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. (C) 2015 Elsevier Ltd. All rights reserved.