G. Sekaran

Enhanced photocatalytic activity of ZnO/CuO nanocomposite for the degradation of textile dye on visible light illumination

The photocatalytic degradation of organic dyes such as methylene blue and methyl orange in the presence of various percentages of composite catalyst under visible light irradiation was carried out. The catalyst ZnO nanorods and ZnO/CuO nanocomposites of different weight ratios were prepared by new thermal decomposition method, which is simple and cost effective. The prepared catalysts were characterized by different techniques such as X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and UV-visible absorption spectroscopy. Further, the most photocatalytically active composite material was used for degradation of real textile waste water under visible light illumination. The irradiated samples were analysed by total organic carbon and chemical oxygen demand. The efficiency of the catalyst and their photocatalytic mechanism has been discussed in detail.

Nano-silica fabricated with silver nanoparticles: antifouling adsorbent for efficient dye removal, effective water disinfection and biofouling control.

A nano-silica-AgNPs composite material is proposed as a novel antifouling adsorbent for cost-effective and ecofriendly water purification. Fabrication of well-dispersed AgNPs on the nano-silica surface, designated as NSAgNP, has been achieved through protein mediated reduction of silver ions at ambient temperature for development of sustainable nanotechnology. The coated proteins on AgNPs led to the formation of stable NSAgNP and protected the AgNPs from oxidation and other ions commonly present in water. The NSAgNP exhibited excellent dye adsorption capacity both in single and multicomponent systems, and demonstrated satisfactory tolerance against variations in pH and dye concentration. The adsorption mainly occurred through electrostatic interaction, though π-π interaction and pore diffusion also contributed to the process. Moreover, the NSAgNP showed long-term antibacterial activity against both planktonic cells and biofilms of Gram-negative Escherichia coli and Pseudomonas aeruginosa. The antibacterial activity of AgNPs retarded the initial attachment of bacteria on NSAgNP and thus significantly improved the antifouling properties of the nanomaterial, which further inhibited biofilm formation. Scanning electron and fluorescence microscopic studies revealed that cell death occurred due to irreversible damage of the cell membrane upon electrostatic interaction of positively charged NSAgNP with the negatively charged bacterial cell membrane. The high adsorption capacity, reusability, good tolerance, removal of multicomponent dyes and E. coli from the simulated contaminated water and antifouling properties of NSAgNP will provide new opportunities to develop cost-effective and ecofriendly water purification processes.

Removal of diazo and triphenylmethane dyes from aqueous solutions through an adsorption process

Direct Red 31, Acid Black 1 and Acid Green 16 belonging to diazo and triphenylmethane classification of dye chemicals are widely used during the manufacture of leather. The spent dyestuffs in wastewater escape biological treatment owing to their poor biodegradability. An adsorption procedure was used in this study for the removal of dyes from aqueous solution using Rice Bran-based Activated Carbon (RBAC). The molecular weight of the dye chemicals, the mass of RBAC and the diameter of RBAC particle had positive effects on the rate of adsorption. Initial concentration of dye chemicals, pH of the dye solution and temperature of adsorption showed a negative impact on adsorption. The enthalpies of adsorption for Direct Red 31, Acid Black 1 and Acid Green 16 were -32.1, -23.4 and -21.7 KJ mol -1 respectively, indicating the adsorption was an exothermic physical process. The entropies of adsorption for Direct Red 31, Acid Black 1 and Acid Green 16 were -96.94, -59.92 and -26.96 J K -1 mol -1 respectively, suggesting that RBAC favours the adsorption process.

Characterization of an alkaline active – thiol forming extracellular serine keratinase by the newly isolated Bacillus pumilus

Aims:  The aim of the study was to optimize microbial degradation of keratinous waste and to characterize the alkaline active keratinase showing its biotechnological importance.

Microbial products (biosurfactant and extracellular chromate reductase) of marine microorganism are the potential agents reduce the oxidative stress induced by toxic heavy metals.

The present study demonstrates hexavalent chromium reduction and trivalent chromium tolerance behavior of marine Bacillus sp., MTCC 5514 through its extracellular enzyme reductase and biosurfactants production. The isolate reduces 10-2000 mg/L of hexavalent chromium to trivalent chromium with in 24-96 h respectively and the release of extracellular chromium reductase, found responsible for the reduction. Upon reduction, the concentration of trivalent chromium in the medium found comparatively less. Experimental results reveal, biosurfactants activity found responsible for the less concentration of Cr(III). Hypothetically, trivalent chromium upon formation get entrapped in the micelle of biosurfactants, prevents microbial cells from exposure towards trivalent chromium. Thus, the chosen isolate exhibit tolerance and growth with the increasing concentration of chromium.

Application of Two-and Three-Parameter Isotherm Models: Biosorption of Acid Red 88 onto Azolla microphylla

ABSTRACT Biosorption potential of Azolla microphylla for acid red 88 from aqueous solution was investigated under laboratory conditions as a function of initial pH and temperature. The algal biomass exhibited the highest dye sorption capacity at optimum conditions of pH 3 and temperature 30°C. The experimental isotherms were analyzed using five two-parameter models (Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, and Flory-Huggins) and five three-parameter models (Redlich-Peterson, Sips, Khan, Radke-Prausnitz, and Toth). Three error analysis methods were used to evaluate the experimental data: correlation coefficient, residual root mean square error (RMSE), and chi-square test to find the best fitting isotherm. In particular, Langmuir (two-parameter) and Khan (three-parameter) models described the dye biosorption isotherm data well at all pH and temperature conditions examined.

