Insights on the solubilization products after combined alkaline and ultrasonic pre-treatment of sewage sludge.

This work provides insights on the solubilization products after a simultaneous combination of alkaline and ultrasonic (ALK+ULS) pre-treatment of sewage sludge. Soluble chemical oxygen demand (SCOD) increased from 1200 to 11,000 mg/L after such treatment. Organics with molecular weight around 5.6 kDa were solubilized because of the synergistic effect of ultrasound and alkali. Organics with molecular weight larger than 300 kDa increased from 7.8% to 60%, 16% and 42.3% after ULS, ALK and ALK+ULS treatment, respectively. Excitation emission matrix fluorescence spectroscopy analysis identified soluble microbial product-like and humic acid-like matters as the main solubilization products. Sludge anaerobic biodegradability was significantly enhanced with the simultaneous application of ALK+ULS pre-treatment. ALK+ULS pre-treatment resulted in 37.8% biodegradability increase compared to the untreated sludge. This value was higher compared to the biodegradability increase induced by individual ALK pre-treatment (5.7%) or individual ULS pre-treatment (20.7%) under the same conditions applied.

Interpreting the synergistic effect in combined ultrasonication-ozonation sewage sludge pre-treatment.

The sequential combination of ultrasonication and ozonation as sewage sludge treatment prior to anaerobic digestion was investigated. Synergistic volatile suspended solids (VSS) solubilization was observed when low energy ultrasonication (⩽12kJg(-1) TS) was followed by ozonation. 0.048gO3g(-1) TS ozonation induced the maximum VSS solubilization of 41.3% when the sludge was pre-ultrasonicated at 9kJg(-1) TS; while, the same ozone dosage applied without prior ultrasonication only induced 21.1% VSS solubilization. High molecular weight (MW) components (MW>500kDa) were found to be the main solubilization products when sludge was only ozonated. However, solubilization products by ozone were mainly in the form of low MW components (MW<27kDa) when sludge was pre-ultrasonicated. The high MW products generated by ultrasound were effectively degraded in the subsequent ozonation. Anaerobic biodegradability increased by 34.7% when ultrasonication (9kJg(-1) TS) and ozonation (0.036gO3g(-1) TS) were combined sequentially. The maximum methane production rate increased from 3.53 to 4.32, 4.21 and 4.54mL CH4d(-1) after ultrasonication, ozonation and ultrasonication-ozonation pre-treatments, respectively.