Feasibility of using ultrasonic irradiation to recover active biomass from waste activated sludge

The results indicate that ultrasonic irradiation of WAS at 800 W l−1 followed by 30 min of settling can produce a supernatant with heterotrophic specific oxygen uptake rates (SOURs) of over two times the SOUR measured in the bulk mixed liquor. Under these conditions 26% of the initial heterotrophic activity was recovered within only 11% of the initial volatile mass. Similarly, autotrophic analysis revealed that nitrifying organisms, while sensitive to the effects of ultrasonic irradiation, can be separated from the activated sludge floc and recovered. An irradiation density of 200 W l−1 with an exposure time between 1 and 2 min produced a supernatant with a specific ammonia removal rate of over two times the initial mixed liquor rate.