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DETERMINING THE ACTUAL HYDRAULIC RETENTION TIME OF A
CONSTRUCTED WETLAND CELL FOR COMPARISON WITH THE
THEORETICAL HYDRAULIC RETENTION TIME
BY
BRANDY HUNT
(Under the direction of Dr. Matthew Smith)
ABSTRACT
The design of constructed wetlands for wastewater treatment is based on
the hydraulic retention time, which is the most easily changed operational
variable in the design. This can be changed by the flow rate, decaying plant
matter, or sludge accumulation, because of changes in volume and depth. A
tracer study was conducted to determine the hydraulic retention time for cell one
of the Tignall Water Treatment Facility. According to the results of the study, the
average hydraulic retention time is approximately 7.7 days which indicates that
the hydraulic efficiency of the system is approximately 0.50, which is average
according to Persson et al. (1999), but other findings of the study, such as plant
density, indicate that the system may be beginning to decline. It is
recommended that wetland cell one be drained, dredged, and replanted.
KEYWORDS: Wastewater, Constructed Wetlands, Hydraulic Efficiency,
Hydraulic retention time
DETERMINING THE ACTUAL HYDRAULIC RETENTION TIME OF A
CONSTRUCTED WETLAND CELL FOR COMPARISON WITH THE
THEORETICAL HYDRAULIC RETENTION TIME
by
BRANDY HUNT
B.S.B.E., The University of Georgia, 1998
A Thesis Submitted to the Graduate Faculty of The University of Georgia in
Partial Fulfillment of the Requirements for the Degree
MASTER OF SCIENCE
ATHENS, GEORGIA
2002
DETERMINING THE ACTUAL HYDRAULIC RETENTION TIME OF A
CONSTRUCTED WETLAND CELL FOR COMPARISON WITH THE
THEORETICAL HYDRAULIC RETENTION TIME
by
BRANDY HUNT
Approved:
Major Proffessor: Matt Smith Committee: Rhett Jackson
David Gattie William Tollner
Electronic Version Approved:
Maureen Grasso Dean of the Graduate School The University of Georgia December 2002
iv
Dedication
To Jill Davenport, thanks for the help, the data, the discussions. This is a better
thesis because of those discussions.
To Dr. Matthew Smith, thanks for the challenges and the occasional boot to the
head.
To every member of Watershed Assessment Office, past and present, I can
never thank you enough for the support and help you have given for the
first two years of the graduate student career.
To every member of the Environmental Quality Water Lab, I can also never
thank you enough for the support and help you have given me the last
year and a half.
To my Mom and Dad, thanks for always standing behind me and giving me the
tools I needed to survive the last four years of frustration that have been
my graduate school career.
To my friends, especially Mikey, Dan, Aimee, and Alexandra, I’ve been at this
as long as most of you have known me, and your support and kibitzing
have been appreciated.
To my husband, Christopher “The Tigger” Smith, thank you for being the most
caring, supportive human being it has been my pleasure to meet, love,
and marry. I promise, babe, the insanity is almost over.
v
Table of Contents
Page
SECTION
1.0 INTRODUCTION ...................................................................................... 1
2.0 LITERATURE REVIEW ............................................................................ 6
3.0 Methods.................................................................................................. 12
3.1 Choice of dye..................................................................................... 12
3.2 Calibration of the dye concentrations to the absorbance ................... 12
3.3 Dye degradation ................................................................................ 15
3.4 Prototype Run.................................................................................... 17
3.5 Experimental Run .............................................................................. 18
3.6 Climate Conditions............................................................................. 21
3.7 Bathymetry survey ............................................................................. 21
4.0 Results.................................................................................................... 24
4.1 Middle-Mixing zone grab samples ..................................................... 24
4.2 Hydraulic retention time analysis ....................................................... 26
4.3 Bathymetry survey ............................................................................. 30
5.0 DISCUSSION AND CONCLUSIONS...................................................... 35
6.0 REFERENCES ....................................................................................... 38
7.0 APPENDIX ............................................................................................. 39
1
1.0 Introduction
In the past, environmental engineers have relied on first order
approximations of rates of transformation, reduction, and the removal of
pollutants from water. However, because ecological process descriptions are
complex, close scrutiny must be paid to each of the above categories for a
complete understanding of the system as a whole. This particular project
examines the application of constructed wetlands within the larger category of
the treatment of municipal wastewater. While soils, sediments, microbes, and
macrophytes are all important to a constructed wetland, it is necessary to
understand the movement of water within the wetland, since hydraulic retention
time (HRT) is the basis for most wastewater treatment designs. (Kadlec 1994)
The movement of water within a constructed wetland can be influenced by
various interactions. A wetland may have excluded zones like plant and
accumulated sludge volumes (Kadlec 1994). Excluded zones are areas where
water is stagnating or otherwise not getting treated. These excluded zones are
taken into account during the design phase; however, when these zones
increase in volume, they become impediments to the treatment of the
wastewater. While interactions that influence the water budget, like precipitation
and evapotranspiration, can cause the wastewater to flow unpredictably through
the wetland, the excluded zones are the easiest interactions to control. There
are of course more interactions that can influence the movement of water, but
they cause unsteady flow patterns, which can be difficult to analyze in a
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constructed wetlands hydraulic regime. This is because unsteady flow is almost
impossible to isolate and model. (Rash and Liehr 1999)
Tracer studies indicate that treatment in subsurface flow wetlands is more
influenced by velocity profile effects than by dispersion, and in free water surface
wetlands, velocity profiles can lead to a distribution of hydraulic residence times.
Velocity profiles are formed by friction, as the water flows over surfaces that slow
it down. The distribution of hydraulic residence times is originates because the
shortest residence time is experienced by water moving at the maximum velocity
in the profile. Hilton et al. (1998) found that for free water surface wetlands dye
concentrates in the top few inches of the water column, but over the course of
the study, the dye gradually spread vertically and longitudinally. Since this study
took place in Boston harbor, it is impossible to say that the dye was mixed well
when it was released, which is why Hilton et al. (1998) never considered the dye
well mixed. However, these findings were also confirmed by Werner and Kadlec
(2000) in a study of fresh water free water surface wetlands. (Werner and
Kadlec 2000)
In the tracer study conducted in Tignall, GA, there was an attempt to mix
the tracer dye in to the mixing zone at the inlet. This should have taken care of
velocity profile effects when the dye was added. Also, the mixing zone in the
middle of the wetland cell should have also negated velocity profile effects. This
will be discussed in more detail later.
Since the system in the Tignall, GA, has been running for several years,
the expected result of this study is that the mean hydraulic retention time differs
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from the nominal retention time of the constructed wetland cell enough to
suggest that the cell is not adequately meeting design standards and, by
extension, treatment standards. The overall goal of this project was to
experimentally determine the mean hydraulic retention time of a constructed
wetland cell and to compare it to the nominal hydraulic retention time. Other
goals included determining how well the mixing zones are mixing.
