Laura L. Machuca

Biosurfactant and Degradative Enzymes Mediated Crude Oil Degradation by Bacterium Bacillus subtilis A1

In this work, the biodegradation of the crude oil by the potential biosurfactant producing Bacillus subtilis A1 was investigated. The isolate had the ability to synthesize degradative enzymes such as alkane hydroxylase and alcohol dehydrogenase at the time of biodegradation of hydrocarbon. The biosurfactant producing conditions were optimized as pH 7.0, temperature 40°C, 2% sucrose and 3% of yeast extract as best carbon and nitrogen sources for maximum production of biosurfactant (4.85 g l-1). Specifically, the low molecular weight compounds, i.e., C10–C14 were completely degraded, while C15–C19 were degraded up to 97% from the total hydrocarbon pools. Overall crude oil degradation efficiency of the strain A1 was about 87% within a short period of time (7 days). The accumulated biosurfactant from the biodegradation medium was characterized to be lipopeptide in nature. The strain A1 was found to be more robust than other reported biosurfactant producing bacteria in degradation efficiency of crude oil due to their enzyme production capability and therefore can be used to remove the hydrocarbon pollutants from contaminated environment.

Microbial Corrosion Resistance of Stainless Steels for Marine Energy Installations

A range of stainless steels has been investigated for resistance to microbiologically influenced corrosion in seawater. The corrosion potential was monitored for stainless steel coupons exposed to sterilized seawater and to microbiologically active seawater, which showed the effect of the growth of microorganisms. Cyclic potentiodynamic polarization scans confirmed that 13%Cr stainless steel is very susceptible to localized corrosion under these conditions. 316L stainless steel was also quite susceptible to localized corrosion, whereas 2205 duplex stainless displayed good resistance to localized corrosion. Naturally occurring microorganisms in the seawater were shown to exacerbate the localized corrosion.

Influence of drain holes in jacketing on corrosion under thermal insulation

Jacketing or a weather barrier is usually installed in insulated piping systems and pressure vessels to prevent water ingress and protect the insulation. In the event of water penetration and accumulation resulting from poor design and/or aging of the jacketing, drain holes are proposed to accelerate the water dry-out process. This study investigated the influence of jacketing and drain holes on corrosion under insulation of carbon steel. In an enclosed system without the drain holes, where the water dry-out process is reduced, the underlying steel remains exposed to the corrosive environment for a longer period of time. Severe pitting corrosion was observed, which could be a result of limited oxygen diffusion into the insulation creating differential aeration environments favorable for pitting corrosion. The presence of drain holes promoted the water dry-out rate and oxygen diffusion into the insulation. As a result, the average corrosion rate increased in short-term exposure tests, but over a longer ter...

Crevice Corrosion Studies on Corrosion Resistant Alloys in Stagnant Natural Seawater

Crevice corrosion (CC) was investigated for a number of selected corrosion resistant alloys in natural seawater containing microorganisms for up to 18 months under stagnant conditions. Experimental controls consisted of tests in natural seawater filtered in accordance with hydrostatic testing procedures. The corrosion potential of alloys was monitored throughout exposure and corrosion was evaluated by weight loss and 3D optical microscopy. CC was initiated on several alloys and corrosion rates in time indicated a positive effect of seawater filtration on the long-term performance of the alloys. Microbial adhesion, as indicated by fluorescence microscopy, occurred mainly outside the crevice and differed according to the nature of the substratum surface.