Trupti Das

Factors affecting bioleaching kinetics of sulfide ores using acidophilic micro-organisms

Recovery of metal values from sulfide ores by use of acidophilic microorganisms is gaining importance. A number of commercial/pilot plants are setup to find out the techno-economic feasibility of the overall process. The main drawback in the process is the slow kinetics of dissolution of metal values from the sulfide ores. To make the technology e attractive the kinetics should be improved considerably. There are various factors which determine the overall kinetics such as bacterial activity and concentration, iron and sulfur oxidation, oxygen consumption, reactor design and nature of ore. A brief review has been made dealing with the above parameters

Water disinfection through photoactive modified titania.

TiO(2), N-TiO(2) and S-TiO(2) samples have been prepared by various chemical methods. These samples were characterized by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), Laser Raman spectrometer, UV-Visible spectrophotometer, field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). X-ray powder diffraction study reveals that all three samples are single anatase phase of titania and the crystallinity of titania decreases with sulphur doping whereas nitrogen doping does not affect it. UV-Visible (diffuse) reflectance spectra shows that doping of titania with nitrogen and sulphur shift the absorption edge of titania from ultraviolet to visible region. XPS study confirms that both nitrogen and sulphur are well doped in the titania lattice. It is observed that nitrogen occupies at both substitutional and interstitial position in the lattice of titania. FE-SEM and TEM studies demonstrate that the particles are below 50nm range. It is found that S and N doping of titania increased its water disinfection property in the order TiO(2)

Bio-oxidation of iron using Thiobacillus ferrooxidans

The effects of pH, ferrous and ferric ion concentrations on iron oxidation by Thiobacillus ferrooxidans were examined. The initial temperature and bacterial concentration were maintained at 37°C and 2±1×104cells/ml, respectively. The iron oxidation rate increased with increased initial ferrous iron concentration to 4g/l and thereafter decreased. The presence of iron(III) showed a negative effect on the bacterial iron oxidation rate. The increase of pH also showed an increase in the oxidation rate up to pH 1.75. The oxidation rate followed first order kinetics for the parameters studied. A rate equation has been developed.

Synthesis and characterization of titania nanorods from ilmenite for photocatalytic annihilation of E. coli

Titania nanorod structures have been obtained by thermal plasma reduction of ilmenite (FeTiO₃) followed by chemical treatments. Inherently present iron in the titania nanorods acts as a dopant which results in shifting the absorption edge of titania from ultraviolet to visible region. X-ray diffraction (XRD) study confirms the existence of rutile phase of titania. X-ray Photoelectron Spectroscopy (XPS) reveals the presence of Ti(4+), O(2-), Fe(3+) and surface hydroxyl group. Transmission Electron Microscopy (TEM) confirms the formation of nanorod structure having width of 6 nm and length of 32 nm. Photocatalytic annihilation property of titania nanorods derived from ilmenite (titania-I), rutile titania obtained from titanium(IV) butoxide (titania-A) and Degussa P25 titania was studied under UV and UV-Visible irradiation conditions separately and compared. The time required for complete photocatalytic annihilation of Escherichiacoli cells are 10, 15 and 45 min under UV irradiation whereas it has taken 15, 10-15, 30 min under UV-Visible irradiation for titania-A, Degussa P25 titania and titania-I respectively. It is observed that titania-I shows significantly stronger antibacterial property under UV-Visible irradiation compared to UV alone.

Kinetics of SO4−2 reduction under different growth media by sulfate reducing bacteria

Sulfate Reducing Bacteria (SRB) were used to reduce the SO4−2 concentration in waste water. The growth pattern of SRB was found by varying the concentration of nutrients and the biomass. The specific reaction constant was evaluated in each case.

Evaluation of Reduction Potential of Selected Heavy Metals from an Indian Coal by Conventional Coal Cleaning

Coal preparation can play an important role in reducing the emissions and discharges of toxic heavy metals that occur during utilization of coal. To evaluate the reduction potential of selected heavy metals by coal cleaning through gravity separation, a detailed study was conducted on a run-of-mine noncoking coal of the Indian origin. Different sizes of the crushed coal were subjected to float sink tests at specific gravities in the range of 1.30 to 1.80. Characterization data obtained from this study indicated that mercury, cobalt, and copper were dominantly associated with ash-forming constituents of the coal. Some elements, for example, selenium and cadmium, were found to be concentrated in the coal organic matrix. Characterization data also indicated that if the coal is washed at 1.70 specific gravity, the clean coal of improved quality will contain lesser concentrations of the toxic heavy metals. However, enrichment of selenium and cadmium was observed in the washed coal as compared to the feed coal.

