha. These relatively high nutrient uptake
7
rates in wetland plants and the potential accumulation of these nutrients have caused
some wetland treatment experts to suggest that routine harvesting of plant material might
optimize nutrient removal potential (Breen, 1990; Reed et al., 1995; Wile et al., 1985).
Breen (1990) reported a 32 percent nitrogen mass removal due to the harvesting of
Typha orientalis. Adcock et al. (1994) report that a Phragmites and Typha treatment
wetland in Byron Bay, Australia with daily loading of 25 to 40 grams of nitrogen per m2
of wetland per year removed approximately 65 percent of this loading in the macrophyte
biomass (35 g/m2 in the roots and rhizomes and 92 g/m2 in the leaves and stems).
However, two other constructed wetland research projects concluded that harvesting of
cattail stands at the end of the growing season resulted in less than 10 percent of the
systems’ nitrogen removal (Gearhart et al, 1983; Wile et al., 1985). However, Wile et al.
(1985) suggest that several harvests per season would be more effective for nutrient
removal purposes. Wieder et al. (1988) found that, the usefulness of plant harvesting in
wetland treatment systems depends on several factors, including climate, plant species,
and the specific wastewater objectives. Consequently, if plant uptake is the design
pathway used to meet wastewater objectives for nutrient removal, the harvesting of
wetland plants is a necessary design guideline (Reed et al., 1995). However, Wieder et al.
(1988) state that harvesting plants to remove wastewater contaminants taken up by plants
is inefficient. Kadlec and Knight (1995) suggest that although nutrient storage in wetland
plants is frequently significant, regular harvest of wetland plants from treatment systems
has not been successful in full-scale applications because of cost and sustainability. In
summary, most wetland scientists, except Breen (1990), believe that plant harvesting has
a negligible effect upon the total mass removal of nitrogen, especially when the increased
costs and access problems associated with frequent harvesting are included in the analysis
(Kadlec and Knight, 1995; Gearhart et al., 1983; Reed et al., 1995; Wieder et al., 1988;
Wile et al., 1985). Consequently, if plant harvesting is to be used as a significant sink for
nitrogen in treatment wetlands, a more cost-effective and productive means of harvesting
these plants must be developed.
The objectives of this research were as follows: (1) to delineate the various
pathways for the removal of nitrogen constituents in wastewater in constructed wetlands;
(2) to determine the effectiveness of a constructed wetland in removing nitrogen from
cattle feedlot agricultural wastewater; and 3) to examine the plant removal of nitrogen
with frequent harvests.
MATERIALS AND METHODS
Simulated wetlands were constructed during the Fall of 1995. This system
became fully functional in January 1996, initiating a one and one-half year start-up
phase. The over-all layout of the system is shown in Figure 1. A total of 23 tanks were
used to simulate the effectiveness of wetlands for treatment of agricultural wastewater.
Wastewater for this research was obtained from the Lubbock Feedlot, located southeast of
8
Lubbock, Texas. Each of 6 treatment series of tanks was loaded with 136.2 liters of
diluted wastewater each day. Wetland treatment effects of four different total nitrogen
loading rates were determined.
Wastewater was diluted to specific loading rates in 6 - 140 liter head tanks for
addition into the 6 treatment series. Table 1 summarizes, for each treatment series, the
series designation, the average TN loading rate, the number and sequence of tanks, and
the total wetland surface area (Figure 1). In order to obtain the specific TN loading rates,
the wastewater was diluted with freshwater in the 140-liter head tanks, located adjacent to
the first tank in each series. Table 2 describes the volume of wastewater and freshwater
mixed in each head tank to facilitate TN loading for a total daily loading volume of 136.2
liters. These wetland loading procedures were followed for the experimental period of
July 11, 1997 to February 15, 1998. Similar loading procedures were adhered to in the
start-up phase of operation from January, 1996 to June, 1997.
Table 1. Summary of Wetland Treatment Series
Series
Series Designation
1
2
3
4
5
6
Wetland Tank Number
1-4
5-8
9-13
14-17
18-21
22-23
Daily TN Loading Rate, g/day
11.4
0.5
2.3
2.3
8.0
2.3
Number of Tanks
Total Wetland Surface Area, m2
4
7.44
4
7.44
5
9.30
4
7.43
4
7.43
2
3.72
During the initial set-up of the constructed wetland, the wetland tanks were filled
with three different types of soil media: 1) washed plant roots in sand, 2) washed plant
roots in gin trash, and 3) plant roots with their soil matrix intact. Table 3 summarizes the
use of these three soil media. Additionally, each of the wetland tanks were graded so that
they would have three distinct soil depths. The three soil depths dictate water levels of
0.1 m, 0.2 m, and 0.3 m. As seen in Figure 2, water depths increase in the direction of
wastewater flow. Additionally, the three depths define each of three 1.02 m long wetland
cells. A baffle was installed at the downstream edge of the first two cells in each tank in
order to separate the wetland plant species in each cell and to eliminate any potential soil
subsidence that could render the soil grading ineffective.
9
Table 2. Soil Media in Each Treatment Series
Wetland Tanks
Soil Media
1
1-4
WS
2
5-8
WS
Series
3
9-13
WGT
4
14-17
WS
5
18-21
WS
6
22-23
SMI
Note: WS indicates washed plant roots in organic sand
WGT indicates washed plant roots in gin trash
SMI indicates plant roots with soil matrix
intact
Eight aquatic plant species were systematically planted in each of the 23 wetland
tanks. These plants included: bulrush (Scirpus spp.), cattails (Typha spp.),curly dock,
duckweed (Lemna spp.), knotgrass (Paspalum distichum), smartweed (Polygonum spp.),
spiked bulrush (Eleocharis spp.), and sulfuria. Three of each plant species were planted
in each cell of the 23 wetland tanks.
At the Lubbock Feedlot, a pumping system was installed at the first wastewater
storage pond in the series of three. The wastewater was pumped into a 760-liter tank and
transported to the constructed wetlands site. The wastewater was stored at the site in an
elevated 760-liter tank for gravity flow distribution to each of the wetland treatment
series.
