In this study, thin layer drying experiments of direct and indirect natural convection solar drying of wastewater sewage sludge in Algeria were conducted. The purpose of these was to analyze the effect of two methods of drying on different parameters, namely: drying rate, efficient diffusion of moisture, and thermodynamic parameters. Three new universal drying kinetic models were proposed and compared with four other models existing in the literature to model the drying process. The effective diffusivity of moisture of sludge (D-eff) changed from 1.91 10(-8) to 9.12 10(-8) m(2) s(-1). It was obtained by using Fick's second law, based on the resolution by Laplace's transformation method and the Fourier series. Thermodynamic parameters, to know, activation energy, free energy change, enthalpy and entropy change, were also determined using a new methodology build on the evolution of effective diffusion coefficient in terms of temperature by adopting the Eyring equation. (C) 2019 Published by Elsevier Ltd.