Removal of Cr(VI) and Cu(II) ions from aqueous solution by rice husk ash—column studies

Cr(VI) adsorption by a green adsorbent walnut shell: Adsorption studies, regeneration studies, scale-up design and economic feasibility

Abstract: Natural water resources are polluted due to human activities like discharge from municipal and industrial wastewater. In general industrial wastewater contains toxic chemicals like heavy metals, dyes, acids etc. To save the water bodies it is necessary for industries to treat their wastewater before disposal. Agricultural wastes like green adsorbents may be considered as an alternative to minimize the problems regarding heavy metal pollution particularly for small and medium sized industries. In this study walnut shell, an agricultural waste is used for Cr(VI) removal as green adsorbent. Brunauer-Emmett-Teller (BET), Scanning electron microscopy (SEM), Point of zero charge (pHpzc) and Fourier transform infrared spectroscopy (FTIR) were used to characterise the walnut shell. Column studies were performed for different operating conditions and low influent flow rate, low influent Cr(VI) concentration and higher bed depth give better adsorption. Langmuir isotherm model fitted well for Cr(VI) adsorption equilibrium (KL = 0.6754 L/mg, R2 = 0.9996). Different kinetic models are applied on experimental data to evaluate model parameters and their applicability. Yan et al. model fitted well for the specified operating range (KY = 5903.63 mL/(mg min), R2 = 0.9785) and applied for scale-up designing. Regeneration studies are conducted by using different concentration of NaOH to investigate the reusability characteristics of walnut shell. Scale-up design for Cr(VI) removal using walnut shell as an adsorbent and its economic feasibility are done to find out its applicability in real life. This study reveals that walnut shell is an efficient and cost effective adsorbent for Cr(VI) removal and it can be a solution for Cr(VI) discharging industries.

Investigations on the properties of geopolymer mortar and concrete with mineral admixtures: A review

Abstract: The climatic changes associated with global warming due to greenhouse gases emission from cement production attracted researchers towards geopolymer based cementitious materials. Nowadays researchers are in a continuous process to improve the mechanical properties of geopolymer mortar and concrete at ambient temperature curing condition so as to broaden its scope of utilization in building construction. The review paper summarizes the effect of various mineral additives on mechanical, durability and microstructure characteristics of geopolymer mortar and concrete. Research findings revealed that geopolymer products blended with these materials showed a significant improvement in mechanical and durability properties at normal temperature conditions. The results advocate that geopolymer mixtures with desired properties can be designed for ambient temperature curing condition with minerals additives which may further promote them as an environmentally friendly construction material.

Comparative study of adsorptive removal of Cr(VI) ion from aqueous solution in fixed bed column by peanut shell and almond shell using empirical models and ANN

Abstract: Cr(VI) is a toxic water pollutant, which causes cancer and mutation in living organisms. Adsorption has become the most preferred method for removal of Cr(VI) due to its high efficiency and low cost. Peanut and almond shells were used as adsorbents in downflow fixed bed continuous column operation for Cr(VI) removal. The experiments were carried out to scrutinise the adsorptive capacity of the peanut shells and almond shells, as well as to find out the effect of various operating parameters such as column bed depth (5–10 cm), influent flow rate (10–22 ml min−1) and influent Cr(VI) concentration (10–20 mg L−1) on the Cr(VI) removal. The fixed bed column operation for Cr(VI) adsorption the equilibrium was illustrated by Langmuir isotherm. Different well-known mathematical models were applied to the experimental data to identify the best-fitted model to explain the bed dynamics. Prediction of the bed dynamics by Yan et al. model was found to be satisfactory. Applicability of artificial neural network (ANN) modelling is also reported. An ANN modelling of multilayer perceptron with gradient descent and Levenberg-Marquardt algorithms have also been tried to predict the percentage removal of Cr(VI). This study indicates that these adsorbents have an excellent potential and are useful for water treatment particularly small- and medium-sized industries of third world countries. Almond shell represents better adsorptive capacity as breakthrough time and exhaustion time are longer in comparison to peanut shell.

Sustainable bioremadiation of Cd(II) in fixed bed column using green adsorbents: application of kinetic models and GA-ANN technique.

Abstract: This paper is continuation of our earlier paper in batch studies (Nag et al., 2018) and aims to deliver efficient and affordable solution for Cd(II) remotion from their wastewater of small to medium scale industries operating in India and worldwide. Three biowaste materials, jackfruit, mango and rubber leaves are used for Cd(II) bioremediation from synthetic wastewater in continuous down flow in packed bed columns. The influence of influent concentration (20–80 mg L−1), flow rate (10–25 ml min−1) and bed depth (3–9 cm) on Cd(II) removal has been examined at pH 6. Rise in bed height favoured the adsorption process whereas the decrease in bio-sorption efficiency was recorded at high influent flow rate and concentration. 98.26% Cd(II) was removed at breakthrough by jackfruit leaves at a flow rate of 10 ml min − 1 when the influent concentration was 20 mg L−1 and 5 cm bed height. Different kinetic models were evaluated for their comparative applicability. Applicability of hybrid artificial intelligence GA-ANN was attempted as a tool for simulation and optimization of Cd(II) removal efficiency prediction as a function of influent variables. The network performed appreciably well in terms of cross-correlation coefficient (R) value (between 0.997 to 0.999) and minimization of errors.