This study takes place at the Water Reclamation Facility, in Tignall, GA.
The system consists of two Lemna cells and an aeration pond that pre-treats the
wastewater before it goes to the constructed wetlands system. The constructed
wetlands system consists of eight free water surface wetland cells that are
connected by a system of inlet and outlet structures that will allow for series,
parallel, or series/parallel flow. Each cell is 400’ by 60’, with three deep zones to
promote mixing. These deep zones will be referred to in this paper as inlet,
middle and outlet mixing zones according to its position in the wetland cell. The
flow rate for the period of time that the study took place ranged between 13
ft3/min to 16 ft3/min, so it is approximated as 14.5 ft3/min. This means that
approximate volume of the wetland cell was 160,776 ft3. Using information from
Precision Planning, this left the design depth at approximately 0.84 ft, and the
hydraulic retention time was approximately 15.5 days.
This study was done on the first wetland cell, which is one of the oldest
cells in the system, while the system was in series. Figures 1 and 2 on the
following pages shows the entire system, and how they are arranged.
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2.0 Literature Review
Different particles of water remain in the constructed wetland for varying
amounts of time. This produces varying amounts of treatment. Persson (2000)
found that plug flow is considered the optimal flow, because all fluid elements
reside around the nominal residence time. When the particles of water are
recombined at the outlet, this will produce an overall level of treatment, which is
dependent on the average retention time. This is because the biological
processes that provide treatment are time dependent. (Werner and Kadlec
2000)
One of the primary ways of characterizing this behavior is to calculate the
nominal detention time, which is the average contact time in the wetland. This is
because changes in hydraulic retention time can be deliberately caused by
changes in depth and flow rate. Plant and accumulated sludge depths can cause
these changes to become uncontrollable. This is defined as tn = Q/V, where Q is
the flow rate and V is the design volume. The nominal detention time assumes
no stagnation, short-circuiting, or dead zones occur so the relationship to the
actual flow behavior in a mature cell is minimal. Another way to characterize a
constructed wetland is by saying that the mean hydraulic retention time times the
flow rate defines the active volume, Va, which is where the treatment actually
takes place (Simi and Mitchell 1999). (Rash and Liehr 1999)
An alternative way of looking at the detention time is to construct a
residence time distribution (RTD). This represents a probability density function
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of the amount of time that a particle spends in the reactor and/or wetland. It is
scaled so that the integration of the curve is unity. The RTD function, or E(t), is
based on the flow rate and the effluent concentration of whatever the study has
used for a tracer, and to find a more accurate representation of the detention
time one must integrate the expression tE(t)dt. RTD is most often used in
constructing models, which will be briefly discussed later (Rash and Liehr 1999)
Since most constructed wetlands are designed as a sort of biochemical, or
biological, reactor, it seems prudent to go through some of these definitions
before going further. It has become apparent from a variety of research projects
that wetland reactors do not fit any particular set of limiting conditions and seem
to be an intermediate between a continuously stirred tank reactor (CSTR) and a
plug flow reactor (PRF) (Kadlec 1994). If completely mixed, all water particles, or
parcels, have an equal probability of leaving the wetland at a given moment, and
the system is thought of as a CSTR. If there is no distribution of times and all
parcels spend the same amount of time in the system, it is a PFR. Most
constructed wetlands are designed based on plug flow assumptions, which is an
ideal situation that does not often occur. Plug flow design has also been found to
result in over design (King et al. 1997). Deviation from plug flow can occur
because of channeling through preferential flow paths or exchanging of flow with
stagnant regions (Simi and Mitchell 1999). (Werner and Kadlec 2000)
In order to determine the average hydraulic retention time and gather
information for a residence time distribution (RTD), a tracer study is conducted.
The object of a tracer study is to build a tracer response curve. This curve is a
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graph of the concentration of the tracer versus time. Care must be taken
determining the frequency of sampling, because a missed dip or peak can
introduce inaccuracy when calculating the mean hydraulic retention time (Werner
and Kadlec 2000). The mean hydraulic retention time is characterized by the
centroid of the distribution under the curve (Simi and Mitchell 1999).
The shape of the curve can imply information about what conditions exist
in the constructed wetland. An asymmetrical curve with an extended tail may
mean that there are dead zones and channeling (Simi and Mitchell 1999). The
presence of two separate peaks clearly indicates the presence of two parallel
paths, where the first peak indicates the shorter route (Batchelor and Loots
1997). A curve with a large standard deviation suggests the presence of short-
circuiting flow paths and flow re-circulating zones (Persson et al. 1999). Finally,
a large difference between the observed mean detention period and the nominal
detention period suggests the presence of zones of stagnation in the system
(Persson et al. 1999).
After graphing the tracer response curve, it is possible to find the retention
time distribution, or RTD. As stated above, the RTD is the distribution of times
that parcels of water spend in the constructed wetland. RTD is often used in the
modeling of the hydraulic retention time for a specific wetland. Considering the
wetland as a series of CSTRs and PFRs makes this acceptable. (Werner and
Kadlec 2000) While the data from this study can be used to construct such a
model, this study is more concerned with the actual hydraulic retention time of
the constructed wetlands.
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One concept that will be used in this study is the idea of hydraulic
efficiency, λ. This efficiency is based on design standards, or how close the
wetland cell is to design specifications. Persson (2000) also defines the
hydraulic efficiency as “how well the incoming water distributes within the pond.”
This is a proportion that reflects the ability of the constructed wetland to distribute
the inflow evenly across the detention system and the amount of mixing or
recirculation. Dividing the mean hydraulic retention time by the nominal hydraulic
detention time derives this proportion. This proportion is also equal to the
effective volume divided by the design volume, which will aid the analysis of the
data. When stated in terms of volume, the proportion is referred to as e (Persson
2000). Persson et al. (1999) found that a good hydraulic efficiency is
characterized by a � higher than 0.75; satisfactory hydraulic efficiency is
characterized by a � between 0.50 and 0.75; and poor hydraulic efficiency is
characterized by a � less than 0.50. Most of the wetland designs in the Persson
et al. (1999) study had � of less than 0.50, but still give satisfactory treatment.
This could be because of the over design inherent in the plug flow models used
to design constructed wetland cells. (Persson et al. 1999)
Persson et al. (1999) evaluated thirteen different wetland designs using a
computer program called MIKE-21, which is a two dimensional depth integrated
hydraulic model that simulated the hydraulic regime based on length to width
ratios, impediments, and inlet and outlets. The layouts with the best hydraulic
efficiencies were an elongated pond, a pond with baffles, and a system with three
inlets and one outlet. The elongated pond’s length to width ratio was greater
10
than 4:1, or the results were to close to the pond layout that had a length to width
ratio of 3:1.
Another important factor in tracer studies is the tracer dye itself.
