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PRETREATMENT OF ACTIVATED SLUDGE BY ULTRASONIC IRRADIATION

Congress: 2008
Author(s): Rana Kidak, Berthe Ratsimba, Anne-Marie Wilhelm, Henri Delmas
Laboratoire de Genie Chimique, INP-ENSIACET, Site Basso-Cambo, 31106 Toulouse, France

Keyword(s): waste activated sludge, pre-treatment, sonochemistry, power intensity
Article:
AbstractThe waste activated sludge (WAS) is an environmental problem as it is produced in very large amounts in the wastewater treatment plants. The ultimate solution to this problem is considered to be the complete stabilization of the organic content, complete disinfection of the pathogenic bacteria and the reduction of the sludge volume by removing the water portion (initially up to 90%). Catalytic oxidation is one of the innovative techniques used for sludge treatment. The aim of this study is to provide better conditions for the catalytic oxidation of sludge treatment by applying ultrasound as a pre-treatment. These improvements cover the disrupting of the flocs and/or lysing the bacterial cells, leading to a reduction in particle size in the solution and providing availability of the organic materials for further oxidation. In this study, by using the 20 kHz ultrasonic probe system, we have treated the waste domestic sludge. A gross amount of sludge sample with 25% humidity was obtained from a municipal wastewater treatment plant. An ultrasonic homogenizer Autotune (Bioblock Scientific), was used as the ultrasonic apparatus. This apparatus was equipped with an ultrasonic probe and a generator which work with an operating frequency of 20 kHz and the maximum applied power of about 240W. Batch experiments were carried out in a reactor without and without temperature regulation. During the 1 hour treatment process, samples were taken to investigate the chemical kinetics. Several analytical parameters were investigated through the samples which were obtained from the treated solution before, during and after the treatment process. These parameters include: solubilized COD, solubilized TOC, dp50 (average particle size diameter) and the total protein content. In order to observe the changes in the bacterial population of the sludge, we have measured the protein content in the liquid phase which is an indirect method. The release of the bacterial protein materials into the liquid phase increases by the application of ultrasound. This difference indicates the disintegration rate of the bacterial cells. We have observed that under increasing applied power values, the solubilized COD, solubilized TOC and the protein content in the liquid phase increase up to an applied power intensity of around 50 W/cm2, while the mean particle diameter is decreased. Further increments in the power intensity provide little improvements in some very cases but in most of cases it is in vain.
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