Several low cost biomaterials such as baggase, charred rice husk, activated charcoal and eucalyptus bark (EB) were tested for removal of chromium. All the experiments were carried out in batch ...process with laboratory prepared samples and wastewater obtained from metal finishing section of auto ancillary unit. The adsorbent, which had highest chromium(VI) removal was EB. Influences of chromium concentration, pH, contact time on removal of chromium from effluent was investigated. The adsorption data were fitted well by Freundlich isotherm. The kinetic data were analyzed by using a first order Lagergren kinetic. The Gibbs free energy was obtained for each system and was found to be −1.879
kJ
mol
−1 for Cr(VI) and −3.885
kJ
mol
−1 for Cr(III) for removal from industrial effluent. The negative value of Δ
G
0 indicates the feasibility and spontaneous nature of adsorption. The maximum removal of Cr(VI) was observed at pH
2. Adsorption capacity was found to be 45
mg/g of adsorbent, at Cr(VI) concentration in the effluent being 250
mg/l. A waste water sample containing Cr(VI), Cr(III), Mg, and Ca obtained from industrial unit showed satisfactory removal of chromium. The results indicate that eucalyptus bark can be used for the removal of chromium.
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•Lignocellulosic biomass is a clean energy source for biorefinery applications.•Pretreatment is a key step for biomass transformation to valuable chemicals.•Efficient and ecofriendly ...pretreatment approach to disintegrate biomass is needed.•Recent advances in physical and chemical pretreatment approaches are discussed.•Understanding of pretreatment mechanism is required for overcoming the challenges.
Depleting fossil reserves and growing energy needs have raised the demand for an alternative and clean energy source. The use of ubiquitously available lignocellulosic biomass for developing economic and eco-friendly large scale biorefinery applications has provided the much-needed impetus in this regard. The pretreatment process is a vital step for biomass transformation into added value products such as sugars, biofuels, etc. Different pretreatment approaches are employed to overcome the recalcitrance of lignocellulosic biomass and expedite its disintegration into individual components- cellulose, hemicellulose, and lignin. The conventional pretreatment methods lack sustainability and practicability for industrial scale up. The review encompasses the recent advances in selective physical and chemical pretreatment approaches such as milling, extrusion, microwave, ammonia fibre explosion, eutectic solvents etc. The study will allow a deeper understanding of these pretreatment processes and increase their scope as sustainable technologies for developing modern biorefineries.
Stabilization/solidification (S/S) is used as a pre-landfill waste treatment technology that aims to make hazardous industrial wastes safe for disposal. Cement-based solidification/stabilization ...technology is widely used because it offer assurance of chemical stabilization of many contaminants and produce a stable form of waste. The leaching behavior of arsenic from a solidified/stabilized waste was studied to obtain information about their potential environmental risk. Activated alumina (AA) contaminated with arsenic was used as a waste, which was stabilized/solidified (S/S) using ordinary portland cement (C), fly ash (FA), calcium hydroxide (CH) and various polymeric materials such as polystyrene and polymethyl methacrylate (PMMA). Toxicity characteristics leaching procedure (TCLP) and semi-dynamic leach tests were conducted to evaluate the leaching behavior of arsenic. Formations of calcite along with precipitate formation of calcium arsenite were found to be responsible for low leaching of arsenic from the stabilized/solidified samples. Effective diffusivity of arsenic ion from the matrix and leachablity index was also estimated. Minimum leaching of the contaminant was observed in matrix having AA
+
C
+
FA
+
CH due to the formation of calcite.
► Refractory sulfur compounds from commercial diesel were removed by adsorption. ► Ni/Al2O3 adsorbents resulted in higher sulfur removal as compared to Ni/ZSM-5 adsorbents. ► More than 90% S could be ...removed by 10% Ni/Al2O3 in the presence of H2O2. ► Column experiments were performed to investigate the kinetics of adsorption break through curves.
Adsorptive desulfurization using porous materials is based on the ability of a solid sorbent to selectively adsorb organic sulfur compounds from a refinery stream. In the present study, different sorbents were prepared by varying the Ni/Cu loadings onto ZSM-5 (Si/Al=20) and activated alumina for the removal of sulfur from commercial diesel fuel containing approximately 325ppmw total sulfur (S). To improve the adsorbent efficiency for sulfur removal, hydrogen peroxide was used as an oxidizing agent. The total sulfur in the sample was determined using X-ray fluorescence (XRF) analyzer. Effect of metal loading on sorption performance in the presence of H2O2 oxidant was investigated and compared on the basis of total sulfur removal, sorption capacity and adsorption breakthrough curves. Investigations revealed that sulfur removal strongly depends on the nature of metal, its amount and the nature of the support material. 10% Ni/Al2O3 adsorbent resulted in higher sulfur removal as compared to Ni/ZSM-5 and Cu/Al2O3 adsorbents. More than 90% removal of sulfur was observed with Ni/Al2O3 in presence of H2O2 oxidant. Fixed bed column experiments were carried out using Ni/Al2O3 and the performance of the column break through curves was investigated. Effect of flow rate, bed height and oxidizing agent was investigated in column experiments using 10% Ni/Al2O3. From the analysis of bed depth service time model the values of adsorption capacity and rate constant were found to be 496mgS/kg and 0.006 (mg/kg)−1h−1 respectively.
