Enrichment of anammox bacteria in up-flow bioreactors enhanced with plastic and rock media: Long-term performance monitoring with fluorescence and specific conductivity.

Anaerobic ammonium oxidation (anammox) is a low energy, biological process for removal of nitrogen from wastewater. Here we tracked anammox enrichment and recovery after environmental disruption using two rapid monitoring techniques, fluorescence and specific conductivity, and compared the ability of two readily available media types, plastic (PMR) and lava rock (RMR), to serve as biocarriers for anammox in low-maintenance, up-flow bioreactors. We found that both PMR and RMR became enriched with primarily Candidatus brocadia-dominated microbial consortia. Optimal (> 90 %) ammonium-N and nitrite-N removal was accomplished more rapidly in PMR (after 147 d) than in RMR (after 171 d). However, after long-term operation, RMR was more resilient to disruption than PMR. In both reactors, the increase in effluent/influent ratio of the Freshness Index, and the reduction in specific conductivity from influent to effluent were significantly correlated with ammonium uptake during the start-up phase but not in the stable phase.