United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
EPA 600 2-80 143
June 1980
Research and Development
oEPA
Electrolytic
Treatment of Oily
Wastewater From
Manufacturing and
Machining Plants
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution-sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
-------
EPA-600/2-80-143
June 1980
ELECTROLYTIC TREATMENT OF OILY WASTEWATER
FROM MANUFACTURING AND MACHINING PLANTS
By
R. L. Gealer
A. Golovoy
M. Weintraub
Ford Motor Company
Dearborn, Michigan 48121
Grant No. 580*17*
Project Officer
H. Durham
Industrial Pollution Control Division
Industrial Environmental Research Laboratory
Cincinnati, Ohio *5268
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
• CINCINNATI, OHIO 45268
-------
DISCLAIMER
This report has been reviewed by the Industrial Environmental Research
Laboratory-Cincinnati, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily reflect the views
and policies of the U.S. Environmental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement or recommendation for use.
ii
-------
FOREWORD
When energy and material resources are extracted, processed, converted, and
used, the related pollutional impacts on our environment and even on our health often
require that new and increasingly more efficient pollution control methods be used. The
Industrial Environmental Research Laboratory - Cincinnati (lERL-Ci) assists in
developing and demonstrating new and improved methodologies that will meet these
needs both efficiently and economically.
This report describes a continuous electrolytic treatment process for removal of
emulsified oil from dilute oily wastewater streams, such as is generated in metal
working operations. Results obtained from operating a pilot plant facility demonstrate
the feasibility of the process. The electrolytic process may offer an alternative to
conventional chemical treatment for small to medium size machine shops. TKe
Industrial Pollution Control Division is to be contacted for further information.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
111
-------
ABSTRACT
A continuous electrolytic treatment is being developed to remove emulsified oil
from dilute oily wastewater streams, such as is generated in metal working operations.
In this process, the wastewater permeates through an iron chip bed anode and steel
mesh cathode. A potential is applied to the electrodes, forming ferrous ions at the
anode and hydroxyl ions at the cathode. The ferrous ions react in a complex manner
with the emulsifying agents, destabilizing the emulsion and generating an oil rich
floating sludge and essentially oil-free water.
A pilot plant unit capable of processing about 5700 I/day (1500 gal/day) was
designed, constructed, and evaluated at an actual plant site. Operating parameters and
process equipment were evaluated to assess the potential and problems of the process.
Wastewater with initial oil concentrations in the range of 300 to 7,000 ppm of
solvent extractables has been reduced to less than 50 ppm in 90% of the test runs, and
to less than 25 ppm in 83%. These test runs were done at conditions of minimum
operating cost and minimum sludge generation. When necessary, Freon extractables
generally are reducible to about 10 ppm or less by the addition of more electrolytically
dissolved iron to the system at a small increase in cost.
Preliminary economics look favorable and overall results are quite encouraging
so that further scale-up of the process is recommended.
This report was submitted in fulfillment of Grant No. S-804174 by Ford Motor
Company under the sponsorship of the U.S. Environmental Protection Agency. The
report covers the period May 18, 1976 to August 17, 1978, and work was completed as of
August 17, 1978.
IV
-------
CONTENTS
Foreword il1
Abstract iv
Figures vl
Tables vii
1. Introduction 1
2. Conclusions and Recommendations 3
3. Experimental 4
Experimental facility 4
Experimental procedure 6
4. Results and Discussion 14
Analysis of plant effluent 14
Operating parameters 19
Effluent quality 29
Durability studies 32
Electrode plugging *1
Sludge flotation and sludge characteristics 42
An approach to automatic control 44
System capacity design criteria 45
Economic projections 45
References ^8
-------
FIGURES
Number
1 A schematic diagram of the electrolytic cell 5
2 A flow diagram of the electrolytic process 7
3 Experimental electrolytic treatment test facility 8
4 Flow cell, view from upstream end 9
5 Sludge skimming apparatus 10
6 Oily wastewater receiving and storage tank 11
7 Effect of iron to oil weight ratio on effluent oil content 30
VI
-------
TABLES
Number Page
1. Steady-State Measurement in the Electrolytic Cell 12
2 Analyses of Untreated Wastewater 15
3 Summary of Operating Conditions and Effluent Quality 20
4 Iron Dissolution Rate 27
5 Results of Treatment of Plant Wastewater With and
Without pH Adjustment 28
6 Summary of First Durability Test 33
7 Summary of Second Durability Test 35
8 Summary of Third Durability Test 36
9 Summary of Fourth Durability Test 37
10 Summary of Fifth Durability Test 39
11 Evaluation of the Performance of the Dissolved Air Flotation .... 43
12 Capital Costs of Electrolytic Treatment 47
VII
-------
SECTION 1
INTRODUCTION
Process wastewater from metal working operations contains free or suspended oil
and emulsified oil which must be removed before the water can be discharged or reused.
These oils originate mainly from parts washer overflow and machining coolant dumping,
and the concentration typically ranges from 1,000 - 10,000 ppm as emulsified oil and
perhaps 30,000 ppm as free suspended and floating oil. The free oil can be removed by
gravity separation and a simple skimming operation, but the removal of the emulsified
oil is more complicated. These oil-in-water emulsions are intimate two-phase mixtures
of oil and water with oil dispersed as microscopic droplets (0.1-100 pm diameter) in the
aqueous phase and stabilized by the presence of surface active compounds.
Wastewaters containing these emulsions generally are treated for discharge by pH
adjustments and the addition of salts of such metals as iron or aluminum, to produce a
flocculant precipitate. A common technique is to begin by treating the oily wastewater
with sulfuric acid to effect a primary emulsion break. The freed oil is collected and the
water phase, which still may contain up to 400 ppm of emulsified oil, is further treated
with ferric chloride and sodium hydroxide. The ferric ion destabilizes the emulsion by
neutralizing the charge on the emulsion droplets and precipitates as ferric hydroxide —
the oil is sorbed on and into the flocculant precipitate. These conventional methods,
while yielding water of good quality, generally increase the dissolved solids content of
the water and generate a voluminous sludge containing about 95% water. For small-to-
medium size machining plants to install a new waste treatment facility based on
chemical treatment, space limitations would present the greatest problem. The
electrolytic process being developed by Ford Motor Company has the potential to
overcome the limitations noted above in that it is a continuous process which requires
less space, generates less dissolved solids, and produces less sludge with lower water
content.
Earlier development work on this process is described in References 1-3. The
method is one in which the reactive cation, iron is introduced electrolytically as a
ferrous ion followed by in situ oxidation to the ferric state and subsequent precipitation
as ferric hydroxide. In this method the oil-in-water emulsion is destabilized during the
oxidation reaction before extensive coagulation and flocculation occur. The
demulsification is thought to take place by attack on the emulsifiers by hydroxyl
radicals generated during ferrous ion oxidation, as well as by direct reaction of the
emulsifiers with ferrous ion. The demulsified oil is then removed by adsorption on the
highly dispersed ferric hydroxide microfloc.
The objective of the present work was to develop and demonstrate on a pilot scale
the electrolytic method of removing emulsified oil from oily wastewater generated by
-1-
-------
metal fabrication operations, and to establish its technical and economic feasibility.
The pilot unit was installed at the Ford Motor Company Livonia Transmission Plant and
actual plant discharge was fed to the unit for treatment.
-2-
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SECTION 2
CONCLUSIONS AND RECOMMENDATIONS
The results of the electrolytic pilot unit study for treatment of oily wastewater
indicate that the process is capable of rendering the wastewater suitable for direct
discharge to municipal sewers and possibly to surface waters. The exact nature of the
influent, however, will strongly influence the final effluent quality from the process. In
these studies it was found that by operating the unit at minimum cost and minimum
sludge formation to just break the emulsion, the effluent contained less than 50 ppm
90% of the time and less than 25 ppm 83% of the time, where the influent oil
concentrations ranged from 300 to 7,000 ppm. Reduction in the effluent oil
concentration to about 10 ppm or less generally can be accomplished, when necessary,
by an increase in the iron concentration, since it was observed that the ratio of iron
dissolved to oil concentration is the major parameter determining the water quality-
iron concentration is controlled by controlling the current in the electrolytic dissolution
of iron.
Of the other parameters examined, the salt type (added to increase ionic
conductivity and prevent electrode passivation) is the next important. Calcium chloride
was found to aid in the demulsification of the oily wastewater and was ordinarily the
preferred salt. A concentration of 0.01N was employed in most runs. The use of
calcium chloride does cause an inconvenience since calcium carbonate deposits may
tend to build-up on the cathode. The pH of the as-received wastewater ranged from 8.5
to 10.5 which is typical for machining coolants. Treatment effectiveness is the same in
this pH range as it is with the pH adjusted to 6.5 to 7, thus pH adjustment is
unnecessary. Flow rate through the process should be fixed to handle the plant flow and
slight variations in the flow do not appreciably influence the effluent.
A preliminary economic analysis indicates that the direct costs of the process
(power, calcium chloride, and iron valued as scrap) can range from about $0.09 to
$0.17/1000 1 ($0.34 to $0.64/1000 gal) depending on the type of equipment employed in
the process. Unanswered questions remain with respect to extended durability of the
process, practicability of a completely automated-continuous process and the best
technique for recovering oil from the generated sludge.
To answer these questions, it is recommended that the process be scaled up to
approximately two to five times the pilot unit capacity and that the system be
automated to achieve unattended continuous operation.
-3-
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SECTION 3
EXPERIMENTAL
EXPERIMENTAL FACILITY
A schematic diagram of the electrolytic cell is shown in Figure 1. Wastewater
enters the cell and permeates through a rectangular caged bed of iron or steel
machining chips which acts as anode, and then through a perforated sheet metal
cathode. Sufficient voltage is applied to dissolve the iron forming ferrous ions which
react with the emulsifying agent freeing the oil. This oil is sorbed onto the ferric
hydroxide floe which is formed in-situ by oxidation of the ferrous ion. The oil-rich
ferric hydroxide sludge floats to the surface where it can be skimmed, yielding
essentially oil-free water.
