Multivariable modeling, optimization and experimental study of Cr(VI) removal from aqueous solution using peanut shell biochar.

Peanut shell biomass was selected and utilized to produce biochar through pyrolysis under N2 atmosphere at 923 K. After studying various effects of experimental parameters and by statistical modeling and optimization by RSM using Box-Benken design, optimized conditions of pH 2.0 ± 0.1, temperature 303 K, and adsorbent dose used of 2.5 g L-1 were obtained giving almost 99.99% removal for Cr(VI) from the solution. FESEM, FTIR, XRD, XPS, EDX, elemental mapping, and pHzpc were used for the evaluation of the surface characteristics of peanut shell biochar (PSB). Studies revealed C-O, C-H, CO, and O-H functional groups' presence with the help of FTIR, majorly in control of adsorption mechanism and the EDX confirmed the presence of Cr(VI) onto peanut shell biochar (PSB). Further adsorption mechanism for Cr(VI) adsorption followed the pseudo-second-order rate with adsorption capacity of 29.38 mg g-1 given by the Langmuir isotherm. The thermodynamic study confirmed the exothermic and spontaneous nature of the process for Cr(VI) adsorption onto PSB. The adsorption mechanism showed electrostatic attraction, reduction, and complexation mainly responsible for Cr(VI) adsorption by PSB. Thus, PSB effectively removes Cr(VI) is confirmed by the present study.

Characterization of organophosphate pesticide sorption of potato peel biochar as low cost adsorbent for chlorpyrifos removal.

There has been a growing interest in the scientific world in the production of biochar from natural organic wastes as potential sustainable precursors for bioremediation. Potato peel biochar was produced by slow pyrolysis method under oxygen-limited conditions and used as bio adsorbent in bioremediation of commercial pesticide having Chlorpyrifos as an active component. Chlorpyrifos is an organophosphate pesticide, highly neurotoxic, and primarily targets the central nervous system of pests and insects. The excess residues of chlorpyrifos are hazardous to environmental flora and fauna. Chlorpyrifos was treated against biochar at varying physical parameters and further optimized by using response surface methodology through Box-Behnken design (BBD). 72.06% of pesticide removal was observed post 24 h of treatment against a pesticide concentration of 1346.85 µg/ml with a biochar concentration of 1.04 mg/ml under room temperature at pH 5.04. Biochar was characterized by proximate and ultimate analysis, FTIR, and SEM-EDX. Characterization by SEM-EDX showed the surface morphology and minerals on the peel and biochar. Microgram of potato peel shows pores of larger size than biochar having many cavities with different dimensions. In the plant system, growth morphology, nutritional status, polyphenols, total antioxidant content, and free radical scavenging activity were assessed. Enhancement in presence of biochar was recorded in growth morphology and plant biomolecules including photosynthetic pigments. Better translocation of the nutrient is recorded in biochar treated plants, as evidenced by the low amount of carbohydrate and protein in treated leaves. Biocompatibility assessment of chlorpyriphos in fish erythrocytes showed 43.26% hemolysis by pesticide-treated biochar. The practical use of this approach can also be best utilized if applied to those geographical regions where the soil pH is acidic. Biochar is a marketable bio-product, which can have a positive impact in agriculture, industries, and the energy sector creating a bio-based economy with reduced environmental pollution.

Novel green strategy for CuO-ZnO-C nanocomposites fabrication using marigold (Tagetes spp.) flower petals extract with and without CTAB treatment for adsorption of Cr(VI) and Congo red dye.

The CuO-ZnO-Carbon (CZC) nanocomposites (NCs) were synthesized via a green method at 300 and 400 °C calcinated temperatures, using waste marigold (Tagetes spp.) flower petal extract as a reducing agent and carbon source. A novel green strategy for the synthesis of highly effective CZC NCs was developed which showed better adsorption of toxic Cr(VI) and Congo red (CR) dye compared to unsupported carbon NCs. In this strategy, fine powder of petals as carbon source were passed with the flower liquid extract during the filtration process, which supported the metal oxides nanorods(NRs)/nanoparticles(NPs) on the surface. Furthermore, the surface of the synthesized NCs was modified by Cetyl Trimethyl Ammonium Bromide (CTAB) cationic surfactant to increase surface functionality, surface area, and positive charge density of NCs. Additionally, the adsorption performance of Cr(VI) and CR dye improved from acidic pH to neutral pH after surfactant modification of NCs compared to unmodified NCs. The characterization techniques such as Powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) surface area analysis, Point of zero charge (pHpzc), Field Emission Scanning Electron Microscopy (FE-SEM), Transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were performed to examine physio-chemical properties of NCs and CTAB modified NCs. The FTIR and BET analysis confirmed that CTAB modified NCs showed excellent functionality and more than 49% and ~67% greater surface area than CZC-300 and CZC-400, respectively, which prepared at 300 and 400 °C temperature. XRD analysis confirmed that NCs were highly crystalline and no phase change after surfactant modification. The FE-SEM and TEM analysis confirmed the pentagonal NRs and spherical NPs of ZnO and CuO, respectively, were formed on the carbon surface. After CTAB modification, no change in the surface morphology of NCs was observed. Thus, comparative study of NCs and CTAB modified NCs was done for Cr(VI) and CR dye adsorption by varying batch conditions, such as initial pH, contact time, temperature, and initial concentration of Cr(VI)/CR dye. The equilibrium time and concentration data were fitted with non-linear forms of kinetic and isotherm models, respectively. CTAB modified CZC-300 NCs showed excellent adsorption capacity for both pollutants up to pH 6 compared to CZC-300 and CZC-400 NCs. Additionally, the maximum adsorption capacity of CTAB modified NCs for Cr(VI) and CR dye were 201.56 and 331.36 mg/g, respectively, at pH 2 and 30 °C and increased with increasing temperature. The effect of co-existing anions on adsorption capacity of both NCs for Cr(VI) and CR dye adsorption was investigated. The regeneration and reusability experiments of both NCs were also performed.