A 140-liter head tank was placed at the beginning of each of the six wetland tank
series. Float valves set to the requisite height in each head tank were attached by plastic
tubing to manually operated valves at the freshwater line. The 760-liter elevated
wastewater storage tank was linked to the wetland system by a simple piping network that
included connections for a flexible hose at each of the six head tanks.
The daily loading procedure at the wetland site included first the addition of the
proper amount of freshwater to the head tanks. Once this was completed, the wastewater
was added to a pre-determined level in the head tank for each TN loading rate, resulting
in a total wastewater flow rate of 136.2 L/day.
The wastewater was delivered to the wetland tanks via a manually adjustable
spout. The flow rate from this spout was such that the 136.2 L of wastewater was added
to the first tank in each series over a duration of about 24 hours. Wastewater flow then
proceeded through each of the wetland tanks by gravity flow. As seen in Figure 2,
standpipes were placed in each wetland tank so that when the height of water in the tank
exceeded the height of the top of the standpipe, the flow proceeded to the following
wetland tank through a connecting pipe. Consequently, the wastewater would overflow
into the next tank, which had a standpipe at the influent end. Wastewater flow would
proceed in this manner until the standpipe in the last tank of each series would channel
10
the flow to the effluent collection ponds shown in Figure 1.
Initial hydraulic calculations indicated that with a mean wetland depth of 0.20 m
and aerial hydraulic loading rate of 7.33 cm/day, the mean nominal detention time was
2.8 days per tank. Table 3 summarizes the calculated nominal detention time for each
treatment series.
Table 3. Nominal Detention Time (t) for Each Treatment Series
1
4
11.2
Number of Tanks
Nominal Detention Time, days
2
4
11.2
Series
3
5
14
4
4
11.2
5
4
11.2
6
2
5.6
Note: Detention Times Determined by t = Wetland Volume / Wastewater Flow Rate
The average raw wastewater water quality characteristics are shown in Table 4.
As see here, 173 mg/L of the TN is ammonia-nitrogen, 48 mg/L is nitrate-nitrogen, and
by the definition of organic nitrogen, 117 mg/L of the TN is ON.
Table 4. Average Raw Wastewater Water Quality Characteristics
Constituent
TN
NO32--N
NH3-N
COD
TSS
TDS
Concentration, mg/L
338
48
173
4299
762
5063
Each week, wetland water samples were collected from the last cell of each tank.
These samples were stored in 500-ml plastic sample containers for transport to the
laboratory for water quality analysis. Once the sample was received in the laboratory,
tests to determine the concentration of TSS, COD, TN, NO32--N, and NH3-N for the
effluent and influent wastewater were performed. Approved water quality testing
procedures were followed as depicted in Table 5.
Table 5. Methods of Water Quality Analysis
COD
Source:
HACH
Water / Wastewater Constituent
NO3--N NH3-N
TN
TSS
HACH
HACH
HACH
APHA
8000
8039
8038
10071
N/A
Method
Number
Note:
HACH Indicates Use of HACH DR/2000 Spectrophotometer (1989) Methods
APHA Indicates Use of American Public Health Association Methods, Clesceri
et al. (Editors), 1989
11
Beginning in May, 1997, the emergent wetland plants were harvested
approximately monthly. The plants were cut with the use of hand-held clippers to a
height of 10 cm above the wetland water level. For each tank, the wet-weight biomass
per cell was recorded, along with the number of cattail plants in each cell. Additionally, a
wet-weight to dry-weight ratio was determined for each plant species, in order to
subsequently determine the amount of dry-weight biomass produced per cell and per tank.
Monthly harvests occurred on approximately the 15th day of May, June, July,
August, September, October, January, and February. In May, the wetland plants had not
been harvested prior to this time, and therefore the biomass production rate was not used
in the final analysis. Similarly, the January, 1998 standing biomass was a result of
nitrogen loading from October 15, 1998 (the previous harvest), and a comparison of this
data to dry-weight biomass data obtained in previous months would be disproportionate.
Additionally, during the time between October 15, 1997 and January, 15, 1998, a
greenhouse cover was placed over the treatment wetland, and dry-weight biomass
production with the greenhouse was considered separately from biomass production
without the greenhouse cover. From October 15, 1997 to February 15, 1998, the
constructed wetland was enclosed in a sheet-plastic greenhouse.
RESULTS AND DISCUSSION
Nitrogen Removal Analysis
Table 6 summarizes the average influent and effluent concentrations of ammonianitrogen, nitrate-nitrogen, organic nitrogen, and total nitrogen, as well as the average
percent removal of theses wastewater constituents for each treatment series. Further
analysis of these results indicate that the nitrogen constituent with the greatest percent
removal for each series was ammonia-nitrogen. Additionally, the nitrogen constituent
with the least percent removal for each series except series 4 and 6 was organic nitrogen.
Therefore, generally ammonification of organic nitrogen to ammonia-nitrogen was
incomplete, and the Reed et al. (1995) assumption of complete ammonification is invalid
for this treatment wetland. The largest percent removal of organic nitrogen was found in
series 3 with 77.3 % removal, and the smallest percent removal of organic nitrogen was
for series 2 with -2.9% removal. This negative organic nitrogen removal efficiency
indicates that microbial or plant decomposition resulted in increased organic nitrogen
concentration or nitrogen fixation was prominent. Series 2 received the smallest TN
loading rate, but this series indicated the least removal efficiency for organic nitrogen and
all other nitrogen forms.
Table 7 summarizes the average daily mass loading and removal (kg/ha/day) of
ammonia-nitrogen, nitrate-nitrogen, organic nitrogen, and TN. Additionally, the percent
mass removal of each nitrogen form is presented. This analysis allows assessment of the
12
effect that area has on the removal efficiency of each nitrogen species. As described in
Table 1, three different wetland surface areas were evaluated for their removal efficiency
with a daily TN loading rate of 2.3 g. As seen in Table 7, series 3, which had the largest
wetland surface area (9.29 m2 for series 3, 7.43 m2 for series 4, and 3.72 m2 for series 6),
removed the greatest percentage of each wastewater nitrogen constituent. Conversely,
series 6, which had the smallest wetland surface area, indicated the smallest percent
removal for each nitrogen constituent. In accordance with this relationship of wetland
surface area and nitrogen removal was the hydraulic retention time and nitrogen removal.
