-------
(J8JBM * »|eS)/!U8A|OS
-------
Five stages were obtained for sodium chloride. This gives
an extract nearly in equilibrium with the feed. From the
flow rates obtained in this way, a trial and error stagewise
calculation was made on ethylene glycol until the system was
in close material balance. The overall material balance is:
Flow Glycol,
Stream (Solvent-Free) Salt ppm.
Feed 1 10$ 2000
Extract 1.16 2400
Product .7 2.5$ 2489
Solvent .46 2265
Raffinate -3 28$ 839
On a total flow basis, based on an extract containing 18$
warmer and a solvent 8$ water:
Product _ v
~ • f
Feed
Solvent
Product
Solvent
Feed
= 8.2
= 5-74
The solvent flow rate could be greatly reduced by operating
at a higher extract water content (lower temperature). It
is uncertain how this would affect equilibrium. The only
comparison is the 10°C and 15°C data at 27 to 29$ salt and
the 25° and 22°C data at 10$ salt. In each case, the K's
are of the same order of magnitude. The effect of lowering
temperature more than offsets the water effect, confirmed by
low K's at separation, so much lower solvent rates could be
obtained only by dropping the temperature. The effect on
salt content in the product of lowering the temperature will
be adverse, and it appears likely that some extract reflux
will be necessary.
Solvent extraction seems to be technically feasible but would
be uneconomic due principally to the high solvent-to-feed
ratio required to produce a Nad-saturated raffinate.
Operation at low temperatures, close to 0°C, represents an
appreciable increase in the difficulty and cost of the ex-
traction process. The necessity of high reflux to produce
a pure product and the cost of solvent recovery from both
the raffinate and product, added to the required large solvent
36
-------
inyentory, and the low temperature operation make solvent
extraction uneconomical for the treatment of wastewater
from glycol production.
B. Carbon Adsorption
Preliminary laboratory tests of glycol adsorption on acti-
vated carbons resulted in the selection of Witco carbon
(20-40 mesh) as the best adsorbent available. Although the
adsorptive capacity of carbon for ethylene or propylene glycol
appeared to be too small for economical operation, further
studies of the kinetics of glycol adsorption in batch and
column operation were conducted with the hope that a simple
regeneration procedure could be found that would result in
the recovery of a product, thus improving the economics of
the process.
Ethylene and propylene glycol solutions of two different con-
centration levels were prepared with and without 10$ salt.
A volume of 200 milliliters of each solution was dispensed
into 250-ml. glass stoppered bottles. About 5 grams of
carbon were weighed accurately and added to each bottle. The
bottles were then tightly stoppered and placed in an
oscillating shaker for three days. Samples of all solutions
were collected at intervals of from 1 to 72 hours and
analyzed for glycol by gas chromatography. Batch carbon
adsorption tests were also conducted with both ethylene and
propylene glycol solutions in 10$ NaCl, at pH' s ranging from
2 to 12.
In Figure V-4 is plotted the ratio of glycol concentration
remaining in solution to the original concentration (C-t/Co)
as a function of time. The initial rate of adsorption of
propylene glycol is higher than that for ethylene glycol,
and equilibrium seems to be reached in a shorter time.
The equilibrium capacity of carbon for propylene glycol from
a 10$ NaCl solution is 263 mg/gram of carbon while that for
ethylene glycol is 118 mg/gram of carbon. The presence of
10$ NaCl in the glycol caused a slight increase in the
adsorptive capacity.
In Figure V-5, the ratio of propylene glycol concentration
remaining in solution to the original concentration, Ct/Co,
is plotted as a function of time at different pH's. The up-
take of both glycols increases with increasing pH's. An
increase in pH quite probably results in an increase of the
negative charges at the surface of the carbon, thus enhancing
the adsorption of the positively charged glycols which are
known to be hydrogen bonded with the water molecules.
-------
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Figure V-5
EFFECT OF pH ON UPTAKE OF PROPYLENE GLYCOL
BY WITCO .CARBON 20-40 MESH. (Co = 2000 ppm)
o
^
o
Time, hours
-------
Fixed-Bed Column Adsorption of Glycols
The column adsorption of ethylene and propylene glycols from
10$ NaCl solutions of pH 11.0 on 20 x 40 mesh Witco carbon
was also studied. Methanol was used to regenerate the ex-
hausted carbon and the glycol was recovered by distilling the
methanol.
Propylene Glycol
A 7/8 inch i.d. column was packed with 18 inches (73 grams)
of carbon. The propylene glycol solution was then passed
through the column under constant pressure at a flow rate
of 1.26 gal./min./ft.2.
Samples of the effluent were collected periodically and
analyzed. After saturation of the carbon with glycol, as
determined by the breakthrough curves, the carbon was
regenerated with two bed volumes of methanol at a flow rate
of 0.57 gal./min./ft.2. The carbon was then washed with
several bed volumes of distilled water and another adsorption
run repeated.
The results of eight adsorption regeneration cycles are
given in Table V-4. Figure V-6 is a plot of the break-
through of propylene glycol for the first and second ad-
sorptions .
The capacity of carbon for propylene glycol was 66 milli-
grams of propylene glycol per gram of carbon for the first
cycle, reduced by about 13$ for the second run, then re-
maining constant at about 53 milligrams of propylene glycol
per gram of carbon for the 8 runs reported in Table V-4.
The exhaustion point remained the same—around 18 bed
volumes—while a change in the position of the break point
was observed. This may be due to incomplete regeneration.
At room temperature, at least two bed volumes of methanol
were required to recover the adsorbed glycol. At tempera-
tures of 40° to 50°C, only one bed volume of methanol was
sufficient to recover over 90$ of the glycol.
Ethylene Glycol
The adsorption breakthrough curve for ethylene glycol from a
column similar to that described for propylene glycol is
given in Figure V-7 (I)•
Because of the slow adsorption of ethylene glycol, another
column was built with a carbon depth of 7^ inches and an
inside diameter of 1/2 inch. The ethylene glycol solution
was passed through the column at a rate of 0.97 gal./min./ft.2
40
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FIXED BED ADSORPTION OF PROPYLENE GLYCOL ON WITCO CARBON
l.Or-
o
o
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0.5
• 1st adsorption
O 2nd adsorption
100
Time, minutes
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Flow Rate: 1.26 gal/ltVmin.
