text: Solar thermal dryers rely on the collection of the solar thermal energy for drying and pasteurization of fecal sludge. In these systems, the sludge is placed inside an enclosure of transparent or opaque walls, with a ventilation system for moisture evacuation. The sludge can be dried by hot air that was heated by a solar thermal collector (indirect solar dryer), by direct exposure to solar radiation (direct solar dryer), or by both modes (mixed solar dryer).