REGULATORY AND TECHNOLOGICAL 

DEVELOPMENTS IN THE TREATMENT 

OF OILY BILGE WATER 

Presented at the International 

Conference on Marine Engineering 

Systems 

ICMES 2003 

Finland 

May 2003 

Author: Hal Alper 

 

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INTERNATIONAL COOPERATION ON MARINE ENGINEERING SYSTEMS

Paper presented at the 9TH International Conference on Marine Engineering Systems 

at the Helsinki University of Technology (HUT) Ship Laboratory and on board MS SILJA SERENADE 

19-21 May 2003

REGULATORY AND TECHNOLOGICAL DEVELOPMENTS 

IN THE TREATMENT OF OILY BILGE WATER 

Author: Hal Alper, MYCELX Technologies Corporation, Gainesville, Georgia, U.S.A. 

1. INTRODUCTION 

Of the oil released by vessels, 25% is reported to come

from spills and 75% from operational discharges. Oily 

bilge discharge is second only to oily ballast tank 

discharge in its contribution. Historically, oily bilge water 

has been treated using Oil/Water Separator technology 

(OWS) or discharged with minimal treatment. OWS 

technology alone is not capable of meeting current oily

bilge water discharge standards in many cases. There has 

been much work in the past in regard to determining what 

the discharge standard should be for oily bilge water and 

how best to detect and monitor the discharge. The result

appears to be that 15 ppm will be the standard of

discharge for oily bilge water, although within localities 

more stringent limits exist. 

A variety of technologies have arisen to fill the gap 

between OWS Capability and discharge standards. 

Among these are systems based on gravity separation, 

size separation, chemical affinity separation and 

flocculation. There has also been a gap between 

regulation and enforcement. Unregulated discharges have 

been problematic. There have been significant advances 

in the ability to detect such discharges in the past few 

years; the most significant is Synthetic Aperture Radar 

(SAR). This paper will review developments in detection

technology and oily bilge water treatment. 

2. Regulatory Developments 

2.a. Regulations 

 

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In the past decade the regulatory horizon in regard to 

treatment and disposal of oily bilge water has changed 

greatly. The IMO (International Maritime Organization)

has been the leader in development of regulations. The 

International Convention for Prevention of Pollution 

from Ships (MARPOL 73/78) sets the standard in regard 

to bilge water and other forms of ship-generated 

pollution. The Act to prevent pollution from ships 

(33.U.S.C. # 1901 et seq.) is the US legislation 

implementing certain provisions of MARPOL. Coast

guard regulations (33 CFR # 151,153 and 155) as 

amended by Oil pollution act (OPA) and Clean water act

require oily wastes discharged within 12 nautical miles of 

shore have an oil content fewer than 15 ppm. Various 
localities have more stringent requirements and some

restrict any discharge and require onshore treatment. 

The National Defense Authorization Act of 1996 

amended Section 312 of the Federal Water Pollution 

Control Act (also known as the Clean Water Act (CWA) 

to require that the Secretary of Defense and the 

Administrator of the Environmental Protection Agency

(EPA) develop UNDS (Uniform National Discharge 

Standards) for vessels of the armed forces. (Section 312 

(n) (1)). 40 CFR Part 9 and Chapter 7 (EPA), 40 CFR 

Chapter 7 (Department of Defense) completes the first 

phase of the three phases to set UNDS for armed forces 

vessels. The phase 1 rule determines the type of vessel

discharges that require control by MPCD’s (Marine 

Pollution Control Devices), which includes surface bilge 

water and oil water separator discharge. This rule creates 

a new 40 CFR part 1700 establishing UNDS that apply to

discharges. This regulation is promulgated under the 

authority of section 312 and 502 of the Clean Water Act 

(333 U.S.C. 1322 and 1362). Any new device must

conform to MEPC .60(33) (Marine Environmental

Protection Committee) as promulgated by MARPOL in

which the standards of performance are set for oil 

filtering equipment.

