Modelling of simultaneous nitrogen and thiocyanate removal through coupling thiocyanate-based denitrification with anaerobic ammonium oxidation.

Thiocyanate (SCN)-based autotrophic denitrification (AD) has recently been demonstrated as a promising technology that could be integrated with anaerobic ammonium oxidation (Anammox) to achieve simultaneous removal of nitrogen and SCN. However, there is still a lack of a complete SCN-based AD model, and the potential microbial competition/synergy between AD bacteria and Anammox bacteria under different operating conditions remains unknown, which significantly hinders the possible application of coupling SCN-based AD with Anammox. To this end, a complete SCN-based AD model was firstly developed and reliably calibrated/validated using experimental datasets. The obtained SCN-based AD model was then integrated with the well-established Anammox model and satisfactorily verified with experimental data from a system coupling AD with Anammox. The integrated model was lastly applied to investigate the impacts of influent NH-N/NO-N ratio and SCN concentration on the steady-state microbial composition as well as the removal of nitrogen and SCN. The results showed that the NH-N/NO-N ratio in the presence of a certain SCN level should be controlled at a proper value so that the maximum synergy between AD bacteria and Anammox bacteria could be achieved while their competition for NO would be minimized. For the simultaneous maximum removal (>95%) of nitrogen and SCN, there existed a negative relationship between the influent SCN concentration and the optimal NH-N/NO-N ratio needed.