APPENDIX F Time Series Plots of Experimental Results ...20... · This appendix contains time series...

APPENDIX F

Time Series Plots of Experimental Results

Experiments 1 - 7

F - 1

This appendix contains time series plots of all experimental data collected in this study,

as well as a description of difficulties encountered in each experiment. Only a summary

description of each experimental setup is provided. For more detail on the conditions of any

experimental setup, the reader is referred to the Materials and Methods Chapter.

First Experiment

The first experiment employed a single CSTR reactor, which was configured to

represent a reach of the Occoquan Reservoir from Bull Run Marina to the confluence of the

Bull Run and Occoquan Creek arms of the reservoir. The extraction of samples from the

reactor began after approximately one hydraulic detention time (HRT) had elapsed. The

principal purpose was to monitor the system when it was at or near steady state. Sampling of

the feed water and the reactor water column was begun after 6 days. Data were collected for

an additional 5 days before it was found that difficulties were being encountered in the

accuracy of the nitrate assay. Variability in the analytical results for nitrate in retrieved samples

of the UOSA effluent and Bull Run introduced unacceptable variability into the concentration

of the volume-weighted mixture made up to provide a feedwater concentration of 5 mg/L

NO3--N. Without accurate knowledge of the feedwater nitrate concentrations, it was

impossible to make satisfactory estimates of the removal by denitrification in the microcosm.

An additional operating problem was identified with the calibration of the ORP

electrodes. The experimental protocol initially developed required removal of the electrodes

from the microcosm for calibration 2 to 3 times per week. Ultimately, this was found to

introduce unacceptable quantities of air into the reactor, thereby altering the oxidation state of

the system. Therefore, in later experiments, the electrodes were not calibrated while the

reactors were sealed. This was not expected to introduce unacceptable errors into the water

column ORP measurements because Briley and Beauchamp (1971) found that the uncalibrated

electrodes produced the same results as the calibrated electrodes for the measurement of water

column ORP. In contrast, however, the sediment ORP measurement was more problematic.

Because Briley and Beauchamp (1971) found that long-term insertion into the reduced

sediment environment resulted in poisoning of the electrodes; the sediment ORP values may

not be usable in a quantitative sense. However, it was concluded that the relative values of

sediment ORP time series had relevance to the experimental results. For example, the changes

F - 2

of ORP values from day to day may reveal the trend of oxidation-reduction potential in the

sediment. Below are the time series plots of the first experiment results.

F - 3

0

1

2

3

4

5

6

7

8

9

7 8 9 10

Days

Con

cent

ratio

ns (m

g/L

N)

Feed AFeed BEff

Figure F-1. Time series of first experiment nitrate concentrations in the fresh feed water (Feed A), the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff).

0

1

2

3

4

5

6

7

8

9

7 8 9 10

Days

Con

cent

ratio

ns (m

g/L

N)

Feed AFeed BEff

Figure F-2. Time series of first experiment total Kjeldahl nitrogen concentrations in the fresh feed water (Feed A), the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff).

F - 4

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

7 8 9 10

Days

Con

cent

ratio

ns (m

g/L

P)

Feed AFeed BEff

The values below detection limit plotted at half the limit.

Detection Limit (0.01 mg/L P)

Figure F-3. Time series of first experiment orthophosphate concentrations in the fresh feed water (Feed A), the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff).

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

7 8 9 10

Days

Con

cent

ratio

ns (m

g/L

P)

Feed AFeed BEff

Figure F-4. Time series of first experiment total phosphorus concentrations in the fresh feed water (Feed A), the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff).

F - 5

0

5

10

15

20

25

7 8 9 10

Days

Con

cent

ratio

ns (m

g/L)

Feed AFeed BEff

Figure F-5. Time series of first experiment COD in the fresh feed water (Feed A), the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent.

0

0.05

0.1

0.15

0.2

0.25

7 8 9 10

Days

Con

cent

ratio

ns (m

g/L)

Feed AFeed B Eff


Detection Limit (0.1 mg/L)

Figure F-6. Time series of first experiment soluble iron concentrations in the fresh feed water (Feed A), the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff).

F - 6

0

0.1

0.2

0.3

0.4

0.5

7 8 9 10

Days

Con

cent

ratio

ns (m

g/L)

Feed AFeed BEff



Figure F-7. Time series of first experiment soluble manganese concentrations in the fresh feed water (Feed A), the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff).

0

50

100

150

200

250

300

350

400

450

500

0 2 4 6 8 10

Days

E h (m

V) Water

Sediment

The electrodes w ere taken out for calibration.

Figure F-8. Time series of first experiment Eh in the water column (Water) and sediment surface (Sediment).

