Methane Production and Sludge Reduction During the Anaerobic Digestion of Sewage Sludge by Ultrafine Bubble/Microbubble Ozonation

The ability of ultrafine bubble/microbubble ozonation to enhance the disintegration and solubilization of sewage sludge for methane fermentation was investigated in this study. Waste activated sludge (WAS) and digested sludge were ozonated and subsequently used as feed sludges to promote sludge reduction and biogas production. During the methane fermentation of WAS, the rate of sludge reduction based on the total chemical oxygen demand increased to 75% from 40% in untreated sludge, and biogas production, 0.558 NL per gram volatile solids (VS) added, was increased 1.87-fold compared with untreated WAS at an ozone dosage of 53 mg-O₃ per gram of suspended solids (SS). To facilitate the methane fermentation of digested sludge, reducing agents were removed by aeration as a pretreatment prior to ozonation of the digested sludge. The sludge reduction rate increased by 26% from an initial rate of 7%, and biogas production, 0.185 NL g-VS-added⁻¹ at an ozone dosage of 54 mg-O₃ g-SS⁻¹, increased threefold compared with that of untreated digested sludge. Ultrafine bubble/microbubble ozonation reduced the viscosity of the sludge, although it also decreased its dewaterability at high ozone dosages. These findings demonstrate the effectiveness of ultrafine bubble/microbubble ozonation as a pretreatment for methane fermentation of sewage sludge.