United States /
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Cincinnati OH 45268
EPA-600/2-78-069
April 1978
Research and Development
£EPA
Oil/Water Separation:
State of the Art
Environmental Protection
Technology Series
-------
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-600/2-78-069
April 1978
OIL/WATER SEPARATION
STATE-OF-THE-ART
by
Fidelis A. Osamor
Robert C. Ahlert, Ph.D.
Department of Chemical and Biochemical Engineering
Rutgers, The State University of New Jersey
New Brunswick, New Jersey 08903
Grant No. R803978
Project Officer
Leo T. McCarthy, Jr.
Oil & Hazardous Materials Spills Branch
Industrial Environmental Research Laboratory-Cincinnati
Edison, New Jersey 08817
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, 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, con-
verted, 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 (IERL - Ci) assists in developing and demonstrating
new and improved methodologies that will meet these needs both efficiently
and economically.
Effluent discharge guidelines for oil have been established for
existing onshore and offshore industries, and performance standards have
been stipulated for new point sources.
This report identifies, organizes, and interprets technical and
commercial literature resources on oil/water separation. As such, this
state-of-the-art report will be most useful to regulatory personnel of
Federal and State agencies in assessing the capabilities of existing
technology to meet standards established for the control of oil discharges.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
iii
-------
ABSTRACT
This report reviews the state-of-the art for oil/water separating
devices and processes. Devices and processes are classified according to
the primary mechanism that induces separation of oil/water mixtures. The
basic concepts, specific design features, operational conditions, and
limitations of each category are discussed.
Literature on test evaluation of a variety of devices is critiqued on
the basis of actual or potential success in treating various oil/water
systems states. No single technique can separate all oil/water system
states efficiently. Specific deficiencies in existing technology have
been identified.
Reverse osmosis, ultrafiltration, and carbon adsorption possess great
potential, but high equipment and operational costs will continue to limit
their use for treating oily wastestreams. A combination of devices in a
process chain is therefore necessary for production of effluents with
desired discharge quality (<10 ppm of oil). The specific characteristics
of an oily wastewater determine the combination of devices that will yield
required effluent concentrations.
This report was submitted in fulfillment of Research Grant No.
R803978 by Rutgers University under the sponsorship of the U.S.
Environmental Protection Agency. The report covers the period July 1,
1975, to June 30, 1977, and work was completed as of July 31, 1977.
IV
-------
CONTENTS
Foreword ill
Abstract iv
Figures vi
Tables vi
Acknowledgments vii
1. Introduction 1
Background 1
Objective of report 2
Approach 2
2. Conclusions 4
3. Recommendations 8
4. System Characterization 10
Oil/water systems 10
Free oil 10
Dispersed oil (emulsions) 10
Chemically stabilized dispersions ....... 11
Molecularly dissolved oil 11
Solubilized oil 12
Oil-coated suspended solids 12
5. Characterization of Oily Wastewaters 13
Ballast water 13
Tank-cleaning water 14
Bilge water 14
Oil-field production water 14
Summary 14
6. Devices and Processes 16
Technology 16
7. Critical Review of Selected Literature 54
8. Selected Manufacturers of Oil/Water Separating Equipment .... 81
9. References 84
10- Bibliography 93
-------
FIGURES
Number Page
1 API Oil/Water Separator 20
2 Shell Parallel-Plate Interceptor 22
3 Shell Corrugated-Plate Interceptor 23
4 Total Pressurlzation System 31
5 Partial Pressurization System 32
6 Recycle Pressurlzation System 33
7 A Complete Liquid/Liquid Coalescing System 44
8 Coanda-Effect Separator 50
9 Orbiting Buttress Threaded Device 52
10 Vortex-Flow Separator 57
TABLES
Number Page
1 Potential of Separation Techniques to Separate Various Oil/
Water System States 5
2 Oil Removal in API Separators 25
3 Oil and Suspended-Solids Removal in Gravity-Type Separators . 26
4 Estimated Effluent Quality from Primary Oil/Water Separation
Processes 26
VI
-------
ACKNOWLEDGEMENTS
The authors are indebted to Frank Freestone and Leo McCarthy of the
U.S. Environmental Protection Agency, Edison, New Jersey, for their
suggestions and assistance.
vii
-------
SECTION 1
INTRODUCTION
BACKGROUND
The rising demand for energy by a growing population has led to con-
tinued increases in world production of crude oil. As an immediate conse-
quence, there is a worsening problem of oil pollution of waterways and the
marine environment'by discharges of oily wastewaters.
There are various sources of oily substances, and the following key
sources have been identified:
a) natural seeps;
b) petroleum mining and refining operations;
c) accidental oil spills;
d) discharges from transporting vessels;
e) discharges from chemical and industrial plants; and
f) stormwater runoff.
The magnitude of the oily waste problem has been described in the literature
(Boesch et al., 1974; SCEP, 1970), but data on the amount of the discharge
from these key sources are at best speculative.
In response to public demand for a clean environment, laws and regula-
tions have been promulgated. Effluent discharge guidelines have been
established for existing onshore and offshore industries, and performance
standards have been stipulated for new point sources (U.S. EPA, 1974, 1975).
Industries are approaching oil pollution abatement by process modifica-
tions and the use of advanced waste treatment technology for end-of-pipe
treatment. Secondary and tertiary recovery methods for crude oil are
minimizing the volume of production water generated during production
operations. New ship designs, incorporating separate holding tanks for bilge
and ballast water, and use of the load-on-top procedure have cut down on the
volume of oily wastewater discharged at sea. Separation devices for oil/
water mixtures are being installed onboard ships, and there is an increasing
number of dockside treatment facilities for bilge and ballast waters.
However, large volumes of oily wastewaters must be treated by even more
advanced methods to meet effluent standards before discharge into United
States waters.
-------
OBJECTIVE OF REPORT
Strict pollution control laws place heavy emphasis on the development
of economical and reliable devices for separation of oil/water mixtures.
The objective of this report is to review the state-of-the-art for oil/water
separation devices and processes. The scope of this investigation will be
the technology available for shipboard and shoreside treatment of bilge and
ballast waters and the oily wastewaters associated with crude oil produc-
tion. Separation devices will be classified according to the primary mech-
anism that induces separation of oil/water mixtures. The basic concepts of
each class of equipment, specific design features, operational conditions,
and limitations of each device will be discussed. An evaluation of each
category of equipment will be based on the overall performance standard.
Finally, a list of some major manufacturers of commercially available
equipment, presently used worldwide for oil/water separation, will be
compiled.
APPROACH
This project will identify, organize, and interpret technical and com-
mercial literature resources on oil/water separation.
The first effort will be a description of the various states in which
oil can co-exist with water after intimate contact of both liquids. Each
of the states will be characterized in operational terms, as well as in the
physical-chemical sense. Next, the process streams to be considered—oily
wastewaters generated onboard ship, oil in process water, and formation
water from crude oil production—will be characterized based on oil/water
system states. Other parameters to be considered for an efficient separa-
tion will be outlined.
The second phase will be devoted to a review of the state-of-the-art
of separation devices and processes. A distinction will be made between
device performance and the performance of a chain of several devices or a
process. Since the performance standard of each device is of utmost
importance, the review of a device will be reported using the following
format:
a) title of report;
b) report number and date of report;
c) author(s);
d) manufacturer of equipment;
e) design features;
f) characteristics of wastewater on which device was tested-
g) method(s) of analysis;
h) results (performance of standard based on published data)•
i) approximate purchase price of equipment (if specified); and
j) critical comments.
-------
The overall effectiveness of each class of devices for separation of oil/
water system states will be noted.
Finally, a list of manufacturers for each equipment category will be
compiled. Material to be reviewed is generated through searches in available
commercial literature and unpublished reports of industries and laboratories
involved in the manufacture or testing of equipment and new techniques.
Since existing literature is vast, the search and review process will focus
primarily on utility, rather than exhaustiveness.
-------
SECTION 2
CONCLUSIONS
This report is a review of the state-of-the-art for oil/water separating
devices and processes. Techniques proposed as feasible but not yet evalu-
ated as candidates for oil/water separation are discussed also. Discussion
does not include coagulation-flocculation processes with chemical addition,
nor is the list of devices exhaustive.
The problems associated with the removal of oil from water are complex;
to meet effluent guidelines or discharge limits, many oil/water treatment
facilities must be upgraded. Before a choice of separating equipment can be
made, the specific nature of the oil/water separation problem has to be
examined thoroughly. Sources of oily wastewaters are diverse; oily waste-
waters produced by different processes have characteristics that differ from
each other depending on the type of oil(s), oil(s) and suspended-solids
concentrations, physical and chemical properties of the aqueous phase, the
process originating the oily wastes, salinity, temperature, etc. Moreover,
the characteristics of oily wastewaters may change with time. The problem
is complicated further by the different states in which oil can exist in
water. The. thermodynamic states in which oil can exist in water have not
been identified completely; only the major states have been described.
These states can co-exist in wastewater depending on oil type, degree of
mixing of the oil and water phases, concentration of surfactants, and other
factors. Also, it is difficult to estimate oil concentrations in given oily
wastewaters, because of inadequate analytical methods. Concentrations of
states depend on the chemical interactions between oil and water, number of
days of equilibration, and the dissolution processes (physical, bacterial,
or chemical oxidation) occurring during the equilibration period.
Each state has a certain degree of difficulty associated with its re-
moval. There are many devices available commercially capable of removing
one or a few states, but a single device capable of separating all states is
still lacking. With progress in membrane technology, reverse osmosis and
ultrafiltration may qualify eventually as the best technologies available
for separating oil/water mixtures. For economic reasons, carbon adsorption
should continue to be used in polishing states. The potential and
limitations of devices and processes are presented in Table 1.
The degree of difficulty of separating oil from wastewaters depends
largely on the number of states present. Because of the inability of devices
to effectively separate several states, combination of separation techniques
into process trains is necessary to produce effluents that will meet dis-
charge standards. A modern oil wastewater treatment system may include an
API gravity separator and dissolved air flotation for removing free oil
-------
TABLE 1. POTENTIAL OF SEPARATION TECHNIQUES TO SEPARATE VARIOUS OIL/WATER SYSTEM STATES
Ul
Stabilized
Oil-coated solids Unstabilized dispersions Molecularly
Free Settle-
Technique oil able
A. Gravity
Differential
API XXX *
Hydro gard XXX
Circular XXX
PPI XXX
CPI XXX
Fram-Akers XXX
Curved-plate
finger XXX
Gravi-Pak XXX
Centrifuges XXX
Hydro cyclones XX
Vortex XX
Dispersed air
flotation XXX
Dissolved air
flotation XXX
Vacuum desorp-
tion XXX
Electro-
chemical
B. Filtration
Granular media
Multimedia
C. Coalescence/
Filtration
Fibrous media XXX
Centrifuge XXX
Bimetallic
XX
XX
XX
XX
XX
XXX
XXX
XXX
XXX
XXX
XX
XXX
XXX
XXX
XXX
XXX
Neutrally dispersions Surface Solubilized dissolved
buoyant Primary
X
X
X
XX
XX
XXX XXX
XX XX
XXX
XXX
X XX
XX XXX
XX XXX
X XX
XXX XXX
XXX XXX
XXX
XXX
Secondary Chemically charge oil oil
X
XX
X
XX
XX
XX XXX
XX XX
XXX XX XX
XXX
XXX
XX XXX
*X, poor separation; XX, average separation; XXX, excellent separation.
-------
TABLE 1. POTENTIAL OF SEPARATION TECHNIQUES TO SEPARATE VARIOUS OIL/WATER SYSTEM STATES (cont.)
Oil-coated solids
Free Settle- Neutrally
Technique oil able buoyant
D . Memb rane
Electro-
dialysis XX *
Reverse
osmosis XXX
Ultrafil-
tration XXX
E. Adsorption
Carbon XXX
F. Electric
& Magnetic
Electro-
phoretic
Magnetic
G. Thermal
H. Coanda
Effect X
I. Viscosity-
Actuated X
J. Chroma-
tography
K. Sonic &
Ultrasonic
Stabilized
Unstabilized dispersions Molecularly
dispersions Surface Solubilized dissolved
Primary Secondary Chemically charge oil oil
XX XX XX XX X X
XXX XXX XXX XXX XXX XXX
XXX XXX XXX XXX XXX XX
XXX XXX XXX XXX XXX
X XX
XX
XX X
XXX XXX
XX X
*X, poor separation; XX, average separation; XXX, excellent separation.
-------
oil-coated suspended solids, and unemulsified primary dispersions; a co-
alescer equipped with a prefilter for removing neutrally buoyant, oil-coated
solids and remaining unemulsified primary and secondary dispersions; reverse
osmosis for removing emulsified, solubilized, and dissolved oil; and carbon
adsorption for removing the last traces of dissolved oil. A combination of
other separation methods can be used; however, the general trend is gross
separation followed by finer separation and, finally, a polishing state.
This trend should prove to be most economical; desired effluent quality can
be achieved, the life of the polishing stage is extended, and throughput is
reasonable. Therefore, utilization of several separation techniques is an
efficient means of separating oil/water mixtures.
An attempt to review patent literature was unsuccessful, because of the
limited information usually available in patents and absence of performance
data.
It is hoped the information developed in this report will be useful to
both manufacturers and users of oil/water separating equipment.
-------
SECTION 3
RECOMMENDATIONS
1. The thermodynamic states in which oil can co-exist with water are not
defined completely. Identification of oil/water system states present
in a given wastewater is necessary to a good choice of separating
devices.
2. Dissolution rates of a variety of oils, petroleum products, and other
toxic organic pollutants are in need of measurement.
3. Until recently, it was thought that the concentration of dissolved oil
present in effluents could not be higher than the solubility of the oil.
The phenomenon of solubilization of oil, in the presence of surface-
active agents and dissolved organic matter, increases oil concentrations
considerably. Therefore, removal of dissolved oil is necessary if
effluents are to meet discharge limits. Solubilization of oil should
be investigated.
4. Estimating oil content with on-line oil/water monitors, turbidity mea-
surements, visual observation, and other dubious analytical techniques
should be avoided. Oil/water monitors and turbidity meters are highly
variable. Since regulations are aimed at the total oil content of
effluents, total organic carbon analysis should be preferred over
extraction-gravimetric or extraction-infrared-spectrophotometric tech-
niques for measuring oil content of oil/distilled water samples.
5. The efficiencies of different organic solvents—heptane, hexane, chloro-
form, carbon tetrachloride, petroleum ether, pentane, and methylene
chloride—commonly used in extracting oil for analysis, must be investi-
gated. Efficiencies of solvents for different hydrocarbon groups
(paraffins, aromatics, etc.) merit investigation. Depending on the
solvent and the number of extractions, results of oil concentrations in
effluents can be in great error.
6. Since oil dispersions are formed through turbulent mixing during pumping
operations, the efficiency of separation can be enhanced by gravity flow
or use of low-shear pumps having limited emulsification tendencies
7. A method to characterize oily wastewaters in terms of separation
requirements is needed.
8. For any oily-waste problem, segregation of wastes containing detergents
proper water management techniques, maintenance of devices in good '
-------
operating condition, and adequate operator training are useful.
9. Presently, there is no format for evaluating the performance of oil/
water separation devices. Oil/water mixtures used in test evaluations
should be characteristic of the oily wastewaters that the equipment will
treat upon installation. Tests using oil/water'emulsions formed by
passage through a centrifugal pump do not demonstrate equipment capa-
bility to separate other emulsions without data on comparative emulsion
stability. Factors that affect the efficiency of the separation process
should be varied systematically.
10. Many performance claims are substantiated with limited test results,
using inexact analytical methods. Performance data are not stated, often
because data are considered proprietary. Often, devices have not been
tested adequately. Therefore, evaluation can be made only by comparing
the principles of separation, instead of design variations and/or special
design features.
11. For comparison of promising techniques and adequate evaluation of
existing technology, a test facility similar to OHMSETT is needed.
-------
SECTION 4
SYSTEM CHARACTERIZATION
OIL/WATER SYSTEMS
Before a separation device or process can be selected, there Is need
for an understanding of the type of oily wastewater to be treated. As such,
a characterization of oil/water systems is necessary. In this discussion,
"oil" will be used in a generic sense to refer to the non-aqueous phase and
"water" will refer to the aqueous phase.
After intimate contact of oil and water, oil can contaminate the water
by existing in the aqueous phase in various forms. These states have already
been identified and reported in the literature as free oil, dispersed oil,
chemically emulsified oil, molecularly dissolved and solubilized oil, and
oil-coated suspended solids.
FREE OIL
When a mixture of oil and water is left undisturbed for a short time, a
continuous layer of oil forms at the surface of the aqueous phase if the oil
is less dense than water. Separation of the mixture into two separate layers
is due to the action of buoyant forces on the large oil masses initially
present in the water body. The oil in the top layer has the essential physi-
cal and chemical properties of the source (parent) oil, unless it has been
modified by extrusion or reaction with chemicals present in the aqueous
environment. Modification may be due, also, to the action of any or all of
the following mechanisms: evaporation of the volatile components, atmo-
spheric oxidation, microbial activity, and dissolution of soluble fractions
of the oil. These processes occur if there is prolonged contact of the
liquids, e.g. ballast and bilge waters retained onboard vessels for several
days or weeks.
DISPERSED OIL (EMULSIONS)
Due to turbulent mixing, oil droplets may be dispersed in the aqueous
phase to form an oil-in-water emulsion, depending on phase volume ratios and
other factors. The particle size of the dispersed oil in an emulsion is
important in characterizing the type of dispersion. Depending on the inten-
sity of mixing, primary or secondary dispersions result. Both dispersions
usually account for only a very small volume fraction of oil, in the order
of 50 to 1,000 ppm.
10
-------
Primary dispersions are formed from macroscopic oil droplets that range
in diameter from 1,000 to 10,000 A and remain in suspension due to Brownian
motion. These droplets are generally unstable thermodynamically and agglom-
erate or coalesce into larger droplets, if allowed to remain undisturbed for
periods of approximately 24 hours. Primary dispersions are produced by low
shear pumps, e.g. diaphragm and vane pumps, as well as low-speed centrifugal
pumps.
Secondary dispersions are formed from very fine, microscopic oil drop-
lets that have mean diameters between 50 and 600 A and do not separate from
water if left undisturbed for a very long time; they are stable thermody-
namically. Highly turbulent flow conditions are favorable to the formation
of secondary dispersions.
Interfacial tension is an effective stabilization mechanism for disper-
sions. Additional stability of dispersions arises if electrical charges are
present on the surfaces of oil droplets. A detailed discussion on this
electrokinetic phenomenon can be found in the literature (Kruyt, 1952; Over-
beek, 1952; Adamson, 1967). A double layer of charges is formed at the oil/
water interface of each droplet, and coalescence of adjacent droplets is
prevented by mutual repulsion. The potential difference in the diffuse
double layer is called the zeta potential. Stable emulsions exhibit zeta
potentials in excess of 25 mV (Churchill and Kaufman, 1973; Orr and Kang,
1974). Measurement of this potential is a useful tool in estimating the
stability of emulsions (Orr and Kang, 1974).
CHEMICALLY STABILIZED DISPERSIONS
The presence of surfactants favors formation of chemically stabilized
dispersions. These have the same particle sizes as the primary and secondary
dispersions discussed above. The oil droplets have additional stability
because of the presence of a third component in either the oily or the
aqueous phase. The third component is variously referred to as a surfactant,
surface-active agent, detergent, soap, stabilizing agent, emulsifier, etc.
Small concentrations of this agent are enough to chemically stabilize oil
droplets. Extensive literature is available on surfactants and their effects
on the stability of emulsions (Jefferson and Boulavare, 1973; Churchill and
Kaufman, 1973; Gloyna and Ford, 1974). The chemical nature of the surfactant
is important. A theory has been advanced for surfactant modification of an
oil/water interface. It states that surfactants are molecules composed of
lipophilic and hydrophilic end groups that orient themselves in an emulsion
such that their lipophilic ends project into the non-aqueous phase while
their hydrophilic ends are anchored in the aqueous phase. A protective
"film" is formed around each droplet, as a result of surface interaction.
Reduction in interfacial tension leads to a low free energy, which is
unfavorable to coalescence of the oil droplets.
MOLECULARLY DISSOLVED OIL
Generally, hydrocarbons exhibit limited solubilities in water, with
aromatic hydrocarbons somewhat more soluble than aliphatic hydrocarbons
11
-------
(McAuliffe, 1969a,b). Molecularly dissolved oil is oil that is in true
chemical solution in the aqueous phase. Dissolved oil is generally classi-
fied as submicroscopic oil droplets, below 50-A diameter. Because of limited
solubility of oils in water, the concentration of molecularly dissolved oil
is probably less than 20 ppm. However, after prolonged equilibration, oil
concentrations can be higher than 200 ppm. Dissolution of petroleum-derived
products has been studied extensively, but is not completely understood
(McAuliffe, 1969a; Boehm and Quinn, 1974; Lysyj and Russell, 1974). One
reason for the inadequacy of knowledge in this subject is the lack of tech-
nology for measuring soluble oil without interference from emulsion droplets.
Lai and Adams (1974) developed a method for determining the molecular solu-
bility of Navy oils in water, using an osmometric device.
SOLUBILIZED OIL
Studies indicate that, in the presence of dissolved organic matter (DOM)
in the aqueous phase, the solubility of oils increases, particularly oils
containing large fractions of aliphatic hydrocarbons (Boehm, 1973; Boehm and
Quinn, 1974). Acceleration of organics transfer into the aquous phase is
due to chemical modification of water-insoluble petroleum fractions. The
presence of surface-active agents in petroleum products can cause solubiliza-
tion, also. Solubilized oil droplets are less than 0.5 p in size. Solubili-
zation of hydrocarbons in seawater may not be appreciable if the DOM concen-
tration is so low that the concentration of dissolved surfactants does not
exceed the critical micelle concentration (Elworthy et al., 1968).
OIL-COATED SUSPENDED SOLIDS
Solids suspended in the aqueous phase become coated with oil. These
solids have a wide range of origins, densities, compositions, and sizes
(Finger and Tabakin, 1973; Freestone and Tabakin, 1975) . These solids are
mainly clays, silica, drill muds, corrosion products, asphaltenes, heavy
metals or alkaline-earth salts, and the fine sediments that are abundant in
natural waters and oil field brine formation water. Finely divided solids
play a major role in crude oil emulsion stabilization. Solids that are
neutrally buoyant require special treatment before they can be separated
effectively. Oil adsorbed on the surfaces of solids enhances solubilization.
12
-------
SECTION 5
CHARACTERIZATION OF OILY WASTEWATERS
Since this review focuses primarily on technology available for separat-
ing oily wastewaters from ships and crude oil production operations, a brief
characterization of these wastewaters in parallel with the characterization
of oil/water systems follows.
Oily wastewaters generated onboard ships and vessels are ballast water,
tank cleaning water, and bilge water.
BALLAST WATER
After discharging fuel oil cargo, a ship pumps water or seawater into
storage tanks to maintain stability. This water may contain large amounts
of silt or fine solids if picked up in a river or estuary, or offshore from
a large seaward river flow. Oil that adheres to tank walls mixes with the
water as a result of ship motion. During deballasting operations, the oily
wastewater is pumped out, usually by a high-speed centrifugal or reciprocat-
ing pump, in order to minimize turnaround time. The phase-forming effects of
various pumps on mixtures of oil and water have been reviewed (Shackleton et
al., 1960; Fruman and Sundaram, 1974). Many factors affect the dispersion
of oil/water mixtures as they pass through pumps and piping (Shackleton et
al., 1960):
a) excessive velocities and accelerations;
b) restricted ducts;
c) rapid changes in fluid direction; and
d) varying speeds and discharge pressures.
It is likely that debaliasted water contains all the oil/water systems
discussed in Section 4, depending on the following factors:
a) type of fuel cargo;
b) characteristics of water used as ballast water;
c) duration of voyage between ballasting and deballasting operations;
and
d) the emulsification characteristics of the pump used in deballasting.
Ballast water from cargo tanks usually contains oily residues from prior
loads. Occasionally, washwater from tank cleaning is added to ballast
water.