F - 7

Second Experiment The second experiment was set up similarly to the first, with the only difference being

the sediment surface area. In the first experiment, the sediment surface area was the same as

the reactor cross-sectional area while the sediment surface area of second experiment was

calculated from the computed effective depth of the investigated reach of the Occoquan

Reservoir. As indicated in the previous section, the nitrate assay used in the first experiment

gave unreliable results, causing early termination of the experiment. To address this problem, a

pre-packaged analysis kit from the Chemetrics Corporation (Calverton, VA) was used instead

for this experiment. During the experiment, variability of feed water nitrate concentrations

was, however, still observed as shown in Figure F-9. Therefore, the experiment was terminated

after 6 days and other ways were considered to reduce the nitrate concentration variability of

the feed water. Ultimately, it was concluded that obtaining high accuracy with the field test kits

used was not possible; however, using the same mixture for a period of time could reduce

variability of the nitrate concentration in the feed water during that period. In the latter

experiments, a volume-weighted mixture of the UOSA effluent and Bull Run water was fed to

the microcosm for one to two weeks. Although the analysis from the Chemetrics Corporation

(Calverton, VA) did not solve the problem with variability in the analytical results of nitrate in

retrieved samples from the UOSA discharge and Bull Run, it was found to be more

convenient and suited the experimental protocol better. Therefore, the kit analysis system was

used for the rest of the study. Time series plots of this experiment results are as follows:

F - 8

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6

Days

Con

cent

ratio

ns (m

g/L

N)

Feed AEff

Figure F-9. Time series of second experiment nitrate concentrations in the fresh feed water (Feed A) and the effluent (Eff).

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6

Days

Con

cent

ratio

ns (m

g/L

N)

Feed AEff

The ammonia concentrations were close to or below detection limit (0.01 mg/L N).

Figure F-10. Time series of second experiment ammonia concentrations in the fresh feed water (Feed A) and the effluent (Eff).

F - 9

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6

Days

Con

cent

ratio

ns (m

g/L

N)

Feed A

Eff

Figure F-11. Time series of second experiment total Kjeldahl nitrogen concentrations in the fresh feed water (Feed A) and the effluent (Eff).

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 1 2 3 4 5 6

Days

Con

cent

ratio

ns (m

g/L

P)

Feed AEff



Figure F-12. Time series of second experiment orthophosphate concentrations in the fresh feed water (Feed A) and the effluent (Eff).

F - 10

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 1 2 3 4 5 6

Days

Con

cent

ratio

ns (m

g/L

P)

Feed AEff

Figure F-13. Time series of second experiment total phosphorus concentrations in the fresh feed water (Feed A) and the effluent (Eff).

0

2

4

6

8

10

12

14

16

0 1 2 3 4 5 6

Days

Con

cent

ratio

ns (m

g/L)

Feed A

Eff

Figure F-14. Time series of second experiment COD in the fresh feed water (Feed A) and the effluent (Eff).

F - 11

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 1 2 3 4 5 6

Days

Con

cent

ratio

ns (m

g/L)

Feed AEff



Figure F-15. Time series of second experiment soluble iron concentrations in the fresh feed water (Feed A) and the effluent (Eff).

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 1 2 3 4 5 6

Days

Con

cent

ratio

ns (m

g/L)

Feed AEff



Figure F-16. Time series of second experiment soluble manganese concentrations in the fresh feed water (Feed A) and the effluent (Eff).

F - 12

0

2

4

6

8

10

12

14

0 1 2 3 4 5 6

Days

pH

Figure F-17. Time series of second experiment pH

-200.00

-100.00

0.00

100.00

200.00

300.00

400.00

500.00

0 1 2 3 4 5 6

Days

E h (m

V) WaterSediment

The platinum electrode in the sediment was pushed deeper into the sediment.

Figure F-18. Time series of second experiment Eh in the water column (Water) and sediment surface (Sediment). The Eh was not corrected to E7 because the pH was recorded only once a day while the Eh was recorded each minute. The acquisition system started 214 minutes after the experiment had stared. On Day 4, the platinum electrode was pushed deeper into the sediment because the author speculated that the sediment might have settled and the tip of the electrode was getting out of the sediment, causing the sediment Eh to rise.

F - 13

Third Experiment

The third experiment was conducted with a single CSTR configuration, and was set up

in the same manner as to second experiment. The only difference was that the 50-mL beakers

containing the sediment were filled to the rim, thereby eliminating the stagnant volume from

the sediment surface to the rim. The experiment was started at a low nitrate concentration with

the reactor filled with Bull Run water only. The system was sealed from the atmosphere at the

end of Day 3 by closing all the unused ports on the reactor lid with neoprene stoppers. In

contrast with the first two experiments, N2 gas was not introduced directly into the solution.

