Response of nitrification system to co-exposure of sucralose and single or combined disinfectants: Reducing damage to nitrification performance and aggravating the spread of intracellular resistance genes

Abstract

Sucralose (SUC) is an artificial sweetener for everyday consumption and often co-exists with disinfectants such as triclosan (TCS) and dialkyldimethyl ammonium compound (DAC) in sewage. Considering their continuous accumulation in sewage, it is essential to understand the impacts of their single and combined stress on the evolution of resistance genes (RGs) and microorganisms. In this study, three sequencing batch reactors (SBRs) were established, which were added with SUC, disinfectant, SUC and disinfectant, respectively, and named SSBR, DSBR and SDSBR in turn. There were four stages in total, the first two stages and the latter two stages were set to explore the effects of co-exposure of SUC and single disinfectant (TCS), SUC and combined disinfectants (TCS and DAC) on nitrification system, respectively. SSBR showed excellent ammonia oxidation performance in the whole operation stages. Compared with DSBR, the microorganisms in SDSBR under the combined stress of SUC and TCS were less inhibited. TCS and DAC destroyed the ammonia oxidation performance of DSBR and SDSBR. Within 120 days, the removal efficiency of TCS reached 90 %. In SSBR, 1 mg/L SUC promoted the proliferation of RGs, especially induced free RGs in water (w-RGs) to maintain high abundance and persistence. Compared with single stress, the abundances of intracellular RGs in sludge were higher under the combined stress of SUC and TCS, and the risk of RGs transmission was greater. The combined stress of SUC and disinfectants (TCS and DAC) led to a higher enrichment of w-RGs, exacerbating the risk of w-RGs transmission.