Municipalities around the world are challenged with growing populations, changing regulations and rising costs. Heat drying technologies have been used for many years to reduce biosolids volumes, and recently, there have been developments in the drying industry surrounding safety, air quality, beneficial reuse and heat recovery (Igoe, 2002).
There are two main categories of drying technologies: convective (or direct) and contact (or indirect). In this paper, the direct Convective Thermal Dryer (CTD) system and indirect Ecoflash® Thin Layer Dryer are discussed and illustrated through municipal examples.
The projects discussed in this paper are:
The City of Corona, California, USA, which uses a Convective Thermal Dryer (CTD) system to reduce volume and disposal costs of biological biosolids generated at the city's two wastewater treatment plants. The project is unique because the CTD system uses waste heat from the City's power plant to promote the production of beneficial reuse, Class A biosolids.
The Dundalk drying plant in Ireland, which is the first plant designed and built by Siemens Water Technologies to be in full compliance with the European ATEX (Atmosphere Explosible) Safety Regulation Directive 94/9/EC.
Disposal of dewatered sludge quickly becomes a big problem for Cagliari, a city on Sardinia Island in Italy, whose economy is based on tourism. They use the Ecoflash® dryer to reduce biosolids hauling and disposal costs.