2.b. Enforcement 

Enforcement of regulations has traditionally been 

problematic in regard to bilge water discharges. Satellite 

monitoring data indicates that the highest concentration 

of bilge water discharge is right before sunrise, indicating 

that most of the discharges occur at night. Technological

developments in the last two decades have made 

detection of illegal discharges more feasible. The 

technologies currently utilized for this purpose are as 

follows: 

2.b.1. Technologies/Sensors for Oil spill 

Surveillance 

• Detection of the potential presence of oil: 

Airborne SLAR, Satellite SAR. 

• Identifying oil spills: Airborne LFS (Laser 

Fluoro Sensor). 

• Determination of Oil spill thickness: Airborne

IR/UV Line Scanner, MWR (Microwave 

Radiometer). 

• Detect potential presence of a likely pollution

culprit: Airborne SLAR, Satellite SAR. 

• Identification of the likely pollution culprit: 

Airborne FLIR (Forward-Looking InfraRed). 

2.b.2. SAR Development 

• Early Imaging Radar – SLAR

The first imaging radars were Side-Looking Airborne 

Radars (SLAR’s) developed for reconnaissance purposes. 

SLAR is known as “Real Aperture Radar” because its 

along-track resolution is determined by the size of the 

physical antenna footprint.

These radars at wavelengths of 2 cm, can image the 

Earth’s surface under day/night conditions. The track 

resolution of SLAR is limited by antenna length. 

The development of SAR (Synthetic Aperture Radar) 

overcomes this problem by incorporation of a pulsed 

coherent radar in conjunction with a synthetic aperture 

which is not limited by the fixed footprint of the radar 

dish. The size of an aperture in a SAR system is 

proportional to the length of the arc described by the 

satellite during signal collection. This results in the 

curious property of SAR systems having higher 

resolution at greater distances. SAR systems can be used 

at longer wavelengths than SLAR. Oil spills can often be 

detected in SAR imagery because the oil changes the 

back- scatter characteristics of the ocean. Radar backscatter from the ocean results primarily from capillary 

waves through Bragg scattering. The presence of oil

 

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dampens the capillary waves, thereby decreasing radar 

back-scatter. Thus, oil slicks appear dark in SAR images 

relative to oil-free areas (Figure 1). 

 

Fig.1 The SAR Wide Swath image above was 

acquired over the Galician coast in Spain on 17

November 2002, i.e. few days after the Prestige

tanker start to spill massive amount of oil. 

• Seasat SAR 

The first space based imaging radar to be used for 

imaging of the earth was the L-band SAR on Seasat, 

launched in 1978. Seasat SAR was a single parameter 

instrument using a fixed wavelength, polarization and 

incidence angle and hence produced severe geometric 

layover distortions. 

• Shuttle imaging radars (SIR) 

SIR-A, SIR-B space based SAR’s followed Seasat SAR 

with articulating antennas providing variable incidence 

angles (15-60 degrees). This demonstrated potential for 

using incidence angle back-scatter signatures which later 

led to the second generation SIR-C/X-SAR’s 

incorporating multi-frequency, multi-polarization, 

variable incidence angle. The multi-parameter capability 

of the SIR-C/X-SAR, coupled with the introduction of 

routine sensor calibration, opened a new regime in SARbased scientific applications. Oil spills are detectable and

the multi-parameter capability permits oil type and oilsurfactant differentiation to be determined. 

For oil spill detection, low resolution (LRI) SAR images 

with a spatial resolution of 100m*100m have been found 

to be suitable. 

• ERS-1, ERS-2

Based upon the Seasat experience, the European space 

agency (ESA) embarked on the development of the ERS1, ERS-2 satellites which incorporated a C-band SAR 

with a single frequency, single polarization and fixed 

incidence angle-23 degrees. The ERS-1 and ERS-2 are 

being flown in tandem mode (flying one after the other 

along the same track) to allow inter-ferometric processing 

of images from both spacecrafts. The SAR onboard the 

ERS satellites are the most suitable single instruments for 

oil spill detection onboard present and near-future 

satellites. 

The oil spill detection capabilities of different radar 

satellites: 

• ERS-1, ERS-2: Adequate for oil spill detection

at low and moderate winds (2-8m/s). 

• RADARSAT-1 (Canadian Radar Satellite): 

acceptable for oil spills when operating in 

Narrow-Scan SAR-Near-Range Mode. 

• ENVISAT: The wide Swath mode of this unit is

useful in oil spill monitoring.

