Certificates for sewage treatment plants: How to recognise non-conformities and magic boxes


Certification of sewage treatment plants without conformity to the rules is a real problem as the certification process does not always live up to the required standards. As regrettable as it is, it is a fact. We take a closer look at the problem and show you how to determine whether a plant is legitimately carrying its certificate or not.

Many ships have a sewage treatment plant (or marine sanitation device in U.S. terminology) that is approved under the inter-related regulatory regimes such as the IMO’s MEPC Guidelines (IMO certificates), the European Marine equipment Directive (EU-MED certificates), and the Code of Federal Regulations (CFR) of the US (USCG certificates), who is not party to the IMO’s sewage rules. The approval authorities are the gate keepers responsible for testing and evaluating candidate technologies of various features and claims. A successfully type approved sewage treatment plant is the basis for a series of models with the same design principles covering a wide range of treatment capacities.

However, some sewage treatment plants on the market are certified to the current standards of IMO MEPC.227(64) and/or the U.S. 33 CFR 159 despite obvious non-conformities or even scientific impossibilities. Ship owners and operators should be aware of this fact. Having a sewage treatment plant on board which is not only certified, but which actually complies with the rules and performs as required by the rules can save them a lot of trouble if their pollution prevention equipment is inspected and tested by the authorities.

Non-conformities and “magic box” issues are related to these four areas:

  • Handling of sewage sludge
  • Use of chlorine
  • Recirculation
  • Handling of greywater

The good news is that it is fairly easy to determine whether a particular plant is in breach of the rules. By asking the following four questions, you will get straight to the heart of the matter.


A sewage treatment plant that is claimed not to produce sludge is the classic example for what we call a “magic box”. This is not only a certification without conformity to the rules, it is a scientific impossibility, as sludge is an inevitable by-product of sewage treatment (further reading here). These magic boxes do not have the technologies to separate the sludge that develops in the treatment process. They cannot perform no matter how well they are operated. To identify the magic box is easy: Simply check if there are any de-sludge instructions and provisions, e.g. that a dedicated sludge holding tank is required.


Chlorination can be effective in disinfecting biologically treated sewage. But to meet the residual chlorine limit of 0.5mg/l, a de-chlorination step is necessary. However, many sewage treatment plants have been certified without de-chlorination –another scientific impossibility, given the level of chlorination and the short contact time (further reading here). To identify this magic box, check whether de-chlorination is provided for in the treatment process.


Recirculating sewage sludge back to a treatment plant’s inlet is explicitly prohibited by the Guideline for type approval tests (see IMO MEPC.227(64) Paragraph 5.2.1 and 5.2.3, and Figure 1  and 33 CFR 159.121 Paragraph (c) and (d). Also further reading here) It can artificially inflate treatment capacity, and, by replacing raw sewage with sewage sludge that has already been through the treatment process, invalidate the challenging characteristics of raw sewage. To identify such a certification without conformity to the rules, ask if the sewage sludge is required to be returned to the sewage treatment plant’s feed tank.


For ecological and economic reasons, it makes a lot of sense to treat grey water together with sewage (black water) in one process. It this is to be done, it inevitably leads to an increased size and capacity of the sewage treatment plant to accommodate the additional wastewater volume. However, in a few cases, certification has been awarded to sewage treatment plants having the grey water connected to the final sewage disinfection stage. This not only renders the disinfection stage ineffective, resulting in poor performance, it is a non-conformity (further reading here). IMO MEPC.227(64) introduced a Dilution Compensation Factor with the intention to rule out sewage treatment plants relying on dilution (e.g. with seawater) as a “treatment principle”. This factor Qi/Qe =1 means that influent volume to the plant must equal effluent volume from the plant. If greywater is sent to the sewage treatment plant downstream of the influent sample point Qi, then the factor is Qi/Qe <1. To identify such a certification without conformity to the rules is easy: If the sewage treatment plant treats grey water but does not receive it at the beginning of the treatment process, it is in breach of the rules.


Be critical! Certification without conformity to the rules is more common than one might think. While it is very unfortunate that an IMO, MED or USCG certificate cannot be trusted blindly, it is fairly easy to check whether a sewage treatment plant is legitimately carrying its certificate or whether it should not have been certified in the first place. When considering the costs that can be imposed on owners and operators if plants fail official tests in real operation, only few arguments remain in favor of installing such a plant, however small or low-priced it may be.

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Food waste and wastewater handling onboard ships

Food waste and wastewater: Don’t mix and match!

