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

WASTEWATER TREATMENT TERMS: LET’S GET THEM STRAIGHT!

There are several terms around that are used in the context of wastewater treatment. Some of them are very specific while others aren’t specific at all. Let’s dive into it and get it straight!

WHAT IS WASTEWATER?

“Wastewater” is a generic term and can mean either black and grey water together or separately, depending on the context. The term “wastewater” is also used synonymously with the term “sewage”. While “wastewater” is the most commonly used term, it is less selective than “Sewage”, “Black water” or “Grey water”.

WHAT IS SEWAGE?

“Sewage” is the most official among the wastewater treatment terms. It is the term used by the IMO (International Maritime Organization) both in the MARPOL Convention (International Convention for the Prevention of Pollution from Ships; “MARine POLution”) as well as by the IMO’s Marine Environment Protection Committee (MEPC) when dealing with the subject. All IMO resolutions issued by the MEPC on this subject speak of “Sewage” and “Sewage treatment”. Therefore, IMO certificates are issued for “Sewage treatment plants”, they don’t say “Wastewater treatment plants”.

MARPOL Annex IV gives the following definition of “sewage”:

“3. Sewage means:
drainage and other wastes from any form of toilets and urinals;
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; or
other waste waters when mixed with the drainages defined above.”

WHAT IS BLACK WATER?

Among all the wastewater treatment terms, the term black water is not officially used by the regulatory authorities and is therefore not clearly defined. In general, the term black water is used to mean “Sewage” as defined in Annex IV of the MARPOL Convention.

WHAT IS GREY 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. Grey water is defined in IMO (International Maritime Organization) resolution MEPC.227(64) as follows:

“2.7 Grey water – is drainage from dishwater, galley sink, shower, laundry, bath and washbasin drains and does not include drainage from toilets, urinals, hospitals, and animal spaces, as defined in regulation 1.3 of MARPOL Annex IV and does not include drainage from cargo spaces.”

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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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SEWAGE MANAGEMENT IS MORE THAN HAVING A SEWAGE TREATMENT PLANT

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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IMO CERTIFICATE: A GUIDE FOR OWNERS AND SHIPYARDS

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.

 

CHALLENGE

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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