Synergistic action of adsorption and reductive properties of ash derived from distilled Mentha piperita plant waste in removal of Cr(VI) from aqueous solution.

Adsorption behavior of Mentha Plant Ash (MPA) in removal of Cr(VI) from aqueous solution was analyzed as a function of different pH (3.0-8.0), different concentration of Cr(VI) (10-50 mg L-1), contact time (0-90 min) and doses of adsorbent (0.1-0.5 g/100 mL). Adsorption of Cr(VI) onto MPA was found to be dependent on pH condition of the solution and showed maximum removal of Cr(VI) at pH 3.0. The study of adsorption kinetics on Cr(VI) removal by MPA showed that pseudo-second order kinetic model was more suitable to describe the Cr(VI) removal by adsorption onto MPA. Results on Cyclic Voltammetry study of MPA treated with Cr(VI) solution revealed the reduction of Cr(VI) to Cr(III) and Cr(II) by MPA particles through multi-step electron transfer reactions. A combined effect of adsorption and reduction properties of MPA was particularly responsible for removal and transformation of Cr(VI). These attributes of MPA were contributed by many active Cr(VI) binding and electron donating ligands present on the MPA surface as evident from FTIR and XPS analysis of MPA.

Decolourization of malachite green dye by mentha plant biochar (MPB): a combined action of adsorption and electrochemical reduction processes.

Adsorption behavior of mentha (mint) plant biochar (MPB) in removal of malachite green (MG) dye from aqueous solution was analyzed as a function of different pH (4.0-10.0), initial dye concentration (20-100 mg/L), contact time (0-45 min) and dose of adsorbent (0.05-0.3 g/100 mL). The zeta potential of the MPB particles was found to be -37.9 mV, indicating a negatively charged sorption surface of MPB particles. MPB was found to be more effective in removal of MG dye at pH 6.0 due to combined action of physico-chemisorption and a reductive electron transfer reaction. Results on the Brunauer-Emmett-Teller (BET) analysis of the N2 adsorption-desorption isotherm of MPB as adsorbent showed sigmoidal shape similar to the type IV isotherm and mesoporous nature. The cyclic voltammetric analysis of MG dye showed a reversible, coupled redox reaction at the interface of dye molecules and MPB particles. The maximum monolayer adsorption capacity (qmax) of MPB was found to be 322.58 mg g-1. The separation factor (RL) value was between 0 and 1, indicating a favourable adsorption of MG dye onto MPB. The results fitted well to a pseudo-second-order kinetic model. Further results from desorption experiments showed recovery of MG dye by about 50% in the presence of 1 N HCl.

Preparation, characterization and agri applications of biochar produced by pyrolysis of sewage sludge at different temperatures.

Sewage sludge (SS) is an abundantly available feedstock, which is generally considered as potential threat to human health and environment. Its utilization in any process would be of great help for environmental sustainability. Accordingly, this work aimed to prepare and characterize the sewage sludge biochar (SSB) at temperatures, i.e. (500, 450, 400, and 350 °C), and further analyze the available nutrients and contaminants as well as agri application potential. The results indicated that the total nitrogen (TN), electrical conductivity (EC), and total organic carbon (TOC) content in SSBs decreased with increasing pyrolysis temperature. The overall concentration of polycyclic aromatic hydrocarbons (PAHs) in SSBs was substantially lower (1.8-9.7-fold depending on pyrolysis temperature) than in SS. Pyrolysis of SS enriched the heavy metals content in SSBs and the relative enrichment factor (RE) factor varied between 1.1 and 2.1 depending on the pyrolysis temperature. Furthermore, compared to SS, the leaching rate of heavy metals was significantly decreased in SSBs (1.1-100-fold depending on the pyrolysis temperature) and the pyrolysis temperature of 400-450 °C prevented the Ni, Pb, Cr, and Zn leaching in SSB. The total PAH and heavy metals content in biochars were below the control standard for land application. Finally, testing of the growth-promoting effect of biochar extracts on fenugreek plants revealed that SSB prepared at 350 °C significantly stimulated the root and shoot length of 5-days old seedlings. This study provides important data for potential environmental risks of SSB applications.