Only the reactor headspace was filled with N2 gas in order to allow a more natural rate of

oxygen depletion in the microcosm water column. After the reactor was sealed, the DO slowly

declined, but never reach 0 mg/L as may be seen in Figure F-19. Ultimately, it was determined

that opening the system in order to perform a daily calibration of the pH probe was allowing

unacceptable quantities of oxygen to enter the reactor from the atmosphere. The re-aeration

problem was solved by resuming the sparging of N2 gas directly into the water column.

Sparging began on Day 6 and effectively eliminated the remaining dissolved oxygen within 2

hours. Sparging also allowed the pH probe calibration to be accomplished without increasing

the dissolve oxygen concentration. However, concern remained about the N2 gas also

removing other dissolved gases, particularly carbon dioxide, and thereby making fundamental

changes in the system chemistry. With water column sparging, the ORP of the sediment

remained higher than that of the solution, and denitrification was not observed to occur even

under completely anoxic conditions. The N2 gas sparging was stopped on Day 16 and two

measures were taken to maintain anoxia in the reactor as previously described in the

Experimental Setup subsection. Two days after the sparging had stopped, some denitrification

could be observed as shown on Figure F-21.

Up to this point, no control was exerted over the pressure of nitrogen gas in the

headspace. When the N2 gas sparging was stopped, additional reactor maintenance was also

performed to minimize air leaks at the effluent outlet, and this probably served to increase

nitrogen gas pressure in the headspace. Initially, the pressure may have been sufficiently high in

the headspace to reverse the solution flow through the salt bridge, and into the reference

electrode. This may have been the cause of the erroneous ORP measurement after sparging

was stopped, as shown on Figure F-31. The sediment ORP increased immediately when the

F - 14

N2 gas flow was turned off and dropped back when the flow was turned back on. In the latter

experiments, the N2 gas pressure was maintained at less than 1 inch of water so that the reactor

solution would not flow into the reference electrode. The response of the sediment ORP to

the N2 gas flow had not been observed in these latter experiments. The time series plots of the

third experiment results are shown below.

F - 15

0

1

2

3

4

5

6

7

0 5 10 15 20 25

Days

Con

cent

ratio

ns (m

g/L)

Figure F-19. Time series of third experiment reactor DO.

0

1

2

3

4

5

6

0 5 10 15 20 25

Days

Con

cent

ratio

ns (m

g/L

N)

Feed AFeed BEff

Figure F-20. Time series of third experiment nitrate concentrations in the fresh feed water (Feed A) and the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff).

F - 16

0

1

2

3

4

5

6

0 5 10 15 20 25

Days

Con

cent

ratio

ns (m

g/L

N)

Mea Eff

Pre EffMixing Only

Pre Eff withDenit

Figure F-21. Comparison between measured effluent nitrate concentrations (Mea Eff), and predicted effluent nitrate concentrations in case of mixing only (Pre Eff Mixing Only) and in case of denitrification starting on Day 18 (Pre Eff with Denit). The first-order denitrification-rate constant assumed was -0.022 day-1.

0

1

2

3

4

5

6

0 5 10 15 20 25

Days

Con

cent

ratio

ns (m

g/L

N)

Feed AFeed BEff

The concentrations of ammonia were mostly close to the detection limit (0.01mg/L N)

Figure F-22. Time series of third experiment ammonia concentrations in the fresh feed water (Feed A) and the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff). Many data points were missing. The samples were collected, but the analysis failed due to instrument problems.

F - 17

0

1

2

3

4

5

6

0 5 10 15 20 25

Days

Con

cent

ratio

ns (m

g/L

N)

Feed AFeed BEff

Figure F-23. Time series of third experiment total Kjeldahl nitrogen concentrations in the fresh feed water (Feed A) and the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff).

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0 5 10 15 20 25

Days

Con

cent

ratio

ns (m

g/L

P)

Feed AFeed BEff



Figure F-24. Time series of third experiment orthophosphate concentrations in the fresh feed water (Feed A) and the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff).

F - 18

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0 5 10 15 20 25

Days

Con

cent

ratio

ns (m

g/L

P)

Feed A

Feed B

Eff



Figure F-25. Time series of third experiment total phosphorus concentrations in the fresh feed water (Feed A) and the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff).

0

5

10

15

20

25

0 5 10 15 20 25

Days

Con

cent

ratio

ns (m

g/L)

Feed AFeed BEff

Figure F-26. Time series of third experiment COD concentrations in the fresh feed water (Feed A) and the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff).

F - 19

0

0.05

0.1

0.15

0.2

0.25

0.3

0 5 10 15 20 25

Days

Con

cent

ratio

ns (m

g/L)

Feed AFeed BEff



Figure F-27. Time series of third experiment soluble iron concentrations in the fresh feed water (Feed A) and the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff).

