Marine Sanitation Systems Talking Points
Marine and offshore work applications generate sewage that can contain contaminants which have a
detrimental effect on water quality and the overall marine environment. As a result, marine sanitation
treatment methods are required to lessen the environmental impact. The new MEPC.159(55) effluent
standards, adopted by the International Maritime Organization’s Marine Environment Protection Committee,
apply to all sewage treatment systems installed on board on or after January 1, 2010.
Meeting the stringent standards require more robust treatment effectiveness, often using larger, heavier
equipment. Users, meanwhile, are motivated to minimize system footprint and weight from a cost-efficiency
standpoint. The new effluent standards will make the already challenging job of cleaning up global
waterways even more difficult.
With this challenge in mind- Severn Trent De Nora worked to develop a light weight system, designed with a
small footprint, to provide effective electrolytic treatment of both black and gray water through a patented
and certified treatment process. As a result, the company introduced the new OMNIPURE™ Series 55 and
MARINER OMNIPURE® Series M55 marine sanitation systems. The systems have received Type
Certification Approval from Bureau Veritas for IMO Resolution MEPC.159(55) regulation.
Comparison of MSD Standards
Standard
USCG
BOD5 (Mg/l)
Suspended Solids (Mg/l)
Thermotolerant Coliforms/100 ml
COD (Mg/l)
Residual Chlorine (Mg/l)
pH Value
n/a
150
200
n/a
n/a
n/a
IMO
Previous
50
100
250
n/a
n/a
n/a
IMO
MEPC.159(55)
25
35
100
125
> 0.5
6.0 -8.5
OMNIPURE
Series 55*
14.6
15.2
11.1
35.7
0.13
7.28
* Results are Geometric Mean of 40 samples taken over 10 days of testing. OMNIPURE Series 55 systems
exceed the treatment requirements of the IMO MEPC.159(55) regulation.
These systems are the only marine sewage treatment devices that oxidize sewage in an electrochemical
cell as well as generate sodium hypochlorite from natural seawater for the disinfection of sewage streams.
Electrolytic treatment of marine sewage eliminates chemical storage issues, dosing equipment and costs
associated with the use of hazardous chemicals since the disinfection solution is produced on site while the
unit is in operation.
The OMNIPURE Series 55 systems accommodate treatment capacities up to 598 persons (black water) and
up to 197 persons (black and gray) and range in capacity up to up to 65 m3/day. The MARINER OMNIPURE
Series M55 systems accommodate treatment capacities up to 75 persons (black water) and up to 25
persons (black and gray) and range in capacity up to 8.2 m3/day of human wastewater per day.
Marine sanitation methodologies
Over the years a number of sanitation methodologies have been developed – from
physical/chemical separation to biological treatment to electrolytic treatment systems.
Physical/chemical separation systems involve a flow-through device that treats liquid waste with
a chemical (e.g. chlorine or sodium hypochlorite) or non-chemical disinfection process (e.g.
ultraviolet disinfection or ozone) and pumps treated (DC) sewage overboard as permitted. Larger
solids are separated from liquids by a screen at the raw influent point, then macerated and
transferred to storage for dumping in non-restricted zones. This process involves the
transportation, storage and handling of hazardous chemicals, resulting in increased operational
costs – and the off-gassing of chlorine. Physical/chemical separation typically provides no surge
capacity, often requiring additional tank capacity. As a result, the equipment requires a larger
footprint then other marine sanitation systems. The equipment could have up to four times the
amount of rotating equipment as electrolytic or biological systems, too. From a maintenance
standpoint, physical/chemical separation systems require the periodic manual cleaning of
separation screens which could be considered a biological hazard.
Biological treatment is a common land-based method that involves the use of microorganisms
(bacteria colonies) to feed on the waste in the presence of oxygen and naturally digested waste.
Large collection tanks receive and aerate the wastewater, and excess/dead microorganisms with
inert sludge are separated by settling. The clarified liquid from the process is disinfected, typically
with tablet form chlorine, and discharged as permitted. The disadvantages of this process are
numerous. The process can take approximately 30 hours, depending on the hydraulic capacity of
the particular unit, to complete and requires a large footprint. Biological treatment requires a
lengthy waste storage time, too, necessitating the use of several large tanks. The equipment is
extremely heavy, often exceeding physical/chemical or electrolytic system weights by a larger
factor. In periods of low flow or shutdown, the bacterial colonies can be destroyed by the
introduction of certain influents (i.e., cleaning fluids), and the destruction of bacteria colony can
cause the sewage to go septic, creating a toxic gas such as hydrogen sulfide and a flammable gas
such as methane. The ship’s motion also has the potential to affect the settling process, creating
an erratic flow that produces an uneven treatment process. These biological processes produce
odor problems, too. One major maintenance requirement is the removal of the sludge deposits
from the bottom of the tanks, which can be time consuming and require a complete shutdown
along with manual removal of the sludge. Lastly, the cleaning fluids and caustics introduced into
plumbing lines during the process can shut down the entire system.
