Recommandations for the quantitative assessment of metal inputs in the marine environment from the galvanic anodes of offshore renewable energy structures
|Type||Book / Conference proceedings|
|Author(s)||Michelet Nicolas1, Julian Nais2, Duarte Rui1, Burgeot Thierry2, Amouroux Isabelle2, Dallet Melissa3, Caplat Christelle4, Gonzalez Jean-Louis2, Garreau Pierre2, Aragon Emmanuel5, Perrin Francois-Xavier5, Safi Georges1|
|Publisher||France Energies Marines Editions|
The fast-growing offshore wind industry represents a potential new anthropogenic pressure for the marine environment. Despite the fact that it is considered as a green/clean energy source, the large-scale deployment of these devices could induce some environmental impacts that need to be studied. Understanding these impacts is in line with the Marine Strategy Framework Directive (MSFD) (European Commission, 2008) of the European Union which targets good environmental status for the marine environment.
The development of offshore renewable energies (ORE), in particular floating and fixed offshore wind structures in France, gives rise to new and more precise questioning from the French public authorities and civil society. In particular, a lot of questions have emerged in relation to the use of Galvanic Anode Cathodic Protection (GACP) systems and about the release of heavy metals associated with their functioning. These anodes are composed of different metals which are more reducing than the metal to be protected. The anodes are generally made with magnesium, aluminium or zinc. In offshore industries such as offshore wind turbines or oil & gas platforms, the anodes used are mainly composed of an aluminium alloy which contains zinc and other trace metals.
Their installation in fishing zones is a source of major concern and this affects several offshore wind farm projects (such as Île d’Yeu and Noirmoutier). This growing concern from public authorities and civil society has even led to galvanic anodes being abandoned in certain projects in order to overcome this problem. For example, the chosen solution for the jacket foundations of the Dieppe Le Tréport project is to implement cathodic protection by impressed current (ICCP) with titanium anodes). GACP has been replaced by ICCP in several projects although no scientific study has been conducted to prove the environmental impact of GACP in the ORE context, and no scientific study has proven that ICCP has no environmental impact.
In this context, a chemical risk assessment process has been conducted through a 1-year collaborative R&D project called ANODE in order to determine whether the chemicals released from GACP may represent a risk for the marine environment. Such chemical risk assessments are based on the comparison of the predicted or measured concentration (PEC - Predicted Environmental Concentration) for a contaminant with its hazard data (PNEC - Predicted No Effect Concentration) for all environmental compartments (water column, sediment and biota for the marine environment). This is an iterative process the first step of which is based on a worst-case approach in order to ensure a high protective level for the marine environment. Through the ANODE project, the risk assessment was conducted on the water column only. A hydrodynamic model was developed as a first approach for the prediction of the dispersion of these metals in the water column. From this numerical model, a predicted concentration PEC was determined to be compared with existing PNECseawater. Three sites were studied representing different hydrodynamic conditions directly influencing the metal dispersion and different technologies (i.e. fixed and floating offshore wind turbines). The project objectives were as follows:
To perform a literature review of the different cathodic protection systems used in the offshore industry with a focus on GACP and current knowledge of its potential impact on the marine environment.
Following these objectives, this report summarises the main results of the project and outlines a number of recommendations. This report is constructed as follows: