Aloke Kumar Ghoshal

Phenol degradation by Bacillus cereus: Pathway and kinetic modeling

The microbial degradation of phenol by pure cultures Bacillus cereus MTCC 9817 strain AKG1 and B. cereus MTCC 9818 strain AKG2 is studied in batch mode for several initial concentrations of phenol in the range of 100-2000 mg/L with an interval of 100mg/L. Degradation pathways are investigated at initial phenol concentrations of 100, 500, 1000, 1500, and 2000 mg/L. The bacteria are able to degrade phenol of concentration as high as 2000 mg/L. The maximum degradation rate is obtained at an initial phenol concentration of about 800 mg/L for the strain AKG1 and about 200mg/L for the strain AKG2. Both the strains degrade phenol via meta-cleavage pathway through formation of 2-hydroxymuconic semialdehyde (2-HMSA) as an intermediate product. Modeling of the biodegradation of phenol indicates that the Haldane inhibitory model predicts the experimental data fairly well for both the strains.

Novel pore-expanded MCM-41 for CO2 capture: synthesis and characterization.

Recently, amine-functionalized mesoporous silica materials have attracted considerable attention as a promising chemical sorbent for postcombustion CO2 capture applications. However, the grafting of amines in the conventional MCM-41 support induces the subsequent reduction of surface area and pore volume of the sorbents, affecting the CO2 adsorption-desorption kinetics significantly. To mitigate this problem, expensive pore expansion agents have been used to increase the pore size as well as the pore volume. The present study provides an innovative approach to the development of novel pore-expanded MCM-41 without the application of any swelling agent. The average pore size (~30 nm) obtained in our work is remarkably higher than the values (9 to 10 nm) reported in the literature. On the basis of the fundamental understanding of micelle properties under different alkaline conditions, a mechanism for the pore expansion process is proposed. The outcome (1.2 mmol/g) of the preliminary CO2 adsorption studies carried out on the novel support material grafted with monoamine silane is very promising.

Isolation and characterization of hyper phenol tolerant Bacillus sp. from oil refinery and exploration sites.

Bacillus cereus MTCC 9817 strain AKG1 and B. cereus MTCC 9818 strain AKG2 were isolated from petroleum refinery and oil exploration site, respectively. The 16S rDNA sequence of strain AKG1 showed the closest relation to B. cereus 99.63% and Bacillus coagulans 99.63% followed by 99.34% homology with Bacillus thuringiensis strain 2PR56-10. AKG2 is mostly related to B. thuringiensis strain CMG 861 with 99.37% homology. The similarity search between AKG1 and AKG2 gave the lowest similarity 99.19% among same genus similar sequences. At phenol concentration of 1000 mg/L, the optimum growth conditions for AKG1 were found to be 37 degrees C and pH 7.0 and the same were found to be 37 degrees C and pH 7.5 for AKG2. The growth kinetics of the strains AKG1 and AKG2 are best fitted by Yano model (maximum growth rate, mu(max)=1.024 h(-1) and inhibition constant, K(I)=171,800 mg/L) and Edward model (mu(max)=0.5969 h(-1) and K(I)=1483 mg/L) respectively. Growth kinetics of both the strains are also well fitted by the Haldane model with mu(max)=0.4396 h(-1) and K(I)=637.8 mg/L for AKG1 and mu(max)=0.9332 h(-1) and K(I)=494.4 mg/L for AKG2.

SEM analysis and gas permeability test to characterize polysulfone membrane prepared with polyethylene glycol as additive.

Phase inversion method is applied to prepare flat sheet asymmetric polymeric membranes from homogeneous solution of 12 wt% polysulfone (PSf) with two different solvents--N-methyl-2-pyrrolidone (NMP) and dimethyl acetamide (DMAc). 5.0 wt% polyethylene glycol (PEG) of three different molecular weight (400, 6000, and 20,000 Da) is used as the polymeric additives in the casting solution. Membranes are characterized by two different techniques viz. scanning electron microscopy (SEM) and gas permeation tests. Finally, the results of both the techniques are compared with those calculated from pure water permeation tests using Hagen-Poiseuille equation. It is found that though the values obtained from all the techniques vary from each other, their trend with increase in molecular weight of PEG seems to be the same. It is seen that when molecular weight of PEG increases from 400 to 20,000 Da, the mean pore size of the prepared membranes decreases, while the porosity and pore density show an increasing trend; the pressure normalized gas flux rises significantly and the thickness of the top layer of the prepared membrane sheet increases.

Enhanced CO2 sequestration by a novel microalga: Scenedesmus obliquus SA1 isolated from bio-diversity hotspot region of Assam, India.

The present study aimed to isolate a high CO2 and temperature tolerant microalga capable of sequestering CO2 from flue gas. Microalga strain SA1 was isolated from a freshwater body of Assam and identified as Scenedesmus obliquus (KC733762). At 13.8±1.5% CO2 and 25 °C, maximum biomass (4.975±0.003 g L(-1)) and maximum CO2 fixation rate (252.883±0.361 mg L(-1) d(-1)) were obtained which were higher than most of the relevant studies. At elevated temperature (40 °C) and 13.8±1.5% CO2 maximum biomass (0.883±0.001 g L(-1)) was obtained. The carbohydrate, protein, lipid, and chlorophyll content of the CO2 treated SA1 were 30.87±0.64%, 9.48±1.65%, 33.04±0.46% and 6.03±0.19% respectively, which were higher than previous reports. Thus, SA1 could prove to be a potential candidate for CO2 sequestration from flue gas as well as for the production of value added substances.

