WATER POLLUTION CONTROL RESEARCH SERIES • 17010DHT09/7O
METHANOL REQUIREMENT
AND TEMPERATURE EFFECTS
IN WASTEWATER DENITRIFICATION
ENVIRONMENTAL PROTECTION AGENCY • WATER QUALITY OFFICE
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WATER POLLUTION CONIROL RESEARCH SERIES
The Water Pollution Control Research Reports describe the results
and progress In the control and abatement of pollution In our
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METHANOL REQUIREMENT AND TEMPERATURE EFFECTS
IN WASTEWATER DENTTRIFICATION
by
Gulf South Research Institute
New Iberia, Louisiana 70560
for the
WATER QUALITY OFFICE
ENVIRONMENTAL PROTECTION AGENCY
Program #17010 DHT
Contract #14-12-527
WQO Project Officer, E. F. Earth
Advanced Waste Treatment Research Laboratory
Cincinnati, Ohio
August, 1970
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C., 20402 - Price SO cents
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WQO Review Notice
This report has been reviewed by the Water
Quality Office and approved for publication.
Approval does not signify that the contents
necessarily reflect the views and policies
of the Water Quality Office, nor does mention
of trade names or commercial products constitute
endorsement or recommendation for use.
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ABSTRACT
Biological denitrification was studied in two types of continuous -
flow reactors as a function of the concentration of an organic addi-
tive (methanol), at 3 temperature regimes, and 3 dissolved oxygen
(D.O.) levels. One of the reactors was packed with small diameter,
about 3 mm, glass beads and is called the packed column reactor; the
other reactor was a container having a concentration of suspended
solids of about 2000 tng/1 and is called the suspended growth reactor.
The temperatures used were 30°C, 20°C, 5°C and dissolved oxygen levels
were level I, less than or equal to 0.5 pptn, level II, 1.3 to 2.5
ppm, and level III, greater than or equal to 4.0 ppm.
The most efficient methanol:N03~N ratio for both reactors is between
2:1 and 3:1. The optimum ratio varies to a slight extent with tempera-
ture. For example, at 30°C, greater than or equal to 907o denitrif ica-
tion in both reactors was achieved with a methanol:NO.,-N ratio of 2:1.
At 20°C, greater than 90% denitrification was achieved in the packed
column reactor with a ratio of 2:1 but the suspended growth reactor re-
quired a ratio of 3:1 to achieve equivalent denitrification. At 5°C, the
packed column reactor was functional at a tnethanol:NOo-N ratio of 2:1
but the most efficient ratio was 3:1; the data from the suspended growth
reactor indicate a ratio slightly greater than 3:1 was required at this
temperature.
Dissolved oxygen was not a major factor governing the efficiency of
either of the two denitrifying units. The most apparent effect was
at D.O. levels I and III and this was usually, but not consistently,
most apparent at methanol:NO--N ratios of less than or equal to 1:1.
Both reactors were slightly more efficient at D.O. level I than at D.O.
level III. The most effective methanol:NOo-N ratio was between 2:1 and
3:1 for all D.O. levels, in both reactors.
This report was submitted in fulfillment of Contract No. 14-12-527,
Program No. 17010 DHT, between the Federal Water Quality Administration
and Gulf South Research Institute.
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CONTENTS
Section Page
I Conclusions v
II Recommendations v*
III Introduction *
IV Materials and Methods 3
Q
V Objectives
VI Results and Discussion
VII References
l8
ii
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FIGURES
Page
1 Diagram of Pilot Plant 20
2 Diagram of Packed Column Reactor 25
3 Diagram of Suspended Growth Reactor 27
4 Denitrification Graph for Packed Column Reactor 28
5 Denitrification Graph for Suspended Growth Reactor 29
6 Acclimation Graph for Packed Column Reactor 30
7 Acclimation Graph for Suspended Growth Reactor 3^
iii
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TABLES
No. Pa,ge
I Temperature experiments with packed column
reactor 33
II Temperature experiments with suspended growth
reactor 34
III Dissolved oxygen experiments with packed column
reactor 35
IV Dissolved oxygen experiments with suspended growth
reactor 36
V Total solids data from packed column reactor 37
VI Individual test results from both reactors 38
iv
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SECTION I
CONCLUSIONS
1. The optimum methanoltNOg-N ratio for biological denitrification
is between 2:1 and 3:1 at 20°C and 30°C, and slightly greater than
3:1 at 5°C.
2. Temperature affects biological denitrification only slightly,
particularly at methanol:N03~N ratios less than optimum; at lower
temperatures methanol:N03~N ratios have to be increased slightly to
achieve the same amount of denitrification.
3. Dissolved oxygen does not appreciably affect biological denitri-
fication; however, at lower dissolved oxygen levels the efficiency of
the process is slightly enhanced.
4. The packed column reactor, described in the body of this report,
is a more efficient denitrifying unit than the suspended growth reac-
tor because it requires a shorter detention time.
5. An acclimation period is necessary if large temperature changes
are experienced during biological denitrification.
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SECTION II
RECOMMENDATIONS
This research was done with a pilot plant on a small scale as des-
cribed elsewhere in this report. It is recommended that future
work be done on a larger scale and that the design incorporate
provisions for making several test runs per day or operational
period, in order that a sufficient amount of data could be collec-
ted for suitable statistical analysis. This type of analysis would
provide a more rigorous indication of optimum methanol:N03~N ratios
between 2:1 and 3:1 for various temperatures.
The design of methanol storage facilities in an actual wastewater
operation should be based on a maximum methanol:N03~N ratio of about
4:1 since varying environmental conditions, i.e., temperature, will
necessitate a ratio between 2:1 and 3:1 and on occasion slightly
more than 3:1. In order to avoid adverse temperature effects the
methanol:N03~N ratio should always be greater than or equal to 2:1
and in lieu of specific information for lower temperatures (about 5°C)
the ratio should be set at 3:1.
Additional design improvements could be made to the suspended growth
reactor, particularly the manner in which the wastewater flows through
it. An upward flow pattern would prevent clogging and insure a con-
stant volume.
Some provision in plant design may be necessary for acclimation time,
particularly at lower temperatures, i.e., 5°C, and at methanol:N03~N
ratios well below the optimum.
Finally, a positive technique, such as gas chromatography, is needed
to measure the utilization of methanol.
vi
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SECTION III
INTRODUCTION
The removal of eutrophying nutrients from wastewater effluent is
of first rank priority in pollution control. One of the major
problems is the removal of low concentrations of nitrogen from large
volumes of water at an acceptable cost.
Biological denitrification seems to offer a practical solution to
this problem since a satisfactory degree of nitrogen removal is pos-
sible and has been achieved by a number of workers using different
process designs (1, 2, 3, 4, 5, 6, 7).
A variety of organic additives have been used to satisfy the metabolic
hydrogen donor requirements of the denitrifying organisms. Of these,
methanol appears to be one of the most satisfactory and economical (6,
7, 8, 9, 10, 11). In studies using methanol a high percentage removal
of nitrogen was achieved but reports vary on the amount of methanol re-
quired in relation to nitrate-nitrogen (N03~N) removed. This variation
ranges between 2 and 4 parts of methanol per part of nitrate-nitrogen
on a weight basis. Some of these discrepancies may have been due to
differences in experimental conditions, particularly temperature and
the presence of dissolved oxygen in the nitrified effluent. Temperature,
of course, affects sludge production and the endogenous metabolism of
wastewater microbes, while dissolved oxygen is believed to be the pre-
ferred hydrogen acceptor when present with nitrate (12, 13) and thus will
exert a "methanol demand," requiring approximately one part of methanol
per part oxygen on a weight basis (9, 10, 11).
