Support for Major Reshape of MARPOL Annex IV

file photo courtesy of Diamantino Rosa
file photo courtesy of Diamantino Rosa

Published Jan 12, 2020 4:05 AM by Wei Chen

Disinfecting raw sewage is ineffective and harmful. The comminuting and disinfecting systems are a disservice to the IMO's aspirations. In the light of Norway's constructive proposal to reshape the IMO's sewage rules, let bygones be bygones.

The joint paper below supports the call for a major reshaping of MARPOL Annex IV and its Guidelines. 

Sewage Comminuting and Disinfecting Systems - A Disservice to MARPOL Annex IV 

Co-authored by: 

Dr. Wei Chen, Future Program Development Manager, Wärtsilä Water Systems Ltd, UK 
Dr. Daniel Todt, Project Manager R&D, Ecomotive AS, Norway

Endorsed by: 

Benny Carlson, Chairman and owner, Marinfloc, Sweden
Niclas Karlsson, Managing Director, Clean Ship Scandinavia AB, Sweden
Antony Chan, Engineering Manager, Victor Marine Ltd., UK
Helge Østby, Senior Technical Advisor, Jets Vacuum AS, Norway
Dr. Ramona Pristavita, Director, Product Development, Health & Safety, Terragon Environmental Technologies, Canada
Tobias Kaulfuss, Manager - Marine Sewage Treatment, RWO - Veolia Water Technologies Deutschland GmbH, Germany

The IMO’s MARPOL Annex IV regulations permit three ways of discharging ship’s sewage into the sea; 1) via an approved sewage treatment plant, 2) via an approved comminuting and disinfecting system at a distance of more than three nautical miles from the nearest land, or 3) at a distance of more than 12 nautical miles from the nearest land under certain operational conditions. 

A comminuting and disinfecting system, as its name suggests, combines the maceration and disinfection processes. It is a rudimentary device which neither separates/produces sewage sludge nor removes residual disinfectant. This is because it is not subject to any numeric discharge limits or test procedures, rendering its approval by the Administration a meaningless burden. 

The regulations for the provision of comminuting and disinfecting systems date back to the 1970s. Since then, scientific and engineering advances have been achieved in wastewater processing, and environmental rules and regulations are similarly being advanced. 

First of all, disinfecting raw sewage is not effective. Sewage should be adequately treated prior to disinfection in order for any disinfectant to be effective [1,2,3,4,5]. In addition, disinfectants have been found to react with organic compounds and produce toxic residuals and mutagenic or carcinogenic compounds, known as disinfection by-products (DBPs) [6,7,8,9,10]. The higher the organic concentrations, the greater the level of DBPs being produced [11]. 

This means disinfecting raw sewage is not only ineffective, but it also risks doing more harm than good. Over the past decade, the IMO has introduced stringent residual disinfectant limits and total residual oxidant (TRO) limits to environmental technologies such as sewage treatment plants and ballast water treatment systems. These developments have rendered a comminuting and chlorinating system out of date, and its regulation inconsistent with environmental rule-making in the 21st century. 

However, being out of date is only part of the problem. More importantly, it weakens the sewage treatment plant - the IMO’s remaining treatment option intended for those technologies designed and tested to meet stringent discharge standards.

For many years, devices resembling features of a comminuting and disinfecting system have been approved as sewage treatment plants. With no sludge and no de-chlorination, these devices performed tricks that are scientifically impossible. The credibility of the IMO’s approval regime has been eroded by approving and certifying these ‘magic boxes’ as sewage treatment plants. Such rudimentary sewage treatment plants, popular in certain marine sectors, have widened the gap between rules and realities. The provision of comminuting and chlorinating systems has served as a breeding ground for these 'magic boxes.' 

In summary, comminuting and chlorinating systems have clearly done a disservice to the aspirations of MARPOL Annex IV. Thanks to Norway’s initiative, we now have an opportunity to give due consideration to the regulation propping up these devices ‘as to whether this regulation is still necessary’ (PPR 7/16), now that a new decade has begun.


[1] Wastewater Technology Fact Sheet: Chlorine Disinfection, EPA 832-F-99-062, USEPA, 1999 https://www3.epa.gov/npdes/pubs/chlo.pdf 

[2] Wastewater Technology Fact Sheet: Ozone Disinfection, EPA 832-F-99-063, USEPA, 1999 https://www.epa.gov/sites/production/files/2015-06/documents/ozon.pdf 

[3] Wastewater Technology Fact Sheet: Ultraviolet Disinfection, EPA 832-F-99-064, USEPA, 1999 https://www3.epa.gov/npdes/pubs/uv.pdf 

[4] Alternative Disinfection Methods Fact Sheet:  Peracetic Acid, EPA 832-F-12-030, USEPA, 2012 https://www.solvay.us/en/binaries/EPA_Fact_Sheet-236719.pdf 

[5] Disinfection of Treated Wastewater, Guidelines for environmental management, EPA Victoria, Australia, 2002. 

[6] Occurrence of disinfection byproducts in United States wastewater treatment plant effluents, Krasner, S.W.,Westerhoff, P., Chen, B.Y., Rittmann, B.E., Amy, G., Environ. Sci. Technol. 43 (21), 8320e8325, 2009.

[7] Chlorinated Wastewater Effluents. Canadian Environmental Protection Act, Priority Substances List Assessment Report TD196.C5C46. CAEPA, 1993. 

[8] Spoilt for choice: A critical review on the chemical and biological assessment of current wastewater treatment technologies, Prasse, C., Stalter D., Schulte-Oehlmann U., Oehlmann J., Ternes, T. A., Water Research 87, 237e270, 2015.

[9] Chlorination Disinfection By-Products (DBPs) in Drinking Water and Public Health in Canada, A Primer for Public Health Practitioners Reviewing Evidence from over 30 Years of Research, Hrudey, S. E., University of Alberta, 2008. 

[10] Drinking Water Disinfection Byproducts (DBPs) and Human Health Effects: Multidisciplinary Challenges and Opportunities, Li, X. F., Mitch, W. A., Environ. Sci. Technol., 52, 1681−1689, 2018. 

[11] Formation of disinfection byproducts during chlorination of secondary effluent and renovated water, Rebhun, M., Heller-Grossman, L., Manka, J., Water Environ. Res. 69 (6), 1154e1162, 1997.

The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.