13
-------
TANK-CLEANING WATER
Before a change in fuel cargo is made, cargo tanks are washed. Oily
wastewater generated by tank cleaning is similar to ballast water, except
detergent cleaning of cargo tanks may be necessary. Cleaning with deter-
gents leads to formation of chemically emulsified oil. The amount of oil
that clings to tank walls may be up to 1% of the total cargo, depending on
the viscosity of the oil. This portion of the load ends up in ballast and
tank-cleaning waters. Dirt and scale are produced by tank cleaning, also.
BILGE WATER
Bilge water comprises leakages of lubricating oil, fuel oils, and hy-
draulic fluids, and water resulting from drains and drippings in the engine
room. It contains solids and rust scale, also. Oils present in bilge water
contain many additives. Bilge water must be pumped out of the ship, and
chemically emulsified oil will be the dominant of the two types of emul-
sions discussed previously. Becuase of the complexity of bilge waters,
there is, as yet, no meaningful characterization scheme (Budininkas and
Remus, 1974). In undiluted bilge water, the ratio of oil-to-water is higher
than in ballast water. Therefore, multiple emulsions are probably present.
The rate at which a ship generates bilge depends on the age, condition, and
maintenance history.
OIL-FIELD PRODUCTION WATER
There is increasing interest in development of offshore oil production
facilities. During crude oil exploration, drill cuttings and mud chemicals
are the main pollutants. In the production phase, the wastewater generated
is oily brine formation water (production water). The composition of forma-
tion water differs from well to well. However, these wastewaters are char-
acterized by a high content of dissolved and suspended solids. Therefore,
the potential for formation of oil-coated solids and stable emulsions is
high.
Crude oils are complex mixtures; they differ in characteristics,
according to geologic age, chemical constitution, and associated impurities.
They contain many natural emulsifiers, usually naphthenic and other organic
acids, resinous substances, and asphaltenes (Reisberg and Doscher, 1956).
Formation brines for different wells have different compositions (USEPA,
1975). Consequently, emulsions resulting from crude oil production are
stabilized by a variety of mechanisms, depending on origin.
Discharge pressures during crude oil production are usually high, and
entrainment of fine gas bubbles in the oil/water mixture is likely to occur.
SUMMARY
The various states in which oil and water can co-exist have been dis-
cussed. Oily wastewaters from vessels and crude oil production have been
characterized crudely. Technology available for the separation of these
oily wastewaters will be reviewed.
14
-------
In addition to the oil/water system states already presented, other
parameters influence the performance of a separation device or process:
a) oil concentration of the influent stream;
b) flow rate;
c) physio-chemical properties of the wastewater, including
1) temperature,
2) pH,
3) salinity,
4) ionic strength, and
5) dielectric constant;
d) density ratio of the oily and aqueous phases; and
e) mechanical motions during separation.
15
-------
SECTION 6
DEVICES AND PROCESSES
Available methods for separating oil/water mixtures include: physical,
chemical, mechanical, electrical, magnetic, and thermal treatments, and
combinations of these. Because manufacturers' trade names are often mislead-
ing, devices are classified according to the primary mechanism which induces
separation in wastewaters. The basic principle of each group of; devices is
stated. Variations in devices and processes, including the different modes
of operation, are specified. Pertinent literature on a device, particularly
literature on text evaluation of equipment, is summarized and reviewed
critically.
Since the performance standard for each class of devices is of utmost
importance, the workability of each group relative to what is known about
oil/water system states is discussed. The specific oil/water system(s)
which each group of devices (if adequately designed and operated) is capable
of treating is noted.
Applicability of devices relative to some additional constraints is
stated. These include: limiting space requirements, low weight, and sensi-
tivity to motion during processing. These are imposed by shipboard or off-
shore platform operations, but are not necessarily important for shoreside
facilities. Finally, it should be noted that this survey does not purport to
include all devices presently available.
TECHNOLOGY
Commercial and experimental oil/water separation devices are listed
below. Devices operating on principles proposed as feasible but which are,
as yet, in the developmental stage are included.
Gravity Differential Separation
API Oil/Water Separators
Circular Separators
Plate Separators
Shell parallel-plate interceptors (PPI)
Shell corrugated-plate interceptors (CPI)
Curved-Plate Finger Separators
Rotational Separation
Centrifuges
Hydrocyclones
Vortex flow
16
-------
Gas Flotation
Dispersed air
Dissolved air
Vacuum desdrption
Electrochemical
Filtration
Layer Filtration
Granular media
Multimedia
Membrane
Electrodialysis
Reverse osmosis
Ultrafiltration
Coalescence/Filtration
Fibrous-Media
Membrane
Centrifuge
Bimetallic
Granular-Media
Other Porous Materials
Adsorption and Absorption
Electric and Magnetic Separation
Electrophoretic
Magnetic
Thermal Separation
Heating
Evaporation and Distillation
Freezing and Crystallization
Sonic and Ultrasonic Separation
Coanda-Effect Separation
Viscosity-Actuated Phase Separation
Chromatographic Separation
Gravity Differential Separation
Gravity differential separation is the oldest and most common method for
separating oil/water mixtures. It is usually the first step in the treatment
of oily wastewaters and provides coarse separation of oil and water. In
17
-------
general, oil/water mixtures will separate naturally into two distinct layers
of oil and water, if allowed to stand undisturbed for a sufficient period of
time. Ease of separation depends on the magnitude of the difference in den-
sities of the two immiscible liquids; the basic principle governing this
technique is Stokes 's Law, which is applicable to the rate of rise of oil
globules in water. 9
v
where v = rate of rise of an oil globule
g = acceleration due to gravity
D = diameter of an oil globule
6 ,6 = densities of the aqueous phase and oil, respectively
0) O
]i = absolute viscosity of the aqueous phase
Stokesfs Law applies to solids suspended in water (oil-coated), also. From
this equation, oil globules and/or suspended particles will rise to the sur-
face or fall to the bottom, depending on the sign of the density differen-
tial. The difference in densities between most contaminant oils and water is
usually small, and the viscosity of the aqueous phase is temperature-depen-
dent but is essentially constant. Therefore, the rate of rise of an oil
globule is dependent to a large extent on the particle size. Hence, for an
appreciable separation to occur, within reasonable residence times, the oil
droplets and suspended solids must be large. As oil globules rise to the
surface, collisions occur, coalescence takes place, and a floating oil film
forms at the surface. Coalesced oil is subsequently skimmed off.
Gravity separation is inefficient when the density difference is small,
viscosity of the aqueous phase is low, and oil droplets are small. As parti-
cle size becomes smaller, residence times and space requirements increase.
Because of these limitations, gravity separation methods are used only to
separate free oil, primary dispersions, and large oil-coated solids. Devices
operating on the gravity principle will not separate dissolved oil or emul-
sions (API, 1969). Neutrally buoyant solids, coated with oil, are not sep-
arated. If gravity separation is used in conjunction with chemical addition,
stable emulsions can be broken and separated.
The most economical state-of-the-art methods in oil/water separation are
of the gravity type. Devices can handle large flow rates, have low power re-
quirements, and need minimum operator attention; but processes are slow,
necessitating large equipment. Gravity separation is basic to almost all
oil/water separators. Several methods have been devised for accelerating the
process. These include provisions for heating the influent to reduce the
viscosity of the aqueous phase, extended plate surfaces to increase the hori-
zontal distance traveled by oil globules, rotational forces instead of gravi-
tational force, and air flotation. In attempts to increase oil/water separa-
tion efficiency, there have been modifications of existing designs. As a
result, devices in this category are the most abundant. The slight varia-
tions and modifications in designs have already been reviewed excellently by
Harris (1973). Of major concern are the improvement of the hydraulic
18
-------
characteristics of the devices and the reduction of turbulence in separators.
Almost all gravity-type separators produce effluents that must be treated fur-
ther, in subsequent separating devices. However, they are reliable, simple,
and inexpensive to operate, and serve to attentuate fluctuations in flow and
oil concentration in lieu of more sophisticated oil/water separators.
API Oil/Water Separators—The design of gravity-type separators has been
studied extensively by several investigators and particularly by the American
Petroleum Institute (Ingersoll, 1951; Rohlich, 1951; University of Wisconsin,
1949, 1950, 1951). As a result of these efforts, the API has set forth de-
sign recommendations for oil/water separators in the Manual on Disposal of
Refinery Wastes; Volume on Liquid Wastes (API, 1969). Construction details
of API separators are found in Chapter 6 of the manual. Important design
considerations are minimum horizontal area, minimum vertical cross-sectional
area, and minimum depth-to-width ratio of 0.3-0.5. The API design is based
on Stokes's Law and hydraulic overflow rates. An oil-droplet rise rate of
0.2 ft/min, with a forward wastewater flow of 3.00 ft/min, is used. Deten-
tion time is about one-half hour. Separators are designed to remove non-
emulsified oil particles of 130-150 u and larger for oils having typical
specific gravity. Design nomographs are presented in the manual, with cor-
rections for turbulence, short-circuiting, and wastewater temperature. API
separators are usually rectangular in shape and multichanneled; expansion is
possible, and single channels can be cleaned without interrupting operation.
The API oil/water separator consists of inlet and outlet sections, a pre-
treatment stage, separating stages, baffles, skimming devices, and flight
scrapers. Some separators are equipped with covers or floating roofs. In
operation, oily wastewater enters the separator at the inlet, flow is slowed
down, and turbulence is minimized by the inlet structure and baffles. Oil
globules larger than 150 y rise to the surface and settleable solids (oil-
coated and non-oil-coated) sink to the bottom. Provision is made for skim-
ming the oil and removing the sludge. A schematic diagram of an API
oil/water separator is given in Figure 1.
Hydrogard separators are prepackaged oil/water separator units, manu-
factured by Inland Environmental Corporation. These separators are designed
according to API guidelines. Units with flow rates up to 210 gpm are avail-
able. Cleaning and maintenance are carried out easily. Inland Environmental
Corporation claims that effluents from these separators can contain as little
as 5 ppm of oil.
Circular Separators—Oil/water separators designed according to the con-
ventional arrangement of a circular clarifier are used in some oil refineries
with satisfactory results, but a rational design procedure for circular sep-
arators has not been developed. An advantage of circular units is the ease
of installing oil-skimming and sludge-scraping devices. The capacity of
these devices can be varied by adjusting the height of the oil skimmer. Oily
wastewater is fed through a central inlet; effluent outlets are located in
the peripheral wall. Circular units are more compact than API separators.
Plate Separators—Concern over the large space requirements of API oil/
water separators led to studies on methods of reducing equipment size without
decreasing oil-removal efficiency. Different methods were used to reduce
19
-------
h-
SEPARATOR CHANNEL
J
DIFFUSION DEVICE
(VERTICAL-SLOT BAFFLE)
GATEWAY PIER
\
-A
\
±
JJ.
/ /
/ /
FOREBAY i
SLOT FOR
CHANNEL GATE
FLIGHT SCRAPER
CHAIN SPROCKET
ROTATABLE OIL
SKIMMING PIPE
\
WOOD FLIGHTS
FLIGHT
SCRAPER
CHAIN
\
\
WATER \
LEVEL .
* \
=yt
\
1 I I
FLOW
OIL-RETENTION
BAFFLE
"--SLUDGE-COLLECTING HOPPER
DISCHARGE WITH LEAD PIPE
EFFLUENT
/WEIR AND
WALL
EFFLUENT FLUME
EFFLUENT SEWER
SLUDGE-COLLECTING
HOPPER '
SLUDGE PUMP
SUCTION PIPE
Figure 1. API Oil/Water Separator
-------
settling length, because the time required for oil particles to rise to the
surface depends on the depth of the separator. Flat plates, plate packs,
convoluted plates, perforated conical plates, and perforated plates of other
geometry have been used to subdivide the settling chamber into a number of
sections. Plates increase the surface area and reduce the maximum rise
height of oil globules. It is observed that coalescence of oil globules
occurs on these plates, also, Therefore, the maximum distance oil droplets
have to travel, before coalescence occurs, is dependent on plate spacing in-
stead of depth as in the API design. To improve coalescence, plates are
manufactured from oleophilic materials and inclined at an angle to the incom-
ing flow. As oil globules rise to the surface, they coalesce on the under-
side of the plates, creep up plate surfaces and break loose as large particles
that rise rapidly to the top. Because of these design modifications, plate
separators are approximately one-fifth to one-half the size of API separa-
tors. Oil skimming and sludge removal are easier; the main problem with
these units is plugging of the spaces between plates with solids, biological
growth, or highly viscous oils. Several types of plate separators are avail-
able commercially.
Shell parallel-plate interceptor. The Shell parallel-plate inter-
ceptor (PPI) oil/water separator has parallel plates spaced 100 mm (approxi-
mately 4 inches) apart. Two such systems are available. One system consists
of one or more sets of plates inclined at an angle of 45° to the long axis of
the separator. The other system consists of one set of plates parallel to
the long axis and inclined at an angle of 45° to the horizontal. The spacing
between the plates can be varied. Because of the inclination, the effective
surface area for coalescence is increased and the net path oil globules trav-
el before reaching the surface is decreased (Kirby, 1964). These added fea-
tures make the Shell PPI oil/water separator capable of separating oil drop-
lets of 60 y in diameter or larger. In spite of improvement in performance,
stable emulsions and dissolved oil cannot be separated in these devices.
Shell corrugated-plate interceptor (CPI). An improvement on the
Shell PPI oil/water separator design is the Shell CPI separator. It features
plates arranged at an angle of 45° to the horizontal in the direction of
wastewater flow, similar to the Shell PPI unit; the major difference is that
the plates are corrugated and the spacing between plates is smaller, only
approximately 20 to 40 mm. Plates are made of fiber glass-reinforced poly-
ester. Because of closer spacing, CPI units are more compact than PPI units
and oil-removal efficiency is greater. Reduction in space requirement can be
as high as two-thirds, but plugging from solids is a major problem. Newer
designs feature accesses for easy cleaning. Schematic diagrams of the Shell
PPI and CPI are given in Figures 2 and 3, respectively.
The Fram Corporation manufactures an oil/water separating system fea-
turing a combination of two separation processes. The separator has three
stages: the first stage contains two preconditioners (filter-cartridge type,
having 75-y pore openings) for suspended-solids removal; the second stage
utilizes parallel-plate-type gravity separation; and the third stage contains
a cartridge-type coalescer. Because of the presence of a cartridge-type
coalescer, this system is capable of breaking and separating emulsions.
pact design makes the system suitable for use on board ship. Oil-removal
Com-
21
-------
OVERFLOW PIPE FOR
TREATED WATER
VENT AND OIL
OVERFLOW PIPE TREATED
WATER
ISJ
l-o
TRASH
CONTAINER
SCREEN
PACKS OF PARALLEL
INCLINED PLATES
SLUDGE SUMP
SUCTION HOSE
FOR SLUDGE
SAND SUMP
Figure 2, Shell Parallel-Plate Interceptor
-------
U>
ADJUSTABLE WEIR
\
\
OIL
SKIMMER
_ ,
LAYER
/ OIL GLOBULES
v\\\\\\\\\\\\\\\\\
INLET
\\\ \Y\\A\
SEDIMENT TRAP
PACKS OF CORRUGATED
PARALLEL PLATES
TREATED WATER
OUTLET CHANNEL
— SLUDGE PIT
Figure 3. Shell Corrugated-Plate Interceptor
-------
efficiency is reasonable, but effluents require some further treatment before
discharge. Media plugging and low liquid flow rates are disadvantages.
System backwashing, when head loss reaches a specified level, is automatic.
Curved-Plate Finger Separators—The basis for the design of the curved-
plate finger separator is accelerated gravity settling of oil from oily
wastewaters. This separation technique is a combination of gas flotation and
parallel plate-type gravity separation. Incoming wastewater feed is first
mixed with air, as in dispersed gas flotation; the separation of oil and
water takes place between curved steel plates. The plates are inclined hori-
zontally and arranged in the direction of flow- Oil films form at the under-
sides of the plates, rise gradually toward the upper ends of the plates, and
leave as "fingers" at the plate tips. Oil that collects at the surface is
removed by an oil-skimming device. Because of the gas flotation character-
istics of this device, small oil globules can be separated. Space require-
ments are less than for API oil/water separators, for the same throughput.
The Gravi-Pak oil/water separator is manufactured by Keene Corporation.
Units are multistaged, and consist of a primary separation chamber of the
parallel-plate type and a secondary separation stage in which natural gravity
settling occurs. Devices are suitable for gross separation of oil and water
and are more compact than the API design, but larger than Fram-Akers units.
Manufacturers claim effluents from these units can contain less than 30 ppm
of oil, with wastewater having up to 20,000 ppm of oil.
Design—Stokes's Law is the fundamental principle governing design of
gravity-type oil/water separators. Design considerations are flow rate,
rise rate of oil globules, turbulence correction factors, type and concentra-
tion of oil, characteristics of wastewater, and geometry of basin.
Performance—Gravity-type oil/water separators are used primarily to
remove free oil, large oil globules (unstable primary dispersions), and oil-
and/or non-oil-coated solids in suspension. Stable emulsions (surface- or
chemically stabilized), solubilized oil, and dissolved oil are not separated
by devices operating on the gravity differential principle. Devices can
handle varying influent oil concentration and are normally used for gross
separation. Effluents from these devices usually require some further treat-
ment before discharge. Factors affecting oil-removal efficiency are flow
rate, oil particle size, density of oil, characteristics of wastewater,
temperature, and separator design. For good separation, it is essential
that feed velocity distribution is as uniform as possible at the inlet
section of the device.
The API oil/water separator is an effective and versatile device for
removing oil and suspended solids. Because of design limitations, API sep-
arators are only effective in removing oil globules having a lower limit of
130 y in diameter. Neutrally buoyant particles may pass out with the efflu-
ent. Beychok (1973) has summarized the available performance data on API
separators. His data are presented in Table 2. Data indicate that oil con-
tent of effluents can be as high as 120 ppm, when the oil content of influ-
ents is small. Operation of devices at flow rates grossly below design
24
-------
rates yields lower efficiences. In experiments with a cylindrical-type sep-
arator having a residence time of about 20 minutes, at a flow rate of 10 gpm,
Finger and Tabakin (1973) report that more than 80% of the oil was removed
from oily wastewaters containing up to 4% oil. The performance data of
several gravity-type separators, published by Gloyna and Ford (1974), are
presented in Table 3. Oil-removal efficiencies, for refinery wastes, range
from 50 to 90%. Data indicate that oil-removal efficiencies in parallel-
plate separators may be higher than achievable in API separators. A compari-
son of results of API and PPI separators by Kirby (1964) indicates reductions
in oil content of up to 67% more in the PPI than in the API. Data presented
by Brunsmann et al. (1962) substantiate the belief that PPI separators
achieve higher oil removal than comparable API separators. Harris (1973)
presents estimated effluent quality from primary oil/water separation proces-
ses, as shown in Table 4. The oil content of effluents from devices operat-
ing on the gravity differential principle can be much higher. Effluents con-
taining more than 500 ppm of oil should be expected, if the influent contains
high concentrations of emulsified and dissolved oil. Average oil removal,of
25 to 65% should be expected; oil-removal efficiency can be increased to more
than 80%, if the process is used in conjunction with chemical addition. Sus-
pended-solids (oil-coated and/or non-oil-coated) removal of up to 65% can be
accomplished. Gravity-type separators will continue to be basic to treatment
of oily wastes; and operation of devices, at design flow rates by trained
personnel, will yield reasonable separation.
TABLE 2. OIL REMOVAL IN API SEPARATORS*
Oil content (ppm)
Influent Effluent % Removal Shape
-
-
-
-
50-100
90-98
42
108
20-70
20
80-115
75
20-40
40-44
20
20
-
-
-
-
60
55
52
54
Rectangular
ir
it
ii
it
it
it
Circular
* Reproduced with permission, from Aqueous Wastes
from Petroleum and Petrochemical Plants, by
Milton R. Beychok.
Copyright ©1967, John Wiley & Sons Limited
25
-------
TABLE 3. OIL AND SUSPENDED-SOLIDS REMOVAL IN GRAVITY-TYPE SEPAEATORS*
Oil content (ppm)
Influent
300
220
108
108
98
100
42
2000
1250
1400
Effluent
40
49
20
50
44
40
20
746
170
270
% Oil % Suspended-
removal solids removal
87
78
82
54
55
60
52
63 33
87 68
81 35
Type
PPI
API
circular
"
API
n
"
n
ti
n
* Gloyna and Ford (1974).
TABLE 4. ESTIMATED EFFLUENT QUALITY FROM PRIMARY OIL/WATER
SEPARATION PROCESSES*
Separators commercially
available
Effluent oil
concentration
(fflg/D
API rectangular
Circular
Inland Steel—Hydrogard
Shell PPI
Shell CPI
Finger-plate separator
Fram-Akers plate separator
Keene—Gravi-Pak
50-75
50-75
50-75
35-50
35-50
35-50
50-100
20
* Harris (1973, p. 85).
Rotational Separation—Successful separation of oil from water by uti-
lizing rotational motion has been reported in the literature (Guzdar et al.
1975; Yu, 1969; Sinkin and Olney, 1956; Sheng and Welker, 1969). However,"
this separation method is practical and economical only when the concentra-
tions of oil and suspended solids are high. Rotational separation is an
accelerated gravity differential separation method and Stokes's Law applies-
gravitational force is replaced by centrifugal force. The centrifugal force
26
-------
can be 1000 to 5000 times the gravity force, and the rate of separation is
faster than in ordinary gravity separation. There are three basic types of
rotational separators: (1) centrifuges, (2) hydrocyclones, and (3) vortex
flow.
Centrifuges. Centrifuges have been used extensively in sludge-
dewatering applications and for removal of solid contaminants from waste-
waters. In recent applications, centrifuges have been used to separate oil
from oil/water mixtures. In centrifugation, the oil/water mixture is moved
along a circular path by the rotational motion of the device. The centri-
fugal force developed by rapid rotation of the system enhances the separation
of the two phases. The phase with the higher density has a larger momentum
and moves toward the outer periphery of the centrifuge; the less dense phase
concentrates at the center line of the centrifuge. These phenomena occur as
a result of the centrifugal force field and the difference in densities of
the two phases. The greater the difference in the densities of the two
phases, the faster the separation and the less the energy requirement. A
minimum density difference of 5% is enough for separation. The location of
the boundary between the two liquid phases can be predicted in theory, and it
is possible to determine the critical oil-droplet size that will be present
in the separated water phase.
Hydrocyclones. The basic principle of separation by a hydrocyclone
is similar to that of a centrifuge. In a hydrocyclone, the liquid is forced
into circular motion due to tangential injection of the oil/water mixture
against the circular configuration of the hydrocyclone (Yu and Ventriglio,
1969) . The advantages of a hydrocyclone over a centrifuge are low initial
cost, ease of maintenance, and absence of moving parts. But hydrocyclones
require considerable pumping power to achieve the centrifugal force needed
for separation. Separation by a hydrocyclone is similar to vortex flow sep-
aration, and problems associated with the turbulence created during operation
have made both methods inefficient for treating oil/water mixtures.
Design—The design of centrifuges has not changed much since their first
introduction. Emphasis is in providing centrifuges capable of achieving
greater throughput, at low speed. The three types of centrifuges most often
used in marine oil/water clarification applications are the barrel, tubular,
and disc or plate types (Harris, 1973). Centrifuges can be designed for
radial or axial flow. The Navy, Coast Guard, and Maritime Administration are
sponsoring jointly a contract to develop a centrifuge. It is to incorporate
axial flow, allowing for,comparatively high throughput and low speed. Axial
flow design allows sufficient residence time for interdrop coalescence to
occur, increasing the effectiveness of separation (Finger and Tabakin, 1973).
