The biodrying concept: an innovative technology creating energy from sewage sludge

Area of Science:

• Environmental Engineering
• Biotechnology
• Waste Management

Background:

• Waste activated sludge (WAS) presents a significant disposal challenge.
• Thermophilic biodrying offers a potential solution for sludge volume reduction and resource recovery.

Purpose of the Study:

• To evaluate the performance and sustainability of a full-scale biodrying installation for WAS.
• To assess the quality of the final product for energy generation and fertilizer applications.
• To quantify energy recovery and by-product generation.

Main Methods:

• A full-scale, two-step forced aeration biodrying process operating at thermophilic conditions (65-75 °C).
• Treatment of 150 kton (wet weight) of dewatered WAS annually.
• Monitoring of weight reduction, product quality (caloric value, microbial/heavy metal content), energy balance, and ammonia recovery.

Main Results:

• Achieved a 73% reduction in wet sludge weight.
• Produced a final product with high caloric value (7700-10,400 kJ/kg), suitable for combustion.
• The product met European standards for use as organic fertilizer.
• Recovered 9.3 MW of heat for internal use and produced 7.3 kton/year of ammonium sulfate solution for sale as fertilizer.
• The facility consumed <0.5 MW of electricity.

Conclusions:

• Biodrying is a sustainable sludge management process offering significant volume reduction.
• The process generates valuable by-products (energy and ammonium sulfate), improving economic viability.
• The final product meets quality standards for both energy recovery and agricultural application, reducing reliance on traditional disposal methods.