Food waste does not belong in the wastewater system of a ship, not only regarding the efficiency of the system but also from a legal point of view. The handling of food waste is strictly regulated for good reasons, and making it disappear with the help of the sewage system is at best non-compliance. Disposing of ship sewage mixed with food waste on land is in breach of national biosafety regulations and poses a potential biohazard to local communities and the environment. Mixing food waste with wastewater on board a ship already violates Annex V of IMO’s MARPOL convention as such.

Food waste can spread plant pests, as well as livestock and poultry diseases such as swine fever, rabies, foot and mouth disease or avian flu. Some countries have strict biosecurity regulations falling under the jurisdiction of the national agricultural authorities, while others have ad-hoc measures.

In short, these rules demand that food waste be either discharged to the sea beyond 3 nm or 12 nm from the nearest land or transferred to the approved facilities for disposal. In the meantime, it must be managed in a way that is leakproof.

Annex V of IMO’s MARPOL Convention permits three routes for a ship’s food waste: to the sea (beyond 3 or 12 nm from the nearest land); to an onboard incinerator; and to port reception facilities. The actual disposal route must be recorded in a Garbage Record Book.

However, on many ships, food waste and its derivatives are sent, in whole or in part, to the grey water system, where it vanishes without a trace. The technical standards of some classification societies permit food waste to be sent to the sewage treatment plant instead of a food waste holding tank as stipulated in section 2.9.2 of IMO MEPC.259(71). Such standards create further non-conformity because sewage treatment plant is not one of the three permitted routes in the Garbage Record Book, which is completed and signed by the ship Master.

The diagram below illustrates the extent of potential non-compliances, looking at a food waste disposer as one of many potential examples.Non-conform food waste handling through wastewater system

Food waste entering the system from the top left corner of the diagram never comes out from the system; it simply vanishes. Tracing the lines to the port reception facilities (PRF), it is clear how food waste gets ashore in disguise, escaping the ‘approved facilities’ intended by the local biosecurity rules. From there it can end up on the agricultural land, carrying biosecurity risks with it.

Read the full article by Dr. Wei Chen on The Martime Executive

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Wastewater treatment terms: Wastewater, sewage, blackwater, greywater, graywater. Which term means what?


What is wastewater, sewage, black water, grey water? There are a multitude of definitions of these terms, which sometimes differ more, sometimes less. These definitions are given by the INTERNATIONAL MARITIME ORGANISATION (IMO), the U.S. ENVIRONMENTAL PROTECTION AGENCY or classification societies. Here you can find out what is meant and what it is all about!


Wastewater is to be understood as a generic term that can include many different substances. Ballast water, bilge water, wash water from exhaust gas cleaning systems, residual water from food waste, drainage from toilets, showers, wash basins, etc. – all this basically falls under the term wastewater.  The term wastewater is therefore not very selective.

When we speak of wastewater in our field of activity, we mean sewage. Both terms are often used as synonyms, although this is not very accurate.


HAMANN AG defines Sewage as follows:

  • Drainage and other wastes from any form of toilets, urinals and WC scuppers
  • Drainage from medical premises (dispensary, sick bay, etc.) via wash basins, wash tubs and scuppers located in such premises
  • Drainage from spaces containing living animals
  • Grey water when mixed with the drainages defined above

Sewage therefore contains black water in any case and can also contain grey water.  The technology of HAMANN sewage treatment plants is designed to always process a mixture of black water and grey water – i.e. sewage in its entirety.

Different definitions of the term sewage come from e.g. the IMO, the EPA and classification societies.  Our definition above is largely congruent with that of the IMO. The IMO, however, formulates the last point more openly and speaks of “other waste waters when mixed with the drainages defined above”. We are more specific here by limiting this point to grey water. One reason for this is, for example, that mixing black water with residual water from food waste (which would fall under “other waste water”) would mean that the rules of MARPOL Annex IV (Sewage) would no longer apply to this mixture, but those of MARPOL Annex V (Food Waste).


The term blackwater is not officially used by regulatory authorities such as the IMO, but it is used by the industry and classification societies. As with the term sewage, the definitions of black water also differ depending on the source.

HAMANN AG defines blackwater as follows:

  • Drainage containing faecal matter, e.g. from toilets
  • Drainage from medical premises if present

Black water is therefore a subcategory of sewerage. The terms blackwater and sewage are often used synonymously, as they both contain faecal matter.  However, HAMANN AG distinguishes between the two due to the higher concentration of faeces, pathogens and other potentially hazardous substances in black water.


