MICROFOULING ON CATHODICALLY PROTECTED MILD STEEL IN SEA WATER

ABSTRACT The influence of cathodic protection on the rate of microfooling on mild steel was investigated in natural seawater. Cathodic protection was applied at current densities of 0.12 and 0.22 mA/cm2 using sacrificial zinc anodes. The rate of attachment of bacteria and diatoms was observed to increase dramatically as a function of applied current, particularly during the first few days of exposure. It was also found that sulphate-reducing bacteria come into the scene as early as the fourth day white freely corroding specimens encourage SRB activity only by the twelfth day of exposure. The growth rate of calcareous depos~ts was also investigated to make it comparable with that of microorganisms

Microfouling on cathodically protected mild steel in sea water

The influence of cathodic protection on the rate of microfooling on mild steel was investigated in natural seawater. Cathodic protection was applied at current densities of 0.12 and 0.22 mA/cm2 using sacrificial zinc anodes. The rate of attachment of bacteria and diatoms was observed to increase dramatically as a function of applied current, particularly during the first few days of exposure. It was also found that sulphate-reducing bacteria come into the scene as early as the fourth day white freely corroding specimens encourage SRB activity only by the twelfth day of exposure. The growth rate of calcareous depos~tsw as also investigated to make it comparable with that of microorganisms

Marine microbial films and the corrosion of steel

Succession of aerobic and anaerobic bacterial films on mild steel has been studied for 100 days in two contrasting seawater sites at Mandapam. The relation between primary film microfouling and initiation of anaerobic corrosion has been attempted The ecological aspects in anaerobic corrosion beneath marine fouling are discussed in the light of the results of present work and already available data on marine corrosio

A possible role for phototrophic sulphur bacteria in the promotion of anaerobic metal corrosion

Bacteria associated with the biological sulphur cycle play a particularly dominant role in the process of metallic corrosion. This is largely due to the ubiquitous presence of these bacteria in natural environments1,2. Unsurprisingly, sulphatereducing bacteria have been the main highlight in numerous bio-corrosion investigations. A vast number of mechanisms3–8 have been proposed in the literature to explain the rather multifarious process of anaerobic corrosion. The deterioration of iron and concrete by aerobic sulphur bacteria (thiobacilli) is more straightforward. These bacteria oxidize sulphur and/or sulphide to sulphuric acid9

Biofouling studies relating to cathodic protection of some metals in seawater

Biofouling studies relating to the cathodic protection of mildsteel, stainless steel and brass in seawater have been conducted in the shallow waters of mandapam coast, to understand the role of biological factors operating. Rationale for the investigations were the response to cathodic protection of marine fouling, the occurence and growth rate of calcareous deposits. Cathodic protection to the metals was effected using zinc. Results indicate that the severity of fouling on mildsteel and brass is increased and inhibition of fouling on stainless steel is obtained due to cathodic protection. Barnacles, the chief calcareous shell dwelling group were found to occur with selective abundance on cathodically protected mildsteel and brass panels, with a significant increase in their shell size. These organisms were found to contribute largely to the calcareous deposits on mild steel and brass and to a smaller extent on stainless steel. The selective abundance of barnacles on cathodically protected mildsteel and brass is discussed in the light of the chemical, biological and electrochemical bases for their gregariousnes

An adsorbed inhibitor theory for biofilm-assisted ennoblement

The open circuit potrntial of titanium in water may significantly vary under illumination. It has been suggested that this shift might have some relation to light effects on oxide film. Experiments were, hence designed to study the effect of illumination on corrosion potential on titanium and platinum in the pond water. The results indicated that the photoelectrochemical and organic photochemical reaction influence on the excursion of potential during day and night hours. Besides, the negative photo-potential were observed for titanium and platinum, indicating the presence of n-type semiconducting film even in presence of biofilm covering the respective surfaces. In addition, the dissolved nutrients within the biofilms were also estimated. It is concluded that “Mixed inhibitor” may strengthen the n-type semi conducting oxide films on these metal surfaces during the processes of ennoblement. The result based on these factors are discussed in detail

Abundance of indicator and general heterotrophic bacteria in Port Blair bay, Andamans

65-68Viable counts of indicator and general heterotrophic bacterial populations were enumerated from 6 stations in Port Blair bay during different seasons. High counts of coliforms and indicator bacteria were generally recorded in the Aberdeen zone of Port Blair bay. Other zones in the bay showed few, if any, coliforms or indicator species during non-monsoon periods. During periods of intensive rainfall, the entire bay waters showed positive results for Vibrio cholerae, Vibrio parahaemolyticus, Streptococcus faecalis and Escherichia coli like organisms. Pseudomonas aeruginosa was mostly absent, except during a dinoflagellate bloom when counts as high as 102 CFU ml-1 were recorded. Viable heterotrophic bacteria showed a specific pattern of variation in which the numbers decreased progressively from the entry channel to inner portions of the bay. On the whole, results point to the large probability of coastal water contamination from rainwater runoff effects

Occurrence of thiobacilli in Tuticorin harbour waters

107-109The number of thiobacilli obtained as colony forming units on thiosulphate agar was the highest ever reported from marine sources. Seven isolates, out of 15 from enrichment cultures, were Thiobacillus spp., T. thiooxidans and T. ferroxidans produced the most acidic conditions in liquid cultures. Laboratory experiments with decaying alga Ulva lactuca in seawater showed that thiobacilli were involved in the oxidation of protein sulphur. The study not only indicates the status of pollution in harbour waters but also shows that thiobacilli may have wide distribution in coastal waters

Marine fouling and corrosion studies in the coastal waters of Mandapam, India

Results of a comprehensive study on marine fouling conducted in the coastal waters of Mandapam, India, are presented. Based on data from different tests, the effects of fouling organisms on the phenomena of corrosion and cathodic protection are discusse

Short communication On microalgal settlements and the sluggish development of marine biofouling in Port Blair waters,Andamans.

Settlement of microalgae was investigated on Perspex1, aluminium and zinc coupons immersed in Port Blair Bay waters for over 3 months. Commencement of fouling was exceptionally slow, and few microalgae were found until 14 days. Settlement occurred thereafter, and 47 microalgal species contributed to the fouling. The dominant forms belonged to the genera Navicula and Nitzschia, whereas Coscinodiscus eccentricus, Gyrosigma balticum and Trichodesmium erythraeum also accounted for high proportions of the settlements. The dominance of Nitzschia sigma was particularly marked on zinc coupons, suggesting an ability by the organism to resist toxicity. Settlement of both centric and pennate diatoms was observed in the early and mid periods, and absolute dominance of the pennate diatoms subsequently. The foulingmass was low even after 103 days, and it is speculated that strong ultraviolet radiation might be the prime reason for the sluggish development of marine biofouling in these oceanic island waters