Alkaline assisted hydrodynamic cavitation for disintegration of waste activated sludge

Abstract

Alkaline treatment with NaOH in a hydrodynamic cavitation system consisting of a single-hole orifice plate was evaluated for use as a disintegration method for waste activated sludge (WAS). The results indicated that the solubilization of WAS can be effectively performed using alkaline assisted hydrodynamic cavitation. In addition, the results revealed that more SCOD and STKN increments were achieved in the WAS when a cavitation number of 0.3 was used than when cavitation numbers of 0.4 and 0.5 were used. After an experimental period of 30 minutes, a maximum SCOD value of 2325 mg l(-1) (corresponding to a disintegration degree of 57.6 %) was obtained by combining the alkaline treatment at pH 11 with hydrodynamic cavitation with a cavitation number of 0.3. However, the synergistic effect was only observed for the combination of low-level alkaline treatment with an initial pH level of 9 and hydrodynamic cavitation with respect to both SCOD and STKN. The observed SCOD and STKN values in this combination were significantly greater than the arithmetic sum of the individual alkaline treatment process and hydrodynamic cavitation (28% and 22%, respectively). Accordingly, the retarding effect of the rate limiting step of anaerobic sludge digestion would most likely be reduced, which would result in greater efficiency in the digesters when using the proposed sludge disintegration method with low-level alkaline-assisted hydrodynamic cavitation.