In a biological denitrification system involving large volumes of waste-
water, it is obviously necessary to ensure that the methanol added is
just sufficient to remove the nitrate present; addition of too little
will leave residual nitrate and too much will cause an unnecessary in-
crease in cost of treatment as well as an undesirable increase in the
oxygen demand of the effluent. It is necessary, therefore, to determine
how changes in operating temperatures affect denitrifying efficiency and
methanol requirements, since systems of this type are required to operate
over a wide range of seasonal temperature changes.
A recent, study (7) of a continuous-flow suspended growth denitrifying
reactor using methanol suggests that a contact time of about 180 minutes
is required for a unit of this type. In contrast, studies with denitrify-
ing flora developed on packed columns of sand or granular carbon, also
using methanol, indicated that very rapid denitrification can occur; a
concentration of 28 mg/1 N03~N was reduced by 86 percent after a contact
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time in the column of 5.5 minutes; after 22 minutes contact, the
reduction was 93 percent (9). A coke-packed unit (3) using raw
wastewater as the hydrogen donor also achieved rapid removal of
nitrogen, 72 percent in 20 minutes. These reports suggest that
packed columns may offer advantages over suspended growth reactors
but there is a need for further data on their comparative opera-
tional performance.
This report describes the results of an experimental program in which
biological denitrification was studied in the two types of continuous-
flow reactors, packed column and suspended growth, as a function of
methanol concentration at 3 temperature regimes and 3 dissolved oxygen
levels.
Outline of Denitrification
Biological denitrification is the microbial conversion of nitrate and
nitrite to nitrogen and nitrous oxide but molecular nitrogen is the
usual and major end product. This reaction requires an organic energy
source and, in the absence of oxygen, can be considered a two-step
process when methanol is the energy source.
(1) N03~ + 1/3 CH3OH » N02" + 1/3 C02 + 2/3 H20
(2) N02~ + 1/2 CH3OH ^ 1/2 N2 + 1/2 C02 4- 1/2 H20 + OH~
If there is not enough methanol present or in the presence of excessive
dissolved oxygen, the reaction will not go to completion, resulting in
water high in nitrites.
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SECTION IV
MATERIALS AND METHODS
A diagramatic layout of the denitrification pilot plant is given in
Fig. 1 and appropriate explanatory legends are included. The system
included two holding tanks (A and B), one for mixed liquor and one
for the nitrified effluent. These were connected to a temperature-
controlled reservoir (C) fitted with a recirculation system. The
nitrified effluent flowed from the temperature-controlled reservoir
into both the suspended growth reactor (J) and the packed column re-
actor (L). Continuous-flow through the reactors was maintained by
means of pumps (H and M) and the appropriate methanol dose was main-
tained by means of infusion pumps (F and G) with a constant rate of
infusion. Flowmeters (I and N) monitored the flow-rate into the two
reactors. The methanol was stored in reservoirs (D and E).
Wastewater Collection and Nitrification
Sewage was collected once a week from the local sewage plant in New
Iberia, Louisiana by means of a portable pump and three 190-liter
polyethylene tanks carried in the back of a pickup truck. Mixed li-
quor was pumped from the point in the secondary treatment tank where
aerated liquor flows into the final settling tank and just prior to
the final chlorination. The mixed liquor was then trucked to the
test facility, approximately 3 miles, and pumped into the first hold-
ing tank (A in Fig. 1), where it was aerated (S of A in Fig. 1) for
24 hours to insure maximum nitrification. After 24 hours, aeration
was discontinued and the effluent transferred by means of gravity flow
to the second holding tank (B in Fig. 1) but only after the sludge had
settled. A screen was provided on the outflow of tank A to prevent
large particles from entering tank B. The nitrified effluent in tank
B was held no longer than 6 to 7 days after which a fresh supply was
collected and prepared.
Deoxygenation Techniques
Initially, the nitrified effluent was deoxygenated by means of nitro-
gen gas. This was done by flushing the effluent with nitrogen (gas)
in a column approximately 3 meters long and 7.5 cm in diameter. This
technique was not satisfactory as the dissolved oxygen could not be
lowered below 2.0 ppm, and it took a considerable time to deoxygenate
a small amount (1 hr. for 5 liters) of nitrified effluent to this D.O.
level. The 3-meter column was located where item C is (Fig. 1) and was
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later replaced by Item C - the temperature-controlled reservoir.
In order to achieve D.O. levels of less than 2.0 ppm, it was neces-
sary to discontinue aeration of the mixed liquor in tank A and hold
it under these conditions for 1 to 2 hours; the holding time depen-
ded on the desired D.O. level and the temperature of the nitrified
effluent. When the specified D.O. level was reached, the nitrified
effluent was transferred to tank B, where the D.O. level was continu-
ously monitored; it remained constant for at least 6 days for the
particular test period. For each D.O. level, a fresh batch of nitri-
fied effluent was brought in. No significant denitrification occurred
in tank B under these procedures, and so nitrogen flushing in the 3-
meter column was discontinued.
Dosing Systems
The nitrified effluent was pumped from the temperature-controlled
reservoir (C) into the two reactors by means of two Cole-Palmer
Masterflex infusion pumps (H and M in Fig. 1). The flow rates of
these pumps could be adjusted separately to constant values.
The amount of methanol injected from reservoirs D and E (Fig. 1) into
each reactor was controlled by means of separate infusion pumps (brand
EMCEMO; F and G in Fig. 1). These pumps work at a constant flow set-
ting. The dosing system devised for introducing the methanol proved
to be reliable and particular confidence is placed in it. Briefly, it
worked as follows: The particular methanol dosing ratio was calculated
on a weight basis (methanoltNOyN ratio) and controlled by means of
the infusion pumps and flowmeters. For example, if a 3:1 (methanol:
N03~N) ratio was to be used for denitrifying an effluent containing 20
mg/1 of N03~N then this requires 60 mg/1 of methanol. If the rate of
flow through the reactor is 15 ml/min then 0.9 mg/min of methanol is
the necessary dose rate. Since the infusion pump had a set rate of 0.2
ml/min, each 0.2 ml it pumped must contain 0.9 mg of methanol. Thus,
the concentration of methanol used in the reservoir was 4.5 g/1.
Denitrifying Units
A detailed diagram of the packed column reactor is given in Fig. 2
and appropriate explanatory legends are attached to it. This reactor
(F in Fig. 2) had a capacity of approximately 2 liters and was packed
with small-diameter, about 3 mm, glass beads to provide a large surface
area for the denitrifying flora. It was also provided with a water
jacket (E, through I and out D in Fig. 2) for temperature control and
4 outlets (J, K. L, and M in Fig. 2) for sampling. The 4 separate samp-
ling points did not prove to be feasible from a plant management point
of view and were not used. The flow of the nitrified effluent and the
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.methanol dose was upward; that is, the effluent entered through A,
and was pumped by means of the pump (N) through the flowmeter (p),
mixed with methanol and then forced upward into the column (F) and
out C into a stainless steel collecting tank (Q).
A detailed diagram of the suspended growth reactor is given in Fig.
