Suhail Sabir

Bioremediation of 2-chlorophenol containing wastewater by aerobic granules-kinetics and toxicity.

2-Chlorophenol (2-CP) degrading aerobic granules were cultivated in a sequencing batch reactor (SBR) in presence of glucose. The organic loading rate (OLR) was increased from 6.9 to 9.7 kg COD m(-3)d(-1) (1150-1617 mg L(-1)COD per cycle) during the experiment. The alkalinity (1000 mg L(-1) as CaCO(3)) was maintained throughout the experiment. The specific cell growth rate was found to be 0.013 d(-1). A COD removal efficiency of 94% was achieved after steady state at 8h HRT (hydraulic retention time). FTIR, UV, GC, GC/MS studies confirmed that the biodegradation of 2-CP occurs via chlorocatechol (modified ortho-cleavage) pathway. Biodegradation kinetics followed the Haldane model with kinetic parameters: V(max)=840 mg2-CPgMLVSS(-1)d(-1), K(s)=24.61 mg L(-1), K(i)=315.02 mg L(-1). Abiotic losses of 2-CP due to volatilization and photo degradation by sunlight were less than 3% and the results of genotoxicity showed that the degradation products are eco-friendly.

Degradation pathway, toxicity and kinetics of 2,4,6-trichlorophenol with different co-substrate by aerobic granules in SBR.

The present study deals with cultivation of 2,4,6-trichlorophenol (TCP) degrading aerobic granules in two SBR systems based on glucose and acetate as co-substrate. Biodegradation of TCP containing wastewater starting from 10 to 360 mg L(-1) with more than 90% efficiency was achieved. Sludge volume index decreases as the operation proceeds to stabilize at 35 and 30 mL g(-1) while MLVSS increases from 4 to 6.5 and 6.2 g L(-1) for R1 (with glucose as co-substrate) and R2 (with sodium acetate as co-substrate), respectively. FTIR, GC and GC/MS spectral studies shows that the biodegradation occurred via chlorocatechol pathway and the cleavage may be at ortho-position. Haldane model for inhibitory substrate was applied to the system and it was observed that glucose fed granules have a high specific degradation rate and efficiency than acetate fed granules. Genotoxicity studies shows that effluent coming from SBRs was non-toxic.

Bioelectricity Generation and Bioremediation of an Azo-Dye in a Microbial Fuel Cell Coupled Activated Sludge Process

Simultaneous bioelectricity generation and dye degradation was achieved in the present study by using a combined anaerobic-aerobic process. The anaerobic system was a typical single chambered microbial fuel cell (SMFC) which utilizes acid navy blue r (ANB) dye along with glucose as growth substrate to generate electricity. Four different concentrations of ANB (50, 100, 200 and 400 ppm) were tested in the SMFC and the degradation products were further treated in an activated sludge post treatment process. The dye decolorization followed pseudo first order kinetics while the negative values of the thermodynamic parameter ∆G (change in Gibbs free energy) shows that the reaction proceeds with a net decrease in the free energy of the system. The coulombic efficiency (CE) and power density (PD) attained peak values at 10.36% and 2,236 mW/m2 respectively for 200 ppm of ANB. A further increase in ANB concentrations results in lowering of cell potential (and PD) values owing to microbial inhibition at higher concentrations of toxic substrates. Cyclic voltammetry studies revealed a perfect redox reaction was taking place in the SMFC. The pH, temperature and conductivity remain 7.5–8.0, 27(±2°C and 10.6–18.2 mS/cm throughout the operation. The biodegradation pathway was studied by the gas chromatography coupled with mass spectroscopy technique, suggested the preferential cleavage of the azo bond as the initial step resulting in to aromatic amines. Thus, a combined anaerobic-aerobic process using SMFC coupled with activated sludge process can be a viable option for effective degradation of complex dye substrates along with energy (bioelectricity) recovery.

