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Boron Adsorption by Soils as affected by Dissolved Organic Matter from Treated Sewage Effluent

Institute of Soil, Water and Environmental Sci., the Volcani Center, Agricultural Research Organization (ARO), P.O. Box 6, Bet Dagan 50250, Israel

View larger version (24K): [in this window] [in a new window]   Fig. 1. Schematic representation of the interactions between B, dissolved organic matter (DOM), and soil. The presence of DOM in soil solution leads to formation of nonadsorbed B–DOM complexes. Adsorption of free B and DOM occurs on different soil sites (i.e., with no competition) but a surface-linked DOM is considered as a potential sorbent for B. The DOM–soil interaction results in adsorption of DOM by soil or in release of native organic matter to soil solution.

View larger version (12K): [in this window] [in a new window]   Fig. 2. Boron concentration adsorbed on the flocculated dissolved organic matter (DOM) from sewage as a function of aqueous B concentration (Langmuir adsorption isotherm) at pH = 7.7 and at 24 ± 2°C. The symbols represent the experimental data. Errors bars take into account an uncertainty in B chemical analysis. The dashed lines were calculated using the Langmuir equation (Eq. [10]) and the DOM adsorption capacity for B, bmDOM, and the DOM affinity for B, kB-DOM, of Table 3.

View larger version (14K): [in this window] [in a new window]   Fig. 3. Concentration of dissolved organic matter (DOM) as organic C (OC) released from whole loamy sand and sandy loam soils by background solution (Na adsorption ratio = 5.0, pH = 7.7). The symbols represent the experimental data. The dashed lines represent fitting Eq. [12] to the data to obtain the DOM–soil distribution coefficient kDOM and initial reactive soil pool SDOM values given in Table 4. The solid line was calculated using Eq. [9] and kDOM value of Table 4.

View larger version (21K): [in this window] [in a new window]   Fig. 4. Amount of dissolved organic matter (DOM) released from whole loamy sand and sandy loam soils as a function of DOM concentration as organic C (OC) for (a) DOM-1 and (b) DOM-2 effluents, and and linear regression (Eq. [13]) of relative DOM concentration (CDOM/CDOM0) vs. soil mass/solution volume ratio (ms/vs) for (c) DOM-1 and (d) DOM-2 effluents. The slope () and the intercept (m) values of linear regressions are given in Table 5. Errors bars indicate standard deviations in DOM analysis.

View larger version (15K): [in this window] [in a new window]   Fig. 5. Representative isotherms for dissolved organic matter (DOM) adsorption by the loamy sand and sandy loam soils leached with the background solution (Na adsorption ratio = 5.0, pH = 7.7). The symbols represent the experimental data. The solid line was calculated using Eq. [16] and the DOM–soil distribution coefficient values, kDOM, given in Table 4 for DOM adsorption. Error bars indicate standard deviations in DOM analysis.

View larger version (16K): [in this window] [in a new window]   Fig. 6. Boron adsorption isotherm for the loamy sand soil at different dissolved organic matter (DOM) concentrations: (a) adsorbed B vs. total B solution concentration and (b) adsorbed B vs. free-B concentration in solution. The symbols represent the experimental data. Errors bars indicate standard deviations. The lines were calculated using Eq. [17] and [18] and the adsorption coefficients bm, kB, and EB-DOM of Table 6.

View larger version (18K): [in this window] [in a new window]   Fig. 7. Boron adsorption isotherm for the sandy loam soil at different dissolved organic matter (DOM) concentrations: (a) adsorbed B vs. total B solution concentration and (b) adsorbed B vs. free-B concentration in solution. The symbols represent the experimental data. Errors bars indicate standard deviations. The lines were calculated using Eq. [17] and [18] and the soil adsorption capacity for B, bm, the B affinity coefficient, kB, and the B–DOM complexation coefficient, EB-DOM, of Table 6.