With a retention time of 14 days, series 3, indicated the largest percent removal of each
nitrogen form. Series 4, which had a retention time of 11.2 days indicated removal
efficiency intermediate between series 3 and series 6, which had a hydraulic retention
time of 5.6 days.
Figure 3 illustrates the average total nitrogen concentration from the influent to
the effluent of each 1.86 m2 wetland tank in the four treatment series with four tanks with
a total wetland area of 7.43 m2 per series (series 1, 2, 4, 5). The fractional distance
through each series indicates the concentration of TN in the proportional length of flow
between the influent (zero distance through the wetland) and the effluent (through the
entire wetland, denoted as 1).
As seen in Table 6 and illustrated in Figure 3, series 4 indicated the largest percent
removal of TN (average influent TN concentration was 16.71 mg/L; average effluent TN
concentration was 3.68 mg/L; and percent removal is 78.0 %) of the four treatment series
with total wetland surface area equal to 7.43 m2. Series 4 was loaded with 2.3 g TN/day,
which was intermediate between the two larger loading rate series (series 1 with TN
loading of 11.4 g TN/day and series 5 with 8.0 g TN/day) and the smallest loading rate
series, series 2 with 0.5 g TN/day. Series 1 and series 5 removed a larger mass of TN
than series 4 (7.74 kg/ha/day for series 1; 6.69 kg/ha/day for series 5; and 2.33 kg/ha/day
for series 4). Because series 4 was loaded with a lesser amount of TN per day than series
1 and series 5, the percent removal of TN was greater. Contradictorily, series 2, which
was loaded with the smallest amount of TN, had the least TN removal efficiency.
Figure 4 illustrates the effectiveness of the constructed wetland for treatment of
cattle wastewater for removing total nitrogen. Figure 4 is a graphical representation of a
treatment scenario that includes 17 tanks. By assuming that the TN effluent from series 1
is approximately the same as the TN influent concentration in series 5, and so forth
through series 3 and series 2, the TN concentration can be reduced from 84 to 3 mg/L in a
17 tank series, with a total surface area of 31.62 m2 and a total retention time of 48 days.
Based on this analysis, a retention time longer than approximately 30 days provides little
added benefit to nitrogen removal.
Wetland Plant Analysis
Table 8 summarizes the dominant and limited growth of emergent plant types in
13
the constructed wetland during the research time period of July, 1997 through February,
1998. Of the eight plants types initially planted in the constructed wetland (bulrush,
cattails, curly dock, duckweed, knotgrass, smartweed, spiked bulrush, and sulfuria), only
cattails (Typha spp.), knotgrass (Paspalum distichum), and duckweed (Lemna spp.)
resulted in significant biomass production. Additionally, only limited growth of sulfuria
was observed in series 2 and 3.
Table 8. Emergent Plant Species Survival and Growth
Series
1
2
3
4
5
6
Dominant Plant Type C, Kn, D Kn, D C, Kn, D C, Kn, D C, Kn, D C, Kn, D
Limited Plant Growth
C, Sulf.
Sulf.
C = Cattails; Kn = Knotgrass; D= = Duckweed; Sulf. =
Sulfuria
On the 15th day of June, July, August, September, October, and February, the
cattails and knotgrass were harvested from the constructed wetlands and dry-weight
biomass production per month was recorded. Duckweed was not harvested from the
constructed wetlands. A general relationship exists between biomass production and
nitrogen loading in constructed wetlands. Figure 5 illustrates this trend of average dryweight biomass production per series with average total nitrogen mass loading rate in the
constructed wetlands. A model of dry-weight biomass production (Y) to TN mass
loading rate (X) was found to be:
Y = 227 * EXP(-0.33*X)
R2 =0.978
 = 0.010.
(3)
As described in Equation 3 and in Figure 5, the average maximum dry-weight biomass
production rate for this wetland was approximately 227 kg/(ha*day) at a maximum TN
loading rate of approximately 15.5 kg/(ha*day). Although these results indicate the
maximum dry-weight biomass growth rate, the loading rate at which phytotoxic responses
are seen was not achieved.
In order to determine the amount of total nitrogen removal attributed to the
harvesting of cattail and knotgrass biomass, an analysis of the total nitrogen removal per
harvesting month in each wetland series was completed. Additionally, given the total
biomass harvested per month and the concentration of nitrogen in the cattails and
knotgrass biomass, the amount of TN removed by the harvesting of these plants was
calculated. Finally, the percentage of TN removal attributed to plant harvesting was
calculated. Table 9 summarizes the TN mass removal of each wetland series; Table 10
summarizes the total biomass harvested per month; Table 11 summarizes the amount of
14
TN removed by harvesting; and Table 12 indicates the percentage of TN removal in each
wetland series attributed to plant harvesting. Of significant importance to these data were
the assumptions made concerning the amount of TN in the cattails and knotgrass. TKN
was measured for the cattails and knotgrass found in several of the treatment series.
Because Kadlec and Knight (1995) state that plants generally are made up of 1 to 7
percent nitrogen, and Reed et al. (1995) assume that cattails contain 14 percent nitrogen, a
conservative assumption was made to determine the amount of TN in the cattails and
knotgrass, and cattails were assumed to contain 8.0 percent TN, and the knotgrass was
assumed to contain 4.0 percent TN.
As indicated in Table 12, series 2 displayed the largest percent removal of TN
through plant harvesting (14.9 %). Additionally, the standard deviation of series 2 percent
removal was 14.8, indicating considerable variation in nitrogen removal. Series 2
indicated the largest percent removal of TN in July, when it removed 34.0 percent of the
TN added to the series in the form of plant harvesting. Contradictorily, series 2 also
displayed the least TN removal of any series at any time, in February, when it removed
only 0.26 percent of the TN added via harvesting. It should be noted that the predominant
plant species in series 2 was knotgrass. These data indicate that the lower temperatures
observed in February (inside the greenhouse) limited growth of the knotgrass.
