MARPOL Annex IV and Sewage Treatment Systems

MARPOL ANNEX IV
AND
SEWAGE TREATMENT PLANT
Mohd. Hanif Dewan, Chief Engineer and
Maritime Lecturer & Trainer, Bangladesh.
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MARPOL Annex IV
“Regulations for the Prevention of Pollution by Sewage”
• Entry into force: 27 September 2003.
• The second of the optional Annexes, Annex IV
contains requirements to control pollution of the sea
by sewage. (A revised Annex was adopted in 2004.)
Certificates issued under Annex IV:
• International Sewage Pollution Prevention Certificate
• Surveys: Initial & Renewal
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Special Area for Annex IV:
- Baltic Sea
Date of entry into force:
1st Jan, 2013
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SEWAGE
6/3/2014

Sewage means
- Drainage and other wastes from any forms of
toilets and urinals
- Drainage from medical premises ,wash tubs and
scuppers located in these premises
- Drainage from spaces containing living animals
and other waste waters mixed with drainage as
above
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Regulation 10:
Standard discharge connections
OD: 210 mm
ID: as per pipe OD
Bolt dia: 170mm
Slots in flange: 4 hole 18mm
Flange thickness: 16mm
Bolts and nuts: 4 x 16mm
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REGULATION 11: DISCHARGE OF SEWAGE
1. Discharge of sewage into the sea is prohibited except when,
The ship is discharging comminuted and disinfected sewage using
a system approved by the organization at a distance of 3 nautical
miles from the nearest land and that which is not comminuted or
disinfected at a distance of 12 nautical miles from the nearest land
2. Sewage shall not be discharged instantaneously, but at a
moderate rate when the ship is en route and doing a speed of not
less than 4 knots.
3. Ship has in operation a sewage treatment plant or an approved
sewage comminuting and disinfecting system with storage tank or a
holding tank of adequate capacity certified by the organization,
4. Test results of the plant are laid down in the INTERNATIONAL
SEWAGE POLLUTION PREVENTION certificate. The validity of
this certificate shall not exceed more than 5 years.
5. It should not cause any discoloration of the surrounding waters
nor produce visible floating solids
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Legislation preventing the discharge of untreated
waste overboard has been in place for some
time with a requirement that it should be
retrofitted where not already in use. American
legislation defines three types of sewage
treatment units.
SEWAGE
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Sewage systems Regulations.
Legislation preventing the discharge of untreated waste
overboard has been in place for some time with a
requirement that it should be retrofitted where not already in
use. American legislation defines three types of sewage
treatment units.
Type 1
A device capable of discharging effluent having no floating solids and a coliform count of less than 1000 per
100ml of effluent.
Type II
A device capable of discharging effluent with suspended solids not in excess of 150mg/litre and a coliform count
of less than 200 per 100ml
Type
III
A device to prevent the discharge overboard of treated or untreated waste.
Ventilation systems are to be kept independent of other
vents A log is to be kept of any discharge overboard from a
holding tank
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Human sewage is disposed of naturally by the action of
bacteria the human digestive system.
Most modern sewage systems encourage the growth of
human bacteria by supplying Oxygen to the bacteria which
helps the colony thrive and therefore literally eat the raw
sewage.
Most human sewage is 98% water so can be broken down
effectively by this simple action.
However the bacteria must be killed before the sewage
effluent (water) is disposed overboard otherwise it would
absorb all oxygen in the water.
SEWAGE
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Historically Chlorine has been used for this role, but in
many parts of the world chlorine damage is greater than
sewage damage.
The most common marine sewage system is called the “
AEROBIC ACTIVATED SLUDGE” system, and was
pioneered by Hamworthy in 1914.
SEWAGE
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ACTIVATED SLUDGE PROCESS
The Hamworthy Super Trident Sewage Treatment
Plant utilises the activated sludge process which
was developed in England by Ardern and Lockett in
1914, and was so named because it involved the
production of an activated mass of micro organisms
capable of stabilising a waste aerobically.
SEWAGE
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Basically the microbial population uses waste materials to
obtain energy and grow.
Waste consists mainly of several biochemical compounds
(carbohydrates, proteins, nucleic acids and lipids) which
contain mainly carbon, but also nitrogen, phosphorous and
other elements in lesser amounts.
Microbes consist of primary and secondary feeders who use
the waste material for energy and growth.
Primary feeders are bacteria, they use soluble waste
molecules for food, secondary feeders such as protozoa are
larger microbes and ingest particulate food, mostly bacteria
that has grown on waste molecules
SEWAGE
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Oxygen is provided to supply micro-organisms with the
means to oxidise a portion of the organic compounds 'in the
waste.
A portion of the energy released during oxidation is
converted to chemical energy which permits the organisms
to use the remaining organic carbon as building blocks to
synthesize the particular compounds needed for their
structure and function.
The amount of oxygen used during the process of obtaining
energy and extracting organic carbon from the waste for
growth is termed biochemical oxygen demand (BOD).
SEWAGE
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Principle
Biological system require a steady and relatively
constant flow of solid sewage so the bacteria can exist in
sufficient quantity to maintain effluent discharge at the
correct quality. sludge build up is a possible problem
although extended residence in the aeration chamber
greatly reduces the amount.
For example, sewage with 80% solid waste is reduced to
20% of its original weight after 12 hours in the aeration
tank.
The process of aerobicity strips oxygen from the water
and creates more water, carbon dioxide and bacteria.
SEWAGE
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- The Trident sewage treatment unit shown above consists
of three chambers.
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1. Sewage enters into the primary chamber of aeration
chamber via a coarse mesh filter where large solids are
broken down.
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-The aeration chamber is where the main biological action takes
place.
- Here air blowers mounted on the outside of the unit oxygenate
and stir the effluent and bacteria mix via a series of pipes and
nozzles.
- The sewage remains in this aeration tank for some time.6/3/2014