200
-------
Figure V-7
•
FIXED BED ADSORPTION OF ETHYLENE GLYCOL
ON ACTIVATED CARBON
1.0
o
o
o
0.5
I
100
200
Time, minutes
I- Column: 7/8" i.d. 18" deep, Wt carbon = 73 grams, flow rate = 1.26 gal/ltVmin
IT- Column: 1/2" i.d. 74" deep, Wt carbon = 97 grams, flow rate = 0.97 gal/1tz/min
-------
The breakthrough curve obtained with this column is shown
in Figure V-7
The total capacity of the carbon for ethylene glycol was cal-
culated to be 14 . 9 mg/gram carbon, much smaller than the
capacity obtained for propylene glycol. The capacity of
activated carbon for ethylene glycol remained about the
same through seven cycles --an average of 15 milligrams of
ethylene glycol per gram of carbon, (Table V-5) . The re-
generation of the carbon with methanol required about one
bed volume at ambient temperature, and over 90$ of the
adsorbed glycol was recovered.
Competitive Adsorption of the Chlorinated Hydrocarbons
A solution of 1200 parts per million ethylene glycol and 30
parts per million ethylene chlorohydrin (ECH) was passed
through the 74 -inch carbon column. The glycol breakthrough
occurred after 3 bed volumes. No ECH was detected in the
column effluent after 170 bed volumes. The ECH concentration
was increased to 60 ppm. , and after 26o bed volumes, it still
had not broken through the column.
A solution of 1200 ppm. propylene glycol and 100 ppm. epi-
chlorohydrin (EPCH) was passed through the 18-inch carbon
column at a rate of 1.26 gallons per minute per square foot.
The propylene glycol broke through at about 7 bed volumes
while EPCH was retained through 273 bed volumes. At this
point the flow rate was increased to 4 . 1 gallons per minute
per square foot, and the EPCH broke through after 23 bed
volumes .
The capacity of activated carbon for ECH and EPCH is very
high compared to the glycols. Similar tests with dichloro-
ethylether and dichlorodiisopropylether showed a very high
capacity of the carbon for the ethers over the glycols.
The high adsorptive capacities found may be useful in removing
the low concentrations of chlorinated hydrocarbons, that may
be toxic, as a pretreatment before the activated sludge
process .
Glycol Wastewater Treatment by Carbon Adsorption
Actual propylene glycol wastewater was fed to the 18-inch
carbon column, packed with virgin Witco activated carbon.
On the first pass 6.3 liters of propylene glycol waste was
passes through the column before saturation with propylene
glycol was obtained and 34.4 milligrams of propylene glycol
was adsorbed per gram of carbon. The column was heated to
60 °C and regenerated with hot methanol. Only 82^ of the
44
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propylene glycol was recovered. On the second run 6.5 liters
of propylene glycol were passed "before the column was
saturated and 27.5 mg of propylene glycol was adsorbed per
gram of carbon. On regeneration of the bed, 89$ of the
adsorbed propylene glycol was recovered.
From 5 "to 7 bed volumes of water were required to remove the
regeneration methanol from the bed. The capacity of carbon
for propylene glycol from the wastewater feed is about half
of its capacity when a synthetic propylene glycol solution
is fed under the same operating conditions. This lower
capacity is partly due to the lower propylene glycol concen-
tration in the wastewater, and partly because of the com-
petitive adsorption of the chlorinated organics in the waste
stream.
Carbon adsorption is not considered to be economically
feasible because of the low adsorptive capacity under the
actual conditions and because of the inefficient regeneration
and of the loss of solvent, if one is required.
C. Membrane Separations
During the period of the present grant, the State of Louisiana
Department of Commerce and Industry, also had an R. and D.
grant (Porject No. 12020 DQ,C) for the investigation of
Polymeric Materials for Treatment and Recovery of Petro-
chemical Wastes". Their results have been published by EPA,
Report 12020 DQC-03/71. The objective of the reverse
osmosis work conducted by their research contractor, Gulf
South Research Institute, was to screen membranes that have
a small reflection coefficient for NaCl, and to evaluate
them for the rejection of the glycols and other organic
components in the glycol waste stream.
Commerically available membranes having a small rejection
coefficient for NaCl were evaluated with a synthetic solution
containing:
NaCl, % 9-3-10.4
Propylene glycol, ppm. 500 - 2000
Propylene chlorohydrin, ppm. 20 - 70
Propylene oxide, ppm. 100 - 500
Samples from the tests conducted by GSRI were forwarded to
us and analyzed for glycol content in our laboratories in
Freeport, Texas. A summary of the results obtained from the
screening tests on a flat plate cell are given in Table V-6.
Most of these membranes were of Eastman cellulose acetate
with low salt rejection.
46
-------
TABLE V-6
EVALUATION OF CELLULOSE MEMBRANES FOR THE
SEPARATION OF PROPYLENE GLYCOL AND SALT
Membrane
Number
B112
B112
G16
G17
G19
G20
G21
G22
G2J
G24
G25
Operating
Pressure
p. s . i .
600
600
800
800
800
800
800
800
800
800
800
Flux
GFD
7.
V
1 •
54.
35-
29-
91.
21.
23.
10.
35-
12.
5
5
5
1
c,
I
1
5
C;
^
0
4
Rejection, %
Nad
9-
9.
5.
15-
20.
13.
21.
20
35-
17.
55-
5
7
5
4
7
6
0
6
8
i
Organic s
5-
11.
0
0
20
6.
0
-i.
13.
12.
41
5
3
-7
1
2
5
Note: Data from Gulf South Research Institute EPA Report
12020DQC 03/71.
47
-------
The results of this limited screening tests indicate the
lack of rejection of the low molecular weight organic com-
ponents. This may be due to the fact that when a membrane
is selected to give a low enough NaCl rejection to reduce the
osmotic effect to an acceptable level, pore flow becomes a
dominant mode of transfer, therefore, very little separation
of solutes is observed. Tt was concluded that membranes
with low salt rejection exhibit a high pore flow of propylene
glycol and thus offer no significant separation of the salt
and the glycol.
-------
SECTION VI
BIOLOGICAL TREATMENT
Since the glycol wastewater contains a large amount of salt,
any organism that would be useful in biological treatment
must be able to metabolize glycol in the presence of the
high salinity. Dr. W. A. Taber of Texas A. and M. University
isolated organisms from natural saline environments and from
the waste carrying ditches and canals in the Dow plants, and
screened them for their capacity to utilize glycols in the
presence of high concentrations of salt. The results of this
investigation are reported separately in Appendix E. The
acclimation of mixed cultures to the glycol wastewater in
both batch and continuous reactors was accomplished in the
Dow laboratories at Freeport.