0

0.05

0.1

0.15

0.2

0.25

0.3

0 5 10 15 20 25

Days

Con

cent

ratio

ns (m

g/L)

Feed AFeed BEff



Figure F-28. Time series of third experiment soluble manganese concentrations in the fresh feed water (Feed A) and the feed water 24 hours after it was taken out of the refrigerator (Feed B), and the effluent (Eff).

F - 20

0

10

20

30

40

50

60

70

80

0 5 10 15 20 25

Days

Con

cent

ratio

ns (m

g/L

CaC

O3)

Feed AEff

Figure F-29. Time series of third experiment alkalinity concentrations in the fresh feed water (Feed A) and the effluent (Eff). The alkalinity had not been measured until Day 14.

0

2

4

6

8

10

12

14

0 5 10 15 20 25

Days

pH The pH probe was not properly treated after a long storage, causing raised readings

Figure F-30. Time series of third experiment reactor pH.

F - 21

-500

-400

-300

-200

-100

0

100

200

300

400

500

0 5 10 15 20 25

Days

E h (m

V) WaterSediment

Started sparging nitrogen gas

Stopped sparging nitrogen gas

Figure F-31. Time series of third experiment Eh in the water column (Water) and surface sediment (Sediment). The Eh was not corrected to E7 because the pH was only measured daily while the Eh was measured each minute.

F - 22

Fourth Experiment

The reactor set-up for the fourth experiment was a system of three CSTRs in series.

The first reactor was configured to simulate the same reach of the reservoir as the past two

experiments. The second reactor was configured to simulate the portion of the reservoir from

the confluence of the Bull Run and Occoquan Creek to some point downstream of Station

RE20. The last reactor was configured to simulate the reservoir below that point to some point

upstream of Station RE15. As indicated previously in the “Experimental Setup” section, an air

leak was identified at the DO probe insertion point, and a satisfactory way could not be found

to eliminate it while measuring dissolved oxygen. As a result, reactor DO values were not

measured in this experiment.

On Day 4, the system was spiked with 20 mg/L COD using dextrose in order to

insure that sufficient organic carbon was available to support denitrification. Denitrification

was still, however, not observed. Consequently, on Day 11, the system was spiked with 0.5

mg/L phosphate as P using sodium hydrogen phosphate (Na2HPO4) to insure that sufficient

phosphorus was present to support microorganism growth. The feed water was continued

with both COD and phosphorus spikes. The phosphorus addition immediately stimulated

denitrification. The denitrification rates observed have been discussed in the “Results and

Discussion” section. The amount of phosphorus added to the feed water was reduced to 0.1

mg/L as P on Day 14.

After the feed water had been spiked with phosphate, the organic carbon in the feed

water was utilized rapidly. Within 24 hours, the feed water contained less than half of the

added COD as shown in Figure F-38. In order to mitigate the stimulatory effect of the

phosphate nutrient spike, the feed water source was kept at 4° C from Day 17 until the end of

the experiment and also in all following experiments.

F - 23

0

1

2

3

4

5

6

0 5 10 15 20

Days

Con

cent

ratio

ns (m

g/L

N)

Feed AFeed BR1R2Eff

Spiked the reactor with additional 0.5 mg/L phosphate as P

Figure F-32. Time series of fourth experiment nitrate concentrations in the fresh feed water (Feed A), the feed water 24 hours after it had been taken out of the refrigerator (Feed B), Reactor 1 (R1), Reactor 2 (R2), and the effluent (Eff).

0

1

2

3

4

5

6

0 5 10 15 20

Days

Con

cent

ratio

ns (m

g/L

N)

Feed AFeed BR1R2Eff

Most of the ammonia concentraions were close to the detection limit (0.01 mg/L N)

Figure F-33. Time series of fourth experiment ammonia concentrations in the fresh feed water (Feed A), the feed water 24 hours after it had been taken out of the refrigerator (Feed B), Reactor 1 (R1), Reactor 2 (R2), and the effluent (Eff).

F - 24

0

1

2

3

4

5

6

0 5 10 15 20

Days

Con

cent

ratio

ns (m

g/L

N)

Feed AFeed BR2EffR1

Figure F-34. Time series of fourth experiment total Kjeldahl nitrogen concentrations in the fresh feed water (Feed A), the feed water 24 hours after it had been taken out of the refrigerator (Feed B), Reactor 1 (R1), Reactor 2 (R2), and the effluent (Eff).

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 5 10 15 20

Days

Con

cent

ratio

ns (m

g/L

P)

Feed AFeed BR1R2Eff

Spiked the system with0.5 mg/L phosphate as P and continued spiking the feed water

Lowered the amount of phosphate added to the feed waterto 0.1 mg/L as P

Started refrigerating the feed water

Figure F-35. Time series of fourth experiment orthophosphate concentrations in the fresh feed water (Feed A), the feed water 24 hours after it had been taken out of the refrigerator (Feed B), Reactor 1 (R1), Reactor 2 (R2), and the effluent (Eff).