Bio-electro degradation of azo-dye in a combined anaerobic–aerobic process along with energy recovery

A combined anaerobic–aerobic process involving a single chambered microbial fuel cell (SMFC) followed by an aerobic downstream treatment process is selected for the complete removal of reactive orange 16 (RO 16) from contaminated water. The degradation of azo-dye in SMFC results in the formation of aromatic amines with simultaneous production of electricity. The degradation products of the SMFC were further treated in an activated sludge downstream process in order to provide complete solution from dye wastewater. More than 90% of the chemical oxygen demand (COD) was removed in the combined process for all the test concentrations. The maximum output cell potential and the coulombic efficiency (CE) were 423 mV and 3.4% respectively. SEM images of the mixed microbial culture showed the presence of cocci, diatoms and rod shaped bacteria. Cyclic voltammetry revealed that a perfect redox process took place in the SMFC system. The results of the gas chromatography coupled with the mass spectroscopy (GC/MS) technique showed that RO 16 was first converted into aromatic amines in SMFC which were further transformed into phthalic acid and finally into benzoic acid. The results of the present work demonstrate that wastewater containing complex and toxic dyes can be successfully treated in SMFC followed by aerobic post-treatment along with energy recovery.

Polyaniline/Palm Oil Blend for Anticorrosion of Mild Steel in Saline Environment

The corrosion protective performance of polyaniline/palm oil (PAni-PO) blend coated on mild steel in 3% NaCl aqueous solutions has been evaluated by electrochemical methods, namely, open circuit potential (ocp), potentiodynamic polarization, and EIS spectroscopy. The surface of mild steel was covered by a dark green protective layer due to the physical interaction between the coating and steel. The permanent shifts of ocp and potentiodynamic polarization towards higher positive value of oxidation potential by about 800 mV and by a decrease in corrosion current density by sixfold in magnitude and an increase of 10 orders of magnitude in charge transfer resistance are due to protective coating.

Ag2S sensitized mesoporous Bi2WO6 architectures with enhanced visible light photocatalytic activity and recycling properties

To harvest solar energy more efficiently, novel Ag2S/Bi2WO6 heterojunctions were synthesized by a hydrothermal route. This novel photocatalyst was synthesized by impregnating Ag2S into a Bi2WO6 semiconductor by a hydrothermal route without any surfactants or templates. The as prepared structures were characterized by multiple techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmet-Teller (BET) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDS), UV-vis diffuse reflection spectroscopy (DRS) and photoluminescence (PL). The characterization results suggest mesoporous hierarchical spherical structures with a high surface area and improved photo response in the visible spectrum. Compared to bare Bi2WO6, Ag2S/Bi2WO6 exhibited much higher photocatalytic activity towards the degradation of dye Rhodamine B (RhB). Although silver based catalysts are easily eroded by photogenerated holes, the Ag2S/Bi2WO6 photocatalyst was found to be highly stable in the cyclic experiments. Based on the results of BET, Pl and DRS analysis, two possible reasons have been proposed for the enhanced visible light activity and stability of this novel photocatalyst: (1) broadening of the photoabsorption range and (2) efficient separation of photoinduced charge carriers which does not allow the photoexcited electrons to accumulate on the conduction band of Ag2S and hence prevents the photocorrosion.

Efficient visible light photocatalytic activity and enhanced stability of BiOBr/Cd(OH)2 heterostructures

Novel BiOBr/Cd(OH)2 heterostructures were synthesized by a facile chemical bath method under ambient conditions. A series of BiOBr/Cd(OH)2 heterostructures were obtained by tuning the Bi/Cd molar ratios. The obtained heterostructures were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). Optical properties were studied by UV-visible spectroscopy, diffuse reflectance spectroscopy and photoluminescence (PL). Photocatalytic studies on rhodamine B (RhB) under visible light irradiation showed that the heterostructures are very efficient photocatalysts in mild basic medium. Scavenger test studies confirmed that the photogenerated holes and superoxide radicals (O2˙−) are the main active species responsible for RhB degradation. Comparison of photoluminescence (PL) intensity suggested that an inhibited charge recombination is crucial for the degradation process over these photocatalysts. Moreover, relative positioning of the valence and conduction band edges of the semiconductors, O2/O2˙− and ˙OH/H2O redox potentials and HOMO–LUMO levels of RhB appear to be responsible for the hole-specificity of degradation. Photocatalytic recycling experiments indicated the high stability of the catalysts in the reaction medium without any significant loss of activity. This study hence concludes that the heterojunction constructed between Cd(OH)2 and BiOBr interfaces play a crucial role in influencing the charge carrier dynamics and subsequent photocatalytic activity.

