Ranjana Chowdhury

Reaction Kinetics and Product Distribution of Slow Pyrolysis of Indian Textile Wastes

Abstract In this present investigation, textiles samples of non-polymeric nature, e.g, cotton, silk etc. of Indian origin were pyrolysed in a 50 mm diameter and 640 mm long packed bed pyrolyser placed in a tubular furnace from 573K to 1173K in a nitrogen atmosphere. Experiments were designed to investigate the effects of temperature of pyrolysis on yields of char, pyro-oil and gas and their characteristics. A kinetic scheme has been proposed where two parallel reactions occur simultaneously to produce volatiles and char. The kinetic rate constants of both the reactions have been determined in the temperature range under study. The activation energies and pre-exponential factors of all products (solid reactant, volatile and char) have been determined. A mathematical model for the pyrolysis of textile waste has been developed using the kinetic parameters determined under the present study. Calorific values of pyro-oil and char obtained at different temperature have been determined. The structural characteristics of char at different temperatures of 573, 873 and 1173K has also been analysed using SEM.

De-mercurization of wastewater by Bacillus cereus (JUBT1): Growth kinetics, biofilm reactor study and field emission scanning electron microscopic analysis

Removal of mercuric ions by a mercury resistant bacteria, called Bacillus cereus (JUBT1), isolated from the sludge of a local chlor-alkali industry, has been investigated. Growth kinetics of the bacteria have been determined. A multiplicative, non-competitive relationship between sucrose and mercury ions has been observed with respect to bacterial growth. A combination of biofilm reactor, using attached growth of Bacillus cereus (JUBT1) on rice husk packing, and an activated carbon filter has been able to ensure the removal of mercury up to near-zero level. Energy dispersive spectrometry analysis of biofilm and the activated carbon has proved the transformation of Hg(2+) to Hg(0) and its confinement in the system.

Mixed consortia in bioprocesses: role of microbial interactions

The utilization of mixed consortia or mixed culture has become a current research trend of applied microbiology, bioprocess engineering and biotechnology. The constituent microorganisms of such mixed cultures can jointly perform complex processes efficiently, yielding the desired product at an augmented rate, in comparison to monocultures. It is understandable that the interactions between the microbial partners in these mixed cultures are expected to have a significant impact on the combined performance of the microorganisms and the bioprocess as a whole. Prevalence of positive interactions (commensalism or mutualism) among microbial members of a mixed culture or consortia can significantly enhance the product outcome of the bioprocess, ensuring their industrial application and long-term stability. On the contrary, negative interaction (parasitism, predation or ammensalism) leads to elimination of microbial members from the consortia causing the destruction of community structure as well as disruption of cumulative performance. Therefore, a priori knowledge on the type of interaction between the microorganisms is also essential for the optimization of the performance of the designed consortia. This could only be achieved through the study of inter-microbial interaction prevailing in a mixed culture. In the present article, different bioprocess applications of mixed cultures, currently in practice along with types of positive microbial interactions involved, have been reviewed. Complexity of mixed cultures from the perspective of multiple types of intra-culture relationships has been explained in detail. Overall, the necessity for more in-depth research studies on “microbial interaction” in mixed culture bioprocesses has been stressed in the article.

A green chemistry approach for the synthesis and characterization of bioactive gold nanoparticles using Azolla microphylla methanol extract

This article reports the environmentally benign synthesis of gold nanoparticles (GNPs) using methanol extract of Azolla microphylla as the stabilizing and reducing agent. The GNPs were characterized by UV-vis spectrophotometry and FTIR, and the morphological characteristics were analyzed by XRD, FESEM-EDX and HRTEM. The GNPs could be formed in very short time, even in less than 30 min. The nanoparticles measured by UV-spectrophotometer demonstrated a peak at 540 nm corresponding to surface plasmon resonance spectra, and the peaks showed by FTIR suggested the presence of organic biomolecules on the surface of the GNPs. XRD results confirmed the crystalline nature of the GNPs, and FESEM-EDX and HRTEM analyses had been performed in the size ranges of 17–40 nm and 1.25–17.5 nm respectively. The synthesized GNPs showed excellent antioxidant activity. This study shows the feasibility of using plant sources for the biosynthesis of GNPs.

Experimental studies and mathematical modeling of an up-flow biofilm reactor treating mustard oil rich wastewater.

Bioremediation of lipid-rich model wastewater was investigated in a packed bed biofilm reactor (anaerobic filter). A detailed study was conducted about the influence of fatty acid concentration on biomethanation of the high-fat liquid effluent of edible oil refineries. The biochemical methane potential (BMP) of the liquid waste was reported and maximum cumulative methane production at the exit of the reactor is estimated to be 785 ml CH(4) (STP)/(gVSS added). The effects of hydraulic retention time (HRT), organic loading rate (OLR) and bed porosity on the cold gas efficiency or energy efficiency of the bioconversion process were also investigated. Results revealed that the maximum cold gas efficiency of the process is 42% when the total organic load is 2.1 g COD/l at HRT of 3.33 days. Classical substrate uninhibited Monod model is used to generate the differential system equations which can predict the reactor behavior satisfactorily.

