Improvements to increase the efficiency of solar dryers for different waste sludge management

Abstract

BACKGROUND AND OBJECTIVES: In this study, an integrated phase change material drying system was designed to evaluate the efficiency of the system with the use of renewable solar energy for different types of sludge with different moisture content. METHODS: This study was performed on the wastewater treatment plant sludge, paint, and marble sludge. By distributing the screws on the sludge tray, covering the system floor with a black trash bag, and mounting the reflector around the absorber tubes has increased the efficiency of the system. FINDINGS: All the types of equipment used in the construction of the system are used as heat storage material and increase the internal air temperature, and the sludge temperature of the system. Temperature is transferred sequentially through air and objects. This research was conducted in winter by 1156 Wh/m2 mean internal cumulative solar radiation. Due to the reduction of solar radiation, as the system was upgraded, more water was released from the sludge surfaces. By Scanning Electron Microscopy imaging, the porous surface was observed after sludge drying. CONCLUSION: In this study, the waste sludge moisture decreased from 80% to 52.2% during three improvement stages. The paint sludge moisture content reduced from 56% to 25%, and marble sludge moisture in the final stage reached from 26% to 5.2%. The proposed solar dryer system is an economical way to reduce the sludge volume in the transportation process.