Also of note from these data, is the relationship between series 3, 4, and 6, which
all had the same TN loading rate (2.3 g TN per day) but had different wetland surface
areas (9.29, 7.43, and 3.72 m2, respectively). Series 3 had the largest plant nitrogen
removal percentage (13.1 %), series 4 the next greatest (10.6 %), and series 6 indicated
the least biomass removal of TN (8.2 %) of these three similarly loaded series. These
data indicate that with increasing wetland surface area, a greater percent removal of TN
attributed to plant harvesting was observed.
Series 1 and series 5 had the largest of the TN loading rates (11.4 g TN/day and
8.0 g TN per day, respectively). However, these series displayed the least ability of all
treatment series to remove TN via harvesting. Series 1 removed an average of 4.9 percent
of the nitrogen loading via harvesting, and series 5 removed an average of 7.0 percent of
its TN loading by plant uptake and harvesting. In summary, although series 2 removed
the highest average percent of its TN with the greatest variability, a general trend of the
data indicates that with increasing TN loading, a decreasing amount of TN removal can
be attributed to plant harvesting. Finally, with the exception of series 2, no series
removed more than an average of 13.1 percent of the TN loading via plant harvesting.
SUMMARY AND CONCLUSIONS
A constructed wetland was operated from July 11, 1998 to February 15, 1998 in
order to analyze the agricultural wastewater nitrogen removal capacity of this wetland
Additionally, the processes inherent to wetlands which allow for nitrogen removal in
15
accordance with the nitrogen cycle were presented.
Wetland hydrology, wetland soils, and wetland plants define the nitrogen removal
potential of constructed wetlands for wastewater treatment. These three processes in-turn
define the physical water quality characteristics of pH, dissolved oxygen content, and
redox potential found in the wetland environment. Special attention must be paid to each
of these characteristics because they define the occurrence and magnitude of nitrogen
removal in constructed wetlands via the processes inherent to the nitrogen cycle. The
most important of these characteristics to nitrogen removal in wetlands is the
concentration of DO. Nitrification, or the oxidation of ammonia-nitrogen to nitratenitrogen, requires DO concentrations greater than 0.3 mg/L in the wetland water column,
while denitrification, or the reduction of nitrate-nitrogen to nitrogen gas, is performed by
facultative bacteria in the absence of DO. Consequently, these basic nitrogen cycle
reactions require a stratified wetland water column that includes zones of aerobic and
anaerobic conditions. The wetland water column is routinely an anaerobic environment,
due to the presence of large concentrations of oxygen demanding constituents, and the
limited capacity of water for oxygen transport. Because wetland plants have shown the
ability to transport sufficient quantities of oxygen from the atmosphere to the root zone,
aerobic microsites can be found in the vicinity of the roots, facilitating oxygen requiring
processes such as nitrification and plant survival. Additionally, wetland plants have the
ability to take-up nitrogen in the form of ammonia, and to a lesser extent nitrate, further
reducing the nitrogen content of wetland wastewater effluent.
The nitrogen removal effectiveness of the constructed wetland was reported:
A.) Average ammonia-nitrogen percent removal was 74.4 percent  12.1
B.) Average nitrate-nitrogen percent removal was 48.4 percent  25.3
C.) Average organic nitrogen percent removal was 41.0 percent  30.0
D.) Average total nitrogen percent removal was 59.0 percent  19.1
E.) Monthly harvesting of cattails and knotgrass resulted in limited
nitrogen removal attributed to plant uptake with the largest removal in
treatment series with the smallest nitrogen loading. The largest
average removal of total nitrogen was 14.9 percent, in treatment series
2, which was loaded with 0.5 g TN per day.
16
REFERENCES
Adcock, P.W., G.L. Ryan, and P.L. Osbourne, 1994. Nutrient Partitioning in a ClayBased Surface Flow Wetland. In Proceedings of the Fourth International Conference on
Wetland Systems in Water Pollution Control, Guangzhou, China, pp. 162-170.
Armstrong, W., 1978. Root Aeration in the Wetland Environment. Chapter 9 in D.D.
Hook and R.M.M. Crawford (Editors), Plant Life in Anaerobic Environments. Ann
Arbor, MI, Ann Arbor Science, pp. 269-297.
Armstrong, W.J., Armstrong, and P.M. Beckett, 1990. Measurement and Modeling of
Oxygen Release from Roots of Phragmites australis. In P.F. Cooper and B.C. Findlater
(Editors), Constructed Wetlands in Water Pollution Control, Oxford, U.K., Pergammon
Press, pp. 41-52.
Baldwin, A.P., and T.N. Davenport, 1994. Constructed Wetlands for Animal Waste
Treatment: A Progress Report of Three Case Studies in Maryland. In DuBowy, P.J., and
R.P. Reaves (Editors), Constructed Wetlands for Animal Waste Management. Papers
from the Constructed Wetlands for Animal Waste Management Workshop, Lafayette, IN,
April 4-6, 1994, pp. 103-117.
Bankson, D., 1994. Constructed Wetlands as an Alternative for Swine Management. In
DuBowy, P.J., and R.P. Reaves (Editors), Constructed Wetlands for Animal Waste
Management. Papers from the Constructed Wetlands for Animal Waste Management
Workshop, Lafayette, IN, April 4-6, 1994, pp. 118-123.
Boon, A.G., 1985. Report of a Visit by Members and Staff of Water Resources Centre to
Germany to Investigate the Root Zone Method for Treatment of Wastewaters. Water
Research Centre, Stevenage, England.
Bowes, G., and S. Beer, 1987. Physiological Plant Processes: Photosynthesis. In K.R.
Reddy and W.H. Smith (Editors), Freshwater Wetlands: Ecological Processes and
Management Potential. New York, Academic Press, pp. 155-167.
Breen, P.F., 1990. A Mass Balance Method for Assessing the Potential of Artificial
Wetlands for Wastewater Treatment. Natural Resources, Vol. 24, No. 6, pp. 689-697.