F - 25

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 5 10 15 20

Days

Con

cent

ratio

ns (m

g/L

P)

Feed AFeed BR1R2EffSpiked the system with

additional 0.5 mg/L phosphate as P and continued spiking the feed water

Lowered the amount of phosphorus added to the feed waterto 0.1 mg/L P


Figure F-36. Time series of fourth experiment total phosphorus concentrations in the fresh feed water (Feed A), the feed water 24 hours after it had been taken out of the refrigerator (Feed B), Reactor 1 (R1), Reactor 2 (R2), and the effluent (Eff).

0

5

10

15

20

25

30

35

40

0 5 10 15 20

Days

Con

cent

ratio

ns (m

g/L)

Feed AR1R2Eff

Spiked the system with additional 20 mg/L COD and continued spiking the feed water

Figure F-37. Time series of fourth experiment COD in the fresh feed water (Feed A), the feed water 24 hours after it had been taken out of the refrigerator (Feed B), Reactor 1 (R1), Reactor 2 (R2), and the effluent (Eff).

F - 26

0

5

10

15

20

25

30

35

40

0 5 10 15 20

Days

Con

cent

ratio

ns (m

g/L)

Feed AFeed B

Started spiking the system with additional 0.5 mg/L phosphate as P


Figure F-38. Comparison between the COD of the fresh feed water (Feed A) and the feed water 24 hours after it had been taken out of the refrigerator (Feed B).

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 5 10 15 20

Days

Con

cent

ratio

ns (m

g/L)

Feed AFeed BR1R2Eff



Figure F-39. Time series of fourth experiment soluble iron in the fresh feed water (Feed A), the feed water 24 hours after it had been taken out of the refrigerator (Feed B), Reactor 1 (R1), Reactor 2 (R2), and the effluent (Eff).

F - 27

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 5 10 15 20

Days

Con

cent

ratio

ns (m

g/L)

Feed AFeed BR1R2Eff



Figure F-40. Time series of fourth experiment soluble manganese in the fresh feed water (Feed A), the feed water 24 hours after it had been taken out of the refrigerator (Feed B), Reactor 1 (R1), Reactor 2 (R2), and the effluent (Eff).

0

2

4

6

8

10

12

14

0 5 10 15 20

Days

pH

R1R2R3

Figure F-41. Time series of fourth experiment pH in Reactor 1 (R1), Reactor 2 (R2), and Reactor 3 (R3).

F - 28

-600

-500

-400

-300

-200

-100

0

100

200

300

400

0 5 10 15 20

Days

E h (m

V)

WaterSediment

Spiked the system with additional 0.5 mg/Lphosphate as P

Figure F-42. Time series of fourth experiment Eh of Reactor 1 in the water column (Water) and surface sediment (Sediment). The Eh was not corrected to E7 because the pH was recorded daily while the Eh was recorded each minute.

-600

-500

-400

-300

-200

-100

0

100

200

300

400

0 5 10 15 20

Days

E h (m

V)

WaterSediment



F - 29

-600

-500

-400

-300

-200

-100

0

100

200

300

400

0 5 10 15 20

Days

E h (m

V)

WaterSediment



F - 30

F - 31

Fifth Experiment

Denitrification was successfully induced in the fourth experiment by adding some

phosphorus to the system. The overall objective of the study, however, was to estimate the

denitrification rate in the reservoir under natural summer conditions. Investigating the OWML

phosphorus data at Stations ST40, RE30, RE15, and RE02 from 1982 to 2000, it was found

that the ambient phosphorus concentrations were lower than the 0.5 mg/L spike added to the

microcosm system in the fourth experiment, thereby creating an unrealistic simulation of the

reservoir. It was also suspected that some of the difficulty in achieving an environment that

would be conducive to denitrification was due to continuing air leaks in the reactor. It was

ultimately concluded that design and construction of a new reactor was the only practical way

to achieve the experimental objectives. The reactor design, which is described in the “Materials

and Methods” section, was equipped with features to improve exclusion of air from the system

and facilitate sampling without introducing significant amount of oxygen.

The fifth experiment was set up similarly to the third experiment, but using the

improved reactor system. During the experiment, it was discovered that the automated

measurement of ORP with a data acquisition board as described in the “Materials and

Methods” section was giving incorrect values because poor matching of the impedances (10

Mohm) of the board and the sensing element(s). The measured ORP were found to be in error

on the low side. Therefore all the ORP values in the past experiments and the first half of this

experiment were incorrect. On Day 18, the automated ORP measurement was terminated, and

manual measurements were started using a pH/mV meter. As is shown in Figure F-45, the

last-day data recorded with the acquisition board appeared to be significantly lower than the

first-day values recorded with a Fisher Accumet Model 925 pH/mV meter (Pittsburgh, PA).

