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Published on 29/12/2021

Understanding Sewage Effluent

Understanding sewage effluent will help with crew welfare and ship performance.

Since the UN’s COP26 in Glasgow in October 2021, companies worldwide have been firmly focused on increased efforts to reduce the collective impact on our natural habitat. Although much of the discussion is dominated by carbon emissions, fossil fuels and plastic pollution, there are many faces to the human impact on planet earth, concerning marine ecosystems in particular. Our oceans provide between 50-80% of the earth’s available oxygen, more than 6x that of the Amazon rainforest – so it’s vital that we protect them for generations to come.

Sewage pollution control was in fact the first environmental initiative in history – but we still have a long way to go before we achieve a solution that everyone can get on board with for the development and conservation of safer, cleaner oceans.

It’s not everyone’s favourite subject – but talking about sewage effluent is incredibly important when considering safety at sea – as well as the protection of delicate marine eco-systems worldwide. 

Please see our official sewage effluent page.

Understanding sewage effluent at sea

Operations at sea are bound by many multi-faceted considerations to ensure safe and responsible shipping – but one thing many often forget is the need for a robust and well-thought-out sewage management system.

There has been legislation in place for over 100 years prohibiting the release of untreated sewage into the sea, designed to protect our oceans from the environmentally damaging effects of untreated effluent. The recently updated MARPOL Annex IV came into force in 2003, with additional updates made during the revised 2006 MLC regulations.

Vessels have a variety of options available to them when it comes to the management, storage and treatment of sewage effluent – which you choose depends on the size and type of vessel as well as its function and capacity.

A number of environmental groups are advocating for increased regulation and more widely implemented and enforced legislation surrounding sewage effluent management at sea to protect human and marine health – so keeping up with (or ahead of) current guidelines with an innovative, forward-thinking approach ensures you can remain up to date and compliant even as things progress.


One principal concern covered by the MARPOL regulations is the effect of raw sewage dumping on the health of our oceans. Although sewage is ‘natural’ waste, it doesn’t simply disappear when released into open water, especially when present in large quantities. Sewage released directly into the ocean within close proximity of land masses poses a risk to swimmers and people living and working in coastal areas, as well as contaminating seafood and polluting beaches and beauty spots.

Polluted water doesn’t just pose a risk to human health – it can also result in the destruction of natural marine habitats and the suffocation of sea-life due to the oxygen demand required for the breakdown of raw sewage.

As well as protecting against the potentially devastating environmental impact of mismanaged sewage and effluent, properly maintaining your sewage management system has a number of advantages to be aware of, including:

*Maintaining the best possible condition of your vessel including sewage treatment systems

*Keeping crew and passengers safe

*Aligning with ethical and environmental efforts to prevent risk to marine life and human health

*Full compliance with regulations, preventing the risk of fines and penalties – legislative consequences include heavy financial losses but can also result in vessel detention, losing valuable hours at sea


Managing SE at sea requires a well-planned and multi-faceted approach to ensure safety and compliance at every step of the way. Some key considerations include:

*Understanding MARPOL regulations which prohibit discharge of sewage into the sea at specified distances (for untreated sewage the standard distance is 12 nautical miles), apart from in certain circumstances such as situations where there is operation of an approved sewage treatment plant on board, or when a ship is discharging processed and disinfected sewage using an approved system. This can also include considering the use of government-provided reception points at ports and terminals – noting that revised MARPOL guidelines also apply to ships engaged in international voyages

*Investing initially in a good quality, efficient sewage management system – not doing so could prove to provide false economy should issues arise at a later date.  

*Considering eco-friendly initiatives adopted by an increasing number of shipping companies, such as biological sewage treatment systems that use aerobic bacteria, which also decreases the generation of harmful gases such as methane and hydrogen sulphide.

*Ensuring compliance through regularly and thoroughly testing and maintaining your sewage system and taking timely corrective action where necessary.


At Martek Marine safety and sustainability are amongst our top priorities – so we’ve devised a variety of sophisticated solutions to ensure straightforward, reliable and economical sewage management on-board as well as continued compliance with current legislation.

Our Sewage Effluent Kit ensures full compliance with MARPOL Annex IV and localised regulations, as well as sustainable and safe waste management to ensure the continued protection of marine eco-systems. The kit makes testing sewage and potable water simple, quick and easy – the most comprehensive testing apparatus on the market.

Learn more about our Sewage Effluent Test Kit here – trusted by thousands of vessels worldwide for easy and effective SE management.