Biofouling is one of the concerns in the use of titanium for seawater cooled condensers of power plants. Earlier studies have shown that anodized titanium and its alloys with a thin film of anatase (TiO(2)) on its surface can inhibit attachment of Pseudomonas sp. when illuminated with near-UV light (350 - 380 nm). In the present study, a comparison of the photocatalytic inhibition of microbial attachment on titanium surfaces anodized at different voltages was carried out. Thin films of anatase of varying thickness were produced on titanium grade-2 by anodizing in dilute orthophosphoric acid solution at 30 V, 50 V and 100 V. The photocatalytic efficiency of these anodized surfaces was measured by the methylene blue degradation method. The anodised surfaces were exposed to liquid cultures of Gram-negative Pseudomonas sp., Gram-positive Micrococcus sp. and to a mixed algal culture. Photocatalytic inhibition of microbial attachment was maximum on the titanium surface anodized at 30 V, followed by the surface anodized at 50 V and then at 100 V. The photocatalytic inhibition of microbial attachment was also found to be dependent on the cell wall characteristics of the organism. The Gram-negative Pseudomonas sp. with a lipoproteinaceous outer membrane was the most susceptible to the photocatalytic effect, while the Gram-positive Micrococcus sp. with peptidoglycan cell wall showed moderate susceptibility and the algae with siliceous cell wall showed no susceptibility at all.
A study was carried out to understand the influence of the surface characteristics/microstructure of a type 304 stainless steel on bacterial adhesion by exposing solution-annealed, sensitized and air-oxidized stainless steel specimens in a culture of Pseudomonas sp. in dilute nutrient broth. Epifluorescence microscopy of the exposed surfaces revealed that the pattern of adhesion as well as number density of bacterial cells was different depending on the metallurgical condition of the substratum. Among the specimens with different microstructures, the sensitized specimens had the highest bacterial density, followed by the solution annealed and the oxidized specimens. The same trend was shown by the total viable counts on the various surfaces, estimated by a plate count technique. The study assumes significance in the context of the widely reported observation of preferential attack of the welded region during microbiologically influenced corrosion of fabricated components.
The effects of repeated pickling and polishing on biofouling of titanium surfaces were investigated using a confocal laser scanning microscope (CLSM) and standard microbiological methods. Titanium surfaces (i) once pickled (control), (ii) repeatedly pickled (five pickling cycles of 5 min duration) and (iii) polished (surface finish of 1000 grit silicon carbide paper) were exposed to seawater. A decrease of one order of magnitude in bacterial and algal attachment was recorded on the repeatedly pickled and polished titanium surfaces compared to the control surfaces. Statistical analysis of the data was carried out using MYSTAT software involving Tukey-Kramer Multiple CLSM used as an effective tool to measure the microroughness of the test surfaces as well as to quantify the biofilm forming tendency on these surfaces. The results indicated that microroughness reduction leads to significant decrease in biofouling.
Titanium, an otherwise perfect condenser tube material in sea water applications, is challenged by the problem of severe biofouling. Anatase, one of the two commercially important crystalline forms of titanium dioxide, possesses excellent photocatalytic activity (PCA). It has been shown in the earlier studies by the authors that anodisation of titanium produces anatase type of TiO 2 capable of photocatalytic inhibition of microbial adhesion under near UV light illumination. The present study investigates the influence of anodising voltage and anodising time on the photocatalytic inhibition of Pseudomonas sp., a frequent coloniser of natural biofilms formed on titanium surfaces. The effect of heat treatment of anodised surfaces on PCA was also studied. The results showed that heat treatment resulted in a significant enhancement of PCA. The surface oxide was characterised using glancing incidence X-ray diffraction and atomic force microscopy and the results indicate a marked increase in the cystallinity of the anatase film on the heat treated anodised surfaces. Attempts have also been made to understand the mechanism underlying the photocatalytic inactivation of the bacterial cells on TiO 2 surfaces by studying their growth characteristics.
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