It was also found at the onset of the fifth experiment that the DO measurements had

not been performed correctly because the probe stirring mechanism had not been used during

measurements. Because the measurement lacked the energy to drive oxygen across the

membrane, erratic responses (APHA, 1998) were obtained. According to Standard Methods

(APHA, 1998), DO measurements by a membrane electrode method give lower readings than

the actual values at low stirring. Because of the mounting system used to fix the DO probe on

the reactor lid, it was not possible to initiate stirring. During DO probe calibration on Days 8

F - 32

and 21 and before the system was been sealed, an attempt had been made to measure DO with

a meter equipped with a self-stirring probe. The values obtained were higher than those

measured with the in situ DO meter as shown in Figure F-46.

Near the end of the experiment, an additional 0.1 mg/L phosphate as P was added to

the feed water to study the effect of the phosphate on stimulating denitrification. However, the

experiment was terminated shortly thereafter.

F - 33

-400

-200

0

200

400

600

800

1000

0 5 10 15 20 25 30 35

Days

E 7 (m

V)

Water

Sediment

Started using pH/mV meter

Air leaked into the system w hile calibrating the DO probe

Figure F-45. Time series of fifth experiment E7 in the water column (Water) and in the surface sediment (Sediment).

0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25 30 35

Days

Con

cent

ratio

ns (m

g/L)

DO(DOmeter)

DO(BOD Meter)

Calibrated DO Probe

FigureF-46. Time series of fifth experiment reactor DO.

F - 34

0

2

4

6

8

10

12

14

0 5 10 15 20 25 30 35

Days

pH

InfReactor

Figure F-47. Time series of fifth experiment pH in the influent (Inf) and reactor (Reactor).

0

1

2

3

4

5

6

7

0 5 10 15 20 25 30 35

Days

Con

cent

ratio

ns (m

g/L

N)

Inf

Eff

Figure F-48. Time series of fifth experiment nitrate concentrations in the influent (Inf) and effluent (Eff).

F - 35

0

1

2

3

4

5

6

7

0 5 10 15 20 25 30 35

Days

Con

cent

ratio

ns (m

g/L

N)

InfEff

The ammonia concentrations were mostly near the detection limit (0.01 mg/L N)

Figure F-49. Time series of fifth experiment ammonia concentrations in the influent (Inf) and effluent (Eff).

0

1

2

3

4

5

6

7

0 5 10 15 20 25 30 35

Days

Con

cent

ratio

ns (m

g/L

N)

InfEff

Figure F-50. Time series of fifth experiment total Kjeldahl nitrogen in the influent (Inf) and effluent (Eff)

F - 36

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 5 10 15 20 25 30 35

Days

Con

cent

ratio

ns (m

g/L

P)

Inf

Eff

Started feeding feed water containingadditional 0.1 mg/L phosphate as P



Figure F-51. Time series of fifth experiment orthophosphate concentrations in the influent (Inf) and effluent (Eff).

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 5 10 15 20 25 30 35

Days

Con

cent

ratio

ns (m

g/L

P)

InfEff

Started feeding feed water containingadditional 0.1 mg/L phosphate as P



Figure F-52. Time series of fifth experiment total phosphorus concentrations in the influent (Inf) and effluent (Eff).

F - 37

0

5

10

15

20

25

0 5 10 15 20 25 30 35

Days

Con

cent

ratio

ns (m

g/L)

InfEff

Figure F-53. Time series of fifth experiment COD in the influent (Inf) and effluent (Eff).

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35

Days

Con

cent

ratio

ns (m

g/L

CaC

O3)

InfEff

Figure F-54. Time series of fifth experiment alkalinity in the influent (Inf) and effluent (Eff).

F - 38

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 5 10 15 20 25 30 35

Days

Con

cent

ratio

ns (m

g/L)

InfEff



Figure F-55. Time series of fifth experiment soluble iron in the influent (Inf) and effluent (Eff).

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 5 10 15 20 25 30 35

Days

Con

cent

ratio

ns (m

g/L)

InfEff



Figure F-56. Time series of fifth experiment soluble manganese in the influent (Inf) and effluent (Eff).

Sixth Experiment As indicated in the “Experimental Setup” section, the experiment was 2 reactor

systems in series to provide simulation of the reservoir from the tail waters on the Bull Run

arm to Station RE15. The sampling frequency in this experiment was lower than the past

experiments because it had been observed that the slow pace of the biological processes did

not warrant more frequent sampling. The sampling on alternate days was determined to be

sufficient to capture changes. The author speculated from the prior work that the

denitrification would occur many days after the onset of the experiment or after the complete

reduction of oxygen. Therefore, the experiment was planed to run for a prolonged period of

time to ensure that the denitrification rate at equilibrium was observed.

