Nutrient Removal Project
Simultaneous Nitrification and Denitrification in
a Sequencing Batch Reactor
Will Lambert
Robert Nwaokoro
Stephen Russo
CEE 453
12/8/04
Abstract
Nitrogen removal is important part of wastewater treatment, especially in coastal
regions where nitrogen loading of oceans and estuaries can cause algal blooms. The most
common method of removal uses microbes. Unfortunately, there are several steps to
achieve denitrification with an organic nitrogen feed. Many bacteria convert organic
nitrogen to ammonia, but only certain anaerobes, namely Nitrobacter and Nitrosomonas,
are responsible for the conversion of ammonia to nitrite and nitrate, or nitrification.
Furthermore, it is only from the nitrite or nitrate form that anaerobic denitrifying bacteria
can produce nitrogen gas. Therefore, traditional nitrogen removal in waste treatment
plants occurs in first and aerobic stage and then an anaerobic stage. This can either occur
in separate tanks or in one tank that is sequenced to go through each state. Recently,
further research has been done on simultaneous nitrification and denitrification. It seems
that at very low levels of dissolved oxygen, anaerobic zones can be produced, allowing
both processes to occur concurrently.
The purpose of this research is to explore the possibilities of simultaneous
nitrification and denitrification in a sequencing batch reactor at a laboratory scale. We
used aeration cycles of 8, 18, and 24 hours and a dissolved oxygen level of 0.5 mg/L.
Removal efficiencies were on the range of 10-20%, and increased with longer aeration
times. Due to unexpected experimental difficulties, we were not able to take as many
samples as we would have liked, so there are many options for further research.
Introduction
The objective of our research is to evaluate the efficiency of simultaneous
nitrification and denitrification (SND) in a sequencing batch reactor (SBR). Nitrogen
removal is an important part of wastewater treatment. Nitrogen is a limiting nutrient for
algal growth in oceans and estuaries. Furthermore, organic nitrogen in wastewater is
converted to nitrates, which can cause Methemoglobinemia (“blue-baby” syndrome) if it
is present in drinking water. Biological nitrogen removal has been highly favored by
wastewater treatment plants due to the increasingly stringent effluent discharge
requirements on nitrogen. Biological nitrogen removal involves ammonification
(converting organic nitrogen to ammonia), nitrification (biological oxidation of
ammonium nitrogen to the nitrite), and denitrification (reduction of nitrate to free
nitrogen gas via a nitrite intermediate). Traditional nitrogen removal in wastewater
treatment plants occurs in separate aerobic and anaerobic stages. SND systems tend to be
a cheaper means of achieving these requirements as it uses less bio-reactor volume,
consumes less time, produces less sludge and has lower energy costs than current
sequential nitrification and denitrification systems.
A potential problem with the SND setup is the anoxic requirement of the
denitrification process which we intend to synchronize with the aerobic nitrification
process. An aerobic condition (a measurable bulk liquid dissolved oxygen (DO)) inhibits
the nitrifying bacteria Nitrosomonas and Nitrobacter, while an anaerobic situation (bulk
liquid DO  0.5 – 2 mg/L) inhibits denitrifying bacteria such as Thiobacillus
denitrificans and Pseudomonas denitrificans. Denitrification occurs in a series of steps
where nitrate is converted to nitrite and ultimately to gaseous nitrogen. A general
schematic of the nitrogen cycle as it occurs in activated sludge treatment is given below:
Organic
Nitrogen
Ammonification
Ammonia
Fixation
Nitrification (aerobic)
Nitrosomonas
N2 (gas)
Assimilation
Denitrification (anaerobic)
Nitrite
Nitrification (aerobic)
Nitrosobacters
Denitrification (anaerobic)
Nitrate
Figure 1: Schematic of the nitrogen cycle in wastewater treatment plants.
A compromise situation at which both nitrification and denitrification can occur
simultaneously requires the bioreactor to operate at the minimum DO concentration
necessary to support nitrification (  0.5 mg/L) (Munch, et al 1996).
