Saroj S. Baral

A preliminary study on the adsorptive removal of Cr(VI) using seaweed, Hydrilla verticillata.

The Cr(VI) adsorption efficiency of the seaweed, Hydrilla verticillata, was studied in batches. The adsorbent was characterized using SEM, BET surface area analyzer, Malvern particle size analyzer, EDAX and FT-IR. Cr(VI) removal efficiency of the adsorbent was studied as a function of different adsorption parameters such as contact time, stirring speed, pH, adsorbent dose, particle size, adsorbate concentration, and temperature. Langmuir, Freundlich, and Temkin adsorption isotherm equations were used in the equilibrium modeling. The adsorption process followed pseudo second-order kinetics and intra-particle diffusion was found to be the rate-controlling step. Experimental data follow Langmuir adsorption isotherm. Thermodynamic parameters such as Gibbs free energy and enthalpy of the adsorption process were evaluated to find out the feasibility of the adsorption process. The negative values of Gibbs free energy and positive enthalpy values show the feasibility and endothermic nature of the process. The significance of different adsorption parameters along with their combined effect on the adsorption process has been established through a full 2(4) factorial design. Among the different adsorption parameters, pH has the most influential effect on the adsorption process followed by adsorbate concentration and combined effects of all the four parameters were tested. The correlation among different adsorption parameters were studied using multi-variate analysis.

Attribute based specification, comparison and selection of feed stock for anaerobic digestion using MADM approach

Organic wastes are common in nature and generated at different sources which need to be treated before disposing into the environment. Anaerobic digestion (AD) process is a primary technique used for digestion and reduction of the ill effects of disposing the organic waste. Selection of appropriate feed stock for anaerobic digestion among the available options is a primary concern and the process efficiency and stability largely depend on this. The present paper describes a methodology for evaluation, comparison, ranking and optimum selection of a feed stock for anaerobic digestion. A 30 attribute coding scheme is proposed to evaluate the existing alternatives for feed stock of anaerobic digester. A three stage procedure which includes the elimination search is proposed to evaluate the available alternatives with the help of attributes quickly. Technique for order preference by similarity to ideal solution (TOPSIS) is a Multiple Attribute Decision Making (MADM) approach and graphical methods namely line graph and spider diagrams are used for optimum selection of feed stock among the available options. MATLAB code is written to execute the three stage procedure. The proposed methodology is explained through an illustrated example.

Removal of Cr(VI) from aqueous solution using waste weed, Salvinia cucullata

Biosorption studies of Cr(VI) were carried out using waste weed, Salvinia cucullata. Various adsorption parameters were studied, such as agitation speed, contact time, pH, particle size, and concentrations of adsorbent and adsorbate. The equilibrium was achieved in 12 h. A lower pH favoured adsorption of Cr(VI). The kinetics followed pseudo-second-order rate equations. The adsorption isotherm obeyed both the Langmuir and Freundlich models. The calculated activation energy (1.1 kJ mol−1) suggested that the adsorption followed a diffusion-controlled mechanism. Various thermodynamic parameters such as Δ G °, Δ H °, and Δ S ° were also calculated. The positive values of enthalpy indicated the endothermic nature of the reaction, and Δ S ° showed the increasing randomness at the solid liquid interface of Cr(VI) on the adsorbent, which revealed the ease of adsorption reaction. These thermo-dynamic parameters showed the spontaneity of the reaction. The maximum adsorption of uptake (232 mg g−1) compared well with reported values of similar adsorbents. The rate-determining step was observed to follow an intra-particle diffusion model.

Trend in chemical composition of precipitation during 2005–2009 at a rural station of Bhubaneswar, eastern India

Precipitation samples collected during 2005–2009 from a rural forest station of Bhubaneswar were analyzed for their chemical composition. The samples were collected through a wet-only (WO) collector and two bulk (B1 and B2) collectors. The ions were evenly balanced indicating good data quality. The overall pH of rainwater was slightly acidic and ~47% of all rain events during the period were acidic (pH < 5.6). Multilinear regression analysis showed relation between the free acidity (H+) and other components in rainwater. Enrichment factors (EF) of the major components with respect to their sources such as marine and crustal were calculated. Maximum EF was observed for NO3− for both marine and crustal sources for all the three collectors. Source apportionments were also carried for the ions. Trend analysis showed continuous increase in most of the ions over years during the study period driven by anthropogenic emissions. Statistical/factorial analysis established correlation among different ions.

