Influence of forced air volume on water evaporation during sewage sludge bio-drying

• Temperature, superficial air velocity and evaporation were measured and calculated.
• Peaks of superficial air velocity and evaporation were in the thermophilic phase.
• Air velocity during aeration was 43–100% higher than without aeration.
• Evaporation was significantly dependent on the air volume from day 1 to 15.
• Forced aeration controlled the pile temperature and improved evaporation.

Mechanical aeration is critical to sewage sludge bio-drying, and the actual water loss caused by aeration can be better understood from investigations of the relationship between aeration and water evaporation from the sewage sludge bio-drying pile based on in situ measurements. This study was conducted to investigate the effects of forced air volume on the evaporation of water from a sewage sludge bio-drying pile. Dewatered sewage sludge was bio-dried using control technology for bio-drying, during which time the temperature, superficial air velocity and water evaporation were measured and calculated. The results indicated that the peak air velocity and water evaporation occurred in the thermophilic phase and second temperature-increasing phase, with the highest values of 0.063 ± 0.027 m s−1 and 28.9 kg ton−1 matrix d−1, respectively, being observed on day 4. Air velocity above the pile during aeration was 43–100% higher than when there was no aeration, and there was a significantly positive correlation between air volume and water evaporation from day 1 to 15. The order of daily means of water evaporation was thermophilic phase > second temperature-increasing phase > temperature-increasing phase > cooling phase. Forced aeration controlled the pile temperature and improved evaporation, making it the key factor influencing water loss during the process of sewage sludge bio-drying.

Forced air volume and water evaporation during the process of sewage sludge bio-drying. Temperature-increasing phase: days 1–2, thermophilic phase: days 3–9, second temperature-increasing phase: days 10–15 and cooling phase: days 16–20.Figure optionsDownload high-quality image (102 K)Download as PowerPoint slide