In the previous experiment, the author found that DO probe must be stirred during

the measurement in order to get an accurate reading. To do so without introducing significant

amount of air into the system, he installed 32-mm ID, glass tube on the lid in the same manner

as the 5/16” ID, glass tube as described in the “Materials and Methods” section. During a DO

measurement, while the DO probe was immersed in the reactor solution through the tube, it

could be moved in the vertical direction to get the same effect as horizontal stirring.

F-39

0

1

2

3

4

5

6

7

8

9

0 10 20 30 40 50 60 70 80

Days

Con

cent

ratio

ns (m

g/L)

R1R2

Figure F-57. Time series of sixth experiment dissolved oxygen concentrations in the solution of the first (R1) and second (R2) reactors. DO in Reactor 2 was not measured until Day 18 because, during the early stage of the experiment, the author believed that the DO measurement could introduce significant amount of air to the reactor.

0

100

200

300

400

500

600

700

0 10 20 30 40 50 60 70 80

Days

E 7 (m

V) R1R2

Pump tube failed, causing air-leak into Reactor 2

Nitrate concentrations in Reactor 1fell below the detection limit on Day 70.

Figure F-58. Time series of sixth experiment E7 in the solution of the first (R1) and second (R2) reactors.

F-40

-350

-300

-250

-200

-150

-100

-50

0

0 10 20 30 40 50 60 70 80

Days

E 7 (m

V) R1R2

Figure F-59. Time series of sixth experiment E7 in the sediment of the first (R1) and second (R2) reactors.

0

2

4

6

8

10

12

14

0 10 20 30 40 50 60 70 80

Days

pH

InfR1R2

Figure F-60. Time series of sixth experiment pH in the influent (Inf), the first (R1) and second

(R2) reactors.

F-41

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50 60 70 80

Days

Con

cent

ratio

ns (m

g/L

N)

InfR1Eff

Started feeding the system withBull Run water only

Figure F-61. Time series of sixth experiment nitrate concentrations in the influent (Inf), first reactor (R1) and effluent Eff)

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50 60 70 80

Days

Con

cent

ratio

ns (m

g/L

N)

InfR1Eff

The ammonia concentrations were mostly close to the detection limit (0.01 mg/L N)

Figure F-62. Time series of sixth experiment ammonia concentrations in the influent (Inf), first reactor (R1) and effluent (Eff).

F-42

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50 60 70 80

Days

Con

cent

ratio

ns (m

g/L

N)

InfR1Eff

Figure F-63. Time series of sixth experiment total Kjeldahl nitrogen concentrations in the influent (Inf), first reactor (R1) and effluent (Eff).

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 10 20 30 40 50 60 70 80

Days

Con

cent

ratio

ns (m

g/L

P)

InfR1Eff



Figure F-64. Time series of sixth experiment orthophosphate concentrations in the influent (Inf), first reactor (R1) and effluent (Eff).

F-43

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 10 20 30 40 50 60 70 80

Days

Con

cent

ratio

ns (m

g/L

P)

Inf

R1

Eff



Figure F-65. Time series of sixth experiment total phosphorus concentrations in the influent (Inf), first reactor (R1) and effluent (Eff).

0

2

4

6

8

10

12

14

16

18

20

0 10 20 30 40 50 60 70 80

Days

Con

cent

ratio

ns (m

g/L)

InfR1Eff

Figure F-66. Time series of sixth experiment COD in the influent (Inf), first reactor (R1) and

effluent (Eff).

F-44

0

20

40

60

80

100

120

140

0 10 20 30 40 50 60 70 80

Days

Con

cent

ratio

ns (m

g/L

CaC

O3)

InfR1Eff

Figure F-67. Time series of sixth experiment alkalinity in the influent (Inf), first reactor (R1) and effluent (Eff)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 10 20 30 40 50 60 70 80Days

Con

cent

ratio

ns (m

g/L)

InfR1Eff

The values below detection limit plotted at half the li it


Figure F-68. Time series of sixth experiment soluble iron in the influent (Inf), first reactor (R1) and effluent (Eff).

F-45

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 10 20 30 40 50 60 70 80

Days

Con

cent

ratio

ns (m

g/L)

InfR1Eff



Figure F-69. Time series of sixth experiment soluble manganese in the influent (Inf), first reactor (R1) and effluent (Eff).

F-46

Seventh Experiment

This experiment was conducted to investigate the possibility of denitrification under

aerobic conditions. The sixth experiment result showed that the nitrate in the reactor, which

contained sediment from the most upstream site as shown in Figure 3.20, was declining even

under aerobic conditions. A batch reactor was set up containing only sediment from this site

and was filled with a volume-weighted mixture of the Bull Run water and UOSA discharge.

