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Title: Effect of dissolved organic carbon in recycled wastewaters on boron adsorption by soils

Author
item GOLDBERG, SABINE - Retired ARS Employee
item Suarez, Donald

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2017
Publication Date: 3/1/2017
Citation: Goldberg, S., Suarez, D.L. 2017. Effect of dissolved organic carbon in recycled wastewaters on boron adsorption by soils. Soil Science. 182(3):94-100. doi: 10.1097/SS.0000000000000199.

Interpretive Summary: Boron is a nutrient ion that is toxic to plants at elevated concentrations. Elevated boron and dissolved organic carbon concentrations can occur in recycled municipal wastewaters that are being used as water resources for irrigation. A better understanding of the adsorption behavior of boron on soils in the presence and absence of dissolved organic carbon is necessary to evaluate whether applications of recycled municipal wastewaters will cause a boron toxicity problem due to their dissolved organic carbon content. Boron adsorption on soils was investigated using synthetic wastewater and recycled wastewater. The magnitude of boron adsorption as a function of solution pH and equilibrium solution boron concentration was unaffected by the presence of dissolved organic carbon in recycled wastewaters. This result indicates that the treated recycled wastewaters, due to their low dissolved organic carbon contents, will not affect boron adsorption behavior of soils when used for landscape irrigation.These findings are of interest to wastewater treatment managers, irrigation specialist and consultants, and producers using wastewater for irrigation.

Technical Abstract: In areas of water scarcity, recycled municipal wastewaters are being used as water resources for non-potable applications, especially for irrigation. Such wastewaters often contain elevated levels of dissolved organic carbon (DOC) and solution boron (B). Boron adsorption was investigated on eight arid-zone soils from California and one from Arizona as a function equilibrium B concentration (0-100 mg L-1) and solution pH (4-10). The B equilibrating solutions were prepared using either recycled wastewaters or synthetic wastewaters with DOC up to 10 mg L-1. The synthetic wastewaters were synthesized to have the same chemical composition as the recycled wastewaters but contained no DOC. Boron adsorption on the soils increased with increasing solution pH, reaching an absorption peak near pH 9, and then decreased with further increases in solution pH. The pH dependent amounts of B adsorption were not statistically significantly different at the 95% level of confidence for both types of waters. For all soils, B adsorption as a function of solution B concentration conformed to the Langmuir adsorption isotherm equation. Boron adsorption maxima, obtained using the Langmuir isotherm, were not statistically significantly different at the 95% confidence level for both types of waters. The constant capacitance surface complexation model was able to predict B adsorption as a function of solution pH using the soil chemical properties: aluminum oxide, inorganic carbon, organic carbon contents and surface area. The magnitude of B adsorption as a function of solution pH and equilibrium solution B concentration was unaffected by the presence of DOC in the recycled wastewaters. This result indicates that the treated recycled wastewaters, due to their low DOC contents, will not affect B adsorption behavior of soils when used for irrigation of crops and landscape vegetation.