S.N. Das

Removal of Cr(VI) by thermally activated weed Salvinia cucullata in a fixed-bed column

The present study evaluates the feasibility of using a thermally activated fresh water weed in removing Cr(VI) from wastewater through column studies. The effect of flow rate, bed height and Cr(VI) concentration of the feed solution on the adsorption capacity of the activated weed was investigated. The adsorption capacity increased with decrease in both flow rate and bed height but increased with an increase in initial adsorbate concentration. Four different kinetic models, such as. Adams-Bohart, Bed Depth Service Time (BDST), Thomas and Yoon-Nelson models were first applied to the experimental data to predict the breakthrough curve and to determine the characteristic parameters of the column useful for designing large-scale column studies. Different statistical methods such as Sum of the Square of the Error (SSE), Sum of the Absolute Error (SAE), Average Relative Error (ARE), Average Relative Standard Error (ARS) and regression coefficient, were applied to evaluate the prominent and unique characteristic features of the experimental and predicted parameters under the respective models to find out the best fit. The performance stability of the adsorbent was tested by continuous adsorption-desorption studies.

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.

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.

Emission of N2O from farmer's field during black gram cultivation and incubation experiments in laboratory

N2O emission was measured during the cultivation of black gram in an upland farmers field following traditional agricultural practices. The land is exclusively used for the cultivation of black gram without using chemical or organic fertilizers. The N2O flux increased appreciably during rain and flowering stages. The N2O emission was found to correlate well with soil carbon (C) and among the parameters studied. The diurnal measurements showed that N2O emission increased with an increase of ambient temperature, i.e., during day time. The seasonally integrated flux (SIF) was found to be 8.26 ±0.19 g ha−1, which is much lower compared to the reported values due to lower soil C and N. Incubation experiments were carried out in the laboratory taking the same soil collected up to a depth of ∼30 cm. Two principal soil parameters, such as soil N content in the form of externally added urea and water filled pore space (WFPS) were varied for incubation experiments. In both the cases, the emission of N2O increased with the increase of these two variables. The rate kinetic equations were derived using both the variables. Some experiments were carried out in the presence and absence of C2H2, a known inhibitor, to evaluate the extent of reduction of N2O to N2. Statistical analysis showed the direct correlation of soil C and moisture to N2O emission.

Assessment of methane from agricultural field during the entire paddy cropping seasons – a case study

A systematic effort was made to assess the emission of methane from paddy fields using closed chamber technique. Methane emission measurements were performed over a year during the Kharif (wet season), Rabi (dry season), and fallow periods. Various soil parameters like redox potential, organic carbon and ferrous ion were determined to evaluate their control on methane emissions. Diurnal measurement of the flux showed a minimum (0.44 mg m−2 h−1) in the morning (8 a.m.), which increased gradually to a value of 1.16 mg m−2 h−1 till the evening due to the rise in soil temperature. The seasonally integrated flux (E SIF) for CH4 was calculated. The E SIF for methane during Kharif and Rabi crops were found to be 5.97 g m−2 and 2.59 g m−2, respectively. It was observed that the methane flux was maximum during flowering and fertilizer application stages for both paddy cropping seasons. The redox potential was low and the ferrous ion was higher during flowering and tiller stages. The methane emission was higher at <−200 mV redox potential values. Based on the emission data obtained from the cropping and fallow period measurements, an annually integrated flux (E AIF) was calculated for methane to make a budget estimate of methane emission from rice cultivated under rain fed drought prone water regime.