Phosphate Sorption Characteristics of Soils Treated with Domestic Waste Water
1975
Sawhney, B. L. | Hill, D. E.
Phosphate 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.
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