The electrolytic cell is constructed of 1.27 cm thick plexiglas in an angle iron
frame. The cell is 91 cm wide, 61 cm high, and 244 cm long. Wastewater enters the
cell through a manifold with multiple outlets to assure uniform distribution of flow
through the electrode. The 7.6 cm thick anode cage is constructed of expanded
titanium with diamond shaped holes with approximate size of 1.5 x 0.5 cm. Since bare
titanium was found to corrode under some circumstances because of galvanic action, it
was coated with a protective coating of insulating varnish which alleviated the problem.
The front face of the anodic cage is lined with a polyethylene screen with a hole
size of about 0.15 on. The screen is installed to ensure that the iron chips do not
extend outward and contact the cathode or, when small enough, fall in the space
between the electrodes.
The anodic cage is filled with low carbon steel chips obtained from machining
operations in the plant. The optimum size of the chips was found to be 1-2 cm long and
with diameter of 0.2-0.5 cm. Smaller diameter chips tend to fall through the screen,
and longer ones tend to form entanglements causing difficulties in packing the chips in
the anodic cage. The cathode, spaced 1.27 cm from the anode, is constructed of a
perforated steel plate. A clearance of about 4 cm is maintained between the bottom of
the cathode and the bottom of the anodic cage to reduce the possibility of electrical
short circuiting by loose iron chips. The cathode height was extended up to about 1 cm
below the water level to allow oily sludge to float over it and avoid sludge accumulation
between the electrodes. Demulsification reactions and sludge flotation occur in the
remaining length of the cell.
The introduction of air for oxidation of the ferrous ion and for flotation of the
sludge is accomplished by forcing air through a porous membrance on the cell bottom.
The membrane has an average pore size of 1 ym. In later experiments, the use of
dissolved air flotation in place of air bubble flotation was evaluated.
-4-
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OILY EMULSION
WASTE WATER
DC POWER
SUPPLY
OIL-FERRIC HYDROXIDE SLUDGE
TREATED
WATER
IRON CHIP BED ANODE7 AIR IN MESH CATHODE ^ BUBBLE
GENERATOR
Figure 1. A schematic diagram of the electrolytic cell
-------
The cell and ancillary equipment (pumps, sand filter, sludge skimmer, power
supplies, etc) are installed in a specially constructed enclosure within the plant. A flow
diagram for the system is shown in Figure 2, and photographs of the cell and system are
shown in Figures 3 through 6. The 11.3 m (3000 gal) wastewater receiving and storage
tank is outside the enclosure but inside the plant. Nominal capacity of the system is
about 3.8 1/min (1 gal/min).
EXPERIMENTAL PROCEDURE
Both simulated and actual plant wastewater were processed through the cell. The
simulated wastewater was processed according to techniques developed in the
laboratory to evaluate the overall cell performance and to compare the operational
parameters to those obtained in previous experiments with a laboratory bench size unit.
Simulated wastewater was prepared by continuous flow mixing of machining
coolant emulsion concentrate with water in a ratio to give the desired oil concentration.
The standard evaluations were carried out using 2,000 ppm emulsified oil processed at
3.8 1/min (1 gal/min) using a current of 25 amp with an average potential of 15 v for 8
hr. Hydrochloric acid was added to adjust the pH to 7 and sodium chloride was added to
maintain the conductivity at 1500 ymho/cm (0.58 g/1 of sodium chloride). Results of
these experiments indicated that steady-state conditions are reached after about 6 hr of
operation which is approximately 1.5 times the plug flow residence time. This is seen in
Table 1 which shows turbidity reading in nephelometer turbidity units (NTU) as a
function of time and position in the cell past the cathode.
Before October 1977, the plant wastewater, which was collected from the
combined plant wastewater wet well over a period oL 2 hours, was carried in mobile
tanks to the receiving tank in batches of about 11.3 m (3000 gal). Prior to processing,
the plant effluent was analyzed for pH, conductivity, turbidity, dissolved and suspended
solids, and Freon extractables. Several runs were made with each of the batches in
which the current and/or the flow rates were varied and the corresponding effluent
quality determined. Each run lasted 6-8 hours and used about 1.89 m (500 gaU of
wastewater. Before passing through the cell, sodium chloride or calcium chloride may
be added for conductivity and to avoid anode passivation, (which would result in current
being expended to generate oxygen rather than dissolve iron), and the pH may be
adjusted with hydrochloric acid. Following the electrolytic treatment the water may be
passed through a sand filter to remove suspended solids. Some batches, when received,
were treated with about. 7.6 1 of household bleach and 200 g of cup'ric chloride to
minimize bacteria growth and odor development because of long standing in the
receiving rank. Laboratory batch experiments indicated that the bleach and cupric
chloride addition did not significantly influence the emulsion stability.
In October 1977 a pumping system which can continuously supply the pilot unit
with fresh wastewater was installed. The inlet of the pumping system is located at a
manhole which receives wastewater from most of the plant operations via three
streams. The composition of wastewater delivered to the pilot unit was found to be
essentially the same as that received at the wet well of the wastewater treatment
plant.
After the installation of the pumping system the receiving tank could be filled
daily with enough water for one day of operation. Because it was now convenient to
-6-
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ACID SALT
\l
FREE
OIL
r
FLOW
EQUALIZATION
TANK
rv
AIR
PLANT OILY
WASTEWATER
PRETREATMENT
AS REQUIRED
BY PLANT
WASTEWATER
IRON CHIP
CAGE ANODE
DISCHARGE
OIL RICH-
IRON HYDROXIDE
SLUDGE
— 1
ELECTROLYTIC
CELL
Ttttt
.BELT
SKIMMER
AIR
STEEL MESH
CATHODE
.BACKWASH
1^" TO TANK
CLEAN
WATER
TANK
TO FILTER BACKWASH
Figure 2. A flow diagram of the electrolytic process
-------
I
oo
Figure 3. Experimental electrolytic treatment test facility
-------
I
o
Figure 4. Flow cell, view from upstream end
-------
Figure 5. Sludge skinning apparatus
-------
I
Figure 6. Oily wastewater receiving and storage tank
-------
TABLE 1. STEADY-STATE MEASUREMENT IN THE ELECTROLYTIC CELL
Time, hr. Turbidity (at distance past cathode),
5 cm
0 2500
3 540
4 45
5 26
6 26
7 16
8 19
45 cm
2500
270
47
28
19
15
14
100 cm
2500
180
22
23
17
15
12
150 cm
2500
130
23
17
10
11
8
NTU
exit
2500
150
13
5
5
6
6
-12-
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have a holding time of only one day, the biocidal treatment with bleach and cupric
chloride was no longer necessary. As before, the wastewater was analyzed for pH,
conductivity, turbidity, Freon extractables, solids, and anionic surfactants. In addition,
a one liter sample of the wastewater was treated electrolytically in a beaker to
determine the proper setting of the operating parameters for effective treatment. This
was done by adding an amount of salt to the wastewater to give the desired
conductivity, setting the current at 0.5 amp and observing the time required to just
break the emulsion. The results were used to calculate the concentration of iron which
is necessary to break the emulsion. The flow rate and current in the pilot unit were
then set to give the same iron concentration.
The electrolytic unit has been operated with a single set of electrodes and
provided with air bubblers for oxidation and flotation of the sludge. During a run the
current, voltage, pH, conductivity, wastewater flow rate, and turbidity are checked and,
if necessary, adjusted every hour. After 6-8 hours, when steady state conditions are
reached, samples of the effluent and floating sludge are collected for analyses.
During most of the program period the floating sludge was removed by a belt
skimmer at the end of the unit. In April, 1978 a dissolved air flotation unit was
installed to improve the flotation of the sludge and reduce the level of suspended solids
in the effluent. The unit is a Komline-Sanderson pilot flotation unit—model HR/SR-1.
(Komline-Sanderson Corp., Peapack, NJ). The flotation area is 929 cm (1 ft ).
Dissolved Air Flotation (DAF) is a liquid-solid separation process that takes
advantage of the fact that if air is dissolved in water under pressure, and the pressure is
later released, the dissolved air will be released from solution in the form of vast
numbers of minute bubbles. Actual flotation occurs when these bubbles become
attached to suspended solid particles, oils, or immiscible liquids, thus increasing their
buoyancy and causing them to rise to the surface of the liquid in which they are
suspended. Floated material is skimmed from the surface, and the clarified liquid
overflows from the rear of the unit.
-13-
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SECTION 4
RESULTS AND DISCUSSION
ANALYSIS OF PLANT EFFLUENT
Oily wastewater from the Livonia Transmission Plant is usually white in color with
some tramp oil and scum floating on top. Occasionally, the color of the wastewater
may be gray, the result of excess free oil and dirt. The wastewater has a mild odor of
machine oil which sometimes turns rancid upon standing. This rancid odor is caused by
a bacterial reaction which releases hydrogen sulfide. Details of the composition,
bacterial reactions and general comments relating to cutting fluids can be found in
References 4, 5, and 6.
The Livonia Transmission Plant represents one of the most varied machining
operations that would be encountered in the industry. The Livonia plant does drawing,
broaching, grinding, machining etc. on various cast iron, aluminum, and steel
compositions. As a result of this, the wastewater is one of the most complex to treat.
The major components of the wastewater are emulsified ("soluble") oils, surfactants,
and tramp oils. In addition, it sometimes contains hydraulic oils, drawing compounds,
transmission fluids, etc. The chemical composition and physical characteristics of the
plant effluent change frequently and unpredictably.
Samples of the plant effluent were analyzed for oil by Freon extraction (Freon
extractables), turbidity, anionic surfactants, pH, and conductivity and periodically for
dissolved and suspended solids. In the first nine months of the program the batches
were collected from a wet well just before the wastewater treatment plant. In the
following 8 months the batches were collected from a process sewer line which leads to
the wet well. Unless otherwise indicated, the tests were performed according to
procedures recommended by the U.S. Environmental Protection Agency (7). The results
of the analyses of over 80 samples, which were subsequently used in the evaluation of
the electrolytic pilot unit, are presented in Table 2.
