Arunima Nayak

Chemical treatment technologies for waste-water recycling—an overview

The global population is increasing and because of this, the world may experience great fresh water scarcity. Our water resources are limited and, hence, water treatment and recycling methods are the only alternatives for getting fresh water in the coming decades. Therefore, there is a great need for the development of a suitable, inexpensive and rapid wastewater treatment techniques and reuse or conservation methods in the present century. The different types of water treatment and recycling techniques have been discussed in terms of their basic principles, applications, costs, maintenance and suitability. Additionally, a systematic approach to water treatment and recycling involving their understanding, evaluation and selection parameters has been presented. A brief guideline for the selection of the appropriate technologies for specific applications has been evaluated. This review adds to the global discussions on water scarcity solutions.

Adsorptive removal of dyes from aqueous solution onto carbon nanotubes: a review.

Adsorption is a widely used technique for the separation and removal of pollutants from wastewaters. Carbon nanotubes (CNTs) are emerging as potential adsorbents because of its well defined cylindrical hollow structure, large surface area, high aspect ratios, hydrophobic wall and easily modified surfaces. In this review, dye adsorption capability of CNTs and CNT based composites from aqueous system has been compiled. This article provides the information about the defect, adsorption sites on CNTs and batch adsorption studies under the influence of various operational parameters such as contact time, solution pH, temperatures etc. and deals with mechanisms involved in adsorption of dyes onto CNTs. From the literature reviewed, it is observed that single walled carbon nanotubes (SWCNTs) show higher adsorption capacity than multi walled carbon nanotubes (MWCNTs) and functionalized and CNT composite have better sorption capacity than as grown CNTs. It is evident from the literature that CNT based nanosorbents have shown good potential for the removal of dyes from aqueous solution. However, still more research work should be focused on the development of cost effective, higher efficient and environmental friendly CNT based nanosorbents for their commercial applications.

Photo-catalytic degradation of toxic dye amaranth on TiO2/UV in aqueous suspensions

The photo-catalytic degradation of an azo dye - Amaranth (AM) - has been investigated in TiO(2)/UV aqueous suspensions. The results obtained from the experiments during H(2)O(2)/TiO(2) addition show that the highest decolorization rate is provided by the combination of (UV+TiO(2)+H(2)O(2)). The decolorization efficiencies were 17%, 26%, 38% and 64% in the runs UV, UV+H(2)O(2), UV+TiO(2) and (UV+TiO(2)+H(2)O(2)) after approximately 100 min illumination periods, respectively. The observed dye degradation rates followed pseudo-first order kinetics with respect to the substrate concentration under the experimental conditions used. Different experimental conditions, such as temperature, pH and presence of electron acceptor were investigated. The temperature effect was investigated at the range of 293-313 K and it was observed that decolorization rate increased by the increase in temperature. Chemical oxygen demand and dye absorbance of the photodegraded dye solution substantially decreased. Effect of pH was also investigated and it was observed that the lower the pH the higher the degradation. In addition, an enhancement in the photodegradation rate was observed by the addition of hydrogen peroxide as an electron acceptor. The adsorption trends of Amaranth at various initial concentrations followed the Langmuir isotherm trend. This work adds to the global discussion on the role of the advanced oxidation processes in water treatment.

A comparative investigation on adsorption performances of mesoporous activated carbon prepared from waste rubber tire and activated carbon for a hazardous azo dye—Acid Blue 113

A mesoporous carbon developed from waste tire rubber, characterized by chemical analysis, FTIR, and SEM studies, was used as an adsorbent for the removal and recovery of a hazardous azo dye, Acid Blue 113. Surface area, porosity, and density were determined. The adsorption of the dye over the prepared adsorbent and a commercial activated carbon was achieved under different pH, adsorbate concentration, sieve size, adsorbent dosage, contact time and temperature conditions. Langmuir and Freundlich adsorption isotherm models were applied and thermodynamic parameters were calculated. Kinetic studies indicated that the adsorption process follow first order kinetics and particle diffusion mechanisms are operative. By percolating the dye solution through fixed-bed columns the bulk removal of the Acid Blue 113 was carried out and necessary parameters were determined to find out the percentage saturation of both the columns. Recovery of the dye was made by eluting 0.1 M NaOH through the column.