Comparative wetland studies demonstrate that bromide, lithium, and fluorescein
dyes are all approximately equivalent (Kadlec 1994). Before conducting this
study, bromide and fluorescein dyes were compared in the literature. Bromide is
often used because of its low background concentration in most soils, and its low
biological and chemical reactivity in a soil environment. Bromide concentrations
in ryegrass grown in well-drained soil were greater than that of ryegrass grown
on poorly drained soil close to wetland conditions. However, in soils with a
higher fertility, or more nitrogen, there was no difference (Schnabel et al. 1995.
The proper instrumentation was not immediately available to conduct any tests to
confirm this would be the case for the wetland cells in Tignall, GA. )
Rhodamine, as an example of fluorescein dyes, is fluorescent, resists
adsorption, and is detectable at very low concentrations (0.1 mg/L). It has been
reported to produce no major problems when released in low concentrations and
is light sensitive. Eventually, it degrades in sunlight and is no longer present in
the environment. Rhodamine concentrations are determined by extrapolation
from a standard curve of fluorescence units versus a range of standard
concentration. (Simi and Mitchell 1999)
For this study, a flourescein dye seems to be the best tracer dye. The
plant material does not absorb it, and it is detectable in small concentrations.
11
The type of dye used in this study will, according to the manufacturer, eventually
completely break down and not be noticeable to downstream inhabitants.
Once the mean hydraulic retention time is found, the effective volume can
be determined. Then suggestions can be given for increasing the hydraulic
retention time. Such suggestions could indicate that modifying the vegetation
layout or dredging the mixing zones which would immediately improve the
hydrodynamic conditions.
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3.0 Methods
3.1 Choice of dye
The choice of dye had been discussed in the literature review. The use of a
flourescein dye was the best solution, but there are several types of flourescein
dyes. Rhodamine is a type of red dye that lasts about three to five days
according to the manufacturer; however, according to the HRT that the cells were
designed for, a dye that lasted longer was needed. It was decided that the
yellow/green dye distributed by Bright Dyes would be the best dye to use for the
following reasons.
1. The manufacturer states that the dye breaks down in seven days.
2. A spectrophotometer could be used to instead of a flourometer to analyze
the samples, thereby solving any scheduling conflicts with other
researchers. This also solves the problems of masking by other
chemicals.
3. It comes in several forms—the liquid form being the least messy and the
most desirable.
3.2 Calibration of the dye concentrations to the absorbance
The yellow/green dye is best seen in a spectrophotometer at 490 nm and
520 nm wavelengths according to the manufacturer. By using wastewater
without dye in it as the blank that the spectrophotometer needs to compare the
samples to, the change in absorbance is calibrated to the concentration in those
samples that have dye in them.
13
Using Beer’s Law, which states that if absorbance values are below
1.0000 a better linear relationship between absorbance and concentration is
found, it was decided that 520 nm was the best wavelength since at 520 nm the
more samples with absorbances below 1.0000 were found so that a better
calibration relationship could be obtained at this wavelength. All samples and
calibration sets have been analyzed at this wavelength. This has given
significant linear relationships between the concentration of dye in the samples
and the absorbance.
In the beginning, the calibrations were done at the beginning of the
experiment, but when replicating the experiment it was found that it is best to
calibrate each time the samples are retrieved from the ISCOs. Further, the
calibrations were divided into sets to increase the significance of the linear
relationship sought. These calibration sets where divided as follows:
1. 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 mg of active dye/L,
2. 0.0, 2.0, 4.0, 6.0, 8.0,10.0 mg of active dye/L,
3. 0.0, 20.0, 40.0, 60.0, 80.0, 100.0 mg of active dye/L, and
4. 0.0, 200.0, 400.0, 600.0, 800.0, 1000.0 mg of active dye/L.
This provided significant linear relationships with R2’s ranging from 0.99 to 0.86,
which are very good for this type of calibration.
3.2.1 Initial dye concentrations
Previous experience with cell 4 had indicated that the concentration had to
be high, or the dye was too diluted to find with either a flourometer or a
spectrophotometer. Even at 350 mg active dye/L this held true. From the
14
calibrations, it was known that at 700 mg active dye/L the absorbances were
approximately 3.0 almost every time, which allowed for dilution. This was three
times what was needed to comply with Beer’s Law, so 700 mg active dye/L was
decided to be the most acceptable.
Working at the maximum design operating depth, the depth of the wetland
cell was approximately six inches deep and knowing that the mixing zones were
three feet deep, calculations revealed that the volume of the mixing zone was
about 7200 ft3 or 219.5 L. It required about three liters of dye to bring the inlet
mixing zone up to the target concentration.
3.2.2 Quality Control
Because the characteristics of wastewater are always changing, it is very
important to keep the calibration as current as possible. To this end, the
following procedure was used to insure that the relationship found in the
correlation remains as accurate as possible.
Every time samples were retrieved, another liter of wastewater was taken
as a blank sample for calibration and quality control. Then one 20 mL sample
was chosen from each sampler set. After the 3 mL were taken for analysis, the
sample was spiked with enough dye to bring a 3 mL volume without any dye in it
to a 5 mg active dye/L. After each sample is analyzed, the spiked sample’s
absorbance was compared to the appropriate absorbance for that concentration
using:
%D = ((true value-found value)/true value) 100,
where %D = percent difference, true value = absorbance of the spiked sample, and
15
found value = absorbance according to the calibration relationship. If the percent difference is more than 5%, then the calibration was redone with
the new wastewater blank, and the samples re-analyzed.
3.3 Dye Degradation
This experiment was set up to check the manufacturer’s claims as to how
long the dye existed in the wetland cell. Since the prototype run had been
affected by the recycling of wastewater, it seemed relevant to also test how
quickly the dye degraded. Two aquariums were borrowed from the
Environmental Water Quality lab. By placing the aquariums in the cell, the water
should undergo all of the conditions of the dye in cell 1, except flow. This will be
used to gauge how long Experiment 2 should run and examine degradation rates
The aquariums were filled with wastewater from wetland cell 2, and dye
was added so that each would have a concentration of 700 mg active dye/L. The
aquariums were placed in the inlet-mixing zone of cell 2, in case of over flow, and
left for the duration of the study. Samples were taken from each aquarium at the
same time that samples were picked up from the ISCO samplers for Experiment
2. These samples were analyzed using the spectrophotometer and were used
as a measure of how the dye degraded in the wetland cell.
The dye in this experiment did not actually degrade the way the
manufacturer explained it would. According to the manufacturer, the dye
degrades as the BOD in the wetland cell does, or at most in twenty-one days.
The following tables, however, show that the manufacturer could be wrong.
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Table 1. Absorbance from the dye in Aquarium 1
Date Absorbance Concentration, mg/L 02/22/02 2.9341 700.46 02/26/02 3.0060 717.63 02/28/02 3.0243 722.00 03/08/02 2.9467 703.47 03/12/02 2.5970 612.00
Table 2. Absorbance from the dye in Aquarium 2
Date Absorbance Concentration (mg/L) 02/22/02 3.0909 737.8964 02/26/02 3.1690 756.5414 02/28/02 3.1546 753.1037 03/08/02 2.3290 556.0066 03/12/02 0.9191 219.4185
Aquarium 2 overflowed on 3/4/2002, and both aquariums were iced over
so that it was impossible to get a sample. By 3/9/2002, there was no more dye in
the samples from the outlet-mixing zone. As can be seen there was little
variation in the absorbances from aquarium 1, and what variation there is could
be the result of evaporation or dew. Therefore, it can be suggested that there
was no actual dye degradation going on in the wetland cell, unless flow plays a
more important part than any other variable.
