Changes in the process performance and microbial community by addition of the metabolic uncoupler...

A complete study about the effects of 3,3',4',5-tetrachlorosalicylanilide (TCS) on organic matter elimination performance, sludge production and on the microbial community of a biological wastewater treatment process has been performed. For this purpose two sequencing batch reactors (SBR) worked in parallel for 43 days with 0.8 mg·L^-1 of TCS (SBR-1) and without this metabolic uncoupler (SBR-2). Results indicated that 63.3% of sludge reduction was achieved in SBR-1. However, COD removal efficiency was maintained in similar values in both reactors (89.1% and 92.1% in SBR-1 and SBR-2, respectively). The exhaustive mixed liquor characterization led to know deeply the action mechanism of TCS. In this way, a 69% of adenosine triphosphate (ATP) reduction was observed in SBR-1 in comparison with values measured in SBR-2. On the contrary, an increase in soluble microbial products (SMP) and DNA concentrations occurred as a consequence of TCS addition. Thus, it could be concluded that sludge reduction due to TCS addition was due to both uncoupling effect and cellular lysis. Also, increase in all microbial hydrolytic enzymatic activities measured was observed, which explained the stable performance achieved in SBR-1 despite to the results explained above. It should be highlighted that this uncoupler should not be used in biological treatments that require nitrogen elimination because nitrifying bacteria were affected by its addition (Nitrosomonas and Nitrospira). Finally, the 16S rRNA gene amplicon sequencing informed that an important reduction of bacterial diversity resulted in SBR-1 due to TCS addition.