Adsorption studies on the removal of hexavalent chromium from aqueous solution using a low cost fertilizer industry waste material

Low cost fertilizer industry waste material called carbon slurry, produced in generators of fuel oil-based industrial generators, was converted into an effective and efficient adsorbent for the removal of hexavalent chromium(VI) from aqueous solutions. The waste was chemically treated, activated, characterized, and used for the adsorption of chromium. The work involves batch experiments to investigate the effect of contact time, pH, temperature, concentration, and adsorbent dose on the extent of adsorption by carbon slurry. The maximum adsorption was found at 70min, 2.0 pH, 4.0g/L dose, and 303K temperature. Maximum adsorption capacity (15.24mg/g) of Cr(VI) on carbon slurry was observed at 100mg/L initial Cr(VI) concentration. Langmuir and Freundlich adsorption isotherm models were applied to analyze adsorption data, and both were found to be applicable to this adsorption system, in terms of relatively high regression values. Thermodynamic parameters showed that the adsorption of Cr(VI) onto carbon slurry was feasible, spontaneous, and exothermic under the studied conditions. Kinetics of adsorption was found to follow the pseudo-second-order rate equation. Column studies have been carried out to compare these with the batch capacities. The recovery of Cr(VI) and chemical regeneration of the spent column have also been tried. In all, the results indicated that the adsorbent used in this work proved to be effective material for the treatment of chromium-bearing aqueous solutions.

BIOSORPTION OF NICKEL ONTO TREATED ALGA (OEDOGONIUM HATEI): APPLICATION OF ISOTHERM AND KINETIC MODELS

Oedogonium hatei was developed into an effective and efficient adsorbent for the removal of Ni(II) ions from aqueous solution. The adsorption studies of untreated and treated algal biomass (with 0.1M HCl) were compared in batch mode. Optimum biosorption conditions were determined as a function of pH, biomass dosage, contact time, and temperature and the Langmuir and Freundlich isotherms were found applicable in terms of relatively high regression values. The maximum monolayer adsorption capacity of the biosorbents (untreated and acid-treated algae), as obtained from the Langmuir adsorption isotherm, was found to be 40.9 and 44.2mg/g, respectively at 80min contact time, 5.0 pH, 0.7g/L algal dose, and 298K temperature. The thermodynamic parameters showed that the adsorption of Ni(II) ions onto algal biomass was feasible, spontaneous, and exothermic under the studied conditions. Kinetics of adsorption followed both first- and second-order rate equations and the process involving the rate-controlling step is complex involving boundary layer as well as intraparticle diffusion processes. The FTIR results of algal biomass showed that biomass has different functional groups and these functional groups are able to react with metal ion in aqueous solution. Biosorbent could be regenerated using 0.1M NaOH solution, with up to 70% recovery. The performance of this biosorbent was then compared with many other reported biosorbents for nickel removal and it was observed that the proposed adsorbent is effective in terms of its performance.

Pesticides removal from waste water by activated carbon prepared from waste rubber tire