In order for a biological treatment system to meet the new IMO standards, ultra filtration
membranes are used in combination with the biological process. As a result, another level of
complexity is introduced to the treatment process since both the membranes and the live bacteria
must be properly maintained. Routine maintenance is undertaken to ensure the membranes are
not fouled or damaged. Additionally, the membranes will require periodic cleaning which creates a
solution that must be properly disposed of.
Electrolytic treatment systems mix sewage with available seawater which flows through an
electrolytic treatment cell. A DC electrical current electrolyzes the seawater creating an oxidant
(typically sodium hypochlorite) that oxidizes the organic material and kills off the disease-carrying
pathogens within the process stream. The lightweight process has a smaller footprint and does not
require the use and storage of hazardous chemicals for treatment, eliminating the costs associated
with their use. Cleaning fluids and caustics will not hamper the system’s operation. The treatment
time is much shorter than with biological treatment systems – approximately 2 hours compared to
other types of systems requiring about as low as 8 hours or as high as 30 hours. The process
creates no odor, and is self contained.
An example of a technology in which on-site generated sodium hypochlorite is produced from
seawater is the novel OMNIPURE™ Series 55 system from Severn Trent De Nora. The
OMNIPURE system is the only marine sewage treatment system that oxidizes sewage in an
electrochemical cell as well as generates sodium hypochlorite from natural seawater for the
disinfection of sewage streams. OMNIPURE systems provide effective electrolytic treatment of
both black and gray water, meeting personnel treatment capacities ranging from one to more than
500 people (65 m3/day or 17,000 gallons/day).
The electrolytic treatment process
The OMNIPURE Series 55 units feature an Adaptive Algorithm Wastewater Management system
to facilitate varying inlet wastewater conditions commonly found in offshore applications. Based on
the baseline compliance and criteria of the MEPC.159(55) requirement, the units are factory
calibrated to effectively oxidize and treat normal inlet wastewater streams of 500 mg/l (ppm) of TSS
and BOD to at, or below, the discharge effluent requirements. For those installations where higherthan-normal sewage influent is expected, the appropriate inlet waste algorithm can be pre-selected
prior to system shipment.
The automatic three-stage treatment process is simple and proven effective, utilizing continuous
collection and treatment of the accumulated black and gray water. In the first stage, sewage is
macerated while BOD and fecal coliform are significantly reduced as the wastewater stream flows
through the patented electrolytic cell.
In stage two, an electrocoagulation cell enhances the sewage stream with dissolved iron particles
that serve as nucleation sites, forming a flocculation with the fibrous organic matter that readily
drops out of solution. A defoaming agent is injected into the waste stream between the electrolytic
and electrocoagulation cells to enhance gas-liquid separation of the stream exiting the cell. Gas
generated in both cells is removed in a degassing column mounted on top of the primary settler. A
proprietary design encourages disengagement of the entrained process gases from the stream
which percolates gently into the primary settler tank. Finally, an internal standpipe provides
significant reaction time for coagulated solids to fall to the bottom of the settler, and liquid with
minimal solids is routed through the internal standpipe to the clarifier.
Stage three comprises an additional settling or clarification-concentration step. The process stream
enters the unique clarifier tank where velocity is kept at a minimum to further encourage settling of
any remaining flocculants to the bottom of the clarifier. This results in a clear effluent from the
discharge of the unit that meets and/or exceeds the effluent composition requirements for
MEPC.159(55). The solids from the settler and concentrator, which are classified as Class B
sludge requiring no special transportation criteria or disposal restrictions, can be handled by the
operator as a concentrated waste stream or further processed using Severn Trent De Nora’s solids
handling unit.
OMNIPURE Series 55 Features/Benefits:
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No odor or bio-active sludge associated with process
Easy to install, operate and service
No additional surge tank required
No microorganisms to keep alive
Easy to disassemble for better access
Operation is not hampered by cleaning fluids
Operates on-demand, instantaneous on-off operation
Small footprint and weight
Bureau Veritas Certification for IMO Resolution MEPC.159(55)
MARINER OMNIPURE Series M55 Features/Benefits:
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Accommodates varying crew complements
Automatic operation
Compliant to CE/ATEX norms
Easy to install, start up, operate and service
Eliminates storage, handling and purchasing of hazardous chemicals
No complicated pre-treatment of raw inlet sewage stream
No odor or bio-active sludge associated with process
No raw sewage screens, vibrators or filters to manage
Not affected by typical cleaning agents
Small footprint and weight
Bureau Veritas Certification for IMO Resolution MEPC.159(55)
OMNIPURE Series 55 Process Diagram
OMNIPURE Series 55 Model 5513