Using the relationships, C = C0e-kt, where k is the rate constant for dye
degradation, and C0 is the original concentration of 750 mg active dye/L, Figure 3
is generated. Using linear regressions, the R2 for Aquarium 1 is 0.46, and the R2
for Aquarium is 0.58. This suggests that degradation did not occur during the
experiment, or if it did occur, not as the manufacturer expected.
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-0.35
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0 2 4 6 8 10 12 14 16 18
Time, days
ln(C
/Co)
Aquarium 1 Aquarium 2
Figure 3. The relationship between time and the degradation of the dye.
3.4 Prototype run
The first sampling run was approximately 3 weeks long, and occurred
during the fall of 2001. The dye was added 10/9/01. To provide the appropriate
mixing, the dye was introduced to system via the weir station above the wetland
cells. An ISCO sampler will be used to automate the sampling process, and the
tracer used was the FLT Yellow/Green, a specially formulated version of
flourescine dye. It was reported to not absorb to organic matter and to exist for
five to seven days. The sampling frequency was to occur in the following
manner: every two hours when the tracer is expected to go through the sampling
point, and every four hours during those times when the tracer is not expected to
go through the sampling point. However, after the first run, this sampling
18
frequency was revised to reflect difference between the design hydraulic
retention time and what is actually going on in the wetland cells. A sampling
point was set up in the last mixing zone of the wetland cell. Each sample was
about 20 mL.
There were six sampling points set up in the middle-mixing zone. These
were in pairs of three on either side of the middle-mixing zone. One pair will be
at 15’, the next at 30’, and the last at 45’. These will used to determine whether
or not the mixing zone is actually doing what it is supposed to be doing—mixing
the wastewater to improve homogeneity of the wastewater to improve treatment.
The experimental run did provide good data for the mixing zone analysis;
however, as was found out after the prototype run, the operator of the facility was
recycling wastewater. This recycled the dye, which as explained above, was not
degrading as expected. However, the middle mixing zone data was still good,
which was fortuitous because of some mechanical problems during the
experimental run. The samples taken from the middle mixing zone could be
used to test the claim that the mixing zone increased mixing of the wastewater,
because the absorbances could be analyzed to show if there was any decrease
in difference in the wastewater on the outlet side of the mixing zone.
3.5 Experimental Run
The second sampling run was about 18 days long and occurred during the
late winter of 2002. The dye was added 2/18/02. To provide the appropriate
mixing, the dye should be introduced to system via the weir station above the
wetland cells. An ISCO sampler will be used to automate the sampling process.
19
The Environmental Water Quality Laboratory had several programmable ISCO
6700s available. An ISCO sampler is programmable with the capacity to hold
twenty-four bottles. The tracer used will be the FLT Yellow/Green, a specially
formulated version of flourescein dye. It was reported to not absorb to organic
matter and to exist for five to seven days. The sampling frequency should occur
in the following manner: every two hours when the tracer is expected to go
through the sampling point, and every four hours during those times when the
tracer is not expected to go through the sampling point. A sampling point was
set up in the last mixing zone of the wetland cell. Each sample was about 20 mL.
There were six sampling points set up in the middle-mixing zone. These
were in pairs of three on either side of the middle-mixing zone. One pair will be
at 15’, the next at 30’, and the last at 45’. These sampling points were used to
determine whether or not the mixing zone is actually doing what it is supposed to
be doing—mixing the wastewater to improve homogeneity of the wastewater to
improve treatment.
Next, approximately one liter of water was taken from the inlet structure as
a blank and to construct a calibration curve for the experimental run. Third, the
ISCO samplers were put into place—one at each mixing zone. Then, enough
dye was placed into the inlet-mixing zone of cell 1 so that the water there had a
concentration of 700 mg active dye/L. Fifth, the mixing zone was stirred using a
long pipe for approximately 3 minutes. This was the last disturbance in the
wetland cell until the end of the experiment.
20
The ISCO sampler, sampler 1, was placed at the inlet-mixing zone. This
sampler sampled (20 mL) once a day to give an idea of how long it takes the dye
to dissipate and/or travel from the first mixing zone. The next ISCO sampler,
sampler 2, was placed at the next mixing zone. This sampler sampled (20 mL)
once a day, from the middle (30’) line on the inlet side. It was also used to draw
samples (20mL) from each side of the mixing zone (inlet and outlet) at the 15’,
30’, and 45’ lines that were installed there.
The last ISCO sampler, sampler 3, was placed at the end of the wetland
cell. This sampler sampled (20 mL) every four hours, until dye traces were
confirmed in the middle-mixing zone. Then it was set up to sample every two
hours. Figure 4 will show the position of the sampling points.
21
3.6 Climate conditions
Table 3. Rainfall data for the experimental run
Date Tignall Dearing Watkinsville Weighted Average (in)
18-Feb 0 0 0 0.00 19-Feb 0 0 0 0.00 20-Feb 0.25 0.15 0.16 0.20 21-Feb 0 0 0.01 0.00 22-Feb 0 0 0 0.00 23-Feb 0 0 0 0.00 24-Feb 0 0 0 0.00 25-Feb 0 0 0 0.00 26-Feb 0 0.01 0.01 0.01 27-Feb 0 0 0 0.00 28-Feb 0 0 0 0.00 1-Mar 0 0 0 0.00 2-Mar 0 1.79 1.68 0.00 3-Mar 2.35 0.23 0.34 2.19 4-Mar 0 0 0 0.00 5-Mar 0 0 0 0.00 6-Mar 0 0 0 0.00 7-Mar 0 0 0 0.00 8-Mar 0 0 0 0.00 9-Mar 0 0.21 0.24 0.11
10-Mar 0 0.01 0 0.00 11-Mar 0 0 0 0.00 12-Mar 1.45 0.42 0.84 1.04 13-Mar 0 0 0.11 0.03 14-Mar 0 0.01 0 0.00 15-Mar 0 0 0 0.00 16-Mar 0 0 0 0.00 17-Mar 0 0 0.02 0.01 18-Mar 0 0 0 0.00 19-Mar 0 0 0 0.00 20-Mar 0 0 0.13 0.03
3.7 Bathymetry survey
It was felt that plant density and wetland topography were important to the
interpretation of the results of this study. Plant density and sludge volume are
22
excluded zones that are planned for in the design of a wetland cell. The survey
done of the wetland cell was done to ascertain how the wetland has changed
over time. While no data points were taken in the mixing zones because of the
sludge depth, enough data points were taken of the wetland cell to characterize
the changes that have occurred. The plant density survey was a little more
basic. By constructing a ten foot grid, the plant density of each square was
estimated on a scale of 1 to 0, 1 being fully vegetated, 0.5 being half vegetated,
and 0 being open water.
