Sewage Sludge Solar Drying Practise and Characteristics Study

The aim of this work consists in investigating the sewage sludge solar drying speed with the objective to find out the natural solar drying application possibilities in different seasons. The sewage sludge samples were drying in a lab greenhouse without active ventilation during summer, autumn and winter and the correlations between drying speed and weather were found out. Furthermore, surface configuration of the sludge layer during solar drying was investigated and it is found that the surface area is only connected to its moisture content whether in summer or in autumn. Investigation found that the sludge layer of 25 mm in thickness decreased its moisture content from 5.16 kg _water/kg _{dry matter} (83.76% by total mass) to 0.78 kg _water/kg dry matter (44% by total mass) after 125 hours even there were rains during the drying process in summer; while in winter time it took almost 23 days for the same drying effect. The surface area was found to change only according to its moisture contents during the drying process. Finally the paper recommends the applicable natural solar drying speed for different seasons.