Effects of different exogenous signal molecules on the reactor performance, sludge properties and microbial community structures of mixotrophic nitrogen removal process

As a form of microbial interaction, quorum-sensing signal molecules can control the expression and functionality of related genes within microorganisms. The current study looked into the effects of various signal molecules on the process of nitrogen removal. The findings illustrated that 2µM signal molecules, namely C6-HSL, C8-HSL, C10-HSL, C12-HSL, and 3-oxo-C8-HSL diminished the overall nitrogen removal efficiency (TRE) from 37.8% in the control, down to 26.8%, 26.0%, 28.1%, 27.6%, and 27.7%, respectively. Nevertheless, these molecules only slightly affected ammonia removal efficiency, reducing it from 67.9–63.7%, 62.8%, 62.6%, 63.7%, and 62.9%, respectively. C8-HSL, C10-HSL, and 3-oxo-C8-HSL significantly enhanced the relative abundance of denitrifying bacteria from an initial value of 36.3–37.00%, 35.76%, and 36.86%, in contrast to C6-HSL and C12-HSL, which caused a reduction to 24.39% and 26.56% respectively. The signal molecules were suspended in methanol, resulting in an elevation of the relative abundance of denitrifying bacteria from an initial 14.31–30.09%, paralleled by an increased TRE value of 27.6–37.8%. Environmental alterations, together with methanol provision, both constrained the Anammox activity. Furthermore, the incorporation of C6-HSL led to a decrease in the secretion of extracellular polymeric substance while a corresponding increase in soluble microbial products was noted. This research implies that 2 µM signal molecules could considerably influence reactor performance and microbial components of the mixotrophic nitrogen removal operation. The information presented will contribute additional insights into the impact of signal molecules on both the Anammox and mixotrophic nitrogen removal procedures.