Anaerobic tapered fluidized bed reactor for starch wastewater treatment and modeling using multilayer perceptron neural network.

Anaerobic treatability of synthetic sago wastewater was investigated in a laboratory anaerobic tapered fluidized bed reactor (ATFBR) with a mesoporous granular activated carbon (GAC) as a support material. The experimental protocol was defined to examine the effect of the maximum organic loading rate (OLR), hydraulic retention time (HRT), the efficiency of the reactor and to report on its steady-state performance. The reactor was subjected to a steady-state operation over a range of OLR up to 85.44 kg COD/(m3 x d). The COD removal efficiency was found to be 92% in the reactor while the biogas produced in the digester reached 25.38 m3/(m3 x d) of the reactor. With the increase of OLR from 83.7 kg COD/(m3 x d), the COD removal efficiency decreased. Also an artificial neural network (ANN) model using multilayer perceptron (MLP) has been developed for a system of two input variable and five output dependent variables. For the training of the input-output data, the experimental values obtained have been used. The output parameters predicted have been found to be much closer to the corresponding experimental ones and the model was validated for 30% of the untrained data. The mean square error (MSE) was found to be only 0.0146.

Controlled synthesis and characterization of electron rich iron(III) oxide doped nanoporous activated carbon for the catalytic oxidation of aqueous ortho phenylene diamine

This work reports the degradation of biorefractory aqueous ortho-phenylenediamine (OPD) by hydrogen peroxide and iron(III) oxide doped nanoporous activated carbon (Fe-NPAC). The Fe-NPAC was prepared by a hydrothermal method. The catalyst was characterized using BET surface area and porosity analyzers, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The effect of pH, (1–10); catalyst dosage, (Fe-NPAC, 0.1 g, 0.2 g, 0.3 g); H2O2 concentration, (1.76 mmol, 3.52 mmol, 5.29 mmol, 7.05 mmol and 8.82 mmol) and OPD concentration on the catalytic activity was evaluated. The catalytic oxidation of OPD by H2O2–Fe-NPAC400 was confirmed using UV-Visible and emission spectroscopy. The chemical oxygen demand (COD) was reduced by 96% within 180 min in the presence of Fe-NPAC400, which is about 20-fold higher than the control (without Fe-NPAC400). Moreover, Fe-NPAC400 was demonstrated to have excellent stability and reusability characteristics.

In situ generation of hydroxyl radical by cobalt oxide supported porous carbon enhance removal of refractory organics in tannery dyeing wastewater.

In this study, cobalt oxide doped nanoporous activated carbon (Co-NPAC) was synthesized and used as a heterogeneous catalyst for the Fenton oxidation of organic dye chemicals used in tannery process. The nanoporous activated carbon (NPAC) was prepared from rice husk by precarbonization followed by chemical activation at elevated temperature (600 °C). The cobalt oxide was impregnated onto NPAC and characterized for UV-visible, Fluorescence spectroscopy, FT-IR, HR-TEM, XRD, BET surface area and XPS analyses. The hydroxyl radical generation potential of Co-NPAC from hydrogen peroxide decomposition was identified (λ(exi), 320 nm; λ(emi), 450 nm) by Excitation Emission Spectra (EES) analysis. The conditions for the degradation of tannery dyeing wastewater such as, Co-NPAC dose, concentration of H2O2, and temperature were optimized in heterogeneous Fenton oxidation process and the maximum percentage of COD removal was found to be 77%. The treatment of dyes in wastewater was confirmed through UV-Visible spectra, EES and FT-IR spectra analyses.

Characterization of iron impregnated polyacrylamide catalyst and its application to the treatment of municipal wastewater

The persistent organic pollutants and bio diversities (pathogenic and non-pathogenic) present in treated municipal wastewater cause environmental deterioration besides adversely affecting human health. In the present investigation, an attempt was made to treat the municipal wastewater using iron impregnated polyacrylamide (IIPA) powder catalyst in a fluidized reactor. The IIPA catalyst was characterized by carbon, 12.23%, hydrogen, 1.63%, nitrogen, 2.93%, iron, 58%, silicon, 15.25%, surface area 96.66 m2 g−1 and pore diameter, 58.32 A. IIPA was crystalline with an energy gap of 1.93 eV and it was capable of generating hydroxyl radicals for the oxidation of dissolved organics in municipal wastewater with minimum sludge yield (0.05 g VSS/g of COD). The oxidation of dissolved organics in municipal wastewater by IIPA was carried out under batch and continuous mode operations. The pseudo first order rate kinetic constants for the oxidation of organics in municipal wastewater were found to be 2.2 × 10−2, 3.01 × 10−2, 3.33 × 10−2 and 3.72 × 10−2 min−1. The activation energy for the oxidation of dissolved organics in municipal wastewater was 13.15 kJ mol−1. The pollution parameters BOD5, COD, ammonia, TKN and sulphide were removed from the municipal wastewater by 72.72%, 82.87%, 71.76%, 65.3% and 86.66% respectively.