Sibdas Bandyopadhyay

Synthesis of NaP zeolite at room temperature and short crystallization time by sonochemical method

NaP zeolite nano crystals were synthesized by sonochemical method at room temperature with crystallization time of 3h. For comparison, to insure the effect of sonochemical method, the hydrothermal method at conventional synthesis condition, with same initial sol composition was studied. NaP zeolites are directly formed by ultrasonic treatment without the application of autogenous pressure and also hydrothermal treatment. The effect of ultrasonic energy and irradiation time showed that with increasing sonication energy, the crystallinity of the powders decreased but phase purity remain unchanged. The synthesized powders were characterized by XRD, IR, DTA TGA, FESEM, and TEM analysis. FESEM images revealed that 50 nm zeolite crystals were formed at room temperature by using sonochemical method. However, agglomerated particles having cactus/cabbage like structure was obtained by sonochemical method followed by hydrothermal treatment. In sonochemical process, formation of cavitation and the collapsing of bubbles produced huge energy which is sufficient for crystallization of zeolite compared to that supplied by hydrothermal process for conventional synthesis. With increasing irradiation energy and time, the crystallinity of the synthesized zeolite samples increased slightly.

Tape-cast ceramic membranes for microfiltration application

Alumina membrane filters in the form of thin (0.3–0.8 mm) discs of 25–30 mm diameter suitable for microfiltration application, have been fabricated by the tape-casting technique. Their pore size could be varied in the range 0.1–0.7 μm and porosity in the range 25%–55% through optimization of experimental parameters. The most important factor which determines the pore size, is the initial particle size of ceramic powders used for this purpose. Temperature of firing, and also the soaking time are crucial parameters which determine the porosity. Water permeability under suction conditions varies in the range 110–900 lm−2h−1 depending on porosity, pore size and thickness of the membrane. Most of these membranes, particularly those with pore sizes less than 0.5 μm, are found to be suitable for complete removal of bacteria from water and are also reusable after cleaning by acid or heat sterilization.

As(III) oxidation by MnO2 coated PEEK-WC nanostructured capsules

PEEK-WC nanostructured capsules were prepared by the phase inversion technique and used as support for the coating of a manganese dioxide layer. The coating was done by a chemical treatment of the capsules followed by a thermal one. The presence of the MnO(2) layer was confirmed by scanning electron microscopy (SEM), back scattering electron (BSE), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis. The produced capsules were, then, tested for As(III) oxidation in batch. The experiments consisted in treating 165 ml of As(III) solution with 1g of coated capsules at fixed temperature (15°C) and pH (5.7-5.8). In particular, the efficiency of the system was investigated for different As(III) concentrations (0.1, 0.3, 0.7 and 1 ppm). For feeds at lower As(III) content (0.1-0.3 ppm), tests lasted for 8h, while prolonged runs (up to 48 h) were carried out on more concentrated solutions (0.7 and 1 ppm). The produced capsules were able to oxidize As(III) into As(V) leading to complete conversion after 3 and 4h for feed concentrations of 0.1 and 0.3 ppm, respectively.

Highly oriented improved SAPO 34 membrane on low cost support for hydrogen gas separation

In this paper we investigated a path towards preparation of a highly oriented improved SAPO 34 zeolite membrane on a silica modified low cost clay-Al2O3 support by selective deposition of oriented seed crystals, followed by an epitaxial secondary growth hydrothermal technique. The membrane thickness was found to be ∼26 μm. The silica layer that have an abundance of reactive hydroxyl groups while its interior is connected by the siloxane group Si–O–Si. These Si–OH groups on the silica-coated substrate could provide a hydrogen bonding interaction with surface hydroxyl groups of SAPO 34 seed crystals. This outcome is a possible result of the formation of a uniform seed monolayer with the same orientation. The stronger intensity of the single peak in XRD pattern confirms the formation of an oriented membrane layer. For comparison, a seed layer was deposited on an unmodified support surface. A discrete and randomly oriented membrane layer was obtained on that support. Highly oriented SAPO 34 membranes on the silica modified support are better for hydrogen gas separation and attained higher selectivity values for the gas mixture. A selectivity of 16.66 and 20.91 was achieved for H2–CO2 and H2–N2, respectively, at room temperature. The obtained values were improved compared to the reported literature values. Herein, we report for the first time, that this work is an improvement towards a highly crystallographic orientation of the SAPO 34 membrane layer with reduced defects and higher gas separation efficiency. The synthesized membrane enhanced the reproducibility and long term durability for hydrogen gas separation with good results.