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2. Incoming sewage displaces some effluent of the settling tank
(or hopper) where under inactive conditions biological floc,
activated sludge and bacteria, settle out and is returned to the
aeration chamber via air lift pumps also driven by the blowers.
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3. A second transfer pipe scum's the surface of the settling tank and
returns it back to the aeration chamber.
- This returned sludge contains the bacteria to digest the incoming
sewage. Thus the importance of this floc return can be seen
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4. Effluent passing over from this chamber should be clean and
ready for disinfecting in the chlorinating chamber.
- The level in this chamber is controlled by a pump and float switch
arrangement. typical chlorine levels at discharge is 5ppm.
5. Valves are fitted to the aeration and primary chambers to allow
them to be pumped out and back flushed as necessary.6/3/2014

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The bacteria are susceptible to water conditions including
temperature and the presence of toilet cleaning agents.
In this way the system is fitted with by-pass valves so
passing contaminated water overboard.
Should the bacteria be killed it takes some time before a new
colony forms.
There are special 'feeds' which promote the reestablishment
of these colonies
SEWAGE
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GENERAL MAINTENANCE
Daily:
The air supply pressure should be checked to ensure it
is within the limits specified in the handbook.
Too high a pressure may indicate blocked distribution
pipe work or air diffuser elements,
Too Iow a pressure may indicate broken or leaking
distribution pipe work, dirty compressor air inlet filter or
compressor/motor failure.
An investigation of the problem and any necessary
remedial action will need to be carried out.

