Response Surface Methodological Approach for the Assessment of Thermal Drying of Dewatered Municipal Sludge

Abstract

Thermal drying of dewatered municipal sludge was studied in the temperature range 50–180°C for different times from 10 to 120 min. The Box–Wilson response surface experimental method was used to investigate the effects of temperature and time on sludge drying. Statistical analysis using the methodology was employed to determine the response function coefficients for each variable: temperature and time. The response functions of the study were dry solids (DS) content, volatile solids (VS) content, and low heating value (LHV). Experimental and predicted results from the model indicated excellent agreements. Higher drying temperatures and time led to higher DS content. Higher temperatures increase the drying kinetics and longer drying times allow more time for water to evaporate. The elevated temperatures and time did not drastically change the VS content values. Only small-scale changes were observed regarding the increases in temperature and time. Higher shrinkage percentages were achieved via increased temperature and time. The drying kinetics exhibited increased drying rates depending on the decrease in water content. This study showed that the response surface methodology could be used as a tool for drying process optimization.

Keywords:

• Activated sludge
• Shrinkage
• Sludge cake
• Sludge drying
• Thermal gravimetric analysis
• Water fractions

ACKNOWLEDGMENTS

The authors acknowledge the Department of Mining Engineering at Dokuz Eylul University for extensive use of the bomb calorimeter in the Chemistry Laboratory. The authors thank the personnel at the Izmir Cigli Municipal Wastewater Treatment Facility for their assistance.