Use of Manganic Ferrihydrite to treat As(V) contaminated water

The As(V) removal efficiency of Manganic Ferrihydrite, having a different mole ratio to Fe-Mn, were evaluated. The As(V) removal efficiency of the adsorbent increased with the increase in Mn up to 40–60 mole% in the Ferrihydrite. Thereafter, further increase in the Mn concentration showed an opposite trend. The adsorption efficiency was constant at pH range of 6–7 whereas the efficiency slightly decreased at > pH 7. Adsorption studies were also carried out varying the adsorbent and the adsorbate concentrations, respectively. The adsorption process followed both Freundlichs and Langmuirs adsorption isotherm models. The maximum theoretical uptake was calculated using the two investigated models. Since adsorption efficiency showed better results when the Mn concentration was 40–60 mole%, Manganic Ferrihydrite compound (Fe:Mn ratio 1:1) was used to conclude the experiments. The adsorption kinetics followed dual rates, faster at the beginning and then slower. The adsorption kinetics followed 1st order kinetics. The IR and TGA analyses displayed that the compound was Manganic Ferrihydrite.

Pretreatment of organic composite waste mixtures for enhanced biomethanantion

ABSTRACT Hydrolysis is the rate-limiting step for the anaerobic digestion of wastewater. overcome this rate-limiting step, pretreatment of organic waste is required. The objective of the present study is to find the effects of various pretreatment parameters along with their optimal values to make the process economically feasible. A full factorial design was used to design the experiments with temperature, duration of heat treatment, pH, and the volume of inoculum added as independent variables and cumulative methane volume (CMV) as the dependent variable. Residual curve shows that the errors are having a constant variance. Contour plots and three-dimensional surface plots show variation in the response variables. Among the independent variables, inoculum has the most significant effect on the degradation process followed by pH and temperature. Duration of heat treatment induces little effect on biogas yield. The interaction terms have a significant effect on the CMV.

Biosorption of Cr(VI) from wastewater using Sorghastrum Nutans L. Nash

ABSTRACT Sorghastrum Nutans L. Nash is used as an adsorbent for the removal of Cr(VI) from wastewater. Adsorption coupled reduction i.e. indirect reduction is the mechanism of Cr(VI) removal by the biomaterial. The adsorbent surface became highly positively charged at lower pH, adsorption rate of Cr(VI) is faster and reduction reaction also accelerates at lower pH since the binding of negatively charged Cr(VI) ion species to the cationic groups is enhanced and protons take part in this reaction. The adsorbent is characterised by using XRD, FTIR, SEM and EDAX analysis. OH bending, CN stretching/bending and NH stretching play a major role in Chromium adsorption. Experimental values follow pseudo-second order reaction and Langmuir adsorption isotherm. Surface diffusion is the rate controlling mechanism for the process. The maximum percentage of Cr(VI) removal obtained is 75.5% with 7 g/L dosage at pH 1.3 and adsorbate concentration was 100 mg/L. From the normal probability, residual, contour, 3D surface, main effect and interaction plot along with t-test, ANOVA, and F-test, it is observed that pH has the most significant effect on the percentage removal followed by adsorbent dosage and time. The adsorbate concentration has the least effects and interaction effects are found to be significant.

Dissolution kinetics of cerium from red mud

ABSTRACT Leaching kinetics of rare earth element (REE) cerium (Ce) from red mud was investigated using different shrinking core models. The effect of various pertinent parameters such as acid concentration, liquid–solid ratio (LS), average particle size (PS), temperature and leaching time on the leaching efficiency was studied. The maximum recovery of 70.32% was obtained for 2 M HCl solution and an LS of 20:1 v/v. It was observed that the leaching process was limited by diffusion within the porous ash layer of the solid, thus making it ash diffusion controlled. The apparent activation energy was 11.38 kJ/mol, and the Arrhenius constant was 3.36 min−1.

Modeling and simulation for the adsorptive removal of Cr(VI) from aqueous solution

Cr(VI) adsorption experiments were carried out using activated carbon obtained from a waste weed Salvinia cucullata. The adsorbent was characterized using SEM, BET, EDAX, FT-IR, etc. Matrix method was used to develop an empirical mathematical model. Factorial design of experiments was used to minimize the number of experiments required to develop an empirical model. In the mathematical model, percentage adsorption of Cr(VI) was represented as a function of process variables like contact time, initial pH of the solution, and temperature. pH had the most influential effect on the adsorption process followed by contact time and temperature. The significance of different adsorption parameters and their combined effect on the adsorption process was established. The empirical model was simulated and solved using MATLAB and LabVIEW. The goodness of fit of the developed mathematical models to the experimental values was examined using different error analysis methods such as SSE, SAE, ARE, and ARS.