Chlorine is often used, and ...

Chlorine is often used, and yes the pH must be elevated to keep it in solution.  However a stronger oxidizer is often needed, and hydrogen peroxide is a stronger oxidizer with none of the toxic products that may be produced with chlorine in several forms.  That being said  chelated cyanides present a slightly different problem because they may be more stable.   When you mention detergents, you are probably having a problem with chelated cyanides and may move to a stronger oxidizer, and a longer time for cyanide removal.  The CN bond is easy to break when alone and simple.  This sounds like something more complex, otherwise you could remove the cyanide with simple aeration  with exposure to UV light from the sun.

To comment further, yes cyanide is biodegradable with the addition of certain strains.  I have done it with combinations of added air with bacillus and pseudomonas strains (they both need air) grown for this specific purpose.  But, again the time of reaction is slowed by chelants such as EDTA.   Time can be achieved  with larger holding tanks.  Adding air injections should help the process.   You may need all of the above suggestions to get the job done with that much detergents.  Also look at methods to remove the detergents first.   By the way, chlorine is probably being stripped out, of the process - as it often is.