A. Biodegradability of Glycols in Saline Waters
The biodegradability of glycols, using an acclimated acti-
vated sludge seed, has been reported in the literature to
vary from 35 to 85$ (Mills, 1954 and Hatfield, 1957). A
96$ oxidation of ethylene glycol and 39% oxidation of glycerol
was obtained using a pure culture of Alcaligenes Faecalis
(Marian, 1963)• An activated sludge seed, under treatment
plant conditions, was reported to oxidize 75$ of the glycol
present and 28$ of the glycerol (Placak, 1947).
Activated sludges in a conventional biological system has
been found to be much more tolerant to high salinities than
an anaerobic digestion system. Operation of an activated
sludge was found to be possible with salinities up to the
equivalent of 2.% NaCl (Ludzack, 1965). It has been found
previously, however, that significant microbial population
variety and activity changes occur at high salinities. The
presence of sustained high chlorides generally depresses
respiration, but periodic operation at low chlorides was
found to improve the tolerance of activated sludge to high
chlorides.
No information was found in the literature on the utilization
of halophilic bacteria for the biological oxidation of
organic contaminants in brine wastes, although numerous
bacterial species living in very high salt concentrations
have been investigated.
"Halobacterium", isolated from the Dead Sea, has an optimum
NaCl concentration between 17-5 to 20.5$ with a generation
time of 4 hours. "H. salinarium", obtained from Norway, has
an optimum NaCl concentration of 20 to 23$. A unicellular
49
-------
halophilic algae, "Dunaliella parva", was found to grow
optimally in 6 to 9% NaCl with a generation time of one day.
The requirement for NaCl does not appear to be entirely an
osmotic phenomenon, since the bacteria were unable to
tolerate the presence of sucrose instead of sodium chloride.
B. Treatability Studies
The biological treatability of wastewaters from ethylene and
propylene glycol production plants was determined by the fill
and draw procedure (Symons, 1960). A unit containing ten
compartments, 2 inches wide by 5 inches deep by 18 inches
high, was constructed of Plexiglas. The drawdown nozzles
were at the 500 ml. level, and a mark was located at the
1500 ml. level. Each compartment was equipped with an
aeration frit located near the bottom. The supply of oil
free air, at reduced pressure, was manually adjusted to
deliver about 0.55 liter of air per minute to each compart-
ment.
Two cultures were acclimated to the glycol-sodium chloride
solutions and the actual wastewater from the ethylene and
propylene systems. In each set of test solutions, one com-
partment was not inoculated with bacteria and was used as a
control.
Mixed Culture Acclimation
The starting culture was a mixture of sewage sludge and slimes
obtained from the ditches and holding ponds exposed to the
wastewaters from glycol production plants. The acclimation
of this culture to glycol-sodium chloride solutions and
diluted wastewater was begun at a salt concentration of
about 3$ which was raised gradually over a period of 6 weeks
to the concentration of the full strength waste, about 10$
salt. The feeding solution contained glycol as the main
carbon source. Nutrients were added in the form of ammonium
sulfate (0.25 gm/1.), and potassium hydrogen phosphate (0.25-
0.375 gm/1.).
The wastewater-bacteria mixture was aerated for 23 hours, then
the suspended solids were settled for 1 hour, and the
supernatant drained to the 500 ml. level. Each compartment
was then fed with 1,050 ml. of the prepared solution or
diluted waste, with nutrients added and the pH controlled
at 7-0. Aeration was then resumed and a sample collected
within 5 minutes after pH adjustment. At the end of 23 hours
of aeration, another sample was collected before the air was
cut off. All samples were analyzed for pH, % NaCl, glycol
and other organics, total oxygen demand, and volatile sus-
pended solids.
50
-------
During the acclimation period, the salt content was increased
gradually up to the full strength waste, but the glycol con-
centration was kept the same as that in the waste. The daily
composition of the treated waste and the rate of bacterial
growth in each of the compartments dictated the rate at which
changes in conditions were made.
The results obtained in the acclimations when full strength
propylene glycol waste was fed are presented in Figures VI-1
and VI-2. A mixed liquor volatile suspended solids (MLVSS)
of over 1000 ppm. could be maintained and settled quickly
leaving a fairly clear supernatant. The loading-removal
curve for propylene glycol waste (Figure VI-1) shows that
biodegradation was accomplished with an efficiency of 91
by the well-acclimated mixed culture. A treated effluent of
less than 200 ppm. TOD was produced at a loading of 1.0 to
2.0 pounds of TOD per pound of MLVSS per day (Figure VI-2).
Bacterium No. 32
This culture was isolated from mud-water samples from the
Great Salt Lake, during the screening of microbes for
tolerance to high salt content and glycol metabolism.
Since this culture had already been acclimated to the full
strength waste streams, no gradual acclimation to the salt
was necessary. Bacterium No. 52 exhibited a dispersed phase
growth with no appreciable settling when aeration was stopped,
therefore, the fill and draw procedure used with the accli-
mated mixed culture had to be modified. Sufficient feeding
solution was added to the testing compartments to replace
the samples removed, but was enriched with glycol to replace
the substrate oxidized. Near the end of these tests, it
was found that reduction of the nutrient concentrations to
less than half resulted in some improved settling of
Bacterium No. 52. The supernatant was always very turbid.
The results obtained with ethylene and propylene glycol
wastes are presented in Figures VI-3 and VI-4. A mixed liquor
volatile suspended solids (MLVSS) of 1500 ppm. to 2500 ppm.
could be maintained, but the filtered treated effluent had a
high TOD concentration even when it contained no unreacted
glycol.
Bacterium No. 52 showed a lower efficiency of TOD removal
(88$) from propylene glycol waste and even lower (70$) from
ethylene glycol waste (Figure VI-3) than the mixed culture.
At a loading of 1.0 to 1-5 pounds TOD per pound MLVSS per
day, the treated effluent contained over 300 ppm. TOD
(Figure VI-4).
