Stratified biofilm structure of MABR enabling efficient ammonia removal from aquaculture medicated bath wastewater

Abstract

The presence of high concentrations of residual antibiotics in aquaculture medicated bath wastewater poses challenges to conventional biological nitrogen removal processes. Membrane aerated biofilm reactor (MABR), known for its energy efficiency and stratified biofilm structure that supports diverse ecological niches, was therefore introduced. Experimental results revealed that MABR achieved an exceptional NH₄⁺-N removal efficiency of 98.2 ± 1.8 % even under high oxytetracycline exposure, attributed to the protective effects of the biofilm on functional bacteria colonized in the inner layer (e.g., ammonia- and nitrite-oxidizing bacteria). Genes mediating the nitrification process, such as amoA/B and nxrA, showed an overall upward trend, with the activation of efflux pumps synergistically constituting the microbial response. Conversely, total nitrogen removal efficiency decreased from 95.3 ± 2.5 % to 76.0 ± 8.8 %, despite enrichment of Denitratisoma oestradiolicum (14.5 %) and denitrifying bacterium clone NOA-1-C (41.7 %), likely due to limited expression of the narG gene. After ceasing oxytetracycline dosing and adjusting operational parameters, total nitrogen removal improved to 87.4 ± 5.8 %. The results of this study underscore the significance and resilience of MABR technology in the treatment of aquaculture medicated bath wastewater.