Promotion of the start-up of the anammox reactor with exogenous boron

In this study, boron, an essential element of interspecies quorum sensing (QS) signals, was first proposed to enhance the start-up of the anaerobic ammonium oxidation (anammox) process. Exogenous boron was added into the anammox reactor, and its effect on the ammonia removal, granulation, AI-2 QS, and microbial community was examined. The results showed that the total nitrogen conversion rate in the experimental upflow anaerobic sludge blanket (UASB) with exogenous boron added (denoted as e-UASB) was 0.7 & PLUSMN; 0.05 kg N m(-3) d(-1), approximately three times that in the control UASB without boron (0.23 & PLUSMN; 0.05 kg N m(-3) d(-1), denoted as c-UASB). The exogenous addition of boron elevated the AI-2 concentration, increased the content of extracellular polymeric substances (EPS), and promoted granulation in the UASB during start-up. Microbial community analysis indicated that the abundances of anammox bacteria, i.e. Candidatus Brocadiales and Candidatus Jettenia, in the e-UASB were much higher than those in the c-UASB (25.5% vs. 19.7%). Additionally, Anaerolineaceae, which is known to play an important role in the granulation of anammox bacteria, had an abundance of 21.13% in e-UASB and 17.74% in c-UASB. It is demonstrated that exogenous boron could be promising in enhancing the start-up of an anammox reactor through promoting QS, granulation, and anammox.