-------
Figure VI-1
BIOTREATABILITY TESTS
LOADING - REMOVAL CURVE FOR PROPYLENE GLYCOL
WASTE (NaCI 9-10.5%)
(Acclimated Mixed Culture]
4.0
Slope =0.912
3.0
Q
C5
2.0
O
o>
cc.
1.0
I
I
1.0 2.0 3.0
Loading - IDS T.O.D./lb MLVSS.Day
4.0
-------
Figur* VI-2
BIOTREATABILITY TESTS
EFFLUENT LOADING CURVE FOR PROPYLENE GLYCOI
WASTE (Nad 9-10.5%)
^Acclimated Mixed CultureJ
300
200
o
o
s 100
O
O
E = 40L +70
I
I
1.0 2.0 3.0
Loading - Ibs T.O.D./lb MLVSS.Oay (L)
4.0
-------
Figur. VI-3
BIOTREATABILITY TESTS
LOADING - REMOVAL CURVES
O Propylene Glycol Waste (NaCI 10-12%)
• Ethylene Glycol Waste (NaCI 11-13.5%)
Q Bacterium No. 52J
2.50
2.00
«9
O
1.50
- i.oo
"to
>
O
§
0.50
Slope = 0.705
I
0.50 1.00 1.50
Loading- Ibs T.O.D./lb MLVSS.Day
2.00
lope 0,
2.50
-------
Fi«w« VI-4
BIOTREATABILITY TESTS
EFFLUENT LOADING CURVE FOR PROPYLENE GLYCOL WASTE
(NaCI 10-12%)
[^Bacterium No. 52]]
a
o
K
g
600
500
400
300
200
100
E = 70 L + 238
I
I
I
0.50 1.00 1.50
Loading - Ibs T.O.D./lb MLVSS.Day (L)
2.00
2.50
-------
C. Batch Kinetics
The rates of bio-oxidation of ethylene and propylene glycols
in synthetic sodium chloride solutions and in actual glycol
wastewaters was followed by measuring the decrease in glycol
and TOD concentrations with time in the fill-and draw com-
partments used for the biotreatability tests.
The TOD removal from a propylene glycol-10% NaCl solution
at a loading of 0-94 pounds TOD per pound MLVSS is shown in
Figure VI-5- The method of calculating the rate of removal
is illustrated in this figure, where r is defined by:
r =
where
r = rate of removal, 1/hr.
Lj_ = initial TOD concentration, ppm.
Le - TOD concentration at equilibrium, ppm.
te = time to reach equilibrium, hr.
The equilibrium is established between the oxidation and
synthesis reactions in which TOD is removed and the endogenous
reactions where the end products of cell lysis return to the
substrate. This model of TOD transfer rate in a batch bio-
logical oxidation system is adopted from Bhatla et. al.
(1966) .
In Figure VI-6 is shown a plot of the concentration of propylene
glycol and an unknown metabolite as a function of time. The
unknown metabolite that peaks around 5 to 6 hours after the
propylene glycol feed is added , elutes from the VPC column
at the same spot as epichlorohydrin.
The batch kinetics of a propylene glycol waste containing
epichlorohydrin is given in Figure VI -7- The sum of the
intermediate metabolite of the propylene glycol plus the
epichlorohydrin is plotted in the lower curve. This
metabolite has been identified by mass spectroscopy and gas
chromatography as acetol. Traces of acetic acid were also
detected in some of the intermediate samples. Acetol appears
to be the first oxidation product of propylene glycol:
CH3CH-CH2 - ~ - > CH3-C-CH2OH
OH OH 0
Propylene glycol Acetol
-------
1200
Figure VI-5
BATCH KINETICS
PROPYLENE GLYCOL-10% Nad
ACCLIMATED MIXED CULTURE
Loading = 0.94 Ibs TOD per Ib MLVSS
'" "cOMShr1
10 12 14
Reaction Time, Hours
16
18
20
22
24
-------
Figure VI-6
BATCH KINETICS
PROPYLENE GLYCOL-10% Nad
ACCLIMATED MIXED CULTURE
1000
Loading = 3.13 Ibs TOD per Ib MLVSS
10 12 14 16
Reaction Time, Hours
18
20
22
-------
Figur. VI-7
BATCH KINETICS
PROPYLENE GLYCOL WASTEWATER, ACCLIMATED MIXED CULTURE
1200
Loading = 1.32 Ibs TOD per Ib MLVSS
Epichlorohydrin + Metabolite
10 12 14
Reaction Time, hours
-------
The bio-oxidation rate of an ethylene glycol wastewater is
shown in Figure VT-8, at a loading of 0.37 Pounds TOD per
pound MLVSS per day. The reaction rate of ethylene glycol
is much slower than that found for propylene glycol.
The biological oxidation of a propylene glycol-10$ NaCl
solution with Bacterium No. 52 is presented in Figure VI-9-
These results show a fast rate of propylene glycol removal,
but the remaining TOD is high, a characteristic of the well
dispersed Bacterium No. 52.
Effect of Dilution on Reaction Rates
Several runs were made using the acclimated mixed culture
and Bacterium No. 52, at various dilutions of propylene glycol
waste with river water, to observe the effect of lower
sodium chloride concentrations on TOD removal rates. These
dilutions were:
River Water (6-6.5$ NaCl)
River Water (7-7-5$ NaCl)
River Water (8-8.5$ NaCl)
The rates of TOD removal at various loadings and dilutions
are given in Table VI-1 for both the acclimated mixed culture
and Bacterium No. 52. Dilution of the propylene glycol waste-
water to a salt content of 6 to 8$ appears to increase the
rate of TOD removal appreciably, for either of the two
bacterial cultures used.
Calculation of Removal Efficiency in a Continuous Treatment
From Batch Kinetic Data
The model used to calculate a rate constant at the equilibrium
point is based on the assumption that the substrate equilibrium
curve follows a first order relationship:
Wastewater -
75$ Wastewater - 2
7o Wastewater -
The rate constant, r = 0.48 hr."1, for the propylene glycol
system was used to calculate the degree of completion of the
reaction, D = 1 - (1-r)*, as shown in Figure VI-10.
To translate the batch reaction data to a continuous system,
mixing kinetics in a continuous system must be utilized. A
curve for complete mixing kinetics in a single basin is shown
in Figure VI-11.
