Combination treatment of ultrasound and ozone for improving solubilization and anaerobic biodegradability of waste activated sludge
The hydrolysis is known to be the rate-limiting step of biological sludge anaerobic degradation. The
disruptions of sludge flocs and microbial cell walls by ultrasound combined with ozone treatment (US/O3)
were investigated in laboratory-scale experiments. The results showed that temperature, O3 dose, US
energy density and pH had a positive effect on the disintegration of sludge. The organic substrates were
released into the liquor, which induced the increases of soluble chemical oxygen demand (CODS) and
turbidity in the aqueous phase. Accordingly, the biodegradability of sludge was improved. The CODS
increased from 1821 to 2513 mg/l after reaction for 30 min when NaHCO3 was added, which indicated
that the ozone molecule played a major role in the disintegration of waste activated sludge. The CODS
was 2483 mg/l after 60 min O3 treatment followed by 60 min US treatment, and it changed into 3040 mg/l
after 60 min US/O3 treatment, which proved that US/O3 induced a synergetic effect. The pH-drop of sludge
from 6.8 to 5.21 might be attributed to the increase of volatile fatty acid from 61.35 to 111.96 mg/l during
the US/O3 treatment process.
