Assessment of microalgae caused corrosion of steel in marine environment under varying concentration of growth nutrients (CO2, NO3, and PO4)

Microbial influenced corrosion (MIC) is microbes driven corrosion process that cost billions of dollar each year. Extensive work has been done, but still MIC is not understood well. Majority of studies are conducted on bacteria such as on sulphate reducing bacteria (SRB) and iron-oxidizing bacteria (IOB) but few on yeast, archaea, diatoms and microalgae. Microalgae are photosynthetic microorganisms that live and thrive in both marine and fresh water. The growing problem of algal bloom in water bodies is not only an environmental problem but it is a concern for infrastructural stability due to bio-fouling and bio-corrosion potential of microalgae. As a result of anthropogenic activities, CO2 level in atmosphere is increasing, resulting into global temperature increase as well. Moreover, discharge of wastewater containing nutrients (NO3, PO4) in water bodies such as lakes and sea will further increase the growth of microalgae. Today economy is driven by sea transportation supported by network of ports, fleets of ships. On-shore fossil fuels facilities are standing on metal structure. Sea water is a good electrolyte and growth of microbes especially microalgae can accelerate the corrosion rate in sea infrastructure. Few studies are reported on freshwater microalgae and their potential to cause corrosion. However, work on marine microalgae is very limited. The objective of this work is to assess the corrosion of carbon steel and stainless steel in the presence of marine microalgae. During the project microalgae, Tetraselums sp. will be grown in artificial sea water (ASW) media along with real sea water (sterilized and un-sterilized) with same concentration of nutrient as ASW media and corrosion potential will be evaluated. Later, during the project un-sterilized seawater will be supplemented by different amount of growth nutrients (NO3, PO4) as different N/P ratio to check the effect of nutrients being released in water by anthropogenic activities. In order to check the effect of CO2 concentration, different amount of CO2 will be used starting with CO2 in air as control. Corrosion rate and metal surface chemistry will be evaluated using electrochemical methods and using different surface analysis techniques. Experiments in real seawater will help us to understand the role of microalgae and its associated bacteria on corrosion. Bacteria community will be monitored using dye staining and 16RNA analysis.