Mitigating quinolones contamination using Cyanophyta, Chlorophyta, and Bacillariophyta: Removal efficiency, degradation pathways and products

Microalgae-based water treatment is considered to be an environmentally friendly technology. The revelation of the degradation pathway of trace organic contaminants by microalgae is helpful to propose targeted ways to improve the degradation efficiency of trace organic pollutants based on microalgae. This study compares the efficiency of hydrolysis, photolysis, adsorption, and biodegradation in the removal of ciprofloxacin (CIP) and norfloxacin (NFLX) by three different algal phyla: Cyanophyta , Chlorophyta , and Bacillariophyta . The results showed that all six algal species tested were capable of removing quinolones , with total removal efficiency ranging from 4.39 % to 29.41 %. Among them, Nostoc sp. exhibited the highest capacity for quinolone removal, while the adsorption efficiency of Cylindrospermopsis sp. and Nitzschia sp. was higher than their biodegradation rates. Specifically, CIP resulted in the formation of seven degradation products , whereas NFLX resulted in the formation of four degradation products. The principal degradation reactions were identified as defluorination , devinylation, piperazinyl substitution, and decarboxylation . Although the intermediates CIP-4, CIP-7 and NFLX-1 could pose a more significant ecological risk to organisms, most degradation products resulting from the algal degradation of QNs exhibited lower toxicity than the parent compound indicating that the risk associated with their toxicity remains limited. This study offers data support for the removal of quinolones in aquatic environments . • Cyanophyta , Chlorophyta , and Bacillariophyta differ in their ability to remove QNs. • Nostoc sp. demonstrated the highest ability to remove QNs. • CIP produced seven degradation products and NFLX produced four degradation products. • The risk of toxicity of the degradation products is minimal.