Freon Extractables
Freon extractables ranged from 313 ppm to 7164 ppm and averaged 1822 ppm with
standard deviation of 1370 ppm. It is comprised mostly of soluble oil and surfactant,
and some tramp oil. Occasionally it may include hydraulic oils, drawing compounds,
etc.
Turbidity
The average turbidity as measured in Nephelometer Turbidity Units or NTU's
(Model 2424 Analytical Nephelometer, Hach Chemical Company, Ames, Iowa) was 1780
NTU with standard deviation of 1280 NTU. The minimum turbidity was 300 NTU and
-14-
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TABLE 2. ANALYSES OF UNTREATED WASTEWATER
Date
12-16-76
02-01-77
02-11-77
03-08-77
03-28-77
04-04-77
06-15-77
06-21-77
06-29-77
08-09-77
10-03-77
10-04-77
10-12-77
10-13-77
10-18-77
10-19-77
10-20-77
10-21-77
10-25-77
10-26-77
11-01-77
11-03-77
11-08-77
Freon
extractables
ppm
1300
864
3771
4973
3110
1075
7164
2004
5178
2300
1934
1326
1850
1414
3253
3058
1230
2451
848
2980
870
2472
492
Anionic
Turbidity surfactants
NTU ppm
880
1200
3300 250
3800
1600 75
1250
3250
920
2700
970 70
2700
2200
2400
1900
4300
5500
1750
3000
1100 224
3500 247
1150 121
3300 285
520 108
PH
9.4
7.3
9.1
9.1
9.6
9.0
10.2
7.8
8.0
8.1
9.5
10.1
10.0
9.6
9.4
9.8
9.3
9.6
10.1
10.0
10.1
10.6
10.3
Conductivity
;ifl~l cm~l
870
1040
1090
3000
1100
950
1080
840
700
940
1600
850
900
1500
800
870
850
480
610
500
900
1420
800
(continued)
-15-
-------
TABLE 2. (continued)
Date
11-10-77
11-22-77
11-23-77
12-13-77
12-15-77
12-19-77
12-20-77
01-09-78
01-10-78
01-11-78
01-12-78
01-13-78
01-16-78
01-17-78
01-18-78
01-19-78
01-20-78
01-26-78
01-30-78
01-31-78
02-01-78
02-02-78
Freon
extractables
ppm
700
708
313
624
591
375
664
736
2369
1045
1450
704
825
557
586
1205
3328
3230
622
2300
1600
1250
Anionic
Turbidity surfactants
NTU ppm
800
1200
310
650
550
300
450
800
2900
1200
1700
900
900
550
560
1100
2000
4500
600
2000
1900
1500
206
150
130
180
170
120
90
170
120
90
95
160
95
70
280
-
-
-
-
-
-
Conductivity
pH yfl"1 cm"1
4
10.0 1250
9.6 620
9.9 560
10.2 780
11.4 3300
10.3 750
10.3 800
9.9 1000
10.2 1350
10.2 1400
9.6 1100
9.8 1040
10.2 1200
10.2 1340
10.1 1050
9.7 1220
9.9 1280
9.8 750
9,. 6 650
9.2 750
9.7 750
9.9 900
(continued)
-16-
-------
TABLE 2. (continued)
Date
02-14-78
02-15-78
02-16-78
02-20-78
02-21-78
02-22-78
02-23-78
02-24-78
02-25-78
02-26-78
02-27-78
02-28-78
03-01-78
03-02-78
03-03-78
03-09-78
03-10-78
03-13-78
03-14-78
03-15-78
03-16-78
03-17-78
03-20-78
Freon
extractables
ppm
745
1004
2544
1725
1708
1331
5388
4984
3154
2050
1260
1117
1071
2538
1270
935
1296
1956
1444
3315
1342
1200
900
Anionic
Turbidity surfactants
NTU ppm
640
1300
2600
1750
2200
1750
5200
4900
5300
2400
1150
950
1200
2000
1150
1000
1200
1500
800
1900
1200
1300
750
-
100
40
60
45
130
150
90
90
40
25
30
35
45
50
60
55
35
60
45
50
-
PH
8.4
8.3
8.5
9.2
9.4
9.1
8.9
8.0
8.0
7.5
8.2
8.8
8.7
8.5
8.6
8.6
8.9
9.2
9.2
9.2
9.2
9.0
8.6
Conductivity
yfT1 cm"*
650
650
660
750
1000
950
850
850
950
750
750
1450
700
750
770
680
950
880
1000
1150
1050
780
600
(continued)
-17-
-------
TABLE 2. (continued)
Date
03-21-78
04-06-78
04-11-78
04-12-78
05-02-78
05-03-78
05-04-78
05-05-78
05-11-78
05-23-78
05-24-78
05-25-78
X
ff
Freon
extractables
ppm
970
826
1305
1102
968
1526
1217
2230
1186
1361
3218
3842
1822
1370
Turbidity
NTU
1100
620
1400
780
720
770
870
1600
1000
1400
2900
4200
1780
1280
Anionic
surfactants
ppm
-
50
70
40
35
40
30
45
30
45
80
90
102
70
Conductivity
pH pfl"1 cm"1
8.4
9.9
9.8
10.3
10.6
10.1
10.3
10.0
10.4
9.7
9.5
10.4
9.3
1.4
600
950
860
900
1000
1050
1080
860
850
740
800
1200
963
469
-18-
-------
the maximum 5500 NTU. The turbidity correlates relatively well with Freon
extractables with a correlation coefficient of 0.79.
Anionic Surfactant
The surfactants in the wastewater are mainly petroleum sulfonates (sodium salt)
and carboxylates which are used to stabilize the oil-in-water emulsion and in washing
operations. The average concentration of the anionic surfactants was 102 ppm with a
standard deviation of 70 ppm. The maximum value was 285 ppm and the minimum 25
ppm.
The pH of the plant wastewater varied between 7.3 and 11.4. The average pH was
9.3 with standard deviation of 1.4.
Conductivity
The conductivity of the wastewater varied between 480 and 3300 y mho/cm.
The average conductivity was 963 ij mho/cm.
Dissolved Solids
The dissolved solids are comprised mainly of the inorganic salts in the wastewater.
The dissolved solids, which contribute to the conductivity of the effluent, ranged
between 750 and 1160 ppm and averaged 1000 ppm for the few runs analyzed.
Suspended Solids
The suspended solids, comprised of dirt, fine metallic particles, scum, paper
particles, etc., ranged between 300 and 460 ppm. The suspended solids tend to stick to
the walls of pipes, flowmeter and pumps eventually leading to reduced and inconsistent
flow rates
OPERATING PARAMETERS
The operating parameters which were monitored and controlled during the
experimental runs are current, flow rate, pH, and type and concentration of salt. These
parameters were adjusted according to the influent compositions with the major
objective of obtaining an effective treatment at a minimum cost and with the
generation of a sludge with as little iron content as possible. A second objective was to
assess the influence of these variables on treatment effectiveness. The operating
conditions of the experimental runs conducted in the program are presented in Table 3
along with the quality of the treated effluent.