Supercritical water is a promising medium for the reforming of hydrocarbons and alcohols for the production of hydrogen at high pressures in a short reaction time. Water serves both as a dense ...solvent as well as a reactant. In this work, hydrogen is produced from glycerol by supercritical water reforming over a Ru/Al2O3 catalyst with low methane and carbon monoxide formation. Experiments were conducted in a tubular fixed-bed flow reactor over a temperature range of 700-800 deg C, feed concentrations up to 40 wt% glycerol, all at short reaction time of less than 5 s. Glycerol was completely gasified to hydrogen, carbon dioxide, and methane along with small amounts of carbon monoxide. At dilute feed concentrations, near-theoretical yield of 7 mol of hydrogen/mol of glycerol was obtained, which decreases with an increase in the feed concentration. Based on a kinetic model for glycerol reforming, an activation energy of 55.9 kJ/mol was observed.
Contamination of drinking water due to fluoride is a severe health hazard problem. Excess of fluoride (>1.5
mg/l) in drinking water is harmful to the human health. Various treatment technologies for ...removing fluoride from groundwater have been investigated in the past. Present investigation aims to remove fluoride by activated alumina. Adsorption isotherm has been modeled by Langmuir equation and isotherm constants. The dependence of the adsorption of fluoride on the pH of the solution has been studied to achieve the optimum pH value and a better understanding of the adsorption mechanism. It was found that maximum adsorption takes place at pH value of 7. Breakthrough analysis revealed that early saturation and lower fluoride removal takes place at higher flow rate and at higher concentrations. Predicted simulation results of one-dimensional model for isothermal, axially dispersed fixed bed on the assumption of pore-diffusion rate-control conditions matches with the experimental data in the initial zone of the breakthrough curve, but deviated marginally in the final tailing zone. Bed depth service time (BDST) model was also applied successfully.
The importance of ethyl levulinate (EL) as a fuel additive and a potential biomass-derived platform molecule is noteworthy. EL is obtained from the esterification of levulinic acid (LA) in the ...presence of ethanol. Besides LA, the acid-catalyzed ethanolysis reaction to produce EL can be carried out on a variety of biomass-derived substrates including furfuryl alcohol (FAL), chloromethyl furfural, monosaccharides, polysaccharides and lignocellulosic biomass. The acid catalysts employed for such conversions cover a wide range of structure and properties. The nature of the acid catalysts and the key intermediates formed during the reaction dictate the overall yield of the desired product. For example, in the ethanolysis reaction of FAL to produce EL, diethyl ether (DEE) and ethoxymethylfuran (EMF) produced as side products are suggested to influence the selectivity of EL. Similarly, in the ethanolysis of glucose, formation of ethyl-
d
-glucopyranoside (EDGP) results in a slow conversion to product EL. The review, therefore, focuses on highlighting the importance of catalyst structure, acidity and reaction mechanism and the role of key intermediates in the production of EL from biorenewable resources.
Reaction mechanisms and properties of catalyst materials for the synthesis of ethyl levulinate.
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•An integrated approach for WPCB recycling using pyrolysis and ultrasonication.•Recovery of the metallic fraction is around 90%•Gaseous product obtained mainly consists of H2, CH4, CO ...and CO2.•The first report on the metallic fraction recovery from WPCB using ultrasonication.•Chemical-free recycling of WPCB.