Performance—Oil/water separation by centrifugation is practical only
when the oil and/or solid particles are present in relatively high concentra-
tion and the densities of the oily and liquid phases are not close. Centri-
fugation is effective in removing oil- and non-oil-coated suspended solids,
free oil, and primary dispersions, if the average oil globule size is greater
than the critical drop size. It is ineffective in removing stable emulsions
and solubilized and dissolved oil. With chemical addition, this method has
been used to destabilize and coalesce stable emulsions. Hence this method is
27
-------
used mainly to concentrate and recover fuel oil from oily wastewaters with
little water content. Finger and Tabakin (1973) report, in laboratory tests,
effluent concentrations in the range of 10 ppm were obtained with feeds con-
taining 1000 ppm of #2, #4, and Nigerian crude oil. At higher concentra-
tions, ranging up to about 59,000 ppm of #2 oil and 19,000 ppm of #4 oil,
effluent concentrations were higher, but did not exceed 100 ppm. The oil
content of effluents reported by these authors is unusually low, and higher
values should be expected. Efficiences of centrifuges are usually in the
range 60-80%, depending on the specific nature of the oily wastes concerned,
oil and suspended-solids concentrations, temperature, etc. The presence of
detergents has an adverse effect on device performance.
Efficiencies ranging from 77 to 91% have been reported for hydrocy-
clones, but the oil content of effluents was persistently high and the sep-
arated oil phase contained water droplets (Sinkin and Olney, 1956) . Sheng
and Welker (1969) suggest the use of several hydrocyclone units, in a cascade
operation, to produce effluents containing less than 100 ppm of oil; informa-
tion on this process is currently not available. Centrifuges and hydrocy-
clones can be useful for gross separation, in lieu of more advanced and
better separation methods.
Vortex flow. Separation of liquid/liquid mixtures, utilizing the
fluid phenomenon known as confined vortex flow, can be achieved if the
liquids differ in density. Vortex flow is similar to centrifugation; as
such, it is an accelerated gravity settling technique. The separation of
oil/water mixtures is accomplished by imparting relatively large rotational
motion to the mixture, in a cylindrical vessel. As a result of the confined
vortex flow, the lighter fluid (in most instances the oil) is accelerated
radially inward faster than water. Therefore, oil accumulates and forms a
central core, where it is removed by extraction tubes (or a perforated core)
located at the center line of the cylinder.
Two types of vortex-flow separators are available commercially. In one
type, the influent or recycle stream is injected tangentially into the cylin-
der through various inlet ports. Injection points are located at the circum-
ference on one end of the cylinder. In the second type, a shrouded axial-
flow pump impeller is used to rotate the fluid; this type is very similar to
a centrifuge. However, vortex separation is different from centrifugation
because the volume of fluid rotated at any time is smaller, and reinjection
of some effluent water is necessary to maintain the vortex formed within
the tube.
Design—Vortex separators consist primarily of a vortex tube, a cylin--
drical vessel with a perforated tube or extractor located at the center line
and have no moving parts. Important design parameters are: operating pres-
sure, location of injection and exit ports, and length-to-width ratio of
vortex tube. Several geometric variations are possible.
Performance—Several factors affect the performance of vortex-flow sep-
arators. These include: separator geometry, feed-oil concentration, oil
type, oil-droplet-size distribution, debris, external motion, oil-collection
rate, and temperature. In tests conducted with the United Aircraft vortex
28
-------
separator, separation was poor; slightly emulsified oil could not be separ-
ated. Average oil content of effluents was above 50 ppm, and separated oil
contained as much as 90% free water. Better separation was obtained when the
unit was followed by a gravity separator. Because of physical limitations,
vortex separation is capable of separating only free oil or oils with large
droplet sizes. Even then, oil-removal efficiency can be lower than that of
ordinary API gravity separators. Furthermore, injection of oil/water mix-
tures creates turbulence, which reduces oil-droplet sizes and hinders
separation.
Gas Flotation—The success of gas flotation in the mineral industry led
to its use for separating oil from wastewater (Gaudin, 1957). Gas flotation
is an accelerated gravitational separation technique in which flotation of
oil dispersions, wax and grease, and suspended solids in wastewater is accom-
plished by numerous microscopic gas bubbles. The process is a composite of
the following steps (Vrablik, 1957):
a) introduction of gas bubbles into wastewater;
b) collisions between gas bubbles and suspended matter;
c) attachment of fine bubbles to the surfaces of suspended matter;
d) collisions between gas-attached suspended particles forming
agglomerates;
e) entrapment of more gas bubbles into agglomerates; and
f) upward rise of floe structures in a "sweeping" action ("sweep
flocculation").
A froth layer is formed at the surface of the wastewater and is removed by
an appropriate skimming device.
The rise rate of the floe structures is expressed by a modified
Stokes's Law:
v
o 18y
where v = rise rate of oil-air-particle agglomerates
o
g = gravitational constant
D = effective diameter of oil-air-particle agglomerates
o
S = density of aqueous phase
to
6 = density of oil-air-particle agglomerates
y = absolute viscosity of aqueous phase.
The attachment of gas bubbles to suspended matter in the flotation process
affects density and diameter in the Stokes's Law equation. The result is a
net increase in rise rate. Two- to tenfold increases in rise rate are
encountered, depending on other factors, e.g.,
a) gas-input rate and volume of gas released per unit volume of liquid;
b) bubble-size distribution and degree of dispersion;
c) surface properties of suspended matter;
29
-------
d) hydraulic design of flotation chamber;
e) concentration and type of dissolved material;
f) concentration and type of suspended matter; and
g) temperature, pH, etc.
Different gases have been used for the flotation process (Vrablik, 1957;
Berry and Engel, 1969), but flotation by air is most common. The essential
property of the gas is limited solubility in water. Different flotation
methods are practiced: dispersed air flotation, dissolved air flotation
(DAF), vacuum desorption flotation, and electrochemical flotation. The first
two methods differ in the way air is introduced to the wastewater; in the
other two, the air bubbles are generated from the wastewater itself.
Dispersed air. In dispersed (diffused) air flotation, air is in-
troduced through a special type of disperser (e.g., diffuser, sparger, re-
volving impellers, perforated tubes, etc.) to the influent of a flotation
tank. The use of diffusers poses problems, particularly in oily wastewaters
having high concentrations of suspended solids, waxes, and greases, because
diffusers are susceptible to plugging. Air bubbles generated in dispersed
air flotation have diameters of approximately 1000 p and higher.
Dissolved air (DAF) . In DAF, wastewater is saturated with air at
an elevated pressure (usually 15 to 60 psig) in a retention tank for 1 to 5
minutes. Then, the pressure on the air-saturated wastewater is reduced to
atmospheric, at the inlet to a flotation chamber. Reduction in pressure
leads to the release of tiny air bubbles from solution. These have diameters
ranging upwards from 50 y. Retention time in the flotation chamber is about
15 minutes. Dissolving air in wastewater provides the maximum possible con-
tact that can be established, and oil droplets or suspended particles may act
as nucleation sites for bubble precipitation (Churchill, 1973) . Three meth-
ods are used in operating DAF units: full-stream (total) pressurization,
split-stream (partial) pressurization, and recycle-stream (recycle) pressuri-
zation. These three methods are shown in Figures 4 to 6. Each mode has its
advantages and disadvantages (Churchill, 1973), but recycle-stream pressuri-
zation is considered superior to others (Rohlich, 1954; Simonsen, 1962).
Typical recycle rates are about one-third of influent flow. Recycle units
are the most common of all four flotation methods.
Vacuum desorption. Vacuum desorption flotation is accomplished in
three steps (Rohlich, 1954):
a) a preaeration period to saturate wastewater with air at atmospheric
pressure;
b) release of larger air bubbles; and
c) application of vacuum to the wastewater.
Depending on the vacuum applied, air bubbles have sizes similar to those in
dissolved air flotation but, because of limited solubility, the desorption
process may require higher energy than the dissolved flotation process
However, there is a reduction in turbulence relative to that which occurs in
DAF units (flotation chamber). This turbulence is a deterrent to eff f
particle/bubble collisions. ective
30
-------
AIR
OIL/WATER
MIXTURE
SCUM
FLOTATION
CHAMBER
CLARIFIED
EFFLUENT
PRESSURE
RETENTION
TANK
Figure 4. Total Pressurization System
-------
OIL/WATER
MIXTURE
N3
FLOCCULATING
AGENT
FLOCCULATION
CHAMBER
PRESSURE
RETENTION-
TANK
FLOTATION
CHAMBER
OILY SCUM
CLARIFIED
EFFLUENT
Figure 5. Partial Pressurization System
-------
OILY SCUM
OIL/WATER
MIXTURE
to
LO
FLOCCULATING
AGENT
FLOCCULATION
CHAMBER
PRESSURE
RETENTION
TANK
CLARIFIED
EFFLUENT
RECYCLE
PUMP
Figure 6. Recycle Pressurization System
-------
Electrochemical. Electrochemical flotation is a recent concept.
In this process, microgas bubbles are produced in'wastewater by electrolysis.
Bubble-size distribution is in the colloidal range, 0.001 to 0.1 u; it is
estimated that about 10 times as many bubbles are generated by this flotation
process than are produced by air pressurization systems. Furthermore, gas
bubbles produced electrolytically possess surface charges of either polarity.
These surface charges can be effective in neutralizing oil dispersions and
suspended solids stabilized by surface charges.
Design—Commercially available DAF units are rectangular or circular in
shape and are constructed of steel. Important design parameters are: pres-
sure, recycle ratio, inlet oil concentration, and residence time. DAF units
generally consist of horizontal flow chambers, with inside configurations
required for operation as gravity separators. The hydraulic design of DAF
units is critical. Length-to-width ratios vary from 2/1 to 5/1. API has
made recommendations on the design of DAF units (API Manual, 1969). Multi-
cell DAF units are manufactured and are claimed to be more efficient than
single-cell units (Ellis and Fisher, 1970). DAF units are generally more
compact than API gravity separators.
Performance—Air flotation is used for removal of large oil globules
and suspended solids. Flotation units are normally preceded by API gravity
separators. The efficiency of air flotation depends, to a large extent, on
air-bubble size. The gas bubbles are in a state of motion; collisions with
suspended matter must occur before attachment takes place. If a suspended
particle is much smaller than a bubble, the former may follow the viscous
streamlines of the bubble and not make contact.
Because the bubble sizes expected in dispersed air flotation are of the
order of 1000 y, only unstable primary dispersions and large, oil-coated
suspended solids will be separated. Consequently, oil-removal efficiencies
lower than 25% and suspended-solids removal of about 20% can be achieved.
Despite the smaller bubble-size distribution in DAF, oil-removal efficiencies
are in the range of 60 to 90% (Stormont, 1956; Quigley and Hoffman, 1966).
Suspended-solids removal as high as 95% have been reported. Particles exhib-
iting neutral buoyancy may be removed by flotation, if they are not stabi-
lized by surface charges. D'Arcy (1951) reported an unusually high final
effluent quality (between 5 and 7 ppm). If properly designed and operated,
oil concentrations of effluents from DAF units can be kept below 50 ppm.
The efficiencies of vacuum desorption flotation units are generally
lower than those of DAF units, even when high vacuums are used. Electro-
chemical flotation may be capable of separating oil droplets and suspended
solids stabilized by surface charges.
Motion during the separation process has significant effect on device
performance; motion interferes with skimming of the froth layer. Floated
oil and solids may redisperse in the aqueous phase. For an efficient separa-
tion, oil concentration in influent should not vary significantly.
34
-------
Filtration
Filtration through granular materials is one of the oldest methods for
separating oil/water mixtures. This technique is useful for removing sus-
pended matter and associated materials, particularly oil, from oily waste-
waters. It is best suited for removing oil-coated solids that are a major
cause of fouling in coalescing devices. Neutrally buoyant oil-coated solids
that may require infinite settling times can be removed, also. As a result,
this technique is becoming very important in the petroleum industry because
of its capacity to reduce the concentratiori of oil and level of suspended
solids in production waters that are passed, subsequently, to secondary and
tertiary recovery operations.
The mechanisms involved in removal of suspended solids by filtration are
very complex and little understood. With deep granular filters of coarse
material, removal is primarily within the filter bed (commonly referred to as
depth filtration) . Some solids may be removed by a process of interstitial
straining, and oil may be removed by adsorption on the bed material.
There are three main filtration techniques: layer, membrane, and
fibrous-media. Membrane filtration is discussed in the section on membrane
processes, and filtration by fibrous media is essentially a coalescence/
filtration technique which has been discussed elsewhere. The present discus-
sion focuses on layer filtration only. Layer filtration can be divided into
two types: deep granular and multimedia.
Layer Filtration—Granular media. Several materials have been used as
granular media; these include sand, crushed anthracite coal, perlite, diato-
maceous earth, garnet or ilmenite sand, and powdered or granular activated
carbon. A granular-media filter normally utilizes a bed of these materials
to remove the contaminant. The most common and economical filter material is
fine, graded sand (slow and rapid sand filtration). The effective size of
the filter media may vary from 0.35 to 1.0 mm. In the backwash cycle, hy-
draulic grading of the sand occurs, with the finest sand forming the top of
the bed. Therefore, if a suspended solid present in the process stream is
not trapped in the top layer, it is most likely to be found in the effluent
because larger voids occur in the direction of liquid flow.
Multimedia. To overcome the shortcomings of layered systems,
multimedia filters were introduced. The principle of multimedia filtration
is that coarser grains of lower specific gravity will settle more slowly
than heavier but finer grains, during the backwash cycle, provided the size
ratio between different materials is properly selected (Hsiung et al.,1974).
With dual media, combinations of two materials are used, e.g. crushed an-
thracite coal and silica sand. The dual media have the largest grains
(coal) at the top and the smaller sand grains below, but the average grain
size at the bottom is still relatively large.
To decrease average grain size, mixed-media filters are used. A mixed-
media filter uses three or more materials, each of different size and den-
sity, that intermix, not stratify, to form'a filter.grading from coarse at
the top to fine at the bottom in the direction of flow. Typically,
35
-------
anthracite coal, silica sand, and garnet are used (Evers, 1975). The main
advantage of using mixed-media filters is pressure-drop reduction at'high "
flow rates, without deterioration of effluent quality. Longer filter runs
can be achieved, also. Increasing the number of filter materials (different
densities and sizes) approaches an ideal filter, one in which the size of
media particles decreases uniformly. However, the additional advantages of
the ideal filter, for three-media or four-media cases, do not offset the
extra cost.
Design—Deep granular filters consist generally of 18 to 30 inches of
filter medium. The filter material is supported on an under-drain system
inside a pressure or gravity-flow vessel. Concrete systems are available,
also.
The design of mixed-media filters depends on several factors: the de-
sired effluent quality, the oil and suspended-solids content of feed, desired
flow rate, and maximum allowable head loss. An excellent filter can be made
from 18 inches of 1.0-mm "effective"-size coal (sp. gr. 1.6), 0.5-mm
"effective"-size sand (sp. gr. 2.6), and 0.3-mm "effective"-size garnet (sp.
gr. 4.0). The size and quantity of each filter material can be varied inde-
pendently to meet specific requirements. The average oil-droplet and
suspended-solids sizes are the primary determinants of the size of the vari-
ous materials used. After the first backwash, the materials become inter-
mixed but the filtration efficiency increases in the direction of liquid
flow. Typical filtration rates are 5 to 10 gal/min/sq ft. The preferred
surface wash system is the rotating-arm type; during backwash, the bed is
expanded at least 15% for efficient cleaning. Air wash is sometimes used for
cleaning mixed media, but it is not as effective as backwashing unless suffi-
cient water is provided for fluidization of the filter, after the air scour.
Multistage filters are being designed, so there is no interruption of opera-
tion during backwash of one unit. Devices are equipped with automatic back-
wash systems which initiate backwash cycles on a time cycle or on the basis
of filter head loss.
Performance—Oil-removal efficiency and storage capacity of a filter
depend upon the media design. Filters have a limited oil-retention capacity,
and when effluent quality deteriorates and becomes unacceptable, or when
pressure drop through the filter reaches a predetermined value, operation is
discontinued and filters must be washed to restore capacity. Literature on
the subject of backwashing filters used for oil removal shows that fouling
of media is a common problem. Fouling results from the accumulation of sus-
pended solids within the bed and/or from biological growth in the bed. Cak-
ing or mud-balling in filters is common; filters are not well suited for
intermittent flows. Failure of automatic backwashing devices is a major
cause of poor effluent quality. Scheduling, or backwash frequency, consti-
tutes a problem, also. Properly designed surface-wash and backwash facili-
ties can keep filter media clean over prolonged periods of use.
Tests using multimedia filtration to precondition production waters for
reinjection during secondary and tertiary recovery operations indicate the
absence of visible oil in effluents. Pilot tests conducted at the University
of Houston indicate that mixed-media filters are very effective in separating
36
-------
unstable oil/water emulsions formed by pumping light Iranian crude oil into
the suction side of a fresh-water feed pump. This filter was operated at 10
to 12 gal/min/sq ft, with an influent containing 750 ppm of oil; COD measure-
ments indicated a 95 to 100% oil-removal efficiency, in runs of up to 6 hours.
With 100 ppm of oil in the feed, a run lasted more than 30 hours and effluent
contained about 10 to 20 ppm of oil (COD measurements) . Tests of a deep-bed
sand filter at the same loading rate indicated an oil-removal efficiency of
85 to 90%, when the feed contained 250 ppm of oil. A filter run lasted about
16 hours (Hooper and Myrick, 1972). It should be noted, however, that the
very long operating times and high oil-retaining capability of the bed were
probably due to the absence of suspended solids in the feed.
Results of these tests show that filtration using granular materials is
a candidate for separating oil/water mixtures containing unstable emulsions,
oil-coated solids in suspension, and some free oil. However, the process
generates secondary wastes (backwash) which have to be treated before dis-
charge. The volumes of such wastes are generally small. When used in con-
junction with chemical treatment, filtration can separate chemically stabi-
lized oil emulsions but, because of physical limitations, dissolved oil will
still be present in effluents from devices operating on the filtration
principle.
Membrane—During the last decade, there has been rapid progress in the
development of artificial membranes. As a result, membrane processes are
becoming increasingly important in wastewater treatment. Hydrophobic and
hydrophilic membranes have been used for oil/water separation, particularly
for polishing purposes, because membrane fouling is a major problem. For
efficient separation, the membrane has to be matched to the oil/water system
to be separated, and the feed must be free from suspended solids. Pore size
and structure of the membrane determine the quality of effluent. Membrane
processes for separating oil/water mixtures are still in the developmental
state; some of their disadvantages are limited rates and throughputs achiev-
able and high cost. Processes are slow, but effluents from membrane devices
usually have oil content below acceptable discharge limit.
Membrane processes are different from conventional microporous filtra-
tion. Membranes are semipermeable, extremely fine in porosity, and easily
fouled. Depending on a membrane's surface characteristics, it will pass oil
but not water, or vice versa. If the viscosity of the oily phase is too high
for passage through a membrane at a practical rate at ambient temperature, a
method has to be devised for heating the feed mixture. The energy require-
ment for processing large volumes of wastewater is large. If the oily phase
has a low viscosity, a large surface area is required to process a volume of
wastewater. Therefore, membrane processes are prohibitively expensive and
can be justified only for handling small-volume wastewaters or for removing
the last traces of oil, notably soluble oils and chemically stabilized emul-
sions. In membrane processes, little pretreatment of feed is necessary.
New membranes are being developed that can process untreated feeds. As the
research activity currently in progress yields good results, and if membranes
can be made cheaply, membrane processes will become more attractive and may
eventually replace other treatment and separation methods because of the
high-quality effluents that are possible.
37
-------
The major membrane processes are electrodialysis, reverse osmosis, and
ultrafiltration.
Electrodialysis. Electrodialysis has been used extensively for de-
salting applications. The driving force for this technique is electrical
potential gradient; separation is based on selective ion transport across a
membrane. The flow of electrical current in electrodialysis causes water to
flow (electro-osmosis) and to be separated from the oil phase by a water-
selective membrane across the current path. Desired membrane properties are
high water-transport number, high electrical conductivity, good chemical re-
sistivity, and high mechanical strength. Electrodialysis has not been inves-
tigated extensively as a possible separation technique, but it may be useful
for separating wastewaters containing emulsions stabilized by surface char-
ges . This technique may be practical for small-volume wastewaters; however,
pretreatment of feed will be necessary to diminish membrane plugging. Some
of the disadvantages of this technique are high energy requirements, dissoci-
ation of water at high current densities, imperfectly selective membranes,
low liquid flow rates, and concentration polarization. These phenomena re-
duce the overall efficiency of this technique.
Reverse osmosis. Like electrodialysis, reverse osmosis has found
application to desalting operations for brackish water. The principal driv-
ing force for this technique is pressure; reverse osmosis is essentially a
membrane filtration technique, in which pressures are greater than the os-
motic pressure exerted by species in solution. Separation is on the basis of
molecular size. Applied pressure forces water, and species smaller in size
than the rejection level of the membrane, through the membrane. Oil and
larger species will be rejected at the membrane surface. The smaller the
size of the species present in the oily wastewater, the greater the osmotic
pressure generated; therefore, reverse osmosis has an added advantage of
being able to remove species of atomic dimensions by using tight membranes
and operating pressures higher than the osmotic pressure. Experiments have
shown that conventional dialysis membranes of the semipermeable, molecular
diffusion type are not appropriate for use in reverse osmosis. Cellulose
acetate membranes are presently used most widely. New casting techniques
have led to production of ordinary and modified cellulose acetate membranes
which appear adequate for reverse osmosis processes on the bases of high
water flux and good rejection of organic molecules. A wide variety of mem-
branes and backing systems is being developed. One important commercial
system is based on a polyamide membrane. Fluxes greater than 25 gal/day/sq
ft of membrane are possible, at applied pressures up to 1500 psig. One
problem encountered is the slow decrease, with time, of oil rejection because
of membrane hydrolysis. As a result, operation is applicable to a narrow pH
range, to increase membrane life. Fouling is not a serious problem because
rejected matter is usually passed downstream by the flowing process stream,
but periodic cleaning is necessary.
Ultrafiltration. Ultrafiltration is similar to reverse osmosis,
differing because it is not impeded by osmotic pressure. Reverse osmosis'
systems operate at elevated pressures of 250 to 1500 psig, while ultrafiltra-
tion systems are operated at lower pressures of only 50 to 200 psig. Because
of lower operating pressures, ultrafiltration membranes are more open, and
38
-------
rejection of only colloidal or suspended matter and other macromolecules is
possible. The predominant mechanism in ultrafiltration is selective sieving
through pores. In the ultrafiltration process, feed is pumped through the
center of a porous tube on which a membrane has been cast integrally. Hy-
draulic pumping pressure causes water and some dissolved, low molecular
weight materials to pass; however, emulsified oil, free oil, and oil-coated
solids are retained and concentrated in the tube. To be useful for ultrafil-
tration, membranes must have a narrow molecular weight cutoff and a high
solvent flux at low-pressure differentials. Early work in ultrafiltration
was done using cellophane or porous cellulose nitrate membranes, but repro-
ducibility was poor; adsorption on pore walls and plugging were common. Be-
cause of breakthroughs in membrane technology, a variety of synthetic poly-
meric membranes is being tested in the ultrafiltration process. The most
promising, thus far, are non-cellulosic in nature and allow operation over a
wide range of pH and temperature. The limitations of this process are flux
decline with time and the phenomenon of concentration polarization. Flux
decline is the sum of membrane compaction and fouling. Economic studies have
shown that the most fruitful areas for significant gains are higher water
fluxes and longer membrane life.
Design—Ultrafiltration and reverse osmosis plants consist of a series-
parallel arrangement of modules. About four different module designs are
possible: plate and frame, tubular, spiral-wound, and hollow-fiber configu-
ration. Fibers are housed in cartridges that allow for expansion. A de-
tailed comparison of module designs has been investigated and summarized by
Schatzberg et al. (1975) . Ease of cleaning modules varies and backflushing
systems, with or without detergent cleaning, are incorporated into some of
the newer units. A typical membrane has an asymmetric structure, consisting
of a thin, dense skin on a porous support. It is approximately 100 y thick,
with a surface skin of approximately 0.2 y that acts as the rejecting sur-
face. The pore size is of the order of 5 to 50 A and, thus, is approximately
1000 times smaller than emulsified oil droplets (Nordstrom, 1974).
