Harnessing hydrodynamic cavitation, alkaline treatments and advanced oxidation processes for enhancement of sludge disintegration

Anaerobic digestion (AD) is widely recognized as an effective technique for the safe and sustainable treatment of sewage sludge. However, the process is inherently slow, particularly during the hydrolysis phase, which is hindered by the presence of complex organic constituents such as extracellular polymeric substances (EPS), ultimately limiting overall digestion efficiency. To address this limitation, the present study evaluates the efficacy of various sludge pretreatment strategies – both individually and in combination – including hydrodynamic cavitation (HC), alkaline treatment, and advanced oxidation processes (AOPs) employing hydrogen peroxide (H₂O₂) and Fenton reagents. Experimental results demonstrated that HC alone, utilizing an orifice plate (β = 0.10) with 16 holes (2 mm diameter) under an inlet pressure of 5 bar for 30 minutes, achieved a disintegration degree (DD%) of 22.83%. Alkaline pretreatment at pH 12 (adjusted with NaOH for 30 minutes) resulted in a DD% of 18.35%. In contrast, H₂O₂ oxidation (40 mg H₂O₂/g TS for 30 minutes) and Fenton treatment (pH 3, 40 mg H₂O₂/g TS, 10 mg Fe²⁺/g TS for 30 minutes) yielded significantly lower DD values of 2.06% and 1.93%, respectively. Moreover, the combination of HC with alkaline treatment produced the highest sludge disintegration performance among the tested hybrid approaches. This synergistic effect led to a substantial increase in soluble chemical oxygen demand (SCOD) from 1490 mg/L to 7578 mg/L and a maximum DD% of 38.32%, highlighting the enhanced effectiveness of this integrated pretreatment strategy