Effectiveness of Biosorption-Assisted Microfiltration Process for Treatment of Domestic Wastewater

ABSTRACT The efficiency of a biosorbent prepared from Eichhornia crassipes roots (ECR) was explored for the treatment of domestic sewage water in combination with low-cost ceramic microfiltration membrane. Batch sorption studies were conducted as a function of biosorbent dose, initial chemical oxygen demand (COD) loading, and temperature. Sorption equilibrium data of varying initial COD values (116–800 mg/L) indicated high potential of ECR for COD removal. Using 0.25 g/L of biosorbent dose, the equilibrium adsorption capacity was obtained as 2480 mg/g at 20°C for an initial COD loading of 800 mg/L. Microfiltration study was performed using ceramic membrane made from composition of α-alumina and clay. The effect of operating parameters on filtration characteristics was observed in terms of permeate flux. Permeate samples were characterized in terms of various parameters both for the direct filtration, as well as biosorbent-assisted filtration. The filtration behavior of wastewater at varying transmembrane pressure was explained using various membrane fouling models. The results suggested that microfiltration of domestic wastewater with incorporation of biosorbent (0.25 g/L) was highly effective for removal of organic load (>90%), turbidity (>99%), and total suspended solids (TSS) (93–95%) and the treated water quality was suitable for reuse in various purposes, such as gardening, floor and car washing, etc.

Reaction sequences in the synthesis of silicon nitride from quartz

Carbothermal reduction and nitridation of pure silica have been performed to synthesize pure Si3N4 powder. Iron was used to serve as a catalyst. The reduction reaction was studied with respect to different parameters such as temperature, soaking time and gas flow rate, etc. Almost pure Si3N4 powder with predominating β-phase could be synthesised at 1540°C. Below this temperature SiC and Si2N2O are the associated phases. SiC is unstable to Si3N4 in nitrogen atmosphere and disappears at 1540°C or under a longer holding at 1440°C. There is a critical flow rate of the nitrogen gas of 1·32 × 104 litre m−2 h−1, above which the yield on nitridation almost flattens. It has been suggested through thermodynamic arguments that the Si3N4 formation at 1440°C takes place through the intermediate formation of SiC and Si2N2O as follows: SiO2(s ) + 2SiC(s) + 2N2(g) = Si3N4(s) + 2CO(g) SiO2(s) + Si2N2O(s) + 3C(s) + N2(g) = Si3N4(s) + 3CO(g) At 1540°C the following reaction may predominate: 3SiO2(s) + 6C(s) + 2N2(g) = Si3N4(s) + 6CO(g)

Potential of biosorbent developed from fruit peel of Trewia nudiflora for removal of hexavalent chromium from synthetic and industrial effluent: Analyzing phytotoxicity in germinating Vigna seeds

Chromium (VI) removal efficiency of a biosorbent prepared from fruit peel of Trewia nudiflora plant was studied. The effect of pH, sorbent dose, initial metal concentration and temperature was studied with synthetic Cr+6 solution in batch mode. About 278 mg/g of Cr+6 sorption was obtained at 293 K at an optimum pH of 2.0 and biosorbent dose of 0.75 g/L. Equilibrium sorption data with varying initial concentration of Cr+6 (22–248 mg/L) at three different temperatures (293–313 K) were analyzed by various isotherms. Biosorption kinetics and thermodynamics were described using standard model equations. Encouraging results were obtained by the application of the biosorptive treatment for removal of Cr+6 from wastewater collected from common effluent treatment plant of tannery industry. In addition, Cr+6 desorption behavior was studied on different systems. Biosorbent was characterized by FESEM, FT-IR and XRD, etc. Effect of the biosorptive treatement with respect to the phytotoxicity of Cr+6 was analyzed by studying the seed germination behavior and enzyme activity of a pulse seed (Vigna radiata L.). Different concentrations of Cr+6 solution in both synthetic medium, as well as, in tannery effluent was employed and the results were compared with that of biosorbent treated medium. The study showed that due to efficient removal of Cr+6 from aqueous phase, considerable enhancement of seed germination, as well as, increase in root length was obtained for the biosorbent treated solutions which were close to that of the control values. Significant decrease (P < 0.01) in POD activity was observed in seeds irrigated with biosorbent treated wastewater compared to untreated wastewater. The study showed that the novel biosorbent prepared might be utilized for abatement of heavy metal toxicity, i.e., Cr+6 from industrial effluent.