The major challenge is creating the optimal conditions necessary for an efficient
SND process: appropriate hydraulic/solids retention times, optimal aeration rates, and
suitable feed introduction strategy. These conditions must be met while minimizing odor
generation and the accumulation of free ammonia gas. Another potential difficulty is the
selection of filamentous bacteria at low DO that interfere with settling and can cause
sludge bulking in a reactor. However, these same bacterial flocs (sludge bulking) may
provide sites of anoxic zones where denitrification can take place.
Ideally, dissolved oxygen control should be based on levels of nitrate and nitrite
in the system, but access to reliable nitrogen probes is limited. Therefore, airflow rates
will be controlled by the DO level in the system using the proportional integral derivative
(PID) control. Nitrate and nitrite levels will be measured using the Hach Cadmium Test
with the aid of a UV Spectrophotometer. Ammonia levels in the system are monitored
using the micro-phenate test, also with the aid of a UV Spectrophotometer. Assuming
that all organic nitrogen is converted to ammonia, these tests allow us to measure total
nitrogen in an effluent sample. The nitrogen input of the waste is known, so nitrogen
removal is easily calculated. Reported total nitrogen removal efficiencies vary between
73% and 91% (Sverdlikov, et al 1999). The Sverdlikov Group also found that complete
nitrification, 90% denitrification, and 91% total nitrogen removal efficiency is attainable
at high hydraulic and volumetric loading rates (1999).
Plant Setup and Characteristics
To implement Simultaneous Nitrification-Denitrification, we used an automated
Sequencing Batch Reactor. The reactor system was built using these main components:








4 L reactor vessel
magnetic stirrer
peristaltic pump
pipe-thread solenoid control valves
tubing, bulk head fittings, clamps and clamp holders.
dissolved oxygen probe and pressure sensors
diffuser stone
data acquisition and process controller
The reactor vessel was mounted on the magnetic stirrer base, set to a stir speed of 5.
The synthetic waste solution stored in the shelf refrigerator was input to the reactor using
the peristaltic pump controlled by the process controller. The solenoid control valves
were an integral part of the plumbing system by controlling:
 the flow of compressed air
 the drainage of effluents
 the regulation of waste and tap water influent
The dissolved oxygen probe was fastened by the clamps and situated such that
contact with aeration bubbles via the diffuser stone was limited. The pressure sensor
provided the process controller with reactor fluid volume. The process control software
allowed us to automate the SBR using desired set points.
Plant Operation
200 kPa
Pressure
sensor
7 kPa
Pressure
sensor
(optional)
Accumulator
DO probe
N2
S2
Solenoid Valve
S1
Stir bar
Needle Valve
1.5 mm ID x 5 cm restriction
Air Supply
Figure 2: Schematic of the reactor system used. Air delivery system shown in detail.
To operate the plant, the above components were configured as illustrated in Figure 2
above. A test run of the system identified and led to the repair of any leaks in the
plumbing connections. The plant was then configured to execute five states involved in
wastewater treatment cycle in a SBR:





Fill with waste
Fill with water
Aerate
Settle
Drain
The above setup was designed to automatically cycle through the five states in
sequence, repeating at the completion of each cycle. The process controller automatically
defaults to an off-status if any error occurs in any of the steps. However, we were unable
to implement a configuration for a system shutdown in case of a sensor read failure.
Fill with Waste
A 100x stock synthetic waste was diluted to a 20x feed waste and both were kept
in the shelf refrigerator. Table 1 below shows the recipe for the desired solution in our
plants.
Table 1: 100x stock synthetic waste contents and their concentrations.
