Variations of dissolved nitrogen and phosphorus levels in disintegration of active sludge using hydrodynamic cavitation

In the present study, waste activated sludge (WAS) that originated from a food processing facility was disintegrated mechanically on a laboratory scale using an orifice-based hydrodynamic cavitator. To determine optimum operation conditions for sludge disintegration, orifice plates with varying vent hole diameters (3, 4, and 5 mm) were used, and the cavitation setup was operated at three different cavitation numbers (0.2, 0.5 and 0.8). The maximum soluble total kjeldahl nitrogen (STKN) value at the end of 150 minutes of cavitation was observed in trials with orifice diameters of 3 and 4 mm and with cavitation number (C-v) of 0.2. However, when the initial levels of STKN were considered, more marked increase was occurred in case of the cavitation number of 0.2 and orifice diameter of 3 mm. The applied hydrodynamic cavitation method also caused an increase in soluble total phosphorus (STP) contents. Especially, the increment occured in the first 90 minutes of cavitation was more pronounced. The results showed that 47% of TKN and 50% of TP, were solubilized after a cavitation period of 150 minutes. According to the increases in STKN and STP, orifice-based hydrodynamic cavitation appeared to be an efficient method for sludge disintegration.