3 and appropriate explanatory legends are attached to it. This re-
actor consisted of a tube within a tube with a total capacity of
approximately 4.5 liters. It was provided with a water jacket (E;
cooling and/or heating water enters through item I and out item D;
in Fig. 3) for temperature control. The inner cylinder (G in Fig.
3) was water permeable and made of polyethylene commercially known
by the trademark VYON. It retained most of the suspended solids of
the mixed liquor while allowing the effluent to pass through. Some
loss of solids probably did occur, however. A magnetic stirrer (J
in Fig. 3) insured proper mixing of the effluent and methanol (both
entered the reactor through A in Fig. 3). The effluent passed through
C (Fig. 3) into the annular space labeled F and eventually out through
K into a stainless steel collecting tank. Temperature was monitored
with a mercury thermometer.
The usual enrichment technique of continuous-flow inoculum of denitri-
fying organisms in both reactors over several weeks were used to de-
velop an. adequate growth of microbes. Periodic cleaning of both
reactors was required in order to insure a continuous-flow operation;
this usually resulted in a loss of denitrification efficiency for
several days until the biomass of the microbes built up again to a
maximum level.
In the beginning, detention time for the suspended growth reactor was
arbitrarily set at 100 minutes. No denitrification was achieved at
this holding time so the time was increased to 180 minutes and 78%
denitrification was achieved at a methanol:NO3~N ratio of 5. The de-
tention time was then increased to 210 minutes and efficient denitri-
fication was obtained. Since the suspended growth reactor had a
volume of approximately 4.5 liters, a flow rate of 20 ml/min was used
for the 210-minute detention time.
The empty-bed detention time of 15 minutes used for the packed column
reactor was also arbitrarily decided on. Previous reports from work
done elsewhere guided this initial time estimate. The packed column
reactor had a volume of approximately 250 ml and a flow rate of 15
ml/min was used.
Daily Test Procedures
Experiments were carried out simultaneously with both the packed column
and suspended growth reactors. Studies at 20°C and 30°C were initiated
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first and then the temperature was stepped down in 5°C decrements
over 11 days to the 5°C level. No operating problems resulted dur-
ing the temperature changes.
Generally the plant was run continuously, on a 24 hour basis, with
the exception of occasional breakdowns. Day to day continuous
operational work consisted of (1) mechanical maintenance of the
plant, (2) spot checking on various aspects of the nitrified effluent
including temperature, dissolved oxygen, and methanol concentrations
as required for each test run and (3) the tests for denitrification
efficiency on both reactors.
For each methanol concentration tested, both reactors were allowed
to equilibrate for 24 hours. This was done by changing methanol con-
centration, after the denitrification tests, for the experiment to be
run on the following day. Denitrification tests were run in the after-
noon hours. Methanol concentration for the next run was calculated on
the basis of initial nitrate level in the effluent and this was deter-
mined by standard nitrate analysis. Methanol:NO-j-N ratios are expressed
hereafter by a single integer or fraction and this always means X parts
of methanol to 1 part of NO^-N.
Temperature and dissolved oxygen were checked and recorded for each ex-
perimental setup on a daily basis. Temperature was maintained within
the reactor at at plus or minus 0.5°C, and the dissolved oxygen level
was not affected, provided the ambient temperature in the area of the
holding tanks were maintained below or within 20°C to 25°C,
The size and design of the pilot plant caused operational problems.
Breakdown of the small pumps on both the reactors and on the heating
and cooling system was frequent until a suitable quality of pump could
be obtained. Clogging of the discharge outlet (item K) was frequent
in the suspended growth reactor. A larger-siaed suspended growth re-
actor with minor modifications in design would be desirable. Such a
reactor should be provided with an inlet at the bottom of the reactor
rather than the top in order to provide an upward flow through the re-
actor which would prevent clogging and would insure an accurate means
to maintain a constant volume.
Chemical Analyses
The laboratory analyses were carried out by procedures recommended by
Standard Methods (14). The physical and chemical parameters that were
monitored, usually on a daily basis, included temperature, pH, dissolved
oxygen, NOo-N, NC^-N, and total suspended solids.
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Temperature was measured by the usual mercury-type probe and/or a
thermistor-type probe (Yellow Springs brand). The pH of the effluent
was measured with a Beckman II Zeromatic pH meter.
Dissolved oxygen was measured by means of a D.O. meter (Yellow Springs
brand) calibrated by the Standard Winkler chemical test.
Nitrate-nitrogen (NO^-N) was determined by the phenoldisulfonic acid
method. No prior treatment of the sample was required since the nit-
rified and denitrified effluents were relatively free of turbidity
and color. Generally, 100 to 150 ml samples were collected. Sulfonic
acid and potassium permanganate were used to convert all nitrite into
nitrate form, followed by treatment with silver sulfate to remove
chloride present in the sample. Chloride was removed by precipitation
and filteration. The filtrate was neutralized with NaOH to about pH 7.
A suitable aliquot was taken and heated; residues were digested with
phenoldisulfonic acid. Color was developed with ammonium hydroxide.
Samples were then diluted to 100 ml and read at 410 my in a Beckman
DU Spectorphotometer.
Nitrite determinations were run by taking a suitable aliquot and dilut-
ing it to 50 ml. Sulfanilic acid was added and after a 3 to 5 minute
period the color was developed by adding napthalamine hydrochloride.
The solution was buffered with sodium acetate. Color was measured at
520 my in a Beckman DU Spectrophotometer.
Total suspended solids were measured by taking well-mixed samples in a
volumetric flask. The sample (100 ml) was filtered through a weighed
membrane filter using suction. The filter then was washed with 10 ml
distilled water to remove soluble salts and dried with the solids at
103°C for 1 hour approximately in a mechanical convection oven until
constant weights were achieved. It then was allowed to cool to room
temperature in a dessicator before weighing. Results were expressed in
terms of mg/1 total suspended solids.
Units for Data Expression
Tables I through IV give the major results of this study. They have
been expressed in a variety of ways. For example, the initial concen-
trations and residual concentrations of NC^-N and N02-N are given in
terms of mg/1 and also in terms of percent change; that is, the per-
centage the residual concentration differs from the initial concentra-
tion. In some cases for NO--N, the residual was greater than the
initial concentration. In short, there was an increase and, therefore,
the percent change is greater than 100%. These percentage values have
been marked with a plus sign. In addition, the overall percent of
oxidized nitrogen removal is given. These values were derived by adding
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both initial concentrations for NO--N and NO^-N and dividing by
the sum of the residual concentrations of NO-j-N and NC^-N and sub-
tracting from 100.
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SECTION V.
OBJECTIVES
The objectives of this work were as follows:
1. To determine the most efficient methanolrNO^-N ratio required
to denitrify wastewater effluent at 30°C, 20°C, and 5°C in both
packed column and suspended growth reactors.
2. To determine the effect of various concentrations of dissolved
oxygen on the methanol required to achieve maximum denitrification.
3. To compare the packed column reactor with the suspended growth
reactor, particularly with reference to their efficiency, consis-
tency of operation, and feasibility of management.
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SECTION VI.