24
4.0 Results
4.1 Middle-Mixing Zone Grab Samples
Table 4. The Absorbances and Concentrations from the Inlet side of the Middle-
Mixing Zone
Absorbance Concentration, mg/L
Date 15 ft 30 ft 45 ft 15 ft 30 ft 45 ft 10/10/01 ---** --- 0.0004 0 0 0.13 10/11/01 --- 0.0010 0.0234 0 0.18 2.22 10/12/01 0.0057 0.0088 0.0075 0.61 0.89 0.77 10/13/01 0.0110 --- --- 1.09 0 0 10/15/01 0.0692 0.0505 0.0163 6.38 4.68 1.57 10/16/01 0.2940 0.0355 --- 26.82 3.32 0 10/17/01 0.0293 0.0219 0.0250 2.75 2.08 2.36 10/18/01 0.1247 0.0204 0.0122 11.43 1.94 1.20 10/19/01 0.1263 0.0246 0.0110 11.57 2.33 1.09 **--- takes the place of a negative absorbance. Since this is technically a sample with less absorbance then the blank, it is not considered to have any dye in it. Table 5. The Absorbances and Concentrations from the Outlet side of the
Middle-Mixing Zone
Absorbance Concentration, mg/L
Date 15 ft 30 ft 45 ft 15 ft 30 ft 45 ft 10/10/01 --- --- --- 0 0 0 10/11/01 --- 0.0132 --- 0 1.29 0 10/12/01 0.0140 0.0059 0.0036 1.36 0.63 0.42 10/13/01 --- --- --- 0 0 0 10/15/01 0.0173 0.0346 0.0120 1.66 3.24 1.18 10/16/01 --- --- 0.0035 0 0 0.41 10/17/01 0.0222 0.0228 0.0197 2.11 2.16 1.88 10/18/01 0.0151 0.0115 0.0091 1.46 1.14 0.92 10/19/01 0.0055 0.0213 0.0158 0.59 2.03 1.53
First, an analysis of variance was done to test the interaction between the
position of the sampling points and the distance from the edge. These results
25
are summarized by the following table and chart. This indicates that the
interaction between distance and position significantly influences the dye
concentration. The mean concentration at the outlet position for each distance is
very close to each other.
Table 6. Analysis of variance for the interaction between position and distance.
Source Term DF Sum of Squares
Mean Square
F-Ratio Probability Level
A: Distance 2 84.84373 42.42187 3.03 0.057757 B: Position 1 69.81407 69.81407 4.98 0.030300*
AB 2 90.8718 45.4359 3.24 0.047750* S 48 672.5117 14.01066
Total (Adjusted) 53 918.0413 Total 54
* Term significant at alpha = 0.05
0.00
7.50
15.00
22.50
30.00
Inlet Outlet
Means of DyeConc
Position
Dye
Con
c
Distance153045
Figure 5. Comparison of the mean dye concentration at each distance and
position
By testing the analysis of variance the two positions, inlet and outlet,
based on distance, it was found that there was not a significant difference
between the two positions. To get more information, a paired t-test was done
26
between the two positions, or between the dye concentrations into the mixing
zone and the dye concentrations out of the mixing zone. The results are in Table
8. So in one case the mean dye concentrations going out of the mixing zone and
into the mixing zone is equal to zero. And in the other two cases where H0 is
rejected, the difference is significant.
Table 7. Results from a paired t-test of the dye concentrations into and out of the
mixing zone
Alternative Hypothesis
T-Value Probability Level Decision (5%)
Dye In-Dye Out<>0 2.0726 0.04826 Reject Ho Dye In-Dye Out<0 2.0726 0.97587 Accept Ho Dye In-Dye Out>0 2.0726 0.02413 Reject Ho
4.2 Hydraulic Retention Time Analysis
The data from the experimental run from the outlet-mixing zone is
presented in the two tables below. The codes used in Table 8 are:
• E means no sample collected,
• C means contaminated by a previous sample, and
• S means sludge affected the analysis of the sample.
This table is referenced from the introduction of the dye. Using this table, the
graph in Figure 6 was compiled.
The trapezoidal rule was used to estimate the mean hydraulic retention
time, which is the centroid under the curve. This rule states that the sum of the
product of concentration and time, divided by the sum of the concentrations
should estimate the average time, or � (concentration � time)/� (concentration)
=average time. Therefore, the mean hydraulic retention time is 7.7 days. There
27
Table 8a. Dye Concentrations in the Outlet Mixing Zone
Sample #
Conc., mg/L
Time, hrs
Sample #
Conc., mg/L
Time, hrs
Sample #
Conc., mg/L
Time, hrs
1 0 0 27 E 104 53 2.6 197.2 2 0 4 28 0 108 54 2.6 199.2 3 0 8 29 4.6 112 55 2.5 201.2 4 0 12 30 4.2 116 56 1.4 203.2 5 0 16 31 6.9 120 57 E 205.2 6 0 20 32 5.6 124 58 E 207.2 7 0 24 33 3.6 128 59 E 209.2 8 0 28 34 2.3 132 60 6 211.2 9 0 32 35 E 136 61 2.2 213.2
10 0 36 36 2.2 140 62 0.7 215.2 11 0 40 37 4.7 144 63 3.5 217.2 12 0 44 38 4.4 148 64 4.3 219.2 13 0 48 39 4.6 152 65 E 221.2 14 0 52 40 3.2 156 66 E 223.2 15 0 56 41 E 160 67 E 225.2 16 0 60 42 3.3 164 68 E 227.2 17 0 64 43 3.9 168 69 E 229.2 18 0 68 44 5.2 172 70 S 231.2 19 0 72 45 5.9 176 71 4.1 233.2 20 0 76 46 8.4 180 72 7 235.2 21 0 80 47 5.7 184 73 C 235.5 22 0 84 48 6.2 188 74 0.4 239.5 23 0 88 49 0 189.2 75 0.5 243.5 24 0 92 50 1.7 191.2 76 E 247.5 25 8.4 96 51 2.1 193.2 77 E 251.5 26 3.3 100 52 1.6 195.2 78 E 255.5
28
Table 8b. Dye Concentrations in the Outlet Mixing Zone, Continued
Sample #
Conc., mg/L
Time, hrs
Sample #
Conc., mg/L
Time, hrs
79 0.2 259.5 105 0.2 363.5 80 0.5 263.5 106 E 367.5 81 0.8 267.5 107 E 371.5 82 3.1 271.5 108 0.3 375.5 83 0.5 275.5 109 0.3 379.5 84 0.6 279.5 110 0.3 383.5 85 0.6 283.5 111 0.8 387.5 86 0.1 287.5 112 1 391.5 87 0.4 291.5 113 0.6 395.5 88 0.3 295.5 114 0.5 399.5 89 0.3 299.5 115 0.2 403.5 90 0.5 303.5 116 E 407.5 91 0.1 307.5 117 E 411.5 92 0.3 311.5 118 0.8 415.5 93 0.3 315.5 119 0.5 419.5 94 0.3 319.5 120 0.6 423.5 95 0.5 323.5 121 0 427.5 96 E 327.5 122 0 431.5 97 0.2 331.5 123 0 435.5 98 0 335.5 124 0 439.5 99 E 339.5 125 0 443.5
100 E 343.5 126 0 447.5 101 E 347.5 127 0 451.5 102 0.1 351.5 128 0 455.5 103 0.5 355.5 104 0.3 359.5
also appears to be a range of hydraulic retention times that appear to fall
between 4.5 days to 17.8 days.