Generally, the membrane must be maintained wet at all times, although
some of the newer membranes can be handled dry. More recently, there has
been a trend toward development of thin-channel hollow fibers (Messinger,
1974). Hollow-fiber reverse osmosis systems are smaller in size than ultra-
filtration systems, but require greater power inputs (Finger and Tabakin,
1973). Ultrafiltration systems can be operated in batch or continuous modes;
throughput rates are usually small in both cases. Permeate rates in ultra-
filtration are higher than obtainable in reverse osmosis systems.
Performance—Applications of reverse osmosis and ultrafiltration systems
to the separation of oily wastewaters have been investigated (Desai, 1971;
Goldsmith and Hossain, 1973; Nordstrom, 1974; Schatzberg et al., .1975). Re-
sults of these tests indicate good separation, even though membrane processes
are still in the developmental stage. Studies at the Naval Ship Research and
Development Center, Annapolis, with reverse osmosis systems, reveal that
treated oily wastewater, containing 500 ppm of oil, gave an effluent contain-
ing approximately 10 ppm of oil. Permeate fluxes ranged from 10 to 25 gal/
day/sq ft, but periodic cleaning was necessary to minimize decline in per-
meate rates as a result of fouling (Finger and Tabakin, 1973). Results of
39
-------
experiments with ultrafiltration systems tested at the Center showed 90% oil-
removal efficiency, with a feed containing 100 ppm of oil. Permeate was free
of emulsified oil and contained less than 10 ppm of dissolved oil. Membrane
fouling was a problem, and only a detergent wash restored membrane flux
capacity. Finger and Tabakin (1973) note that chemically emulsified oil
wastes from bilge cleaning would actually improve ultrafiltration, by mini-
mizing fouling, but detergents are known to cause membrane disintegration.
Membrane processes are very useful for separating stable emulsions, oil-
coated solids, and free oil. Processes can achieve close to 100% oil-removal
efficiency, if adequately maintained and operated. Removal of dissolved oils
cannot be achieved in these systems but, with the advent of tighter membranes
capable of withstanding very large operating pressures, reverse osmosis will
become a candidate for separating dissolved oil. Ultrafiltration and reverse
osmosis are expensive processes, throughputs are low, and membrane replace-
ment is necessary as a result of fouling and other aging factors. It is pos-
sible to minimize concentration polarization in ultrafiltration by operating
at high feed velocities parallel to the membrane surface and/or utilizing
thin-channel hollow fibers.
Coalescence/Filtration
Coalescence of dispersed oils in aqueous suspension occurs in almost all
liquid/liquid separation processes. Originally, the coalescence process was
used to remove water from oil in aerosol filtration and, because it was suc-
cessful, it was adapted for removing oil from oil/water mixtures. The term,
as used in this report, refers to the coalescence process induced by flow
through porous media. Coalescence is a complicated operation; it has been
studied extensively, but the phenomenon is not completely understood (Jordan,
1953; Voyutskii et al., 1955, 1958; Redmon, 1963; Farley and Valentin, 1965;
Sareen et al., 1966; Spielman, 1968; Splelman and Goren, 1972a,b) . Several
theories have been advanced to explain the mechanism of coalescence (Vinson,
1965; Hazlett, 1969a, Jeffreys and Davies, 1971).
The following major steps were proposed by Voyutskii et al. (1955):
a) collisions of emulsion globules with the ends of filter fibers;
b) adhesion of droplets to the fiber;
c) coalescence of the microdrops;
d) adhesion of microdrops to the surfaces of fibers; and
e) trickling of coalesced drops down the fibers.
Hazlett (1969a) proposed dividing the coalescence process into three main
steps: approach of a droplet to a fiber or to a droplet attached to a fiber
attachment of a droplet to a fiber or to a droplet already attached to a '
fiber, and release of an enlarged droplet from the fiber surface. Each step
involves considerable complexity or alternative mechanisms. The fibers and
coalesced liquid matrix may capture droplets by a number of mechanisms-
interception, Brownian diffusion, inertial impaction, gravity settling 'and
long-range attractive forces. Except for-small particles, interception is
considered the dominant mechanism (Spielman and Goren, 1970). Therefore in
40
-------
coalescence, oil dispersions are retained in the porous media where the drops
grow larger, until they are large enough to be swept away by fluid-flow
forces. Coalesced oil snakes through the porous media until it reaches the
downstream face of the media, where it is released in individual droplets
large enough to separate from the aqueous medium by gravity.
Jordan (1965) classified liquid/liquid coalescing into two general
types:
a) depth-type: the coalescing operation occurs within the porous
material and both phases of the liquid system pass through the porous
material; and
b) surface-type: coalescence occurs on the surface of the porous mate-
rial and only one liquid phase passes through the porous material.
Surface-type coalescence and ordinary filtration are similar. In fact, some
filtration occurs in any coalescence process. Therefore, devices operating
on the coalescence principle are often called filter-coalescers.
A wide variety of materials has been used as coalescing media: natural
fibers (cotton and wool), synthetic materials (fiber glass, viscose, nylon,
orlon, and felt), reticulated (open-pore) foams, membranes (hydrolyzed and
cellulose acetate), screens, mats, and granular materials (pebbles, sand,
and diatomaceous earth). Because of the complex nature of coalescence, var-
ious approaches to coalescence processes have been identified. The major
differences in these modes are almost entirely the type of porous media used.
Fibrous-Media—Coalescence using fibrous media is the most important of
the coalescence types mentioned above. Fibrous materials with different
internal, geometric, and surface properties have been used. Voyutskii et al.
(1958) used viscose and wool fibers. Cotton and glass wool were used by
Gudesen (1964) . The most common fibrous material in use is fiber glass
(Burtis and Kirkbride, 1946; Hayes et al., 1949; Graham, 1962; Rose, 1963;
Sweeney, 1964). Coalescence performance of fiber glass can be enhanced by
coating the fiber surfaces with certain synthetic resins, e.g. phenolic
resins, to render them hydrophobic or hydrophilic. The use of fibrous media
implies depth-type coalescence.
Membrane—Membrane coalescence belongs to the surface-type discussed
above"Several separatory membranes are available. Membrane materials are
usually such that they can be treated to render them hydrophobic or hydro-
philic. Liquid flow rates are small. Membrane coalescence devices are
normally preceded by fibrous-bed coalescers, i.e. they are used as polishing
stages. This mode is similar to membrane filtration and is covered in that
discussion.
Centrifuge—As mentioned, gravity separation is an integral part of the
coalescence process. In centrifugal coalescence, fibrous material is used
as the coalescing medium, but the final gravity separation of the oil and
water phases is enhanced by centrifugation. Literature on this technique
has been reviewed.
41
-------
Bimetallic—Coalescence of dilute o/w emulsions by passage of the mix-
ture through a bed containing a granular mixture of dissimilar metals (iron
and aluminum) or carbon and a metal is a new concept proposed by Fowkes et
al. (1970). Various bimetal and carbon-metal beds have been tested, but no
complete engineering assessment of this technique's potential has been re-
ported. The process is essentially an electrokinetic phenomenon (Koelmans
and Overbeek, 1954), similar to electrophoresis and electrodeposition, but it
has coalescence/filtration characteristics (Ghosh and Brown, 1975).
Granular-Media—Beds of gravel, pebble or sand have been investigated as
coalescing media for oil/water separation (Douglas and Elliot, 1962;
Shackleton et al., 1960). Coalescence using diatomaceous earth and other
granular materials has been reported. This type of coalescence process is
discussed further in the section on layer filtration.
Other Porous Materials—Fine-mesh screens, non^woven mattings (polyester
felt, polypropylene felt, and glass mats) and reticulated foams have been
used as coalescence media (Vinson, 1965; The Permutit Company, 1966; Chieu et
al., 1975). In this coalescence process and that using granular media, oil
droplets are adsorbed until the bed is saturated or the breakthrough oil con-
centration in effluent is reached. Then, operation is discontinued so that
adsorbed oil can be removed by backwashing or squeezing the media.
Design of Fibrous-Media Coalescers—Since the mechanisms which lead to
coalescence are not fully understood, design of filter-coalescers is largely
empirical. The most common configuration for fibrous-media coalescers is a
cartridge. Fibers are arranged and bonded together to provide a tortuous
path for fine oil droplets in order to achieve reliable coalescence (Finger
and Tabakin, 1973; Freestone and Tabakin, 1975). Desired properties of car-
tridge elements are: uniform structure, sufficient pore openings, and ade-
quate mechanical strength to withstand operating pressures of 25 to 75 psig.
The direction of liquid flow through the coalescing element is usually radi-
ally outward. Cartridges (filter elements) are housed in cylindrical vessels
that can be mounted vertically or horizontally.
Coalescing elements are available in different sizes depending on unit
capacity. Coalescing devices normally contain more than one cartridge, each
cartridge can be removed independently, and the entire unit can be assembled
easily. Fiber sizes vary from less than 5-p to 25-y diameter. Failures of
cartridge-type coalesce^ occur as a result of improper end-cap sealing (poor
end cap-to-element sealing and/or poor gasket-to-end cap sealing) and poor
quality control (defective elements and voids in filter media) . Because of
the problems associated with solids, most devices are equipped with a screen
or prefilter ahead of the coalescer elements. The main purpose of the pre-
filter is to remove solid particles that may plug the pores of the coalescing
filter elements. However, the prefilter also acts as a coalescing filter and
preconditions the feed. Coarse filter cartridges, with approximately 25- to
100-y-diameter fibers, are used as prefilters.
Since gravity separation is an integral part of coalescence, commercial-
ly available coalescers are multistaged. The first stage is used as a gross
gravity separator or may contain a prefilter. Succeeding stages alternate
42
-------
coalescence and gravity separation. Important design parameters are: amount
of fibrous material (voidage), arrangement of fibers, and hydrodynamic
factors.
Coalescers are compact and easily assembled, and operation is flexible.
The? are usually not regenerated through fluidization or backwashing; there-
fore, replacement of coalescing elements is necessary. Coalescers equipped
with automatic cartridge-cleaning devices are available commercially. Figure
7 is a schematic diagram of a cartridge filter/coalescer.
Performance of Fibrous-Media Coalescers—In coalescence, a principal
driving force is interfacial tension (Yu and Ventriglio, 1969). Lowering the
interfacial tension of the oil and water phases promotes coalescence of the
dispersed oil phase. But coalescence can also occur in systems having high
interfacial tension, if the density difference between the two phases is high
and coalescing surfaces have a high degree of roughness (Jeffreys and Davies,
1971). Attempts have been made to analyze the performance of fibrous-bed
coalescers using filter coefficients. Theoretical expressions for filter
coefficients have been developed by several investigators using various co-
alescence models (Spielman and Goren, 1970, 1972a,b; Sherony and Kientner,
1971; Rosenfeld and Wasan, 1974). Important coalescing parameters are:
a) physical properties of coalescing media-preferential wettability of
bed, bed-spreading characteristics, fiber size, packing, pore-size
distribution, uniformity of structure, surface roughness of fibers,
and two-phase permeability of bed;
b) interfacial tension and contact angle;
c) flow velocity; and
d) physicochemical properties of fluids (viscosity, density,
temperature, etc.).
Combinations of small- and large-size fibers improve oil-removal effi-
ciency, if the larger-size fibers are located at the downstream end of the
cartridge (Voyutskii, 1958; Hazlett, 1969b; Jeffreys and Davies, 1971).
Resins used in bonding fibers together usually give an intermediate contact
angle (Hazlett, 1969a). Preferentially oil-wetted mats are believed to be
less efficient than aqueous-wetted mats for separation of o/w emulsions
(Spielman and Goren, 1972b). Voyutskii (1955) found a critical flow veloc-
ity, less than 1 cm/sec, below which separation was possible. Gloyna and
Ford (1974) found that oil-removal efficiency of coalescers is related to
two major factors:
a) variation in type of oil, degree of emulsion, droplet size, and
suspended-solids concentration; and
b) fluctuations in flow rates, influent oil concentration, and equipment
upsets.
For successful operation of filter beds, it is important that solid par-
ticles are removed from the oil/water mixtures before passage through the
bed. Solid matter deposited in the bed will not only change the voidage and
local fluid velocities in the bed but, more important, the surface properties
of the bed will be changed. Particulate matter (suspended solids and
43
-------
TREATED WATER EFFLUENT
OIL/WATER
MIXTURE
\\v\\\\\\\\\\\\\ >
\\\\ \\v\\\\\\\\\\
CARTRIDGE
COALESCING
ELEMENT
t
V
J
\
\
\
SEPARATORY
MEMBRANES
SEPARATED OIL
Figure 7. A Complete Liquid/Liquid Coalescing System
44
-------
gelatinous materials) interferes with effective coalescing. Plugging of
coalescing media often is the cause of coalescer failure. Plugging results
in, an increase in head loss and coalescer elements require elaborate cleaning
to restore efficient separation or replacement of filter elements.
The effects of surfactants on coalescence have not been studied exten-
sively. Detergents concentrate at the oil/water interface during coalescence
(Lindenhofen and Shertzer, 1967), limit droplet growth prior to detachment,
and hinder droplet release from the downstream face of the filter (Hazlett,
1969b) . It has been suggested that surfactants degrade coalescer performance
by absorption on the fibers, resulting in an increase in the contact angle
and decrease in wettability (Hazlett, 1969b). This alteration of the surface
properties of the coalescing fibers leads to poisoning of the coalescer and
eventual failure.
Coalescers are particularly suited for removal of oil dispersions, but
segregating phases after separation is difficult and expensive. Small quan-
tities of water may be present in the separated oily effluent of coalescers.
Oil content of influents to coalescers should be limited to 200 ppm and
should fluctuate only within a narrow range. However, if coalescers are well
operated and maintained, oil-removal efficiencies can be as high as 99%.
Typical values are higher than 90%. Results of studies at the Annapolis
evaluation facility indicate that 10 ppm of oil in effluent water can be at-
tained with some commercially available coalescers (Finger and Tabakin,
1973). Coalescers are not designed to remove dissolved and non-colloidal
oils (solubilized oil); therefore, oil/water mixtures containing these sys-
tems cannot be treated effectively. Oil dispersions stabilized by surface
charges cannot be treated adequately, although bimetallic coalescers have a
potential for treating this system. Solids, stabilized oil emulsions, and
suspended slimy materials, if present in influents to coalescers, may reduce
efficiencies below those obtained with gravity separators (Gloyna and Ford,
1974).
Adsorption and Absorption
Sorption on solids, particularly activated carbon, has become a widely
used operation for purification of waters and wastewaters. Activated carbon
has an affinity for organic matter present in petrochemical and refinery
wastewaters and, thus, is an effective means of removing dissolved oil, solu-
bilized oil, and chemically stabilized emulsions that cannot be destabilized
by chemical addition and other methods. These oil/water systems pose serious
problems in various oil/water separating devices.
Activated carbon has demonstrated large adsorptive capacity and desired
surface properties, making it adequate for adsorption processes; it is the
material most widely used. Adsorption is an interface phenomenon; oil is
selectively adsorbed on the surface of the carbon, but the adsorbed film is
only a few molecules thick. Adsorption of oil molecules from the aqueous
phase to the carbon surface occurs as a result of a combination of various
forces: adhesive, cohesive, electrical, surface tension, and van der Waals.
Contact between carbon surfaces and oil wastewater is achieved through
fixed-bed or expanded-bed carbon columns. As adsorption of oil and other
45
-------
organic matter present in the waste stream is accomplished, the carbon loses
its adsorptive capacity and breakthrough occurs. Spent carbon must be re-
placed or reactivated. The process is uneconomical if the spent carbon is
wasted; therefore, it must be reactivated and reused with new carbon added to
make up the losses of regeneration. Regeneration is an extremely important
consideration in the use of activated carbon for treatment of oily waste-
waters. Currently, regenerative methods are mainly thermal. The regenera-
tive process requires a large capital investment and has high operational
costs. It is presently feasible to regenerate carbon, by conventional ther-
mal techniques, for several cycles of successful saturation and regeneration.
The feasibility of other regenerative techniques is being investigated.
These are (1) the use of steam to drive off the adsorbed oil and (2) repeated
washings of the spent carbon with solvents. The results of these attempts
have been disappointing because of high cost and the small efficiency
achieved.
Design—The basic design and operating concepts of gravity flow, pres-
sure, and expanded-bed-type-flow adsorbers are essentially similar to those
for granular-bed filters of the corresponding types. Fixed-bed units are
usually vertical pressure vessels containing activated carbon supported on an
under-drain system. Important design considerations are flow rate, contact
time, depth of carbon, influent oil and suspended-solids concentrations, and
desired effluent quality. Multiple adsorption columns are usually provided
in series or in parallel so that a unit can be taken out for regeneration.
Moving-bed carbon adsorption columns are also being used to eliminate the
spare columns required for regeneration. Chiyoda, Japan, uses a new method
of contacting carbon and wastewater. Unlike conventional fixed-bed systems,
the Chiyoda multistage, fluidized-bed system is based on a unique process in
which activated carbon is circulated in continuous, countercurrent contact
with the wastewater and, when spent, carbon is reactivated for re circulation.
The advantage of this system is the absence of the removal of spent carbon
and replenishment with fresh carbon. The system can be operated without
interruption. Design is compact, space requirements are reduced, and there
is a flexibility of future expansion (Chiyoda Company, 1974) .
Performance—If properly operated, carbon adsorption columns provide
effluents that will meet practically all discharge limits for oil. Pilot
tests conducted by the Ben Holt Company, California, using carbon adsorption
columns in lieu of coalescing devices, indicated oil and surfactant present
in the influent were removed efficiently. Feed to the combined system was
typical Navy oily waste containing seawater, oil, sludge, dirt, and chemi-
cally stabilized emulsion. Influent to the carbon columns had an oil content
varying from 35 to 530 ppm. The highest effluent oil content was 2.5 ppm,
measured by chloroform extraction and IR spectrophotometry. Surfactant con-
centration at the carbon inlet varied from 63 to 630 ppm and was removed to
a level not detectable by IR analysis (Ben Holt Company, 1974) . Feasibility
studies of variations of the adsorption process by Calspan Corporation, New
York, showed efficient separations. In the latter studies, carbon adsorption
was used in conjunction with plain sedimentation, dissolved air flotation,
mixing and filtration, and polyelectrolyte coagulation. The average oil
content of effluents was 1 ppm, with contact times of less than 3 minutes
and influents containing up to 2000 ppm of oil. All samples were analyzed
46
-------
for oil content by percent transmittance measurement. Though results showed
efficient separation, the carbon dosages required were quite large: 1 g of
activated carbon per liter of wastewater (Wang et al., 1973).
Oil-removal efficiencies in carbon adsorption are usually very high: in
the range 95 to 100%; a typical value is 98%. An obvious disadvantage of the
simple adsorption process is low capacity, necessitating huge surface areas.
Therefore, carbon adsorption columns are used as polishing stages in lieu of
other separators. Removal of suspended solids is accomplished, also, because
of the filtration characteristics of carbon columns. However, in spite of
the high efficiencies achievable with this process, it has not found wide-
spread use because of the large expenditure involved. Attempts to use coke,
instead of activated carbon, as the absorption medium and to regenerate a
saturated adsorption surface by coking have not provided any encouragement
(Freestone and Tabakin, 1975). Nonetheless, carbon adsorption has proven to
be the answer where other physical and chemical treatment techniques have
failed and, as wastewater control regulations become more stringent, the
process has become indispensable.
Electric and Magnetic Separation
Separation of oil from water by electric and magnetic means has not been
fully investigated because of the high cost involved and the low liquid flow
rates achievable in such devices. These disadvantages, together with the
technological problems encountered, have made these methods unattractive.
The two methods in this category are electrophoresis and magnetization.
Electrophoretic—Electrophoretic separation has been used in oil refin-
eries for recovering oil from oil-rich wastewaters, but its application has
been limited to processing small volumes of wastes in which w/o emulsions are
the major contaminant. Electrophoresis, an electrokinetic phenomenon, is the
principle of separation in this technique. A strong electrical field is es-
tablished in the wastewater; dispersed particles move along the lines of
force and become separated from the continuous medium because of the net
electrical charge on each particle. The electrophoretic mobility of a water
particle is greater than that of an oil globule of the same size. Therefore,
this method is practical for separating w/o emulsions which are produced
during drilling operations. This method becomes more effective as the sizes
of the water droplets become smaller. When the water droplets are larger
than 10 y in size, a considerable electrical energy has to be used for an
appreciable separation to occur. An increase in the energy requirement can
lead to hydrolysis of water; hydrogen and/or chlorine gas may be generated
at the electrodes. Gas generation makes the wastewater turbulent and further
degrades separation efficiency. Separation of oil-in-seawater emulsions is
difficult because of the high electrical conductivity of seawater and the
possibility of concentration polarization. In general, electrophoretic
separation is a slow, inefficient process and is not suitable for the
treatment of large volumes of oily wastewater.
Magnetic—The feasibility of recovering oil from fine, stable, o/w
emulsions by magnetic means has been investigated by Kaiser et al. (1971). In
operation, a ferrofluid is added to the wastewater to make the dispersed oily
47
-------
phase magnetically responsive. The wastewater is passed through a packed bed
placed in a magnetic field. Packed beds are composed of magnetic particles
or screens. Results of experiments indicate virtually complete removal of
oil particles, as small as 1 y in diameter, using air-gap fields of several
thousand oersteds, bed packing of several inches in length, and oil-phase
magnetization of about 2 to 10 gauss. Residence times of less than a minute
were used. Magnetic separation is practical for separating small volumes of
oily wastewater in which the major oil/water system present is secondary
dispersions; energy requirements are large, and operational costs are high.
Thermal Separation
Separation of oil/water mixtures using thermal treatments is a feasible
concept, but impractical if large volumes of wastewater are handled. How-
ever, thermal methods have been used to resolve emulsions present in oily
wastewaters from crude oil production. After the emulsions are destabilized,
oil can be separated from wastewater through use of other separation tech-
niques . These methods have found only limited application and are adapted
specifically for those wastewaters which contain mainly w/o emulsions or when
water is present in small amounts. In systems such as these, the wastewater
can be demulsified using thermal treatment. The process is economically
attractive, if oil recovered from the wastewater has a high heating value or
can be reprocessed and used as fuel oil. The major thermal treatment methods
are heating, evaporation and distillation, and freezing or crystallization.
Heating—Heating has been used extensively to resolve crude oil emul-
sions. It has been used in conjunction with chemical addition to destabilize
chemically stabilized emulsions. The process also increases the amount of
dissolved oil in the wastewater. It is simple: the basic principle of this
technique is alteration of the vapor pressure difference between oil and
water. Energy requirements for large volumes of wastewater make this process
uneconomical. Large equipment sizes are required, also.
Evaporation and Distillation—These separation techniques are similar to
heating and suffer from the same disadvantages, even when the distillation
process is carried out at reduced pressure. Complete separation of waste-
water into distinct oil and water phases is impossible because, during opera-
tion, the oil fractionates and some fractions will be present in both con-
densate and distillate. Even when the distillation process is carried out in
stages, there is a large energy demand for heating and providing reduced
pressure before oil can be removed completely.
Freezing and Crystallization—In these methods, the difference in the
freezing points of the two liquids is used to effect separation. Oil/water
separation by freezing and crystallization is generally considered as
economically infeasible when large volumes of wastewater are handled. Little
literature on these techniques for oil/water separation is available. How-
ever, there is obvious need for complex refrigeration equipment and
relatively large inputs of energy (Yu and Ventriglio, 1969).
Thus, thermal separation, though feasible, is not practical because of
the high cost involved.
48
-------
Sonic and Ultrasonic Separation
The use of sonic and ultrasonic devices to separate liquid/liquid mix-
tures is prevalent in the dairy industries, but the capability of these tech-
niques to separate oil from oil/water mixtures has not been investigated
fully. The lack of engineering assessment of these separation methods is a
consequence of the use of sonic and ultrasonic devices, originally, in emul-
sification processes; they were deemed unsuitable for the reverse operation
(demulsification). There are suggestions that these techniques may be fea-
sible, if the appropriate wave frequency is used, for destabilizing emul-
sions. Destabilized emulsions can be coalesced and separated, using other
separation techniques.
