With respect to both phenol ...

With respect to both phenol and cyanide, it is best to keep both from entering the wastewater system. However, some will always get to the wastewater unit. Biological treatment is both possible and efficient depending upon concentration and biological unit capacity. The use of oxidants or chemical treatment should be considered an emergency response rather than a daily application. In one high CN wastewater system, I have seen constant adding of permanganate at the secondary clarifier to control potential CN releases - putting oxidants after biological treatment lowered the required dose.