First of all this term is spelled in two different ways: Graywater with an “a” is mostly used in American English and greywater with an “e” is used in British English.

HAMANN AG defines greywater as follows:

  • Drainage free from faecal matter or fat, e.g. from dishwashers, showers, wash basins, laundry, etc.
  • Galley water after it has been processed in a grease separator.

The IMO (International Maritime Organization) resolution MEPC.227(64) point 2.7 also includes galley water in its definition of grey water, without making the treatment in a grease separator a requirement. However, due to the high fat content in galley water, separate treatment in a grease trap is important not only for the performance of sewage treatment plants, but e.g. for the entire piping system for sewage and greywater on board, which can otherwise quickly become clogged by fat deposits.


At HAMANN AG, we distinguish between grey water and galley water – unlike IMO, for example. The reason for this is the high fat content in galley water. Fat impairs the performance of sewage treatment plants and can, for example, clog the piping system for sewage and greywater on board due to deposits. That is why we require galley water to be treated in a grease separator so that it can subsequently be considered greywater and processed further in our wastewater treatment plants.

HAMANN AG defines kitchen wastewater as follows:

  • Drainage from kitchen premises via sinks and scuppers located in such premises as it likely contains fat


Sludge, or sewage sludge, is an unavoidable byproduct of sewage treatment. Sewage treatment plants always generate two output streams:

  • Treated sewage, also referred to as effluent
  • Sewage sludge

Treated sewage (effluent) can be discharged into the sea (local/regional discharge bans such as in no-discharge areas must be complied).

Sewage sludge mus first be kept on board in holding tanks. There are two options for the discharge of sludge:


Solid garbage is to be considered separately from wastewater. Garbage is defined in MARPOL Annex V as follows:

“1.1 Garbage means all kinds of victual, domestic and operational waste excluding fresh fish and parts thereof, generated during the normal operation of the ship and liable to be disposed of continuously or periodically except those substances which are defined or listed in other Annexes to the present Convention.”

Garbage also includes food waste. Important: If garbage as defined in MARPOL Annex V, e.g. food waste from the galley, is mixed with sewage as defined in MARPOL Annex IV, i.e. mainly from the toilets, the stricter requirements of MARPOL Annex V apply to the treatment of the mixture.

HAMANN sewage treatment plants are exclusively designed for the treatment of sewage according to MARPOL Annex IV and grey water according to IMO resolution MEPC.227(64) and are not suitable for the treatment of garbage according to MARPOL Annex V.

To find out more on HAMANN sewage and wastewater technology, click here!

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HAMANN AG is supplying sewage and wastewater management systems for three new US REGIONAL CLASS RESEARCH VESSELS currently under construction at GULF ISLAND SHIPYARD in Houma, Louisiana, USA.

The 199 feet / 60 meters long REGIONAL CLASS RESEARCH VESSELS were designed by Glosten from Seattle, USA, in cooperation with OREGON STATE UNIVERSITY. They provide accommodation and workplaces for up to 16 scientists and are operated by a crew of 13. Their purpose is the exploration of the coastal marine environment. The highest environmental protection requirements and the lowest possible noise emission played an important role in the development of the vessels design. The extensive new building project is financed by the NATIONAL SCIENCE FOUNDATION (NSF) and managed by the OREGON STATE UNIVERSITY.

Regional Class Research Vessel equippend with HAMANN sewage and wastewater technology

The first of the three research vessels will be launched this year as “RCRV Taani 1” and will be commissioned by the OREGON STATE UNIVERSITY on the west coast as part of the UNIVERSITY-OCEANOGRAPHIC LABORATORY SYSTEM (UNOLS).

The sewage and wastewater management systems on board the vessels are designed to treat black water from toilets and grey water from showers, washbasins, kitchen sinks and laundries, and can process a peak of 6,000 litres of wastewater per day. HAMANN HL-CONT PLUS 025 wastewater treatment plants with IMO MEPC.227(64) and USCG Type 2 (33 CFR 159) certification are used as a basis. The HAMANN DISSOLVED AIR FLOTATION (DAF) technology used in these plants does not require any filters or membranes, making the plants particularly low-maintenance and reliable. Even strong fluctuations in the volume of wastewater to be treated due to fluctuating numbers of people on board are no problem for these plants.