Determination of the appropriate wave frequencies necessary to destabi-
lize emulsified oil/water systems is a costly operation. The characteristics
of untreated wastewaters change and volumes of oily wastes to be processed
are usually large. Using the wrong frequencies may break stable emulsions
into finer dispersions or shatter already coalesced globules.
Coanda-Effeet Separation
Separation of oil/water mixtures by utilizing the fluid-dynamic phenom-
enon called the "Coanda effect" is a new concept in liquid/liquid separation.
The basic principle of this process was proposed by Henry Coanda, and the
Navy has designed a separator capable of treating bilge and ballast waste-
waters by the wall-attachment (Coanda-effeet) phenomenon (Navy, 1974; Paszyc
et al., 1975). In this process, an oil/water mixture is injected into an
unbounded region. The jet splits into two subjets at the apex of concave
walls; each subjet is deflected toward an adjacent wall, becomes attached,and
flows along the wall enclosing a separation-bubble zone. The curved flow of
each subjet creates a centrifugal force and the separation-bubble zone is
formed. An oil droplet released at the jet nozzle experiences an inward
motion due to the centrifugal force and undergoes radial displacement toward
the bubble zone; it can coalesce with other oil droplets trapped there. Oil
which accumulates in the bubble zone can be drawn off by suction. A
schematic diagram of the process is shown in Figure 8.
Design—Important design parameters are: length of the attachment walls,
radii of curvature of the splitting walls, velocity of fluid at the nozzle,
and the size of the nozzle. Basically, a Coanda-effeet separator comprises:
inlet and outlet ports, an oil-collection chamber, oil/water interface detec-
tion probes, and an oil suction device. Multistage units are under design.
Performance—Results of test evaluations indicate that devices cannot
achieve greater oil-removal efficiency than an API gravity separator or other
primary separation technique. A major difficulty encountered with these
devices is the turbulence that arises during processing, as a result of jet
flow. Turbulence breaks oil dispersions into smaller droplets that are more
difficult to separate. However, in the absence of turbulence, devices will
be capable of separating only free oil and unstable primary dispersions.
Oils with the same density as the aqueous phase will not be separated.
49
-------
CLARIFIED
EFFLUENTS.
REATTACHED JETS
. VELOCITY
PROFILES
NOZZLE
OIL/WATER
MIXTURE
INLET
SEPARATION
BUBBLE
ZONE
MIXTURE
JETS
Figure 8. Coanda-Effeet Separator
50
-------
Viscosity-Actuated Phase Separation
A new concept for separating a mixture of two immiscible liquids has
been proposed and tested by Union Carbide Corporation. The principal driving
force for the separation is the difference in viscosity of the liquids. The
basic principle of this separation technique was proposed after laboratory
observations of flow fields induced when a mixture of two immiscible liquids
was subjected to pressure gradients. These laboratory tests revealed that if
a drop of a mixture of oil and water is placed in the V-notch formed by two
flat plates that can be squeezed together, separation of the liquids occurs
because the low-viscosity water flows from the pressurized area more rapidly
than the higher-viscosity oil (Union Carbide Corporation, 1973).
An apparatus was constructed to subject oil/water mixtures to the proper
type of flow field in order to achieve separation of the mixture. The appa-
ratus consists of a screw capable of rotating inside a threaded hollow cylin-
der. The rotor and stator are fitted so there is maximum eccentricity be-
tween the two parts during motion of the rotor. In operation, the changing
clearance between the rotor and stator induces a squeezing action on oil/
water mixtures and separation occurs.
Design—During a test evaluation, two types of viscosity-actuated phase
separation devices were used. One unit (Orbiting Buttress Threaded Device)
consists of an orbiting-screw rotor and a threaded hollow cylinder; both
rotor and stator are constructed of rigid material. The second unit (Rotat-
ing Buttress Threaded Device) is similar to the first unit; however, the
rotor is threaded and the stator is smooth. Later in the test evaluation,
both units were constructed of an elastomeric material.
Important design parameters include the degree of eccentricity between
the rotor and stator and the clearance between the two parts. Figure 9 is a
diagram of an Orbiting Buttress Threaded Device.
Performance—Factors that influence device performance are separator
geometry, the viscosity differential between the two liquids, and the balance
between feed and separation rates. Results of test evaluations were not
encouraging, and the poor performance reported was attributed to excessive
clearances between the rotor and stator. For an effective separation, the
oil-droplet size must be larger than the clearances between the stator and
rotor. Because of geometric design limitations and inaccuracies in machin-
ing, the lower limit of the clearances could not be achieved. Results indi-
cate that the devices increased emulsification instead of effecting separa-
tion. Some success was reported during separation of oil/water mixtures
with oil as the continuous phase. These devices cannot qualify as oil/water
separators, at present.
Chromatographic Separation
Chromatographic techniques are widely used in liquid/liquid separation
and purification applications. Gas, liquid, and gel chromatographic methods
have been suggested as processes capable of separating oil/water mixtures.
However, there is no literature available on the use of these methods for
51
-------
OIL/WATER MIXTURE INLET
OIL EFFLUENT
ORBITING
SHAFT
ECCENTRIC
DRIVE SHAFT
WATER
EFFLUENT
Figure 9. Orbiting Buttress Threaded Device
52
-------
bulk oil/water separation (Yu and Ventriglio, 1969). Chromatography has use
in several applications, but the technique suffers from the following disad-
vantages: small throughput, high head loss, and very low rates. Selection
of column packings capable of extracting the oil phase from oil/water mix-
tures is difficult and expensive. Disposal of spent column materials is a
problem and, if material is regenerated using an appropriate solvent, a
secondary waste is generated. Therefore, the high cost of these methods has
discouraged investigation as candidate oil/water separation processes.
Such sophisticated and costly separation methods may prove useful for
small volumes of oily wastes containing little oil as regulations and
discharge limits become more stringent.
53
-------
SECTION 7
CRITICAL REVIEW OF SELECTED LITERATURE
Title: Coalescing Plates and Packs for Oil/Water Separation in Various
Shipboard Applications
Report No. and Date: CG-724305.2/6, January 1973
Authors: J. G. Merryman and E. R. Osterstock
Manufacturer of Equipment: General Electric Company, Philadelphia, Pa. 19101
Design Features: Device is a gravity-differential, parallel-plate
separator. Plates are convoluted and made of polypropylene. Plates are per-
forated, also, to enhance oil-globule coalescence. Equipment is divided into
four compartments; each compartment contains a plate pack.
Wastewater Characteristics; Four oils were used in the tests: (1)
Navy Special Fuel, (2) Navy Distillate Fuel, (3) Venezuelan Crude, and (4)
a mixture of hydraulic fluid and lubricating oil. Aqueous test fluids were:
(1) tap water and (2) seawater. Mixing of oil and water was accomplished by
three different methods, yielding different levels of emulsification. In the
first two methods, a Lightning mixer was operated at two speeds. In the
third method, oil and water were mixed and re circulated through a centrifugal
pump. Bilge water was simulated by adding detergent and sand to the oil/
water mixture containing test oil (4).
Methods of Analysis; Oil content of samples was measured by (1)
chloroform extraction and transmittance measurement in a B & L spectrophotom-
eter and (2) gravimetric analysis. All samples were acidified before analy-
sis. Results of both analytical techniques were comparable. In most tests,
the colorimetric method was used, because of accuracy in the low concentra-
,tion range.
Results: Several parameters that affect separation efficiency were
investigated. These parameters were plate length, oil concentration, temper-
ature, and flow rate. Results showed the oil content of effluents was always
less than 50 ppm, for influent containing 500 ppm of oil. When influent oil
concentration was increased to 5000 ppm, effluent oil content was higher than
100 ppm. Effluents in tests using the centrifugal pump had more oil than
those produced in tests using the Lightning mixer. Addition of detergents
degraded device performance, also. Poor performance was observed when ship
motions were simulated by rocking the separator.
54
-------
Critical Comments; Plate- type, gravity-differential separators can-
not separate emulsions effectively. They are adequate for gross separation
only. Effluents from these devices have to be processed further to achieve
desired discharge quality.
Title: Feasibility Test Program of Application of Coalescing Phase Oil/Water
Separators to Self-compensating Fuel Tanks in Surface Ships
Report No. and Date: CG-D-88-74, May 1974
Authors: J. B. Arnaiz and E. Batutis
Manufacturer of Equipment: General Electric Company, Philadelphia, Pa. 19101
Design Features; Equipment is a commercial, parallel-plate-type,
gravity separator, capable of flow rates up to 1150 gpm. Length of the sep-
arator is 14 feet; plate length is 8 feet. This device has provision for
connecting the inlet to a ship fuel tank discharge port.
Wastewater Characteristics; Actual ballast water discharged from a
Navy oiler (U.S.S. Koelsh) during routine fueling operations. Ship had been
docked a few days .
Method of Analysis; During the test evaluation, on-line measurements
of entrained particle size and number were obtained for influent and efflu-
ent, using an HI-AC particle counter. On-line turbidity measurements were
made on the effluent, using a Keene turbidity meter. All samples were as-
sayed for oil content by carbon tetrachloride extraction and spectrophototn-
etry. Prior to extraction, samples were acidified with a mixture of sul-
furic and hydrochloric acids in a one-to-one ratio.
Results ; Data reported by the performing agency were generally lower
than the results of chemical analyses of samples carried out by U.S. Navy
Laboratories. However, both sets of results indicate the oil content of
effluents was less than 8 ppm, in all tests . Influent oil concentration
varied from 4 to about 1000 ppm.
Critical Comments^ Device functioned satisfactorily and separating
efficiency was unusually high. This may be the result of the absence of
emulsions in the oil/water mixture. Ship had been docked some time before
deballasting; it is conceivable that considerable separation had occurred
before the test evaluation was begun.
Title: Oil/Water Separator Evaluation
Report No. and Date: NCSL 252-75, July 1975
Author: John Mittleman
Manufacturer of Equipment: Assembled by author
55
-------
Design Features: Device is a gravity-differential, plate-type sep-
arator. Plates are made of oleophilic material and arranged in stacks verti-
cally in one chamber and horizontally in others. Equipment contains auto-
matic valves, sensors, and other hardware items necessary for maintaining
control of the movement of fluids in the system.
Wastewater Characteristics; In preliminary tests, synthetic waste-
water was produced by emulsifying Navy Distillate Fuel Oil in tap water.
Later, ballast and bilge water pumped from a naval vessel were used as feed.
Methods of Analysis: Two methods were used to quantify oil concen-
trations in samples: (1) visual quantification for those effluent samples in
which there was a persistent sheen and (2) extractions with carbon tetrachlo-
ride followed by light-transmittance measurements at 420 nanometers.
',
Results; Data were presented graphically, and indicate poor perfor-
mance throughout the test period. The oil content of all effluent samples
averaged more than 50 ppm. Separated oil contained a high concentration of
water, also. Device could not separate oil-coated solids.
Critical Comments: Gravity-differential separators are useful only
for gross separations. Oily wastewater containing high oil concentration, as
emulsions, cannot be separated in such devices. Results of this test evalu-
ation are indicative of the limitations of plate-type oil/water separators.
Title: Vortex Concept for Separating Oil from Water
Report No. and Date: 4105.2/1, January 1973
Authors: R. C. Stoeffler and C. E. Jones
Manufacturer of Equipment: United Aircraft Corporation, East Hartford,
Conn. 06108
Design Features: Separators tested consist of 6-inch and 9.5-inch
vortex tubes having four injection points; tubes were made of Lucite to allow
visual inspection of operation; end walls were plain discs fastened to the
vortex tube. A schematic diagram of the device is shown in Figure 10.
Wastewater Characteristics; Six types of oil (different densities
and viscosities) were injected separately into the water feed line using a
pressurized injection probe. In some tests, screens of different mesh sizes
were inserted in the input line to emulsify the oil; in other tests, a
centrifugal pump was used.
Method of Analysis; Oil content of samples was measured by carbon
tetrachloride extraction and infrared analysis; values of the actual and
measured oil concentrations were close.
Results; Overall, separator performance was poor. Oil content in
56
-------
r
01
=n
EXIT END-x
WALL \
\
N
WATER EXIT-v
DUCT
r
"
__\J
Ij
=r==:v
•L^^
£ 1
1
-,
1h-
^=3
1
s
r-OIL-COLLECTOR
DUCT
D ,
f ¥ °
r
- -\
t
^~ — SUPPORT STRUTS)
i SECONDARY /
NJECTOR (TYPICAL)j
/
i
;
c
r-LUCITE/ 1
b \
1 -
r"
A—a —
/
r
/
0
/
o
1 0 '
1 Or
j=>
y- INLET E^
,/ WALL
^-MIXTURE
INJECTOR
(TYPICAL)
TYPICAL
INJECTOR
BI-
SECTION B-B
B
SECTION A-A
NOMINAL SEPARATOR
CAPACITY, QM- GPM
10
50
DIMENSIONS
L - IN.
18, 36
28.5, 57
D - IN.
6
9.5
d* - IN.
0.6, 1.2
0.95, 1.9
do-
0.18
0.305 .
Dj - IN.
0.209, 0.272, 0.323, 0.453
0.609, 0.718, 0.922
-------
effluents was generally greater than 50 ppm; separated oil contained up to
95% water.
Critical Comments; Test data indicate the vortex concept is not
feasible as an oil/water separation technique; the devices fail to meet
stringent discharge limits. Separators were unable to separate emulsified
oil; separated oil contained excessive free water, making reprocessing
necessary. Slightly better separation was achieved when the process was
followed by gravity separation.
Cost: The following prices were reported:
100 gpm unit: $10,000
1,000 " " : $94,000
10,000 " " : $940,000
Title: Investigation of the Use of a Vortex Flow to Separate Oil from an
Oil/Water Mixture
Report No. and Date: 714103/A/001, November 1970
Authors: A. E. Mensing, R. C. Stoeffler, W. R. Davison, and T. E. Hoover
Manufacturer of Equipment: United Aircraft Corporation, East Hartford,
Conn. 06108
Design Features; Device is a 10-inch-diameter by 29.25-inch-long
vortex tube; tube was made of Lucite to allow visual inspection; end walls
were made of plain discs fastened directly to the tube. Injection points
were located on the peripheral wall of the vortex tube.
Wastewater Characteristics; Influent oil/water mixtures.were pre-
pared by metering oil into a water line; four types of oil were used but
none of the oils were emulsified.
Method of Analysis; Samples were left quiescent for several hours
until the oil and water phases separated; then, the respective volumes of
the two liquid phases were measured.
Results: Authors claim that it is possible to "capture" up to 85%
of the injected oil and the separated oil can contain less than 15% water.
Critical Comments: The analytical method is unacceptable, because
natural gravity separation is possible as the influent did not contain emul-
sified oil. Data presented graphically indicate overall performance was
poor even when the process was followed by gravity separation. The authors'
claims cannot be verified; thorough testing of the device is necessary and
test data need to be reported in a better way before meaningful conclusions
can be drawn.
58
-------
Title: Vacuum Desorption Concept for Removing Oil from Water
Report No. and Data: USCG 734305.2/8, March 1973
Author: George M. Pomonik
Manufacturer of Equipment: Mechanics Research, Los Angeles, Calif. 90045
Design Features; System consists basically of: collection tank,
vacuum separation tank, vacuum pump, revolving drum skimmer, and flow-control
devices. A modification included polypropylene coalescing plates added to
the vacuum tank.
Wastewater Characteristics; Mechanically emulsified oil/water mix-
tures were prepared with tap water and various oils. Occasionally, salt was
added to simulate bilge and ballast water. A few tests were conducted with
detergent and fine sand added to the influent. Mixing of oil and water was
done by pump.
Method of Analysis; Oil content of samples was determined by extrac-
tion with petroleum ether, evaporation to dryness, and weighing of the
residue.
Results; Oil concentration in effluents varied from 5 to 1000 ppm.
Oil injected ahead of the main centrifugal pump could not be separated. The
best effluents (5 and 7 ppm of oil) resulted when oil was added to tap water
effluent from the main pump.
Critical Comments; This system is not suitable as a final oil/water
separation device because of the poor performance. Improved design may en-
hance system capability for treating oil dispersions and suspended solids
free of surface charges.
Title: Electrochemical Flotation Concept for Removing Oil from Water
Report No. and Date: USCG 734305.2/4, January 1973
Authors: Q. H. McKenna, H. Helber, L. M. Carrell, and R. F. Tobias
Manufacturer of Equipment: Lockheed Aircraft Service Company, Ontario,
Calif. 91761
Design Features; The system consists of a rectangular flotation
cell, approximately 4 feet long, constructed from glass-reinforced polyester.
The cathode is stainless steel mesh. The anode is made from fine platinum-
10% iridium alloy wire, spot-welded to a Columbian substrate.
Wastewater Characteristics^ Simulated bilge and ballast waters using
a combination of tap water, sea salts, and different oils were tested. Emul-
sification involved blending the mixture with a Lightning mixer for 5 minutes
before feeding, by gravity, to a high shear pump operating at 500 psig.
59
-------
Stability tests indicated that the mixtures contained unstable emulsions
after they were prepared. Oil concentrations in the aqueous phases dropped
to about 100 ppm from higher initial concentrations after a few hours.
Methods of Analysis; Two methods were used for analyzing samples.
One method involved extraction with solvent, followed by UV analysis. Sol-
vent was a mixture of the following components: 60% 2-propahol, 10% petro-
leum ether, 20% seawater, and 10% tap water. In the second method, pure
ether was used as the extracting solvent. Oil concentrations determined by
both methods were similar.
Results; Experimental data indicate the oil concentration of all
effluents was lower than 20 ppm, for influents containing oil concentrations
of 3000 to 4000 ppm.
Critical Comments: If developed adequately, the electrochemical
flotation concept can separate oil from water effectively. The oil/water
systems most susceptible to separation will be oil dispersions and suspended
solids stabilized by surface charges. Consistent effluent quality of less
than 10 ppm of oil can be achieved. The system was not tested thoroughly for
the effects of variable oil concentration in the influent. Simulated ship
motion did not degrade system performance. Cell volume is large and the cost
of chemicals and equipment is very high. Problems encountered in the process
are: (1) production of chlorine gas which dissolves in the effluent, to a
concentration of 250 ppm—concentration is beyond the allowable discharge
level for chlorine, making further treatment a necessity; (2) production of
hydrogen gas, causing a fire hazard; and (3) temperature elevation of efflu-
ent, due to ohmic heating of the electrodes, leading to thermal pollution and
energy wastage.
Cost; 10 gpm unit: $10,000
100 " " : $80,500
1000 " " : $600,000
Title: Separation of Oil in Bilge Water by Semipermeable Membrane
Report No. and Date: AD-A023-289, May 1971
Authors: W. L. Adamson and M. W. Titus
Manufacturer of Equipment: Bench-scale apparatus assembled by authors
Design Features; Device consists of a 3-inch-inside-diameter, stain-
less steel cylinder in which was mounted the cellulose-acetate membrane
(Eastman Chemical type HF) . The membrane was placed on a porous stainless
steel disk supported on a perforated metal disk. Operating pressures ranged
from 550 to 675 psig.
Wastewater Characteristics: The feed solution was prepared from dis-
tilled water and 2190-TEP lubricating oil. The oil/water solution was
stirred mechanically for 1 hour, in a mixing tank, and gravity-fed to a
60
-------
reciprocating pump. A magnetic stirrer located at the feed inlet provided
further emulsification of the feed.
Method of Analysis; All samples were analyzed for oil content using
carbon tetrachloride extraction and infrared absorbance measurement. Two
extractions with carbon tetrachloride were made: 25 ml of CCl^ in the first,
and 15 ml of CC14 in the second.
Results; The average oil content of all effluent samples was below
25 ppm of oil with feed containing up to 10,000 ppm of oil. The longest run
lasted for about 15 hours.
Critical Comments: This test evaluation shows the feasibility of
using cellulose-acetate membranes for separating oil/water mixtures. The
device was not tested in detail, because the feed wastewater characteristics
were different from those of bilge and ballast water or petrochemical waste-
waters. There was a sharp decline in permeate flow rate with increasing
operating time, indicating that fouling of the membrane may have occurred.
Repeated cleaning with trichloroethylene partially restored permeate flow
rate.
Title: Study of Hydrophilic Membranes for Oil-Water Separation
Report No. and Date: 4305.2/7, January 1973
Authors: C. E. Milstead and J. F. Loos
Manufacturer of Equipment: Gulf Environmental Systems Company, P. 0. Box
81608, San Diego, Calif. 81608
Design Features: Twenty membrane materials were evaluated as candi-
dates for use in ultrafiltration. Hydrolyzed asymmetric cellulose-acetate
was selected, and tests were conducted with this membrane in a spiral-wound
configuration.
Wastewater Characteristics; Four different oils were used: Gulf
Harmony lubricating oil, diesel fuel, a California crude oil, and actual
bilge water from a U.S. Navy ship (U.S.S. Monti cello) that had been in harbor
for 2 weeks. Oil/water mixtures were prepared in a feed reservoir by a mix-
ing pump, with tap water and oil.
Methods of Analysis; Oil content of samples was determined using an
extraction-gravimetric technique and Total Carbon Analysis. The precision
of the extraction-gravimetric technique, based on data, was better than +5%
for lubricating oil/water mixtures but large errors were encountered with
crude oil/water mixtures.
Results; Test results indicate the following:
a) Oil content of effluents averaged 1.3 ppm with feeds containing
up to 50,000 ppm of lube oil, 2.4, 5 and 1.5 ppm with feeds containing 2,500
61
-------
ppm of crude oil, 2,500 ppm of diesel oil, and actual bilge water, respective-
ly.
b) Oil content of effluent reached a maximum of 18 ppm with feeds
containing 10,000 ppm of diesel oil.
Critical Comments; The surface-hydrolyzed cellulose-acetate membrane
performed satisfactorily in all tests and can produce effluents that contain
less than 10 ppm of oil. Variations of operating conditions did not affect
device performance adversely. Membrane fouling is a problem, and an adequate
cleaning method to restore product flux is lacking. For consistent perfor-
mance, feed should be free of suspended solids.
Cost; The estimated costs of two units are as follows: 100 gpm unit:
$27,000; 1000 gpm unit: $245,000.
Title: Ultrafiltration Concept for Separating Oil from Water
Report No. and Date: 734305.2/2, January 1973
Authors: R. L. Goldsmith and S. Hossain
Manufacturer of Equipment: Abcor, Inc., 341 Vassar Street, Cambridge,
Mass. 02139
Design Features; Ultrafiltration membranes tested were (1) moderate-
ly hydrophilic cellulose-acetate and (2) highly hydrophilic cellulose-acetate.
Both were studied in a tubular configuration; each tube had an internal
diameter of 1 inch and membrane pore sizes were less than 0.01 v~. Ultrafil-
tration rates were high, generally in the range 25-150 gal/day/sq ft.
Wastewater Characteristics: The oils tested were No. 6 fuel oil, a
Venezuelan crude, lubricating oil, and kerosene. Very unstable emulsions
were obtained by gravity feeding these oils into recirculated tap water.
Methods of Analysis: The analytical methods used were:
a) Gravimetric—samples were acidified with sulfuric acid and oil in
the samples was extracted with petroleum ether; extract was dried
and the residue from the drying step was weighed.
b) Infrared spectrophotometry following extraction with carbon.
tetrachloride.
c) UV spectrophotometry following extraction with carbon tetrachlo-
ride. Method (b) was the least sensitive. Samples were kept
refrigerated (35°F) for 1 to 5 days before analysis.
Results; The authors claim that, at oil input ratios of up to 90%,
effluents were uniformly free of visible oil and had less than 10 ppm of oil.
All effluents were reported to be completely free of turbidity and floating
oil sheen, and were crystal-clear. However, a very faint oil odor and taste
were generally detectable.
Critical Comments; Test results from the gravimetric and infrared
spectrophotometric techniques were quite dissimilar. Most analyses were by
62
-------
the gravimetric technique, which is very sensitive to drying temperature.
