Shubhalakshmi Sengupta

Thermodynamics and kinetics study of defluoridation using Ca-SiO2-TiO2 as adsorbent: Column studies and statistical approach

Fluoride contamination of water is a potential health and environmental hazard worldwide. This study focuses on defluoridation efficiency in aqueous system by novel adsorbents, i.e., calcium impregnated silica (Ca-SiO2) and calcium impregnated silica combined with titanium dioxide (Ca-SiO2-TiO2). Comparative batch study was carried out using both adsorbents Ca-SiO2 and Ca-SiO2-TiO2 for fluoride removal efficiency in different experimental conditions where it was observed that chemically modified Ca-SiO2-TiO2 acted as a better adsorbent for defluoridation than Ca-SiO2. Thus, further batch isotherm and kinetics studies were performed using Ca-SiO2-TiO2. The phenomenon of fluoride ion uptake is realized by Langmuir and Freundlich isotherm model. Langmuir isotherm shows satisfactory fit to the experimental data. The rate of adsorption shows that the pseudo-second-order rate fitted the adsorption kinetics better than the pseudo-first-order rate equation. The mechanism of adsorption process was illustrated by calculating Gibbs free energy, enthalpy and entropy from thermodynamic studies. To further confirm the applicability of the adsorbent, a fixed bed study was carried out in column mode. Thomas and bed-depth-service-time (BDST) model were well-fitted to the experimental results. The optimal operating conditions of defluoridation were found by using response surface methodology (RSM) with the help of Design Expert Software. The maximum percentage of fluoride removal was 92.41% in case of calcium impregnated silica combined with titanium dioxide (Ca-SiO2-TiO2). Thus, it may be concluded that chemically synthesized Ca-SiO2-TiO2 could be used as an environmentally and economically safe adsorbent for defluoridation of waste water.

Assessment on the decolourization of textile dye (Reactive Yellow) using Pseudomonas sp. immobilized on fly ash: Response surface methodology optimization and toxicity evaluation

This study focuses on the investigation of removal of textile dye (Reactive Yellow) by a combined approach of sorption integrated with biodegradation using low cost adsorbent fly ash immobilized with Pseudomonas sp. To ensure immobilization of bacterial species on treated fly ash, fly ash with immobilized bacterial cells was characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and fluorescence microscopy. Comparative batch studies were carried out using Pseudomonas sp, fly ash and immobilized Pseudomonas sp on flyash and were observed that immobilized Pseudomonas sp on flyash acted as better decolourizing agent. The optimized pH, temperature, and immobilized adsorbent dosage for highest percentage of dye removal were observed to be pH 6, 303 K, 1.2 g/L in all the cases. At optimum condition, the highest percentage of dye removal was found to be 88.51%, 92.62% and 98.72% for sorption (flyash), biodegradation (Pseudomonas sp) and integral approach (Pseudomonas sp on flyash) respectively. Optimization of operating parameters of textile dye decolourization was done by response surface methodology (RSM) using Design Expert 7 software. Phytotoxicity evaluation with Cicer arietinum revealed that seeds exposed to untreated dye effluents showed considerably lower growth, inhibited biochemical, and enzyme parameters with compared to those exposed to treated textile effluents. Thus this immobilized inexpensive technique could be used for removal of synthetic dyes present in textile wastewater.

Dye Removal Using Microbial Biosorbents

Due to the rapid urbanization and industrialization, huge amounts of toxic sludge are being disposed into the environment. Improper management of this toxic sludge contaminates all components of the environment. Dyes are being used from very ancient period of time as colouring substances for almost every commodity. Some dyes are toxic to living organisms. Dyes may initiate cancer, mutation in the genetic sequences and suppress enzyme activities.

Biodegradation Behaviour of Cellulose-Reinforced PMMA Composites in Pond Water

Acrylics and polyolefins are widely used synthetic plastics in daily consumer products which are non-biodegradable in nature. An accumulation of these solid wastes in the environment poses ecological threats and requires novel management techniques. Researchers have now focussed their work on developing novel biodegradable polymer materials and isolating and identifying microorganisms which have the potential to degrade these polymeric materials. Isolating and identifying these microorganisms having potential to degrade polymers and polymer composites are required for developing newer biotechnological techniques for management of these solid wastes in the environment. The present work studies the biodegradation behaviour of PMMA and micro-/nano-cellulose-reinforced PMMA (polymethyl methacrylate) composites in pond water. The weight loss data revealed improved biodegradability in cellulose-reinforced PMMA composites in comparison to the synthetic PMMA. Scanning electron microscopy (SEM) images revealed effective biodegradability of the composites in pond water. The microorganism (fungus) was isolated, and its biodegradation behaviour was studied.