Current
The current has the most pronounced effect on the treatment of the oily
wastewater. It is also the most convenient variable to control. For a given influent
composition and flow rate the current determines the rate of iron dissolution (assuming
no anodic passivation) and, thereby, the ratio of iron to oil. Throughout this program
-19-
-------
TABLE 3. SUMMARY OF OPERATING CONDITIONS AND EFFLUENT QUALITY
Influent
Freon
Flow
extractables rate
Date ppm 1/mln
12-16-76
02-01-77
02-11-77
03-08-77
03-28-77
04-04-77
06-15-77
06-21-77
06-29-77
08-09-77
10-03-77
10-04-77
10-12-77
10-13-77
1300
864
3771
4973
3110
1075
7164
2004
5178
2300
1934
1326
1850
1414
3.8
3.8
1.9
1.9
3.8
3.8
1.9
3.8
3.8
3.8
3.8
3.8
3.8
3.8
Operating conditions
Salt
concentration Current
Normality pH amp
0.01N
NaCl
ii
»
0.02N
CaCl2
0.01N
NaCl
0.01N
CaCl2
"
0.01N
NaCl
0.01N
C«C12
"
ii
ti
n
»
8.1
7.0
7.3
8.3
7.8
7.3
6.9
7.5
6.9-
7.0
7.0
6.8
7.0
9.0
35
20
35
35
35
25
35
35
25
25
30
30
30
30
Conduc-
Voltage tivity
volt ufl"1 cm"1
18
8
13
12
10
11.5
12
11
11
16
6
8
8
8
1750
2200
2200
1650
2200
1900
2100
2200
1600
2000
2800
2000
2000
2000
Freon
extrac-
tables
PPn
22
-
230
16
8
5
71
18
11
10
281
5
-
_
Effluent quality
Tr.rbidity
NTU
5
330
170
2
115
1
110
8
12
7
570
3
650
440
Dissolved
Surfactant solids
ppm ppm
-
-
20 1480
— mm
-
— _
1
-
1200
-
_
(continued)
-------
TABLE 3. (continued)
Influent
Freon
extractables
Date ppm
10-18-77
10-19-77
10-20-77
i 10-21-77
(X)
*•" 10-25-77
10-26-77
11-01-77
11-03-77
11-08-77
.11-10-77
11-22-77
11-23-77
12-13-77
12-15-77
3253
3058
1230
2451
848
2980
870
2472
492
700
708
313
624
591
Flow
Operating conditions
Salt
rate concentration Current Voltage
1/min Normality pH amp volt
3.8
1.9
3.8
3.8
1.9
3.8
3.8
1.9
3.8
3.8
3.8
3.8
7.6
1.9
0.01N
CaClo
it
11
.01N
NaCl
.01N
NaCl
.01N
CaCln
11 *
11
it
ii
0.01N
CaCl2
"
ii
0.02N
CaClo
6.8
6.2
6.8
6.8
6.7
7.5
9.8
9.6
10.1
9.7
9.4
9.6
9.9
11.3
35
35
30
35
35
35
20
30
30
25
20
20
30
35
14
16
16
16
14
18
12
12
14
14
12
14
13
11
Conduc-
tivity
pfl""1 cm~l
1700
1750
1430
1450
1900
1580
1450
1690
1400
1400
1500
1250
1350
3400
Freon
extrac-
tables
ppn,
_
15
16
286
35
9
61
13
13
8
11
6
190
145
Effluent quality
Dissolved
Turbidity Surfactant solids
NTU ppm ppm
390
9
9
440
40
8
110
14
2
2
1
1
90
140
_ -
1180
1610
_ _
1000
1260
930
980
990
880
1070
1220
1080
90 2020
(continued)
-------
TABLE 3. (continued)
I
Is)
Influent
Freon
extractables
Date ppm
12-19-77
12-20-77
01-09-78
01-10-78
01-11-78
01-12-78
01-13-78
01-16-78
01-17-78
01-18-78
01-19-78
01-20-78
01-26-78
01-30-78
375
664
736
2369
1045
1450
704
825
557
586
1205
3328
3230
622
Flow
rate
1/min
3.8
3.8
3.8
3.8
3.8
3.8
1.9
3.8
3.8
3.8
3.8
3.8
3.8
Operating conditions
Salt
concentration Current Voltage
Normality pH amp volt
0.01N
CaCl2
,'•
ti
ii
ii
it
ii
0.005N
CaCl2
0.01N
CaCl2
ii
0.01N
CaCl2
10.1
9.7
9.3
9.6
9.8
9.6
9.3
9.8
9.9
9.6
9.4
Pump Failure
9.0
8.7
30
25
25
35
35
30
12
20
10
10
20
30
15
14
14
13
14
14
12
13
9
6
5
9
17
6
Conduc-
tivity
1300
1220
1400
1700
1850
1600
1650
1650
1400
1780
1500
1350
1400
Freon
extrac-
tables
ppn
7
7
14
122
31
8
14
12
32
9
27
-
10
Effluent quality
Dissolved
Turbidity Surfactant solids
NTU ppm ppm
1 20 920
6 12 780
4 — —
215
4 - -
10
3
4
13
4
8 - -
110 -
5
(continued)
-------
Influent
Freon
extractables
Date ppm
01-31-78
02-01-78
02-02-78
02-14-78
M 02-15-78
i
02-16-78
02-20-78
02-21-78
02-22-78
02-23-78
02-24-78
02-25-78
02-26-78
02-27-78
2300
1600
1250
745
1004
2544
1725
1708
1331
5308
4984
3154
2050
1260
Flow
rate
1/min
3.8
3.8
3.8
3.8
3.8
3.8
3.8
3.8
3.8
1.9
1.9
3.8
3.8
Operating conditions
Salt
concentration
Normality pH
0.01N
CaCl2
"
ii
"
»
ii
0.01N
Nad
0.01N
CaCl2
"
ii
0 . 02N
CaCl2
0.01N
CaCl2
It
8.4
8.6
9.2
8.2
8.1
8.2
9.3
9.3
9.1
8.0
7.2
*Pn*im
6.7
8.0
Current
amp
30
30
25
20
30
35
35
35
35
30
30
r allure — —
25
25
Conduc-
Voltage tivity
volt ufl'1 cm~l
16
12
15
9
13.5
17
J.1
12
12
9
11
19
22
2000
1400
1400
1450
1200
1300
1850
1950
1900
1600
2500
1720
1550
Effluent quality
Freon
extrac-
Dissolved
tables Turbidity Surfactant solids
ppm NTU ppm ppn
10
18
8
4
8
15
_
36
37
20
5
7
8
7 1
5
5
4
3
3
140
150
90
13
8
___«._M__Pttmn 1?d~f 1 tit*
__.«._«»«j-mjj^ ^ OAJUJH.
5
8
_
-
-
-
-
850
_
-
1810
-
1760
-
-
(continued)
-------
TABLE 3. (continued)
i
N)
Influent
Freon Flow
extractables rate
Date ppm 1/min
02-28-78
03-01-78
03-02-78
03-03-78
03-09-78
03-10-78
03-13-78
03-14-78
03-15-78
03-16-78
03-17-78
03-20-78
03-21-78
04-06-78
1117
1071
2538
1270
935
1296
1956
1444
3315
1342
1200
900
970
826
3.8
3.8
3.8
3.8
3.8
1.9
3.8
3.8
3.8
1.9
3.8
3.8
3.8
Operating conditions
Salt
concentration Current Voltage
Normality pH amp volt
0.01N 8.6
CaCl?
" 8.5
8.1
8.2
" 7.8
8.0
8.5
8.5
11 8.0
" 8.2
—————Pump Failure — —
0.01N 8.2
CaCl2
8.0
" 9.2
25
25
25
35
15
12.5
20
10
25
10
20
20
20
25
39
27
27
7
6
8
5
10
5
12
13
10
Conduc-
tivity
ufl""l c«~l
1800
1470
1800
1670
1560
1680
1520
1760
1850
1650
1650
1400
1650
Freon
extrac-
tables
ppm
11
4
10
17
10
15
7
14
15
8
18
-
12
Effluent quality
Dissolved
Turbidity Surfactant solids
NTU ppm ppm
4
2
7
12
4
43
6
5
37
5 _
12
60
7
1520
1860
1420
1640
-
910
1290
1390
1250
890
.
-
-
(continued)
-------
TABLE 3. (continued)
i
N>
Influent Operating conditions
Freon Flow Salt
extractables rate concentration Current
Date ppm 1/min Normality pH amp
04-11-78
04-12-78
05-02-78
05-03-78
05-04-78
05-05-78
05-11-78
05-12-78
05-23-78
05-24-78
05-25-78
X total
X CaCl2
1305 3.8 0.01N
CaCl2
1102 3.8 "
968 3.8 "
1526 3.8 "
1217 3.8 "
2230 3.8 "
1186 3,8 "
Batch of
05-11-78 3.8 "
1361 3.8 "
3218 3.8 "
3842 3.8 "
8.8
8.5
8.4
8.3
8.4
8.5
9.0
9.0
8.7
8.7
9.1
20
20
20
20
35
35
35
35
70
35
35
Freon
Conduc- extrac-
Voltage tiyity tables
volt yfl~* co~l ppm
11 1450
11 1400 13
13 1350 17
13 - 104
19 1450 22
17 - 32
20 1500
22 - 12
20 - 69
11 1600 25
12 1500 28
35
27
Effluent quality
Turbidity
NTU
9
68
30
340
120
120
6
14
65
8
30
70
60
Dissolved
Surfactant solids
ppm ppm
890
-
-
-
-
-
-
-
-
1257
-------
current adjustment was primarily relied upon to obtain effective treatment. Only with
difficult-to-treat batches, where maximum operating current was not sufficient at the
usual flow rate of 3.8 1/min, were other parameters such as flow rate or salt
concentration adjusted. Maximum operating current is limited by the onset of excessive
oxygen evolution at the^inode at the expense of iron dissolution. This occurs at current
density of 10 mA/cm _ of projected electrode which for the exposed electrode
dimensions used (3820 cm ) corresponds to 38 A.
In this program the current ranged between 10 and 35 A. The current used in each
case was the minimum required to break the emulsion as determined by visual
observation of the change in turbidity. Usually the flow rate was at the design value of
3.8 1/min, however, in several cases the flow rate was reduced to 1.9 1/min resulting in
an equivalent current of twice that for standard conditions.
The average current required for effective treatment was 31.5 A (adjusted to 3.8
1/min) with standard deviation of 15.6 A. Generally, the required current was found to
increase with the influent oil concentration. But as mentioned previously the proper
setting of the current for effective treatment was determined by a beaker test.
The beaker test was found to be useful because our experience at the Livonia
Transmission Plant has shown that knowledge of the concentration of oil and surfactants
in the wastewater may not always be sufficient to establish the proper operating
conditions, since other unidentified components in the plant wastewater may effect the
performance of the electrolytic cell. Therefore, simple correlations, which would
predict the setting of the operating parameters with certainty based on influent
properties, could not be established. While this situation may be true at the Livonia
Transmission Plant where wastewater is received from a large number of diversified
operations, it is likely that in other plants, where the composition of wastewaters
remains fairly constant, simple correlations could be established. In any event, a
feedback control based on effluent quality may be feasible. This is discussed in a later
section.
Operating Voltage
The voltage across the electrode was found to depend on the current, the
conductivity of the wastewater, and the extent of anodic fouling. Generally, the
voltage varied between 5 and 30 volts and averaged 13 volts. In some instances the
operating voltage increased to 4-0 volts or more due primarily to anode fouling. In these
cases the tests were stopped and corrective measures were taken to reduce the voltage
to normal levels. A detailed discussion of voltage increase is presented later in
conjunction with the durability studies.
Based on the data of current and voltage, the average electrical energy
consumption fpr the electrolytic dissolution of iron was calculated to be 5.76 M3/m
(1.6 kW-hr/m ; 6 kW-hr/1000 gal) of wastewater for the range of oil concentrations
encountered. The calculation was based on the use of 0.01N CaCl and flow rate of 3.8
1/min.
pH Effects
To study the influence of pH on the performance of the electrolytic cell two sets
of experiments were conducted. One set of experiments was conducted to determine
-26-
-------
the influence of pH on the rate of iron dissolution, the other to compare the
performance of the electrolytic cell with and without pH adjustment of the influent.
To study the effect of pH on the rate of electrolytic dissolution of iron the cell
was filled with clean tap water and the pH adjusted to a desired value. The electric
power was turned on at a specified current and the water recirculated in the cell. The
concentration of iron in the water was determined hourly over a period of 5 hours. The
data were used to calculate the rate of iron dissolution in ppm/hr. The results
presented in Table *, show that pH does not affect the rate of electrolytic dissolution of
iron. It should be noted that this is true only as long as the cell operates below the
limiting current density.