A fixed bed column study of natural and chemically modified Lagerstroemia speciosa bark for removal of synthetic Cr(VI) ions from aqueous solution.

The present study evaluates the feasibility of using natural Lagerstroemia speciosa bark (NLSB) and chemically modified Lagerstroemia speciosa bark (CLSB) in removing Cr(VI) from aqueous solution in fixed bed column process. The effect of influent flow rate, bed depth and inlet Cr(VI) ion concentration on the Cr(VI) removal capacity of NLSB and CLSB was investigated. The column exhaustion time increased with increase in bed depth and reverse trend was obtained with increase in flow rate and influent Cr(VI) ion concentration. The Bohart-Adams, Thomas and Yoon-Nelson dynamic models were applied at various studied experimental conditions to predict the breakthrough curve behavior and to determine the characteristics fixed bed column parameters that are very crucial in scale up of the column process for its industrial scale application. Both Thomas and Yoon-Nelson models showed very good agreement with the column data and explained the mechanism of Cr(VI) adsorption by NLSB and CLSB in column process. The high Cr(VI) adsorption capacity and regeneration efficiency of NLSB and CLSB in column suggest its applicability in removal of Cr(VI) present in industrial effluents.

Study of biological and thermo-chemical pretreatment of organic fraction of municipal solid waste for enhanced biogas yield.

Biogas production from organic fraction of municipal solid waste (OFMSW) not only helps in solid waste management but also combat the food vs fuel dilemma. The presence of lignocellulosic material and other complex compounds in OFMSW hinder biogas production. Therefore, pretreatment is an essential step to increase the hydrolysis rate by converting complex compounds to simpler ones. This work was aimed at effective pretreatment of OFMSW by biological and thermo-chemical means. For biological pretreatment lignin degrading fungal strains, Phanerochaete chrysosporium and Pleurotus ostreatus were employed. Thermo-chemical treatment resulted in higher solubilisation yield in terms of sCOD and VFA making it a more effective method as compared with biological pretreatment. The optimisation of thermo-chemical pretreatment was done by the Box-Behnken design of response surface methodology (RSM). The interactive effect of influencing factors NaOH dose, temperature and time were studied on the response of sCOD, VFA and phenolic content. The sCOD and VFA values were significantly increased by increasing the NaOH concentration, temperature and time to a certain limit. The optimised condition from RSM for maximum solubilisation yield in terms of sCOD, VFA and phenolic content was found to be NaOH dose of 4.72 g/L, temperature 180 °C and time 30.3 min. Biogas production was increased by 169.5% after pretreatment at RSM optimised conditions as compared with untreated OFMSW.

Correction to: Study of biological and thermo-chemical pretreatment of organic fraction of municipal solid waste for enhanced biogas yield.

The original publication of this paper contains an error.

Experimental process parameters optimization and in-depth product characterizations for teak sawdust pyrolysis.

Pyrolysis is an efficient thermochemical route to obtain biofuels in the form of bio-oil, biochar and pyrolytic gas from the processing of biomass. Pyrolysis experiments were performed with teak sawdust to determine the yield and main characteristics of solid, liquid and gaseous products. Experiments were carried out in the temperature range of 400-700 °C in 100 °C intervals, nitrogen flow rate of 150-250 mL/min, packed bed height in between 2 and 8 cm and particle size in between 0.18 and 0.60 mm. The maximum bio-oil and biochar yield were observed at 600 °C (48.8%) and 400 °C (37.42%), respectively. Physical properties (viscosity, density, carbon residue, pH and HHV) of bio-oil were determined and the chemical properties were investigated using FTIR and GC-MS. Further, biochar was characterized with proximate, ultimate, HHV, FTIR, SEM-EDX, BET surface area and XRD analysis. Non-condensable gases coming out during pyrolysis were analyzed using gas chromatography and amount of H2, CH4, CO and CO2 were determined. According to characterization results, bio-oil can be used as biofuel after up gradation or as source of valuable chemicals, biochar can be utilized as solid fuel or seems to be suitable in waste stream purification as it has very high BET surface area. In addition, pyrolytic gases have significant amount of methane and hydrogen that provides good combustion properties.

