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Maandag 15 april 2013 verdedigt Anne Heyer haar proefschrift " Microbiologically influenced corrosion in ship ballast tanks” in de Senaatzaal van de Aula van de Technische Universiteit in Delft (TUD). Aanvang van de plechtigheid is 12.00 uur. Geïnteresseerden zijn welkom hierbij aanwezig te zijn.

Het onderzoek dat heeft geleid tot dit proefschrift, is uitgevoerd in het laboratorium van TNO in Den Helder in samenwerking met TUD en M2i. Haar werk heeft gezorgd voor een veel beter begrip van microbiële processen die zeer ernstige corrosieschade tot gevolg kunnen hebben. Met de opgebouwde kennis en nieuwe microscopische technieken, beschreven in talrijke  publicaties, heeft TNO MMPC een sterke positie verworven in dit onderzoeksgebied wat zich ook al heeft vertaald in een aantal belangrijke onderzoeksopdrachten.

Hieronder een korte samenvatting van de inhoud van het proefschrift.

Title: “Microbiologically  influenced corrosion in ship ballast tanks”

Microbiologically influenced corrosion (MIC) is known to be a dangerous process in ship tanks due to its rapid and yet unpredictable occurrence, leading to extremely fast local corrosion, possibly jeopardizing the structural integrity, in a relatively short time. This project focuses on a fundamental understanding of MIC processes in ship ballast tanks (SBTs) as a basis for the development of effective counterstrategies that offer an appropriate protection against MIC attack. Local conditions typically consist of oxic-anoxic environments where both aerobic and anaerobic biofilms develop resulting in aggressive corrosion. Fundamental understanding of the dominant parameters considering material, environment and microbes were addressed. In chapter 1 a review of the conditions in ship ballast tanks, possible MIC mechanisms and practical counterstrategies is presented.

Chapter two deals with the impact of MIC in a real scale SBT to understand community characteristics within SBTs. The study highlights the impact of attached biofilms on local corrosion in a ship ballast tank environment.

The application of molecular techniques in combination with electrochemical techniques provides a better and synergistic monitoring tool in the enclosed seawater environment. The work in this chapter provides a systematic future research and analysis approach to build up a database of bacterial species, which are involved in corrosion or coating degradation on-board of ships. A more effective treatment system for treating biofilms on sidewalls of ship ballast tanks will help to reduce costly material replacements.

In chapter three the usability of electrochemical techniques for monitoring MIC is discussed in detail. Three individual approaches were studied in the lab comprising: (i) corrosion impact of a dual species biofilm, (ii) implementation of a simulated ship tank model system and(iii) the study of the biodeterioration of a ship ballast tank coating.

The fourth chapter comprises different highly sensitive and spatially resolved techniques to study MIC on a very local scale. The first step included the development of a novel analysis approach for the preparation and visualization of metal surfaces, suitable for combined imaging by epifluorescent microscopy (EFM), AFM and SEM. By combining three different microscopes, the complementary use of these high-resolution techniques to study surface changes and accumulation of biological substances on stainless steel surfaces was proven.

The last experimental part of the thesis covers the use of local electrochemical techniques. The scanning vibrating electrode technique (SVET) and scanning electrochemical microscope (SECM) were used for their high spatial resolution close to the metal/solution interface. By combing these techniques in-situ changes at metal/solution interfaces in the presence and absence of aerobic bacteria could be followed up. Therefore it was possible to demonstrate that the application of local scanning electrochemical techniques with high-spatial resolution is a powerful tool for a better understanding of microbial activity on metal systems providing in-situ information of the processes taking place at the metal/biofilm/solution interface.

Chapter five summarizes the conclusions drawn in the preceding chapters. In addition, the general discussion in this chapter links together some of the preceding results and suggestions. The last part of the thesis gives a future outlook on MIC monitoring and prediction and reviews options to mitigate MIC failures based on a multidimensional approach.