Sorption and biodegradation of tetracycline by nitrifying granules and the toxicity of tetracycline on granules

This paper examines the simultaneous sorption and biodegradation performance of tetracycline (TC) by the nitrifying granular sludge as well as the short-term exposure toxicity of TC. The removal of TC was characterized by a quick sorption and a slow process of biodegradation. The adsorption process fits pseudo-second-order kinetic model, with a complex mechanism of surface adsorption and intra-particle diffusion. Both temperature and mixed liquor suspended solid (MLSS) influenced TC sorption to the granules. TC biodegradation was enhanced with the increase of COD and NH4+-N concentrations, with except of the NH4+-N concentrations higher than 150 mg/L. With the ATU addition, TC degradation was weakened remarkably, indicating a synergistic effect of multiple microbes. Results of the short-term exposure (12 h) effects showed that the respirometric activities of the microbes decreased greatly. The addition of TC also decreased the rate of NH4+-N utilization considerably, with the half saturation constant (Ks) increasing from 297.7 to 347.2 mg/L.