Seawage treatment Plant on board ship | Explained

The discharge of untreated sewage in controlled or territorial waters is usually banned by legislation. International laws is in force to cover sewage discharges at certain distances from the earth. Accordingly, and to meet certain standards, all new ships have installed sewage treatment plants.

Two types of sewage treatment plants are used, using chemical or biological methods. The chemical process is essentially a reservoir that collects the solids for disposal in authorized zones or areas collection site. The biological process treats waste water, so it is acceptable to discharge near the coast.

Legal Regulations and  Ship’s  Sewage Discharge

Unloading the sewage and storage of sanitary water from ships and equipment and containers must be certified to meet the prescribed standards, it has been regulated according to national and international standards. The problem of marine pollution by ships is the International Convention for the Prevention of Pollution from Ships, 1973-1978 (MARPOL 73/78) introduced by the IMO.
MARPOL lays down rules and regulations that prevent downward marine pollution by using oil, chemicals, harmful substances in any form of packaging, waste water and waste, harmful gas emission and ballast.

The Convention comprises of a number of Annexes and Annex IV contains provisions regulating prevention and supervision of marine pollution by sewage waste waters from ships. Annex IV to the Convention refers to:
a) prohibiting or limiting discharge,
b) issuance of certificates and inspections,
c) equipment and supervision of discharge,
d) shore reception facilities.

MARPOL Annex IV, is applicable to ships on international voyages that are 400 gross tonnage and greater; or less than 400 gross tonnage when certified to carry more than 15 persons. The board discharge monitoring equipment should include at least one of the following sewage systems: 

• The sewage treatment plant will be managed by the administration taking into account the standards and testing procedures of the IMO.
• A grinding plant and waste water disinfection approved by the administration.
• Such a system will have for the temporary storage of sewage systems to the satisfaction of the administration, if the ship less than 3 miles from the next country.

Annex IV of MARPOL 73/78 (IMO) regulates the disposal of ships at international level. In addition, some countries have their own national and regional controls.

The board discharge monitoring equipment should include at least one of the following sewage systems:
The sewage treatment plant will be managed by the administration taking into account the standards and testing procedures of the IMO. A System liquidation and waste water disinfection approved by the administration. Such a system will have for the temporary storage of sewage systems to the satisfaction of the administration, if the ship less than 3 miles from the next country.

The Hazards and regulations regarding the Sewage Systems:

Water drainage and waste water narrow limits reduce the ability of self cleaning. You can see in the sediment to the water, along with hydrogen sulfide has a pungent smell. The combined hydrocarbon and carbon stimuli plant oxygen back into the water.

With less oxygen, the best aerobic bacteria or infections cause anaerobic bacteria to rise due to lack of oxygen and so requires a control. Together with the decomposition solution and the smell of decay and its process produce  gas (toxic). Consequently, the action of packing station a group of aerobic, is necessary for type of waste water.

Principle of Biological Treatment Plant

The system require slow and steady fluid flow. The accumulation of heavy slime is a problem even , longer stay in the aeration chamber significantly reduces the cost. For example, 80% of the waste water contains solid reduced waste after 12 hours of aeration tanks in 20% of its original weight.

The aerobic process to remove dissolved oxygen in water generates water, carbon dioxide and bacteria.

Operation of Biological Treatment Plant

Image Source : http://www.marineengineering.org.uk (Used For reference purpose only)

The above plant shown has 3 chambers. The sewage enters the aeration chamber through a coarse filter where large solids decomposes, Then it goes to the ventilation chamber  where the main biological effect takes place. Here air blower mounted on the sides of the unit used to pump in air for the survival of aerobic bacteria, product flow of oxygen and bacteria was stirred through a series of pipes and nozzles. Then the waste is in the aeration pool for a sometime.

Move sewage from settling basin (or funnel) into the biological flocculate under resting conditions, aeration enters and bacteria settles and to the aeration chamber by pumping air by using blowers. A second transfer line is from the surface of the settling basin and extends to the aeration chamber. This transfer mud which contains bacteria that the waste water enters to digest.

Safety Parameters:

Anaerobic bacteria in all forms in a given situation, give away toxic and flammable gases. There is a need to participate in reducing the required anaerobic in treatment plant. You can carry the gas freeing so it can not enter the damage limit.

Here are some ways you can help reduce the risk:
Use air bathroom to reduce the risk. There must be a positive pressure in the chamber at all time to avoid any further gassing and risk of aerobic bacteria to die out. When the water storage tank is flushed out, maintain a system of oxygen in the water. For example, it can be entrained in the water so can be injected directly into the air, or air is pumped in. You should check the container. If you use aerobic treatment device, always check that the direction of operation of the plant should be considered positive. You should refer maintenance system whenever needed.

Maintenance of Aerobic treatment units

1. Check for regular cleaning and care 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. The chlorination of the sample should be between 1-5 ppm

# Various books, study material and other online sources has been refereed prior to writing this article but no part is copied or produced  from any of the source but explained same thing in better detailed way.

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Author Amit                                                                            

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