Saima Sultana

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.

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.

Studies on the biodegradation of two different azo dyes in bioelectrochemical systems

A comparative study on the degradation of acid navy blue R (ANB) and reactive orange 16 (RO 16) was performed in two identical microbial fuel cells (MFCs) under similar conditions and the microbial communities were quantified using a quantitative real time polymerase chain reaction (qPCR). Electricity and methane gas were produced as the end products along with the significant removal of chemical oxygen demand (COD) during the study. The overall performance in terms of degradation rate, COD removal efficiency and biogas production rates were slightly better in the case of the reactor using RO 16 as the carbon source, while electricity production was slightly greater in the reactor treating ANB. A negative standard reduction potential of the reaction mixture indicates the presence of oxidized species in the reactor. Scanning electron microscopy images show the presence of diatoms and rod shaped bacteria in the mixed microbial culture and also confirmed the formation of a biofilm on the anode surface. The qPCR technique was used as a quantitative tool to estimate the abundance of methanogens, sulphate reducing bacteria (SRBs) and electrochemically active Geobacter species. The relative abundance of methanogens was comparatively higher and Geobacter was lower in the case of the reactor treating RO 16. Although the output power was low, this technique can be used for the effective degradation of complex and toxic compounds.

Electrical properties of V2O5-doped TlI

This paper reports the effect of heterogeneously doped vanadia on the ionic conductivity of thallium iodide (TlI). These compounds have been prepared and studied by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and electrical conductivity. The materials were found to be binary phase systems with the vanadia particles dispersed in the grains of TlI. The electrical conductivity shows an upward trend in the composition range x=0.1–0.5; however, with further increase in vanadia content, conductivity decreases. This behavior is attributed to disordering phenomena at interface boundaries and space-charge layers formed in the bulk grains of TlI. In addition to this, the increased content of vanadia in the system leads to the disappearance of the β−α phase transition of TlI, which is usually observed in the pure compound.

Novel bio-nanocomposite materials for enhanced biodegradability and photocatalytic activity

Novel bio-nanocomposites containing a biodegradable polymer and graphene oxide (Cellulose/Polypyrrole–graphene oxide or C/Ppy–GO) were prepared by chemical in situ polymerization and the materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) spectroscopy. The biodegradable polymer was prepared by chemical grafting of polypyrrole (Ppy) onto cellulose chains. The samples showed excellent biodegradability with low toxicity against food borne pathogens and can be used for biomedical applications. The samples also exhibited superior photocatalytic activity and can be used for the mineralization of dyes present in industrial effluents. Fluorescence spectra revealed that incorporation of graphene into the polymer chain supports charge separation and lowering of the charge carrier recombination, which in turn favours the photocatalytic activity of the composite. Moreover, cyclic voltammetry was used to measure the redox properties and the current producing ability of the samples. The studies suggest that electrically conducting, biodegradable and biocompatible bio-nanocomposites can be successfully prepared by chemical in situ polymerization for various applications.

A critical review on the prospect of polyaniline-grafted biodegradable nanocomposite

Among the various electrically conducting polymers, polyaniline (PANI) has gained attentions due to its unique properties and doping chemistry. A number of electrically conducting biodegradable polymers has been synthesized by incorporating a biodegradable content of cellulose, chitin, chitosan, etc. in the matrix of PANI. The hybrid materials are also employed as photocatalysts, antibacterial agents, sensors, fuel cells and as materials in biomedical applications. Furthermore, these biodegradable and biocompatible conducting polymers are employed in tissue engineering, dental implants and targeted drug delivery. This review presents state of the art of PANI based biodegradable polymers along with their synthesis routes and unique applications in diverse fields. In future, the synthesis of PANI-grafted biodegradable nanocomposite material is expected to open innovative ways for their outstanding applications.

Immobilization of peroxidase on polypyrrole-cellulose-graphene oxide nanocomposite via non-covalent interactions for the degradation of Reactive Blue 4 dye

In the present study novel polypyrrole-cellulose-graphene oxide nanocomposite (PCeGONC) was employed for the immobilization of ginger peroxidase (GP) via simple adsorption mechanism. Immobilization of enzyme on the obtained support resulted in enhancement of the enzyme activity. The recovery of activity was 128% of the initial activity. Consequently, in 3 h stirred batch treatment, PCeGONC bound GP exhibited higher decolorization efficiency (99%) for Reactive Blue 4 (RB 4) dye as compared to free GP (88%). The immobilized GP exhibited higher operational stability and retained approximately 72% of its initial activity even after ten sequential cycles of dye decolorization in batch process. The kinetic characterization of PCeGONC bound GP revealed slightly lower Km and 3.3 times higher Vmax compared to free GP. Degraded products were identified on the basis of GC-MS analysis and degradation pathway was proposed accordingly which confirms enzymatic breakdown of RB 4 into low molecular weight compounds. Genotoxic assessment of GP treated RB 4 revealed significant reduction of its genotoxic potential. In-silico analysis identified that binding site of PCeGONC on enzyme is distinct and lies far away from the active site of the enzyme. Furthermore, it also revealed higher affinity of 1-hydroxybenzotriazole (a redox mediator) and RB 4 for PCeGONC bound enzyme as compared to the free enzyme. This is in consensus with the observed decrease in Km of the immobilized GP.

Microbial Fuel Cell: Waste Minimization and Energy Generation

Microbial fuel cells (MFCs) have gained a recent attention as a mode of converting organic waste into electricity using variety of biodegradable substrate as fuel. Different designs of MFCs are available for different purposes, however dual and single chamber MFCs are common used for energy generation. Type of electrode materials, membrane, pH, electron transfer rate, reactor design and operating conditions affects the performance of MFC. Microbes actively catabolize substrate and transform their chemical energy into electrical energy. MFCs could be utilized as power generator in small devices such as biosensor, pacemakers and by doing small modification (Microbial Electrolysis Cell) can produce hydrogen a potential fuel in cathodic chamber. Besides the merits of this technology, it is still immature and faces practical limitations such as low power and current density. The construction and analysis of MFCs requires knowledge of different disciplines ranging from microbiology and electrochemistry to materials and environmental engineering. This article presents various aspects of MFC technology for proper understanding of the readers. This article present an extensive literature survey of some selected papers published on MFC technology in the last decade. Various practical solutions have been suggested to overcome the practical challenges of this technology.

Bioelectrochemical Systems for Transforming Waste to Energy

In recent years, BES has emerged as a new and promising approach for wastewater treatment. BES use microorganisms to convert chemical energy to electric energy and other value added chemicals. Compared to the conventional techniques available, it has evolved as a low energy intensive technology with an approach of integrated management of wastewater and recovering energy. This chapter presents a review on the different types of BESs with a brief discussion of their principle and anodic and cathodic reactions involved. Further, an overview is presented of recent work with different types of wastewater used as substrate, utilising different donors and acceptors of electrons involved and the various kind of electrodes used in various BES setups. BES is still a relevantly new and emerging field that deals with harnessing energy from wastewater with the potential to change the wastewater remediation techniques in future with gross positive energy recovery.