TABLE 4. IRON DISSOLUTION RATE
Iron dissolution rate
pH ppm/hr
6
10
25 amp
15
15
35 amp
21
19
To evaluate the influence of pH on the performance of the electrolytic cell, large
batches of wastewater were collected in the storage tank. Each batch was treated in
the electrolytic cell with and without pH adjustment, while maintaining other operating
parameters constant. A direct comparison of the Freon extractables is shown in Table 5
along with detailed operating conditions. These runs indicate that pH adjustment may
not be necessary for effective treatment of the plant wastewater. Subsequent
experimental runs have, in fact, shown that the electrolytic cell performs well without
adjusting the pH of the influent, which simplifies and reduces the cost of the process.
Salt Effects
The main purpose of salt addition is to avoid passivation of the iron chips and
increase the conductivity of the wastewater, thereby reducing power consumption. In
addition, the type and concentration of salt influences the effectiveness of the
electrolytic treatment. It is known, for example, that bi- and tri- valent salts, because
of their high ionic strengths, are much more active in destabilizing and breaking
emulsions than mono-valent salts (8). An increase in concentration also affects
emulsion breaking.
In this program two salts were evaluated: sodium chloride and calcium chloride.
Sodium chloride is preferable economically, however, calcium chloride is preferable
with respect to treatment effectiveness. This feature is particularly noticeable with
batches of wastewater which are difficult to treat electrolytically.
Most of the runs listed in Table 3 were done with CaCl-. In a few cases, NaCl
permitted fairly adequate treatment. In cases where it did not, the full run was not
made with NaCl, but with CaCl-.
-27-
-------
Freon Arilgnle surfactant
extractables Salt
before concentration % of
treatment Freon
PPm N ppm extractables pH
2980 CaCl2, 0.01 N 247 8.3 7.5
10
870 CaCl2, 0.01 N 121 13.9 7.1
10
i
iv» •
00
' 2472 CaCl2, 0.01 N 285 11.5 Z.I
9.6
492 CaCl2, 0.01 N 108 22.0 10
700 CaCl2, 0.01 N 206 29.4 7.2
9.7
664 CaCl2, 0.01 N 90 13.5 10.3
7.0
Flow
rate
1/mln
3.8
3.8
3.8
3.8
1.9
1.9
3.8
3.8
3.8
3.8
3.8
Current
amp
35
35
35
20
30
30
30
25
25
25
25
Voltage
volt
18
20
21
12
15
12
14
19
14
14
13
Turbidity
NTU
8
5
135
110
10
14
4
11
6
6
3
Freon
extractables
ppm
9
18
210
61
13
13
14
10
8
7
9
-------
Electrolytic treament of plant wastewater in a 1-liter beaker has also shown the
superiority of CaCl2. For example, a batch of 2-21-78 could not be broken after 18.5
minutes at 0.5 A using 0.01N NaCl but with 0.01N CaCl2 an effective treatment
resulted within 16 min. In another beaker study (2-23-78) it took W minutes at 0.5 A to
break the emulsion using 0.01N NaCl, but with 0.0IN CaCl2 it took only 24 minutes.
Laboratory tests have shown that CaCU, FeS
-------
|l50
CO
Ul
ffi
?
o
g; 100
X
UJ
1
U.
K- 5O
UJ
ID
•
_J
U.
U.
Ul
n
A
—
INFLUENT OIL CONCENTRATION
_ O 700 ppm
A A 4770 ppm
o
A 0
A 0
A ° 0
1 1 I
0.05 0.1 0.15
DISSOLVED IRON/ INFLUENT OIL
0.2
Figure 7. Effect of iron to oil weight ration on effluent oil content
-30-
-------
transmission fluid additives may tend to enhance the emulsion stability or selectively
adhere to or react with the iron rendering it less active.
The presence of small amounts of bacteria does not significantly influence the
operation of the electrolytic cell; however, if the wastewater is allowed to stand, it will
turn rancid with the formation of hydrogen sulfide and the generation of a biological
growth. This resulting wastewater is more difficult to treat than the original since
hydrogen sulfide presumably precipitates some of the iron as iron sulfide. Also, the
Freon extractable value may be in error as to the concentration of oil because the
Freon-water interface is virtually non-existant.
Turbidity
The turbidity of the electrolytically treated and sand filtered wastewater ranged
between 1 and 650 NTU and averaged 60 NTU (excluding NaCl runs and the 7.6 1/min
run). The turbidity results from remaining emulsified oil and fine suspended particles
(mostly iron hydroxide). The turbidity was found to have a positive correlation with
Freon extractables with a correlation coefficient of 0.88. As will be discussed later on
this feature may be used for automatic feed back control.
Surfactants
The concentration of anionic surfactants in the treated water ranged between 1
and 90 ppm. When the treatment was effective the concentration of surfactants was 20
ppm or less. Higher concentrations, accompanied by foaming in the cell, were observed
when the treatment was only partially effective.
BOD
A few tests of biological oxygen demand (BOD) indicated that 5 day BOD value of
the treated wastewater is about 90 ppm.
Dissolved Solids
The effluent dissolved solids varied between 780 and 2020 ppm. The average was
1257 ppm with standard deviation of 346. The process adds a maximum of 550 ppm to
what is present in the influent. By comparison, conventional methods with chemicals
generally add about 2,000-3,000 ppm of dissolved solids.
Suspended Solids
Prior to the use of the dissolved air flotation unit or sand filter the suspended
solids, comprised mainly of iron hydroxide, ranged between 600 and 2240 ppm. It was
observed that the concentration of suspended solids depends on the floating ability of
the iron hydroxide-air sludge. In most cases the oily sludge, generated when treating
actual plant wastewater, did not float well without forced flotation.
When the dissolved air flotation unit was used to force flotation of the sludge the
concentration of suspended solids in the processed wastewater ranged between 25 and
135 ppm. Sand filtered wastwater had a negligible amount of suspended solids. This
will be discussed in more detail later in the report.
-31-
-------
DURABILITY STUDIES
The objectives of the durability studies were to evaluate the performance of the
cell under uninterrupted-continuous operation, to identify any operational problems, and
to alleviate any potential problem areas.
The durability tests were conducted as follows: About 5.6 m (1500 gal) of
wastewater were pumped into the storage tank and analyzed for pH, conductivity,
turbidity, Freon extractables, and anionic surfactants. In addition, a 1 liter sample of
the wastewater was treated electrolytically at an iron chip anode in a beaker to
determine the initial setting of the operating conditions. The procedure for the beaker
test is described in the Experimental section.
During the durability test the treated wastewater was analyzed for pH,
conductivity, turbidity, and Freon extractables, and the operating conditions were
adjusted for minimum iron and minimum sludge formation. Minor maintenance work,
which did not disrupt the test, such as the addition of iron chips and brushing between
the electrodes, was also performed. 3V hen the supply of wastewater in the storage tank
was low, a new batch of about 5.6 m was pumped to the storage tank. In this manner,
the electrolytic cell operated 24 hours a day without interruption.
During the program period five durability tests have been conducted. Each test
started with new iron chips and clean electrodes. The results of the five durability tests
are presented in Tables 6 thru 10. These results show that, when the electrodes are
kept clean, the electrolytic cell provides efficient treatment. Also encouraging is the
fact that the rise in the operating voltage is not as rapid as was experienced in the first
part of the program with interrupted runs.
The major operational problem is the accumulation of oily sludge in the anodic
chip cage and in the space between the anode and cathode which restricts the flow of
wastewater through the electrodes. Eventually, the electrodes become completely
blocked, the influent flows over the iron chips, and the performance of the cell
decreases substantially.
It was found that brushing and purging with air between the electrodes to remove
the accumulated sludge alleviates this problem temporarily. To date we were able to
operate the cell continuously up to 14 days.
First Durability Test
The first durability test is summarized in Table 6. The test lasted 11 days and
used about 60 m (16,000 gal) of wastewater. Throughout the test the space between
the electrodes was brushed several times a day to reduce the rate of sludge
accumulation. After 11 days the test was discontinued because of excessive
accumulation of sludge which blocked the flow of wastewater through the anode.
Second Durability Test
The test, summarized in Table 7, continued for 8 days and consumed about 27 m
(7200 gal) of wastewater. As in the first test frequent brushing between the electrodes
was necessary to avoid rapid sludge accumulation in the electrodes, and the test was
stopped for similar reasons.
-32-
-------
TABLE 6, SUMMARY OP FIRST DURABILITY TEST
V
Influent CaCl_
oil con- concen-
centration tration
Date
1-09-78
1-10-78
1-11-78
1-12-78
1-13-78
Time ppm
1
8
10
2
8
10
2
8
9
3
10
2
:00pm 736
: 00am "
:00am 2369
: 30pm "
: 00am "
:00am 1045
:40pm
: 00am "
:00am 1450
: 00pm "
:00am
:00pm 704
0
0
0
0
0
0
0
0
0
0
0
0
N
.01
.01
.01
.01
.01
.01
.01
.01
.01
.01
.01
.01
Flow
rate
pH 1/min
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9
6
6
6
8
8
8
8
6
6
6
3
3
3
3
3
3
3
3
3
3
3
3
1
.8
.8
.8
.8
.8
.8
.8
.8
.8
.8
.8
.9
Current
amp
25
25
35
35
35
35
35
35
30
30
30
12
Freon
extract-
Voltage Turbidity ables
volt NTU
25
14 4
14.5
13 10
14 215
14
14 16
14 5
12
13 8
12 10
13 3
ppm Comments
Beginning of test.
14 Water level 1.3 cm higher upstream
of electrodes. No sludge
floating.
- Operating conditions adjusted for
new batch.
-
122 Water level 1.9 cm higher upstream of
electrodes and overflowing chips.
% cell covered with floating
sludge.
New batch of wastewater. Space
between electrodes cleaned with
brush to stop flow over chips.
Water level equal on both sides
of electrodes.
31 Water level 2.2 cm higher upstream
Electrodes cleaned with brush.
- Operating conditions adjusted for
new batch.
7
8
Operating conditions adjusted for
running unit unattended through
the weekend.
