The Toxicity of Tetracycline and Disinfection Byproducts on Chlorella Under Ultraviolet/Persulfate Process

Tetracycline (TC), commonly utilized in medicine and aquaculture, frequently enters aquatic environments, raising ecological concerns. This study examined TC-contaminated wastewater treated through ultraviolet (UV), potassium persulfate (PS), and combined UV/PS disinfection processes. The degradation of TC followed pseudo-first-order kinetics, with removal efficiency ranked as UV/PS > UV > PS. High-performance liquid chromatography–mass spectrometry (HPLC-MS) identified 20 disinfection byproducts (DBPs) across all processes. Based on the identified intermediates, the degradation pathways of TC under different disinfection processes (UV, PS, and UV/PS) were elucidated. Using the ECOSAR program, both acute and chronic aquatic toxicities of TC and its DBPs were predicted. The biological effects onChlorellawere also investigated. DBPs from UV and PS treatments inhibited algal growth, reducing it by 4.8–9.4% relative to the control. Conversely, DBPs formed under UV/PS disinfection stimulated growth, increasing rates by 3.4–6.6%. To counteract oxidative stress from TC and its DBPs,Chlorellaenhanced superoxide dismutase (SOD) and catalase (CAT) activities. These findings highlight that while TC degradation occurs efficiently, the nature of DBPs and their ecological impacts vary significantly depending on the disinfection method. Overall, the UV/PS process not only improved TC removal but also reduced harmful effects on microalgal growth compared with UV or PS alone.