A New Technology for Low Temperature Drying of Sewage Sludge with Solar Energy
Abstract:Up to now drying of sewage sludge is considered to be an expensive technique only suitable for big sewage works, since conventional high temperature dryers cause high investments and a high energy consumption.
Therefor the University of Hohenheim started to work on an environmentally friendly technology which requires much lower investments: Low temperature drying by solar energy. In cooperation with the company THERMO-SYSTEM a new drying plant was developed and tested. The plant is based on a greenhouse construction, covered by a transparent, highly UV-stabilized and well isolating air bubble foil. The drying process is microprocessor-controlled and fully mechanized. During the process a small robot, the so called “electric mole” continuously mixes and turns the sludge to improve the vaporization rate and avoid anaerobic reactions in the sludge.
Starting in 1995 several sewage sludge dryers of this type have been installed in German sewage works, treating meanwhile more than 10 000 t of sludge annually. During commercial operation the technology proofed to be suitable and highly cost efficient for small to middle sized sewage works. The achieved dry solids content of the completely stabilized, non smelling end-product is, under German weather conditions, up to 90 % in summer and up to 50 % in winter. The required energy consumption is only 20 to 50 kWh per ton of vaporized water. The required maintenance is almost zero. The achieved vaporization rates per square meter were up to three times higher than in conventional sludge beds. This makes the technology interesting for small to middle sized plants in moderate climate and for bigger sized plants in warm climates. Ongoing research on hygienisation and composting showed very promising results.
The poster shows the function of the plant and the most important results of the ongoing research.
Document Type: Research Article
Publication date: January 1, 2000
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