Compound
Starch
Casein
Sodium acetate
Capric acid
Ammonium chloride
Potassium phosphate
Sodium hydroxide
Glycerol
Chemical Formula
C2H3O2
C10H20O2
NH4Cl
K2HPO4
NaOH
C3H8O3
20
Concentration
(mg/L)
84.40
125.00
31.90
11.60
75.33
6.90
175.00
12.00
Refridgerated storage prevented microbial degradation of the synthetic waste until
its use in the reactor. The synthetic waste contained 40.9 mg/L of nitrogen and a
chemical oxygen demand (COD) of 325 mg/L. The waste flow was configured to enter
the reactor via a Y-piping connection that also fed the tap water. During the Fill with
Waste step, the peristaltic pump was configured by the process controller to:
 flow waste feed for 18.3 seconds
 deliver 140 mL of waste
These configurations were based on the measured peristaltic pump flow rate of 459
mL/min.
Fill with Water
The tap water delivered consisted of “modified” tap water and was made by
adding the contents in Table 1 below to tap water.
Table 2: "Modified" tap water contents and their concentrations.
Compound
Chemical Formula
Magnesium sulfate
Sodium molybdate
Manganese sulfate
Cupric sulfate
Zinc suflate
Calcium chloride
Iron chloride
Cobalt chloride
MgSO47H2O
NaMoO42H2O
MnSO4H2O
CuSO44H2O
ZnSO47H2O
CaCl22H2O
FeCl36H2O
CoCl26H2O
Concentration
(mg/L)
69.60
0.15
0.13
0.08
0.48
22.50
18.33
0.42
This modified tap water was fed from a central supply that was passed through the
same piping as the synthetic waste. This periodic flushing minimized the bacterial buildup on the waste delivery line. The Fill with Water state was configured by the process
controller to deliver the “modified” tap water until two conditions were met:
1. 350 seconds elapsed, which corresponded to the flow rate in the Fill with Waste
state.
2. the reactors volume reach 4 L, averaged over 5 seconds.
The second condition acted as a fail-safe if the peristaltic pump failed to deliver the
appropriate amount of fluid. The pressure sensor attached at the bottom of the reactor
provided the necessary data to monitor the volume.
Aerate
The aeration state was configured to flow air into the reactor and stir the reactor’s
contents. The aeration time was varied (8, 18, and 24 hours) in order to identify its
impact on the extent of the SND process. The aeration rate was controlled by
implementing a Proportional, Integral and Derivative (PID) control system. The target
DO level was set to 0.5 mg/L by the PID control. PID sets the value of the control
parameter (airflow) based on the sum, the integral and the derivate of the error. Equation
1 below is the general PID function:

1
u  t   Kc   
TI

   t  T
D
 
 ,
t 
equation 1
where, Kc is controller gain (tuning parameter), TI is the integral time (tuning parameter),
TD is the derivative time (tuning parameter),  is the difference between measured value
and set point (measured oxygen concentration minus desired oxygen concentration), /
t is the error rate of change (note that this is the same as the dissolved oxygen
concentration rate of change),    t is the area under the curve of the error as a
function of time, and u(t) is the airflow rate that the controller sets. The difference
between the process variables and the user-defined set-point is the error (which is
reduced to zero to find an output, in this case the airflow rate.
Equation 1 is simplified when brought to the user-interface of LabView, as shown
below in Equation 2 :
P

1
u  t   Kc   
TI

I
D
   t  T
D
 
 .
t 
equation 2
For a response to be shown in airflow rate, the values of P, I, and D must be
changed accordingly from their default zero values. LabView then calculates the
respective values of the PID parameters found in Equation 1.
To identify appropriate values for the values of P, I, and D, trial and error method
was utilized to observe the changes in the DO of the reactor. When the DO approached
0.5 mg/L, effective control was established.
The aeration state relied heavily on the performance of the diffuser stone and the
DO probe. The DO probe was recalibrated and its membrane was changed on a weekly
basis, which ensured its accurate acquisition ability. The diffuser stone was changed
once it became clogged and ceased to deliver air.
