Characterization of a combined batch-continuous procedure for the culture of anammox biomass

•A combined batch-continuous method for culturing anammox biomass was investigated.•120-d batch enrichment resulted in an anammox activity of 118 mg NH4+-N/(g VS d).•Biomass was cultured in a continuous fixed-bed upflow reactor using ∼1.2 g N/(L d).•The overall procedure prompted selection of the anammox species Ca. Brocadia sinica.

Interest in autotrophic nitrogen (N) removal through anaerobic ammonium oxidation (anammox) is high in the field of wastewater treatment as a more economic and sustainable alternative than conventional nitrification-denitrification. However, anammox biomass is difficult to enrich, and this can hinder the start-up of new applications. We carried out experimental work to characterize a combined batch-continuous procedure for the enrichment and culture of anammox biomass. In the first stage (time span: 120 d), the enrichment was started in batch mode (sealed vial) using suspended activated sludge as inoculum. Anammox activity was clearly developed since the specific ammonium (NH4+) conversion rate increased from 0 to 118 ±1 mg NH4+-N/(g VS d) (VS, volatile solids); i.e., 560 ±11 mg N/(L d) in terms of N-conversion rate (NCR). Subsequently, the sludge was transferred into a continuous upflow reactor packed with a polyester non-woven material to promote the attached growth of the biomass. Such bioreactor was operated without interruption during 400 d. Under an appropriate feeding regime, the anammox activity increased fast, and a sustained NCR of 1183 ±100 mg N/(L d) was reached according to the N-loading rate applied. Evolution of the microbial community structure was characterized using high-throughput DNA sequencing. The overall procedure prompted the selection of a community enriched in the anammox bacterial species Candidatus Brocadia sinica (up to ∼70% of the total DNA sequences). Other coexisting microbial groups belonged to Rhodocyclaceae (class β-Proteobacteria), Anaerolineae (phylum Chloroflexi) and Ignavibacteriaceae (phylum Chlorobi).

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