Stefano Caserini1, Dario Pagano2, Francesco Campo2, Giovanni Cappello3 and Mario Grosso2, (1)Politecnico di Milano, Milano, 20133, Italy, (2)Politecnico di Milano, Department of Civil and Environmental Engineering, Milano, Italy, (3)CO2APPS, Italy
Among the negative emission technologies (NETs), ocean liming has a potential of mitigation for both ocean acidification and the increase of atmospheric CO2 due to the increased uptake by seawater. Many authors indicate a large potential of carbon removal by ocean liming, as well as technological challenges and potential side effects, but little is known on the practical aspects of spreading large amount of alkaline materials in the sea.

In the framework of the DESARC (DEcreasing Seawater Acidification Removing Carbon)-MARESANUS Project, an evaluation of potential strategies to discharge slaked lime in the Mediterranean Sea has been carried out, using data on the type of vessels elaborated by the International Maritime Organization, data on maritime traffic density obtained from the EMODnet database and conservative values of discharge rates of slaked lime for cargo ships and tankers (ranging between 10-30 kg/s).

Different logistic scenarios for the discharge of slaked lime are compared, such as (i) new dedicated ships (with calcium hydroxide being loaded in some ports in the Mediterranean Sea), (ii) modified existing ships, with loading logistics and discharge rate similar to the previous scenario; (iii) partial load on existing ships and (iv) use of ballast water in existing ships.

The last option has been analyzed in detail, since it will allow a discharge of lower rates of slaked lime from a large number of existing cargo ships and tankers during their commercial ballast navigation. This option has also the advantage of avoiding the ballast water management, since ballast water discharge typically contains a variety of biota, including non-native and exotic species, that can cause extensive ecological and economic damage to aquatic ecosystems because of their displacement worldwide.