Function and Direction of Cyanide in Coking Wastewater: from Water Treatment to Environmental Migration

The secondary effluent of coking wastewater treatment plants often contains a low content but tenacious cyanides. In this study, a full-scale double physicochemical synergistic OHHO process was used to investigate the distribution of various cyanides in each unit. The cyanides tend to dissolve and be released under aerobic conditions and precipitated or be adsorbed under anaerobic/hydrolytic conditions. The toxicity and biochemical stability of cyanide conjugates bring about functional control of ammonification–nitritation–nitrification as total cyanides (TCNs) increase under polymetallic restriction. Polymetallic competitive inhibition and π bond activation between coexisting ligands (OH–, Cl–, NH3, and anionic dissolved organic matter (DOM)) and metal ions allowed us to maintain the balance between ionization and complexation of CN–. This paper explored the biological function and migration behavior of cyanide as an indicator in wastewater and water environments and proposed a feasible cyanide removal strategy via polymetallic competition. The synergy between competitive inhibition and activation owing to the coexistence of diverse ligands may benefit the stable occurrence of cyanides in the natural water environment, which is crucial for understanding the geochemical balance and cycle of characteristic pollutants.