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

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 aprox. 70% of the total DNA sequences). Other coexisting microbial groups belonged to Rhodocyclaceae (class beta-Proteobacteria), Anaerolineae (phylum Chloroflexi) and Ignavibacteriaceae (phylum Chlorobi)