 

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NOAA is exploring the possibility of participation in the 

Marine SAR Analysis and Interpretation system

(MARSIAS) effort. This is a multinational project 

sponsored by the European Union with the goal of 

producing a comprehensive coastal ocean oil spill 

detection and monitoring system using SAR and other 
remote sensing data. 

2.b.3. IMO Mandated Black Box

International Maritime Organization (IMO) has been

studying the possibility of equipping ships with Voyage

Data Recorders (VDR) and Automatic Identification

Systems (AIS). The aim of is to supplement this type of 

equipment with “environmental indicators.” The 

mandatory regulations for certain ships to carry VDR and

AIS (MSC 73/21a2.doc Regulation 20 Annex 7) came 

into force on July1, 2002. 

Utilization of the above should make it possible for the 

first time to be able to detect illegal discharges and track

the discharge back to its specific vessel. 

3. REVIEW OF CHEMISTRY OF BILGE 

WATER AND ESTABLISHED TREATMENT 

TECHNOLOGIES 

3.a. Nature and properties of bilge water 

Bilge water is a chemically complex mixture of solvents, 

surface active agents (surfactants, i.e. soap), metal salts 

such as greases and lubricants and tramp oils (i.e. 

compressor condensate). Some of the above are bioaccumulative persistent organic pollutants (POP’s) such 

as polyaromatic hydrocarbons and chlorinated aromatic

hydrocarbons. Others such as aromatic hydrocarbons 

(BTEX) and oil, copper, iron, mercury, zinc and nickel, 

organic metal salts in addition to detergents and solvents 

are aquatic toxins 

Generally speaking organic non-polar compounds (oils) 

are not soluble in water. However if solids, solvents or

surfactants are present, oils will tend to emulsify in water. 

The degree of emulsification is inversely proportional to

the buoyancy of the micelles. If sufficient emulsification 

occurs to achieve neutral or closed to neutral buoyancy

gravity separation devices lose their effectiveness in

separating the organic compounds from water. One way

to gauge the relative solubility of a surfactant and thereby 

the type and stability of the emulsion is the HLB 

(Hydrophile – Lipophile Balance) method. In this

method a number between 1 and 40 is assigned to many

commercial emulsifying agents, which is indicative of the 

balance of hydrophilic to lipophilic portions of the 

molecule. The higher the HLB, the more water-soluble 

the material. The water solubility of an emulsion or a 

surfactant can be used to make an approximation of its

HLB which is indicative of the stability of the emulsion.

Behavior in Water HLB Range 

No Dispersability 1-4

Poor Dispersion 3-6 

Milky Dispersion After 

Agitation

6-8 

Stable Milky Dispersion 8-10 

Translucent To Clear 10-13 

Clear Solution 13+ 

The average approximated HLB is one criteria which can 

be used to evaluate the optimal bilge water treatment

system for a particular vessel. 

3.b. Review of principles of OWS (Oil Water 

Separator technology) 

Oil water separators are Gravity Separation devices 

which utilize a difference in buoyancy of two immiscible 

liquids to achieve separation. There are variety of 

configurations which are utilized including but not

limited to underflow weirs, parallel plate coalescers and 

centrifugation devices. OWS are very effective when two 

discrete phases are present. When emulsification or 

solvation occurs buoyancy differences are too small to be 

exploited utilizing existing OWS technology. In this case 

upstream or downstream technology must be employed in

 

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order to sufficiently clean bilge discharge. Typical bilge 

water concentrations range from 200-2000 ppm. The 

presence of neutral buoyancy particulate matter tends to

further complicate the waste stream and the treatment 

technology. We will review some emerging technologies 

in regard to oily bilge water treatment which are either 

upstream or downstream of the OWS (as gravity

separation is optimal as a first step for bulk removal of 

non-aqueous phase components).

4. EMERGING TECHNOLOGIES IN THE 

TREATMENT OF OILY BILGE WATER 

4.a. Biological oxidation of OWS-treated oily bilge 

water in a support medium in which hydrocarbon 

degrading bacteria are bound by a biological glue 

(secreted by the bacteria). Oil and related contaminants 

are degraded in this bio-layer as the bacteria oxidize the 

hydrocarbons. One of the U.S.C.G and I.M.O approved 

Biological Oxidation systems is the PetroLiminator100. 

