Ultrasonic lysis of Biological Sludge: A Three-stage Process

Ultrasounds have been known very effective for biological sludge disintegration, which can be used as a pretreatment method prior anaerobic digestion or sludge minimization. This paper is a preliminary investigation of the involution of sludge matrix during sonication. The sludge was treated with 0.8 W/ml ultrasounds at 20 kHz and the changes of the sludge size, supernatant chemical oxygen demand (SCOD), supernatant protein, nitrogen, phosphate, protein, and polysaccharides during sonication were recorded. The results showed that ultrasonic sludge disintegration could be treated as a three-stages process. The first stage lasted around 5 minutes; during which the macro-flocs were destroyed, and the entrapped matters and free-water were released. The second stage lasted 10-15 minutes; during which the micro-flocs were destroyed, the extracellular polymer substances (EPS) were dissolved, the bacteria were disinfected, and the capillary water was released. The primary particulates dominated the last stage; and their small size prevented complete disintegration. As a result, the increase of supernatant organics showed a saturation effect.