Response of nitrogen removal performance, functional genes abundances and N-acyl-homoserine lactones release to carminic acid of anammox biomass.

Carminic acid (CA) can serve as a redox mediator and influence the electron transfer process. CA dosages of 0-5 mg/L were added to anaerobic ammonia oxidation (anammox) biomass. The results illustrated that CA not only reduced the inorganic nitrogen removal efficiency, but also decreased the nitrogen removal rate. The deterioration of nitrogen removal performance was due to the excess production of nitrate-nitrogen. The concentration of extracellular polymeric substances showed a decrease together with a decline in N-acyl-homoserine lactones release. CA addition decreased the activity of anammox bacteria while increasing the nitrifying potential. Quantitative reverse transcription polymerase chain reaction showed a decrease in anammox functional genes (nirS, hzo, and hzsB) and promotion of the expression of the nxrB gene, which corresponded with a decrease in anammox bacteria activity and the improvement of nitrifying potential. As a result, CA should not be added to anammox biomass.