Effect of co-substrates on biogas production and anaerobic decomposition of pentachlorophenol

This study aims to examine the effect of different co-substrates on the anaerobic degradation of pentachlorophenol (PCP) with simultaneous production of biogas. Acetate and glucose were added as co-substrates to monitor and compare the methanogenic reaction during PCP degradation. During the experiment, a chemical oxygen demand (COD) removal efficiency of 80% was achieved. Methane (CH4) production was higher in glucose-fed anaerobic reactors with the highest amount of CH4 (303.3µL) produced at 200ppm of PCP. Scanning electron microscopy (SEM) demonstrates the high porous structure of anaerobic sludge with uniform channels confirming better mass transfer and high PCP removal. Quantitative real-time PCR (qPCR) revealed that methanogens were the dominating species while some sulfate reducing bacteria (SRBs) were also found in the reactors. The study shows that strategic operation of the anaerobic reactor can be a feasible option for efficient degradation of complex substrates like PCP along with the production of biogas.

Oxidative Copolymerization of Aniline with o- and p-Nitroaniline by Ammonium Per Sulfate: Kinetic and Pathway

The kinetic study on the oxidation of aniline with o- and p-nitroaniline by ammonium persulfate (APS) has been carried out. The course of copolymerization was investigated by UV-vis spectroscopy and structural characterization was studied by FTIR spectral analysis. The electronic spectra of the copolymers poly(aniline-co-p-nitroaniline) and poly(aniline-co-o-nitroaniline) show hypsochromic shift. The shift has been observed in the bands corresponding to π → π* transition as well as in the exciton transition. The presence of nitro-group not only affects the oxidative polymerization window but also brings about the remarkable changes in the optical and electronic properties of parent polymer polyaniline. The poly(aniline-co-nitroaniline) has been shown multiple color transition (yellow → lightgreen → darkgreen) as the pH of the system changes with progress of polymerization reaction. The increase in absorbance recorded at various time intervals with increasing concentration of aniline, o- and p-nitroaniline, which indicates the growth of polymer formation. The first order kinetics is suggested as the degradation curve is consistent well byan exponential decay of APS. The resulting first-order rate constant was used to calculate the rate of poly(aniline-co-nitroaniline) formation using the rate equation –d[A]/dt = kcn. The reaction shows first-order dependence for each reactant.

Oxidative Degradation of Acetaminophen by Permanganate in Neutral Medium-A Kinetic and Mechanistic Pathway

The occurrence of pharmaceuticals in the environment is an emerging issue. Several studies observed that the nonsteroidal antiinflammatory drug acetaminophen is ubiquitously present in most of the surveyed surface waters, worldwide. This spectroscopic study presents the kinetics and degradation pathways of oxidation of acetaminophen by permanganate in neutral medium. The variables affecting the reactions were carefully investigated and the conditions were optimized. The higher degradation rate was observed with increase in acetaminophen concentration in the range of 0.4 × 10−3 to 9.7 × 10−3 min−1. The retention time and UV-visible absorption spectrum of the product were found to be identical to those of p-benzoquinone. The spectral change in the course of reaction was observed in the region 400 nm to 700 nm and there was a gradual decrease in absorption intensity at its λmax. Kinetic analysis of these results only gave good linear plots, with regression coefficients >0.996, when they were fitted to a pseudo-first-order reaction. The slope of log k versus 1/T also confirms the first-order dependence on the reactant. Investigations of the reaction at different temperatures allowed the determination of the activation parameters with respect to the slow step of proposed mechanism.