Regional Class Research Vessel equipped with HAMANN sewage and wastewater management system

Highly efficient HAMANN grease separators separate the grease components from the galley wastewater to prevent clogging of the pipelines by grease deposits and the formation of hydrogen sulphide in holding tanks.

Automatically controlled HAMANN tank aerators compensate for the lack of oxygen or oxygen consumption in the wastewater holding tanks, which, especially in connection with too high fat contents in the wastewater, promotes the formation of toxic and odorous hydrogen sulfide and ultimately of aggressive sulfuric acid.

Further information on the REGIONAL CLASS RESEARCH VESSELS can be found under the following link: https://ceoas.oregonstate.edu/ships/rcrv/

All graphics courtesy of Glosten, Seattle, USA

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by Dipl. Ing. Olaf Hansen, Head of Technical Department at HAMANN AG

During the last months, the industry of wastewater and sewage treatment technology has seen some notable and partly confusing actions regarding the certification of products. Due to increasing pressure from both the industry and the legislative side, certificates for some sewage treatment plants on the market have been suspended or withdrawn by certifying bodies. This indicates that the certification system needs to be revised. A group of industry players – we are among them – has issued a call for action to improve the guidelines for the certification of sewage treatment plants.

Fortunately, it is the intention of many ship owners to reduce the environmental impact of their ships or just aiming to comply with existing regulations. As a matter of fact, these owners are exposed to a high financial risk when the sewage treatment systems on board do not comply with required effluent standards.

Public authorities around the world are getting more and more sensitive to marine pollution by sewage from ships. A recent example is the Maritime and Port Authority of Singapore (MPA Singapore) which has just issued a circular to all owners, managers and masters of Singapore-registered ships in which they point out that malfunctions of sewage treatment plants have been the most frequent reason for ships to be detained by Port State Control in the year 2019 so far.

If a certificate of an operating plant gets withdrawn because it does not meet the required effluent standards, the ship owner might be forced to have it replaced by another plant with a valid certificate and/or to pay a significant fine.

Considering this, we encourage all ship owners and shipyards to look beyond the certificates and to challenge us – the manufacturers – to deliver sewage treatment systems that perform in terms of effluent quality, ease of operation and reliability. We suggest to broaden the perspective and to take a look at what a sewage management system actually is – or should be.

Sewage management is more than having a sewage treatment plant. A sewage management system needs to be designed properly: From sewage collection via sludge handling to effluent discharge. Sewage treatment plants, black and grey water lines, grease separators, system separators preventing microbes from spreading against the flow from waste water lines into fresh water systems, holding tanks, tank aerations, transfer systems, sludge tanks, sludge processing facilities and performance monitoring are all part of the system. Off course, every project is different. Therefore a sewage management system has to be customized to cover the specific conditions on board.

There are a few key factors that influence how well a sewage treatment system performs. First and foremost, food waste and sewage lines strictly have to be separated. Food waste has a much higher BOD5 (Biological Oxygen Demand) value than raw sewage and therefore heavily increases the organic load on the sewage treatment plant. Grey water from galleys needs to run through a properly designed and dimensioned grease separator before being stored in a holding tank. Grease from galleys not only plugs up pipes and sensors, but also catalyzes the build-up process of hydrogen sulfide which is a toxic and extremely smelly gas inside the holding tanks. In the worst case, sulphuric acid may be formed inside the holding tanks which then attacks the piping and leads to a degradation of the effluent values.

Last but not least, the organic load of the sewage treatment plant should be monitored and controlled in order to maintain the organic design-load which was certified. For example, IMO resolution MEPC.227(64) requires a sewage treatment plant to produce the defined effluent values based on a TSS (Total Suspended Solids) value of ≥ 500 mg/l in the influent. Our sewage treatment plants are designed within these parameters but with a margin allowing for varying load situations. Operating the plant for a longer period above this margin leads to reduced treatment effectiveness and therefore a degradation of the effluent quality. In extreme cases, overloading can lead to a complete breakdown of the plant.

For us as a manufacturer it is evident that we cannot leave the planning and design of a sewage treatment system to the customers and just sell them sewage treatment plants. An important part of our business is consulting. The earlier we get involved in a project, the better the results can be. We often do workshops with ship design companies and naval architects before or at the very beginning of a project to improve the sewage management system as a whole. During the detail construction we closely work together with the shipyard engineers on creating the best possible conditions on board in order to operate our systems properly.

