Experimental study of sludge drying bed under a Mediterranean climate in Tunisia

The aim of this article is to provide experimental data about sewage sludge drying through a pilot scale drying bed under a Mediterranean climate in the Sahel Region of Tunisia during winter, spring and summer. To achieve a moisture content of 0.15 kg water /kg DS, the drying period of the 2 cm thickness sludge layer was 14 days in winter, 5 days in spring and 4 days in summer. The dry solid content (DS) increased from 4.1 % to 87.25% in winter, 4.8% to 87% in spring and from 4% to 87% in summer. The sludge volume was reduced up to 95 % in the three seasons. The different curves of the moisture and dry solid content evolution were analyzed. The maximum drying rate value observed in spring was 0.38 kg water/ kg DS.h and 0.97 kg water/ kg DS.h in summer. This rate was not calculated in winter because of the moisture content's irregular variation. Concerning the volatile dry solid content, it decreased from 71% to 47% in spring, 84.4% to 51% in summer and from 74 % to 96.8 % in winter. So the drying bed would be able to reduce the vector attraction and stabilize the sludge if the climate was dry (neither humidity nor rain).