Bio-Detoxification of Arsenic Laden Ground Water Through a Packed Bed Column of a Continuous Flow Reactor Using Immobilized Cells

Under the present study arsenic resistant bacterial strain, Rhodococcus equi (JUBTAs02), has been used to remove trivalent arsenic from a simulated aqueous solution of arsenic oxide (As2O3). Batch studies have been conducted to determine the arsenic-intoxicated growth kinetics of the bacteria. The Monod type kinetic parameters like saturation constant KS and maximum specific growth rate μmax have been determined by studying batch mode of growth of microorganisms varying the initial concentration of limiting substrate, i.e. citrate (carbon source), in absence of arsenic ions. The kinetic parameter for intoxicated growth, namely the inhibition constant, Ki, has been determined by varying As3+ concentration for each batch conducted at different initial concentrations of citrate. For ground water a first order kinetics with respect to arsenic concentration has been determined for arsenic uptake rate. The same microorganism has been used in immobilized form to treat simulated water as well as naturally occurring arsenic laden ground water in a continuous packed bed reactor using initial arsenite concentration and inlet flow rate as parameters. A maximum value of arsenite removal efficiency of 95% has been achieved in this process. Deterministic mathematical models capable of explaining the trend of removal of arsenic from simulated and ground water have been developed using the kinetic parameters of intrinsic growth of the microorganism. The simulated results have been compared with the experimental ones satisfactorily.

Co-pyrolysis of paper waste and mustard press cake in a semi-batch pyrolyzer—optimization and bio-oil characterization

ABSTRACT Under the present research study, the co-pyrolysis of paper waste and mustard press cake was conducted in a 50 mm diameter and 640 mm long semi-batch pyrolyzer in the temperature range of 673 to 1173 K in nitrogen atmosphere and synergistic relationship between the pyrolysis of two feed stocks has been observed. The paper wastes were composed of local packing paper, newspaper-based food packets of grocery, and printing paper in the ratio of 6:3:1. During co-pyrolysis, response surface methodology (RSM) technique has been employed using Design Expert Version 7.0.0 to determine the collective effects of factors, namely, A: ratio of paper waste to mustard press cake and B: pyrolysis temperature, on the yield of bio-oil, energy yield, and oxygen content of bio-oil. Optimization has been done by using RSM to identify the individual sets of values of independent parameters corresponding to maximum bio-oil yield (A: 9.0:1, B: 874.75 K), energy yield (A: 8.80:1, B: 812 K), and minimum oxygen content of bio-oil (A: 2.75:1, B: 883.06 K). Bio-oil obtained at maximum energy yield condition has been characterized using the Gas chromatography–mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FTIR) spectroscopic analyses. The array of compounds present in the bio-oil compounds has been compared with literature data available on pyro-oil obtained from similar feed stocks.

Three Phase Biofilter Model for the Removal of Styrene through the Microbial Route

A biofilter of 0.05m diameter and 0.58m height has been studied for the removal of styrene from a simulated air-styrene mixture through the microbial route using Pseudomonas putida. Coconut coir and other waste materials have been used as the immobilization matrix for the microorganisms. Gas flow rate (0.005-0.01kgm-2s-1), micronutrient liquid flow rate (5-10 kgm-2s-1), inlet styrene concentration (0.05-1.20 gm-3) and packing size (de = 0.08 - 0.18cm) have been used as parameters. The kinetic parameters of growth rate equation of bacterial strain have been determined using batch type experimental data. A Monod type reaction model has been observed to be appropriate for the explanation of growth kinetics of the microorganisms. The values of the kinetic parameters used are Ks = 0.8gm-3, µmax = 45h-1. A three-phase deterministic mathematical model has been developed incorporating the synergistic effect of simultaneous reaction and interphase (gas to liquid to biofilm) mass transfer of styrene using experimentally determined kinetic parameters and mass transfer coefficients calculated using standard correlations. Simulated results based on the model have been compared with the experimental ones satisfactorily.

Studies on the separation of proteins and lactose from casein whey by cross-flow ultrafiltration

AbstractA novel strategy has been developed for separation of individual whey protein fractions and lactose from casein whey by a cascade of different molecular weight cut-off (MWCO) cross-flow ultrafiltration (UF) membranes. Centrifugation (166.67 r.p.s., 277 K, 1800 s) followed by microfiltration (MWCO: 0.45 × 10−6 m) were employed for separation of fat molecules and suspended solids from casein whey. Immunoglobulins, such as IgG, IgA, and IgM were separated as retentate of 100 kg mol−1 UF membrane; bovin serum albumin, lactoperoxidase, and lactoferrin were separated as retentate of 50 kg mol−1 UF membrane; lactose were separated by 5 kg mol−1 UF membrane as permeate, and major proteins like β-lactoglobulin (molecular weight 18.3 kg mol−1) and α-lactalbumin (molecular weight 14.2 kg mol−1) were separated by proper control of pH. At pH 5.4 the most dominant whey protein, β-lactoglobulin (isoelectric point 5.2–5.4), formed dimer which was found to have immense effect on the separation characteristics. Hyd...

Production of biosurfactants through biodesulfurization of spent engine oil – an experimental study

Spent engine oil, a mixture of aliphatic and aromatic compounds, is one of the frequent environmental pollutants. In this paper, biodesulfurization of spent oil using Rhodococcus sp. was studied. Batch studies were conducted varying the oil to aqueous medium ratio of 10:90 to 90:10. The results demonstrated that maximum desulfurization of 80% was obtained at the oil to aqueous phase ratio of 70:30. Kinetic parameters of Monod type growth model, namely, µmax, maximum specific growth rate and Ks, the half saturation constant were determined by varying the initial sulfur content of spent oil in the range of 0.16–1.05% (w/v). Gas chromatography–mass spectrometry was done to identify the compounds present in treated and untreated spent engine oil. The surface tension and emulsification indices of both oil and aqueous phases were also determined at different reaction times.