Test results cannot be entirely correct. The presence of oil odor and taste
indicate that dissolved oil passed the membrane, and the concentration of
dissolved oil could be far greater than the 10 ppm reported for all efflu-
ents. Test data were not properly reported, and further testing is necessary
before meaningful conclusions can be made. Membrane fouling is a problem.
Title: Oil-Water Separation with Noncellulosic Ultrafiltration Systems
Report No. and Date: Proceedings of Joint Conference on Prevention and
Control of Oil Spills, 1975, pp. 443-447
Authors: P. Schatzberg, L. R. Harris, C. M. Adema, D. F. Jackson, and
C. M. Kelly
Manufacturer of Equipment: Laboratory models were assembled by authors
Design Features; Four different modules were tested:
a) A tubular module consisted of a bundle of porous carbon tubes,
each having an internal diameter of 0.25 inch and a length of 40
inches; the membrane had an apparent pore diameter of 20 A.
b) Hollow-fiber modules, in two configurations, were used. One con-
sisted of a bundle of hollow fibers having an internal diameter
of 0.017 inch and a length of 24 inches; this system could be
backflushed, and total effective membrane surface area was 25 sq
ft; the membrane had an apparent pore diameter of 38 A and a
nominal molecular weight cutoff of 10,000. In the second config-
uration, the internal diameter of fibers was 0.020 inch and the
effective membrane area of the bundle was 30 sq ft; the nominal
molecular weight cutoff was 80,000 and the apparent pore diameter
was 100 A.
c) The spiral-wound module consisted of a series of membrane sheets,
separated by corrugated spacers and combined in a spiral-wound
cylindrical shape; total membrane area was 35 sq ft and pore
diameter was approximately 50 A. The membrane's nominal molecular
weight cutoff was 5,000 to 10,000.
d) A plate and frame configuration consisted of a series of membrane
sheets separated by fine fiber cloths; the membrane had an effec-
tive area gf 5 sq ft and an apparent pore diameter of approxi-
mately 40 A. The membrane's nominal molecular weight cutoff was
100,000.
Wastewater Characteristics; Two types of oil-in-water emulsions
were prepared, using a lubricating oil and fresh water. Initially a high-
speed blender was used to mix the oil and water; later, stabler emulsions
were prepared using an ultrasonic mixer.
Method of Analysis; Oil-in-^water analyses were made by infrared
spectrophotometry, following carbon tetrachloride extraction.
63
-------
Results; Each of the non-celluloslc memoranes investigated demon-
strated a capacity to separate emulsified and suspended oil from water. All
but the tubular modules consistently produced effluents containing less than
15 ppm of oil.
Critical Comments; All modules tested gave satisfactory performance.
The major problem encountered was a decline of flux rate as testing pro-
gressed. Therefore, permeate flushing and backwashing with detergent were
necessary. However, complete recovery tff flux rate could not be obtained
with any of the non-cellulosic membranes. Despite the good separation re-
ported, it is doubtful if these devices are capable of separating dissolved
oil or emulsified oil much smaller than the membrane pore diameter.
Title: Development of a Coalescing Type Oil/Water Separator for Marine
Service
Eeport No. and Date: Aqua-Chem Technical Report presented at SNAME Meeting,
San Diego, Calif., February 18, 1970
Authors: Lee J. Hartenstein and Thomas E. Lindemuth
Manufacturer of Equipment: Aqua-Chem, Inc., Waukesha, Wis.
Design Features; Device has three stages. The first stage is a
screen; three cartridge-type coalescer elements are present in the second
and third stages. Removal of oil in all stages is controlled by capacitance-
type oil/water interface detectors. Each chamber is equipped with electrical
heaters to reduce oil viscosity and to drive off small amounts of oil
entrained in the separated water phase.
Wastewater Characteristics; Oil is fed into circulating fresh water
(occasionally seawater) at the suction or discharge port of a centrifugal
pump to produce differing emulsified oil/water mixtures.
Method of Analysis; Technique(s) used in analyzing samples for oil
content not stated.
Results; Data were presented graphically and indicate effluent oil
concentrations were below 80 ppm, with influents containing 10% oil.
Critical Compents: Since analytical methods were not stated, data
reported lacked credibility; the operating temperature is high and may alter
solubility of oil in the treated aqueous phase.
Title: Oily Water Separator: Liquid-Liquid Separation by a Commercial
Self-cleaning Edge Filter
Report No. and Date: COM-71-01095, January 19, 1971
Author: J. R. Hefler
64
-------
Manufacturer of Equipment: AMF Beaird, Inc., Uncasville, Conn. 06382
Design Features; The system consists of a tank with internal baffles
and tangential inlets. Cartridge-type filter elements having spacings of
0.0015 inch were designed by Cuno Engineering Corporation. Filter elements
can be cleaned continuously by cartridge rotation. Automatic oil detection
probes provide recirculation of effluent for reprocessing, if oil concentra-
tion is high.
Wastewater Characteristics: Seawater and three grades of Bunker C
oil, of different densities, were used as test fluids. The oils were injec-
ted upstream and downstream of a 3450-rpm centrifugal pump, into seawater,
to provide the wastewater feed.
Method of Analysis; Samples are mixed with "sufficient" chloroform
and evaporated to dryness at 75°C; the weight fraction of oil present in a
sample is determined.
Results; Effluents contained as much as 2000 ppm oil. Separation
efficiency was poor. Oil with specific gravity close to that of seawater
could not be separated.
Critical Comments: Device was poorly designed and separation was not
possible when oil was injected ahead of the pump. Oil dispersions with drop-
let sizes less than 0.002-inch diameter were not separated. Test results
cannot be correlated, due to the poor experimental techniques used.
Title: Experimental Evaluation of Fibrous Bed Coalescers for Separating
Oil-Water Emulsions
Report No. and Date: EPA Project No. 12050DRC, November 1971
Authors: W. M. Langdon and D. T. Wasan
Manufacturer of Equipment: Illinois Institute of Technology, Chicago, 111.
60616
Design Features; Device is a 1-sq ft coalescer unit built into a
filter press framework. The coalescer unit is made of fiberglass filaments,
3.2 y in diameter, coated with isobutyl methacrylate resin for stability.
Wastewater Characteristics: Tap water and a mixture of 50% kerosene
and 50% pollutant material from treated hot mill cooling water (similar to
No. 30 lube oil) were agitated and recycled through a 3450-rpm centrifugal
pump for 1 hour. Primary and secondary dispersions of the oils in water
were produced.
Methods of Analysis; Oil concentrations in samples were determined
by light transmission and Hach turbidimeter measurements. Tabulated data,
on samples analyzed by both methods, were not converted to parts per million
for comparison.
65
-------
Results: Oil-separation efficiency varied from 70 to 99%, at influ-
ent oil concentrations of 50 to 500 ppm. Higher efficiences were reported
for fibers coated with resins than for uncoated fibers.
Critical Comments: The analytical methods used do not detect dis-
solved oil, which may have been appreciable. Therefore, oil concentrations
in effluents are higher than reported. Abrupt increases of oil in effluent
occurred if runs were not continuous; feed pretreatment is required to con-
trol the large pressure drops encountered and to prolong fiber life.
Cost; Equipment cost was not specified; operating costs are esti-
mated at $0.13/103/gal for single-fiber use and $0.01/103/gal if fibers can
be regenerated.
Title: Oily Water Separation System
Report No. and Date: COM-72-10561, January 1972
Author: R. J. Skocypec
Manufacturer of Equipment: Esso Research and Engineering Department,,
Linden, N. J. 07036
Design Features: Separator consists of a coalescing element upstream
of a settling chamber. There is an AMF-Cuno Super Auto-Klean Filter upstream
of the device.
Wastewater Characteristics; Shoreside tests were performed with
ballast water discharged from ships.
Method of Analysis; All samples were analyzed for oil content using
an infrared absorption technique.
Results; Average oil-removal efficiencies reported range from less
than 5 to nearly 90%.
Critical Comments; The coalescer was easily plugged and device was
not tested sufficiently. Performance was poor and the test procedure was
inadequate.
Title: Test and Evaluation of a 50-Gallon-per-Minute Oil/Water Separator
Report No. and Date: AD 785-223, July 1972
Author: E. C. Russell
Manufacturer of Equipment: Separations and Recovery Systems, Inc.,
Santa Ana, Calif. 92705
Design Features: The SRS separator consists of two, skid-mounted,
66
-------
16-inch-in-diameter by 47-inch-long high-pressure vessels, connected in
series. Each vessel contains three 6-inch-in-diameter and 22-inch-long
coalescer elements, mounted in parallel. The device is equipped with a supply
pump and a capacitance-type probe that controls the automatic oil-discharge
cycle of the system.
Wastewater Characteristics; Various quantities of differing oils
were metered into recirculating fresh water, at the suction side of a pump,
to produce an emulsified oil/water mixture. In some test runs, dry sand was
added to the oil/water mixture.
Methods of Analysis; Three methods were used for determining the oil
content of samples: (1) turbidity, (2) visual inspection, and (3) CC14
extraction and infrared spectrophotometry.
Results; Data from the turbidity meter measurements indicate oil
concentrations in effluents were below 60 ppm, but values reported for
infrared analyses were as high as 141 ppm.
Critical Comments; The objective of these tests was no visible
"sheen" in discharged waters, which device easily achieved. Analytical
results from the three methods were not similar.
Title: Test and Evaluation of Oil-Water Separation Systems
Report No. and Date: CR 73.015, November 8, 1972
Author: A. V. Sims
Manufacturer of Equipment: The devices tested are (1) Fram Corporation
separator and (2) Separation and Recovery Systems separator
Design Features: The Fram separator consists of a preconditioning
unit (filter cartridge with 25-y pore size), a gravity separation stage, and
a coalescing stage (5-P pore size filter cartridge). Device is equipped
with an interface controller and a manually operated oil valve. The S"RS
separator has a prefilter (25-u pore size) and two stages of coalescing
filters (5-y pore size).; device is equipped with an interface controller,
and oil and water control valves.
Wastewater Characteristics; Various quantities of Navy Special Fuel
Oil were intimately mixed with seawater by a centrifugal pump. Feed mixtures
contained mechanically emulsified oil.
Method of Analysis; Oil in samples was extracted by chloroform
((three separate extractions) and analyzed by infrared spectrophotometry.
The report states: "At concentrations less than 10 ppm, the average analyti-
cal accuracy was about 20%."
Results: The average oil content of effluents from the Fram separa-
tor was less than 3 ppm, with influents containing 200 ppm oil. The average
67
-------
oil content of effluents from the SRS separator was less than 1 ppm,
-------
Authors: S. M. Finger and T. S. Yu
Manufacturer of Equipment: Laboratory prototype
Design Features; System is a three-stage separation device: the
first stage is a cylindrical gravity separator; the second stage contains a
prefilter; the third stage is the coalescer filter. Coalescer elements used
were of the cylindrical cartridge type, made of resin-coated fiberglass
covered with cotton socks. Four-inch-diameter elements were positioned hori-
zontally in a glass chamber, allowing for visual inspection of element
performance.
Wastewater Characteristics; The influent oil/water mixture to the
system was prepared by metering oil and water through a centrifugal pump.
Severn River water was used, and the oils were Navy Distillate Fuel Oil and
MS-2190-TEP lubricating oil; the shearing action of the pump effectively
mixed the oil and water.
Method of Analysis; Samples were analyzed for oil content by extrac-
tion with carbon tetrachloride followed by infrared absorbance measurements.
Results; Under most conditions studied, effluent water contained
less than 15 ppm oil. Only 10% of the samples analyzed contained oil more
than this amount.
Critical Comments; System was adequately tested for the effects of
several parameters on performance. Report is well written; however,
stability analyses of feed streams should have been performed.
Title: Technologies for Shipboard Oil Pollution Abatement: Effects of
Operational Parameters on Coalescence
Report No. and Date: 3598, August 1972
Authors: S. M. Finger and T. S. Yu
Manufacturer of Equipment: Naval Ship Research and Developmental Center,
Bethesda, Md. 20034
Design Features; System is a three-stage separator; cartridge-type
coalescer elements were made of resin-coated glass fibers. The first stage
is empty, acting as a conventional gravity separator; the second stage is a
prefilter; and the third stage contains the coalescer elements.
Wastewater Characteristics^ Oils were metered into recirculating
river water at the suction side of a centrifugal pump, producing mechanically
emulsified oil/water mixtures.
Method of Analysis; An infrared spectrophotometric analysis devel-
oped at the Naval Shipyard Laboratory (methodology was not stated) was used
to detect oil content of samples.
69
-------
Results: Authors state that 60 out of 66 samples analyzed for oil
content contained less than 15 ppm oil; influent oil concentrations were not
stated.
Critical Comments; Test objective was to determine the effects of
some operational parameters on a coalescence device; the report states that
dirt, silt, and highly viscous oils can clog filter elements. The credibil-
ity of test results cannot be confirmed because the analytical technique used
was not stated in the report.
Title: Test and Evaluation of Oil Pollution Abatement Devices for Shipboard
Use: Phase II
Report No. and Date: AD 762-499, September 1972
Author: L. B. Norton
Manufacturer of Equipment: Not stated
Design Features; Three different separators were tested:
Separator A: a two-stage vertical filter/coalescer unit, containing
automatic oil-discharge control valves; a prefilter was
not provided.
Separator B: a larger version of separator A, but contains a
prefilter.
Separator C: a three-stage filter/ coalescer/gravity unit; this
device has automatic and manual oil—discharge valves
Wastewater Characteristics: Oil and solids were injected in fresh
water circulating through three different pumps: centrifugal, vane, and
double diaphragm. Oil/water mixtures produced contained emulsified oil.
Methods of Analysis; The oil content of samples was determined by
two methods: (1) turbidity and (2) visual observation.
Results: Most effluents had "no visible sheen." Occasionally sep-
aration performance was poor; substitution of vane pumps for the system's
centrifugal pumps did not improve performance. Water content of separated
oils was high.
Critical Comments; Analytical methods did not give a true indica-
tion of the oil content of samples. Tests were not complete and the report
is poorly organized.
Title: Test and Evaluation of Oil Pollution Abatement Devices for Shipboard
Use: Phase III—Final
Report No. and Date: AD 762-488, January 1973
70
-------
Author: L. B. Norton
Manufacturer of Equipment: Omitted
Design Features; Device is a two-staged unit, consisting of a pre-
filter made of 10-y-pore-size elements and 10 pleated paper cartridges, and
a second stage containing 5 cartridge filter elements. Equipment has oil/
water interface probes and discharge valves.
Wastewater Characteristics: Device was installed on a U.S. Coast •
Guard cutter to process feed streams of actual bilge and ballast waters.
Methods of Analysis; Samples were analyzed by (1) microbalance and
(2) Total Organic Carbon measurements.
Results; Data were not stated. The average oil content of the ef-
fluent, in one run, was reported to be 28 ppm; oily effluents generally con-
tained some entrained water. The author claims that overall separator
performance was acceptable.
Critical Comments; The report is badly written. The device was not
tested sufficiently; it is impossible to draw conclusions from reported data.
Analytical techniques are vague. Device was susceptible to dirt loading.
Title: Separation of Oil Dispersions from Water by Fibrous Bed Coalescers
Report No. and Date: Environ. Sci. Technol., 6^ No. 10, 907 (October 1972)
Authors: W. M. Langdon, P. P. Naik, and D. T. Wasan
Manufacturer of Equipment: Illinois Institute of Technology, Chicago, 111.
60616
Design Features; Device is constructed of aluminum and consists of
two types of fibers (Owens Corning glass fiber having 3.2-u diameter and
Owens Corning Aerocor coarse glass fiber of 10.1-y diameter). Glass fiber
mats are clamped between perforated plates; 100-mesh Monel screens, coated
with TFE, precede the coalescer/filter elements.
Wastewater Characteristics; Standardized oil/water mixtures were
prepared by metering oil into tap water, circulating through a ring pump
operating at 3450 rpm. Pollutant oil from a skimming tank at Interlake Steel
Corporation and Interlake Steel Corporation No. 30 grade automotive lubrica-
tion oil were used.
Method of Analysis; Oil concentrations in influent and effluent
streams were determined by light transmission.
Results; Oil content of effluents varied from 7 ppm to generally
non-detectable, with influent oil concentrations of 50 to 500 ppm.
71
-------
Critical Comments; It is doubtful that light transmission can detect
oil in the range 0-50 ppm with accuracy. Since this method was used in
analyzing product samples, the reported efficiency of separation is probably
erroneous.
Title: RFC Division, Midland-Ross Corporation 10-Gallon-per-Minute Liquid/
Liquid Separator
Report No. and Date: 2058, May 1973
Author: E. C. Russell
Manufacturer of Equipment: RFC Division, Midland-Moss Corporation, Roxboro,
N. C. 27573
Design Features; This is a three-stage coalescence-type device. A
cylindrical, horizontal tank, 70 inches long and 12 inches in diameter
houses the coalescer elements. The first-stage element is 12 inches long and
10 inches in diameter; in the second and third stages, cartridge elements are
6 inches long and 10 inches in diameter.
Wastewater Characteristics; Quantities of differing oils were
metered into circulating, prefiltered fresh water, at the suction side of a
supply pump, to produce mechanically emulsified oil/water mixtures.
Methods of Analysis: Four methods were used for analyzing samples:
(1) on-line ultraviolet energy absorption, (2) on-line fluorescence detec-
tion, (3) turbidity, and (4) Total Organic Carbon (TOC) analysis. Oil con-
centrations determined by the different methods were not similar.
Results; Data from TOC analysis indicate oil concentrations in ef-
fluents were below 10 ppm, with influents containing up to 32% oil. Other
analytical methods gave much higher values (200 ppm), with influents
containing 3% oil.
Critical Comments: Pressure drops in this equipment were high after
short operating times, indicating the device can be easily plugged. -The
objective of the test evaluation, i.e. "no visible sheen" in effluents, was
met despite the dissimilarity in the data reported for the various analytical
methods.
Title: Fram Corporation Model OWS-23-FCI-USCG Oil/Water Separator
Report No. and Date: 2059, May 1973
Author: E. C. Russell
Manufacturer of Equipment: Fram Corporation, Tulsa, Okla. 74160
72
-------
Design Features; A multistage, skid-mounted device equipped with a
double-diaphragm pneumatic supply pump. The first stage is a preconditioner;
the second stage is an inclined-plate, gravity separator; the last stage con-
tains a cartridge-type coalescer element.
Wastewater Characteristics; Test fluid was prefiltered tap water.
Various oils were used to produce oil/water mixtures. The shearing action of
a pump emulsified the mixture.
Methods of Analysis; Three methods were used for analyzing samples:
(1) on-line fluorescence detection, (2) turbidity, and (3) Total Organic
Carbon (TOG) analyses. Oil concentrations determined by the different
methods were not similar.
Results; TOC analyses indicate an average oil concentration of 25
ppm in effluents, with influents having up to 9% oil. Concentrations
obtained by on-line fluorescence detection were higher.
Critical Comments; Device was not thoroughly tested; however, per-
formance was poor. System is not capable of treating slightly stable
emulsions.
Title: Separation and Recovery Systems, Inc. 100-Gallon-per-Minute Oil/Water
Separator
Report No. and Date: 2060, May 1973
Author: E. C. Russell ,
Manufacturer of Equipment: Separation and Recovery Systems, Inc., Santa Ana,
Calif. 92705
Design Features; Device is comprised of the following: prefilter;
two skid-mounted (20-inch diameter by 60-inch diameter by 60 inches long)
high-pressure vessels, connected in series; high-shear supply pump; control
valves, etc. Each vessel contains five (6-inch diameter by 22 inches long)
cartridge-type filter elements, mounted in parallel.
Wastewater Characteristics; Various types of contaminant oils were
mixed with prefiltered fresh water and synthetic seawater to produce oil/
water mixtures. Dry fine sand was added occasionally. The shear of the
supply pump emulsified the mixtures.
Methods of Analysis; Two methods were used for analyzing samples:
(1) on-line turbidity measurements and (2) crystal microbalance.
Results; Data from turbidity measurements indicated acceptable per-
formance, but concentrations reported from the crystal microbalance technique
were much higher; oil concentrations in effluents averaged 35 ppm.
73
-------
Critical Comments: Device performance met the test objective of "no
visible sheen" in discharge waters. The analytical techniques used provide
only rough estimates of oil content in effluent samples tested, and
performance efficiency cannot be determined accurately.
Title: Oil/Water Pollution Program: Phase I
Report No. and Date: NAPTC-PE-27, July 1973
Authors: A. P. Pontello, F. G. Woessner, and R. J. Delfosse
Manufacturer of Equipment: Velcon Corporation
Design Features; System consists of an experimental coalescer/filter
element, approximately 20 inches long and 3.75 inches in diameter (Velcon
TE 3-27), installed vertically in a cylindrical vessel.
Wastewater Characteristics; Navy Distillate Fuel Oil was injected
into circulating tap water at the suction end of a vane pump. Primary and
secondary dispersions (emulsions) were produced by pump shearing forces.
Methods of Analysis; Oil concentrations in samples were measured by
two methods: (1) turbidimetry and (2) carbon tetrachloride extractions and
infrared spectrophotometry.
Results; Data were not tabulated. The authors claim that 4 ppm of
oil was present in the effluent, when the influent contained 100 ppm oil.
Critical Comments; Stability tests were not performed on wastewater;
the oily wastewater used was not representative of bilge or ballast water.
Tests conducted on the device were limited; throughput was small because of
excessive differential pressure on the system.
Title: Oil/Water Pollution Program: Phase II
Report No. and Data: AD-A009-093, October 1974
Authors: A. P. Pontello, C. J. Collick, J. J. Palmer, and A. J. Rollo
Manufacturer of Equipment: Several manufacturers of coalescer elements
Design Features; Details of the different coalescer elements are as
follows:
a) FRAM PC-11: element is 14.5 inches long and 3.5 inches in diam-
eter; made of fiberglass, pleated paper, and perforated screen
frames; flow is inside-out.
b) Velcon Corporation: coalescer element is 20 inches long and 1.25
inches in diameter; consists of various layers of fiberglass sand-
wiched between a metal screen and encased in a cylindrical vessel
74
-------
made of synthetic material.
c) Keene Corporation: element is 20 inches long and 1.25 inches in
diameter; made of variable density fiberglass layers, plastic-
coated mesh screen, a pleated paper core, and a perforated metal
screen.
d) SRS: element has dimensions similar to the Keene model but
consists of fiberglass, cloth, and two types of plastic-coated
mesh.
e) Bendix: element has the same dimensions as the Keene coalescer
but consists of two fiberglass materials of different density.
Wastewater Characteristics^ Navy Distillate Fuel Oil was injected
at the suction side of a centrifugal pump circulating tap water; the result-
ing emulsified oil/water mixture was used as test fluid. Detergents were
used, also.
Methods of Analysis; Four methods were used to analyze samples: (1)
samples were rated by visual inspection (method is subjective), (2) turbidity
measurements, (3) CC14 extraction and infrared spectrophotometry, and (4)
estimation of sheen on water surfaces (sheen index).
Results; Oil concentration in influents was varied from 100 to
50,000 ppm; the testing process was not systematic, so that data obtained
on various coalescers could not be compared.
Velcon: oil concentration in effluents averaged 5 ppm; free water
was present in coalesced oil and the quantity of free water
increased with throughput; differential pressure in the
system reached 28.7 psi after 25 hours of operation.
Keene: oil concentration in effluents averaged 4 ppm, without
detergents; performance was unsatisfactory when detergent
was present in the wastewater.
Fram: effluents contained 2 ppm oil, when coalescer was operated
with a prefilter; without a prefilter, oil concentration in
effluents reached 17 ppm.
SRS: in the absence of detergents, effluents contained an average
of 2 ppm oil; with detergents, oil concentration in efflu-
ents rose to 6.5 ppm. Free water (20 ppm) was present in
coalesced oil.
Critical Comments; Stability tests performed on the process streams
indicate that the oil/water mixtures treated were very unstable; separation
of oil (when the mixtures were left undisturbed) was 40 to 80% complete.
Test procedures were not varied, and some of the data obtained were
meaningless. Analytical methods are suspect.