(continued)
-------
TABLE 6. (continued)
I
f
Influent
oil con-
CaCl2
c oncen-
centration tratlon
Date
1-16-78
1-17-78
1-18-78
1-19-78
Time
8: 00am
10: 30am
3: 00pm
3: 20pm
8: 00am
3: 00pm
8: 30am
3: 00pm
8: 30am
3: 00pm
ppm
704
825
it
it
11
557
it
586
M
1205
0
0
0
0
0
0
0
0
0
0
_N
.01
.01
.01
.01
.01
.005
.005
.01
.01
.01
£tL
9.3
9.8
9.8
9.8
9.8
9.9
9.9
9.6
9.6
9.4
Flow
rate Current
1/mln
1.9
3.8
3.8
3.8
0.8
3.8
3.8
3.8
3.8
3.8
amp
12
20
20
15
15
10
10
10
10
20
Voltage
volt
13
10
9
6.5
8
6
5
5
5
9
Turbidity
NTU
9
-
4
4
-
13
33
•38
4
8
Freon
extract-
ables
ppm
14
-
12
—
_
32
38
28
9
27
Comments
Water level 3.2 cm higher upstream
Brushed between electrodes.
Washed chips and added some
fresh chips
Conditions adjusted for new batch.
iQ
Reduced current due to excess FeTJ.
Pump slowed up during night.
Water level 1.9 cm higher upstream
White foam on water surface.
No floating sludge.
Electrodes were brushed.
1-20-78 l:00pm 3328
0.01 9.9 1.9
15
Operating conditions adjusted for
unattended run through weekend.
1-23-78 Pump failed during weekend. Test stopped.
-------
TABLE 7. SUMMARY OF SECOND DURABILITY TEST
Influent
oil con-
CaCl2
concen-
centration tration
Date
1-26-78
1-27-78
1-30-78
1-31-78
2-01-78
2-02-78
2-03-78
Time
10: 00am
2 i 00pm
9: 00am
2: 30pm
8: 00am
3: 00pm
9:00»m
4 : 00pm
8: 20am
3: 30pm
8: 30am
3 : 30pm
8: 30am
1 : 00pm
2: 00pm
ppm
3230
It
II
ft
It
622
II
2300
ft
1600
ii
1250
ti
H
N
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0 -01
0 .01
0 .01
Experiment stopped
£H_
9.0
9.0
9.0
9.0
8.7
8.7
8.4
8.4
8.6
8.6
9.2
9.2
9.2
to
Flow
rate Current Voltage Turbidity
1/min
3.8
3.8
3.8
1.9
3.8
3.8
3.8
3.8
3.8
3.8
3.8
3.8
3.8
improve
amp
30
30
30
15
15
15
30
30
30
30
25
25
25
electrodes
volt
10
10
17
6
6
6
13
17
12
12
16
18
15
design.
NTU
_
12
110
90
18
5
10
7
4
5
60
180
5
Freon
axtract-
ables
ppm Comments
Beginning of test.
Floating sludge over 80% of cell.
Electrodes cleaned with brush.
Operating conditions adjusted for
run through weekend.
Flow of wastewater to cell stopped
during the weekend because of
pump instability.
Test continued with a new batch.
10 Water level higher upstream of
anode. Electrodes brushed.
8
10 Water level higher upstream.
Brushed electrodes. Added some
iron chips
30 Electrodes brushed every 3 hours.
18 Water level 1.9 cm higher upstream of
electrode. Brushed between
electrodes.
- Electrodes brushed hourly.
Wastewater flows over iron chips.
Brushed between electrodes.
8 Electrodes brushed hourly.
-------
TABLE 8. SUMMARY OF THIRD DURABILITY TEST
Influent
oil con-
CaCl2
concen-
centration tration
Date
2-14-78
2-15-78
2-16-78
2-17-78
Time
10: 15am
3 : 00pm
8: 30am
11: 30am
8: 00am
10: 30am
3: 00pm
8: 00am
ppm
745
ii
»
1004
it
2544
it
ii
0
0
0
0
0
0
0
0
N
.01
.01
.01
.01
.01
.01
.01
.01
pH
8.0
8.2
8.5
8.1
8.1
8.4
8.2
8.2
Flow
rate Current
1/min
3.8
3.8
3.8
3.8
3.8
3.8
3.8
3.8
amp
15
20
20
25
30
25
35
35
Voltage
volt
8
9
11
14
14
11.5
17
17
Freon
extract-
Turbidity ables
NTU
_
4
3
—
3
-
3
3
Ppm
_
4
5
"•
8
-
14
15.4
Comments
Beginning of test.
A new batch
A new batch
Test stopped because of excessive
deposits on cathode.
-------
TABLE 9. SUMMARY OF FOURTH DURABILITY TEST
Influent
oil con-
CaCl2
concen-
centration tration
Date
2-23-78
2-24-78
2-25-78
2-26-78
2-27-78
2-28-78
3-01-78
3-02-78
Time
l:00pm
3: 15pm
8: 15am
11 : 30am
9 : 30am
11 : 30am
8: 00am
2: 00pm
8: 00am
12 : 30pm
3 : 30pm
10: 30am
12 : 30pm
3: 30pm
8: 30am
1 : 00pm
3: 30pm
10: 00am
l:20pm
3: 15pm
ppm
5388
11
ii
4984
If
3154
ti
2050
„
1260
II
II
1117
11
1117
1071
11
„
2538
tl
N
0.01
0.01
0.001
0.02
0-02
0.02
_
0.01
0.01
0-01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
o.oi
0.01
0.01
pH
8.3
8.0
8.2
8.0
7.2
8.0
^
7.5
6.7
8.1
6.7
6.4
8.6
8.6
8.6
8.5
8.6
6.8
7.8
8.1
Flow
Freon
extract-
rate Current
1/min
1.9
1.9
1.9
1.9
1.9
1.9
_
3.8
3.8
3.8
3.8
3.8
3.8
3.8
3.8
3.8
3.8
3.8
3.8
3.8
amp
35
30
30
30
30
30
«.
25
25
20
25
25
25
25
25
25
25
16
25
25
Voltage
volt
11
9
17
20
11
12
mm
12
19
14
18
22
23
25
25
30
39
44
17
17
Turbidity
NTU
_
13
560
—
8
-
1
—
5
-
13
8
14
5
4
-
2
7
10
2
ables
ppm
_
20
-
—
5
—
-
•~
7
-
16
8
-
13
11
-
4
13
-
5
Comments
Beginning of test.
CaCl2 flow rate decreased overnight
A new batch
Electrodes brushed
New batch
Flow rate slowed to 0.4 1/min
A new batch
Electrodes purged with air and
brushed.
New batch
Electrodes purged with air
New batch
Electrodes purged with air
New batch
Electrodes purged with air
Overvoltage. Electrodes brushed and
purged with air. Iron chips worked
Kith tap water. Added more chips.
New batch
(continued)
-------
OO
1
3-04-78
TABLE 9. (continued)
Date Tiflw^
3-03-78 8: 15am
l:00om
3
:15pm
Influent
oil con-
centration
ppm
2538
1270
ii
Ca
Cl->
concen-
tration
N
0
0
0
.01
.01
.01
pH
7.0
8.2
8
.0
Flow
rate
JL/JBin
3.8
3.8
3.8
Freon
extract
Current
amp
25
25
35
Voltage
volt
27
27
27
Turbidity
NTU
7
7
12
ables
ppm Comments
10.3 Electrodes purged with air
New batch
17
9:00am
0.01
8.0 3.8
22
44
Water overflowing electrodes.
Overvoltage. Test stopped.
-------
TABLE 10. SUMMARY OF FIFTH DURABILITY TEST
Influent
oil con-
CaCl2
c oncen-
centration tration
Date
3-09-78
3-10-78
3-11-78
3-12-78
3-13-78
3-14-78
3-15-78
3-16-78
3-17-78
Time
l:00pm
3: 30pm
11: 00am
3: 15pm
9: 00am
10 : 30am
8 : 20am
12: 50pm
3 : 00pm
8: 00am
12: 20pm
3: 00pm
11: 00am
1 : 40pm
8: 00am
2 : 30pm
10: 00am
3: 45pm
ppm
935
ii
ii
1296
II
II
II
1956
"
M
1444
II
It
3315
11
1342
II
1200
N
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
o.oi
0.01
0.01
_
0.01
£«
7.8
7.8
7.0
8.4
8.0
7.2
6.9
8.7
8.5
7.7
8.5
8.2
7.3
8.3
8.0
8.2
8.2
8.5
Flow
rate
1/min
3.8
3.8
3.8
1.9
1.9
1.9
1.9
3.8
3.8
3.8
3.8
3.8
3.8
3.8
3.8
1.9
—
1.9
Current
amp
20
15
15
7.5
8
12.5
15
20
20
20
10
10
10
20
25
10
10
10
Voltage
volt
10
6
7
4
3.5
6
6
7
8
7
4
4.5
4.5
9.5
9.5
5.5
5.5
4
Freon
extract-
Turbidity ables
NTU
_
1
4
12
27
43
14
18
8
6
15
5
6
6
37
28
5
-
ppm
-
9.5
-
29
15
10.3
-
3.4
7
-
14
8.6
—
15
—
8
-
Comments
Beginning of test.
Electrodes purged with air.
New batch.
Electrodes purged with air.
Electrodes purged with air.
New batch.
Electrodes purged with air.
New batch.
Electrodes purged with air.
New batch.
Wastewater supply pump failed.
Cell shut down temporarily.
New batch.
Flow rate slowed to 0.8 1/min over
New batch. Cell set to run ni*i&£
3-20-78
9:00am
8.2
10
unattended during weekend
Pumps failed. No flow to cell.
Electrodes brushed and purged with
air.