60
-------
Figure VI-8
BATCH KINETICS
ETHYLENE GLYCOL WASTEWATER;ACCLIMATED MIXED CULTURE
Loading: 0.37 Ibs TOD per Ib MLVSS
16 18 20 22
26
Reaction Time, hours
-------
1700
Figure VI-9
BATCH KINETICS
PROPYLENE GLYCOL- 10% NaCI, BACTERIUM No. 52
Loading = 0.33 Ib TOD per Ib MLVSS
8 10 12 14
Reaction Time, hours
16 18 20 22
24
b2
-------
TABLE VI-1
BATCH KINETICS OF BIO-OXIDATION OF ETHYLENE
AND PROPYLENE WASTEWATERS
Wastewater
Ethylene Glycol
Ethylene Glycol
NaCl Sludge
Loading Rate of TOD
Lbs. TOD/ Removal
Lb. MLVSS
10 Mixed Culture 1.21
10 Mixed Culture 0.37
Propylene Glycol 10 Mixed Culture 1.32
Propylene Glycol 10 Mixed Culture 0.94
Propylene Glycol 10 Bacterium 52
Propylene Glycol
0.33
1.3 Mixed Culture 0.30
Propylene Glycol 6.1 Mixed Culture 0.43
Propylene Glycol 8.1 Bacterium 52 0.34
Propylene Glycol 7-5 Bacterium 52 0.34
T, hr.
0.058
0.138
0.130
0.48
0.44
1.06
0.8o
0.72
0.76
-------
Figure VI-10
BIOLOGICAL REACTION RATE OF
PROPYLENE GLYCOL
1.0
0>
ea
§
I
a.
o
S
D = 1 - (1 - r
r=0.48hr1,
I
4 5 6
Treatment Time, Hours
10
-------
00
UJ
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CD
IO
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A 'Ja3uo| jo }
MOIJ jo UOIJDEJJ
65
-------
The performance of a continuous system at a residence time
of 6 and 12 hours is determined by integrating the values of
degree of completion of reaction and the mixing theory data.
This is accomplished graphically as shown in Figure VI-12,
where the area under the curve, as a fraction of the total
area, is a prediction of the efficiency of a. continuous system
which has the specified retention time.
The results for propylene glycol wastewater treatment, shown
in Figure VI-12 predict a removal efficiency of 86^ of the
TOD at a residence time of 12 hours in a completely mixed
single basin. The design of the bench scale continuous
units and the pilot plant was based on this information as
a starting operating condition.
D. Bench Scale Continuous Units
Two bench scale units were built to determine the removal
efficiency of a continuous system. The unit, shown in
Figure VI-13, was based on a design adopted from Busch (1963).
Operation was difficult and continuous sampling proved to be
impractical. The bench scale continuous units were not
operated long enough to obtain equilibrium values or to allow
measurement of any design parameters.
The units were operated on a neutralized propylene glycol
waste diluted with river water to a 6f0 NaCl concentration.
One unit was seeded with the acclimated mixed culture and
the other with Bacterium No. 52. Sampling was done by
collecting one liter samples, homogenizing, and returning
the unused portion of the sample. The total volume of the
substrate, in each unit, was 5.5 liters. The dilution water
was gradually reduced until the feed was at full strength.
The residence time (to) in the continuous unit can be cal-
culated by the following equation:
t _ V ._ Cp - Ct
U/-\ — ^~
where
Q, ,-dC)
dt'ctMt
V = aeration volume
Q = rate of flow
C0 = initial TOD
Ct = effluent TOD
-------
Figur. VI-12
CALCULATED TREATMENT EFFICIENCY OF PROPYLENE GLYCOL
IN A CONTINUOUS SYSTEM
o
"w
I
'J3
2
u.
0.4 -
0.2 -
0.2
(A)
(B)
Residence Time
t, (hours)
6
12
0.4
0.6
0.8
I-Y
Fraction of Effluent Held Time t or less
Treatment
Efficiency
%
75
86
1.0
-------
Figure VI-13
BENCH SCALE CONTINUOUS BIO-OXIDATION UNIT
2-5 ml./min.
To Aspirator
Feed
Reservoir
Mixed Liquo
Sample
68
-------
(—)
dt C-^Mt - overall reaction rate
Mt = active mass at time t (MLVSS)
The loading-removal data is plotted in Figure VI-14. At a
residence time of 12 hours, a TOD removal of 88$ and a
filtered effluent quality of 150 ppm. TOD was obtained. The
results also indicate, in general, that the loading should
be kept below 1.0 pound TOD per pound MLVSS per day, in order
to produce an effluent quality of less than 200 ppm. TOD.
The TOD concentration in the turbid effluent from the con-
tinuous units averaged about 300 ppm., although it contained
no residual organics present in the feed. Preliminary tests
indicated that the TOD concentration could be reduced to
100-150 ppm. by chemical flocculation. A chemical flocculation
step was, therefore, included in the design of the pilot plant.
69
-------
Figur. VI-14
LOADING-REMOVAL RELATIONSHIP, BENCH SCALE CONTINUOUS UNIT
(Bacterium 52-Propylene glycol-8.5% salt)
o
I—
o
MLVSS = 3000
Loading-lbs T.O.D./lb MLVSS.Day
70
-------
SECTION VII
ACTIVATED SLUDGE PILOT PLANT
The preliminary batch tests and the limited tests on "bench
scale continuous units indicated that glycol waste brines
containing up to 10$ salt could be successfully biodegraded.
The efficiency of TOD removal varied between 85 to 92$ and a
product of less than 200 ppm. TOD was obtained both from
synthetic solutions and samples from the actual wastewater
streams. Larger scale testing was required to study the
operation under continuous feeding from the production
plant, to measure the process parameters under varying con-
ditions of operation, and to obtain accurate engineering
design information for economic appraisal. To meet these
requirements, an activated sludge pilot plant similar to
that described by Mulbarger (1966) was designed and con-
structed for an average waste flow rate of 0.5 gallons per
minute.
A. Plant Description and Operation
A flow diagram of the plant is shown in Figure VII-1. The
plant contains the following major components:
1. A cooling tower with a recirculating pump. The basin of
the tower has a capacity of 28 gallons.
2. A river water supply line to the cooling tower with a
density-controlled automatic valve.
3- An acid tank feeding into the suction line of the re-
circulating pump through a pH controlled automatic valve.
4. A nutrient solution tank supplying nutrients to the feed
through a metering pump.
5- A packed Plexiglas roughing column, 18 inches in
diameter by 96 inches tall, with its recirculating
pump.
