*Xie R J,* Xing Y J,** Ghani Yahya A, **Ooi KE and **Ng SW
*Department of Water Resources Management, Singapore 
**Water Reclamation (Plants) Department, The Public Utilities Board, Singapore


For a tropical country like Singapore with limited natural resources, innovative technologies are required to minimise sludge disposal volume and maximise biogas production to recover energy in the wastewater treatment process. The ultrasound disintegration technology has this feature, i.e., it disintegrates sludge solids and enhances anaerobic digestion. The technology was tested in the field under tropical conditions with a full-scale ultrasonic system and two 5 000 m3 egg-shaped digesters, each was fed with mixed primary (one-third) and thickened secondary activated sludge (two thirds) of identical quality and volume up to 200 m3 d-1.

For the two digesters, all operational conditions were kept the same except one (test) with and the other without (control) the integration of the ultrasonic device to pre-treat the sludge feed. In comparison with the control, the field trial showed that ultrasound pre-treatment of the sludge increased in the daily biogas production up to 45%. There were no significant differences in compositions of the biogas from the two digesters. When tracing the increases in the biogas production back to its source – volatile suspended solids, a 25-30% increase in sludge solids removal is expected under optimal hydraulic retention time.

KEYWORDS Biogas; sonication; anaerobic sludge digestion; hydraulic retention time; sludge solids

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