Settle
The settle state lasted for 1 hour after aeration in order to settle the sludge and
biomass sufficiently, to prevent evacuation from the reactor. The allocated settling time
was observed to be more than ample for settling the bio-solids in the reactor, but was left
unchanged.
Drain
The drain state was the final state in the operational cycle for the SBR, and
discharged water from the reactor. The state ran until a residual volume of 1.2 L in the
reactor remained, which ensured a continual microbial population in the reactor.
Plant Activation
The plant was activated by the introduction of 4 L of waste-mixed liquor from the
City of Ithaca wastewater treatment plant.
Experimental Methods
Testing Methods
The extent of SND occurring in the reactor was assessed by measuring the
ammonia and total nitrate concentrations, as ammonia-nitrogen and nitrate-nitrogen.
These tests were used as indicators of reactor performance, as two different microbial
populations were attempted to be maintained in the reactor. This method was used
instead of the Total Suspended Solids (TSS) method because the dominating bacterial
population was not known. Satisfactory levels of nitrification and denitrification were
hoped to be established via these methods.
Essential Parameters
The essential parameters in the tests were the concentration of nitrogen as
ammonia and the concentration of nitrogen as nitrite/nitrate. The total nitrogen in the
synthetic waste is known, so assuming all organic nitrogen is converted to ammonia, this
information allows us to determine nitrogen removal.
Ammonia Standards via the Micro-Phenate Method
The micro-phenate method was used to determine the total ammonia
concentration in the reactor as ammonia-nitrogen. Standards for the micro phenate
method were prepared with the following species:
 Phenol solution: prepared by introducing 1.11 mL of liquefied phenol (>89%)
into a 1.5 mL cuvet with a micro-pipette. Dilution to 10 mL by
the addition of 95% v/v ethyl alcohol under the fume hood.
 Sodium nitroprusside: prepared by dissolving 50 mg sodium nitroprusside in 10
mL E-pure (deionized) water. Storage in a plastic bottle which
was protected from light.
 Alkaline citrate: prepared by dissolving 200 g trisodium citrate and 10 g sodium
hydroxide in deionized water diluted to 1 L.
 Sodium hypochlorite: Clorox®.
 Oxidizing Solution: prepared for each test by mixing 1 mL of the alkaline citrate
solution with 0.25 mL of Clorox in a 4.5 mL plastic cuvete.
Ammonia standards were prepared by dissolving 1.389 mg of ammonium chloride in
1 mL of water, diluted to 1 L, making a solution containing 1 mg/L of nitrogen. The
stock solution was diluted with deionized water to concentrations of 0, 0.2, 0.4, and 0.6
mg N-NH4/L.
1 mL of each of the ammonium standards was pipetted to a separate 1.5-mL cuvete in
a fume hood, with the following additions:
 40 mL phenol solution
 40 mL sodium nitroprusside solution
 100 mL oxidizing solution
The cuvete samples were covered and left to stand for a minimum of 1 hour inside a
bench drawer. Analysis then followed at an absorbance of 640 nm using a UVspectrophotometer. The measured absorbances were used to obtain a calibration curve.
Nitrate-nitrogen Standards
The nitrate concentration in the reactor was determined as total nitrate-nitrogen,
using the cadmium gravimetric method with Nitriver® and Nitraver® reagent packets
produced by the Hach Corporation. Nitrate-nitrogen standards were prepared by creating
a solution of sodium nitrate in distilled water at a concentration of 100 mg/L. This stock
solution was diluted into concentrations of 0, 2, 6 and 10 mg/L of nitrate-nitrogen. 0.5
mL of each of the standards was pipetted into a cuvete and a Nitraver® packet was added
under the fume hood. The cuvet was then covered, shaken for 3 minutes, and allowed to
stand for 30 seconds. Nitriver® packets were added and the new solutions were shaken
for 30 seconds and allowed to stand for 10 minutes. The absorbance of these standards
was also measured using the UV-spectrophotometer at a wavelength of 542 nm, which
generated a calibration curve.
