Carnival: Scrubber Washwater is Safe for the Environment

Scrubber installation aboard a Carnival-owned AIDA brand vessel (file image)

Published Mar 7, 2019 2:18 PM by The Maritime Executive

Carnival Corporation has released the results of a multi-year study of washwater effluent from its exhaust gas scrubber systems. The findings indicate that open loop scrubber effluent complies with the discharge concentration standards used by IMO, and even with the standards used by shoreside water quality regulators in Europe - including EU limits for inland surface water.

Scrubbers offer dramatic reductions in harmful SOx emissions - in excess of 90 percent - and can reduce particulate matter by between 60 and 90 percent, depending upon model and conditions. Adding a scrubber as a retrofit increases a vessel's CO2 emissions slightly, as the scrubber's power consumption adds to the load on the ship's electrical system. This electrical load is typically higher for open-loop systems, like those used by most shipowners; hard numbers are rare, but one published estimate puts the additional load at about 3-4 percent of normal fuel consumption (an additional 3 tonnes of fuel per day for a 70-tonne-per-day VLCC). However, the financial costs of this efficiency loss, or "fuel penalty," are more than offset by the substantial price spread between traditional HFO and IMO2020-compliant low sulfur fuel oil (LSFO).

Carnival's study was first announced at an industry group meeting in London in late February, and it was presented to IMO's Sub-Committee on Pollution Prevention and Response. The study is based on over 280 wash water samples from 53 scrubber-equipped cruise ships, the largest washwater data set in the marine industry, which were then assessed against 54 different test parameters by accredited laboratories.

The labs' reports were evaluated by DNV GL, and the data were compared against international water quality standards and land-based wastewater discharge limits, including the German Waste Water Ordinance, the EU Industrial Emissions Directive 2010/75/EU, and the EU Surface Water Standards Directive 2013/39/EU. These standards aren't intended to regulate scrubber discharge specifically, but Carnival and the Clean Shipping Alliance 2020 believe that they provide a good reference point to use for evaluating the relative cleanliness of washwater. 

"This is completely consistent with the commitments we have made to our sustainability goals, and to protecting the ocean environment and the destinations we visit around the world," said Mike Kaczmarek, SVP of marine technology for Carnival. "Based on extensive emissions testing, we know that our Advanced Air Quality Systems in some ways outperform marine gasoil (MGO) in providing cleaner air emissions. And although we have known for a long time that the quality of water being returned to the sea is at a high level, based on our years of development of this data set, it was important to release the findings publicly as the latest scientific evidence showing the actual water quality."