Stress Response And Removal Mechanism Of Tetracycline From Water By Freshwater Microalgae

The irrational use of antibiotics and the limitations of wastewater treatment processes have led to a significant amount of them entering surface waters and affecting the safety of aquatic ecosystems.Antibiotic removal in water based on microalgae is a promising technology for wastewater purification,not only for the removal of relevant pollutants,but also for CO₂ fixation purposes.This paper explores the stress response of two microalgae to tetracycline in water.The effect of tetracycline on the physiological level of T.obliquus and C.pyrenoidosa was clarified and the ability of the two microalgae to remove tetracycline was compared.Investigated the mechanism and factors affecting the removal of tetracycline by C.pyrenoidosa.The results can provide a scientific basis for the removal of tetracycline by microalgae in the actual water environment.The main research results are as follows:（1）0.5-6.0 mg/L tetracycline treatment of T.obliquus and 0.5-10.0 mg/L tetracycline treatment of C.pyrenoidosa tetracycline both inhibited the photosynthetic pigment content of the two microalgae and caused the damage of their photosynthetic activity,resulting in a significant decrease in photosynthetic pigment content and Fv/Fm value of microalgae,and the photosynthetic pigment content and photosynthetic activity increased at 96 h compared with 48 h.However,in the study of the oxidative stress mechanism of two kinds of microalgae to tetracycline,the activities of SOD and POD and the contents of GSH,T-AOC and MDA in almost all exposed groups increased significantly.In general,T.obliquus was more sensitive to tetracycline than C.pyrenoidosa.（2）Both microalgae can enrich tetracycline in water,and C.pyrenoidosa has a stronger ability to accumulate tetracycline than T.obliquus.The concentration of tetracycline in C.pyrenoidosa was related to the initial concentration and action time of tetracycline.The tolerance and action time of C.pyrenoidosa to tetracycline were positively correlated.AOM（polysaccharides,proteins and lipids）secreted by algae also had a certain effect on the removal of tetracycline,and the contribution of EOM to tetracycline removal was higher than that of IOM to tetracycline removal.（3）Nine possible degradation products of tetracycline by C.pyrenoidosa were detected by UPLC-Q Exactive Focus:P2（m/z=338）,P3（m/z=182）,P4（m/z=135）,P5（m/z=348）,P6（m/z=318）,P7（m/z=263）,P8（m/z=469）,P9（m/z=321）,P10（m/z=130）.The degradation process is mainly carried out through a series of reactions,such as hydrolytic ring,demethylation（-CH₃）,hydrogenation,dehydroxylation（-OH）,decarbonylation（-carbonylation）and deamination（-NH₂）.（4）The effects of initial algae concentration,initial tetracycline concentration,p H and salinity on tetracycline removal by C.pyrenoidosa were studied by a single factor experiment.The results of kinetic model fitting showed that the removal of tetracycline in different algae initial concentrations（5×10⁵-1×10⁷cells/m L）,different initial tetracycline concentrations（0.5-10.0 mg/L）and p H（5-9）conformed to pseudo-first-order degradation kinetics.When the initial algae concentration,tetracycline concentration and p H were 1×10⁷cells/m L,2.5 mg/L and 8,the half-lives of tetracycline in water were 10.664 h,11.180 h and 1.869 h.