Sampling
Samples were taken from the reactor at the end of the aeration state, filtered using
a Millipore filter and stored in the shelf refrigerator. For the ammonia samples, no smell
of hydrogen sulfide was detected, so no further additional treatment was required. These
samples were diluted by 10x and 100x and were treated using the micro-phenate
procedure described above. The dilution was performed because we were not aware of
the residual ammonia-nitrogen concentration in reactor at the end of the respective
aeration phases. It was discovered from the standards preparation that a highly
concentrated solution would give inaccurate absorbance readings (the absorbance
readings would exceed the accuracy limits of the spectrophotometer). The 10x dilution
fell in the range of the standard calibration curve and its use was continued.
The nitrate-nitrogen samples were acquired from the reactor in a similar way
outlined above. These samples were treated using the nitrate-nitrogen procedure
previously described. The UV-spectrophotometer was used to determine the nitratenitrogen concentration in the samples.
Results and Discussions
PID Control
PID control was set to maintain a DO level of 0.5 mg/L in the reactor during the
aeration state. To assess the performance of the control mechanism two concurrent DO
data sets, during the aeration state, were analyzed against time. The data was collected
on November 30, 2004 and December 1, 2004 from 4:42:54 PM to 9:42:54PM and from
10:55:20 PM to 3:55:20 AM. For each data set, the average DO and its standard
deviation was:
 4:42:54 PM to 9:42:54PM, values taken from 4:51:54PM on, when DO
dropped below target value of 0.5 mg/L
o Average DO: 0.505 mg/L
o Standard Deviation: 0.015
 10:55:20 PM to 3:55:20 AM, values taken from 11:04:20PM on, when DO
dropped below target value of 0.5 mg/L
o Average DO: 0.538 mg/L
o Standard Deviation: 0.042
The graphs of DO response versus time are shown below in Figure 3 and 4. PID
control accurately maintained an approximate DO of 0.5 mg/L in the reactor throughout
the aeration state, as the sample figures below clearly show. We were originally planning
on changing the values for P and I, trying to maximize control, but the program worked
much better than expected and there was no reason to change the values.
1
0.9
0.8
DO (mg/L)
0.7
DO (mg/L)
0.6
0.5
0.4
0.3
0.2
0.1
0
4:42:54 PM
5:54:54 PM
7:06:54 PM
Time
8:18:54 PM
9:30:54 PM
Figure 3: Dissolved Oxygen (mg/L) vs. Time during aeration state on 11/30/04 from 4:42:54 PM to
9:42:54 PM.
1
0.9
0.8
DO (mg/L)
0.7
DO (mg/L)
0.6
0.5
0.4
0.3
0.2
0.1
0
10:55:20 PM
12:07:20 AM
1:19:20 AM
Time
2:31:20 AM
3:43:20 AM
Figure 4: Dissolved Oxygen (mg/L) vs. Time during aeration state on 11/30/04-12/1/04 from 10:55:20
PM to 3:55:20 AM.
UV Spectrometry Analysis: Standards
The results obtained from the UV spectrometry test performed in the Hach
cadmium test and the micro-phenate test are provided below:
2.5
Absorbance
2
1.5
0 mg/L
2 mg/L
1
6 mg/L
10 mg/L
0.5
0
0
200
400
600
800
-0.5
Wavelength (λ)
Figure 5: UV spectrometry curves for nitrate and nitrite standards.
