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 HL-CONT PLUS 0125 seage & wastewater treatment plant model year 2021The HL-CONT PLUS 0125 sewage & wastewater treatment plant is one of our most popular plants. First, it’s 3.000 l/24h capacity fits many use-cases. Then, being part of our HL-CONT PLUS range of plants, it is the epitome of HAMANN quality, with all metal construction on a solid frame. Last but not least, it can be customized to suit exactly what is required in each individual project.  

Now, we have given the HL-CONT PLUS 0125 an extensive update to make it even better. With a redesigned flotation tank and optimised pipe routing, we reduced the size by over 20% and shaved off 30% of the weight. 

The proven technology and trusted working principles of this model remain unchanged. 

This is the model of choice for the highest standards on quality, performance and adaptability with access to the full range of options and accessories. 

For more information, please visit the product page or contact our sales team!



HAMANN HL-CONT COMPACT 0125 sewage & wastewater treatment plant model year 2021In 2019, we introduced the HAMANN HL-CONT COMPACT 0125, the smallest and lightest fully certified sewage & wastewater treatment plant on the market. For the model year 2021, we have added another feature, that makes it also the plant with the shallowest depth on the market. The HL-CONT COMPACT 0125 now comes in two alternative layouts, giving even more flexibilty for installation: Layout A with shorter width but more depth and layout B with minimum depth. This option discloses many more possible locations to install the plant e.g. on walls or along walkways.  

The proven technology and trusted working principles of this model remain unchanged. 

On delivery, all units are set up in layout A and can be quickly and easily converted by the customer if desired. This is the model of choice for market leading quality and performance in an economical and efficient package for a wide range of applications. 

For more information, please visit the product page or contact our sales team!

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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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Remote support by HAMANN AG


While this is a difficult time for the world in general, facing the COVID-19 pandemic, it is a good time to talk about remote support. Technical equipment doesn’t care whether it is an appropriate time to cause trouble or not. So what to do when a customer can’t fix a problem himself and help won’t be able to get there in person? Remote support is the answer.

Remote support is a sustainable way to offer technical customer support, because it does not only make sense in a crisis situation. With all the audiovisual communication tools at hand today, many issues can be solved remotely without having to physically travel thousands of miles. And to reduce travel, specifically air travel, helps us in another crisis that has been pushed from the news top spot by the current virus: the climate crisis.

However, what is HAMANN REMOTE SUPPORT able to do for our customers?

First of all, our highly skilled service engineers will communicate with the customer via telephone or email to narrow down the problem. Then, they will set up a videocall and the customer’s mobile device will enable our service engineers to “come on board” and take a look at the plant or component themselves. Under the guidance of the HAMANN service engineers, the customer carries out the appropriate actions.

No special equipment is needed and the amount of time, effort and cost to set up a remote support session is far less than actually flying in a service engineer in person.

But off course there are limitations to what can be reasonably handled in a remote support session. The need to deploy a service engineer on location rises with the complexity of the issue at hand. Our experienced service team will advice our customers on what is the best way to deal with a given problem.

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