Application of electric fields to mitigate inhibition on anammox consortia under long-term tetracycline stress

Anaerobic ammonium oxidation (anammox) has been recognized as a promising microbial denitrification technique in recent years,duing to  the treatment of high-strength ammonium wastewater. Compared to typical nitrification and denitrification methods, the anammox process transforms ammonium  and nitrite to nitrogen gas , and saves up to 60% of energy on aeration, sludge disposal and organic carbon addition. Furthermore, the process reduces greenhouse gas emissions by more than 25%, particularly in the production of nitrous oxide (N₂O). However, the anaerobic ammonia oxidation bacteria (AnAOB) are very sensitive and vulnerable to many inhibitors, especially antibiotics in wastewater. In this study, the feasibility of applying electric fields to mitigate inhibition of tetracycline (TC) on anammox process and improve system stability was evaluated. Three electric field intensities of 1, 3 and a variable intensity of 1-6 V (VEF) were used to optimize electric field intensity under gradually increasing addition of TC (0.5, 2 and 10 mg·L^-1). Results showed that the application of electric fields (3 V and VEF) could improve TC tolerance and keep relatively high-efficiency nitrogen removal performance, especially at TC ≥ 2 mg·L^-1. Furthermore, applying electric fields contributed to mitigate irreversible inhibition and improve the stability of community structure. Underlying mechanism analysis indicated that the main mechanism of applying electric fields to mitigate inhibition relies on sludge structure strengthening. This study explored a novel strategy to reduce the inhibition of antibiotics on microbial denitrification and broaden the application of anammox in industrial water treatment.