Phosphate Sorption Characteristics of Soils Treated with Domestic Waste Water

Abstract

AbstractPhosphate sorption capacities of several Connecticut soils having widely different physical and chemical characteristics were determined in the laboratory using dilute P solutions. Sorption capacity was defined as the amount of P sorbed by a soil at equilibrium with a 2 × 10−4M P solution which is approximately the concentration of soluble orthophosphate in domestic waste water. Although sorption capacities of the soils varied over a 4‐fold range, calculations based on these determinations revealed that soils surrounding drainfields of septic tank systems can effectively remove P from waste water for a number of years. Treatment of undisturbed soil cores with simulated waste water for 2 years and determination of P sorption by soils from exhumed septic tank drainfields used up to 15 years substantiate these findings and further show that P moved very slowly in the soil from the source of supply. In addition, soils surrounding the oldest drainfields were not completely saturated with P and retained a portion of their P sorption capacity. These observations led to the hypothesis that P sorption sites in soils are regenerated with time. Regeneration was confirmed in further laboratory experiments. Soils that had been successively treated with P solution, showed reduced P sorption capacity but regained the capacity to sorb P after drying and wetting cycles. Thus, phosphate sorption capacities of soils are greater than simple laboratory determinations indicate.