Title: Development of a Batchwise In-Situ Regeneration-Type Separator to
Remove Oil from Oil-Water Suspensions
Report No. and Date: Technical Report 7080-3, December 1974
75
-------
Author: D. H. Fruttlan
Manufacturer of Equipment: Hydronautics, Inc., Laurel, Md. 20810
Design Features; System (HOWS Model 0-600) is a completely self-
contained, fully automated module, capable of treating up to 600 gpm of oily
wastewater. Device consists of a three-compartment chamber, made up of an
upstream header, a middle filtration section containing the filtering mate-
rial between two perforated plates (one fixed and the other free to move),
and a downstream decanter header containing an inclined plate. Filter mate-
rial is a thick, open-reticulated, oleophilic foam which is regenerated by
squeezing with the movable perforated plate.
Wastewater Characteristics: Tests were conducted at the Navy Fuel
Reclamation Plant in Virginia: influents were taken from the middle chamber
of a primary gravity separator and from storage tanks used for ballast and
bilge waters discharged from Navy ships.
Method of Analysis; Samples were analyzed by light transmission
measurements. Some samples were analyzed for oil content by the Naval
Systems Research and Development Laboratory, Annapolis; technique was not
stated.
Results; Oil content of separated water was high; oil-removal effi-
ciency was poor. Oil content of effluents was generally higher than 40 ppm,
with influents containing up to 300 ppm oil.
Critical Comments; System is suitable for gross oil/water separa-
tion; efficiency is comparable to that of ordinary gravity separators. Aging
of foam leads to poor performance; high cost of system may discourage use.
Title: Coalescence of Emulsified Oily Wastewater by Fibrous Beds
Report No. and Date: Presented at the 30th Annual Purdue Industrial Waste
Conference, Purdue University, Lafayette, Ind.,
May 6, 1975
Authors: J.-N. Chieu, E. F. Gloyna, and R. S. -Schechter
Manufacturer of Equipment: Laboratory prototype
Design Features: System is a 2-foot-long Plexiglas cylindrical
column, housing coalescing media. Three types of media were used: polyester
felt, polypropylene felt, and glass mats.
Wastewater Characteristics; Influents were prepared by emulsifying
oil and tap water in a household blender, stabilizing the mixture in an
ultrasonic disrupter, and stirring continuously before use. Oils tested
include refinery slop oil (coker slop oil and API skimmings) and No. 2
heating oil; the slop oils were filtered before use.
76
-------
Method of Analysis; Oil content of all samples was measured using a
Beckman Total Carbon Analyzer. Prior to analysis, each sample was homoge-
nized ultrasonically to insure representative sampling.
Results; With influent containing 100 ppm oil, the following effi-
ciences were achieved:
Glass mats 60%
Polypropylene felt 80%
Polyester felt 90%
Higher efficiences were reached at low flow rates.
Critical Comments: Fibers preferentially wetted by the dispersed
phase favor coalescence and exhibit lower head loss. Oil-removal efficiency
increases about 10-15% after minimum oil saturation. Oil content of
effluents is higher than the desired limit.
Title: Centrifuge Coalescer for Separating Oil from Water in Shipboard
Applications
Report No. and Date: AD-764-006, February 1973
Authors: A. C. Harvey, A. R. Guzdar, V. K. Stokes, and A. T. Fisk
Manufacturer of Equipment: Foster-Miller Associates, Waltham, Mass. 02154
Design Features^ System consists of a three-stage rotor comprising a
primary stage, a swept vane separator to separate large drops; a closely
spaced, axial-plate, spiral-wrap coalescer to coalesce the small drops; and
a secondary-stage swept vane separator to collect and separate coalesced
oil. The conical ends of the rotor contain blades and passageways that act
as centrifugal pump and centripetal turbine elements, at the inlet and
outlet ends, respectively.
Wastewater Characteristics: Oil/water mixtures of No. 2 and No. 4
fuel oils, Nigerian crude, and detergents were emulsified by passage through
a centrifugal pump; oil emulsions had sizes ranging from 2 to 100 p. Sta-
bility analyses indicated that mixtures were quite stable; after 120 hours,
remaining oil droplets had diameters of 2 to 15 v-
Methods of Analysis; Samples were analyzed for oil content by two
methods: (1) integration of the drop-size distribution measured by a Coulter
counter and (2) infrared spectrophotometry. Both measurement techniques gave
about 75 to 80% of the "true" oil concentration in samples measured; concen-
trations measured by the Coulter counter were approximately 90% of the values
obtained by infrared analysis.
Results; Test data indicated good separation with an average of
approximately 100 ppm in effluents, with influents containing greater than
1% oil. Overall oil-removal efficiency was greater than 90%. Performance
worsened when influents contained detergents.
77
-------
Critical Comments; Device was adequately tested. Test procedure is
satisfactory, and if improvements in design can be made, device is capable
of achieving higher oil-removal efficiencies. Equipment is expensive.
Effects of ship motion during processing were not investigated.
Cost: 100 gpm unit $22,900
Title: Development of a Centrifugal System for Separation of Oil and Solids
from Shipboard Discharge Water
Report No. and Date: CG-D-118-75, July 1975
Authors: A. R. Guzdar, A. C. Harvey, J. Potter, and W. M. Mack
Manufacturer of Equipment: Foster-Miller Associates, Inc., 135 Second
Avenue, Waltham, Mass. 02154
Design Features: Device is an oil/solids/water separating system
made up of the following components: (1) a cleanable bag strainer to retain
coarse and fibrous solids, (2) a centrifugal pump to separate settleable
solids, (3) a coalescing centrifuge to separate well-dispersed oil, and (4)
an oil/water monitor to continuously measure and record the oil content of
effluent.
Wastewater Characteristics; Oil/water mixtures were emulsified by
passage through a centrifugal pump operating at 30 psi pressure differential.
Lube oil and No. 2 fuel oil were used. The oil concentration of influent
streams varied from 5 to 100%.
Method of Analysis; An on-line oil/water monitor continuously mea-
sured and recorded the oil content of effluents. Analytical results compared
favorably with results using EPA solvent extraction-spectrophotometric
techniques.
Results; Laboratory testing of individual components showed favor-
able performance. However, the performance of the overall system was poor.
Oil content of effluents was much higher than the expected upper limit of
15 ppm.
Critical Comments: The poor system performance was blamed on "cer-
tain operational difficulties" experienced during the testing program.
Design modifications may improve performance.
Title: Bimetallic Coalescers: Electrophoretic Coalescence of Emulsions in
Beds of Mixed Metal Granules
Report No. and Date: Environ. Sci. Technol., 4_, No. 6, 510-514 (1970)
Authors: F. M. Fowkes, F. W. Anderson, and J. E. Berger
Manufacturer of Equipment: A laboratory prototype assembled by authors
78
-------
Design Features: Device is a cylindrical column packed with carbon
(4-8-mesh size) and aluminum (20-mesh size) granules.
Wastewater Characteristics: Influents contained oil-in-water emul-
sions. Methods of preparation of feed streams were not stated.
Method of Analysis: Influent and effluent samples were analyzed for
oil content by light transmission.
Results: Light transmission data indicate some separation occurred,
with influents containing as much as 1100 ppm oil; coalescence was faster
as influents became more dilute.
Critical Comments: Performance is poor and device is not adequate as
a polishing stage in a treatment process. Consumption of metals is a
problem. Further treatment is a necessity.
Title: Oil Removal by Carbon-Metal Granular Beds
Report No. and Date: J. Water Poll. Control Fed., 47, No. 8, 2101-2113
(1975)
Authors: M. M. Ghosh and W. P. Brown
Manufacturer of Equipment: Bench-scale coalescer assembled by authors
Design Features: Device consists of a glass column packed with a
mixture of carbon and metal granules, supported by a 40-mesh metal screen.
Activated cocoanut charcoal and aluminum or iron were used .as bed materials.
Wastewater Characteristics; Stable emulsions of oil droplets in
water were obtained when small volumes of solutions of silicone oil in ace-
tone were jetted into water, through a small orifice. In some experiments,
a homogenizer was used, at speeds of 12,000 rpm for 12 minutes, in preparing
oil-in-water emulsions. Dispersions were less than 1.0 y in diameter and
did not exhibit any self-coalescence over long periods of time.
Methods of Analysis; Influent and effluent samples were analyzed
for number and size distribution of oil droplets by a particle counter.
Spectrophotometric analyses of some samples were carried out.
Results; The highest oil-removal efficiency achieved, with influents
containing approximately 350 ppm oil, was 82%.
Critical Comments; Analytical methods are only accurate to within
50% of actual value. Throughput is small and head loss gradually increased
during processing. Formation of metal hydroxides that dissolve in effluent
is a disadvantage. The carbon-aluminum system performed better than the
carbon-iron system, because of the higher potential difference of the bime-
tallic couple. Bimetallic coalescers can be used only as polishing devices
79
-------
in oil/water separation, and are useful for separating oil dispersions
stabilized by surface charges.
Title: The Coanda-Effect Oil-Water Separator: A Feasibility Study
Report No. and Date: AD-774-080, February 1974 (NTIS)
Author: D. Pal
Manufacturer of Equipment: Experimental model designed by Civil Engineering
Laboratory, Port Hueneme, Calif. 93043
Design Features; Device consists of inlet and outlet ports, 12-
inch-long attachment wall, oil-collection chambers, and oil/water interface
detection probes. Housing was made of Plexiglas to allow visual observa-
tion.
Wastewater Characteristics; The oil/water mixture used as influent
was prepared by mixing hydraulic oil and tap water.
Method of Analysis: Volumes of oil and water present in settled
samples were measured.
Results; Test data show that about 50% of the oil present in the
influent was separated; the separated oil contained up to 5% free water.
Critical Comments; The Coanda-effeet separator is in a develop-
mental stage; it is useful only for gross separations. Turbulence created
by jet flow will enhance emulsification of oil in wastewater, making
separation very difficult.
80
-------
SECTION 8
SELECTED MANUFACTURERS OF OIL/WATER SEPARATING EQUIPMENT
Gravity-Differential Separators
Aerodyne Development Corporation, Cleveland Ohio
AFL Industries, West Chicago, Illinois
Aqua-Chem, Inc., Waukesha, Wisconsin
Butterworth Systems, Inc., Bayonne, New Jersey
C. E. NATCO, Tulsa, Oklahoma
Chiyoda Chemical Engineering & Construction Company, Ltd., Tokyo
De Laval Separator Company, Poughkeepsie, New York
Envirex, Inc., Waukesha, Wisconsin
FMC Corporation, Lansdale, Pennsylvania
Fram-Akers Corporation, .Tulsa, Oklahoma
FWI, Pollution Control Division, Tulsa, Oklahoma
General Electric Corporation, Philadelphia, Pennsylvania
Heil Process Equipment Corporation, Cleveland, Ohio
Inland Environmental, Chicago, Illinois
MAPCO, Inc., Tulsa, Oklahoma
Midland-Ross, Roxboro, North Carolina
The Permutit Company, Paramus, New Jersey
Pielkenroad Separator Company, Houston, Texas
Separator & Recovery Systems, Inc., Santa Ana, California
Smith Industries, Inc., Houston, Texas
Flotation Equipment
Ecodyne Corporation, Union, New Jersey
Envirex, Inc., Waukesha, Wisconsin
FWI, Pollution Control Division, Tulsa, Oklahoma
The Galigher Company, Salt Lake City, Utah
Joy Manufacturing Company, Denver, Colorado
Lockheed Aircraft Service Company, Ontario, Canada
Mechanics Research, Inc., Los Angeles, California
The Permutit Company, Paramus, New Jersey
Petrolite Corporation, Tretolite Division, St. Louis, Missouri
Rotational Equipment
Air Research Manufacturing Company, Torrance, California
Ametek, Inc., East Moline, Illinois
Centrico, Inc., Northvale, New Jersey
De Laval Separator Company, Poughkeepsie, New York
Foster-Miller Associates, Waltham, Massachusetts
81
-------
Pennwalt Corporation, Warminster, Pennsylvania
Reynolds Submarine Service Company, Richmond, Virginia
Sharpies Division, Pennwalt Corporation, North White Plains, New York
United Aircraft Corporation, East Hartford, Connecticut
FiltratiQn Equipment (granular media)
Combustion Engineering Company, East Hartford, Connecticut
De Laval Separator Company, Poughkeepsie, New York
Hayward Filter Company, Santa Ana, California
Neptune Micro-Floe, Inc., Corvallis, Oregon
Peabody Welles, Roscoe, Illinois
Smith Industries, Inc., Houston, Texas
Filter/Coales cers
Aqua-Chem, Inc., Waukesha, Wisconsin
Fram-Akers Corporation, Tulsa, Oklahoma
FWI, Tulsa, Oklahoma
Inland Environmental, Chicago, Illinois
MAPCO, Inc., Tulsa, Oklahoma
Midland-Ross Corporation, Roxboro, North Carolina
Pall Trincor Corporation, Vauxhall, New Jersey
Selas Flotronics, Spring House, Pennsylvania
Separator & Recovery Systems, Inc., Santa Ana, California
Serfilco, Northbrook, Illinois
Smith Industries, Inc., Houston, Texas
Velcon Filters, Inc., San Jose, California
Membrane Filtration Equipment
Abcor, Inc., Cambridge, Massachusetts
Aqua-Media, Sunnyvale, California
Fluid Systems Division, UOP, Inc., San Diego, California
Gulf Environmental Systems, San Diego, California
Illinois Water Treatment Company, Rockford, Illinois
Osmonics, Inc., Hopkins, Minnesota
Romicon, Inc., Woburn, Massachusetts
Selas Flotronics, Spring House, Pennsylvania
Adsorption Equipment
APV Company, Inc., Tonawanda, New York
Aqua-Media, Sunnyvale, California
Calgon Corporation, Pittsburgh, Pennsylvania
Chem-Pro Equipment Corporation, Fairfield, New Jersey
Chiyoda Chemical Engineering & Construction Company, Ltd., Tokyo
Diamond Shamrock, Cleveland, Ohio
Ecodyne Corporation, Union, New Jersey
Envirex, Inc., Conshohocken, Pennsylvania
General Filter Company, Ames, Iowa
Hydronautics, Inc., Laurel, Maryland
82
-------
Illinois Water Treatment Company, Rockford, Illinois
Liquitech, Inc., Houston, Texas
Met-Pro Systems, Inc., Lansdale, Pennsylvania
Process Equipment Corporation, Bedding, Michigan
Serfilco, Northbrook, Illinois
83
-------
SECTION 9
REFERENCES
Adamson, A. W. (1967) Physical Chemistry of Surfaces. 2nd ed. Inter-
science, New York. 747 pp.
Adamson, W. L., and M. W. Titus (1971) Separation of oil in bilge water by
semipermeable membrane. Naval Ship Research and Development Center
Rept. No. AD-A023-289, NTIS.
API (1969) Manual on Disposal of Refinery Wastes; Volume on Liquid Wastes.
1st ed. American Petroleum Institute, Washington, D. C.
Arnaiz, J. B., and E. Batutis (1974) Feasibility test program of applica-
tion of coalescing phase oil/water separators to self-compensating fuel
tanks in surface ships. U.S. Coast Guard Rept. No. CG-D-88-74, NTIS.
Berry, W. L., and R. F. Engel (1969) One approach minimizes water pollution
from offshore platforms. Pet. Eng., 10:64-66.
Beychok, M. R. (1973) Aqueous Wastes from Petroleum and Petrochemical
Plants. J. Wiley and Sons, New York.
Boehm, P. D. (1973) Solubilization of hydrocarbons by dissolved organic
matter in seawater. M.S. Thesis. University of Rhode Island, Kingston.
Boehm, P. D., and J. G. Quinn (1974) The solubility behavior of No. 2 fuel
oil in seawater. Mar. Poll. Bull., 5(7):101-105.
Boesch, D. F., C. H. Hershner, and J. H. Milgram (1974) Oil Spills and the
Marine Environment. Ballinger Publishing Co., Cambridge, Mass.
Brunsmann, J. J., J. Cornelissen, and H. Eilers (1962) Improved oil separa-
tion in gravity separators. J. WPCF, 34(l):44-55.
Budininkas, P., and G. A. Remus (1974) Development of classification scale
for characterizing bilge waters used in evaluating oil removal tech-
niques . U.S. Coast Guard Report No. AD-778-929, NTIS.
Burtis, T. A., and C. G. Kirkbride (1946) Desalting of petroleum by use of
fiberglass packing. Trans. AIChE., 42:413-416.
Chieu, J.-N., E. F. Gloyna, and R. S. Schechter (1975) Coalescence of emul-
sified oily wastewater by fibrous beds. Presented at the 30th Indus-
trial Waste Conference, Purdue University, Lafayette, Ind.
84
-------
Chiyoda Company (1974) Water treatment technologies from Chiyoda. Tech.
Kept. No. 209-04, Chiyoda Company, Tokyo.
Churchill, R. J. (1973) Air flotation techniques for oily water treatment.
Tech. Rept., Engineering Science, Inc., Pasadena, Calif.
Churchill, R. J., and W. J. Kaufman (1973) Waste processing related surface
chemistry of oil refinery wastewaters. SEKL Rept. No. 73-3, University
of California, Berkeley.
D'Arcy, N. A. (1951) Dissolved air flotation separates oil from wastewater.
Oil Gas J., 6:319-322.
Desai, S. V. (1971) An economically attractive application of reverse
osmosis to refinement of a petrochemical effluent stream. AIChE Symp.
Ser., Water, pp. 379-387.
Douglas, E., and I. G. Elliot (1962) Developments in oily-water separator
design. Trans. Inst. Mar. Eng., 74:164-168.
Ellis, M. M., and P. W. Fisher (1970) Clarifying oil field and refinery
wastewaters by gas flotation. J. Pet. Technol. and Soc. Pet. Engrs.
Rept. No. SPE 3198.
Elworthy, P. H., A. T. Florence, and C. B. Macfarlane (1968) Solubilization
by Surface Active Agents. Chapman and Hall, Ltd., London, pp. 11-116.
Evers, R. H. (1975) Mixed-media filtration of oily wastewaters. J. Pet.
Technol., 2:157-163.
Farley, R., and F. H. H. Valentin (1965) Coagulation as a means of separat-
ing oil from effluents. AIChE-IEC Symp. Ser., 1(1):15-20.
V
Finger, S. M., and R. B. Tabakin (1973) Development of shipboard oil/water
separation systems. Rept. No. 73-ENAs-38, ASME, New York.
Finger, S. M., and T. S. Yu (1972) Technologies for shipboard oil pollution
abatement: Effects of operational parameters on coalescence. Naval
Ship Research and Development Center Rept. No. 3598.
Finger, S. M., and T. S. Yu (1973) Analytical examination of oil/water
separation by coalescence. USEPA Control Technology Research and
Development, pp. 403-408. Also in Proceedings of the Joint Conference
on Prevention and Control of Oil Spills. API, Washington, D. C.
pp. 407-408.
Fowkes, F. M., F. W. Anderson, and J. E. Berger (1970) Bimetallic coales-
cers: Electrophoretic coalescence of emulsions in beds of mixed metal
granules. Env. Sci. Technol., 4(6):510-514.
Freestone, F. J., and R. B. Tabakin (1975) Review of Environmental Protec-
tion Agency research in oil/water separation technology. Proceedings of
the Joint Conference on Prevention and Control of Oil Spills. API,
Washington, D. C. pp. 437-441.
85
-------
Fruman, D. H. (1974) Development of a batchwise in-situ regeneration-type
separator to remove oil from oil-water suspensions. Tech. Rept. No.'
7080-3, Hydronautics, Inc., Maryland.
Fruman, D. H., and T. R. Sundaram (1974) Evaluation of pump emulsification
characteristics. Naval Ship Engineering Rept. No. 6159-00, NTIS.
Gaudin, A. M. (1957) Flotation. 2nd ed. McGraw-Hill Book Co., New York.
Ghosh, M. M., and W. P. Brown (1975) Oil removal by carbon-metal granular
beds. J. WPCF, 47(8):2101-2113.
Gloyna, E. F., and D. L. Ford (1974) Control of refinery and petrochemical
wastewaters and residuals. Presented at the 1st International Symposium
on the Techniques of Liquid-Liquid Separation. Lamar University,
Beaumont, Texas.
Goldsmith, R. L.,,and S. Hossain (1973) Ultrafiltration concept for separ-
ating oil from water. U.S. Coast Guard Rept. No. 4305.2/2, NTIS
AD-758-318.
Graham, R. J. (1962) Separation of immiscible liquids by gravity settling
and induced coalescence. M.S."Thesis. University of California,
Berkeley.
Gudesen, R. C. (1964) Coalescence of petroleum compounds in mixed fibrous
beds. M.S. Thesis. Illinois Institute of Technology, Chicago.
Guzdar, A. R., A. C. Harvey, J. Potter, and W. M. Mack (1975) Development
of a centrifugal system for separation of oil and solids from shipboard
discharge water. U.S. Coast Guard Rept. No. CG-D-118-75, NTIS.
Harris, F. R., Inc. (1973) Port collection and separation facilities for
oily wastes. II. General technology. Maritime Administration Rept. No.
COM-73-11069, NTIS.
Hartenstein, L. J., and T. E. Lindemuth (1970) Development of a coalescing
type oil/water separator for marine service. Aqua-Chem Tech. Rept.
presented at SNAME Meeting, San Diego, California, February 18.
Harvey, A. C., A. R. Guzdar, V. K. Stokes, and A. T. Fisk (1973) Centrifuge
coalescer for separating oil from water in shipboard applications.
U.S. Coast Guard Rept. No. AD-764-006, NTIS.
Hayes, J. G., L. A. Hays, and H. S. Wood (1949) Commercial desalting unit
employing fiberglass as contacting agent. Chem. Eng. Progr. 45:235.
Hazlett, R. N. (1969a) Fibrous bed coalescence of water: Steps in the
coalescence process. IEC, Fund., 8(4):625-632.
Hazlett, R. N. (1969b) Fibrous bed coalescence of water: Role of sulfo-
nate surfactant in the coalescence process. IEC, Fund., 8(4):633-640.
86
-------
Hefler, J. R. (1971) Oily water separator: Liquid-liquid separation by a
commercial self-cleaning edge filter. Maritime'Administration Kept. No.
COM-71-01095, NTIS.
Holt, Ben Company, The (1974) Experimental prototype oily wastewater treat-
ment system. Civil Engineering Lab. Rept. No. CR-74.008, NTIS.
Hooper, M. W., and H. N. Myrick (1972) Comparison of multi-media and deep-
bed sand filter coalescence of oil-water emulsions. Presented at Con-
ference on Application of Filtration Technology in Environmental Pollu-
tion Control and the Chemical Process Industries. University of Houston,
Texas.
Hsiung, K. Y., H. M. Mueller, and W. R. Conley (1974) Physical-chemical
treatment for oily waste. Presented at WWEMA Industrial Water and
Pollution Conference and Exposition, Detroit, Mich.
Ingersoll, A. C. (1951) Fundamentals and performance of gravity separation.
Pet. Refiner, 6:9.
Jefferson, T. H., and S. B. Boulavare (1973) Surfactants and their effects
on filter separators. U.S. Army Mobility Equipment Research and Devel-
opment Center Rept. No. 2066, NTIS.
^
Jeffreys, G. V., and G. A. Davies (1971) Coalescence of liquid droplets and
liquid dispersion. In: Recent Advances in Liquid-Liquid Extraction
(C. Hanson, Ed.). Pergamon Press, Oxford, pp. 561-562.
Jordan, G. V. (1953) Separation of immiscible liquids by means of porous
membranes. Trans. ASME, 77:393-404.
Jordan, G. V. (1965) Coalescence of fluids through porous materials. Selas
Corporation Tech. Bull. LFC. Selas Corporation of America, Flotronics,
Spring House, Pa.
Kaiser, R., C. K. Colton, G. Miskolczy, and L. Mir (1971) Magnetically
induced separation of stable emulsions. AIChE Symp. Ser., Water.
pp. 115-126.
Kirby, A. W. W. (1964) The separation of petroleum oils from aqueous
effluents. Trans. Inst. Chem. Eng. (London), 4a(4):76.