The experiment was divided into 3 phases: in Phase I, the system was open to the atmosphere;

in Phase II, which began on Day 7, the reactor was sealed; and in Phase III, the reactor was

reopened to the atmosphere on Day 13.79. It should be noted that Phase II was characterized

by both anoxic and anaerobic conditions. If one examines Figure 5.7 from the text, it may be

seen that the anoxic and anaerobic conditions are both in Phase II as described in this

appendix.

It is worth noting that the ORP in the water column were recorded both manually and

automatically. As may be seen in Figure F-70, the manual recording could capture the changes

as well as the more frequent automatic recording except for the sudden increase after the

reactor was unsealed on Day 13.79. However, if one data point had been recorded slightly after

the reactor had been opened, the manually recorded data would have been as good as the

automatically recorded data. The other collected data are presented below.

F - 47

0

50

100

150

200

250

300

350

400

450

0 5 10 15 20

Days

E h (m

V)

Phase I Phase II Phase III

Figure F-70. Time series of seventh experiment manually (Manually) and automatically (Automatically) recorded Eh in the water column. The Eh was not corrected to E7 because the automatically acquired data were recorded each minute while the pH data were recorded daily.

Manually

Automatically

0

100

200

300

400

500

600

0.00 5.00 10.00 15.00 20.00

Days

E 7 (m

V)

0

2

4

6

8

10

12

DO

(mg/

L)Phase I Phase II Phase III

Figure F-71. Time series of seventh experiment E7 in the water column (Water) and surface sediment (Sediment), and of the seventh experiment reactor DO in the reactor water column.

Water

Sediment

DO

F - 48

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20

Days

Con

cent

ratio

ns (m

g/L

N)


Figure F-72. Time series of seventh experiment nitrate (NO3

--N), ammonia (NH3-N), and total Kjeldahl nitrogen (TKN) in the reactor water column.

NO3-N

NH3-N

TKN

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 5 10 15 20

Days

Con

cent

ratio

ns (m

g/L

P)




Figure F-73. Time series of seventh experiment orthophosphate (OP) and total phosphorus (TP) concentrations in the reactor water column.

OP

TP

F - 49

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 5 10 15 20

Days

Con

cent

ratio

ns (m

g/L) Phase I Phase III



Phase II

Figure F-74. Time series of seventh experiment soluble iron (Fe) and manganese (Mn) in the reactor water column.

Fe

Mn

100

102

104

106

108

110

112

114

116

118

120

0 5 10 15 20

Days

Alk

(mg/

L C

aCO

3)

0

5

10

15

20

25

CO

D (m

g/L)


Figure F-75. Time series of seventh experiment alkalinity (Alk) and chemical oxygen demand (COD) in the reactor water column.

Alk

COD

F - 50

Sediment Analyses As part of the seventh experiment, the sediment from each sampling site in the sixth

experiment was analyzed for total solids, total volatile solids, pH, and iron and manganese

content. The sediment sampling sites are as shown in Figure 3.20. The sediment from the

most upstream site was sampled three times on August 21, 2001; November 14, 2001; and

December 4, 2001. The sediment from the second site was sampled twice on August 21, 2001

and December 4, 2001. The data presented here are arithmetic averages of the results. The

other two sites were sampled only once on August 21, 2001. All the samples were analyzed on

the same day, December 5, 2001. The results are as follows:

F - 51

0

1

2

3

4

5

6

7

8

9

10

1 2 3 4

Sampling Stations

Perc

ent V

olat

ile S

olid

s

Figure F-76. Profile of sediment percent volatile solids along the Occoquan Reservoir from tail waters on the Bull Run arm to Station RE15.

0

5

10

15

20

25

30

35

40

45

50

1 2 3 4

Sampling Stations

Perc

ent T

otal

Sol

ids

Figure F-77. Profile of sediment percent total solids along the Occoquan Reservoir from tail waters on the Bull Run arm to Station RE15.

F - 52

0

2

4

6

8

10

12

14

1 2 3 4

Sampling Stations

pH

Figure F-78. Profile of sediment pH along the Occoquan Reservoir from tail waters on the Bull Run arm to Station RE15

0

5

10

15

20

25

1 2 3 4

Sampling Stations

mg

Fe/g

Sed

imen

t

Figure F-79. Profile of sediment reactive iron content along the Occoquan Reservoir from tail waters on the Bull Run arm to Station RE15.

F - 53

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

1 2 3 4

Sampling Stations

mg

Mn/

g Se

dim

ent

Figure F-80. Profile of sediment reactive manganese content along the Occoquan Reservoir from tail waters on the Bull Run arm to Station RE15.

F - 54

APPENDIX F Time Series Plots of Experimental Results ...20... · This appendix contains time series...

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Transcript of APPENDIX F Time Series Plots of Experimental Results ...20... · This appendix contains time series...