The flow rate for the period that the study took place ranged between 13
ft3/min to 16 ft3/min, so it was approximated as 14.5 ft3/min. This means that
approximate volume of the wetland cell was 160,776 ft3 (4553 m3 or 1,202,687
gallons). Interpolating from the table provided by Precision Planning, Inc. in the
29
design report, the depth should be 0.84 ft, and the nominal hydraulic retention
time (tN) should be 15.5 days. The actual design depth is 0.5 ft.
Figure 6. Tracer study curve for the second experiment
30
4.3 Bathymetry survey
In the next four figures, there are two three-dimensional maps and two
contour maps of the depth of the cell one and the plant density of cell one.
Figures 7 and 8 are survey maps of relative elevations, and because of the
sludge depth in the mixing zones, surveying points were only taken at the
corners of each wetland zone. Figures 9 and 10 are graphical representations of
a very basic plant density survey, where 1.0 means that grid was completely
vegetated, 0.5 means that the grid was half vegetated, and 0.0 means that the
grid was not vegetated at all. The grid for Figure 8 is also larger, in order to
encompass vegetation that is growing outside of the original wetland cell.
In order to orient the reader for Fig. 7 and 8, the side of the wetland cell
farthest of the x-axis is the side closest to the aeration ponds. It is also the side
from which the sampling points are measured.
In order to orient the reader for Fig. 9 and 10, the side of the wetland cell
closest to the x-axis is the side closest to the aeration pond. The density is done
in proportions. A density of 1.0 is has a density of 100%, and a densities of 0
and less are open water.
35
5.0 Discussion and Conclusions
The tracer study had a very distinctive pattern. It is more like uniform flow
than a normalized or bell curve. For the purposes of this study, the graph will be
called a curve. The curve itself had three very distinctive peaks, with four smaller
ones. This suggests that the wetland cell is experiencing short-circuiting and
stagnation zones. The last peak and the tail of the curve further indicate this.
The mean hydraulic retention time is 7.7 days. Referring to Figure 6,
there is also a range of hydraulic retention times that appear to fall between 4.5
days to 17.8 days. The first peak indicates a short circuit that is faster than the
others, while the stagnation zones are indicated by the lingering tail of the curve.
Now, the hydraulic efficiency should be analyzed. According to Persson
et al. (1997), the hydraulic efficiency is calculated as mean hydraulic retention
time divided by the nominal hydraulic detention time, which gives means that λ is
equal to 0.497, or 0.50. This means that the wetland cell could be on the verge
of sliding into poor hydraulic efficiency, which is the characterized by a λ between
0.50 and 0.25.
Also, as stated in Persson (2000) λ equal to e that is a proportion that is
also equal to the effective volume divided by the design volume. This means that
the effective volume of the wetland cell for this experiment was approximately
601,000 gallons, or half of the design volume. From this, it can be concluded
that cell one is accumulating more sludge and plant matter than is allowed in the
36
design specifications. Once the sludge and plant debris is removed, the mean
hydraulic retention time should become longer and approach design hydraulic
retention time.
This conclusion is not as well supported by the mixing zone data. In two
out of the three cases possible in a paired t-test, the means of the dye
concentrations in and the dye concentrations out were found to be significantly
different (Table 8). However, based on the results of the analysis of variance
tests, it is the interaction between the positions, inlet and outlet side of the mixing
zone, and the distance from the side that the samples were taken that provides
the difference in dye concentrations that suggests mixing is still occurring in the
mixing zones.
From visual observations, it does appear as though the mixing zone is
filling with sludge. In addition, the higher mean at the fifteen feet distance also
indicates that more dye is reaching that point. It appears that the mixing zone
could still be providing homogeneity by acting as a stagnation zone. However,
there is still the preferential flow that is providing a 4.5 days hydraulic retention
time for part of the dye concentration.
Part of the answer may be found in the plant density data. Referring to
Figures 9 and 10, there are areas of open water. These areas may be providing
faster flow conditions when the information is combined with the information from
Figures 7 and 8. The survey maps suggest that the side nearest the aeration
pond, and nearest to the fifteen feet sampling points, has a steeper slope than
the other side. In other areas, the combination of fully vegetated and open water
37
areas may be producing stagnation zones, which the mixing zone data suggests
it has become.
In conclusion, the wetland cell should be monitored carefully. If the
hydraulic efficiency begins to decline, or the interaction between the inlet and
outlet side of the mixing zone and the distance from the side of the wetland cell
decreases, measures should be taken to remove the sludge buildup in the mixing
zones and replant the wetland cell.
38
6.0 References
Batchelor, Allan and Pierre Loots. 1997. "A critical evaluation of a pilot scale subsurface flow wetland: 10 years after commissioning." Water Science and Technology, 35(5), 337-343.
King, Andrew C., Cynthia A. Mitchell and Tony Howes. 1997. “Hydraulic tracer
studies in a pilot scale subsurface flow constructed wetland.” Water Science and Technology, 35(5), 189-196.
Hilton, Amy B., Drew L. McGillivary, and E. Eric Adams. 1998. “Residence time
of freshwater in Boston’s inner harbor. Journal of Waterway, Port, Coastal, and Ocean Engineering, 124(2), 82-89.
Kadlec, Robert H. 1994. "Detention and mixing in free water wetlands."
Ecological Engineering, 3, 345-380. Persson, J., N.L.G Someo, and T.H.F. Wong. 1999. "Hydraulic efficiency of
constructed wetlands and ponds." Water Science and Technology, 40(3), 291-300.
Persson, J. 2000. “The hydraulic performance of ponds of various layouts.”
Urban Water, 2(3), 243-250. Precision Planning, Inc. 1992. Excerpts from design report. Rash, Jonathan K. and Sarah K. Liehr. 1999. "Flow pattern analysis of
constructed wetlands treating landfill leachate." Water Science and Technology, 40(3), 309-315.
Schnabel, R.R., W.L. Stout, and J.A. Shaffer. 1995. "Uptake of a hydrologic
tracer (bromide) by ryegrass from well and poorly drained soils." Journal of Environmental Quality, 24, Sept.-Oct., 888-892.
