Tabrez A. Khan

Low cost adsorbents for the removal of organic pollutants from wastewater

Water pollution due to organic contaminants is a serious issue because of acute toxicities and carcinogenic nature of the pollutants. Among various water treatment methods, adsorption is supposed as the best one due to its inexpensiveness, universal nature and ease of operation. Many waste materials used include fruit wastes, coconut shell, scrap tyres, bark and other tannin-rich materials, sawdust and other wood type materials, rice husk, petroleum wastes, fertilizer wastes, fly ash, sugar industry wastes blast furnace slag, chitosan and seafood processing wastes, seaweed and algae, peat moss, clays, red mud, zeolites, sediment and soil, ore minerals etc. These adsorbents have been found to remove various organic pollutants ranging from 80 to 99.9%. The present article describes the conversion of waste products into effective adsorbents and their application for water treatment. The possible mechanism of adsorption on these adsorbents has also been included in this article. Besides, attempts have been made to discuss the future perspectives of low cost adsorbents in water treatment.

Removal of Arsenic from Water by Electrocoagulation and Electrodialysis Techniques

Electrochemical methods have been described for the removal of arsenic from contaminated water due to their advantages in comparison to other removal methods. Only electrocoagulation and electrodialysis were used for this purpose. The present review article describes state-of-art of arsenic removal by using these techniques. Attempts have been made to explain the optimization for maximum removal of arsenic by controlling metal electrodes, pH of water, current densities, processing time and ionic concentration. The maximum arsenic removal achieved was brought down to the ppb level (10 ppb being permissible limit of World Health Organization in drinkable water). Efforts have also been made to explain the mechanism of arsenic removal by these techniques. Besides, the future perspectives of electrochemical techniques for the removal of arsenic have also been highlighted.

Adsorptive removal of rhodamine B from textile wastewater using water chestnut (Trapa natans L.) peel: adsorption dynamics and kinetic studies

Water chestnut peel, an agricultural bio-waste, was used as a biosorbent for removal of rhodamine B (RhB), basic textile dye, from an aqueous solution. The effects of various experimental parameters were studied. The equilibrium data correlated well with a Freundlich isotherm (R2 = 0.98–0.99) followed by a Halsey isotherm model (R2 = 0.98–0.99) which indicated heterogeneity of the adsorbent surface and multilayer adsorption of RhB dye onto the water chestnut peel waste (WCPW). High correlation coefficients (R2 = 0.99) together with close agreement between experimental qe (0.4–1.7 mg g−1) and calculated qe (0.4–2.5 mg g−1) suggested that the adsorption process followed pseudo-second-order kinetics, with k2 values in the range of 52–3.4 × 10−1 g mg−1 min−1 at different concentrations. The overall mechanism of adsorption was controlled by both liquid-film and intra-particle diffusions. The negative values of change in Gibbs free energy (−ΔG0 = 19.2–29.2 kJ mol−1) and positive values of change in enthalpy (ΔH0 = 30.9–117.6 kJ mol−1) revealed the process to be spontaneous and endothermic. WCPW was found to be an effective adsorbent for removal of RhB, a cationic dye, from an aqueous solution.

Removal of malachite green from aqueous solution using waste pea shells as low-cost adsorbent – adsorption isotherms and dynamics

The adsorptive removal of malachite green (MG) from aqueous solution using waste pea shells (Pisum sativum L.) is reported. Optimized conditions for maximum uptake were established. The adsorption was best described by the Freundlich model. A pseudo-second-order kinetic model correlated best with the data. Liquid-film and intra-particle diffusion control the overall process. Thermodynamic parameters indicated that adsorption was spontaneous, endothermic, and accompanied with an increase in entropy. Low contact time and high removal efficiency at natural pH of water recommend pea shells as efficient low-cost adsorbent for removal of MG from wastewaters.

Adsorptive removal of Pb(II) and Zn(II) from water onto manganese oxide-coated sand: Isotherm, thermodynamic and kinetic studies

Abstract Manganese oxide-coated sand, MOCS, was synthesized and characterized by XRD, FTIR, SEM, and EDX techniques, and was used for the adsorption of Pb(II) and Zn(II) from their aqueous solutions. The metal ion concentration, contact time, MOCS dose and pH of the solutions were optimized. Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms were studied and the maximum adsorption capacities for Pb(II) and Zn(II) were found to be 147.06 and 116.28 µg/g at 40 °C and 27 °C, respectively. These values are higher than many tested adsorbents. The energy 0.011 and 0.079 kJ/mol for Pb(II) and Zn(II) indicated adsorption as physical process. In thermodynamics the free energy change for Pb(II) ranged between −12.344 and −11.371 kJ/mol and that for Zn(II) ranged −9.638 to −11.155 kJ/mol between 27 and 40 °C that predicted the spontaneity of process. The enthalpy change −39.816 and 25.574 kJ/mol indicated the exothermic and endothermic nature of the adsorption of Pb(II) and Zn(II). Kinetic studies indicated that Pb(II) adsorption followed pseudo-second order, whereas Zn(II) followed partial pseudo-first and pseudo-second order rates. The adsorptions of both metals were controlled by film diffusion step.

