Development of four-stage moving bed biofilm reactor train with a pre-denitrification configuration for the removal of thiocyanate and cyanate

•Two four-stage MBBR trains (A and B) completely degraded thiocyanate and cyanate.•The highest total-N removal was observed at a loading rate of 5.6 mg-N L−1 h−1.•Pre-denitrification configuration allowed higher total-N removal in the B train.•Thiobacillus spp. were the predominant bacteria in all MBBRs.•Nitrogen dissimilatory process by anammox would have occurred in the B train.

Two trains (A and B) of four-stage moving bed biofilm reactors (MBBRs) were developed for the degradation of thiocyanate (SCN−), cyanate (OCN−) and ammonia (NH3). A pre-denitrification configuration was established in the first-stage reactor of the B train using SCN− and OCN− as the sole carbon source. SCN−, OCN− and NH3 were completely removed in both trains. The highest removal of total nitrogen equivalent (total-N) occurred at a loading rate of 5.6 mg-N L−1 h−1. The pre-denitrification configuration resulted in increased total-N removal in the B train (62.6%) compared to the A train (38.5%). Thiobacillus spp. were the predominant bacteria in all MBBRs. Bacteria related to bioprocesses involving anaerobic ammonium oxidation were present in the B train, suggesting that part of nitrogen removal occurs via this pathway. Our results showed that the pre-denitrification configuration increases the efficiency of removal of total-N compounds in the SCN−/OCN−-degrading MBBR process.