Optimization of Ni (II) biosorption from aqueous solution on modified lemon peel.

The valorization of agricultural waste peels as a low-cost biosorbent is a promising approach to water treatment. In this work, the improvement of the adsorption capacity of lemon peel to remove Ni (II) from aqueous effluents was explored using several chemical modifiers: HNO3, HCl, H3PO4, CaCl2, NH3 and NaOH. The surface pretreatment using NaOH was selected as the best option because of the improvement of the maximum adsorption capacity. The maximum adsorption capacity was of 36.74 mg g-1 according to the Langmuir model at optimum conditions (pH = 5, S/L = 5 g L-1, 25 °C). The pseudo-first order model of biosorption kinetics provides the best fit for experimental data. From thermodynamic studies, it was concluded that Ni (II) biosorption by modified lemon peel was endothermic and spontaneous. After five consecutives adsorption-desorption cycles using 0.1 M of HNO3 and H2SO4, a recovery of 90% of Ni (II) was obtained. Regarding characterization of the biosorbent, the surface morphology was studied by Scanning Electron Microscopy while the functional groups responsible for Ni (II) adsorption were evaluated by Fourier transform infrared spectroscopy.

Kinetics of the chemical reduction of nitrate by zero-valent iron.

The use of reactive barriers is one of the preferred remediation technologies for the remediation of groundwater contamination. An adequate design of these barriers requires the understanding of the kinetics of the reaction between the target contaminant and the solid phase in the barrier. A study of the kinetics between metallic iron and aqueous nitrate is presented in this paper. Published literature regarding this reaction indicates that researchers are far from a consensus about the mechanism of this reaction. This paper presents the results obtained from experiments performed at different constant pH values and iron dosages, together with a mathematical analysis of the kinetic results. We have found that an Eley-Rideal kinetic model yields a good explanation of the relatively complicated dependence between rate of nitrate reduction and the pH value of the solution.

Biomethanization of mixtures of fruits and vegetables solid wastes and sludge from a municipal wastewater treatment plant.

The possible management of Fruit and Vegetable Solid Wastes (FVSWs) through their simultaneous digestion with the primary sludge of Municipal Wastewater Treatment plants is investigated. This alternative allows the recovery of energy and a solid product that can be used as an amendment for soils that generated the residue, while is not expensive. Results indicate that the ratio of FVSWs to sludge and the pH control are the main variables determining the methane production and concentration. NaHCO3 was selected to achieve the pH control. The results for a ratio of 50% sludge together with 10 g NaHCO3/kg of residue are among the best obtained, with a methane yield of about 90 L per kg of volatile solids, and a methane concentration of 40% (v/v) of the biogas. A 50% reduction of the total solids; 21% reduction of the volatile solids (in terms of total solids); and a pH value of the sludge, which is 6.9 indicate that the digested sludge can be a good material for soil amendment.

A column study of soil contamination by lead: influence of pH and carbonate content. II. Mathematical model.

A mathematical model is used for the interpretation of the results from earlier experimental studies in lab-scale columns on the contamination of a carbonatic soil with lead. Local equilibrium conditions suffice to reproduce the experimental curves for every pH value of the influent contaminant solution and carbonate content of the soils essayed, but heterogeneous contact between the aqueous and solid phase should be included. This heterogeneous contact is responsible for the important tailing effects observed, and is difficult to estimate even for the lab conditions. Then, important uncertainties should be accepted both for risk assessment and in situ remediation feasibility studies.

A column study of soil contamination by lead: influence of pH and carbonate content. I. Experimental results.

The influence of soil carbonate content on the fate of lead in soil was studied in a lab-scale column under different pH values of the contaminant solution. Results indicated that retention of this toxic heavy metal (up to 38% weight at pH = 5) occurred which was proportional to the total carbonate content. A decrease in the pH of the aqueous solution entering the column resulted in a decrease of the retention of lead in the soil. Furthermore, the concentration of lead in the effluent was increased dramatically. Concentrations of lead about 2.5 times higher than in the contaminant solution were measured at pH = 3. Knowledge of these phenomena is important for risk assessment and remediation feasibility studies.

Column study of the influence of air humidity on the retention of hydrocarbons on soil.

Inverse gas chromatography (IGC) is used for the analysis of the influence of air relative humidity on the retention of hexane, benzene, toluene and p-xylene in a sandy soil under experimental conditions similar to those typical of soil vapor extraction (SVE). The advantages of IGC over other techniques, are (a) an efficient use of lab resources, (b) a high sensitivity to low partitioning coefficients and (c) a closer reproduction of field conditions. In our procedure, experiments with only two samples of different mass are necessary to establish if linear isotherms can be used to describe the retention of the contaminants. This approach gives information necessary for analyzing the feasibility and design of remediation technologies with a laboratory effort significantly smaller than the adsorption/desorption cycle for isotherm determination. The retention coefficients of the contaminants decrease as humidity increases in a similar fashion for all of them, probably because the reduction in the number of the adsorption sites available for the organic compounds due to the presence of water is quite similar for all the contaminants studied. These retention coefficients may be related to those obtained for dry air conditions for all the contaminants through (R - 1)RH% = A(R - 1)dry air(B), where the parameter B is found to remain approximately constant (0.90), while the parameter A decreases linearly with the relative moisture.

Cleanup of fractured rock aquifers. II. Effects of matrix diffusion and nonaqueous phase liquid.

Model calculations are used to explore the effects of the kinetics of diffusion of dissolved organic compounds into and out of low-permeability porous materials and of the rate of solution of nonaqueous phase liquid (NAPL) droplets (into the aqueous phase) on the rate of cleanup of contaminated aquifers. Two models are presented: (1) the flushing of organic compounds initially distributed as NAPL droplets in a fracture in a porous rock aquifer, and (2) the removal of organic compounds initially present as NAPL in an aquifer containing low-permeability porous clay lenses. NAPL droplet size is found to be of much less importance than the spacing of the fractures in the porous rock in the first model or the thickness of the clay lenses in the second.

A model with mass transport limitations for pump and treat remediation of soils polluted with NAPL.

A model is presented for the description of the pump and treat (or flushing) remediation of the saturated zone with non-aqueous phase liquid (NAPL) present as droplets. Sensitivity analysis shows that the most important variables are the NAPL droplet size and the distance through which the dissolved organic compound must diffuse to reach the advecting aqueous phase. The time needed to achieve complete remediation for different initial contaminant concentrations in soil depends more on the NAPL droplet radius and the size of the stagnant boundary layer than on the initial contaminant mass itself. Location of wells and flux rates are of little significance over the time needed for completion as long as all the water that flows through the contaminated region is captured in the recovery well.