6. A 280-gallon aerator tank made of Plexiglas with six
removable partitions. Diffused air is introduced into
the bottom of each compartment and controlled by needle
valves on rotameters.
7- Two 50-gallon Plexiglas settlers, each with an adjustable
overflow weir and an airlift to pump the settled solids
from the bottom.
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8. A 5-gallon glass battc-ry ,jar with a stirrer and two
metering pumps for Plocculant mixing.
9- Various composite t L Tie-operated samplers.
All components except the cooling tower and the feed lines
are mounted on a portable structural steel frame. Figure
VII-2 is a photograph showing the aeration tank and the
rotameters on the inlets to the air diffusers in the bottom
of each compartment. The aeration tank is covered and vented
by suction to a water ccrubber.
Figure VII-3 shows the first settling tank where the biofloc
settles and the two samplers that periodically sample the
feed to the aeration tanx as well as the overflow from the
settling tank. Figure VII-4 shows the flocculation vessel,
the metering pumps, and the pH control. This vessel is fed
by gravity from the first settler and flows by gravity to the
second settler where the alum flocculant is settled.
Plant Operation
The waste stream from the glycol production plant was cooled
from 140°F. to a temperature below 100°F. in the cooling
tower. The circulation rate over the natural draft spray
tower was 25 to 30 gallons per minute. Part of the stream
to the tower spray nozzle was diverted to a jet below the
liquid level in the tower basin to thoroughly mix the basin
contents with the raw feed as it enters. The suction line
to the pump operated under a vacuum of 15 to 20 inches of
mercury, which lends itself conveniently to the addition and
mixing of the nutrients and acid.
Good mixing, both in the basin and in the pump, has been
found to be necessary for good pH control, since the
alkalinity of the feed varies between 0.05 and 0. ^$ sodium
hydroxide. The neutralization of the feed to a pH of- around
7-8 with either a 10$ H2S04 solution or, later, with a 38$
HC1 solution, was controlled by an apparatus that measures
and records the pH of the discharge stream from the cooling
tower circulating pump. The pH control circuit shuts off the
feed to the activated sludge aeration tanks If the pH goes
above 8.5 or below 5-5 units.
The nutrient solution, 3.17$ (NH4)2SC4 and 0.73$ K2HP04, Is
fed into the circulation pump suction line by a Model 2M1
Moyno pump. The rate of addition is controlled to result
in the required concentrations of nitrogen and phosphorus
in the feed.
-------
-------
Figure VII-3, First Settling Tank and Composite Samplers
J
75
-------
76
-------
Any entrained air had to be separated from the treated feed
stream to enable proper functioning of the flow recorders
and the density control apparatus. This was achieved by
forwarding the circulating pump discharge to an elevated
Plexiglas vessel with an 8-inch high dividing plate. The
outlet side of the vessel had an overflow near the top,
piped to the cooling tower basin, and a port near the bottom
from which the treated feed was drawn.
Provision was made for the addition of fresh water to the in-
coming glycol effluent at the cooling tower during those
times when the NaCl content increases excessively beyond 10$--
either due to evaporation or to operational changes. The
salt concentration was controlled by the density of the feed.
A sample stream from the air separator vessel was piped into
the bottom end of a 2-inch vertical pipe 10 feet tall, flanged
at its lower end to a 2-inch tee. The stream rose through
the pipe and overflowed at a constant level into a plastic
pan and drained into the cooling tower. The pressure at
the bottom of the column varied with the density of the
fluid and was measured by a differential pressure transmitter
and recorded as density. The sensitivity of the signal from
the transmitter was improved by balancing the column pressure
against a fixed column of mercury while the unit was filled
with pure water. The transmitter signal is also applied to
a pneumatic relay which controls a diaphragm valve on the
fresh water supply line to the top of the cooling tower.
The pre-treated feed was forwarded from the air separator either
to the roughing tower or to the aeration tank by a metering
gear pump (Model 1L2 Moyno) which is adjusted for flow rates
from 0.2 to 0.6 gpm.
The roughing column was packed with 5 feet of porcelain Berl
saddles. A recycle pump was adjusted to give a rate of recycle
five to ten times that of the feed flow rate. The column was
started by recycling about 15 gallons of acclimated culture
and feeding with glycol daily for a period of two weeks to
build up the bacteria on the packing. Then the column was
switched onto the continuous feed. The overflow of the
column basin flowed by gravity to the aeration tank.
Prior to start up, a batch of 400 gallons of the mixed
culture was acclimated to the glycol effluent in a glass
tank equipped with air diffusers. This batch-grown culture
was used to fill the aeration tank and was kept growing by
a fill-and-draw procedure as a standby bacterial supply.
The diffused air to the aeration tank was supplied from a
header, at 8 psig, at a rate of 1.5 cfm to each of seven
diffusers. The total air supply, 10-5 cfm, was about 0-33
cfm per cubic foot of aerator volume.
77
-------
The mixed liquor overflowing from the aerator entered the
first settling tank through an inlet port about 15 inches
above the bottom. The settled sludge was returned to the
feed end of the aerator by means of an air lift pump operated
by a timer adjusted to keep the same concentration of sus-
pended solids in the aeration tank. The overflow from the
first settler was usually slightly turbid. It flows into
the flocculator where alum and caustic solutions are added,
then to the second settling tank.
Automatic composite samplers were used to collect samples
from the treated feed before and after the roughing column
and from the overflow of the first and second settling
tanks. The timer-operated samplers collect 1 to 2 milli-
liters at 15-minute intervals. Samples of the wastes,
after the biological treatment, were collected in bottles
kept cool in dry ice to prevent any further biological
action. The 24-hour composite samples were analyzed daily
for TOD, glycols and other components, percent NaCl, pH
and nutrients. A sample of the mixed liquor in the aeration
tank was collected daily for determination of the suspended
solids.
B. Evaluation of the Roughing Column
A film of bacterial growth was built up on the surface of
the packing in the roughing column by batch feeding the
column with propylene glycol. During the period when the
plant operation was operating on a mixed ethylene and propylene
glycol waste, the feed was directed through the roughing column,
Composite samples before and after the column were analyzed
daily.
The results of two weeks of operation were erratic. The
non-filtered samples from the roughing treatment showed an
increase in TOD value, but the initial dissolved organics,
ethylene and propylene glycol were always reduced.