Brenton, W.H., 1994. A Constructed Wetland in Use: 28 Years. In DuBowy, P.J., and
R.P. Reaves (Editors), Constructed Wetlands for Animal Waste Management. Papers
from the Constructed Wetlands for Animal Waste Management Workshop, Lafayette, IN,
April 4-6, 1994, pp. 72-81.
Brezonik, P.L., 1972. Nitrogen: Sources and Transformations in Natural Waters.
Chapter 1, pp. 1-50. In H.E. Allen and J.R. Kramer (Editors), Nutrients in Natural
17
Waters. Wiley-Interscience, New York, NY.
Brix, H., and H. Schierup, 1990. Soil Oxygenation in Constructed Reed Beds: The Role
of Macrophyte and Soil-Atmosphere Interface Oxygen Transport. In P.F. Cooper and
B.C. Findlater (Editors), Increasing Our Wetland Resources. Washington, D.C., National
Wildlife Federation-Corporate Conservation Council, pp. 173-180.
Campbell, K.L. (Editor), 1995. Versatility of Wetlands in the Agricultural Landscape.
Proceedings of the National Symposium, Tampa, Florida, September 17-20, 1995.
American Society of Agricultural Engineers (ASAE).
Cathcart, T.P., D.A. Hammer, and S. Triyono, 1994. Performance of a Constructed
Wetland -Vegetated Strip System Used for Swine Waste Treatment. In DuBowy, P.J.,
and R.P. Reaves (Editors), Constructed Wetlands for Animal Waste Management. Papers
from the Constructed Wetlands for Animal Waste Management Workshop, Lafayette, IN,
April 4-6, 1994, pp. 9-22.
Clesceri, L.S., A.E. Greenberg, and R.R. Trussell (Editors), 1989. Standard Methods for
the Examination of Water and Wastewater, 17th Edition. American Public Health
Association, Washington, D.C.
DuBowy, P.J., and R.P. Reaves (Editors), 1994. Constructed Wetlands for Animal Waste
Management. Papers from the Constructed Wetlands for Animal Waste Management
Workshop, Lafayette, IN, April 4-6, 1994.
Gearhart, R.A., 1992. Use of Constructed Wetlands to Treat Domestic Wastewater, City
of Arcata, California. Water Science and Technology, Vol. 26, No. 7-8, pp. 1625-1637.
Godfrey, P.J., E.R. Kaynor, S. Pelczarski, and J. Benforado, 1985. Ecological
Considerations in Wetlands Treatment of Municipal Wastewaters. Van Norstrand
Reinhold Company, New York, New York.
HACH Company, 1989. HACH Water Analysis Handbook. HACH Company, Loveland,
Colorado.
Hammer, D.A., 1994. Guidelines for Design, Construction, and Operation of Constructed
Wetlands for Livestock Wastewater Treatment. In DuBowy, P.J., and R.P. Reaves
(Editors), Constructed Wetlands for Animal Waste Management. Papers from the
Constructed Wetlands for Animal Waste Management Workshop, Lafayette, IN, April 46, 1994, pp. 155-181.
Hammer, D.A., 1997. Creating Freshwater Wetlands, 2nd Edition. Lewis Publishers,
Inc., New York, New York.
18
Hammer, D.A., B.P. Pullin, D.K. McMurry, and J.W. Lee, 1993. Testing Color Removal
from Pulp Mill Wastewaters with Constructed Wetlands. In Constructed Wetlands for
Water Quality Improvement, G.A. Moshiri (Editor).
Hammer, D.A. (Editor), 1988. Constructed Wetlands for Wastewater Treatment:
Municipal, Industrial, and Agricultural. Lewis Publishers, Inc., Chelsea, Michigan.
Hammer, D.A., and R.K. Bastian, 1988. Wetland Ecosystems: Natural Water Purifiers?
In D.A. Hammer (Editor), Constructed Wetlands for Wastewater Treatment: Municipal,
Industrial, and Agricultural, pp. 5-19. Lewis Publishers Inc., Chelsea, Michigan.
Healy, J.W., and P.R. McLoud, 1994. Use of Constructed Wetlands and Infiltration
Areas in SCS Approved Waste Management Systems. In DuBowy, P.J., and R.P. Reaves
(Editors), Constructed Wetlands for Animal Waste Management. Papers from the
Constructed Wetlands for Animal Waste Management Workshop, Lafayette, IN, April 46, 1994, pp. 65-71.
Holmes, B.J., G.D. Bubenzer, L.R. Massie, and G. Hines, 1994. A Constructed Wetland
for Treating Milkhouse Wastewater in a Cold Climate – Status Report. In DuBowy, P.J.,
and R.P. Reaves (Editors), Constructed Wetlands for Animal Waste Management. Papers
from the Constructed Wetlands for Animal Waste Management Workshop, Lafayette, IN,
April 4-6, 1994, pp. 54-64.
Hubbard, R.K., G.L. Newton, J.G. Davis, R. Dove, R. Lowrance, and G. Vellidis, 1994.
Grass-Riparian Zone Buffer Systems for Filtering Swine Lagoon Waste. In DuBowy, P.J.,
and R.P. Reaves (Editors), Constructed Wetlands for Animal Waste Management. Papers
from the Constructed Wetlands for Animal Waste Management Workshop, Lafayette, IN,
April 4-6, 1994, pp. 124-143.
Hunt, P.G., A.A. Szogi, F.J. Humenik, J.M. Rice, and K.C. Stone, 1994. Swine
Wastewater Treatment by Constructed Wetlands in the Southeast United States. In
DuBowy, P.J., and R.P. Reaves (Editors), Constructed Wetlands for Animal Waste
Management. Papers from the Constructed Wetlands for Animal Waste Management
Workshop, Lafayette, IN, April 4-6, 1994, pp. 144-154.
Kadlec, R.H., and R.L. Knight, 1995. Treatment Wetlands. Lewis Publishers, New
York, New York.
MacMaster, B.T., P.L. Koch, D.K. Brandt, and D.W. Burgdorf, 1994. Overview of SCS
Plant Material Centers Activities Related to Wetland Plants. In DuBowy, P.J., and R.P.