(continued)
-------
TABLE 10. (continued)
3-20-78
3-21-78
3-22-78
3-23-78
Influent
oil con-
centration
Time ppm
3: 00pm 900*
8: 30am "
2: 00pm "
4: 00pm 970
8: 30am "
3: 00pm 2050
8: 30am "
CaCl2
concen-
tration
N
0.01
-
0.01
0.01
0.01
0.01
0.01
pH
8.2
8.1
8.2
8.0
6.4
8.6
8.4
Flow
rate Current
1 /ruin amp
3.8
-
3.8
3.8
3.8
3.8
3.8
20
20
20
20
20
35
35
Freon
extract-
Voltage Turbidity ables
volt NTU ppm
13
11
12
12.5
13
23
32
-
1
12
3
60
90
2
-
5
18
9
-
5
New batch.
Flow rate
overnight.
Electrodes
New batch.
Electrodes
New batch.
Flow rate
Comments
slowed to 1.9
purged with
purged with
slowed to 2.3
1/min
air.
air.
1/min
.
Test stopped — long weekend.
-------
The first two durability tests demonstrated that the accumulation of oily sludge in
the anodic chip cage and in the space between the two electrodes can be a major
operational problem. To reduce the rate of sludge accumulation in the space between
the anode and cathode, the electrodes were redesigned. The cathode, which in the past
extended above the water level, was shortened to about one centimeter below the water
level to allow the oily sludge to float over it. In addition, pressurized air is bubbled in
the space between the electrodes to provide turbulence and washing action, thereby
minimizing the accumulation of sludge.
Third Durability Test
The test started with the new electrode design. To avoid accumulation of oily
sludge air was bubbled continuously between the electrodes. The test was stopped after
three days because of severe build up of insoluble calcium carbonate deposits on the
cathode. Apparently, the continuous bubbling of air between the electrodes and the
relatively high concentration of calcium ion resulted in a rapid build-up of CaCO-j
deposits. Results are given in Table 8.
Fourth Durability Test
To avoid the deposits of CaCO,, it was decided to replace the CaCU partially or
completely with NaCl. This action, however, resulted in less effective treatment and it
was necessary to return to CaCl. at a concentration of 0.01N.
The fourth durability test (Table 9) continued for nine days and used about 38 m
(10,000 gal) of wastewater. During the test the space between the electrodes was
purged with air twice a day for 5 minutes and sometimes brushed. Accumulation of
sludge between the electrodes was not observed. Also the CaCO, deposits on the
cathode were light and did not interfere with the operation of the cell. Oily sludge did
accumulate in the anodic cage leading, eventually, to elevated voltage and physical
plugging of flow. In-situ washing of the iron chips with cold tap water for 10 minutes
alleviated this condition temporarily.
Fifth Durability Test
The fifth durability test (Table 10) lasted 14 days and used about 57 m (15,000
gal) of wastewater. During the test the space between the electrodes was purged with
air twice a day and occasionally brushed. In addition the water upstream of the anode
was continuously and vigorously agitated to maintain the influent well mixed and avoid
separation of free oil droplets. This action appears to have also slowed the rate of
plugging of the anode. Except for some pump failures the cell performed well
throughout the test.
ELECTRODE PLUGGING
An increase in the operating voltage upon aging of the iron chips, was observed
early in the program. During that time the cell was operating approximately 8 hours
through the day and shut down for the night. After several days of operation the
voltage usually exceeded the limit of the power supply, the chips had to be replaced,
and the electrodes were steam cleaned.
-------
An increase in the operating voltage was also observed during the durability tests,
but at a slower rate. To determine what contributes to the rise in the voltage, the
following experiments were conducted at the end of the fourth durability test when the
operating voltage had increased to 44 volts.
In the first experiment the iron chips were replaced with new ones. The cell was
filled with wastewater and the conductivity was adjusted to 1700 y mho/cm, as at
the end of the fourth durability test. When the power was turned on to 25 A the
operating voltage was 25 volts. Thus replacing the iron chips reduced the operating
voltage by 19 volts. In the next experiment the cathode was cleaned to remove oily and
calcium deposits. This action had no effect on the operating voltage. Next, the anodic
cage was cleaned with steam to remove oily deposits from the front face of the anode.
This action brought the operating voltage down to 14 volts.
Thus, it appears, that the increase in the operating voltage is due primarily to
accumulation of oily sludge in the anode cage.
As mentioned in the Experimental section, the front face of the anode is
constructed of two layers: expanded titanium sheet and polyethylene screen. This type
of construction appears to trap and accumulate oily sludge. By replacing the two-layer
construction with a single titanium sheet with proper hole size, it may be possible to
reduce the rate of sludge accumulation and extend the service life of the anode.
SLUDGE FLOTATION AND SLUDGE CHARACTERISTICS
The sludge generated by the electrolytic process is a mixture of water, oil, and
iron hydroxide. Sludge flotation appears to depend on the ratio' of iron to oil, the
wastewater composition, and the type of assisted flotation equipment. During most of
the program period, sludge flotation was effected by the use of porous membrane air
bubblers which were located at the bottom of the cell. These bubblers were found to be
somewhat deficient. Flotation requires the generation of fine air bubbles which adhere
to the oily floe. If the bubbles are too large mixing instead of flotation may occur. In
these experiments, the membrane properties changed with time and the bubble size
changed from fine to larger bubbles. It should be noted that in laboratory experiments
with simulated wastewater no difficulties were encountered in forcing the sludge to
float with similar flotation equipment, and at about the same iron to oil ratio.
Therefore, it seems that some components of the plant wastewater render the sludge
more difficult to flocculate and to float. Indeed, the wastewater processed occasionally
contained organic solvents, drawing compounds, grinding wheel resins, etc. Therefore,
air bubbler flotation may be more effective with other wastewaters which may have
simpler compositions.
In order to obtain a more effective sludge flotation, a dissolved air flotation unit
(Komline-Sanderson model HR/SR-1) was installed. The treated wastewater was
pumped at a rate of 3.8 1/min to the dissolved air flotation unit (D.A.F.) yielding a
thick, easy to handle, floating sludge.
The performance of the D.A.F. is presented in Table 11. The unit removed from
86 to 98% of the suspended solids, and reduced iron concentration by as much as 97%.
The average removal of suspended solids was 93%. Thus it appears that the sludge
generated by the electrolytic process can be forced to float and that dissolved air
-42-
-------
TABLE 11, EVALUATION OF THE PERFORMANCE OF THE DISSOLVED AIR FLOTATION
Date
5-02-78
5-03-78
5-04-78
5-05-78
5-11-78
5-12-78
5-23-78
5-24-78
5-25-78
Sampling
location*
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
Turbidity
NTU
800
150
30
1200
355
340
650
150
120
1200
260
120
690
57
6
2400
50
14
850
120
65
760
70
8
700
80
30
Freon
extrac tables
ppm
85
17
_
202
104
_
77
22
_
97
32
_
74
-
_
31
12
_
113
69
_
89
25
_-." :
56
28
Suspended
solids
ppm
679
80
nil
1595
135
'
840
57
•
1122
84
-
1643
25
-
2240
40
-
680
33
-
949
131
-
779
57
—
Iron
concentration
ppm
110
22
nil
110
21
'
95
8.5
-
140
22
-
105
7
-
250
7.5
-
100
5
• -
105
6.5
-
65
3
-
1 - Before dissolved air flotation.
2 - After dissolved air flotation,
3 - After sand filtration
-43-
-------
flotation is very effective for that purpose. If final polishing of the effluent through a
sand filter is required to remove the last traces of suspended solids, the use of D.A.F.
would substantially reduce the loading on the filter. In addition, the D.A.F. would
occupy far less floor space than an air bubbler flotation system.
The sludge collected by the D.A.F. unit was analyzed to determine oil and water
content. The sludge as received from the D.A.F. contained 6 to 12% oil, 86% water,
and the balance insoluble solids. The total volume of generated sludge averages about 1
to 2% of the volume of wastewater treated. This volume is immediately decreased by a
factor of two since about one-half of the water drains from the sludge within 30
minutes upon standing. If the sludge is permitted to stand overnight, then agitated, the
water is not as readily drained from the sludge. This presumably is a result of entrained
air being lost from the oil-iron floe and hydration of the iron hydroxide. Thus, the
sludge should be removed and drained within a relatively short time frame.
A few exploratory experiments have been carried out to upgrade the sludge
quality and to recover the oil. For example, by adjusting the pH of the sludge to about
one with HC1, phase separation takes place. Separation by centrifuging was found to
yield an oily sludge phase of about 60% oil. Additional work is necessary in this area to
determine the best technique for oil recovery.
AN APPROACH TO AUTOMATIC CONTROL
To develop any type of automated system, it first is necessary to establish the
parameters to be monitored and controlled. For the electrolytic oily wastewater
treatment process, the response to be measured is the effluent oil concentration. Even
though the treatment effectiveness is not always predictable based strictly on influent
oil content, the degree of treatment, or effluent water quality, as shown in this study is
dependent on the ratio of the amount of iron dissolved to the amount of oil in the
influent. Thus, the effluent oil content will be determined by the iron dissolution rate
which in turn is determined by the electrode current. Consequently, the effluent oil
concentration may be controlled by using it as a response to control the current. Other
parameters such as flow rate and salt concentration would be kept constant.
The effluent oil concentration that can be discharged from the electrolytic cell is
governed by imposed environmental regulations. The standard method employed to
determine oil concentration directly is based upon a solvent extraction technique (7)
which is time consuming and for that reason cannot be used for feedback control.
Analytical instruments to measure directly the oil concentration are available,
such as infrared and ultraviolet spectrophotometers. These instruments were not
evaluated in depth in the present program; however, they are expensive and may require
skilled operators.
As was shown in this study, light scattering or turbidity of the wastewater
correlates with effluent oil content with a correlation coefficient of 0.88. Since
turbidity is a simple measurement with a rapid response, it may be used to monitor
effluent water quality and the signal used to set the current. By using feedback control,
the required water quality with minimum iron addition and minimum sludge generation
can be obtained from the process.