1000
0.3
0.25
Absorbance
0.2
0.15
0 mg/L
0.2 mg/L
0.1
0.4 mg/L
0.05
0.6 mg/L
0
-0.05
0
200
400
600
800
1000
-0.1
Wavength (λ)
Figure 6: UV spectrometry curves for ammonia standards
We chose to analyze the nitrate and nitrite standards at 542 λ and the ammonia
standards were analyzed at 640 λ because these were the wavelengths with the most
observable curves. It should be noted that the cadmium test for nitrate and nitrite had to
be run several times on standards before an acceptable linear relationship was determined
for the standards. We found that it was important to make sure the timing of each step in
the cadmium test was the same from sample to sample in order to achieve accurate
results. Acceptable results for the ammonia standards were achieved on the first try. The
results of the standards analyzed at of the tests at their appropriate wavelengths are
provided below:
1.8
1.6
y = 0.1611x - 0.0451
R2 = 0.9954
Absorbance at 542 λ
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-0.2
0
2
4
6
8
10
12
Concentration (mg N-NO3/L)
Figure 7: The linear region of the nitrogen concentration as nitrate and nitrite as determined by tests
on prepared standards.
0.3
Absorbance at 640 λ
0.25
y = 0.436x - 0.0158
R2 = 0.9737
0.2
0.15
0.1
0.05
0
-0.05
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Concentration (mg N-NH3/L)
Figure 8: The linear region of the nitrogen concentration as ammonia as determined by tests on
prepared standards.
UV Spectrometry Analysis: Samples
These linear calibration curves were used to estimate the concentrations of
ammonia, nitrate and nitrite in the samples extracted from the reactor.
The plant was run with at bulk DO target of 0.5 mg/L with aeration times of 8, 18
and 24 hours. Samples taken from the reactor at the end of these aeration times were
analyzed and the results obtained are presented and discussed below.
Table 3: Nitrate-nitrogen concentrations at different aeration times for a DO of 0.5 mg/L.
Aeration Time
(hr)
24
18
8
Absorbance
at 542 λ
0.63
0.54
1.84
Concentration
(mg N-NO3/L)
4.21
3.64
11.72
Table 4: Ammonia-nitrogen concentrations at different aeration times for a DO of 0.5 mg/L.
Aeration
Time (hr)
24
18
8
Absorbance
at 640λ
Diluted Concentration
(mg N-NH3/L)
1.22
1.22
1.05
3.16
2.83
2.44
Actual
Concentration
(mg N-NH3/L)
31.57
28.34
24.43
Table 5: Nitrogen Removal efficiency.
Aeration
Cycle (hr)
24
18
8
Total N
Remaining (mg/L)
32.33
35.19
36.15
N Removal
(mg/L)
8.57
5.71
4.75
% Removal
20.96%
13.96%
11.61%
At a DO target of 0.5 mg/L, the first aeration cycle was run for 24 hours. At the
end of this aeration cycle, the sample taken from the reactor was analyzed for total nitrate
and ammonia concentrations. The results obtained indicated a total ammonia
concentration of 28.3 mg N-NH3/L and a total nitrate concentration of 4.22 mg N-NO3/L.
We know that the initial nitrogen concentration in the tank is 40.9 mg/L, indicating that a
total of 8.38 mg/L of Nitrogen was removed by the bacterial process. This corresponds to
20.5% removal of nitrogen.
From the 24 hour data, it can be noted that most of the nitrogen remaining is in
the form of ammonia. This could indicate to insufficient DO level being maintained in
the reactor, a plausible explanation considering the predominant dark color observed in
the bio-solids in the reactor during the settling stages. This dark color often serves as an
indicator of a predominantly anoxic condition in the reactor. Another plausible
explanation could be that we allowed the SND process to extend for far longer than
necessary such that the aerobic bacterial population was suffocated in the largely anoxic
zones in the reactor and simply ceased to perform effectively anymore. A flaw in our
process, in this regard, was our inability to test for viable biomass concentrations in the
reactor.
Next, we reduced the aeration period to 18 hours, from which we observed a
nitrogen removal rate of 13.8%. At the 18-hour aeration cycle, we observed an increase
in the residual ammonia-nitrogen concentration to 31.6 mg/L and a decrease in nitratenitrogen to 3.64 mg/L.