Performance assessment of an analcime-C zeolite–ceramic composite membrane by removal of Cr(VI) from aqueous solution

This article describes the synthesis of an analcime-C zeolite membrane on a ceramic support by in situ hydrothermal crystallization. A circular shaped ceramic support was firstly fabricated using low cost raw materials by a uni-axial pressing method and sintering process. Subsequently, the zeolite composite membrane was prepared with the repeated coating of analcime-C on the ceramic support through an in situ crystallization technique. The synthesized zeolite composite membrane was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), porosity, average pore size and pure water permeability. The influence of the number of coatings on the characteristics of the zeolite membrane was also explored. The obtained results clearly demonstrate that the porosity, pore size and water permeability of the membrane decrease significantly with the multiple coating of zeolite over the ceramic support. The porosity, average pore size and pure water permeability of the zeolite membranes are estimated to be 38–24%, 285–155 nm and 2.18 × 10−7 to 4.53 × 10−8 m3 m−2 s−1, respectively for various coatings (1–3). Finally, the separation performance of three times coated zeolite membrane was evaluated by removal of chromium(VI) from aqueous solution by ultrafiltration (UF) at various operating conditions (applied pressure, concentration and pH). The maximum rejection of 84% is achieved at an applied pressure of 207 kPa. Moreover, the separation performance of membrane is better as compared to other membranes reported in the literature.

High cell density lipid rich cultivation of a novel microalgal isolate Chlorella sorokiniana FC6 IITG in a single-stage fed-batch mode under mixotrophic condition

A single-stage mixotrophic cultivation strategy was developed with a novel microalgal isolate Chlorella sorokiniana FC6 IITG for high cell density lipid-rich biomass generation. The strain was evaluated for growth and lipid content under different physico-chemical parameters, nutritional conditions and trophic modes. Finally, a single-stage mixotrophic fed-batch cultivation strategy was demonstrated with intermittent feeding of key nutrients along with dynamic increase in light intensity for high cell density biomass and sodium acetate as elicitor for lipid enrichment. The key findings: (i) glucose and sodium acetate was identified as growth supporting and lipid inducing nutrients, respectively; (ii) mixotrophic batch cultivation resulted in maximum biomass and lipid productivity (mgL(-1)day(-1)) of 455.5 and 111.85, respectively; (iii) single-stage mixotrophic fed-batch cultivation showed maximum biomass productivity of 1.93gL(-1)day(-1) (biomass titer 15.81gL(-1)) and lipid productivity of 550mgL(-1)day(-1); (iv) biodiesel properties were in accordance with international standards.

CO2 biofixation and carbonic anhydrase activity in Scenedesmus obliquus SA1 cultivated in large scale open system

The present study deals with the large scale open system cultivation of the novel microalga: Scenedesmus obliquus SA1 (KC733762) previously isolated in our laboratory. SA1 strain was cultivated in open system at varying CO2 levels ranging from 0.03% to 35% (v/v) and subsequently the carbonic anhydrase activity (CA) and the biochemical properties were monitored. Maximum biomass concentration (1.39 ± 0.023 g L(-1)), CO2 fixation rate (97.65 ± 1.03 mg L(-1)d(-1)) and total CA activity (166.86 ± 3.30 E.U./mg chla) were obtained at 35% CO2. CA inhibitors: acetazolamide and ethoxyzolamide inhibited the external and internal enzyme activity in SA1. High CO2 levels were favorable for the accumulation of lipids and chlorophyll. The present results suggested that SA1 possessed high CO2 tolerance and high carbohydrate, lipid and chlorophyll content when cultivated in open system thus being suitable for CO2 mitigation in outdoor ponds and subsequent generation of value added products.

N 1 -(3-Trimethoxysilylpropyl)diethylenetriamine grafted KIT-6 for CO2/N2 selective separation

In the present study N1-(3-trimethoxysilylpropyl)diethylenetriamine was grafted on various ordered and commonly used mesoporous silica namely MCM-41 (2.2 nm), SBA-15 (6.6 nm) and KIT-6 (6.6 nm) in both anhydrous and aqueous conditions for CO2/N2 adsorption. The structural and physical properties before and after grafting were analyzed by nitrogen adsorption/desorption, X-ray diffraction and electron microscopy techniques. The uptake capacities of three-dimensional K30T and WK30T were 1.89 and 2.59 mol CO2 per kg of adsorbent, respectively at 30 °C which are significantly higher than MCM-41 and SBA-15 based adsorbents. Analysis of the enthalpy of CO2 adsorption, confirmed the adsorption in amine functionalized adsorbents by both chemical and physical interactions. Outstanding equilibrium CO2/N2 selectivity of functionalized KIT-6 over MCM-41 and SBA-15 opens up its practical applicability through a stable performance in several adsorptions/desorption cycles.

Equilibrium and Kinetics Studies for As(III) Adsorption on Activated Alumina and Activated Carbon

Equilibrium adsorption isotherms of As(III) were obtained from the experimentally generated data on activated alumina and activated carbon at temperature 303 K and pH 7.4. The isotherm for As(III) on activated alumina was typically of Brunauer Type – I but in the case of activated carbon equilibrium capacity seems to be increasing with increase in concentration. Langmuir isotherm model best represents the experimental data for As(III) in activated alumina and Freundlich model in activated carbon. Model parameters such as saturation capacity of adsorbent qs, Langmuir constant b, and Freundlich constants K and n were determined. Saturation adsorption capacity of As(III) in activated carbon was much higher than that in activated alumina. Overall effective mass transfer coefficient k was determined using uptake rate method. It is observed that k was independent of concentration of As(III). Values of k for both the adsorbents are of the order of 10−2 min−1.