Kinetics of the removal mechanisms of veterinary antibiotics in synthetic wastewater using microalgae–bacteria consortia

Abstract

The mechanisms involved in the removal of a mixture of four veterinary antibiotics (VA) – tetracycline (TTC), ciprofloxacin (CPF), sulfadiazine (SDZ) and sulfamethoxazole (SMX) – in synthetic wastewater using microalgae–bacteria consortia (MBC) dominated by Scenedesmus almeriensis was studied at different initial concentrations of 1000, 500, 100 and 20 μg/L per antibiotic. Ultra-high performance liquid chromatography and tandem mass spectrometry (UHPLC-MS/MS) were used to determine the removal of the VA for each mechanism. For a hydraulic retention time of 4 days, the overall removal of antibiotics by the MBC was 99.9% for TTC, 78.0% for CPF, 52.6% for SDZ and 5.0% for SMX. A pseudo-first order irreversible model was applied to best fit the experimental data. The degradation constant rates were 0.136 h−1 for TTC, 0.012 h−1 for CPF, 0.010 h−1 for SDZ and 0.0007 h−1 for SMX. Under all the evaluated conditions, CPF and TTC exhibited the highest removal efficiency. Biosorption was the main mechanism for all four antibiotics, followed by biodegradation in the cases of TTC and SDZ. CPF did not show removal via biodegradation. SMX did not show removal via hydrolysis or photolysis. This study (i) integrates and evaluates individually the mechanisms involved in VA removal using an MBC; (ii) determines an overall removal rate constant for a wide array of TTC, CPF, SDZ and SMX concentrations; and (iii) demonstrates the high removal capacity and potential use of microalgae as an ecofriendly wastewater treatment process.