A combined method of hydrodynamic cavitation and alkaline treatment for waste-activated sludge solubilization; N/P recovery from anaerobic granular sludge

Waste-activated sludge (WAS) is typically processed very slowly and only to a certain extent in anaerobic digestion (AD), typically necessitating pre-treatment. In this study, we developed a new and powerful way of pretreating WAS, which is a combination of hydrodynamic cavitation (HC) and alkaline treatment, and examined it for its efficacy. The combined treatment yielded the highest disintegration degree (DD) of 48.4%, while HC alone produced only 11.9% of DD and alkaline alone did 16.2%. The pre-treated sludge led to much enhanced methane production compared with the untreated one; 80.7 ml/g CODadded was the largest amount of CH4 obtained with the pre-treated sludge, while 37.3 ml/g CODadded with the untreated one. The distinctive efficacy of the HC was further exploited to remove nutrients from anaerobic granular sludge (AGS) in a beneficial way: namely, the HC-mediated recovery of N/P by way of struvite precipitation. The highest phosphate removal was found at pH 10 with HC, which was more than twice the value of a simple stirring (63 mg PO43-/L by simple stirring versus 150 mg PO43-/L by HC). It appeared that HC is indeed a sure option for WAS pre- and post-treatment to improve biodegradability and nutrient recovery, respectively.