Simi, Anne L., and Cynthia A. Mitchell. 1999. "Design and hydraulic
performance of a constructed wetland treating oil refinery wastewater." Water Science and Technology, 40(3), 301-307.
Werner, Timothy M. and Robert H. Kadlec. 2000. "Wetland residence time
distribution modeling." Ecological Engineering, 15, 77-90.
39
7.0 APPENDIX
7.1 Prototype Run
Mixing Zone Grab Samples
Table 9. Inlet Side of the Mixing Zone
Absorbance at 520 nm Date 15 ft 30 ft 45 ft
10/10/2001 -0.0137
-0.0044
0.0004
10/11/2001 -0.0059
0.0010 0.0234
10/12/2001 0.0057 0.0088 0.0075 10/13/2001 0.0110 -
0.0149 -
0.0063 10/15/2001 0.0692 0.0505 0.0163 10/16/2001 0.2940 0.0355 -
0.0011 10/17/2001 0.0293 0.0219 0.0250 10/18/2001 0.1247 0.0204 0.0122 10/19/2001 0.1263 0.0246 0.0110
Concentration, mg active indgredient/L
Date 15 ft 30 ft 45 ft 10/10/2001 N/D* N/D 0.1267 10/11/2001 N/D 0.1812 2.2177 10/12/2001 0.6085 0.8903 0.7722 10/13/2001 1.0903 N/D N/D 10/15/2001 6.3815 4.6814 1.5722 10/16/2001 26.8186** 3.3177 N/D 10/17/2001 2.7540 2.0813 2.3631 10/18/2001 11.4271** 1.9449 1.1994 10/19/2001 11.5726** 2.3268 1.0903
40
Table 10. Outlet Side of the Mixing Zone
Absorbance at 520 nm Date 15 ft 30 ft 45 ft
10/10/2001 -0.0145
-0.0075
-0.0056
10/11/2001 -0.0082
0.0132 -0.0069
10/12/2001 0.0140 0.0059 0.0036 10/13/2001 -
0.0100 -
0.0041 -
0.0089 10/15/2001 0.0173 0.0346 0.0120 10/16/2001 -
0.0037 -
0.0069 0.0035
10/17/2001 0.0222 0.0228 0.0197 10/18/2001 0.0151 0.0115 0.0091 10/19/2001 0.0055 0.0213 0.0158
Concentration, mg active indgredient/L
Date 15 ft 30 ft 45 ft 10/10/2001 N/D N/D N/D 10/11/2001 N/D 1.2904 N/D 10/12/2001 1.3631 0.6267 0.4176 10/13/2001 N/D N/D N/D 10/15/2001 1.6631 3.2359 1.1813 10/16/2001 N/D N/D 0.4085 10/17/2001 2.1086 2.1631 1.8813 10/18/2001 1.4631 1.1358 0.9176 10/19/2001 0.5903 2.0267 1.5267
41
Table 11. Outlet Zone Samples Over Time
Sample #
Date Absorbance at 520 nm
Concentration, mg of active ingredient/L
Hours
1 10/9/01 4:18 PM 0.0242 3.1032 0 2 10/9/01 6:18 PM 0.0166 2.4122 2 3 10/9/01 8:18 PM -0.0098 0.0122 4 4 10/9/01 10:18 PM -0.0258 N/D* 6 5 10/10/01 12:18 AM -0.0247 N/D 8 6 10/10/01 2:18 AM -0.0199 N/D 10 7 10/10/01 4:18 AM -0.0284 N/D 12 8 10/10/01 6:18 AM -0.0207 N/D 14 9 10/10/01 8:18 AM -0.0221 N/D 16
10 10/10/01 10:18 AM -0.0213 N/D 18 11 10/10/01 12:18 PM -0.0157 N/D 20 12 10/10/01 2:18 PM -0.0029 0.6395 22 13 10/10/01 4:18 PM 0.0105 1.8577 24 14 10/10/01 6:18 PM 0.0024 1.1213 26 15 10/10/01 8:18 PM 0.0034 1.2122 28 16 10/10/01 10:18 PM -0.0006 0.8486 30 17 10/11/01 12:18 AM -0.0045 0.4940 32 18 10/11/01 2:18 AM -0.0084 0.1394 34 19 10/11/01 4:18 AM -0.0141 N/D 36 20 10/11/01 6:18 AM -0.0121 N/D 38 21 10/11/01 8:18 AM -0.0124 N/D 40 22 10/11/01 10:18 AM -0.0003 0.8758 42 23 10/11/01 12:18 PM -0.0051 0.4394 44 24 10/11/01 2:18 PM 0.0061 1.4577 46 25 10/11/01 4:18 PM 0.0072 1.5577 48 26 10/11/01 6:18 PM 0.0169 2.4395 50 27 10/11/01 8:18 PM 0.0120 1.9941 52 28 10/11/01 10:18 PM 0.0144 2.2122 54 29 10/12/01 12:18 AM 0.0155 2.3122 56 30 10/12/01 2:18 AM 0.0064 1.4849 58 31 10/12/01 4:18 AM 0.0101 1.8213 60 32 10/12/01 6:18 AM 0.0132 2.1031 62 33 10/12/01 8:18 AM 0.0071 1.5486 64 34 10/12/01 10:18 AM 0.0120 1.9941 66 35 10/12/01 12:18 PM 0.0096 1.7759 68 36 10/12/01 2:18 PM 0.0186 2.5941 70 37 10/12/01 4:18 PM -0.0037 0.5667 72 38 10/12/01 6:18 PM 0.0052 1.3758 74 39 10/12/01 8:18 PM 0.0004 0.9395 76 40 10/12/01 10:18 PM -0.0049 0.4576 78
42
41 10/13/01 12:18 AM -0.0078 0.1940 80 42 10/13/01 2:18 AM -0.0026 0.6667 82 43 10/13/01 4:18 AM -0.0100 N/D 84 44 10/13/01 6:18 AM -0.0081 0.1667 86 45 10/13/01 8:18 AM -0.0079 0.1849 88 46 10/13/01 10:18 AM 0.0018 1.0667 90 47 10/13/01 12:18 PM 0.0099 1.8031 92 48 10/13/01 2:18 PM 0.0245 3.1305 94 49 10/13/01 4:18 PM 0.0171 2.4577 96 50 10/13/01 6:18 PM 0.0130 2.0850 98 51 10/13/01 8:18 PM 0.0132 2.1031 100 52 10/13/01 10:18 PM 0.0119 1.9850 102 53 10/14/01 12:18 AM 0.0139 2.1668 104 54 10/14/01 2:18 AM 0.0130 2.0850 106 55 10/14/01 4:18 AM 0.0161 2.3668 108 56 10/14/01 6:18 AM 0.0192 2.6486 110 57 10/14/01 8:18 AM 0.0236 3.0486 112 58 10/14/01 10:18 AM 0.0284 3.4850 114 59 10/14/01 12:18 