Important parameters for the setting up of sludge reduction production processes (Sonication, ozonation and thermal treatment) before aerobic or anaerobic digestion

Several pre-treatment, such as mechanical (ultrasounds), chemical (ozonation), thermal or/and biological (enzymatic) treatments can be used in order to enhance the efficiency of aerobic and anaerobic digestion of waste activated sludge and thus, to reduce the quantity of excess sludge. The objective of this work is to study the effects of thermal, ozonation and ultrasound treatment on the solid content of sludge and its biological activity. During thermal, ozonation and sonication treatment, solubilization of COD, Proteins, Nitrogen, Carbohydrates and solids have been analysed, flocks were broken and compounds (especially refractory compounds) were made soluble and these pre-treatments caused the lysis or disintegration of sludge cells. For thermal treatment, we have used two different treatments: lower than 100°C and higher than 100°C (40°C, 60°C, 90°C for 90 min, 121°C for 15 min and 1.5 bar). For ozone pre-treatment we have selected concentration of 0.1grO3.gr-TSS-1. This sample was subject to ozonation with 180W of power, 0.7 bar of pressure, 600 NL/h (Nioton Lit per Day) of debit, during 60 minute. Also, ultrasound treatment has been applied on the activated sludge with low frequency and high intensity (200,000 kj/kg-TSS, 50W and 80 min). During thermal, ozonation and sonication treatment, solubilization of COD, proteins, nitrogen, carbohydrates and solids have been analysed, flocs were broken and compounds (especially refractory compounds) were made soluble. These pre-treatments caused the lysis or disintegration of sludge cells. Aerobic and anaerobic digestions of the treated sludges were studied and compare to none treated. Consequently, BOD, COD, carbohydrates, protein, nitrogen and solids were removed and a significant reduction of excess sludge production as well as an increase in biogas production was observed. Our data show that the optimal results are achieved by using anaerobic batch reactors in the ultrasonic treatment.