Ultrasound pre-treatment step for performance enhancement in an aerobic sludge digestion process

Ultrasonic pre-treatment of sludge increases the biodegradability and decomposition efficiency in a sludge digestion process, due to its ability to breakdown complex macro-molecular structure of the floc into a micro-molecular structure. The first part of this study focused on determining the optimum operating condition for ultrasonic pre-treatment, for achieving better destruction efficiency of sludge, while the second part focused on investigating the effect of ultrasonic pre-treatment on the aerobic sludge digestion process efficiency at room temperature and thermophilic condition. The results showed that, 30 min of ultrasonic pre-treatment applied at an energy output of 480 W, i.e., when the specific energy output was 397 kJ/g SS, better cell wall destruction efficiency was achieved. This pre-treatment step also increased the dissolution rate of chemical oxygen demand (COD) up to 44.4%, in comparison to without pre-treated sludge. The addition of ultrasonic pre-treatment greatly reduced the retention time of the thermophilic aerobic digestion process from 15 days to 3 days, for about 55% of VSS removal efficiency. This study demonstrates the usefulness of the ultrasonic pre-treatment step in a sludge digestion process.