Comparative study on treatment of kitchen-sink wastewater using single and multichannel ceramic membrane

A comparative study was conducted to explore the potential of ceramic microfiltration membrane alone and in combination with different physicochemical treatments, viz. biotreatment and adsorption using kitchen-sink wastewater. Cross-flow microfiltration (CMF) studies were carried out with tubular ceramic membrane in single channel and multichannel configuration. Biotreatment was studied using activated sludge process and adsorptive treatments were studied using a biosorbent prepared from the dried roots of Eichhornia crassipes, an aquatic weed which is abundantly grown in polluted water. The study showed better performance of 19 channel ceramic membrane compared to the single channel membrane in terms of the permeate quality, viz. BOD, COD, turbidity, TSS etc., as well as, permeate flux. Microfiltration of the adsorbent treated feed appeared to be most promising in comparison with the other feeds wherein, about 98% removal of BOD and 99% removal of COD were obtained. The quality of the treated water was found to be fit for use in horticulture, irrigation, etc.

Algal Biomass as Potential Biosorbent for Reduction of Organic Load in Gray Water and Subsequent Reuse: Effect on Seed Germination and Enzyme Activity

ABSTRACT Biosorptive treatment using algal biomass of Rhizoclonium riparium was proposed for higher-loading gray water for its effective utilization. A batch sorption study was conducted using composite wastewater having a wide range of initial chemical oxygen demand (COD) values (2400–44,800 mg/L). The study showed an optimum dose of 5 g/L of biosorbent resulted in 96% reduction of COD for wastewater with an initial COD of 10,500 mg/L. The equilibrium isotherm data at different temperatures were fitted to linear and nonlinear isotherms. Biosorption kinetics was studied by various kinetic models. Chemical composition and surface morphology of the biosorbent were characterized by infrared, x-ray diffraction, and scanning electron microscopy techniques before and after biosorption. Applicability of the biosorbent-treated wastewater in agricultural uses was explored by studying the effect of untreated and treated wastewater on the germination of two seeds, i.e., Vigna radiata and Lens esculenta, and subsequently the activity of peroxidase (POD) enzymes were studied to understand the toxicity in plants. The study revealed that compared with seeds treated with different dilutions of untreated wastewater, germination (%) was significantly higher for biosorbent-treated wastewater, with a reduced level of POD activity, indicating positive response of the seeds towards the biosorptive treatment.

Potential of ceramic microfiltration and ultrafiltration membranes for the treatment of gray water for an effective reuse

Abstract Gray water may serve as a water resource for agricultural uses due to their high nutrient content. In this study performance evaluation of indigenously developed low-cost ceramic membrane was investigated for treatment and reuse of high organic loaded gray water. The efficiency of microfiltration (MF) and ultrafiltration (UF) process was studied individually and as a two-stage treatment involving MF followed by UF. Effect of time was observed on reduction of chemical oxygen demand (COD) in the permeate stream and permeate flux in different processes. Depending on the variation in feed loading, about 73–90% COD reduction was achieved in the single-stage UF at 30 min of filtration with operating pressure of 2 bar, which was about 84–94% for two-stage treatment. Permeate quality in terms of organic loading, oil and grease and coliform concentration were found suitable according to the discharge norms for agricultural reuse of water. The effect of untreated, MF- and-UF treated wastewater was observed...