Ultrasonic Waste and Sludge Treatment

Biogas is generated from sources, such as municipal organic waste, sewage sludge, muck or manure. Ultrasonication improves the digestability of such organic material leading to more biogas and less residual sludge.

Ultrasonication improves sludge digestion.

Biogas is a byproduct of the decomposition of organic matter by anaerobic or aerobic bacteria. It consists primarily of methane, carbon dioxide and hydrogen sulfide. This makes biogas a renewable alternative for fossil fuels, such as natural gas.

Energy prices and chemical and sludge disposal costs, environmental legislation and other interests, such as the reduction of odor emissions require waste treatment plants to improve their processing efficiency. The ultrasonic disintegration of the organic material before digestion improves the biogas production significantly. Along with that sonication improves the dewaterability of the sludge and it reduces the amount of residual sludge to be disposed.

Feedstocks for the production of biogas are mixtures of various aggregated and flocculated substances, fibers, viruses and bacteria, cellulose, starch and inorganic substances. Ultrasonic cavitation destructs such aggregates and cellular structures. Due to the effect on the on the constituent material structure the sludge can be dewatered more easily. Furthermore, the destruction of the aggregates and cell walls improves the availability of intracellular material to decomposition by bacteria.

Since 1999, Hielscher has been supplying ultrasonic disintegration systems of up to 48kW individual power to various waste water treatment plants as well as to municipal and industrial waste treatment facilities all around the world. Some of these systems improved the biogas yield by up to 25%.

The table to the right shows typical power requirements for various volume flows. The ultrasonic system is generally integrated inline before feeding to the digester. Alternatively, the organic material can be recirulated from the digester through the ultrasonic system back into the digester. Therefore, the ultrasonication step can be easily retrofitted into exisiting facilities.

Flow Rate	Equipment
50 - 200L/hr	UIP1000
200 - 800L/hr	4xUIP1000
1 - 3m³/hr	4xUIP4000
5 - 20m³/hr	6xUIP16000
50 - 200m³/hr	62xUIP16000

The application of ultrasonics to the processing of sludge and waste streams can achieve various results, such as:

Increase in biogas yield
Improved anaerobic decomposition
Improvement of sedimentation behavior due to degassing and flake disintegration
Improvement of C/N-ratio for denitrification
Improvement of surplus sludge thickening
Improved digestion and dewaterability
Reduction of the amount of flocculants
Lower disposal costs due to reduction of residual sludge after digestion
Reduction of required polymer
Destruction of filamentous bacteria

We recommend the conduct of pilot scale trials e.g. using 1 to 4kW systems. This will show the general effects and improvement for your particular process stream. We will be glad to discuss your process with you and to recommend further steps.