UPTAKE OF ORGANIC-COMPOUNDS FROM AQUEOUS-SOLUTIONS BY SOILS - A COMPARISON OF 2 LAPLACE TRANSFORM INVERSION TECHNIQUES

A general expression for the uptake of organic solutes from aqueous so lutions by soil and sediment pellets in the Laplace domain is presente d. This expression, together with the appropriate macroscopic conserva tion equation and initial and boundary conditions, provides a complete description of the movement and distribution of organic solutes throu gh soil and subsurface systems. To obtain the numerical results for a specific system, the inversion from the Laplace domain into the time d omain is required. In the present work, the use of two techniques, the fast Fourier transforms (FFT) and the Fourier series approximation (F SA), for inverting the Laplace transforms in connection with several p roblems concerning organic solute uptake by soils was explored. The FS A technique was found successful in all cases while the results by the FFT technique were strongly influenced by the selection of the algori thm parameters, In comparison with several numerical techniques for th e direct solution of intraparticle diffusion equations, the FSA techni que was found to have advantages in both accuracy and computational ef ficiency.