RESULTS AND DISCUSSION
Methanol ;NO-3-N Ratio and Temperature
The primary objective of this work was to determine the most efficient
methanol:NOo-N ratio (weight basis) in both the packed column and sus-
pended growth reactors. This ratio is defined as that which produces
maximum denitrification with a minimum of methanol under the specified
conditions. In general, our data indicate that the most efficient
methanol:N03-N ratio for both reactors lies between 2 and 3. At these
ratios, denitrification was little affected by temperature and/or dis-
solved oxygen (D.O.); the latter aspect (D.O.) will be discussed in the
next section.
Select data obtained at temperatures of 30°C, 20°C, 5°C and at various
methanol:N03-N ratios are presented in Tables I and II as derived from
the packed column and suspended growth reactors, respectively. These
data are, however, summarized by Figs. 4 and 5, in the form of graphs,
plotting percent denitrification on the basis of NO^-N removal as a
function of various methanol:N03~N ratios. The differences among the
percentages of denitrification on the basis of N03-N removal (Figs. 4
and 5) and on the basis of total oxidized nitrogen removal (Tables I
through IV) are slight (cf., ibid).
The packed column reactor achieved maximum denitrification on the basis
of both N03-N and N02-N removal, at a ratio of 3, where 97%, 97%, and
96% denitrification were obtained at 30°C, 20°C and 5°C, respectively
(Table I; see also Fig. 4). These values are means of at least two
experimental runs. The highest denitrification values of any of the
individual runs were 97% and 96%, at a ratio of 3, for 30°C and 5°C,
respectively. At no time did we achieve a higher percentage of denitri-
fication even though methanol was dosed at ratios of 4, 5, 6, 8, 12, 16,
24, 28, 32 and 40. (Some of these data are not included in this report.)
At these higher ratios, the percent of denitrification was not apprecia-
bly increased and was usually in the low 90's or high 80's. Fig. 4,
based on N03-N removal, indicates a leveling off between methanol:N03~N
ratios of 2 and 3 and if the former data were plotted on it, then a
plateau would be readily apparent. Close examination of this figure
will show that the curves indicate trends only and at ratios greater
than 2 there are no significant differences due to temperature. Indeed,
the curves actually intersect at these higher ratios. At ratios less
than 2 a temperature effect is apparent and the spread (23%) is greatest
at a ratio of 1/2, between 20°C and 30°C (see also Table I). The criti-
cal point therefore, in regard to an efficient methanol:NO3-N ratio, is
evident at a ratio of 2 for the packed column reactor.
11
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The suspended growth reactor also achieved maximum denltrlflcatlon,
on the basis of both N03~N and NC^-N removal, at a ratio of 3, where
96%, 91% and 91% denitrification were obtained at 30°C, 20°C and 5°C,
respectively (Table II; see also Fig. 5). Higher values for percent
denitrification were not obtained from this reactor at methanol :NO-j-N
ratios greater than 3. Fig. 5 also indicates a leveling off between
methanol:N03~N ratios of 2 and 3. Furthermore, denitrification in
this reactor for ratios greater than 3 never exceeded 96%. Nonethe-
less, the test differences are greater for this reactor, though the
spread is probably not significant at a ratio of 3; and hence it is
concluded that there is little difference between the two reactors
in efficiency due to temperature at optimum methanol ratios. Even at
a ratio of 2, denitrification at 30°C is not much greater than at 20°C
(90% vs. 86%) but at 5°C it drops off sharply to 67% which probably
is significant. The spread in the data at ratios less than or equal
to 2 is quite pronounced for the suspended growth reactor when com-
pared to the packed column reactor (Figs. 4 and 5).
The results of temperature acclimation in both reactors to 5°C are
presented in Figs. 6 and 7 in terms of NO^-N removal. No apparent
acclimation differences were found between the two reactors at 30°C
and 20°C and the suspended growth reactor showed no adverse effects
while operating at 5°C (Fig. 7). Only the packed column reactor (Fig.
6) exhibited a significant acclimation effect and this was present
only at ratios less than or equal to 2 but it was apparently readily
overcome within 4 to 6 days. It is difficult to account for this
effect in the packed column reactor.
Additional data given in Table I on the packed column reactor supports
the initial conclusion that the most efficient methanol:NO3~N ratios
lie between 2 and 3. For example, at 30°C, it is probable that this
ratio is closer to 2 since the final N02-N value was zero indicating
that methanol-nitrate reaction went to completion, as compared to
ratios of less than or equal to 1, where the N02-N was either partly
reduced or significantly increased. The latter values occur at ratios
of 1/2 and 1/4 when values of plus 157% and plus 146%, respectively,
were obtained for final N02~N levels. At 20°C, the most efficient
ratio is also probably closer to 2 than 3, as the final nitrite values
exhibit the same patterns as those of the 30°C test level. At 5°C,
some temperature effect on the methanolsNO^-N ratio is suggested since
denitrification is markedly less at a ratio of 1 and the final N02-N
value (44% reduction) at a ratio of 2 indicates an incomplete reaction
and insufficient methanol dose. It is likely that the effective ratio
lies closer to 3 than 2.
Additional data on the suspended growth reactor are presented in Table
II. There is a more pronounced temperature effect on the methanolrNOo-N
12
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ratio for the suspended growth reactor than for the packed column
(see also Fig. 5). For example, at 30°C, the most efficient methanol:
NC>3-N ratio is closer to 2 than 3 as indicated by a 100% reduction of
the initial NC^-N value at a ratio of 2. At 20°C, the ratio lies
closer to 3 since it was the only ratio at which complete removal of
N02-N occurred. At 5°C, the ratio is very likely greater than 3 since
some N02-N was present at the end of the test. Methanol:N03-N ratios
greater than 3 at 5°C were not tested.
Comparing the results of the two reactors (see Tables I and II) at 30°C,
the percent change in both NC^-N and N02~N was virtually identical.
The greatest difference in percentage denitrification was found at
ratios of 1/2 and 1 and both were only of the order of 2%; the suspen-
ded growth reactor being slightly more efficient. This difference is
probably not significant since a greater than or equal to 4% difference
was often obtained between individual replicated runs in both reactors.
For example, the packed column reactor once yielded 83% denitrification
on the basis of N03-N removal at a ratio of 1 which is equivalent to
the value of the suspended growth reactor given in Table II for the same
ratio. It is concluded that there is little or no difference between
the two reactors at 30°C in regard to denitrification except for deten-
tion time. At 20°C, data from the packed column indicate that it is
slightly more efficient than the suspended growth reactor; denitrifica-
tion in this reactor is greater at all ratios except 1, and the final
N02-N values are considerably less than the suspended growth data in
all cases. Because of the few data points, a statistical analysis could
not be done on the results. However, significant differences probably
do not exist between the two reactors at 20°C except in terms of deten-
tion time. At 5°C, data from the packed column suggest that it is more
efficient than the suspended growth reactor. For example, 41%, 89%, and
96% denitrification was achieved at ratios of 1, 2 and 3, respectively,
compared to corresponding results for the suspended growth reactor of
34%, 62% and 91%. For both reactors, our 5°C data suggest an optimum
methanol:N03-N ratio of greater than or equal to 3.
It is concluded that the packed column reactor is a more efficient de-
nitrifying plant than the suspended growth reactor mainly on the basis
of detention time. Some of the results indicate that both reactors
were more efficient at higher temperatures but only at methanol:N03-N
ratios of less than 2. No marked temperature differences were observed
at ratios of 2 and 3, in either reactor, at any of the 3 temperatures.