Koelmans, H., and J. T. G. Overbeek (1954) Stability and electrophoretic
deposition of suspensions in non-aqueous media. Dis. Faraday Soc.,
18:52.
Kruyt, H. R. (1952) Colloid Science. Vol. 1. Elsevier, New York.
Lai, M. G., and C. E. Adams (1974) Determination of the molecular solubil-
ity of Navy oils in water. Naval Ordnance Lab. Rept. No. NOLTR-74-110,
NTIS.
87
-------
Langdon, W. M. , P. P. Naik, and D. T. Wasan (1972) Separation of oil dis-
persions from water by fibrous bed coalescers. Env. Sci. Technol.,
6(10):907.
Langdon, W. M., and D. T. Wasan (1971) Experimental evaluation of fibrous
bed coalescers for separating oil-water emulsions. USEPA Project No.
12050 DRC.11/71, NTIS.
^
Lindenhofen, H., and R. H. Shertzer (1967) Aeronautical Engineering Lab.
Kept. Nos. NAEC-AEL-1852 and NAEC-AEL-1856. Aeronautical Engineering
Lab., Philadelphia, Pa.
Lysyj, I., and E. C. Russell (1974) Dissolution of petroleum-derived
products in water. Water Res., 8:863-868.
McAuliffe, C. (1969a) Solubility in water of normal Cg and CIQ alkane
hydrocarbons. Science, 163:478-479.
McAuliffe, C. (1969b) Determination of dissolved hydrocarbons in subsurface
brines. Chem. Geol., 4:225-233.
McKenna, Q. H., H. Helber, C. M. Carrell, and R. F. Tobias (1973) Electro-
chemical flotation concept for removing oil from water. U.S. Coast
Guard Rept. No. 734305.2/4, NTIS.
Mensing, A. E., R. C. Stoeffler, W. R. Davison, and T. E. Hoover (1970)
Investigation of the use of a vortex flow to separate oil from an oil/
water mixture. U.S. Coast Guard Rept. No. 714103/A/001, NTIS.
Merryman, J. G., and E. R. Osterstock (1973) Coalescing plates and packs
for oil/water separation in various shipboard applications. U.S. Coast
Guard Rept. No. 724305.2/6, NTIS.
Messinger, S. (1974) Ultrafiltration in water and waste treatment.
Presented at the 12th Annual Liberty Bell Corrosion Course No. 4.
Milstead, C. E., and J. F. Loos (1973) Study of hydrophilic membranes for
oil-water separation. U.S. Coast Guard Rept. No. 4305.2/7, NTIS
AD-758-321.
Mittleman, J. (1975) Oil/water separator evaluation. Naval Coastal Systems
Lab. Rept. No. 252-75, NTIS.
Navy, Department of the (1974) Coanda-effect oil-water separation. U.S.
Department of the Navy, Washington, D. C., NTIS AD-D001-437.
Nordstrom, R. P., Jr. (1974) Ultrafiltration removal of soluble oil. Poll.
Eng., 10:46-47.
Norton, L. B. (1972) Test and evaluation of oil pollution abatement
devices for shipboard use. Phase II. U.S. Coast Guard Rept. No.
AD-762-499, NTIS.
88
-------
Norton, L. B., and F. Perrj.nl (1972) Test and evaluation of oil pollution
abatement devices for shipboard use. Phase I. U.S. Coast Guard Rept
No. AD-&62-498, NTIS.
Norton, L. B. (1973) Test and evaluation of oil pollution abatement devices
for shipboard use. Phase III. Final U.S. Coast Guard Rept. No
AD-762-488, NTIS.
Orr, C., and E. Kang (1974) The electrical process in the breaking of
dilute oil-in-water emulsions. Office of Water Resources Research Rept.
No. PB-235-908, NTIS.
Overbeek, J. T. G. (1952) Colloid Science. Vol. I (H. R. Kruyt, Ed.).
Elsevier, New York.
Pal, D. (1974) The Coanda-effect oil-water separator: A feasibility study.
Civil Engineering Lab. Rept. No. AD-774-080, NTIS.
Paszyc, A. J., D. Pal, K. Huang, and J. B. Curry (1975) Fluidic oil-water
separator. U.S. Department of the Navy, Washington, D. C., NTIS
AD-D001-756.
Pomonik, G. M. (1973) Vacuum desorption concept for removing oil from
water. U.S. Coast Guard Rept. No. 734305.2/8, NTIS.
Pontello, A. P., F. G. Woessner, and R. J. Delfosse (1973) Oil/water pollu-
tion program. Phase I. Naval Air Propulsion Test Center Rept. No.
NAPTC-PE-27, NTIS.
Pontello, A. P., C. J. Collick, J. J. Palmer, and A. J. Rollo (1974) Oil/
water pollution program. Phase II. U.S. Department of the Navy,
Washington, D. C., NTIS AD-A009-093.
Quigley, R. E., and E. L. Hoffman (1966) Flotation of oil wastes. Pro-
ceedings of the 21st Industrial Waste Conference. Purdue University,
Lafayette, Ind. pp. 527-533.
Redmon, 0. C. (1963) Cartridge type coalescers. Chem. Eng. Progr.,
59(9):87.
Reisberg, J., and T. M. Doscher (1956) Interfacial phenomena in crude
oil-water systems. Producers Monthly, 4:43.
Rohlich, G. A. (1951) Hydraulic characteristics of gravity-type oil-water
separators. Proc. API, 31M(111):63-85.
Rohlich, G. A. .(1954) Application of air flotation to refinery wastewaters.
Ind. Eng. Chem., 46(2) :304-308.
Rose, P. R. (1963) Mechanisms of operation of a fibrous bed coalescer.
M.S. Thesis. Illinois Institute of Technology, Chicago, 111.
89
-------
Rosenfeld, J. I., and D. T. Wasan (1974) Coalescence of drops in a liquid-
liquid dispersion by passage through a fibrous bed. Can. J. Chem. Eng.,
52:26-34.
Russell, E. C. (1972) Test and evaluation of a 50-gallon-per-minute oil/
water separator (Separation and Recovery Systems, Inc.). U.S. Army
Mobility Equipment Research and Development Center Rept. No. AD-785-223,
NTIS.
Russell, E. C. (1973a) RPC Division, Midland-Ross Corporation 10-gallon-
per-minute liquid/liquid separator. U.S. Army Mobility Equipment
Research and Development Center Rept. No. 2058, NTIS.
Russell, E. C. (1973b) Fram Corporation Model OWS-23-FCI-USCG oil/water
separator. U.S. Army Mobility Equipment Research and Development
Center Rept. No. 2059, NTIS.
Russell, E. C. (1973c) Separation and Recovery Systems, Inc. 100-gallon-
per-minute oil/water separator. U.S. Army Mobility Equipment Research
and Development Center Rept. No. 2060, NTIS.
Sareen, S. S., P. M. Rose, R. C, Gudesen, and R. C. Kintner (1966)
Coalescence in fibrous beds. AIChE J., 12:1045.
SCEP (1970) Man's Impact on the Global Environment: Report of the Study of
Critical Environmental Problems. MIT Press, Cambridge, Mass. 296 pp.
Schatzberg, P., L. R. Harris, C. M. Adema, D. F. Jackson, and C. M. Kelly
(1975) Oil-water separation with noncellulosic ultrafiltration systems.
Proceedings of the Joint Conference on Prevention and Control of Oil
Spills. API, Washington, D. C. pp. 443-447.
Shackleton, L. R. B., E. Douglas, and T. Walsh (1960) Pollution of the sea
by oil. Trans. Inst. Mar. Eng.
Sheng, H. P., and J. R. Welker (1969) Liquid-liquid separation in a conven-
tional hydrocyclone. Proceedings of the AIChE 64th National Meeting,
New Orleans, La.
Sherony, D. F., and R. C. Kintner (1971) Coalescence of an emulsion in a
fibrous bed. II. Experimental. Can. J. Chem. Eng., 49:321.
r
Simonsen, R. N. (1962) Remove oil by air flotation. Hydrocarbon Proc.
and Pet. Ref., 41:5.
Sims, A. V. (1972) Test and evaluation of oil-water separation systems.
Naval Civil Engineering Lab. Rept. No. CR-73-015, NTIS.
Sinkin, D. J., and R. B. Olney (1956) Phase separation and mass transfer in
a liquid-liquid cyclone. AIChE J., 2(4):545-551.
90
-------
Skocypec, R. J. (1972) Oily water separation system. U.S. Maritime
Administration Kept. No. COM-72-10561, NTIS.
Spielman, L. A. (1968) Separation of finely dispersed liquid-liquid suspen-
sions by flow through fibrous media. Ph.D. Dissertation. University of
California, Berkeley.
Spielman, L. A., and S. L. Goren (1970) Progress in induced coalescence and
a new theoretical framework for coalescence by porous media. Ind. Ene.
Chem., 62(10)-.10-24.
Spielman, L. A., and S. L. Goren (1972a) Theory of coalescence by flow
through porous media. Ind. Eng. Chem., Fund., 11(1):66.
Spielman, L. A., and S. L. Goren (1972b) Experiments in coalescence by flow
through fibrous mats. Ind. Eng. Chem., Fund., 11(1):73.
Stoeffler, R. C., and C. E. Jones (1973) Vortex concept for separating oil
from water. U.S. Coast Guard Rept. No. 4105.2/1, NTIS.
Stormont, D. H. (1956) Air flotation used to separate oil at Richfield's
new waste water plant. Oil Gas J., 10:26.
Sweeney, W. F. (1964) Some observations on liquid-liquid settling. M.S.
Thesis. University of California, Berkeley.
Union Carbide Corporation (1973) Viscosity-actuated phase separating
tyAPS) for oil-water separations. Prepared for U.S. Coast Guard, Rept.
No. 734305.2/5, NTIS.
USEPA (1974) Development document for effluent limitations guidelines and
new source performance standards for petroleum refining: Point source
category. USEPA No. 440/1-74-014a, NTIS.
USEPA (1975) Group II. Development document for interim final effluent
limitations guidelines and new source performance standards for the off-
shore segment of the oil and gas extraction point source category.
USEPA No. 440/1-75-055, NTIS.
Vinson, C. G. (1965) The coalescence of micro-size drops in liquid-liquid
dispersions in flow past fine mesh screens. Ph.D. Dissertation.
University of Michigan, Ann Arbor.
Voyutskii, S. S., K. A. Kal'yanova, R. Panick, and N. Fodiman (1955)
Mechanism of separation of the dispersed phase of emulsions during
filtration. Chem. Abstr., 49:12053d.
Voyutskii, S. S., N. M. Fodiman, and R. Panick (1958) Filtration of
emulsions. Chem. Abstr., 52:19266a.
Vrablik, E. R. (1957) An evaluation of circular gravity-type separators and
dissolved air flotation for treating oil refinery waste water.
91
-------
Proceedings of the 12th Industrial Waste Conference. Purdue University,
Lafayette, Ind. p. 73.
Wang, L. K., J. Y. Yang, and D. B. Dohm (1973) Evaluation and development
of physical-chemical techniques for the separation of emulsified oil
from water. Kept. No. 189, Calspan Corporation, Buffalo, N. Y.
Wisconsin, University of (1949) Investigation of the behavior of oil-water
mixtures in separators. Eng. Expt. Sta. Ser. Kept. No. CE-78-1.
University of Wisconsin, Madison.
Wisconsin, University of (1950) Investigation of the behavior of oil-water
mixtures in separators. Eng. Expt. Sta. Ser. Kept. No. CE-78-2.
University of Wisconsin, Madison.
Wisconsin, University of (1951) Investigation of the behavior of oil-water
mixtures in separators. Eng. Expt. Sta. Ser. Kept. No. CE-78-3.
University of Wisconsin, Madison.
Yu, T. S. (1969) A proposed shipboard continuous oil-pollution control
process for bilge water. Naval Ship Research and Development Lab. Kept.
No. 3191, NTIS.
Yu, T. S., and D. R. Ventriglio (1969) Shipboard oil-pollution control
systems for ballast and bilge waters: A state-of-the-art search.
MATLAB Rept. No. 244, NTIS.
92
-------
SECTION 10
BIBLIOGRAPHY
Armco Steel Corporation. 1970. Treatment of Waste Water: Waste Oil Mix-
tures. Federal Water Pollution Control Administration Program No.
12010 EZV.
Battelle Memorial Laboratory (Pacific Northwest Laboratory). 1967. Oil
Spillage Study: Literature Search and Critical Evaluation for Selection
of Promising Techniques to Control and Prevent Damage. NTIS Kept. No.
AD-666-289.
Beebe, A. H. 1953. Soluble Oil Wastes Treatment by Pressure Flotation.
Sewage Ind. Wastes. 25(11):1314-1322.
Blumer, M. 1969. Oil Pollution of the Ocean. In: Oil on the Sea. Ed.
D. P. Hoult. Plenum Press, New York. pp. 5-13.
Blumer, M. 1970. Scientific Aspects of the Oil Spill Problem. Presented at
the Colloquium on Oil Pollution of the Sea. North Atlantic Treaty
Organization, Brussels.
Boyd, J. L., G. L. Shell, and D. A. Dahlstrom. 1972. Treatment of Oily
Waste Waters to Meet Regulatory Standards. AIChE Symp. Ser.
124:393-401.
*
Breslau, B. R., E. A. Agranat, A. J. Testa, S. Messinger, and R. A. Cross.
1974. Hollow Fiber Ultrafiltration: A Systems Approach for Process
Water and By-Product Recovery. Proceedings of the AIChE 79th National
Meeting, Houston, Texas.
Brown and Root, Inc. 1974. Determination of Best Practicable Control Tech-
nology Currently Available to Remove Oil from Water Produced with Oil
and Gas. Offshore Operators Committee, Sheen Technical Subcommittee
Report.
Canadian Plant and Process Engineering, Ltd. 1972. Polyurethane as an Oil
Filter: A Research Study. Final Report, Canadian Department of the
Environment (Fisheries and Forestry), Ontario.
Canevari, G. P. 1969. Some Basic Concepts Regarding the Separation of Oily
Water Mixtures. Trans. ASCE. 12:190.
Cheesman, D. F., and A. King. 1940. The Electrical Double Layer in Relation
93
-------
to the Stabilization of Emulsions with Electrolytes. Trans. Faraday
Soc. 36:241.
Chemical Engineering Deskbook. 1975. Environmental Engineering Pollution
Control Equipment. 82(21). McGraw-Hill Book Co., Hightstown, N. J.
Chieu, J. N., and E. F. Gloyna. 1975. Treatment of Emulsified Oily Wastes
by Fibrous Bed Coalescers. CRWR Report, University of Texas, Austin.
Conley, W. R., and K. Hsiung. 1969. Design and Application of Multi-media
Filters. J. Amer. Water Works Assn. 61:97.
Degler, S. E. 1970. Oil Pollution: Problems and Policies. BNA's Environ-
mental Management Series.
Edwards, V. H., and R. K. Finn. 1969. New Separation Techniques. AIChE,
Today Series, New Orleans, La. pp. 21-22.
Engineering Science, Inc. (Texas). 1971. Preliminary Investigational
Requirements: Petrochemical and Refinery Waste Treatment Facilities.
EPA Project No. 12020 BID, NTIS.
Gloyna, E. F., and D. L. Ford. 1970. The Characteristics and Pollutional
Problems Associated with Petrochemical Wastes. Engineering Science,
Inc., Texas, Report.
Goldsmith, R. L., and S. Hossain. 1973. Oil-Water Separation by Ultrafil-
tration. Proceedings of the Joint Conference on Prevention and Control
of Oil Spills. API, Washington, D. C. pp. 441-456.
Goldsmith, R. L., D. A. Roberts, and D. L. Burre. 1974. Ultrafiltration of
Soluble Oil Wastes. JWPCF. 46(9):2183-2192.
Goren, S. L. 1974. Removal of Oil from Aqueous Wastes by Flotation.
Office of Water Resources Research, Washington, D. C. Rept. No.
PB-234-023, NTIS.
Grosz, R. B., and R. A. Kormanck. 1975. Dissolved Air Flotation. Unpub-
lished report.
Gruenfeld, M. 1973. Extraction of Dispersed Oils from Water for Quantita-
tive Analysis by Infrared Spectrophotometry. Env- Sci. Technol.
7(7):636-639.
Hensen, S. P., G. H. Richardson, and K. Hsiung. 1969. Some Recent Advances
in Water Treatment Technology. Chem. Eng. Progr., Symp. Ser. 65.
Harris, R. F. 1975. Report on Port Collection and Separation Facilities
for Oily Wastes. Volume IV: Determination of Impact of the Construc-
tion of Offshore Terminals on Their Contiguous Ports. Maritime
Administration Contract No. 2-36202, NTIS.
94
-------
Harvey, A. C. , A. R. Guzdar, and D. R. Friswell. 1973. Laboratory Evalua-
tion of the Emulsifying Characteristics of Pumps. U.S. Coast Guard
Rept. No. CG-D-31-74, NTIS.
Harvey, A. C. , and V. K. Stokes. 1973. Evaluation of a Unique Centrifuge
for Separation of Oil from Ship Discharge Waters. Proceedings of the
Joint Conference on Prevention and Control of Oil Spills. API,
Washington, D. C. p. 391.
Hoult, D. P. 1969. Oil on the Sea. Plenum Press, New York.
Hyland, J. R. 1971. Study of Oily Water Marine Treatment Facilities.
USEPA Office of Water Programs Report, NTIS.
Jones, H. R. 1973. Pollution Control in the Petroleum Industry. Noyes
Data Corporation, New Jersey.
King, A. 1941. Some Factors Governing the Stability of Oil-in-Water
Emulsions. Trans. Faraday Soc. 37:168.
Lederman, P. B. , and J. S. Dorrler. 1975. Development of Offshore Oil and
Gas in New England: Environmental Problems and Solutions. USEPA
Report.
Little, R. C. 1974. Breaking Emulsions of Water in Navy Fuel Oils.
Fuel. 53:246-252.
McKay, W. C. 1973. Evaluation of Concepts for Separating Oil from Water
Discharged from Ships. U.S. Coast Guard Rept. No. CG-D-26-74, NTIS
734305.2/9.
Milne, D. 1950. Character of Waste Oil Emulsions. Sewage Ind. Wastes.
22(3):326.
Nelson-Smith, A. 1972. Oil Pollution and Marine Ecology. Elek Science,
London.
Permutit Company (The). 1966. Research and Development for a Shipboard
Oil and Water Separation System. Maritime Administration Contract No.
MA-2722, NTIS.
Poliakoff, M. Z. 1969. Oil Dispersing Chemicals. Federal Water Pollution
Control Administration Rept. No. 15080FHS-05/69-14/12/549.
Pomeroy, R. 1953. Floatability of Oil and Grease in Wastewaters. Sewage
Ind. Wastes. 25:1304-1313.
Redlien, W. H., and J. H. McClintock. 1951. Reducing Water Pollution for
Oil Refineries. Pet. Refiner. 30(6):123-126.
Reid, G. W. , L. E. Streebin, D. W. Rumfeldt, and R. Sweazy. 1972. Evalua-
tion of Waste Waters from Petroleum and Coal Processing. EPA-R2,72-001.
95
-------
Shah, D. 0. 1970. Molecular Interactions at the Oil/Water Interfaces and
the Formation of Microemulsions. Federal Water Pollution Control Admin-
istration Kept. No. 15080EMP-06/70.
Skocypec, R. 1974. Electrolyte Effects on Flotation of Oily Water. M.S.
Thesis. University of California, Berkeley.
Smookler, A. L., and J. W. Harden. 1973. Navy Shipboard Investigation of
Oily Wastes. Proceedings of the Joint Conference on Prevention and
Control of Oil Spills. API, Washington, D. C. pp. 189-193.
Sniegoski, P. J. 1973. The Determination of Water Soluble Components in
Petroleum Products Used by the Navy. U.S. Naval Research Laboratory
2nd Progress Report.
Sollner, S. 1944. The Application of Sonic and Ultrasonic Waves in
Colloid Chemistry. Chem. Rev. 34:371.
Sport, M. C. 1969- Design and Operation of Gas Flotation Equipment for the
Treatment of Oilfield Produced Brines. Presented at the Offshore
Technology Conference, Houston, Texas. Preprint No. OTC 1051.
1:111-145.
Stahl, G. W., D. H. Meyer, and B. H. Rankin. 1972. Separation of Oil in
Bilge Water by Semipermeable Membranes. Naval Systems Engineering
Rept. No. USNA EW-72-7, NTIS.
Thompson, C. S., J. Stock, and P. L. Mehta. 1972. Cost and Operating
Factors for Treatment of Oily Waste Water. Oil Gas J. 53.
Thompson, D. 1951. Ultrasoncs. Chem. Eng. Progr. Symp. Series. 47(1).
Vrablik, E. R. 1959. Fundamental Principles of Dissolved Air Flotation of
Industrial Wastes. Proceedings of the 14th Industrial Waste Conference,
Purdue University, Lafayette, Ind. p. 743.
Weston, R. F. 1950. Separation of Oil Refinery Wastes. Ind. Eng. Chem. 4.
Weston, R. F. 1952. Waste Control at Oil Refineries. Chem. Eng. Progr. 9.
Witmer, P. E., and A. Gollan. 1971. Oil-Water Regenerative Separator—
Phase I. Final Report of Phase I: Development Program of a Continuous
Regenerative Moving Bed to Remove Oil from Oil-Water Suspensions.
Maritime Administration Rept. No. COM-72-11041, NTIS.
96
-------
TECHNICAL REPORT DATA
(Please rcaj Imtmctiom on the rtrcrse before completing)
1. REPORT MO
EPA-600/2-78- 069
i. TITLE AND SUBTITLE OIL/WATER ,
ART
2.
SEPARATION: STATE-OF-THE-
7.AUTHOR(S) Fidelis A. Osamor
Robert C. Ahlert
|9. PERFORMING ORGANIZATION NAME AND ADDRESS
1 Dept. of Chemical & Biochemical Engineering
1 Rutgers, The State University of New Jersey
New Brunswick, New Jersey 08903
112. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory-Gin., OH
Office of Research and Development
1 U.S. Environmental Protection Agency
I Cincinnati, Ohio 45268
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
April 1973 issuinq date
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM CLEMENT NO.
EHE623
11. CONTRACT/GRANT NO.
R803978
13. TYPE OF REPORT AND PERIOD COVERED
Final 7/11/7S - 7/T1/77
t4. SPONSORING AGENCY CODE
EPA/600/12 j
115. SUPPLEMENTARY NOTES
|16. ABSTRACT
This report reviews the state-of-the-art for oil/water separating
devices and processes. Devices and process are classified according to
the primary mechanism that induces separation of oil/water mixtures. The
basic concepts, specific design features, operational conditions, and
limitations of each category are discussed.
Literature on test evaluation of a variety of devices is critiqued
on the basis of actual or potential success in treating various oil/
water system states. No single technique can separate all oil/water
system states efficiently. Specific deficiencies in existing technology
have been identified.
This report was submitted in fulfillment of Research Grant No.
R803978 by Rutgers University Under the.sponsorship of the U.S.
Environmental Protection Agency. This report covers the period July 1,
1975, to June 30, 1977, and work was completed as of July 31, 1977.
17.
a.
KEY WORDS AND DOCUMENT ANALYSIS ]
DESCRIPTORS
Petroleum industry
Oil/water separation
Oily wastewaters
13.
DISTRIBUTION STATEMENT
TJTTT 17 ACT7 TO PTTRTTP
KEj.L£iAo £t L\J JTUlJJ_iiV>
b.lDENTIFIERS/OPEN ENDED TERMS
Oil pollution
Oil /water treatment
Coalescence
Gravity separation
19. SECURITY CLASS (This Report)
UNCLASSIFIED
20. SECURITY CLASS (This page)
UNCLASSIFIED
. COSATI Field/Group J
68D I
21. NO. OF PAGES j
104 |
22. PRICE
EPA Form 222O-1 (9-73)
* u.s. GovwiMBn pimmo OFHCE, i97s-a60-a?o/%
------- |