Sewage management is more than having a sewage treatment plant. It’s a properly designed wastewater management system. But even the best system is useless if operation and maintenance overtaxes the crew on board. It makes no sense to expect a ship’s crew to have expert knowledge in the field of sewage treatment like staff of most land based sewage treatment facilities have. Marine sewage treatment plants should be operated safely without years of prior training. We incorporate this aspect in the design of our systems and put a lot of effort in the automation of routine operations, high usability and low maintenance requirements. Only then, a well-designed sewage management system performs well.

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Stella Australis and Ventus Australis are equipped with HAMANN sewage and wastewater management systems


Australis Expeditions trusts in HAMANN sewage and wastewater management systems for its vessels STELLA AUSTRALIS and VENTUS AUSTRALIS. Both cruise ships operate in the fjords and channels of Tierra del Fuego, Patagonia. The luxury expedition cruise company takes protecting the enviromnment very serious and has chosen us to supply the sewage treatment technology for their vessels. Read their environmental protection policy here: https://www.australis.com/site/en/why-australis/social-and-environmental-responsibility/

Both vessels have been built by ASENAV in Valdivia, Chile. Here are some key facts on the ships:

Year of construction: 2017
Capacity: 200 Guests
Cabins: 100

Year of construction: 2010
Capacity: 200 Guests
Cabins: 100

The sewage and wastewater management systems on board the vessels are designed to treat black water from toilets and grey water from showers, washbasins, kitchen sinks and laundries, and can process a peak of 24.000 litres of wastewater per day. HAMANN HL-CONT PLUS 10 sewage and wastewater treatment plants with IMO MEPC.227(64) and USCG Type 2 (33 CFR 159) certification are used as a basis. The HAMANN DISSOLVED AIR FLOTATION (DAF) technology used in these plants does not require any filters or membranes, making the plants particularly low-maintenance and reliable.

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Brittany Ferries relies on HAMANN technology for sewage treatment on board their new LNG-powered “HONFLEUR”, currently nearing completion at Flensburger Schiffbaugesellschaft. Two HL-CONT Plus 40 sewage treatment plants provide a total treatment capacity of 8.000 litres per hour on board the 42.400 gt vessel that can carry 1,680 passengers and has a vehicle capacity of 2.600 lane meters.

To find out more about the new “HONFLEUR” head over to the microsite that Brittany Ferry has created.

Watch Brittany Ferries’ Honfleur LNG delivery and storage animation:


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We are proud to have been selected to supply sewage treatment technology for Irish Ferries’ stunning new “W.B. Yeats”. The ship is equipped with a system of two HL-CONT Plus sewage treatment plants providing a peak capacity of 12.000 litres/hour. Built by Flensburger Schiffbau-Gesellschaft, she arrived in her home port Dublin on December 20th, 2018. “W.B. Yeats” will serve the route Dublin/Cherbourg.

Head to Irish Ferries’ website to find out more

Picture of “W.B. Yeats” © Irish Ferries

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HAMANN donates sewage treatment plant to SEA SHEPHERD


HAMANN AG has donated a HL-CONT PLUS sewage treatment plant to the Sea Shepherd Conservation Society in support of their efforts to protect our marine environment. The plant has been installed on MY Bob Barker, a former whale catcher built in Norway.

Brian Race, Fleet Technical Superintendent at Sea Shepherd Global: “Sea Shepherd is delighted to be able to fit a HAMANN sewage treatment plant on another one of our vessels. After being tested and proven a success on the MY Ocean Warrior the MY Bob Barker is a proud new owner of this high quality, low maintenance and hassle free unit.  Sea Shepherd has always done its best to minimize our impact on the worlds oceans we fight to protect, and with this added unit we excite to continue our high standard.  HAMANN has provided us excellent technical assistance for our other unit and we are proud to gain their added support with this new unit.”

MY Bob Barker key data:

Purchased by Sea Shepherd Conservation Society: 2009
Built: 1950
Length: 52.2m
Width: 9m
Tonnes: 488
Crew: 32
Speed: 15kn

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The green conscience is one reason for using high quality and efficient solutions for processing sewage. The other not negligible part is the high risk of being caught with no or false records and losing high value of the vessel. A guide for owners and shipyards on IMO certificates.



This will not become a general discussion about the development of standards in the maritime industry. Even though it is not a discussion about technical aspects or the efficiency of sewage treatment plants in detail. It is also well known to us, that specific STP’s are just on board without any relevant usage over years. Nevertheless, from our point of view it is an absolute must to protect the (maritime) environment with appropriate measures. (more…)

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