Initially, at 5°C, the packed column reactor showed (see Fig. 6—on the
basis of N03~N removal) a drop in denitrification efficiency but addi-
tional experiments indicated that it gradually became conditioned to
this test temperature and its efficiency was then comparable to its per-
formance at 20°C and 30°C.
13
-------
MethanoliNO^-N Ratio and Dissolved Oxygen
Experimental results on the effect of various concentrations of
dissolved oxygen on methanol:N03~N ratio are listed in Tables III and
IVfor the packed column and suspended growth reactors, respectively.
These experiments were carried out at 20°C, at 3 dissolved oxygen
(D.O.) levels. The three D.O. levels were: Level I, less than or
equal to 0.5 ppm; Level II, 1.3 to 2.5 ppm; and Level III, greater
than or equal to 4.0 ppm.
In general, dissolved oxygen did not inhibit denitrification in either
reactor to a major extent; this was particularly true for methanol:
NOg-N ratios greater than or equal to 2. For example, denitrification
on the basis of both N03~N and N02~N removal, in the packed column re-
actor, for methanol:N03~N ratios greater than or equal to 2, averaged
97% at D.O. level I, 92% at D.O. level II and 92% at D.O. level III.
These data indicate only a slight improvement in denitrification at
D.O. I level (the lowest level). In order to demonstrate whether this
difference is significant, more data would be required. Similarly,
denitrification, on the basis of both NOg-N and N02-N removal in the
suspended growth reactor, for methanol:N03~N ratios greater than or
equal to 2, averaged 93% at D.O. level I, 92% at D.O. level II and 88%
at D.O. level III. Again these data indicate that the suspended growth
reactor was slightly more efficient at the lowest D.O. (I) level. It
is emphasized that these differences are within the range of variation
that was found between individual and replicated experimental runs.
For example, both reactors achieved maximum denitrification of 98% at
the lowest D.O. level and at methanoliNOg-N ratios of 6 and 28,(data
for the latter ratio are not given) respectively. However, Tables HI
and IV clearly show that almost (1% to 7% difference) identical denitrifi-
cation is possible at ratios between 2 and 3.
Considering the data on the packed column reactor in detail (Table III),
maximum denitrification, on the basis of both NOg-N and N02-N removal,
of 98% was found at D.O. level I and a methanoltNOg-N ratio of 6 but
96% denitrification was also achieved at a ratio of 2. The final values
of N02-N were all zero for ratios greater than or equal to 2, indicating
that the most efficient ratio is probably less than or equal to 2. At
D.O. level II, maximum denitrification was 95% and 96% at methanol:N03~N
ratios of 2 and 3. At a ratio of 4, denitrification was 85% and the
N02~N was not completely removed. This may suggest some effect due to
dissolved oxygen. However, when the results of D.O. level I and D.O.
level II are compared, the packed column is definitely more efficient at
the lower D.O. levels but only for methane1:N03~N ratios of less than or
equal to 1. At D.O. level III, maximum denitrification was 94% at a
ratio of 3, with complete removal of N02~N. At a methanol:N03~N ratio
of 4, denitrification remained the same. For all 3 D.O. levels, the
breaking point indicating the most efficient methanol:N03~N ratio, lies
between 2 and 3.
14
-------
Detailed data for the suspended growth reactor are presented in Table
IV. No measurements of total suspended solids was obtained during
these experiments but it is assumed that they were approximately 2000
mg/1. At D.O. level I the suspended growth reactor had a greater de-
nitrifying capacity at methanol:N03~N ratios of less than or equal to
1 than at the other D.O. levels (this is similar to the packed column).
At ratios of greater than or equal to 1 for D.O. level I, maximum de-
nitrification (93%) was achieved and the final N02-N value was zero
but only D.O. level III showed some loss of denitrification at methanol:
N03~N ratios greater than or equal to 2. The maximum percentage differ-
ences of N03-N change, at ratios greater than or equal to 2, between
D.O. level I and level II is 5%, between D.O. level I and level III is
9% and between D.O. level II and level III is 9%. These differences
are probably not significant. In general, the N02-N data for this re-
actor at D.O. levels II and III are less consistent than for the packed
column in that the final N02~N values are never zero and show no trend
toward their complete removal at the higher methanol:N03~N ratios. This
may have been an effect of low concentration of suspended solids.
Comparing the results from all three D.O. levels there are no consistent
differences at methanol:N03~N ratios less than or equal to 1 in regard to
denitrifying efficiency. For ratios greater than or equal to 2, the re-
sults at D.O. level I and level II are almost identical except the N02~N
values are more consistent at D.O. level I. Some loss of denitrification
efficiency is suggested at D.O. Ill, particularly at methanol:NO3~N ratio
of greater than or equal to 3.
Growth and Development of Suspended Solids
The initial buildup of denitrifying organisms in the packed column re-
actor was done at 20°C and it required 41 days in order to establish a
flora that produced approximately 90% denitrification at methanol:NO3~N
ratios between 6 and 7. Almost 50% of the column was covered by a heavy
microbial growth during the first 6 weeks and thereafter it became com-
pletely covered. The bottom of the column appeared to have the heaviest
growth. Every two to three months the column required cleaning. This
was done by flushing it with effluent but precautions were taken to
avoid excess loss of the growth. The reactor was not used for experimen-
tal runs during the first 2 to 3 days after flushing.
At the end of the experiments, the packed column reactor was disconnected
from the rest of the pilot plant and three separate sections with their
enclosed glass beads were taken from it. These sections were from the
top, middle and bottom of the column; each being 5 cm high by 5 cm in di-
ameter. The beads in each section were carefully removed and washed sev-
eral times until they were completely free of growth. The washings were
collected and total suspended solids determinations were made on them.
15
-------
Each section contained approximately 4000 beads with an average
diameter of 3.28 mm. The total surface area of the beads was
computed and the number of grams of solids was expressed in terms
of this area and volume. The results are given in Table V. In
the top section 0.49 gm of suspended solids were found while cor-
responding values for the middle and bottom sections were 0.66 gm
and 2.99 gm, respectively. The bottom contained 4x to 6x more
suspended solids than the middle or top sections. This would be
expected based on its construction and the upward direction of flow.
Also given in Table V are the amounts of volatile suspended solids
for each of the sections of the packed column.
In the suspended growth reactor, flora adequate for denitrification
was obtained within 6 days. The reactor was considered ready for
operation when trial runs produced approximately 90% denitrification
at methanoltNOj-N ratios greater than or equal to 3. Some loss of
suspended solids occurred during its operation and later on this prob-
lem was probably corrected to some extent by periodic dosing of the
reactor with mixed liquor and determination of suspended solids.
The most efficient methanol:N03~N ratios in these studies for both
the packed column and suspended growth reactors have been found by
these studies to be between 2 and 3. For a particular operating tem-
perature it can only be stated that the most efficient ratio is either
close to 2 or close to 3. For example, in the packed column at 58C
the data indicated that the most efficient methanol:N03~N ratio is
closer to 3 than 2, at 20°C and 30°C it is closer to 2 than 3. For
the suspended growth reactor, the most efficient methanol:N03~N ratio
at 5°C is probably greater than 3, at 20°C it is closer to 3 than 2,
and at 30°C it is closer to 2 than 3.
