Unsaturated Flow Drying Bed (UFDB) principles are based on the ones of wastewater treatment by infiltration-percolation on the one hand and septic tanks sludge solar-drying beds on the other hand. With UFDB, sludge charges are split with low heights, leading to the drying of suspended solids in 2 days, and the infiltration of the flow of liquid in unsaturated middle. For average charges reaching 12.5 cm/d, the treatment efficiency of total oxygen demand and Total Kjeldahl Nitrogen, respectively 95 and 96%, correspond to a treatment capacity of 0.5 kg of O₂/d/m² of drying area. Bacteria reductions of 4 Ulog are obtained from filtrates outlet, with average fecal coliforms charges less than 103 CFU/100 ml. Monitoring the hydrodynamic behavior through rates, moisture, organic matter and respiratory activity demonstrates that the clogging of the massifs is linked to a biofilm growth within them. A four week resting period allows biofilm resorption. Thus, the drying of the infiltration surface in two days, the elimination of carbon, nitrogen and bacterial pollutions, as well as the reversibility of clogging show that UFDB is a credible alternative for the treatment of septic tank sludge in the socio-economic context and climate of tropical Africa.