Reaves (Editors), Constructed Wetlands for Animal Waste Management. Papers from the
Constructed Wetlands for Animal Waste Management Workshop, Lafayette, IN, April 46, 1994, pp. 97-102.
19
McCaskey, T.A., S.N. Britt, T.C. Hannah, J.T. Eason, V.W.E. Payne, and D.A. Hammer,
1994. Treatment of Swine Lagoon Effluent by Constructed Wetlands Operated at Three
Loading Rates. In DuBowy, P.J., and R.P. Reaves (Editors), Constructed Wetlands for
Animal Waste Management. Papers from the Constructed Wetlands for Animal Waste
Management Workshop, Lafayette, IN, April 4-6, 1994, pp. 23-33.
Melzer, A., and D. Exler, 1982. Nitrate and Nitrite Reductase Activities in Aquatic
Macrophytes. In Symoens, J.J., S.S. Hooper, and P. Compere (Editors), Studies on
Aquatic Vascular Plants, Royal Botanical Society of Belgium, Brussels, pp. 128-135.
Mitsch, W.J., and J.G. Gosselink, 1993. Wetlands, Second Edition. Van Nostrand
Reinhold, New York, New York.
Moshiri, G.A. (Editor), 1993. Constructed Wetlands for Water Quality Improvement.
Lewis Publishers, Inc., Ann Arbor, Michigan.
Phipps, R.G., and W.G. Crumpton, 1994. Factors Affecting Nitrogen Loss in
Experimental Wetlands with Different Hydrologic Loads. Ecological Engineering,
3(4):399-408.
Reaves, R.P., P.J. DuBowy, D.D. Jones, and A.L. Sutton, 1994. Design of an
Experimental Constructed Wetland for Treatment of Swine Lagoon Effluent. In
DuBowy, P.J., and R.P. Reaves (Editors), Constructed Wetlands for Animal Waste
Management. Papers from the Constructed Wetlands for Animal Waste Management
Workshop, Lafayette, IN, April 4-6, 1994, pp. 82-96.
Reaves, R.P., P.J. DuBowy, and B.K. Miller, 1994. Performance of a Constructed
Wetland for Dairy Wastewater Treatment in Lagrange County, Indiana. In DuBowy, P.J.,
and R.P. Reaves (Editors), Constructed Wetlands for Animal Waste Management. Papers
from the Constructed Wetlands for Animal Waste Management Workshop, Lafayette, IN,
April 4-6, 1994, pp. 43-53.
Reddy, K.R., and W.H. Patrick, 1984. Nitrogen Transformations and Loss in Flooded
Soils and Sediments. CRC Crit. Rev. Environmental Control, 13:273-309.
Reddy, K.R., and W.F. DeBusk, 1987. Nutrient Storage Capabilities of Aquatic and
Wetland Plants. In K.R. Reddy and W.H. Smith (Editors), Aquatic Plants for Water
Treatment and Resource Recovery. Orlando, FL, Magnolia Publishing, pp. 337-357.
Reed, S.C., R.W. Crites, and E.J. Middlebrooks, 1995. Natural Systems for Waste
Management and Treatment, 2nd Edition. McGraw-Hill Inc., New York, New York
Skarda, S.M., J.A. Moore, S.F. Niswander, and M.J. Gamroth, 1994. Preliminary
Results of Wetlands for Treatment of Dairy Farm Wastewater. In DuBowy, P.J., and R.P.
20
Reaves (Editors), Constructed Wetlands for Animal Waste Management. Papers from the
Constructed Wetlands for Animal Waste Management Workshop, Lafayette, IN, April 46, 1994, pp. 34-42.
Sikora, F.J., 1994. Summary of Research at the Tennessee Valley Authority’s
Constructed Wetlands Research and Development Facility. In DuBowy, P.J., and R.P.
Reaves (Editors), Constructed Wetlands for Animal Waste Management. Papers from the
Constructed Wetlands for Animal Waste Management Workshop, Lafayette, IN, April 46, 1994, pp 1-8.
Smith, A.J., 1988. Wastewaters: A Perspective. In D.A. Hammer (Editor), Constructed
Wetlands for Wastewater Treatment: Municipal, Industrial, and Agricultural. Lewis
Publishers, Inc., Chelsea, Michigan, pp. 3-19.
Stengel, E., 1993. Species-Specific Aeration of Water by Different Vegetation Types in
Constructed Wetlands. In Moshiri, G.A. (Editor), Constructed Wetlands for Water
Quality Improvement, Lewis Publishers, Inc., Ann Arbor, Michigan, pp. 427-434.
Tanner, C.C., 1994. Potential for Constructed Wetlands to Improve the Discharges from
Dairy Shed Oxidation Ponds. New Zealand Water and Wastes Association Symposium,
Hamilton, New Zealand, August, 1994.
Tchobanoglous, G., 1991. Wastewater Engineering: Treatment, Disposal, and Reuse.
Metcalf & Eddy, Inc., 3rd Edition, McGraw-Hill, Inc., New York, NY.
Tettleton, R.P., F.G. Howell, and R.P. Reaves, 1993. Performance of a Constructed
Marsh in the Tertiary Treatment of Bleach Kraft Pulp Mill Effluent: Results of a 2-Year
Pilot Project. In Constructed Wetlands for Water Quality Improvement, G.A. Moshiri
(Editor).
Thut, R.N., 1988. Utilization of Artificial Marshes for Treatment of Pulp Mill Effluents.
In Constructed Wetlands for Wastewater Treatment, D.A. Hammer (Editor), 1988.
Toor, R., and R.H. Eddleman, 1994. Constructed Wetlands for Treatment of Swine
Wastewater in Kentucky. In DuBowy, P.J., and R.P. Reaves (Editors), Constructed
Wetlands for Animal Waste Management. Papers from the Constructed Wetlands for
Animal Waste Management Workshop, Lafayette, IN, April 4-6, 1994, pp 187-189.
U.S. Environmental Protection Agency, 1983. Freshwater Wetlands for Wastewater
Management. Region IV Environmental Impact Statement, Phase 1 Report, EPA 904/983-107
U.S. Soil Conservation Service (SCS), 1987. Hydric Soils of the United States. National
Technical Committee for Hydric Soils, Washington, D.C.
