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Disintegration of sludge using ozone-hydrodynamic cavitation Chanda, Suranjit Kumar


In our study we applied hydrodynamic cavitation and ozonation both separately and combined, to determine the synergistic effect of these two technologies for sludge disintegration. A 2 mm orifice was used as a cavitation device. Ozone was injected after cavitation at a concentration of 35 mg/L at a flow of 3 Lpm. The sludge was subjected to treatment for 90 minutes in all three cases. In a final step, combined ozone and cavitation was applied to disintegrate the sludge for 10 hours. It was found that the combination of ozonation and cavitation exhibited higher sludge disintegration capacity than the individual technologies applied alone. About 31% of VSS was reduced by the combined system, whereas 19% was reduced by ozone and only 4% was reduced by cavitation alone after 90 minutes of treatment. Soluble chemical oxygen demand (SCOD) was increased by approximately 1600 mg/L in the combined system, which was much higher than the individual effect observed with either ozone or cavitation alone. About 75% of this SCOD was found to be biodegradable. In the combined system, soluble TOC increased by approximately 1.5 times the amount released by ozone alone, indicating higher release of organic matter from biomass. Only cavitation did not show any significant release of soluble total organic carbon (TOC) compared to the other treatments. In combined application, soluble biochemical oxygen demand (BOD) increased to 420 mg/L, which was significantly higher than the increase of BOD due to the application of ozone alone which was 260 mg/L. Based on the SCOD, it was found that a maximum of 50% of the sludge could be solubilised in 10 hours of combined treatment. It was also found that with ozone-cavitation, approximately 26% of the total sludge phosphorus was released to the solution after 10 hours, although most of the release occured within the first 2 hours. Within the operating conditions applied, cavitation itself was not sufficient for the disintegration of sludge, although better disintegration was found in combined application at higher inlet pressure. In the case of ozonation alone, higher disintegration was obtained at longer ozonation time.

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