The operation of the packed column without additional air was
found to be oxygen limited and the bacterial film became
anaerobic as the bacteria increased on the packing. The
packing turned black in less than ten days of operation. A
diffuser was installed at the bottom of the column, and air
was supplied, under a pressure of about 2 atmosphere, at a
rate of 2 cubic feed per minute. The column was then
successfully operated for a period of three weeks, with no
indication of anaerobic conditions developing. The flow rate
of 0.4 gpm corresponds to about a 1 hour residence time in
the column at a recycle ratio of 1:20. The results are pre-
sented in Table VII-1. A TOD removal of over J>Q% was obtained
except during period when the air diffuser was plugged.
Cleaning the air diffuser improved the operation of the column
overnight.
78
-------
TABLE VII-1
OPERATION OF THE ROUGHING COLUMN
WITH FORCED DRAFT AIR
Pretreated Feed
Date
11-27
11-28
11-29
11-50
12-1
12-2
12-3
12-4
12-5
12-6
12-7
12-8
12-9
12-10
12-11
12-13
PG
ppm
520
260
300
230
220
650
510
520
500
350
570
470
530
280
560
660
TOD
ppm
1750
1680
1280
1420
1130
1300
1760
1490
1490
126o
1590
128o
1230
1240
1220
1200
Effluent from Column
PG
ppm
150
-
-
-
-
360
310
190
180
l4o
260
290
330
250
270
420
TOD
ppm
1040
1120
830
870
930
1040
1640
1030
1290
950
1170
1090
710
1030
510
750
TOD
Removal
%
40.6
33-4
35-1
38.7
17.7
20.0
6.81
30.8
13. 41
24.6
26.4
14. 91
42.2
17. o1
58.0
37-5
Flow Rate
gals./min.
0.32
0.32
0.32
0.32
0.36
0.36
0.40
0.40
0.40
0.40
0.40
0.40
0.40
0.40
0.40
0.40
1 Air diffuser at bottom of column was plugged with a fine
material that does not resemble the bacteria. When cleaned,
the removal of TOD improved overnight.
7Q
-------
C. Results of Different Modes_ of_ 0_peration
The operation of the pilot plant as a plug flow reactor and
a completely mixed single basin with a feed composition as
obtained from the glycol production plant constituted the
modes of operation studied. The objective was to determine
the minimum residence t;.ne required for the complete oxidation
of the organics components of the feed under the varying con-
ditions of loading. The results obtained under the several
modes of operation are presented and discussed under the
following subsections. The detailed daily records of the
plant operation are presented in Appendix B.
Mixed Ethylene and Propylene Glycol Wastewaters Plug Flow
Operation
The activated sludge pilot plant was started with a bacterial
culture grown batchwise in a 300 gallon glass tank filled
daily with pretreated glycol wastewater. During the period
of operation, from June 2J4 to August 26, 1970, partitions
were placed in the aeration tank. A dye study snowed that
the configuration of the aeration tank was that of a plug
flow reactor with seven completely mixed reactors in series.
The feed was a mixture containing about one third ethylene
glycol and two thirds propylene glycol. The TOD of the feed
varied between 1200 to 2000 ppm. The flow rate of the feed
was brought up gradually to 0.3 gpm, corresponding to a
residence time of 14 hours in the aeration tank. The re-
moval of TOD varied between 86 to 95$ at this flow rate,
yielding a product quality between 100 and 23C ppm. TOD.
When the feed was switched over to propylene glycol waste
for a period of five days (July 31 to August J4) , a higher
percent removal, 90 to 95$., and a product of less than a
100 ppm. TOD was obtaired. Due to mechanical difficulties
with the feed pump, the feed was then sv. itched back to the
mixed waste stream,
A plot of the TOD, in ?jid out, and the concentration of MLVSS
in the aeration tank over this operating period, is shown in
Figure VII-5. A complete daily record of the analyses is
given in Table XI-2 of Appendix B.
On August 22 the feed rate was increased to O.1'- gpm (giving
a residence time of about 10 hours). Good operation was
maintained for three days at this higher flow rate, with TOD
removal of 88 to 91$. As the TOD concentration in the feed
increased, residual glycol and higher TOD were produced in
the treated waste. The sludge settling became less efficient
and it became difficult to maintain a MLSS over 100 ppm.
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During the interruptions of the operation (A, B, C and D in
Figure VII-5) the aeration tank was either fed propylene
glycol or secondary culture was added before startup.
Usually the batch grown bacteria suffered a decrease in con-
centration when exposed to continuous flow conditions, followed
by a culture increase and better settling characteristics, as
the bacteria became acclimated to the flow conditions.
A schematic of the operation showing the range of the results
obtained during ten days of continuous operation at a flow
rate of 0.3 gpm is shown in Figure VII-6. During this period
the roughing column was in operation most of the time. The
loading-removal relationship obtained during this period is
shown in Figure VII-7. The indicated slope of 0.834 corres-
ponds very well with the calculated value from batch tests
for a residence time of 12 hours. The effluent-loading re-
lationship is presented in Figure VII-8. An effluent quality
below 200 ppm. TOD can be obtained at a loading of up to 2.0
pounds TOD per pound MLVSS per day in this mode of operation.
Propylene Glycol Waste - Completely Mixed Reactor
The partitions were removed from the aeration tank, and the
feed was switched to wastes containing only propylene glycol.
A hydrochloric acid (38$) rubber lined tank was installed and
HC1 used for neutralization.
The feed to the completely mixed aeration tanks was started
on July 9> at a rate of 0.325 gpm (12.8 hours residence time).
For the first week of operation the MLVSS remained low and the
feed had a high TOD concentration. This high loading resulted
in only 70 to 77$ removal of TOD with the product containing
higher concentrations of TOD and propylene glycol. From
September 24 to October 2, a TOD removal of over 90$ was
obtained and the MLVSS was building up, while the TOD in the
feed varied from 1940 to 2400 ppm.
On October 3> the temperature of the feed rose to 46°C, due
to the plugging of the spray nozzle in the cooling tower.
This was accompanied by an increase of TOD in the feed to
3240 ppm. The bacteria were killed, anaerobic conditions
developed, and the bacteria were lost by floating and carry-
over. For a period of two weeks following this incident,
it was difficult to build up the concentration of the bacteria.
The settling of the sludge was very inferior and most of the
bacteria were filamentous in nature.
