Ozone combined with mechanical agitation to enhance sludge cell lysis and provide an alternative carbon source for nitrogen removal of bioreactors

Abstract

The activated sludge method results in the production of significant amounts of excess sludge. Moreover, biological nitrogen removal requires an external carbon source, which presents environmental and economic challenges. To address these challenges, this study combined ozone with mechanical agitation to achieve sludge cell lysis. Through both experiments and COMSOL Multiphysics simulations, optimal conditions were identified. These conditions include a six-bladed disk turbine stirrer speed of 800 rpm, an ozone concentration of 40 mg/L, and an ozone dose of 100 mg·g−1 MLSS (Mixed Liquid Suspended Solids). Notably, the sludge solubilization efficiency improved by 20.1 % when compared to using ozone alone. After the sludge dissolution, this paper observed elevated concentrations of soluble chemical oxygen demand (SCOD), total nitrogen (TN) and total phosphorus (TP) in the supernatant, reaching 3126 mg/L, 144.3 mg/L, and 49.6 mg/L, respectively. This study also investigated the feasibility of using this supernatant as an external carbon source in a sequencing batch reactor. The results showed that while the supernatant had minimal impact on COD removal, it significantly enhanced nitrogen removal. Compared to using glucose as an external carbon source, the TN removal rate increased by 16.9 %. However, TP removal was inhibited.