Pretreatment optimisation and kinetics of batch anaerobic digestion of liquidised OFMSW treated with NaOH: Models verification with experimental data.

The enormous generation of municipal solid waste (MSW) due to increased urbanization is causing threat to the environment. MSW is a mixed waste and it comprises of organic fraction as the key fraction called organic fraction of municipal solid waste (OFMSW) along with other fractions. The pretreatment of OFMSW is necessary step to increase the biogas yield. In the present work, NaOH hydrolysis of mechanically liquidised OFMSW was carried out to reduce its complexity and improve the biogas production. Furthermore, hydrolysis parameters were optimised by RSM model for NaOH pretreatment. Optimised conditions achieved from RSM analysis were 0.46 N NaOH loading, 72 h reaction time and 36.05 °C operating temperature. The RSM predicted values of response sCOD and VFA at optimum condition were in good agreement with experimental data signifying the model adequacy. The kinetic of batch anaerobic digestion of OFMSW treated with NaOH at different concentrations and optimised condition had been studied to see the suitability of first order model and modified Gompartz model. The experimental results obtained were best fitted using normalized root mean square error analysis. Biogas production after pretreatment at 0.1, 0.5, 0.9 N NaOH concentration and RSM optimised condition was 369.24, 435.24, 327.84 and 465.67 NL/kg VS, respectively.

Synthesis, characterization and application of Lagerstroemia speciosa embedded magnetic nanoparticle for Cr(VI) adsorption from aqueous solution.

Lagerstroemia speciosa bark (LB) embedded magnetic nanoparticles were prepared by co-precipitation of Fe2+ and Fe3+ salt solution with ammonia and LB for Cr(VI) removal from aqueous solution. The native LB, magnetic nanoparticle (MNP), L. speciosa embedded magnetic nanoparticle (MNPLB) and Cr(VI) adsorbed MNPLB particles were characterized by SEM-EDX, TEM, BET-surface area, FT-IR, XRD and TGA methods. TEM analysis confirmed nearly spherical shape of MNP with an average diameter of 8.76nm and the surface modification did not result in the phase change of MNP as established by XRD analysis, while led to the formation of secondary particles of MNPLB with diameter of 18.54nm. Characterization results revealed covalent binding between the hydroxyl group of MNP and carboxyl group of LB particles and further confirmed its physico-chemical nature favorable for Cr(VI) adsorption. The Cr(VI) adsorption on to MNPLB particle as an adsorbent was tested under different contact time, initial Cr(VI) concentration, adsorbent dose, initial pH, temperature and agitation speed. The results of the equilibrium and kinetics of adsorption were well described by Langmuir isotherm and pseudo-second-order model, respectively. The thermodynamic parameters suggest spontaneous and endothermic nature of Cr(VI) adsorption onto MNPLB. The maximum adsorption capacity for MNPLB was calculated to be 434.78mg/g and these particles even after Cr(VI) adsorption were collected effortlessly from the aqueous solution by a magnet. The desorption of Cr(VI)-adsorbed MNPLB was found to be more than 93.72% with spent MNPLB depicting eleven successive adsorption-desorption cycles.

A comprehensive review on removal of arsenic using activated carbon prepared from easily available waste materials.

Arsenic contamination in water bodies is a serious problem and causes various health problems due to which US Environment Protection Agency (USEPA) set its maximum permissible limit of 10 ppb. The present review article starts with the removal of toxic arsenic using adsorbents prepared from easily available waste materials. Adsorbent either commercial or low-cost adsorbent can be used for arsenic removal but recent research was focused on the low-cost adsorbent. Preparation and activation of various adsorbents were discussed. Adsorption capacities, surface area, thermodynamic, and kinetics data of various adsorbents for As(III) and As(V) removal were compiled. Desorption followed by regeneration and reuse of adsorbents is an important step in adsorption and leads to economical process. Various desorbing and regenerating agents were discussed for arsenic decontamination from the adsorbent surface. Strong acids, bases, and salts are the main desorbing agents. Disposal of arsenic-contaminated adsorbent and arsenic waste was also a big problem because of the toxic and leaching effect of arsenic. So, arsenic waste was disposed of by proper stabilization/solidification (S/S) technique by mixing it in Portland cement, iron, ash, etc. to reduce the leaching effect.