Electronic waste (e-waste) with an annual growth rate of 3–5% is one of the fastest-growing waste streams. The unregulated accumulation and improper recycling can cause grave hazards to human beings and the environment. On the contrary, e-waste can be considered as a secondary source of metals and energy due to its high metal content and polymeric material. Thus, the present study demonstrates technology for the metallic fraction recovery and the production of valuable gases from e-waste. The process involves pyrolysis at a temperature range of 200 °C–600 °C in a fixed bed setup for 10–60 min. Under optimized operating conditions, 35 wt% combustible gases and 60 wt% solid product were obtained at a pyrolysis temperature of 400 °C in 20 min. The gaseous product consisted of CH4, H2, CO and CO2, having the heating value 28 MJ/kg whereas, the solid product is a mixture of metals and other solid residue material. Treatment of the solid product using an ultrasonication process resulted in around 90 wt% recovery of metallic fraction, thereby leaving behind solid residue. Moreover, the transfer of precious metals (Au, Ag, Pd and Pt) was nearly 100% to the metallic fraction. This process combines mild temperature pyrolysis and ultrasonication process to provide a solution for efficient management of e-waste, metallic fraction recovery and valuable gases production.
A state-of-art regional climate modelling system, known as PRECIS (Providing Regional Climates for Impacts Studies) developed by the Hadley Centre for Climate Prediction and Research, is applied for ...India to develop high-resolution climate change scenarios. The presentday simulation (1961–1990) with PRECIS is evaluated, including an examination of the impact of enhanced resolution and an identification of biases. The RCM is able to resolve features on finer scales than those resolved by the GCM, particularly those related to improved resolution of the topography. The most notable advantage of using the RCM is a more realistic representation of the spatial patterns of summer monsoon rainfall such as the maximum along the windward side of the Western Ghats. There are notable quantitative biases in precipitation over some regions, mainly due to similar biases in the driving GCM. PRECIS simulations under scenarios of increasing greenhouse gas concentrations and sulphate aerosols indicate marked increase in both rainfall and temperature towards the end of the 21st century. Surface air temperature and rainfall show similar patterns of projected changes under A2 and B2 scenarios, but the B2 scenario shows slightly lower magnitudes of the projected change. The warming is monotonously widespread over the country, but there are substantial spatial differences in the projected rainfall changes. West central India shows maximum expected increase in rainfall. Extremes in maximum and minimum temperatures are also expected to increase into the future, but the night temperatures are increasing faster than the day temperatures. Extreme precipitation shows substantial increases over a large area, and particularly over the west coast of India and west central India.
An observational evidence of a unique plasma depletion event was captured by an O(1D) 630.0 nm airglow imager on 13 June 2018 over a transition region of geomagnetic low‐mid latitude, Hanle, Leh ...Ladakh, India (32.77°N, 78.97°E; Mlat. ~24.1°N). The observed plasma depletion structures are tilted at an angle of 13° ± 2° west of the geomagnetic north and drifted toward west. Collocated Global Navigation Satellite System‐Total Electron Content measurements confirm that the structures are indeed associated with TEC depletions. Simultaneous ionosonde measurements from Delhi, India (28.70°N, 77.10°E; Mlat. ~20.2°N) shows spread‐F signatures confirming that these structures are associated with the ionospheric irregularities. Interestingly, radar observations over the geomagnetic low‐latitude station Gadanki, India (13.5°N; 79.2°E; Mlat. ~6.5°N) reveal the absence of equatorial plasma bubbles on this night. Therefore, these observations strongly suggest that the observed structures in the airglow images over Hanle are associated with mid‐latitude spread‐F (MSF). These MSF structures are possibly affected by the shear in the zonal plasma drift that forces the field aligned plasma irregularity structures to tilt toward west. These observations, for the first time, bring out the presence of MSF structures over geomagnetic low‐mid latitude transition region. It is suggested that the plasma distribution over low latitudes plays an important role in the occurrence of MSF structures over this transition region. Understanding the source and characteristics of the plasma irregularity structures over this transition region can help in understanding the spatio‐temporal evolution of global L‐band scintillation in a better way.
Plain Language Summary
Understanding the spatio‐temporal distribution of the ionospheric plasma irregularities is important in the operational forecasting of L‐band scintillation and therefore has important ramifications in the satellite‐based communication and navigation systems. Traditionally, plasma irregularities in the low and mid‐latitudes had received focused attentions in the past with very less attention has been paid over the low to mid‐latitude transition region. The present investigation provides an attempt toward that direction and proposes a mechanism on the relationship between the plasma distribution over low latitudes and the occurrence of the mid‐latitude plasma irregularities over the geomagnetic low‐mid latitude transition region. Comprehensive investigations are further needed in the future to understand and characterize the ionospheric plasma irregularity structures over this region.
Key Points
An imaging observational evidence of a unique plasma depletion event was recorded over a transition region of geomagnetic low‐mid latitude
Simultaneous observations from Ionosonde, GNSS‐TEC, and HF radar confirm that the structure is mid‐latitude FAIs with a small westward tilt
The wind in lower thermosphere operated collisional shear instability in mid latitude ionosphere and leads to the tilt in FAIs striation