From October 20 to October 27, 88$ to 94$ TOD removal was
obtained and the sludge settling improved as the bacterial
concentration built up to l66o ppm. The TOD in the feed then
began to fluctuate to very high concentrations, again
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accompanied by a loss of the bacterial concentration. It was
decided to install a 3000-gallon tank in the feed system to
equalize the organic loading to the activated sludge plant,
to maintain a near steady state operation. The results of
this period of operation are plotted in Figure VII-9. The
complete daily analyses are given in Table XI-3 of Appendix B.
Equalized Propylene Glycol Waste Completely Mixed Reactor
The feed was switched to a propylene glycol waste stream
collected from several production trains and was equalized
in a 3000-gallon tank before feeding to the pilot plant. A
residence time of about 3.5 days in the equalizing tank after
neutralization resulted in considerable dampening of the
fluctuations in the TOD concentrations. The nutrients were
added to the feed after equalization. Addition of the
nutrients prior to the tank resulted in the development of
anaerobic activity inside the tank. The pilot plant results
during November and December, 1970 are plotted in Figure VII-10
The daily analyses are shown in Table XI-4 of Appendix B. The
initial flow rate of the feed was 0.32 gpm. It was increased
to 0.4 gpm (10-5 hours residence time) in two weeks. Removal
efficiencies of over 80$ and a product of less than 300 ppm.
TOD was obtained during most of this time. Lower removal
efficiencies were experienced during this period due to the
lowered waste temperatures (60 to 70°F.). Heating the feed to
85°F. resulted in increased activity.
The operation of the activated sludge pilot plant continued
through January and February under steady state conditions
using equalized feed. The obtained results are given in
Table XI-5, Appendix B, and in Figure VII-11. The feed rate
was increased to 0.45 gpm on January 26, giving a residence
time of 8.25 hours in the aeration basin. The loading and
removal relationship is plotted in Figure VII-12, for the
period from January 15 to February 22. A removal efficiency
of 92$ was obtained for loadings between 1.5 to 3.0 pounds
TOD per pound of MLVSS per day. The lower end of the loading
was found to be operationally critical. At loadings below
1.5* "the food to bacteria ratio was too low to maintain the
mixed culture in the aeration basin, and resulted in a sudden
loss of the bacterial concentration due to endogenous res-
piration.
D. Operational and Design Parameters
The operation of the activated sludge pilot plant was main-
tained at nearly steady state during the months of January
and February, 1971. The emphasis during this period was on
collection of the data necessary for process design. The
86
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operational and design parameters of the process are best
discussed under the following headings.
Stability of the Biota to Transients
Equalization of the wastewater feed to the aeration basin
was found to be necessary to dampen the fluctuations of the
organic loading of the activated sludge. Loadings below
1-5 pounds TOD per pound MLVSS per day, resulted in a sudden
loss of the bacterial concentration, while at loadings over
4.0 or 5-0 filamentous bacterial growth resulted, with poor
settling properties and a resultant high concentration of
suspended solids in the effluent from the settling tank.
The recommended range of organic loading of this particular
culture is 1.5 to 3-0 pounds of TOD per pound of MLVSS per
day.
The characteristics of the various components in this culture
are given in Appendix C. Biochemical test reactions of forty-
eight isolates from the activated sludge indicated that there
are no more than 3 or 4 species. The most numerous bacterium
is a Gram negative, non-motile, oxidase positive rod.
The growth of this culture is favored at higher temperatures.
Good operation was maintained during the summer months, at
100°F., but difficulties were encountered at temperatures below
65°F., during the period January 7 to January 13, as indicated
in Figure VII-11. The temperature of the aeration basin was
maintained at 85°F. by heating the feed during the period
from January 14 to the end of February.
The temperature limits were determined in the laboratory
continuous unit shown in Figure VII-16. The unit was filled
daily with mixed liquor from the pilot plant and loaded with
pretreated feed at approximately the same rate as the pilot
plant. The temperature of the aeration vessel was varied
between 10°C. and 50°C. The oxygen uptake rate under loading,
the removal efficiency and sludge production were measured
during a 24-hour period.
In Figure VII-1J5, oxygen saturation, oxygen equilibrium con-
centration and oxygen uptake rate are plotted as functions
of temperature. At 11°C. the oxygen uptake rate decreased
to one-third of the value at 20°C., there was no sludge
production and the removal efficiency dropped off and
residual glycol appeared in the effluent. The bacterial
culture formed dense clumps and was difficult to mix with
the feed. At temperatures over 4o°C., some decrease in
oxygen uptake rate was noted, but removal efficiency and
sludge production was not affected. The optimum oxygen up-
take appears to be at a temperature between 30 and 35°C.
(85 to 95°C.).
91
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Substrate Removal Rate_
For the period of operation from November 20, 1970 to
February 28, 1971, the recycle ratio, to the completely
mixed aeration tank, was varied between 15 and 2^fo of the
equalized propylene glycol waste feed rate. In Figure VTI-14
the effluent TOD is plotted as a function of loading. The
initial loading of the aeration tank (TODi) is calculated as
a weight average of the feed and recycle:
= rJQg_f +_(recycle ratio) (TODe)
i ~ 1 + recycle ratio
(a)
where
TODf - Total oxygen demand in the feed.
TODe = Total oxygen demand in the effluent.
The line of best fit of the data is represented by:
TODe = 9-3 •+ 69.7 (-
(b)
x MLVSS'
The same data can also be presented as in Figure VII-15,
where the rate is plotted as a function of a loading ratio.
The correlation Is given by:
- TODe
t x TODe
- 1.3.5 - 0.412
TODj
MLVSS
(c)
The coefficients of correlation for equations (b) and (c) are
0.725 and 0.8l6, respectively. Both relations can be used to
calculate the residence time (t) and the volume of the reaction
basin required.
Oxygen Utilization Rate
The laboratory activated sludge unit, used for oxygen measure-
ments, is shown In Figure VII-16. The aerator (4.1 liters)
was started dally with mixed "Mquor obtained from the pilot
plant, and air was supplied to it at a rate of 600 ml./min.
The stirrer, at 60 rpin, was just enough to keep the suspended
solids mixed when the air was cut off. The temperature of
the aerator was controlled by immersing it in a water bath.
The unit was fed with the same pretreated waste at the same
loading and recycle as in trie pilot plant, then equilibrated
over a period of 20 hours. At this tine, the air was shut