Mathematical evaluation of activated carbon adsorption for surfactant recovery in a soil washing process

The performances of various soil washing processes, including surfactant recovery by selective adsorption, were evaluated using a mathematical model for partitioning a target compound and surfactant in water/sorbent system. Phenanthrene was selected as a representative hazardous organic compound and Triton X-100 as a surfactant. Two activated carbons that differed in size (Darco 20-40 mesh and >100 mesh sizes) were used in adsorption experiments. The adsorption isotherms of the chemicals were used in model simulations for various washing scenarios. The optimal process conditions were suggested to minimize the dosage of activated carbon and surfactant and the number of washings. We estimated that the requirement of surfactant could be reduced to 33% of surfactant requirements (from 265 to 86.6 g) with a reuse step using 9.1 g activated carbon (>100 mesh) to achieve 90% removal of phenanthrene (initially 100 mg kg-soil^-1) with a water/soil ratio of 10.