Biofilm activity on corrosion of API 5L X65 steel weld bead.

This work aimed to identify microbial colonization and biocorrosion in welded seam areas of API 5 L X65 carbon steel, since microorganisms are ubiquitous and there is a lack of information on their biological and electrochemical interactions with these structures. In the present study, polished and unpolished welded coupons prepared by shielded metal arc welding were assayed to identify the effect of surface roughness and local changes in the metal microstructure on microbial colonization. Experiments were performed in glass cell vessels with fresh and sterile seawater to establish the presence or absence of microorganisms. For comparison, nonwelded coupons were simultaneously tested as a control. On the 15th day, both polished and unpolished welded coupons and the nonwelded coupons immersed in fresh seawater showed microbial colonization, though the corrosion products were more abundant for the welded coupons. Nevertheless, unpolished welded coupons showed a higher predominance of pitting around the beads than polished coupons. These results suggest that filler material creates conditions more favorable for biofilm development, thus intensifying the localized corrosion on the welds. It can be concluded that adhesion and subsequent biocorrosion are directly influenced by surface roughness, whereas microstructural modifications due to welding interfere little with microbial adhesion, regardless of the greater pit depths compared to those of nonwelded coupons. Additionally, although open circuit potential measurements indicated that metal surfaces are protected when coated with biofilms, pitting corrosion was more pronounced in welded coupons immersed in fresh seawater than in those immersed in seawater without microorganisms. Therefore, the use of open circuit analysis alone is not recommended for biocorrosion monitoring of welded coupons.

Biosurfactant production by Pseudomonas aeruginosa grown in residual soybean oil.

Pseudomonas aeruginosa PACL strain, isolated from oil-contaminated soil taken from a lagoon, was used to investigate the efficiency and magnitude of biosurfactant production, using different waste frying soybean oils, by submerged fermentation in stirred tank reactors of 6 and 10 l capacities. A complete factorial experimental design was used, with the goal of optimizing the aeration rate (0.5, 1.0, and 1.5 vvm) and agitation speed (300, 550, and 800 rpm). Aeration was identified as the primary variable affecting the process, with a maximum rhamnose concentration occurring at an aeration rate of 0.5 vvm. At optimum levels, a maximum rhamnose concentration of 3.3 g/l, an emulsification index of 100%, and a minimum surface tension of 26.0 dynes/cm were achieved. Under these conditions, the biosurfactant production derived from using a mixture of waste frying soybean oil (WFSO) as a carbon source was compared to production when non-used soybean oil (NUSO), or waste soybean oils used to fry specific foods, were used. NUSO produced the highest level of rhamnolipids, although the waste soybean oils also resulted in biosurfactant production of 75-90% of the maximum value. Under ideal conditions, the kinetic behavior and the modeling of the rhamnose production, nutrient consumption, and cellular growth were established. The resulting model predicted data points that corresponded well to the empirical information.

Enhancement of rhamnoplipid production in residual soybean oil by an isolated strain of Pseudomonas aeruginosa.

In the present work, the production of rhamnolipid from residual soybean oil (RSO) from food frying facilities was studied using a strain of Pseudomonas aeruginosa of contaminated lagoon, isolated from a hydrocarbon contaminated soil. The optimization of RSO, ammonium nitrate, and brewery residual yeast concentrations was accomplished by a central composite experimental design and surface response analysis. The experiments were performed in 500-mL Erlenmeyer flasks containing 50 mL of mineral medium, at 170 rpm and 30 +/- 1 degrees C, for a 48-h fermentation period. Rhamnolipid production has been monitored by measurements of surface tension, rhamnose concentration, and emulsifying activity. The best-planned results, located on the central point, have corresponded to 22 g/L of RSO, 5.625 g/L of NH(4)NO(3), and 11.5 g/L of brewery yeast. At the maximum point the values for rhamnose and emulsifying index were 2.2 g/L and 100%, respectively.

Optimizing carbon/nitrogen ratio for biosurfactant production by a Bacillus subtilis strain.

A Bacillus subtilis strain isolated from contaminated soil from a refinery has been screened for biosurfactant production in crystal sugar (sucrose) with different nitrogen sources (NaNO(3), (NH(4))(2)SO(4), urea, and residual brewery yeast). The highest reduction in surface tension was achieved with a 48-h fermentation of crystal sugar and ammonium nitrate. Optimization of carbon/nitrogen ratio (3, 9, and 15) and agitation rate (50, 150, and 250 rpm) for biosurfactant production was carried out using complete factorial design and response surface analysis. The condition of C/N 3 and 250 rpm allowed the maximum increase in surface activity of biosurfactant. A suitable model has been developed, having presented great accordance experimental data. Preliminary characterization of the bioproduct suggested it to be a lipopeptide with some isomers differing from those of a commercial surfactin.

Degradation potential and growth of anaerobic bacteria in produced water.

The efficiency of an anaerobic biological treatment for the reduction of essential contaminants of produced water from an offshore oilfield was investigated using a microbial consortium enriched with sulphate-reducing bacteria (SRB). Experiments were conducted in a bench bioreactor at 35 degrees C, 250 rpm, with intermittent purges of N2 gas in order to establish anaerobic conditions and to remove the H2S generated. The results showed that pH control effectively influenced the activity of the anaerobic bacteria leading to COD removal of 57%. Meanwhile, pH control was found to have no influence on the removal efficiencies of oil and grease and total phenols. In all experiments, removals of oil and grease and total phenols of 60% and 58-67%, respectively, were obtained after a 15-day process. In studies carried out with biomass reuse the reductions obtained were 61% for oil and grease and 78% for total phenols over the same period. Such results point to the technical feasibility of anaerobic biodegradation for oilfield wastewater treatment.