Rice straw particles covered with Brevundimonas naejangsanensis DD1 cells can synergistically remove doxycycline from water using adsorption and biotransformation

Doxycycline (DC) is a second generation tetracycline antibiotic and its occurrence in the aquatic environment due to the discharge of municipal and agricultural wastes has called for technologies to effectively remove DC from water. The objective of the study was to characterize the synergistic benefits of adsorption and biotransformation in removing DC from water using rice straw particles (RSPs) covered with DC degrading bacteria, Brevundimonas naejangsanensis strain DD1. First, optimal experimental conditions were identified for individual processes, i.e., hydrolysis, adsorption, and biotransformation, in terms of their performance of removing DC from water. Then, synergistic effects between adsorption and biotransformation were demonstrated by adding DD1-covered RSPs (DD1-RSPs) to DC-containing solution. Results suggest that DC was quickly adsorbed onto RSPs and the adsorbed DC was subsequently biotransformed by the DD1 cells on RSPs. The adsorption of DC to DD1-RSPs can be well described using the pseudo-second-order kinetics and the Langmuir isotherm. The DD1 cells on RSPs converted DC to several biotransformation products through a series of demethylation, dehydration, decarbonylation, and deamination. This study demonstrated that adsorption and biotransformation could work synergistically to remove DC from water.