Stable and rapid partial nitrification achieved by boron stimulating autoinducer-2 mediated quorum sensing at room & low temperature

The stable and rapid initiation of partial nitrification is a long-term interest of researchers. In this study, boron, an activator of autoinducer-2 (AI-2), was first proposed to promote partial nitrification and improve sludge properties. Two concentrations of boron were added to six laboratory-scale nitrification reactors to study the effects of boron stimulated AI-2-mediated quorum sensing on nitrification at room and low temperature. Boron could significantly increase the concentration of AI-2 in the reactor (p < 0.05), and the high concentration of boron showed better performance at two temperatures. The realization of partial nitrification was mainly due to the accumulation of NO2-- N promoted by the increase of AI-2 concentration. NO2-- N accumulation occurred in all the boron-treated reactors, while no NO2-- N accumulation occurred in the reactor without boron at room temperature or the accumulation efficiency was 14% lower at low temperature. Community analysis and qPCR further confirmed that exogenous boron had no significant effect on AOB, but inhibited NOB, especially at room temperature. The changes of EPS were slightly different at the two temperatures: at room temperature, boron increased the total EPS production, while at low temperature it mainly changed the PN/PS value of EPS. It was worth noting that the effect of boron on partial nitrification depended not only on its concentration, but also on NH4+-N concentration and temperature. This study provided a new strategy for the rapid and stable initiation of partial nitrification process.

Automated summary

This study proposes the use of boron as an activator to promote partial nitrification and improve sludge properties. The results show that boron significantly increases the concentration of AI-2 in the reactor, and high concentrations of boron have better performance at two temperatures. Partial nitrification is achieved mainly through the accumulation of NO2--N facilitated by the increase in AI-2 concentration. Boron has no significant effect on AOB but inhibits NOB, especially at room temperature. EPS changes were also observed at the two temperatures. This study provides a new strategy for the rapid and stable initiation of partial nitrification.