Performance testing of a combined solar and heat-drying system for biological sludge

Abstract

The present work has the main aim of testing and implementing the performance of an innovative system for biological sludge drying, which combines an inner high-performance sludge burner with solar air heaters. The research question is how to implement the design and structure of the drying system, defining the best working conditions (best temperature, materials and dimensions of its components, etc.). The state-of-the-art of water treatment and in particular of biological sludge from urban sewage is introduced, with an insight also on management and investment costs. The solar drying technology is then described and the project of the system is presented. In addition, the possible environmental gains that the technology could bring are shown, e.g. saving in transportation because of the diminution in volume of the biological sludge with the drying process. Since the prototype is still not completed, the testing has been done separately in a solar drying system and in an oven, in order to test the response of the biological sludge to solar and thermal heating. In addition, an analysis of the emissions in the atmosphere and a measure of the calorific power during the combustion phase will be done: these data are necessary for the development of the project, because the heat produced with the combustion will be put back inside the system to dry the wet sludge, obtaining a final product with 85% of dry matter. The economical attractiveness of the system is estimated to be high since it can produce large cost savings and it is a product completely new in the market, in terms of expected performances, design, technology and dimensions.