21
van Oostrom, A.J., 1994. Nitrogen Removal in Constructed Wetlands Treating Nitrified
Meat Processing Wastewater. pp. 569-579, In Proceedings of the Fourth International
Conference on Wetland Systems for Water Pollution Control. Guangzhou, P.R. China:
Center for International Development and Research, South China Institute for
Environmental Sciences.
Water Pollution Control Federation (WPCF), 1990. Manual of Practice: Natural Systems
for Wastewater Treatment. Manual of Practice FD-16, Chapter 13: Wetland Systems,
Alexandria, VA.
Whitlow, T.H., and R.W. Harris, 1979. Flood Tolerance in Plants: A State-Of-The-Art
Review. Environmental and Water Quality Operational Studies, Technical Report E-792, U.S. Army Engineer Waterways Experiment Station.
Wieder, R.K., G. Tchobanoglous, and R.W. Tuttle, 1988. Preliminary considerations
Regarding Constructed Wetlands for Wastewater Treatment. In Constructed Wetlands
for Wastewater Treatment, D.A. Hammer (Editor), 1988.
Wildeman, T.R., and L.S. Laudon, 1988. Use of Wetlands for Treatment of
Environmental Problems in Mining: Non-Coal-Mining Applications. In Constructed
Wetlands for Wastewater Treatment, D.A. Hammer (Editor), 1988.
Wile, I., G. Miller, and S. Black, 1985. Design and Use of Constructed Wetlands.
Chapter 2, in P.J. Godfrey, E.R. Kaynor, S. Pelczarski, and J. Benforado (Editors),
Ecological Considerations in Wetland Treatment of Municipal Wastewaters, Van
Nostrand Reinhold Company, pp. 26-37.
Witthar, S.R., 1993. Wetland Water Treatment Systems. In Constructed Wetlands for
Water Quality Improvement, G.A. Moshiri (Editor).
Zimmerman, J.H., 1988. A Multi-Purpose Wetland Characterization Procedure,
Featuring the Hydroperiod. pp. 31-48, in J.A. Kusler and G. Brooks (Editors),
Proceedings of the National Wetland Symposium: Wetland Hydrology, Berne, NY:
Association of State Wetland Managers.
Zimmerman, T., J.L. Lefever, and M. Warns, 1994. Constructed Wetlands for Milkhouse
Wastewater Treatment. Written for Presentation at the 1994 International Summer
Meeting Sponsored by ASAE, Kansas City, Missouri, June 19-22.
22
Figure 1. Layout of constructed wetland site. Wetland tanks are numbered and treatment series daily total nitrogen loading is indicated.
23
Figure 2. Top view and profile view of wetland tanks with wetland wastewater flow direction and soil depths indicated.
24
Table 6. Nitrogen Constituent Influent-Effluent Concentration Removal Summary, 7/11/97 – 2/15/98
Daily TN Loading
Constituent
NH3-N
NO3--N
ON
TN
Series 1
11.4 g TN/day
Average
Concentration,mg/
L
Influent Effluent
42.38
12.02
29.15
83.56
11.02
7.19
19.49
37.70
Series 2
0.5 g TN/day
Average
Percent Concentration,mg/
L
Removal, Influent Effluent
%
74.0
1.70
0.74
40.2
0.48
0.28
33.1
1.17
1.20
54.9
3.34
2.22
Series 3
2.3 g TN/day
Average
Percent Concentration,mg/
L
Removal, Influent Effluent
%
56.1
8.48
1.19
41.9
2.40
0.37
-2.9
5.83
1.33
33.4
16.71
2.88
Percent
Removal,
%
86.0
84.8
77.3
82.8
Table 6. Continued
Daily TN Loading
Series 4
2.3 g TN/day
Average
Concentration,mg/
L
Influent Effluent
Series 5
8.0 g TN/day
Average
Percent Concentration,mg/
L
Constituent
Removal, Influent Effluent
%
8.48
1.29
84.8
29.67
5.55
NH3-N
2.40
0.82
65.9
8.42
4.42
NO3--N
5.83
1.57
73.0
20.41
12.97
ON
16.71
3.68
78.0
58.49
22.94
TN
Note: Percent Removal = ((Influent-Effluent)/Influent)*100
25
Series 6
2.3 g TN/day
Average
Percent Concentration,mg/
L
Removal, Influent Effluent
%
81.3
8.48
3.05
47.4
2.40
2.16
36.4
5.83
4.15
60.8
16.71
9.36
Percent
Removal,
%
64.0
10.3
28.8
44.0
26
Table 7. Nitrogen Constituent Mass Loading and Removal Summary, 7/11/97 – 2/15/98
Daily TN Loading
Constituent
NH3-N
NO3--N
ON
TN
Series 1
11.4 g TN/day
Series 2
0.5 g TN/day
Series 3
2.3 g TN/day
Average
Average
Average
Mass Flux,
Mass Flux,
Mass Flux,
kg/(ha*day)
Percent
kg/(ha*day)
Percent
kg/(ha*day)
Percent
Loading Removal Removal, Loading Removal Removal, Loading Removal Removal,
%
%
%
7.77
5.75
74.0
0.31
0.18
57.1
1.24
1.08
86.9
2.20
0.89
40.4
0.09
0.04
43.5
0.35
0.30
84.8
5.50
1.11
20.1
0.22
0.03
13.9
0.88
0.59
67.0
15.47
7.74
50.0
0.62
0.25
39.8
2.48
1.97
79.5
Table 7.
