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Detoxification of Cr(VI) under alkaline pH requires attention due to the alkaline nature of many effluents. An alkaliphilic gram-positive Bacillus subtilis isolated from tannery effluent contaminated soil was found to grow and reduce Cr(VI) up to 100% at an alkaline pH 9. Decrease in pH to acidic range with growth of the bacterium signified the role played by metabolites (organic acids) in chromium resistance and reduction mechanism. The XPS and FT-IR spectra confirmed the reduction of Cr(VI) by bacteria into +3 oxidation state. Chromate reductase assay indicated that the reduction was mediated by constitutive membrane bound enzymes. The kinetics of Cr(VI) reduction activity derived using the monod equation proved (K s = 0.00032) high affinity of the organism to the metal. This study thus helped to localize the reduction activity at subcellular level in a chromium resistant alkaliphilic Bacillus sp.

The study provides a constructive application of bacterial biofilms for the bioremediation of hydrophobic organic contaminants. The biofilm mode remediation process has the advantage of reusability of bacterial biomass and is also a low cost process as compared to cell immobilization techniques.

This article discusses aspects of biofouling and corrosion in the thermo-fluid heat exchanger (TFHX) and in the cooling water system of a nuclear test reactor. During inspection, it was observed that >90% of the TFHX tube bundle was clogged with thick fouling deposits. Both X-ray diffraction and Mossbauer analyses of the fouling deposit demonstrated iron corrosion products. The exterior of the tubercle showed the presence of a calcium and magnesium carbonate mixture along with iron oxides. Raman spectroscopy analysis confirmed the presence of calcium carbonate scale in the calcite phase. The interior of the tubercle contained significant iron sulphide, magnetite and iron-oxy-hydroxide. A microbiological assay showed a considerable population of iron oxidizing bacteria and sulphate reducing bacteria (10(5) to 10(6) cfu g(-1) of deposit). As the temperature of the TFHX is in the range of 45-50 degrees C, the microbiota isolated/assayed from the fouling deposit are designated as thermo-tolerant bacteria. The mean corrosion rate of the CS coupons exposed online was approximately 2.0 mpy and the microbial counts of various corrosion causing bacteria were in the range 10(3) to 10(5) cfu ml(-1) in the cooling water and 10(6) to 10(8) cfu ml(-1) in the biofilm.

Progression of biofilm formation was monitored at two stations near a nuclear power plant, Kalpakkam, located near coastal waters of Bay of Bengal. These stations are natural marine environment, station 1; and the condenser outfall area of the power plant the modified marine environment station 2. The biofilm formed on plexiglas panels was analysed in triplicates at 24 h intervals for various physical, chemical and biological parameters for 120 h (5 days). The biofilm formation showed both temporal and spatial variation in various parameters assayed. Among the water-quality parameters analysed, seawater temperature showed significant increase (*5°C) at station 2. The increase in water temperature enhanced the metabolism and influenced most of the biofilm parameters assayed at station 2. Biofilm formed at station 2 was very thick (113 lm) than that of at station 1 (22 lm). The distribution of parameters like biofilm thickness, biomass, chlorophyll a, particulate organic carbon, hexose sugar and diatom counts showed similar trend (i.e., a sharp increase after 96 h of biofilm growth) in the biofilm formed at station 2. Moderately high ammonia levels (44 lg l -1 ) were detected in the biofilm formed at station 2. The biofilm microbiota was diverse at both the stations: it constituted bacteria [nitrate reducers (NRB), ammonia oxidizers (AOB) and culturable aerobic heterotrophic bacteria (CAHB)], algae and macrofoulants. The various bacterial types assayed showed a population range from 10 2 to 10 6 cfu cm -2 . The final community after 120 h at station 1 comprised CAHB, NRB, diatoms, barnacle cyprids and juvenile bryozoans. At station 2, the biofilm initially consisted of CAHB, NRB and diatoms but after 120 h, AOB, cyanobacteria and filamentous algae were dominant. The plausible factors that influenced biofilm formation were temperature, nutrients and organic matter. The biofilm phenomenon in natural and modified marine environment was hypothesized and discussed.

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