Cultivation of algal-bacterial granular sludge and degradation characteristics of tetracycline

Due to the increasing use of antibiotics, tetracycline was frequently detected in wastewater. As a novel technology, algal-bacterial granular sludge process is expected to be widely used in wastewater treatment. However, the degradation effect of tetracycline by algal-bacterial granular sludge process and its degradation path is still unknown. In this study, mature and stable algal-bacterial granular sludge was cultured and the degradation of tetracycline by it was investigated. The results showed that the removal amount of 1-25 mg/L tetracycline by algal-bacterial granular sludge was 0.09-1.45 mg/g volatile suspended solids (VSS), in which the adsorption amount was 0.06-0.17 mg/g VSS and the degradation amount was 0.03-1.27 mg/g VSS. Tetracycline biosorption was dominant at its concentration of 1-3 mg/L, while biodegradation was predominant at 5-25 mg/L of tetracycline. At tetracycline concentration of 3-5 mg/L, the contribution of biosorption and biodegradation to tetracycline removal by algal-bacterial granular sludge process was almost equal. Algal-bacterial granular sludge could effectively degrade tetracycline through demethylation, dehydrogenation, deacylation, and deamination or their combination. In addition, the degradation products were nontoxic and hardly pose a threat to environmental health. The research results of this paper provide a solid theoretical basis for tetracycline removal by algal-bacterial granular sludge and a reference for the development of algal-bacterial granular sludge process for wastewater treatment in the presence of tetracycline. Practitioner pointsMature and stable algal-bacterial granular sludge was cultured.Tetracycline was removed by algal-bacterial granular sludge through biosorption and biodegradation.Algal-bacterial granular sludge could degrade tetracycline through demethylation, dehydrogenation, deacylation, and deamination or their combination.The degradation products were nontoxic.