While biological systems can meet the proposed BOD 

discharge limits of 26 ppm, the effluent of the biological

process contains a high concentration of nonbiodegradable organics which do not consistently meet

the proposed limits for COD(Chemical Oxygen Demand) 

and TOC (Total Organic Carbon) when exposed to highstrength oily bilge water. This necessitates post biooxidation treatments like Advanced Chemical Oxidation. 

4.b. Chemical Oxidation :Oxidation processes 

utilizing chemical oxidizers such as peroxides especially 

in the presence of ultraviolet light is a well-known 

technology utilized in the production of high purity 

industrial water. Although these systems can be very

effective, especially at lower influent concentrations, 

fouling and maintenance can result in higher than 

expected costs. Additionally peroxides are dangerous 

compounds which can become unstable and even 

explosive when not properly stabilized. 

4.c. Vapor Phase Extraction: Vapor phase 

extraction of oily and greasy components from oily bilge 

water using supercritical CO2 or steam can be very

effective but costs tend to be high due to the high cost of 

heating and cooling. Studies are still being done on the 

extent of recovery of carbon dioxide from bilge water and 

other economic concerns on the process include the 

recompression costs on the CO2 system. 

4.d. Surface Modified Filtration Devices: Granular 

substrates and absorbents or cartridge filters can be

modified with “curable polymeric surfactants” (referred 

to as “MYCELX”) which have affinity for emulsified 

droplets (Figure 2). These devices are generally used 

post-OWS to remove highly emulsified materials 

(Figures 3-6) and to bring the effluent concentration to

below 1 ppm. These units have affinity for organic 

compounds and do not develop additional differential 

pressure in the presence of very thick oils or under high 

loading conditions. Another advantage of these units is

the time invariance of the affinity reaction, resulting in a 

fixed footprint. A fixed size unit can handle influent

concentrations over 2000 ppm and at flow rates from 5-

150 gpm without affecting the effluent concentration 

which will remain constant at well below 5 ppm. The 

spent filters can be used as an alternative fuel if feasible. 

The disadvantage of this unit is that the spent filters 

cannot be discarded into the sludge tank without

shredding. 

Fig.2: Partially Saturated vs. Unsaturated Filter 

 

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Fig.3 

Fig.4 

Fig. 3 and Fig. 4 MYCELX filters employed in

treatment of Naval bilge water at 300 gpm (Photos by 

Kirk Abbott). 

Fig. 5 

Fig.6 

Fig. 5 and Fig. 6: MYCELX filters cleaning 

emulsified oil on oil drilling rig. Clean water being

discharged directly overboard

 

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4.e. Membrane Filtration (Ultrafiltration): It is 

determined that Ultrafiltration is a viable separation

process for the treatment of bilge water for compliance 

with overboard discharge. Commercial treatments of 

bilge water using membranes include those with noncellulosic and ceramic substrates. Non-cellulosic 

membranes are able to capture most organic compounds 

over 1000 (Daltons) Molecular Weight, and are 

consequently susceptible to irreversible membrane

fouling. Ceramic membranes have been tested and used 

in naval ships for treatment of oily bilge water with

generally good results. They require periodic cleaning 

and maintenance and are overwhelmed by concentrated 

slugs of influent. Combined Centrifugal

separator/Membrane Ultrafiltration systems and

Ultrafiltration/Membrane Distillation systems have also

been investigated for treatment of large volumes of bilge 

water that contain high concentrations of emulsified and 

free-phase oil, as well as suspended solids. 

4.f. Flocculation: Flocculation units are utilized in

conjunction with high performance gravity separation 

devices (generally centrifuge) to good effect. Effluent

concentrations below 15 ppm are obtainable with these 

systems. Centrifuge systems tend to be capital and 

maintenance intensive rendering them costly to operate, 

however they are able to achieve significant reduction in

oil concentrations even with somewhat emulsified waste 

streams. It is necessary to get the influent to fairly low 

concentrations in order for the flocculation system to

work optimally. Flocculation systems can be

overwhelmed by high loading resulting in gel like 

flocculant which is difficult to handle and requires 

shutdown and maintenance. Often secondary treatment

with carbon, clay or other absorbent is required. 