Continued
Daily TN Loading
Constituent
NH3-N
NO3--N
ON
TN
Series 4
2.3 g TN/day
Series 5
8.0 g TN/day
Series 6
2.3 g TN/day
Average
Average
Average
Mass Flux,
Mass Flux,
Mass Flux,
kg/(ha*day)
Percent
kg/(ha*day)
Percent
kg/(ha*day)
Percent
Loading Removal Removal, Loading Removal Removal, Loading Removal Removal,
%
%
%
1.55
1.32
84.8
5.44
4.42
81.3
3.11
1.99
64.0
0.44
0.29
65.9
1.54
0.79
51.1
0.88
0.35
39.3
1.10
0.72
65.5
3.85
1.48
38.5
2.20
0.54
24.7
3.09
2.33
75.2
10.83
6.69
61.8
6.19
2.88
46.5
27
Note: Percent Removal = (Removal/Loading)*100
100
Series 1, 11.4 g TN Loaded per Day
Series 5, 8.0 g TN Loaded per Day
Series 4, 2.3 g TN Loaded per Day
Series 2, 0.5 g TN Loaded per Day
90
TN Concentration, mg/L
80
70
60
50
40
30
20
10
0
0
0.25
0.5
Fractional Distance Through Wetland
Figure 3. Average Total Nitrogen Concentration as a Function of Distance Through the Wetland.
28
0.75
1
29
Nitrogen Constituent Concentration, mg/L
100
Series 1; 11.4 g TN Loaded per Day
90
Series 5; 8.0 g TN Loaded per Day
80
Series 3; 2.3 g TN Loaded per Day
70
Series 2; 0.5 g TN Loaded per Day
60
50
40
30
20
10
0
0
1
2
3
4
5
6
7
8
9
10
11
12
Number of Wetland Tanks
Figure 4. Total Nitrogen Concentration Reduction with Wetland Tank Progression.
30
13
14
15
16
17
18
Dry-Weight Biomass Production Rate, kg/(ha*day)
250
200
Average per Series Dry-Weight
Biomass -- June -> October
Calculated Dry-Weight Biomass
Production
150
Y = 227 * EXP(-0.33*X)
R2 = 0.978
alpha = 0.01
100
50
0
0
2
4
6
8
10
12
Total Nitrogen Mass Loading Rate, kg/(ha*day)
31
Figure 5. Dry-Weight Biomass Production as a Function of Total Nitrogen Loading
14
16
18
Tab Table 9. Total Nitrogen Mass Removed Per Month Corresponding
To Plant Harvesting, kg/ha/month.
Table 10. Total Biomass Harvested, kg/ha/month.
Series
Series
Date
1
2
3
4
5
6
Date
1
2
3
4
5
July
1105.1 2.5 137.2 246.3 211.4 547.7
July
244.3 21.4 183.2 121.6 277.2
August
191.6
5.8
59.5 70.9 171.6 114.3
August
242.4 38.3 161.3 108.7 219.2
September 379.3
6.6
60.1 69.6 221.7 86.0
September 251.3 18.9 138.7 170.9 221.2
October
340.8
7.9
58.3 72.1 223.0 63.3
October
207.3 4.7
82.8 101.6 117.1
February
122.9 12.3 61.6 68.0 192.3 76.9
February
34.4
0.8
27.6 50.2 48.6
Max
1105.1 12.3 137.2 246.3 223.0 547.7
Max
251.3 38.3 183.2 170.9 277.2
Min
122.9
2.5
58.3 68.0 171.6 63.3
Min
34.4
0.8
27.6 50.2 48.6
Avg
427.9
7.0
75.3 105.4 204.0 177.7
Avg
196.0 16.8 118.7 110.6 176.7
Stdev
392.9
3.6
34.6 78.8 21.9 207.7
Stdev
91.9 14.9 63.2 43.3 92.0
Table 11. Nitrogen Removed by Harvesting, kg/ha/day.
Date
July
August
September
October
February
Max
Min
Avg
Stdev
1
19.5
19.4
20.1
16.6
2.8
20.1
2.8
15.7
7.4
2
0.9
1.5
0.8
0.2
0.0
1.5
0.0
0.7
0.6
Series
3
4
14.7
9.7
12.9
8.7
11.1 13.7
6.6
8.1
2.2
4.0
14.7 13.7
2.2
4.0
9.5
8.8
5.1
3.5
5
22.2
17.5
17.7
9.4
3.9
22.2
3.9
14.1
7.4
6
260.7
163.5
145.8
79.4
20.3
260.7
20.3
133.9
90.8
Table 12. Percentage of Nitrogen Removal Attributed to
Plant Harvesting.
Series
Date
1
2
3
4
5
6
July
1.8 34.0 10.7
4.0
10.5
3.8
August
10.1 26.3 21.7 12.3 10.2 11.4
September 5.3 11.4 18.5 19.6
8.0
13.6
October
4.9 2.4
11.4 11.3
4.2
10.0
February
2.2 0.3
3.6
5.9
2.0
2.1
Max
10.1 34.0 21.7 19.6 10.5 13.6
Min
1.8 0.3
3.6
4.0
2.0
2.1
Avg
4.9 14.9 13.2 10.6
7.0
8.2
Stdev
3.3 14.8
7.1
6.1
3.7
5.0
6
20.9
13.1
11.7
6.4
1.6
20.9
1.6
10.7
7.3
32
Paper No. 984123
An ASAE Meeting Presentation
CONSTRUCTED WETLAND NITROGEN REMOVAL
FROM CATTLE FEEDLOT WASTEWATER
by
Michael Ancell
Research Asst
Civil Engr. Dept.
Texas Tech University
Box 41023
Lubbock, TX 79409-1023
Clifford B. Fedler
Professor
Civil Engr Dept.
Texas Tech University
Box 41023
Lubbock, TX 79409-1023
Nick C. Parker
Director
Texas Coop Fish & Wildlife
Research Unit
Box 42125
Lubbock, TX 79409-2125
Written for presentation at the
1998 ASAE Annual International Meeting
sponsored by ASAE
Disneys Coronado Springs Resort
Orlando, Florida
July 12-16, 1998
Summary:
Many granular materials are stored in some type of container and removed through an opening (orifice) in the
bottom of that container under the influence of gravity. In properly designed containers will cause restricted
flows and cost industry millions of dollars in interrupted processing. Knowledge of the laws governing
gravity flow of bulk solids through orifices is of great value to design engineers.
Keywords:
Treatment, Plants, Cattails, Knottgrass
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the official position of ASAE, and its printing and distribution does not constitute an endorsment of views which may be expressed.
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presented as refereed publications.
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33