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With an arbitrary initial current setting, it is envisioned that a water sample
would be acquired downstream of the cathode, sandfiltered to remove iron/oil floe, and
its turbidity measured. The millivolt response from the instrument would be
programmed into a microprocessor and compared to a preset value which corresponds to
the desired water quality. A current change would then be made, either increased or
decreased depending on whether turbidity is above or below the set point. The
magnitude of the current change would be related to the magnitude of the difference
between the signal and the set point. The time interval between resetting and the next
sampling will depend upon the flow time between the electrode and the sampling point.
The system would continue to search for minimum current by examining changes in
turbidity. The uppec, bound on the current would be the passivation current (current
density of 10 mA/cm ).
To avoid large and rapid excursions in influent oil concentration, an equalization
tank, capable of containing a few hours of the plant flow should be employed. This
would allow designing the electrode size for a time averaged oil content (rather than
peak) and reduce the requirement for rapidity of response of the control system.
Maintenance requirements, such as the means to assure clear instrument windows,
remain to be established.
SYSTEM CAPACITY DESIGN CRITERIA
To design a treatment cell, the main feature that needs to be established is the
size of the electrode. This will determine, at the passivation current density, the
amount of iron which can be dissolved to produce a desired effluent quality. The
required total current is proportional to the influent oil flux, which is in turn
proportional to the flow rate and oil concentration (1). For the Livonia Plant
wastewater, examination of the data, along with previous experience (1), indicates that
in most instances, a current of 0.007 amperes per liter per minute of flow per (ppm) of
influent oil concentration is adequate to provide an effluent with less than 25 ppm of
Freon extractables. Since current density is limited by passivation to about 100 A/m ,
the electrode area required can be estimated at about 7x10" square meters per liter
per minute per (ppm). For example, to treal 38 1/min (10 gal/min) of wastewater
containing 2000 ppm of oil would require 5.3 m of electrode area.
In designing a system for a particular plant site, it is recommended that simple
beaker or small bench scale studies be carried out to establish the electrode area design
constant for that wastewater to obtain the desired water quality.
ECONOMIC PROJECTIONS
To establish the overall economics of the electrolytic process accurately is
difficult at this time. It will be necessary to have a scaled-up process handling a major
portion of a manufacturing plant effluent to determine electrode durability, mainte-
nance, manpower requirements, etc. These have not been fully addressed in this study.
Nevertheless, some preliminary economic estimates of operating and capital costs can
be made from the current studies. Economics projections for a few scenarios are
presented below.
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Scheme 1. A process scheme with air bubblers and without automation.
This situation represents the approach used during the first phase of the program.
The system would represent the least expensive approach both from a capital
investment and direct operating cost standpoint. However, as previously noted, there
may be a deficiency of effectiveness of the air bubblers after some time of operation.
This would lead to rapid loading of the sand filter.
Assuming a plant size of about 76 m /day (20,000 gal/day) the capital
requirements would be about $50,000 including flow meters, pumps, power supplies, etc.
The capital costs are itemized in Table 12. Direct operating costs based on the present
study include $0.04/nT ($0.15/1000 gal) electrical (at ,$0.025/kW-hr), $0.04/m3
($0.15/1000 gal) calcium chloride (at $0.07/kgX and $0.01/nrT ($0.04/1000 gal) for iron
based on iron scrap value. This equals $0.09/m ($0.34/1000 gal) of wastewater treated.
This cost would be the same for all of the schemes described in this section since the
major costs are electrical, salt, and iron. Added to this would be the operating costs
associated with flotation air, pumps, motors,-etc. For comparison, direct, chemical
costs for common batch systems generally range from around $0.22-$0.29/m ($0.85 to
$1.10/1000 gals). Credit for the waste oil is not included.
Scheme 2. A process scheme with dissolved air flotation and without automation.
The major advantages of this scheme are that flotation and skimming would be
much more efficient and would occupy much less space than Scheme 1. Both capital
and operating costs would be increased. Capital would be increased by $30,000 for a
dissolved air unit capable of handling from 19 to 114 m /day (5,000 to 30,000 gal/day).
Operating costs for this unit, based on information furnished by the manufacturer,
average about $0.08/m ($0.30/1000 gal). This includes cost of pumping, skimming, etc.
With automatic skimming, manpower costs would decrease and the quality of the sludge
may be improved. Other costs would be similar to Scheme 1 with only minor saving of
manpower.
Scheme 3. A process with dissolved air flotation and automated control.
This scheme would be the most efficient from a manpower standpoint and would
result in optimum operation. The automatic feedback control technique remains to be
evaluated. The feedback system envisioned would control the current by sensing the oil
content in the effluent from the cell. Systems to monitor the oil range from $800 to
$8,000 depending on the plant wastewater to be treated. For Livonia Plant wastewater,
a system to monitor turbidity, which was shown to correlate with oil content, may be
employed. In this case, a total feedback system would be around $5,000 with no
increase in direct operating cost. Manpower would be decreased since adjustment and
settings of the process would be automated. Maintenance cost of the feedback system
is not known.
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TABLE 12. CAPITAL COSTS OF ELECTROLYTIC TREATMENT
1. Process with air bubblers-without automation
Flow equalization tank - $10,000
Pumps - 2,500
Mixing tank - 1,500
Electrolytic cell-shell - 3,000
Power supplies - 8,000
Belt skimmer - 3,500
Sludge collector - 3,000
Flow meters - 1,500
Electrode - 2,500
Air bubblers - 2,000
Air compressor - 2,000
Sand filter - 1,500
Installation -' 9,000
$50,000
2. Process with dissolved air flotation-without automation
Scheme 1 costs - $50,000
Dissolved air flotation - 30,000
$80,000
3. Process with dissolved air flotation-with automation
Scheme 2 costs - $80,000
Automation (turbidity - 5,000
system) $85,000
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REFERENCES
1. Weintraub, M. H., and R. L. Gealer, Development of Electrolytic Treatment of
Oily Wastewater, American Institute of Chemical Engineers, 70th Annual Meeting,
New York, NY, Nov. 13-17, 1977, paper No. 151.
2. Dzieciuch, M. A., M. H. Weintraub, and R. L. Gealer, Electrolytic Treatment of
Oily Wastewater—Laboratory Investigation, 149th Meeting of The Electrochemical
Society, Washington, D.C., May 2-7, 1976, Abstract No. 260.
3. Weintraub, M. H., M. A. Dzieciuch, and R. L. Gealer, Electrolytic Treatment of
Oily Wastewater—Engineering Development, 149th Meeting of Electrochemical
Society, Washington, D.C., May 2-7, 1976, Abstract No. 261.
4. Cutting Fluid Technology, Tribology International, Vol. 1, No. 1, February 1977.
5. Rossmore, H. W., Microbiological Causes of Cutting Fluid Deterioration, Society
of Manufacturing Engineers, Dearborn, MI, 1974, paper No. MR74-19.
6. Tomko, 3., Cutting Fluid Maintenance, Society of Manufacturing Engineers,
Dearborn, MI, 1971, paper No. MR 71-804.
7. Methods for Chemical Analysis of Water and Wastes, U.S. Environmental
Protection Agency, Environmental Monitoring and Support Laboratory, 1974.
Cincinnati, OH.
8. Becher, P., Emulsions: Theory and Practice, Reinhold Publishing Corp., New
York, NY, 1965. p. 183.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
:PA-6UO/Z-80-14o
3. RECIPIENT'S ACCESSION NO.
TITLE AND SUBTITLE
ELECTROLYTIC TREATMENT OF OILY WASTEWATER FROM
MANUFACTURING AND MACHINING PLANTS
5. REPORT DATE
JUNE 1980
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
R.L. GEALER, A. GOLOVOY and M.H. WEINTRAUB
8. PERFORMING ORGANIZATION REPORT NO.
PERFORMING ORGANIZATION NAME AND ADDRESS
FORD MOTOR COMPANY
ENGINEERING and RESEARCH STAFF
DEARBORN, MICHIGAN 48121
10. PROGRAM ELEMENT NO.
1BB610
11. CONTRACT/GRANT NO.
GRANT NO. S804174
2. SPONSORING AGENCY NAME AND ADDRESS
INDUSTRIAL ENVIRONMENTAL RESEARCH LAB-Ci
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
13. TYPE OF REPORT AND PERIOD COVERED
FINAL
14. SPONSORING AGENCY CODE
EPA/600/12
5. SUPPLEMENTARY NOTES
6. ABSTRACT
A continuous electrolytic treament is being developed to remove emulsified oil from dilute
oily wastewater streams, such as is generated in metal working operations. In this process, the
wastewater permeates through an iron chip bed anode and steel mesh cathode. A potential is
applied to the electrodes, forming ferrous ions at the anode and hydroxyl ions at the cathode. The
:errous ions react in a complex manner with the emulsifying agents, destabilizing the emulsion and
generating an oil rich floating sludge and essentially oil-free water.
A pilot plant unit capable of processing about 5700 I/day (1500 gal/day) was designed,
constructed, and evaluated at an actual plant site. Operating parameters and process equipment
were evaluated to assess the potential and problems of the process.
Wastewater with initial oil concentrations in the range of 300 to 7,000 ppm of solvent
extractables has been reduced to less than 50 ppm in 90% of the test runs, and to less than 25 ppm
in 83%. These test runs were done at conditions of minimum operating cost and minimum sludge
generation. When necessary, Freon extractables generally are reducible to about 10 ppm or less
ay the addition of more electrolytically dissolved iron to the system at a small increase in cost.
Preliminary economics look favorable and overall results are quite encouraging so that
further scale-up of the process is recommended.
This report was submitted in fulfillment of Grant No. S-804174 by Ford Motor Company
under the sponsorship of the U.S. Environmental Protection Agency. The report covers the period
May 18, 1976 to August 17, 1978, and work was completed as of August 17, 1978.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
OILY WASTEWATER WATER POLLUTION
INDUSTRIAL WASTES
ELECTROLYTIC PROCESS
EMULSIFIED OIL RE-
MOVAL FROM WASTEWATER
68D
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
ITMTT
21. NO. OF PAGES
2O. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (R«v. 4-77) PREVIOUS EDITION is OBSOLETE
•if U.S. GOVERNMENT PRINTING OFFICE: 1980--657-765/0024
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