Full-scale demonstration of an ultrasonic disintegration technology in enhancing anaerobic digestion of mixed primary and thickened secondary sewage sludge

For a country like Singapore with limited natural resources, innovative technologies are required to reduce sludge disposal volume and increase biogas production to recover energy in the wastewater treatment process. Ultrasound disintegration technology is potentially useful since it disintegrates sludge solids and enhances anaerobic digestion. The technology was tested in the field under tropical conditions with a full-scale ultrasonic facility and two 5000 m³ egg-shaped digesters. Each digester was fed with mixed primary (one-third) and thickened activated (two-thirds) sludge of identical quality and volumes of up to 200 m³·d^–1. For the two digesters, all operating conditions were the same except for the inclusion (test) and omission (control) of the ultrasonic device to pre-treat the sludge feed. In comparison with the control, the five-month field study showed that ultrasound pre-treatment of the sludge increased the daily biogas production up to 45%. There were no significant differences in biogas composition from the two digesters. When translating the increases in biogas production into its source (volatile suspended solids), an increase in sludge solids removal of up to 30% is expected under optimal operation conditions.