Assessment of the significant parameters influencing the bio-oxidation and bio-precipitation of iron from industrial leach liquor

Abstract In the present study, iron oxidation and precipitation experiments were carried out using Acidithiobacillus ferrooxidans. Experiments were conducted in a specially designed bioreactor in batch as well as in continuous mode in order to evaluate the iron oxidation and precipitationparameters. The four basic parameters studied were pH, biomass, Fe(II) and Fe(III) concentration. Iron oxidation rate was observed to follow first order kinetics. The specific growth rate and dependence factorwere determined for each parameter. An Eh–pH diagram was developed to findout the theoretical conditions for iron precipitation. It was observed that by increasing the pH, the iron precipitation rate increased and at pH 2˙7 and 2˙9 precipitation was more than 90%. Iron oxidation and precipitation studies were carried out in a continuous mode and the processwas observed to be effective at a dilution rate of 35 ml/15 min. The technique was also tested using two different leach liquorsobtained from treating Zn tailings and lateritic nickel ore. Iron could be successfully precipitated in a crystalline form from the leach liquor using this process.

Evaluation of Simultaneous Nutrient and COD Removal with Polyhydroxybutyrate (PHB) Accumulation Using Mixed Microbial Consortia under Anoxic Condition and Their Bioinformatics Analysis

Simultaneous nitrate-N, phosphate and COD removal was evaluated from synthetic waste water using mixed microbial consortia in an anoxic environment under various initial carbon load (ICL) in a batch scale reactor system. Within 6 hours of incubation, enriched DNPAOs (Denitrifying Polyphosphate Accumulating Microorganisms) were able to remove maximum COD (87%) at 2g/L of ICL whereas maximum nitrate-N (97%) and phosphate (87%) removal along with PHB accumulation (49 mg/L) was achieved at 8 g/L of ICL. Exhaustion of nitrate-N, beyond 6 hours of incubation, had a detrimental effect on COD and phosphate removal rate. Fresh supply of nitrate-N to the reaction medium, beyond 6 hours, helped revive the removal rates of both COD and phosphate. Therefore, it was apparent that in spite of a high carbon load, maximum COD and nutrient removal can be maintained, with adequate nitrate-N availability. Denitrifying condition in the medium was evident from an increasing pH trend. PHB accumulation by the mixed culture was directly proportional to ICL; however the time taken for accumulation at higher ICL was more. Unlike conventional EBPR, PHB depletion did not support phosphate accumulation in this case. The unique aspect of all the batch studies were PHB accumulation was observed along with phosphate uptake and nitrate reduction under anoxic conditions. Bioinformatics analysis followed by pyrosequencing of the mixed culture DNA from the seed sludge revealed the dominance of denitrifying population, such as Corynebacterium, Rhodocyclus and Paraccocus (Alphaproteobacteria and Betaproteobacteria). Rarefaction curve indicated complete bacterial population and corresponding number of OTUs through sequence analysis. Chao1 and Shannon index (H’) was used to study the diversity of sampling. “UCI95” and “LCI95” indicated 95% confidence level of upper and lower values of Chao1 for each distance. Values of Chao1 index supported the results of rarefaction curve.

Trend in chemical composition of precipitation during 2005–2009 at a rural station of Bhubaneswar, eastern India

Precipitation samples collected during 2005–2009 from a rural forest station of Bhubaneswar were analyzed for their chemical composition. The samples were collected through a wet-only (WO) collector and two bulk (B1 and B2) collectors. The ions were evenly balanced indicating good data quality. The overall pH of rainwater was slightly acidic and ~47% of all rain events during the period were acidic (pH < 5.6). Multilinear regression analysis showed relation between the free acidity (H+) and other components in rainwater. Enrichment factors (EF) of the major components with respect to their sources such as marine and crustal were calculated. Maximum EF was observed for NO3− for both marine and crustal sources for all the three collectors. Source apportionments were also carried for the ions. Trend analysis showed continuous increase in most of the ions over years during the study period driven by anthropogenic emissions. Statistical/factorial analysis established correlation among different ions.

Use of Thiobacillus ferrooxidans for iron oxidation and precipitation

Fe(II) oxidation reaction was carried out using an acidophilic microorganism, Thiobacillus ferrooxidans. Four different parameters such as pH, Fe(II), Fe(III) and biomass concentration were studied. The oxida-tion reaction follows a pseudo first order rate equation. Apparent reaction rate constants were calculated. Unified rate equation was developed using the four parameters. Along with oxidation, a part of the iron also was precipitated. The extent of Fe(III) precipitation in each case was calculated.