Cr(VI) removal from aqueous solution using green adsorbents in continuous bed column – statistical and GA-ANN hybrid modelling

Abstract: Mango, jackfruit, and rubber leaves showed potential for Cr(VI) elimination in a batch mode The present study was performed in fixed bed downflow columns at multiple flow rates, bed depths, and influent concentrations for Cr(VI) elimination using the above green adsorbents The experiments were performed at influent flow rates of 5 to 25 mlmin−1, concentrations of 5 to 80 mlL−1, and bed depths of 3 to 9 cm The adsorption capacity for reduced flow rates and concentrations were more effective Well-known kinetic models had been used to fit the experimental data to determine their associated parameters Thomas model was the best fit, especially for the mango leaf The Thomas maximum adsorption capacity of mango, jackfruit, and rubber leaves was 6952, 2245, and 1579 mgg−1, respectively The multiple linear regression and GA-ANN technique predicted Cr(VI) removal efficiency successfully with a high cross-correlation coefficient

Standard methods for the examination of water and wastewater

Abstract: Set your standards with these standard methods. This is it: the most widely read publication in the water industry, your all-inclusive reference tool. This comprehensive reference covers all aspects of USEPA-approved water analysis methods. More than 400 methods - all detailed step-by-step; 8 vibrant, full-color pages of aquatic algae illustrations; Never-before-seen figures that will help users with toxicity testing and the identification of apparatus used in the methods; Over 300 superbly illustrated figures; A new analytical tool for a number of inorganic nonmetals; Improved coverage of data evaluation, sample preservation, and reagant water; And much more!

Toxicology: The basic science of poisons

Abstract: THIS is a weighty and heavily documented textbook which should prove of great value to experimental toxicologists. It is arranged in four sections, each section consisting of a number of chapters reviewing the literature on a single aspect of toxicology. There are 35 contributors. The first section of 150 pages is concerned with general principles of toxicology, the absorption, metabolism and excretion of toxins, and the way in which these influence the dose response relationship. This rather detailed treatment is probably not appropriate for medical readers who would be better served by consulting medical textbooks of pharmacology and biochemistry. However, it should be valuable to non-medical toxicologists. In the next two sections occupying 400 pages, the current experimental toxicological field is reviewed in two ways. First by going through the systems of the body (central nervous system, liver, kidney, etc.) and second by going through all the groups of toxins (teratogens, carcinogens, pesticides, metals, etc.). Consequently, there is an almost complete duplication of information in these two sections. This is made worse by a duplication of coverage between say the section on carcinogens which deals with metals and the section on metals which deals with carcinogenesis. This duplication of coverage, coupled with the emphasis on information derived from animal experiments and neglect of clinical information, reduces the value of the book to medical readers.

Application of gas adsorption kinetics. I. A theoretical model for respirator cartridge service life.

Abstract: Using the principles of gas adsorption kinetics, we have developed a new theoretical model addressing the adsorption and breakthrough of contaminant vapors or gases with respect to solid sorbents. Specifically, we have applied the theory to predict respirator cartridge service life in connection with individual contaminant exposure to toluene, vinyl chloride, ethyl acetate, and each of several different trichlorinated hydrocarbons at several levels of concentration. Theoretical expressions and contaminant breakthrough curves derived from our new approach are compared with those published previously by Mecklenburg and by Wheeler. The breakthrough curves derived by Mecklenburg and by Wheeler have approximately the same shape as the corresponding experimental curves for 0% to 40% breakthrough. However, these curves deviate in varying degrees from the experimental data at breakthrough values exceeding 40%. By contrast, our new theory agrees with published experimental results over the entire range of 0% to 10...

Batch Cr(VI) removal by polyacrylamide-grafted sawdust : Kinetics and thermodynamics

Abstract: Batch sorption studies have been carried out to determine the effect of adsorbent dose, initial sorbate concentration and pH on the adsorption of Cr(VI) on polymer-grafted sawdust. The process was found to be pH, temperature and concentration dependent. An empirical relationship has been obtained to predict the percentage Cr(VI) removal at any time for known values of sorbent and initial sorbate concentration under observed test conditions. The effect of diverse ions has been studied and it is found that there is very little effect on the sorption of Cr(VI). The process was found to be exothermic with a maximum adsorption of 91.0% at 30°C for an initial concentration of 100 mg l−1 at pH 3. The process follows first-order kinetics and the data fits the Freundlich adsorption isotherm. Thermodynamic parameters were also evaluated. Desorption studies confirmed that adsorbent can be effectively regenerated using 0.2 M NaOH and 0.5 M NaCl and can then be reused.