PM 0.0150 2.2668 116 60 10/14/01 2:18 PM 0.0242 3.1032 118 61 10/14/01 4:18 PM 0.0178 2.5213 120 62 10/14/01 6:18 PM 0.0293 3.5668 122 63 10/14/01 8:18 PM 0.0177 2.5123 124 64 10/14/01 10:18 PM 0.0155 2.3122 126 65 10/15/01 12:18 AM 0.0128 2.0668 128 66 10/15/01 2:18 AM 0.0093 1.7486 130 67 10/15/01 4:18 AM 0.0086 1.6849 132 68 10/15/01 6:18 AM 0.0060 1.4486 134 69 10/15/01 8:18 AM 0.0049 1.3486 136 70 10/15/01 10:18 AM 0.0413 4.6578 138 71 10/15/01 12:18 PM 0.0267 3.3305 140 72 10/15/01 2:18 PM 0.0361 4.1850 142 73 10/15/01 4:18 PM 0.0377 4.3305 144 74 10/15/01 6:18 PM 0.0039 1.2577 146 75 10/15/01 8:18 PM -0.0059 0.3667 148 76 10/15/01 10:18 PM -0.0808 N/D 150 77 10/16/01 12:18 AM -0.0066 0.3031 152 78 10/16/01 2:18 AM -0.0051 0.4394 154 79 10/16/01 4:18 AM -0.0104 N/D 156 80 10/16/01 6:18 AM -0.0071 0.2576 158 81 10/16/01 8:18 AM -0.0093 0.0576 160 82 10/16/01 10:18 AM -0.0064 0.3213 162 83 10/16/01 12:18 PM 0.0010 0.9940 164 84 10/16/01 2:18 PM 0.0115 1.9486 166
43
85 10/16/01 4:18 PM 0.0104 1.8486 168 86 10/16/01 6:18 PM 0.0138 2.1577 170 87 10/16/01 8:18 PM 0.0140 2.1759 172 88 10/16/01 10:18 PM 0.0069 1.5304 174 89 10/17/01 12:18 AM 0.0056 1.4122 176 90 10/17/01 2:18 AM 0.0075 1.5849 178 91 10/17/01 4:18 AM 0.0028 1.1577 180 92 10/17/01 6:18 AM 0.0060 1.4486 182 93 10/17/01 8:18 AM 0.0072 1.5577 184 94 10/17/01 10:18 AM 0.0091 1.7304 186 95 10/17/01 12:18 PM 0.0120 1.9941 188 96 10/17/01 2:18 PM 0.0154 2.3032 190 97 10/17/01 4:18 PM 0.0132 2.1031 192 98 10/17/01 6:18 PM 0.0087 1.6940 194 99 10/17/01 8:18 PM 0.0059 1.4395 196
100 10/17/01 10:18 PM 0.0017 1.0577 198 101 10/18/01 12:18 AM 0.0075 1.5849 200 102 10/18/01 2:18 AM 0.0047 1.3304 202 103 10/18/01 4:18 AM 0.0057 1.4213 204 104 10/18/01 6:18 AM 0.0069 1.5304 206 105 10/18/01 8:18 AM 0.0094 1.7577 208 106 10/18/01 10:18 AM 0.0141 2.1850 210 107 10/18/01 12:18 PM 0.0314 3.7578 212 108 10/18/01 2:18 PM 0.0249 3.1668 214
N/D mean no dye detected.
7.2 Second Sampling Run
Calibrations Sets
44
Table 12. Calibration Set for Date: 2/22/02
Set 1 mg/L abs mg/L abs
0 0 0 0 0.2 0.0041 0.2 0.0041 0.4 0.0089 *** 0.6 0.0071 0.6 0.0071 0.8 0.0089 0.8 0.0089 1.0 0.0109 1.0 0.0109
Set 2
mg/L abs 0.0 0 2.0 0.0193 4.0 0.0456 6.0 0.0678 8.0 0.0703
10.0 0.0913
Set 3 mg/L abs
0.0 0 20.0 0.1861 40.0 0.3649 60.0 0.5145 80.0 0.6708
100.0 0.8732
Set 4 mg/L abs
0.0 0 200.0 1.8043 400.0 2.6331 600.0 2.7806 800.0 2.8729
1000.0 2.9613
45
Table 13. Calibration set for Date 2/26/02
Set 1 mg/L abs
0 0 0.2 0.0045 0.4 0.0059 0.6 0.0091 0.8 0.0144 1.0 0.239
Set 2 mg/L abs
0.0 0 2.0 0.0302 4.0 0.0451 6.0 0.0715 8.0 0.0824
10.0 0.0986
Table 14. Calibration set for Date 2/28/02
Set 1 mg/L abs mg/L abs
0 0 0 0 0.2 0.0013 0.2 0.0013 0.4 0.0045 0.4 0.0045 0.6 0.0201 *** 0.8 0.0121 0.8 0.0121 1.0 0.0107 1.0 0.0107
Set 2 mg/L abs
0.0 0 2.0 0.025 4.0 0.0337 6.0 0.0518 8.0 0.0695
10.0 0.0784
46
Table 15. Calibration set for Date 3/4/02
Set 1 mg/L abs
0 0 0.2 0.0025 0.4 0.008 0.6 0.0096 0.8 0.0114 1.0 0.0321
Set 2 mg/L abs
0.0 0 2.0 0.0322 4.0 0.0615 6.0 0.0872 8.0 0.1157
10.0 0.1496
Table 16. Calibration Set for Date 3/12/002
Set 1 mg/L abs mg/L abs
0 0 0 0 0.2 0.0012 0.2 0.0012 0.4 0.0035 0.4 0.0035 0.6 0.0104 *** 0.8 0.0083 0.8 0.0083 1.0 0.0159 1.0 0.0159
Set 2 mg/L abs
0.0 0 2.0 0.0453 4.0 0.0607 6.0 0.0715 8.0 0.104
10.0 0.1243 Inlet Mixing Zone Concentrations
47
Table 17. Inlet mixing zone concentrations for the experimental run
Date Absorbance Concentration, mg/l
2/18/2002 --- --- 2/19/2002 0.0106 0.923163927 2/20/2002 0.0185 1.611182325 2/21/2002 0.0129 1.123473081 2/22/2002 -0.0211 0 2/23/2002 -0.0113 0 2/24/2002 -0.0041 0 2/25/2002 0.0008 0.069672749 Aquarium Samples Table 18. Dye degradation samples A1
Date Absorbance Time ln (Abs/Abs0)
02/22/02 2.9341 1 -0.02221 02/26/02 3.0060 5 0.001998 02/28/02 3.0243 7 0.008067 03/08/02 2.9467 15 -0.01793 03/12/02 2.5970 19 -0.14426 A2
Date Absorbance Time ln (Abs/Abs0)
02/22/02 3.0909 1 0.02985 02/26/02 3.1690 5 0.054804 02/28/02 3.1546 7 0.050249 03/08/02 2.3290 15 -0.25317 03/12/02 0.9191 19 -1.18297 Where A1 refers to Aquarium 1, and A2 refers to Aquarium 2.