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Maintenance of Aerobic treatment units.
1. Thorough , regular cleaning and inspection with
particular attention being paid to areas behind
internal division plates
2. Checks on alarms and trips
3. Checks on aeration equipment
4. Checks on transfer systems in the tanks
5. It is recommended that a low air pressure switch
rather than a motor failed alarm be fitted to the air
blower motor hence eliminating the danger of the
fan belts snapping and going undetected.
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The contents of the aeration compartment should be checked for
quantity of suspended solids using the graduated cylinder
supplied. Fill the cylinder to the 100ml level and allow to stand for
30 minutes.
If the level of the settled sludge is above the 50ml level the unit
should be desludged by pumping approximately 50% of the
aeration tank contents overboard.
If the aeration tank contents are very dark in colour, exhibit a
tendency to float or settle very poorly and have a strong smell of
raw sewage or "rotten eggs", then the tank can be assumed to
have turned anaerobic.
This is due to the loss of the activated mass of microbes, possibly
due to a lack of air/oxygen or the high use of disinfectants in the
toilets.
SEWAGE
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The only solution is to drain and clean the tank and refill it
with clean sea water or freshwater prior to putting it back
on line.
If for this or any other reason the tank has been
completely drained and refilled then the effluent quality
can be reduced until after an approximate 14 day
conditioning period has elapsed.
SEWAGE
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Physical-Chemical Sewage system
This is based on the separation of the liquid element from
the sewage flow. This is disinfected in a 5% chlorine for 30
minutes to kill off coliform bacteria and then discharged
overboard in full MARPOL compliance.
One problem with this system is the required space, Only a
finite amount of space can be set aside for the storage of the
solid part of the waste which can only be discharged in port
or outside territorial waters when allowed. If these facilities
are unavailable the system become inoperative.
There is also the need to carry quantities of Calcium
Hypochlorite for conversion to Sodium HypoChlorite for the
disinfection of sewage flow.
Calcium Hypochlorite requires very careful handling.
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PHYSICAL CHEMICAL
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Electrocatalytic Oxidation
- Sewage is collected, macerated and passed through a
electrolytic cell.
- Electrolysis produces Sodium Hypochlorite which is used to
oxidise organic material before discharge. Alternately dosing by
chlorine may be used.
- The effluent passes on through to a settling tank were the
oxidation process is completed.
These type of plants can be 50% smaller than biological types,
this and the fact that pass through times are extremely short-
typically 30 minutes compared to the several hours of the
biological unit- are the main advantages of this system.
- The discharge contains no solids and is totally free of coliform
bacteria.
A disadvantage of this system is due to the short exposure time
in the oxidiser relatively high levels of chlorine are required to
ensure destruction of the coliform bacteria. It is possible that this
chlorine level can be present to some degree in the discharge.
Dechlorination plant may be fitted6/3/2014 30

