Certified magic boxes continue plaguing ships – an update in 2020

Many ships have a sewage treatment plant (STP) that is approved under the inter-related regulatory regimes such as the IMO’s MEPC guidelines, the European Marine Equipment Directive (MED), and the Code of Federal Regulations (CFR) of US who is not party to MARPOL’s sewage convention.

The approval authorities are the gate keepers responsible for testing and evaluating technologies of various features and claims. A successfully type approved STP brings a series of models of the same design principles to cover a range of treatment capacities.

See no evil

It must be populated on hundreds if not thousands of ships to be commercially viable. Allowing one STP that does not conform to the fundamental rules and principles to be approved would drag down the technological threshold, encouraging a ‘race to the bottom’ among suppliers.

Unfortunately, at least a dozen of such STPs have been approved. Over the years, these magic boxes have plagued thousands of ships. Over the years, these magic boxes have plagued thousands of ships. As featured by Shipinsight in 2018 [1], these non-conformities as well as a general lack of effective implementation of the regulations have contributed to a widening gap between rules and realities. Now, at a time of global pandemic, it may be a good time to reflect on this different plague unique to the marine and offshore sector.

No-sludge STP

Sewage treatment produces sewage sludge. It is science, and it is a fact. But some approved magic boxes do not separate particles from the treated effluent. Instead of being separated from the treatment process, sewage sludge is flushed out in the effluent. They cannot perform no matter how well they are operated. But how is it possible such impossible solutions deliver ‘good laboratory results’ during the type approval tests? Good question.

The issue has become so serious that it triggered a rule change (see MEPC 71/INF.22, MEPC 71/14/2 and MEPC 74/14).

In 2019, one no-sludge STP of European origin had its MED certificates withdrawn [2]. This withdrawal was said to be the first in the history of the IMO’s MARPOL Convention. Now, this discredited STP remains approved elsewhere [3]. Another no-sludge STP, also of European origin, gained further approval by the authority of a major ship-building nation. These magic boxes are not only sheltered under the wings of their approval authorities, they are advancing. They are heading East.

These no-sludge STPs exist on thousands of ships, mainly with lower tonnage (hence less space) and fewer number of persons onboard. To identify the magic box is easy, simply check to see if a STP has any de-sludge instructions and provisions.

Chlorination without dechlorination

Chlorination can be effective in disinfecting biologically treated sewage. But to meet the residual chlorine limit of 0.5mg/l, a dechlorination step is necessary. But many STPs have been certified without dechlorination – a scientific impossibility given the level of chlorination and the short contact time. The irony is that authorities that have approved such STPs would not approve the same magic feature if it was part of a ballast water treatment system.

To identify this magic box, check if a STP with the said feature is certified to MEPC.159(55) or MEPC.227(64) whereby the residual chlorine discharge limit of 0.5 mg/l applies.

STP recirculation

Recirculating sewage sludge back to a treatment plant’s inlet is explicitly prohibited by the Guideline on STP type approval tests [3, 4]. It can artificially inflate treatment capacity, and, by replacing raw sewage with sewage sludge that has already been through the STP process, invalidate the challenging characteristics of raw sewage.

In 2016, a marine sanitation device (MSD) claiming biological nitrogen removal was approved without a bioreactor. It turns out that the sewage feed tank was turned into a bioreactor during the performance test at a recognised test facility.

In 2017, one approval authority re-visited the test conditions of a STP and confirmed the mistake of recirculation during the type approval test. But the corrective measure of downgrading its capacity is only a half-hearted measure because the test remains a non-conformity. The same product traded under a different name remains certified to its original capacity by a different approval authority. It seems gatekeepers need a level playing field too.

To identify such non-conformities, ask if the sewage sludge is required to be returned to the STP feed tank.

Grey water to STP’s last stage

Grey water, if treated, should be subject to the same treatment process as sewage. But in some cases, grey water is approved to be connected only to the final disinfection stage of a STP. As a result, shipyards often had technical specifications misled by the certified non-conformities, asking grey water to be sent to the STP’s final stage. Tenders who offered customers compliant solutions and refused to meet such inappropriate technical specifications were disqualified.

To address the mistakes, MarED published an Approved Recommendation [5] in early 2019 demanding corrective measures ‘without delay’. However, if there had been any surveillance or corrective actions by the authorities, they have not been evident. Instead, some ship owners and shipyards started to take a lead by have the correct technical specifications. It is an improvement self-initiated by the industry.

To identify this non-conformity is easy. If a STP treats grey water but does not receive it at the beginning of the treatment process, check if the STP it is certified to MEPC.227(64) whereby the Qi/Qe factor applies.


The issues remain largely un-recognised and un-corrected. Inconsistencies exist among different approval regimes and among different approval authorities. There seems to be a lack of means to address these issues in an effective, transparent, and timely manner.

The existing magic boxes continue to spread, and new magic boxes continue to pop up. They continue to pollute marine water, to waste natural and human resources, and to drag down technology threshold.

Can a more rigorous type approval test stop these magic boxes? The answer may be evident: a no-sludge STP often completes a batch process within an hour (in a 10-day test period); the need for de-chlorination is well understood not least for the BWTS; STP recirculation is clearly prohibited by the rule; and the connection to STP’s last stage was actually certified without applying grey water during the test…

There is not yet a proven cure for this plague.

The industry needs environmental regulations that are science based, practicable, and sustainable. But we cannot arrive at such regulations blindfolded, or by sweeping these issues under the carpet.



Dr Wei Chen, Future Program Development Manager, Wartsila Water Systems Ltd, UK

Oliver Jost, Maritime Environmental Affairs, Wasserschutzpolizei (Water Police) Hamburg, Germany

Markus Joswig, Head of Marine Department, PIA GmbH, Germany

Mark Beavis, IEng IMarEng FIMarEST, Sales & Special Projects Director, ACO Marine s.r.o., Czech Republic, ACO Marine Systems GmbH, Germany

Felix von Bredow, Board of Hamman AG, Hamman AG, Germany

Endorsed by:

Dr Daniel Todt, Project Manager R&D, Ecomotive AS, Norway

Benny Carlson, Chairman and owner, Marinfloc, Sweden

Niclas Karlsson, Managing Director, Clean Ship Scandinavia AB, Sweden

Ed White, Environmental Consultant, former Alaska DEC cruise ship compliance manager, USA

Dr. Gerhard Schories, Head of Institute, ttz Bremerhaven, Germany

Helge Østby, Senior Technical Advisor, Jets Vacuum AS, Norway

Tjitse Lupgens, Senior Business Developer, TNO Circular Economy & Environment, The Netherlands

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