Arijit Sengupta

Efficient removal of chemically toxic dyes using microorganism from activated sludge: Understanding sorption mechanism, kinetics, and associated thermodynamics

ABSTRACT A systematic investigation was carried out for demonstrating the simple and cost-effective removal of toxic dyes using activated sludge from municipal wastewater. The sorption process was found to follow Freundlich isotherm and pseudo-second-order rate kinetics. Difference in sorption efficiency for activated and deactivated sludge in aerobic and anaerobic conditions revealed the involvement of different microorganism in sorption process with the indication of biodegradation. The sorption process was found to be spontaneous but entropy driven for Remazol Brilliant Blue R and Eriochrome Black T while enthalpy driven for Congo Red. The process was established to be a combination of adsorption as well as biodegradation.

Novel DyP from the basidiomycete Pleurotus sapidus: substrate screening and kinetics

Abstract A novel Dye-decolorizing peroxidase from the basidiomycete Pleurotus sapidus was screened for dyedecolorizing peroxidase activity with 2,2‘-azino-bis(3- ethylbenzothiazoline-6-sulfonic acid), Remazol Brilliant Blue R and Guaiacol. Additionally, the catalytic efficiency on degrading β-carotene into volatile products, and the catalyst storage stability with three different additives were also studied. The apparent inhibition constant (KS) was 51.7 μM. Optimal reaction rates (Vmax) and affinity constants (Km) towards the reducing substrates were obtained using Michaelis-Menten kinetic theory. The trend in the calculated Km’s was found to be 7.0 mM > 0.524 mM > 0.051 mM for Guaiacol, 2,2‘-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) and Remazol Brilliant Blue R. The storage stability of the catalyst was evaluated with 7.0% w/v PEG400, 7.0% w/v PEG1450 and 0.1% w/v Tween®80 at 5°C over a period of 45 days. The study revealed the longest activity conservation with PEG1450, where rDyP had lost 30% of initial activity. The enzyme solution presented similar pH and temperature dependence to known fungal dye-decolorizing peroxidases with most prolific enzymatic activities registered at pH 4.0 and temperatures below 30°C. An interesting property of the catalyst was oxidation observed in the absence of hydrogen peroxide.

Graphene-induced Tuning of the d-Spacing of Graphene Oxide Composite Nanofiltration Membranes for Frictionless Capillary Action-induced Enhancement of Water Permeability

While dispersing graphene in water is a formidable challenge, π–π stacking between graphene oxide (GO) and graphene is known to enable the dispersion of graphene in water. In this work, graphene-induced tuning of the d-spacing in GO composite membranes was performed by pressure-assisted self-assembly on a polysulphone inactive support. The physicochemical properties of the GO–graphene membranes were examined using numeric techniques, and the surface charges and hydrophilicities of the surfaces of GO–graphene membranes with different relative compositions of graphene were assessed. The incorporation of graphene into the GO layers was effective in inhibiting the swelling effect in the wet state; the different GO–graphene composite membranes also exhibited water permeability and salt rejection. The GO1graphene0.8 composite membrane demonstrated a water flux of 36 LMH; salt rejection values of 88.3% (sodium chloride), 91.03% (magnesium chloride), 97.6% (magnesium sulphate) and 98.26% (sodium sulphate); and a minimal free volume. Hence, this sample is considered the optimal membrane. GO-incorporated graphene influences membrane performance by converting the Donnan effect to the molecular sieve mechanism. The GO–graphene composite membranes were compared via theoretical and experimental studies.