5. DISCUSSION

The technologies for detection, identification and 

enforcement of oily bilge water discharges not in

compliance with local and IMO regulations exist and are 

viable. The will to implement and enforce these 

regulations appears to be the limiting factor in reducing 

illegal oily bilge water discharges. 

 

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It is not possible to select a single bilge water 

treatment technology as the best for all cases. Selection of 

an optimum design will depend on throughput, loading, 

degree of emulsification and the conditions under which 

the units must operate, or robustness the unit must

exhibit. Certainly conventional OWS is well established 

and is the single best technology for making the first

primary cut. OWS are fully capable of achieving numbers 

below 15 ppm in the presence of discrete immiscible

phases. Biological units function very well under 

conditions of moderate throughput with controlled 

loading. Loading spikes can overwhelm and shutdown 

biological units. Capital costs tend to be high and the unit

can become troublesome if proper maintenance is not

performed. Membrane separation technologies such as 

ultrafiltration are desirable in circumstances where 

loading is fairly low and uniform. These systems can 

become overwhelmed due to fouling or overloading of 

the membranes in which case shut down and cleaning and 

or membrane replacement must take place. Additionally 

membrane units do not have fixed footprints and require 

more room or dwell time in cases of higher loading or 

higher throughput. Initial capital outlay is high. Surface 

modified filtration devices exhibit high performance and

the highest degree of robustness in regard to loading and 

throughput. These devices will not shutdown in the 

condition of high loading and will maintain a consistent
effluent concentration and low operating pressure. Initial 

capital costs are low, but replacement filters are required, 

and the spent filters must be used for fuel or stored. 

Centrifugation / Flocculation units exhibit very good 

overall performance but the centrifuges require high 

degree of maintenance and initial capital outlay is high.

Flocculation units involve chemical addition and can be 

overwhelmed if centrifuges are not working properly and 

influent concentrations rise too much above 200 ppm, 

depending on the throughput. At this time evaporation, 

supercritical CO2 and other chemical separation 

technologies do not seem to be utilized in the field very 

much. Additionally operating costs for these types of 

devices are high. Cost to operate can range from

2$/1000gallons or more to less than 50 cents/1000gallons 

depending on the size of the system, the loading and 

degree of emulsification and the unit employed.

5. CONCLUSION 

The technology for detecting and regulating bilge water 

discharge now exists. Enforcement of such regulations is

evermore present, and the potential for significant fines 

continue to mount for major violators. 

There are a number of options in regard to

technology for the treatment of oily bilge water. The 

author does not believe any single type of unit is optimal

in all circumstances. The selection of the appropriate unit 

will depend on the type of ship (i.e. steam ship vs. gas 

turbine), the amount of loading, the degree of 

emulsification, the throughput and the robustness 

required of the unit, in addition to capital and operational

expenses. Evaluation of average bilge water composition 

and degree of emulsification should be taken into account 

in selection of oily bilge water treatment equipment. 

Periodic spikes in influent concentrations should also be 

taken into consideration. The treatment unit should be 

able to operate without shutdown when challenged with

isolated slugs ten times the average loading or higher. 

Acknowledgements: 

The author would like to acknowledge Kirk Abbott 

(Director of Engineering, MYCELX Technologies 

Corporation, USA) for his work and effort on this paper 

and corresponding presentation at ICMES 2003. 

Primary References: 

1.Clean Water Act Section 312 (as amended by Section 

325 of FY96 National Defense Authorization Act). 

2. Nature of Discharge Report for Surface Vessel 

Bilgewater/Oil-Water Separator Discharge as amended 

by UNDS. 

3.International Convention for the Prevention of 

Pollution from Ships, 1973, as modified by the Protocol

of 1978 relating thereto (MARPOL 73/78). The 2001 

amendment - Adoption: 27 April 2001; Entry into force - 

1 September 2002. 

4. EPA 40CFR Part 9 Chapter VIII 

5.“Removal of organic pollutants and warfare agents

utilizing surface modified filtration devices”, presented at 

NDIA 2003 – Hal Alper, MYCELX Technologies 

Corporation. 

(Secondary References available upon request).

 

 

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