Aerobically digested sludge from a small wastewater treatment plant was dewatered on five sand drying pilot beds and four small drainage beds. The experiment was conducted in a controlled environment with constant air humidity and temperature. A total of between 147 and 263 kg of a combined biological-chemical sludge was used on each of the sand drying beds. Initial bed total solids (TS) content was 4. 6-5.5 %. Sludge drainage was completed within 28 days, and the thinner sludge layers were drained within 16 days. The sludge evaporation phase, prior to equilibrium with air moisture, lasted a maximum of 84 days and resulted in a final TS content of 88-92 %. The drying time to achieve 30% TS was 35-40 days, depending on initial sludge thickness. Sludge cracking behaviour or rate did not control the drying time at less than 30% TS.
Godkänd; 1993; 20070423 (ysko)