Improving nitrogen removal in an ANAMMOX reactor using a permeable reactive biobarrier

A novel ANAMMOX biofilm reactor that combines the advantages of conventional biofilm reactors and membrane bioreactors (MBRs) was developed in an attempt to decrease the levels of nitrogen in the reactor filtrate. In this reactor, nonwoven fabric modules served as both biofilm carriers and membrane-like separators, and the biofilm acted as a permeable reactive barrier for the removal of nitrogen species from the bulk liquid. Long-term monitoring suggests that the nitrogen removal rates (NRR) of the reactor reached ca. 1.6 kg-N/(m(3) d). Interestingly, large fractions of the ammonium (ca. 27%) and nitrite (ca. 48%) remaining in the bulk liquid were removed during their transport through the biofilm; thus, the reactive barrier process of the biofilm contributed ca. 11% to the total NRR. With an increase in the imposed flux, the contribution of the reactive barrier process to the removal of nitrogen from the reactor bulk liquid increased significantly, e.g., it contributed 26% to the NRR at 17.4 L/(m(2) h). Additionally, the nonwoven modules could retain free bacteria effectively; they maintained a non-fouling state during the entire operation period of approximately 400 days. Sequence analysis shows that Candidatus Kuenenia-like species dominated the ANAMMOX bacteria in the reactor. These results clearly demonstrate that this innovative reactor holds great promise for improving the ANAMMOX process, thus decreasing nitrogen levels in the effluent.