Electrocatalytic Oxidation
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Vacuum sewage systems
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Operation
- Liquid flows from the aeration tank of an aerobic sewage tank to a coarse
impeller centrifugal pump.
- This delivers the liquid under pressure via an eductor and back to the
tank.
- The eductor reduces the pressure in the sewage system pipework to a
set point after which the pump is stopped.
- When the pressure in the pipework rises above a set value it is restarted.
- The pipework consists of a network of mainly pvc pipes connected into
separate zones- typically by deck- and brought down to a common
manifold via isolating valves. These valves allow work on sections of the
system whilst still maintaining others in use.
- The toilets are connect to the system via a vacuum operated foot valve.
Vacuum timers are also fitted which allow measured quantities of flushing
water to be applied.
Where toilets are connected in the same zone but exist at different heights
non-returning valves may be fitted. In addition filter boxes may be fitted
along with additional isolating valves to improve operation.
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Advantages:
1. Very little flushing water is required and the volume of sewage
dealt with can be much reduced with the downsizing of relevant
equipment and cost saving.
2. This has made them very popular for passenger vessels.Lloyds
regulations state that the capacity of a sewage system for flushing
water with conventional plant is 115 litres/ person/ day and 15
litres for vacuum systems.
Disadvantages:
1. The main disadvantage is blockage due to drying and
crystalisation of urea. Over a period of time this can be so severe
as to completely close the pipes. Chemicals are on the market
which can be added in very small doses which help remove and
prevent this deposits but there success is not guarenteed.
2. In the event of vacuum failure a method must be in place to
prevent dangerous gases passing back into the accommodation.
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The Hazards and regulations regarding the Sewage
Systems
- Raw sewage discharged into restricted waters will
eventually overwhelm the self purification ability of the
limited quantity of water.
- In a closed dock the effect can be seen in a black
sludgy water which when disturbed gives off an
unpleasant smell possibly Hydrogen Sulphide.
- When the quantity of sludge is reasonable aerobic
bacteria digest the sewage breaking it down to simple
compounds and Carbon dioxide using up Oxygen in
the process. These compounds and Carbon dioxide
promote plant life which returns oxygen to the water.
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- When the quantity of Oxygen becomes so depleted
that the aerobic bacteria can no longer function,
anaerobic or bacteria not requiring Oxygen to function
will take over.
- The breakdown of the sludge is then associated with
the same process of decay with foul smelling and
dangerous gasses being produced.
- Therefore the principal means of sludge conditioning
on board is that of aerobic action, Types of sewage
disposal.
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There are four main types of sewage disposal systems
fitted to ships:
1. Discharge from the toilet bowl into a common drain
leading to overboard via storm valves
2. As above except common drain leads to a storage tank
with or without aeration. Contents discharged ashore or at
sea when appropriate.
3. Sewage treatment systems with sewage being collected
and treated to produce an effluent suitable to discharge
without effect on environment.
4. Vacuum collecting system where the drains are kept at a
slightly negative absolute pressure , on flushing water,
sewage and air are drawn into the drains being led to a
collecting or treatment tank which is kept at atmospheric
pressure.
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Aerobic and anaerobic bacterial action
When the sewage enters the drainage system it is acted
upon by aerobic bacteria and is broken down, during this
process the naturally occurring Aerobic Bacteria strip the
water of oxygen and produce; more water, Carbon Dioxide,
and more bacteria.
If, however, there is insufficient oxygen for these bacteria
then alternative bacteria dominates. These Anaerobic
Bacteria produce Hydrogen Sulphide, Methane and
Ammonia. These gasses are either highly toxic or
flammable or both. In particular Hydrogen Sulphide is toxic
to humans in concentrations down to 10ppm and its
flammable vapours are heavier than air so may build up in
lethal pockets in enclosed spaces.
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Safety Parameters
The generation by anaerobic bacteria these toxic
and flammable gasses is present in all types of
systems to some degree. The possibility of
anaerobic action within a sewage treatment plant
should be reduced as far as possible.
Should these gasses be generated and allowed to
enter the accommodation could lead to disaster.
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The following are some methods which may
help to reduce the risks:
The fitting of proper ventilation in toilet spaces and the fitting of water
traps can only be seen as secondary measures to reducing the risk.
The primary concern is to eliminate the possibility of generating the
gasses in the first place.
Where sewage is stored in tanks for discharge, some method of
maintaining an adequate level of oxygen in the water must be in place.
Examples of these may be by direct air injection or by air entraining into
the liquid whilst pumping through a nozzle.
Where active aeration is not fitted then the contents of the storage tank
should be changed within a maximum of a 24 hour period unless some
other means of treatment is used.. The conditions in the tank should be
closely monitored
Where aerobic treatment plants are used then manufacturers operating
instructions should be closely adhered to. A system of maintenance
should be in place.
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Tank Ventilation arrangements.
Ventilation pipes should be in good condition and free
from obstructions. They should be of a size to
minimise pressure drop and ensure good gas
clearance. They should be self draining to prevent
blockage by water.
Any flame gauze's or other fittings should be checked
for cleanliness.
Toilets, showers, washbasins, etc.
The condition of drainage pipes should be checked
regularly, as should the operation of the water seal or
other fitted arrangements to prevent the back flow of
gasses.
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Accommodation ventilation arrangements
The ventilation should be sufficient to ensure proper
balance allowing each compartment to be correctly
supplied. The ventilation system should be correctly
maintained and checked for cleanliness.
Air extraction is of vital importance and the cleanliness
of grills should be checked, the opening under doors
should not be blocked, vent louvers should be
correctly position to ensure all spaces are properly
vented.
The forced ventilation equipment should be regularly
checked and maintained.
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Operational aspects
Only approved toilet cleaning agents should be
used, the use of excessive quantities of bleach
should be avoided as this may kill the bacteria.
. Complaints of foul or musty smells should be
dealt with immediately as these may indicate
anaerobic action. The dangers of these gases
should be explained to all crew.
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Suspended solids
The quantity of solid waste in the effluent is weighed. After drying on
an asbestos mat filter element.
Biological Oxygen demand (B.O.D.)
Aerobic bacteria use Oxygen in the process of breaking down the
sewage. At the end of the process the action of the bacteria reduces
and so does the Oxygen demand. The effectiveness of a sewage
treatment plant may be gauged by taking a one litre sample and
incubating it for 5 days at 20oC. The amount of Oxygen consumed in
milligrams per litre or ppm is termed the B.O.D.
Coliform count
It is possible that the effluent contain bacteria and viruses hazardous
to health if it has not been properly treated at the final stage. An
indication of this is a count of the Coliform bacteria which are found
in the intestine.
A coliform count in a 100ml sample incubated for 48 hrs at 35oC.
Another test at the same temperature but over a 24 hour period
produces a colony of bacteria.
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ANY QUESTION?
THANK YOU!
6/3/2014
45

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