Waste rubber tire has been used for the removal of pesticides from waste water by adsorption phenomenon. By applying successive chemical and thermal treatment, a basically cabonaceous adsorbent is prepared which has not only a higher mesopore, macropore content but also has a favorable surface chemistry. Presence of oxygen functional groups as evidenced by FTIR spectra along with excellent porous and surface properties were the driving force for good adsorption efficiency observed for the studied pesticides: methoxychlor, methyl parathion and atrazine. Batch adsorption studies revealed maximum adsorption of 112.0 mg g(-1), 104.9 mg g(-1) and 88.9 mg g(-1) for methoxychlor, atrazine and methyl parathion respectively occurring at a contact time of 60 min at pH 2 from an initial pesticide concentration of 12 mg/L. These promising results were confirmed by column experiments; thereby establishing the practicality of the developed system. Effect of various operating parameters along with equilibrium, kinetic and thermodynamic studies reveal the efficacy of the adsorbent with a higher adsorption capacity than most other adsorbents. The adsorption equilibrium data obey Langmuir model and the kinetic data were well described by the pseudo-first-order model. Applicability of Banghams equation indicates that diffusion of pesticide molecules into pores of the adsorbent mainly controls the adsorption process. Spontaneous, exothermic and random characteristics of the process are confirmed by thermodynamic studies. The developed sorbent is inexpensive in comparison to commercial carbon and has a far better efficiency for pesticide removal than most other adsorbents reported in literature.

Recent advances on potentiometric membrane sensors for pharmaceutical analysis.

Prime concerns with modern developments are attributed to high level undetected but important biological substances or even toxicants cycled often among individual and populations; which in turn agonizes environmental monitoring, trace-gas detection, water treatment facilities, in vivo detection in biological fluids and other accomplishments. For the detection of such analytes, several analytical devices combined with biological component have been designed with a physiochemical detector component. Here, we essentially focus on drug-based potentiometric membrane sensors known as ion selective electrodes (ISEs). The functionality of ion-selective membrane is quite intricate, challenging, and our understanding is yet to be thrived with more interventions. ISEs have applied explications to enormous variety of analytical inquires as well as informative tools for probing host-guest chemistry. However, expansion of ISEs based applications is aimed to improve the system performance, acquiring enhanced understanding of their response mechanism, and finding new chemical or physical configurations mainly for human welfare. The major strength of ISEs is the precised analytical information, assured by using the ion-selective membrane electrodes used successfully for both in vitro and in vivo assays of pharmaceutical products as well as in clinical analyses. In this review, we attempt to provide a brief prologue to the applicability and advantages of potentiometric sensors in the analysis of pharmaceutically active compounds emphasizing their employment at molecular level for in situ selection of biologically important analytes.

Potential of activated carbon from waste rubber tire for the adsorption of phenolics: Effect of pre-treatment conditions

Rubber tire activated carbon modification (RTACMC) and rubber tire activated carbon (RTAC) were prepared from waste rubber tire by microwave assisted chemical treatment and physical heating respectively. A greater improvement in porosity and total pore volume was achieved in RTACMC as compared to that of RTAC. But both have a predominantly mesoporous structure. Under identical operating conditions, an irradiation time of 10 min, chemical impregnation ratio of 1.50 and a microwave power of 600 W resulted in maximizing the efficiency of RTACMC for p-cresol (250 mg/g) at a contact time of 90 min while RTAC showed a 71.43 mg/g adsorption capacity at 150 min. Phenol, due to its higher solubility was adsorbed to a lesser extent by both adsorbents. Physical nature of interactions, pore diffusion mechanism and exothermicity of the adsorption process was operative in both adsorbents. The outcomes support the feasibility of preparing high quality activated carbon from waste rubber tire by microwave assisted chemical activation.

Photodegradation of hazardous dye quinoline yellow catalyzed by TiO2.

The photocatalytic degradation of hazardous dye quinoline yellow, employing a heterogeneous photocatalytic process using TiO(2) photocatalyst irradiated with 6 W UV light source tungsten lamp, has been studied. The effect of various operational parameters, i.e., dye concentration, photocatalyst concentration, pH of the solution, substrate concentration, and electron acceptor such as hydrogen peroxide on the degradation rate of aqueous solutions of quinoline yellow has been examined. The disappearance of the dye follows a pseudo first order kinetics according to the Langmuir Hinshelwood model. Results show that the use of an efficient photocatalyst and the selection of optimal operational parameters may lead to complete decolorization and to sustainable decrease in the chemical oxygen demand (COD) of the dye waste water.