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

Abstract 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 (NH 3 ). 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 NH 3 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.