TABLE OF CONTENTS This category refers to nonmetallic elements such as boron, selenium, arsenic, sodium, sulfur, potassium, and the compounds, oxides, and salts formed from these materials. The major impact of these substances on land treatment is on the vegetative component and on permeability of certain clays due to high sodium concentrations in the wastewater. Some of these elements, such as potassium, are essential plant nutrients; others serve as micronutrients at low concentrations but can be toxic to plants at high levels. At the concentrations found in typical municipal wastewaters none of these materials are likely to be the LDP for process design. One exception, discussed below, might be high salinity in wastewaters applied to the land in relatively arid climates.
Boron is an essential micronutrient for plants but becomes toxic at relatively low concentrations (<1 mg/L) for sensitive plants. The soil has some adsorptive capacity for boron if aluminum and iron oxides are present. The soil reactions are similar to those described previously for phosphorus, but the capacity for boron is low. A conservative design approach assumes that any boron not taken up by the plant is available for percolation to the groundwater. Plant uptake of boron in corn silage of about 0.005 lb/(acre year) and in alfalfa of 0.81 to 1.6 lb/(acre year) have been reported.30 At the SR land treatment site in Mesa, Ariz., the applied municipal effluent had 0.44 mg/L boron, and the groundwater beneath the site contained 0.6 mg/L. At another SR operation at Camarillo,...