MethanolrNO^-N ratios between 2 and 3 were not tested because of the
variability in the data produced at each of these ratios; that is,
the percent denitrification achieved for methanolrNO^-N ratios of 2
and 3 were often within plus or minus 2% and very often overlapped
one another. Examples of these data are presented in Table VI. For
the packed column reactor at 30°C, there was only plus 1.7% difference
between the highest and lowest experimental runs using methanol:NO~-N
ratios of 2 and 3, respectively. At 20°C the difference in percent
denitrification, using the same ratios, actually overlapped, and at 5°C
the difference was plus 2.1%.
The same situation prevailed for the suspended growth reactor at 30°C
and 20°C in that only plus 0.3% and plus 2.9% differences separated
percent denitrification results for methane1:NO3~N ratios of 2 and 3.
At 5°C, however, the percent denitrification at methanol:N03~N ratios
of 2 and 3 were well separated (plus 18.7% between corresponding high
and low values).
16
-------
On the basis of these data and the experimental schedule, methanol
ratios between 2 and 3 were not investigated. Furthermore, the set-
up of the pilot plant did not allow for more than one run per day.
If a sufficient number of runs at various ratios between 2 and 3
could have been obtained then a statistical determination of the
most efficient ratio would have likely been possible.
The difference between a methanol:NO3~N ratio of 2 and 3 could be
economically significant since chemical cost is directly related to
dose. On the basis of our data, specifications for the design of a
methanol storage should be sized for a maximum methanol:NO3~N ratio
of about 4 as actual operating dosage under environmental conditions
will vary between 2 and slightly more than 3.
Future work should be done on a larger scale, particularly with the
packed column reactor using smaller-sized packing material but this
would probably require flushing being done more frequently. Also a
positive method is needed to measure the utilization of methanol.
Gas chromatographing might be the ideal method for this.
17
-------
SECTION VII
REFERENCES
1. Finsen, P. 0. and Sampson, D. "Denitrification of sewage effluents,"
Water & Waste Treatment J^ (England) (May/June, 1959).
2. Johnson, W. K. and Schroepfer, G. L. "Nitrogen removal by nitrifica-
tion and denitrification," J. Water Pollution Control Federation,
J36, 1015 (1964).
3. Bringmann, G. and Kuhn, R. "Halbtechnische stabilisierung und inten-
sivierung der denitrifikation," Gesundheits-Ingenieur, 85, 1 (1964).
4. Bringmann, G. and Kuhn, R. "Schnell-denitrifikation im unterdruck-
verfahren," £esundheits-Ingenieurt 86, 1. 16. (1965).
5. Wuhrmann, K. "Nitrogen removal in sewage treatment processes,"
Verb.. Internat. Verein. Llmnol.. 15, 580 (1964).
6. Barth, E. F. and Ettinger, M. B. "Managing continuous flow biological
denitrification," Proceedings of the Seventh Industrial Water and
Waste Conference, University of Texas (June, 1967).
7. Barth, et al. "Combined chemical-biological approach to control
nitrogen and phosphorous in wastewater effluents," 41st Confi.
Water Pollution Control Federation. Chicago. (Sept., 1968).
8. Christiansen, et al. "Reduction of nitrate nitrogen by modified
activated sludge," UJS. Atomic Energy Commission. TID-7517 (Pt. la).
264 (1956).
9. Anon. "Denitrification on granular activated carbon at Pomona,
Calif.," 41st Conf. Water Pollution Control Federation. Chicago.
(Sept., 1968).
10. McCarty, P. L. "Removal of nitrate nitrogen from agricultural
drainage waters," 4.1st Conf. Water Pollution Control Federation.
Chicago. (Sept., 1968).
11. McCarty, et al. "Biological denitrification of waste water by
addition of organic materials," 24th Annual Purdue Industrial
Water Conference. Purdue University. Lafayette, Indiana. (May, 1969).
18
-------
12. Skerman, V. B. D. and MacRae, I. C. "The influence of oxygen
availability on the degree of nitrate reduction by Pseudomonas
denitrificans." Can. J. Microbiol.. J3> 505 (1957).
13. Nicholas, D. J. D. "The metabolism of inorganic nitrogen and its
compounds in micro-organisms," Biol. Rev. 38, 530 (1963).
14. Orland, Herbert P., Editor (1967). Standard Methods for the
Examination of Water and Wastewater Including Bottom Sediments
and Sludges. Twelth Edition. American Public Health Associa-
tion, Inc., New York.
19
-------
o
Fig. 1. DIAGRAMMATIC LAY-OUT OF DENITRIFICATION PILOT PLANT.
-------
Explanatory Legend for Fig. 1
Diagrammatic Layout of Denitrification Plant
A. The holding tank for mixed liquor. It was made of polyethylene, had
a capacity of about 570 liters, and was fitted with an air sparger
and a funnel for gravitational transfer of nitrified effluent to the
second holding tank.
B. The holding tank for nitrified effluent was made of polyethylene,
had a capacity of about 570 liters, and was fitted with an air spar-
ger at the bottom.
C. This is a steel tank 76 cm long by 38 cm high by 38 cm wide. It pro-
vided heating and cooling to the inside (dotted lines) stainless steel
tank containing the effluent. The inside tank was 46 cm long by 15 cm
high and 20 cm wide, with a capacity of about 5 liters.
D-E. Methanol reservoirs for the suspended growth and packed column reactors
respectively. Each had a capacity of 2.5 liters.
F-G. Methanol dosing pumps (EMDECO) for the suspended growth and packed
column reactors respectively.
H. Infusion pump (Cole-Palmer Masterflex) for maintaining the flow of
nitrified effluent into the suspended growth reactor.
I. Laboratory flow meter with stainless steel float.
J. Suspended-growth reactor having a capacity of approximately 5 liters.
K. Magnetic stirrer.
L. Packed column reactor with a capacity of approximately 2 liters.
M. Infusion pump (Cole-Palmer Masterflex) for maintaining the flow of
nitrified effluent into the packed column reactor.
N. Laboratory flowmeter with stainless steel float.
0-P. Stainless steel tanks used to collect the denitrified effluent from
the packed column and the suspended growth reactors respectively.
21
-------
Q. Heating and cooling system capable of maintaining temperature
within the range of 4°C to 35°C at ± 0.5°C.
R. A 1/3 H.P. pump for recirculating the heated or cooled water for
the reservoir and the two reactors.
S. Air sparger.
23
-------
Explanatory Legend for Fig. 2
Detailed Diagram of Packed Column Reactor
A. Plexiglass tube for conducting nitrified effluent to the packed
column reactor having an inside diameter of about 0.48 cm.
B. Entrance point for unstopping column.
C. Over-flow for denitrified effluent.
D. Outlet for recirculating water to the heating and cooling system.
E. Water jacket for temperature control of reactor, having dimensions
of 8 cm in diameter by 91 cm high.
F. Plexiglass column, filled with 3 mm (approx.) glass beads. The
column had a capacity of approximately 2 liters and was 5 cm in
diameter and 100 cm high.
G. Methanol feeding line from the reservoir. It had an inside diameter
of approximately 0.16 cm.
H. Infusion pump (double head) for dosing specific amounts of methanol
(rate=0.2 ml/min.).
I. Inlet for recirculating water from the heating and cooling system.
J-K-L-M. Sampling points for denitrified effluent.
N. Infusion pump (Cole-Palmer Masterflex) maintaining flow of nitrified
effluent into the packed column reactor.
0. Junction point where methanol and nitrified effluent were mixed
prior to entrance into column.
