Effect of ultrasonic, thermal and ozone pre-treatments on waste activated sludge solubilisation and anaerobic biodegradability

Abstract

In order to enhance the efficiency of anaerobic digestion, the effects of ultrasounds, ozonation and thermal pre-treatment have been studied on waste activated sludge. The feature of this study was to carry out the comparison of the three pre-treatments in the same conditions and on the same sludge sample. Each treatment was tested in two conditions close to optimum conditions to maximise batch anaerobic sludge biodegradability. All treatments led to chemical oxygen demand and matter solubilisation and had little influence on mineral matter. In terms of solubilisation thermal pre-treatment was better than sonication or ozonation. But, in terms of batch anaerobic biodegradability, best results were obtained with ultrasounds with an energy of 6250 or 9350 kJ/kg TS and a thermal treatment at 170 or 190 • C. Moreover, treatments had effects on physicochemical characteristics of sludge samples: apparent viscosity decreased after all treatments but the reduction was more important with thermal treatment. Median diameter of sludge flocs were reduced after sonication, increased after thermal treatment and did not change after ozonation. Finally, capillary suction time (CST) increased after ozonation, increased highly after sonication and was reduced after thermal treatment.

Effect of Ozonation and Sonication on Biochemical Methane Potential of Biosludge from Textile Mill Effluent

“…If it was continued with an anaerobic fermentation, the biogas amount increased significantly compared with the control. This finding was also agree well with the result of Bougrier et al (2006). Therefore, the pretreatment to textile mill biosludges, either ozonation or sonication, increased biochemical methane potential, then there would be a reduction in the biosludge residue.…”

“…The increase of biodegradability with increasing ozone dosage was in accordance with the finding of Goel et al (2003) and Bougrier et al (2006). They found that CH 4 formation increased with increasing ozone dosage.…”

“…In anaerobic digestions of solid feed such as biosludges, the hydrolysis step was reported as a limiting rate because it can reduce the production of biogas (Bougrier et al 2006). Biosludge pretreatment was developed to increase biogas production by accelerating the hydrolysis step.…”

“…On the other hand, during the sludge sonication pretreatment, bubbles formed and grew in the liquid phase then collapsed violently after reaching a critical size. This phenomena produces high pressure and local heating at the interface of liquid and gas and high turbulence in the liquid phase (Bougrier et al 2006). However, Tiehm et al (2001) found that the disintegration of biosludge was more efficient using low frequency.…”

“…Goel et al (2003) suggested that the anaerobic process was the most important method to reduce the amount of biosludge in the wastewater treatment system. Various researches on anaerobic process were currently focused on different techniques to increase biosludge biodegradability and hydrolisis through pretreatment (Dohanyos et al 2000;Goel et al 2003;Lissens et al 2004;Heredia and Garcia 2005;Bougrier et al 2006).…”