Soil adsorption of humic color

Laboratory studies were conducted on the removal of the characteristic humic color of biologically treated feedlot runoff by adsorption on soil columns. Loading rates ranged from 2.5 to 10.2 cm/day (1 to 4 in./day) on columns 0.92 or 1.83 m (3 to 6 ft) in length. The efficiency of removal was found to be independent of loading rate over the range studied despite evidence of a slow natural process of regeneration. The maximum removals of color and chemical oxygen demand obtained were 99 and 96 percent respectively with the clayey sand studied being found to have an adsorptive capacity of about 2 percent that of the commercially available carbon to which it was compared. The waste was applied at a rate of 5.1 cm/day (2 in./day) to a 1.83 m (6 ft) column for a total period of 6 1/2 months without exhausting the adsorptive capacity of the soil.