P. Laboratory flowmeter with stainless steel float.
Q. Stainless steel collecting tank.
24
-------
Fig. 2. DETAILED DIAGRAM OF PACKED COLUMN REACTOR.
25
-------
Explanatory Legend for Fig. 3
Detailed Diagram of Suspended Growth Reactor
A. Plexiglass tube for input of nitrified effluent having an inside
diameter of about 0.48 cm.
B. Mercury thermometer for measuring the inside temperature of the
suspended growth reactor.
C. Nitrogen gas vent.
D. Outlet for recirculation of water to and from heating or cooling
system.
E. Water jacket for temperature control.
F. Annular space between the water permeable (VYON) screen and the
outer plexiglass cylinder. Total capacity is approximately
1 liter.
G. Water permeable polyethylene cylinder (I.D. 10 cm) to hold the
suspended material (trade name VYON, 0.16 cm thickness).
H. Interior of the water permeable polyethylene cylinder. Total
capacity is approximately 4.5 liters.
I. Inlet of water circulation jacket.
J. Magnetic stirrer for mixing and keeping the solids in suspension.
K. Outlet for denitrified effluent.
L. Magnetic stirrer.
26
-------
D
E
F
A
V j _
Fig. 3. DETAILED DIAGRAM OF SUSPENDED GROWTH REACTOR.
27
-------
100 T
80 +
60 +
NO3-N
REDUCTION %
IN 15 MINUTES
40 +
20 +
20°C
5°C
0 123
PARTS OF METHANOL PER PARTS OF NO3-N ON WEIGHT BASIS
Fig. 4. DENITR1FICATION, BASED ON NO3-N REMOVAL, IN PACKED COLUMN
REACTOR AS A FUNCTION OF METHANOL CONCENTRATION AT THREE
DIFFERENT TEMPERATURES. DISSOLVED OXYGEN LEVELS BETWEEN 2.3
AND 2.5 ppm.
28
-------
loo-r
80--
60- -
NO3-N
REDUCTION %
IN 210 MINUTES
40- -
20- -
30°C
20°C
5°C
I ' ' I
•»—I h
0 123
PARTS OF METHANOL PER PARTS OF NO3-N ON WEIGHT BASIS
Fig. 5. DENITRIFICATION, BASED ON NO3-N REMOVAL, IN SUSPENDED
GROWTH REACTOR AS A FUNCTION OF METHANOL CONCENTRA-
TION AT THREE DIFFERENT TEMPERATURES. DISSOLVED OXYGEN
LEVELS BETWEEN 2.3 AND 2.6 ppm.
29
-------
lOO-i-
80- -
60+
NO3-N
REDUCTION %
IN 15 MINUTES •
40--
20--
/
/
/
i
I I | I I | I I | I I | I I |
6 9
DAYS
12
15
Fig. 6. DENITRIFICATION, BASED ON NO3-N REMOVAL, IN PACKED
COLUMN REACTOR AS A FUNCTION OF TIME DURING
ACCLIMATION TO 5°C AT VARIOUS METHANOL:
RATIOS (WEIGHT BASIS).
NO3-N
30
-------
100-T-
80--
60--
NO3-N
REDUCTION %
IN 210 MINUTES
40- -
20--
I I
I I
-* 3:1
•• •• 2:1
1:1
I I
I I
9
DAYS
12
15
18
Fig. 7. DENITRIFICATION, BASED ON NO3-N REMOVAL, IN SUSPENDED
GROWTH REACTOR AS A FUNCTION OF TIME DURING ACCLIMA-
TION TO 5°C AT VARIOUS METHANOL: NO3-N RATIOS (WEIGHT
BASIS).
31
-------
Table I. Typical results from single pass experiments (15 mins.) with the packed column reactor.
Those data marked with an asterisk represent percent reduction except those marked with
a plus sign, under N02~N column, which represents an increase of the initial value.
u>
30°C
20°C
5°C
1
2
3
Methanol:
N03-N
Weight
Ratio
D.O.
Initial Cone.
(mg/1)
1
2
3
4
5
1/4
1/2
1
2
3
2.5
2.5
2.4
2.4
2.5
11.5
8.3
8.5
6.0
8.9
0.29
0.45
0.19
0.02
0.11
6.0
3.0
1.9
0.6
0.3
0.42
0.70
0.11
0.00
0.00
48
64
78
91
97
+146
+157
43
100
100
N03-N
11.5
8.3
8.5
6.0
8.9
11.3
9.7
9.0
8.9
7.0
9.9
9.0
8.3
N02-N
0.29
0.45
0.19
0.02
0.11
0.15
0.16
0.15
0.20
0.16
0.27
0.27
0.39
Residual Cone.
(mg/1)
N03-N N02-N
1
2
3
4
5
1/2
3/4
1
2
3
2.5
2.4
2.4
2.3
2.3
11.3
9.7
9.0
8.9
7.0
0.15
0.16
0.15
0.20
0.16
6.7
3.5
3.0
0.6
0.3
0.04
0.05
0.04
Trace
0.00
41
64
67
93
96
73
69
73
100
100
1
2
3
2.5
2.5
2.4
9.9
9.0
8.3
0.27
0.27
0.39
4.9
0.9
0.3
1.06
0.15
0.00
50
90
96
+388
44
100
6.0
3.0
1.9
0.6
0.3
6.7
3.5
3.0
0.6
0.3
4.9
0.9
0.3
0.42
0.70
0.11
0.00
0.00
0.04
0.05
0.04
Trace
0.00
1.06
0.15
0.00
Percent
Change*
N03-N N02-N
48
64
78
91
97
41
64
67
93
96
50
90
96
+146
+157
43
100
100
73
69
73
100
100
+388
44
100
Overall Percent
of Oxidized
Nitrogen Removal
45
58
77
91
97
41
64
67
93
97
41
89
96
-------
Table II. Typical data from single pass experiments (210 mins.) with the suspended growth reactor.
Those data marked with an asterisk represent percent reduction except those marked with
a plus sign, under N02-N column, which represents an increase of the initial value.
Test
#
Methanol:
N03-N
Weight
Ratio
Initial Cone.
D.O. (mg/1)
ppm NOq-N NO?-N
Residual Cone.
(mg/1)
NO^-N N02-N
Percent
Change*
NO^-N N02-N
Overall
Percent of
Oxidized
Nitrogen
Removal
Total
Suspended
Solids
(mg/1)
30°C
1
2
3
4
1/2
1
2
3
2.5
2.4
2.6
2.5
3.8
3.8
3.0
4.8
0.08
0.16
Trace
0.27
1.4
0.7
0.3
0.2
0.14
0.12
Trace
0.00
63
82
90
96
+175
25
100
100
60
79
90
96
1985
2016
1724
2035
20°C
1
2
3
4
5
1/2
3/4
1
2
3
2.5
2.4
2.4
2.3
2.3
11.3
9.7
9.0
8.9
7.0
0.15
0.16
0.15
0.20
0.16
6.7
4.7
2.7
1.3
0.6
0.70
0.26
0.26
0.06
0.00
41
52
71
86
91
+467
+163
+173
70
100
36
50
68
86
91
227
610
2103
1997
2009
5°C
1
2
3
1
2
3
2.5
2.4
2.5
9.7
8.3
8.5
0.29
0.39
0.25
5.5
2.3
0.7
1.08
0.61
0.08
43
73
91
+372
+154
68
34
67
91
2050
2115
2064
-------
Table III. Typical data from dissolved oxygen experiments with the packed column reactor at 3 dif-
ferent D.O. levels (15 mins. - single pass). Those data marked with a single asterisk
represent percent reduction except those marked with a plus sign, under NC^-N column,
which represents an increase of the initial value. The points marked with a double
asterisk represent no change.