Recent Trends in Chiral Separations on Immobilized Polysaccharides CSPs

Polysaccharide CSPs are recognized widely in chiral chromatography but the introduction of immobilized phases (Chiralpak IA, Chiralpak IB and Chiralpak IC columns) is a remarkable achievement. The immobilized CSPs can be used with organic, normal and reversed phase modes; even with prohibited solvents too (tetrahydrofuran, chlorofom, dichloromethane, acetone, 1,4-dioxane, ethylacetate, and certain other ethers). Their susceptibilities to work with a wide range of solvents have increased the range of applications including chiral recognition mechanisms. Besides, these are also useful for monitoring the progress of stereo-specific reactions; normally need prohibited solvents. The present review describes the various aspects of commercial available immobilized chiral columns. Attempts have been made to discuss immobilized polysaccharides CSPs, immobilized vs coated CSPs, comparison of immobilized CSPs, method development, optimization, chiral recognition mechanism and applications. The chiral recognition capabilities of commercial columns were in the order of Chiralpak IA > Chiralpak IB > Chiralpak IC columns; but complimentary to each other. Of course, these CSPs are not fully developed and need more advancements and applications. Definitely, the future of immobilized CSPs is quite better. Hopefully, in the coming years they will be the choice of the chromatographers for chiral separations in liquid chromatography.

Removal of cadmium(II), lead(II), and chromium(VI) ions from aqueous solution using clay

Removal of cadmium(II), lead(II), and chromium(VI) from aqueous solution using clay, a naturally occurring low-cost adsorbent, under various conditions, such as contact time, initial concentration, temperature, and pH has been investigated. The sorption of these metals follows both Langmuir and Freundlich adsorption isotherms. The magnitude of Langmuir and Freundlich constants at 30°C for cadmium, lead, and chromium indicate good adsorption capacity. The kinetic rate constants (K ad) indicate that the adsorption follows first order. The thermodynamic parameters: free energy change (ΔG o), enthalpy change (ΔH o), and entropy change (ΔS o) show that adsorption is an endothermic process and that adsorption is favored at high temperature. The results reveal that clay is a good adsorbent for the removal of these metals from wastewater.

Removal of congo red and basic violet 1 by chir pine (Pinus roxburghii) sawdust, a saw mill waste: batch and column studies

The efficiency of chir pine sawdust (CPS) for adsorptive removal of the dyes, congo red (CR) and basic violet 1 (BV), from aqueous solution was evaluated using batch and column studies. The equilibrium was attained in 60 min for CR and 45 min for BV. The adsorption of BV obeyed the Langmuir isotherm model while the Freundlich isotherm fitted the equilibrium data of CR adsorption. The Langmuir monolayer adsorption capacities (Qo) of CPS for BV and CR were 11.3 and 5.8 g kg−1, respectively. The kinetic data for CR were best fitted to the Lagergren pseudo-first-order model and for BV to the pseudo-second-order model. The intra-particle diffusion was found to be the rate-controlling step for CR adsorption, while the adsorption kinetics of BV were controlled by both intra-particle and liquid-film diffusion. The thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic in nature. The adsorption activation energy (Ea) for CR (124 kJ mol−1) implied chemical adsorption while that for BV (5.4 kJ mol−1) indicated physical adsorption. An increase in the Thomas model constant (KTh) with increasing flow indicated that for both dyes the mass transport resistance decreased during adsorption. Thus, CPS may be an efficient low-cost adsorbent for decolorization of dye-containing wastewaters.

Treatment and remediation methods for arsenic removal from the ground water

Globally, ground water is contaminating by arsenic continously, which needs economic treatment and remediation technologies. Physical, chemical and biological treatment methods have been developed, that include different kinds of filters, bucket type units, fill and draw, kalshi etc. The remediation methods discussed are air oxidation, reactive barriers, utilisation of deeper aquifers and sanitary protected dug wells. To the best of our knowledge no technology is available capable to remove arsenic from water at efficient, economic and commercial levels. Therefore, fast, efficient and economic arsenic removal technologies are required. Attempts have been made to suggest the future technologies of arsenic removal.

Chiral Analyses of Pollutants by Capillary Electrophoresis

The determination of enantiomeric composition of chiral xenobiotics and pollutants is a very difficult job due to their low amounts and poor detection by commonly used UV detector. But this sort of analysis is an important issue from the health point of view. The chiral analyses of these notorious pollutants by capillary electrophoresis have been discussed in this article. This review discusses the new trends and advancements, which have been achieved in the analyses of chiral pollutants using capillary electrophoresis and the state-of-art of their enaniomeric resolution. This article focuses on sample treatment, applications, optimization, detection, mechanisms of chiral resolution and future perspectives of CE in chiral resolution of xenobiotics. Besides, efforts have also been made to suggest the improvement in CE machine to make it ideal for the analyses of chiral xenobiotics at trace levels.