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 ₄ ⁺ -N/NO ₂ ^- -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 ₄ ⁺ -N/NO ₂ ^- -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 ₂ ^- 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 ₄ ⁺ -N/NO ₂ ^- -N ratio needed.
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