Residual Cone.
(mg/1)
N NO?-N
Percent
Change *
t-N NQ>-N
Overall Percent
of Oxidized
Nitrogen Removal
OJ
Ln
1
2
3
4
5
6
7
1/2
3/4
1
2
3
4
6
0.3
0.5
0.2
0.2
0.5
0.2
0.4
20.0
8.7
13.5
15.6
8.6
18,0
20,0
0.34
0.10
0.35
0.05
0.16
0.05
0,05
7.5
1.0
2.4
0.5
0.3
0.7
0.3
0.24
Trace
0.70
0.00
0.00
0.00
0.00
63
89
82
97
97
96
98
29
100
+200
100
100
100
100
D.O, II
1
2
3
4
5
6
D.O. Ill
1
2
3
4
5
6
1/2
3/4
1
2
3
4
1/2
3/4
1
2
3
4
2.5
2.4
2.4
2.0
2.2
2.0
5.0
4.2
4.0
4.2
4.0
5.0
11.3
9.7
9.0
8.0
8.0
9.0
15.0
3.3
17.0
8.5
17.0
8.0
0.15
0.16
0.15
0.11
0.05
1.70
0.25
0.10
0.18
0.12
0.08
0.15
6.7
3.5
3.0
0.3
0.3
0.8
7.0
1.0
5.0
1.0
1.0
0.5
0.04
0.05
0.04
Trace
0.05
0.80
0.70
0.15
0.75
Trace
0.00
0.00
41
64
67
96
96
91
53
70
71
88
94
94
73
69
73
100
**
53
+280
+150
+417
100
100
100
62
89
78
97
97
96
98
41
64
67
96
95
85
50
66
67
88
94
94
-------
Table IV. Typical data from dissolved oxygen experiments with the suspended growth reactor at 3
different D.O. levels (210 mins. - single pass). Those data marked with a single
asterisk represent percent reduction except those marked with a plus sign, under N02~
column, which represents an increase of the initial value. The points marked with a
double asterisk represent no change.
u>
Test
D.O. I
1
2
3
4
5
D.O. II
1
2
3
4
5
D.O. Ill
1
2
3
4
5
6
Methanol:
N03-N
Weight
Ratio
Initial Cone.
D.O. (mg/1)
ppm N03-N N02-N
Residual Cone.
(mg/1)
N03-N N02-N
1/2
3/4
1
2
3
0.3
0.5
0.2
0.2
0.5
20.0
8.7
13.5
13.5
8.6
0.34
0.10
0.28
0.35
0.16
10.4
1.0
1.0
1.0
0.6
0.46
0.65
Trace
0.00
0.08
48
89
93
93
93
+135
+650
100
100
50
20.0
8.7
13.5
13.5
8.6
9.0
6.7
10.0
8.0
8.0
15.0
3.3
17.0
12.0
17.0
8.0
0.34
0.10
0.28
0.35
0.16
0.05
0.14
0.15
0.11
0.05
0.25
0.10
0.18
0.65
0.08
0.15
1/2
3/4
1
2
3
2.0
2.0
1.3
2.0
2.2
9.0
6.7
10.0
8.0
8.0
0.05
0.14
0.15
0.11
0.05
3.0
1.7
2.4
0.7
0.3
0.16
0.09
0.15
0.28
0.04
67
75
76
92
96
+320
36
**
+255
20
1/2
3/4
1
2
3
4
5.0
4.2
4.0
4.3
4.0
5.0
15.0
3.3
17.0
12.0
17.0
8.0
0.25
0.10
0.18
0.65
0.08
0.15
8.0
1.7
1.5
1.0
2.5
1.0
0.30
0.05
0.75
0.05
0.25
0.10
47
50
91
92
85
88
+120
50
+417
92
+313
33
10.4
1.0
1.0
1.0
0.6
3.0
1.7
2.4
0.7
0.3
8.0
1.7
1.5
1.0
2.5
1.0
0.46
0.65
Trace
0.00
0.08
0.16
0.09
0.15
0.28
0.04
0.30
0.05
0.75
0.05
0.25
0.10
Percent
Change*
N03-N N02-N
48
89
93
93
93
67
75
76
92
96
47
50
91
92
85
88
+135
+650
100
100
50
+320
36
**
+255
20
+120
50
+417
92
+313
33
Overall Percent
of Oxidized
Nitrogen Removal
47
81
93
93
92
65
74
75
88
95
46
50
87
92
84
87
-------
Table V. Total solids in the packed column reactor per 1668.9 cm
of surface area.
A B
Total Solids Volatile Solids Percent Column B
Location # gms per cm? # gms per cin2 is of Column A
Top 0.49 0.26 53.4
Middle 0.66 0.34 52.0
Bottom 2.99 2.18 72.8
37
-------
Table VI. Typical results of individual experimental runs for dentri-
fication in terms of total oxidized nitrogen removed with the
packed column reactor (A) and the suspended growth reactor
(B) at various temperatures and methanol:NO-j-N ratios.
Dissolved oxygen levels were within the range indicated in
Tables I and II.
Individual Runs in %
Temperature Methanol:N03-N Ratio Denitrification (TONR^
A. Packed column reactor
30°C 2 89.0 89.6 92.4
3 94.1 96.2 98.8
20°C 2 93.2 95.9
3 95.3 96.5
5°C 2 81.6 90.0 92.6
3 94.7 96.6 97.5
B. Suspended growth reactor
30°C 2 89.7 90.0 92.1
3 92.4 96.1 95.1
20UC 2 85.6 88.4
3 91.3 95.9
5°C 2 67.6 66.2 67.2
3 85.9 91.8 92.2
38
-------
1
5
/Icce.ssion Number
2
,Sti6;'ei t Field &. Group
05D
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Organization
Gulf South Research Institute, New Iberia, Louisiana
Title
METHANOL REQUIREMENT AND TEMPERATURE EFFECTS IN WASTEWATER DENITRIFICATION
10
22
Authors)
Dholakia, Shirish G.
Stone, James H.
Burchfield, Harry P.
IX Project Designation
Program 017010DHT, Contract #14-12-527
2] Note
Citation
23
Descriptors (Starred First)
*Biological denitrification, *Wastewater treatment, *Methanol requirement,
*Temperature effects, Dissolved oxygen effects, Packed column reactor,
Suspended growth reactor.
25
Identifiers (Starred First)
*Water renovation, nutrient removal.
27
Abstract
A pilot-scale, denitrifying plant was built using two types of continuous-flow
reactors, a packed column and a suspended growth chamber. Denitrification at
three temperature regimes and three dissolved oxygen levels was studied as a
function of the methanoliNC^-N ratio. The most efficient ratio was usually
found to be between 2:1 and 3:1. Effective denitrification at lower temperatures
and high dissolved oxygen content required ratios equal to or slightly greater
than 3:1,
Abstractor
James H. Stone
Institution
Enlf
South
Research Institute
WR:I02 (REV JULY 19691
WRSIC
END TO: WATER RESOURCES SCIENTIFIC INFORMATION CENTER
US DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C 20240
• CPO: 1969-399-339
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