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

Abstract

Although it is well known that treated sewage effluent enhances trace elements and nutrient solubility in soil solution through their complexation with dissolved organic matter (DOM), no information is available yet for B. The main purpose of this study was to evaluate the effect of DOM with B and native soil organic matter (OM) on B adsorption by soils. Batch equilibrium studies were conducted to measure the B adsorption by DOM (pH 7.7) that was selected from a municipal sewage plant. Effluent DOM was found to have a low affinity for the soils and its application resulted in a release of native soil OM into solution. The OM release was enhanced significantly by an increase in soil mass/solution volume ratio and effluent DOM concentration. The B adsorption capacity of DOM (294–333 mg kg−1) was less than that found for different humic acids (583–2235.6 mg kg−1). Nevertheless, the presence of DOM reduced the free‐B concentration in solution due to formation of B–DOM complexes. As the total DOM concentration increased, the slope of the isotherms for B adsorption by soil decreased. All the B adsorption isotherms obtained for the different DOM concentrations merged into one isotherm, however, when free‐B solution concentration was taken into consideration. The results suggest that the B–DOM complex did not interact with the soil.