Enrichment and characterization of autotrophic Thiobacillus denitrifiers from anaerobic sludge for nitrate removal

•Thiobacillus-dominated (55%) denitrifiers were enriched from anaerobic sludge.•A simple method using thiosulfate to enrich denitrifiers in 28 days was proposed.•Autotrophic denitrification rate of the final enrichment was 21 mg N (g VS d)−1.•No accumulation of nitrite and N2O in the batch and continuous biofilters.•Nanostructured pyrrhotite supports autotrophic denitrification.