Finally, we achieved 11.7% removal in the 8-hour aeration cycle. However, a
much higher percentage of residual nitrogen was in the form of nitrate and nitrite for the
8-hour cycle. The concentration of ammonia for this test was the lowest of the three.
The trends in these results are interesting and possibly a bit suspicious. In all
cases, the ammonia-nitrogen was in the highest concentration, indicating that anoxic
conditions predominated in our tank. However, the nitrogen removal efficiency in the 24hour and 18-hour tests were high compared to the levels of nitrates in the tank, indicating
that denitrification was efficient once nitrogen reached the nitrite or nitrate form. The
concentration of nitrates for the 8-hour cycle was very high. This could be an indicator
that most of the nitrification is occurring early, but that denitrification does not occur
until later. However, the relatively low concentrations of ammonia-nitrogen for this cycle
are hard to explain. Ammonia-nitrogen should increase initially, but we expect to see
decreasing concentrations of ammonia as nitrogen removal increases. The opposite was
observed in our experiment.
A possible solution to this problem would have been to run an aeration cycle for
24-hours and to take samples during that same cycle at more frequent intervals. By doing
this we would eliminate any variance in the waste feed or bacterial population from one
sample to the next, and would be able more accurately show how the nitrogen
concentrations in each form change with time. We ran out of Hach cadmium testing
materials and were unable to perform this test, but it would be an interesting topic for
further investigation.
Conclusion
We were unable to collect enough data to come to any encompassing conclusions
concerning simultaneous nitrification and denitrification. We were able to achieve some
nitrogen removal, so it seems like the process is possible on the laboratory scale. It also
seems like long aeration times are required to get enough oxygen into the system to allow
for nitrification. We were able to measure total nitrogen in our system without a working
nitrogen probe, making the project somewhat successful. We were also able to reach a
very well controlled dissolved oxygen level using the process control software and the
PID program. Finally, we found that there are many options still available to explore on
this topic, but we encourage other research groups to consider our difficulties in planning
their experiments.
Difficulties and Suggestions
The difficulties encountered in running the plant were many, but the major ones
included the tendency of the reactor to produce a lot of effervescent during the initial
aeration stages immediately following the tap water-feed step. This led to our reactor
overflowing regularly creating a messy situation. We also had overflow problems when
there were power supply issues in the lab. We had our “fill with water” step dependent on
the pressure sensor at the bottom of the tank, and found that whenever there was a power
supply problem, these failed, but the peristaltic pump did not, and our tank overflowed.
Probably the most time consuming part of our experiment was getting the Hach
cadmium test for nitrate and nitrite to work correctly. We eventually used almost all of
our materials for the nitrite test just in getting the standard test to work correctly. We
would suggest to anyone using this test to be careful in the timing. It is not crucial that
the timing is exactly as instructed in the testing kit, but it is important to be consistent
from one sample to another. It is also important to make sure that there is no
contamination from once sample to the next because it is done with very small volumes.
The ammonia test, however, was much easier. We would suggest this method for future
experiments, especially those which require collection of a large quantity of data.
If we were to do this project again, we would run the plant at aeration times that
were sequentially increased by 2 hours from a 2-hour initial point. Furthermore, we
would take the samples from the same cycle. For example, we would run a 24-hour
aeration cycle and take samples every 2 hours during that time. This would help reduce
the variability in the reactor conditions and provide more meaningful data. It may be hard
to have a 24-hour time period when an investigator is available every 2-hours, but it
would be worth it when compared to the numerous problems encountered trying to run
several cycles. Other further research could include trying to obtain simultaneous
nitrification and denitrification at different levels that ranging from 0.5 to 2.5 mg/L. We
chose 0.5 mg/L based on our research, but it would be interesting to see how good of a
choice this was.
References
David P. Whichard (2001), Nitrogen Removal From Dairy Manure Wastewater Using
Sequencing Batch Reactors, M.Sc Thesis, Virginia Polytechnic Institute and State
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