I don't know your particulars, so I've thrown in some regulatory info which might be helpful.
Obtain a Wastewater Treatment Permit for Cyanide Destruction from Cal/EPA and your CUPA (local administering agency). Cyanide treatment is not allowed under Permit-By-Rule or other minor WWT permits; I believe a cyanide treatment permit ('Variance') currently costs about $11,000 in California. It costs more if you do it w/o a permit & get caught; unless you like free, state-provided room & board!
Also, it will be easier to get a permit if you simply buy a cyanide destruct system with which Cal/EPA is familiar, rather than D-I-Y. Everything must be approved in advance. Lots of wastewater treatment vendors can supply; plus used equipment dealers listed in the metal finishing magazines.
Give your WWT workers Hazardous Waste Training, which must include all of your specific hazards. There are private schools & UC-Extension for 40-hour OSHA HAZ/WOPER training.
I've excerpted the following from a batch-type WWT procedure for dilute cyanide concentrations in the presence of metals (Ni & Zn).
The two-stage oxidation treatment first breaks down cyanide to cyanate at high pH. The cyanate is then destroyed at moderate pH. Either calcium hypochlorite (granules) or sodium hypochlorite solution may be used. For an automated system, the liquid hypo solution is used.
Personal protective equipment: Gloves, apron, boots, goggles
[provide lots of ventilation. Don't require respirators; it necessitates extra OSHA-mandated costs. Workers won't wear them if they think unnecessary, then an OSHA visit incurs serious fines.]
5) Start the mixer. Check the pH of the BTT [Batch Treatment Tank] solution. Adjust pH to 11-11.5 range.
6) Add hypochlorite to raise the ORP to about 200 mV.
Note: ORP varies with pH (decreases as pH increases). Allow to mix 20-30 minutes.
7) Lower the pH to about 8 (7.5-8.5). Check ORP. It should be about 500-600 mV. Add hypochlorite if necessary. Mix 20-30 minutes.
If you have significant cyanide concentrations, add 10 minutes to each step. More if the temperature is ever below 65oF. Also, at least initially, do a lot of testing to verify the efficacy of each stage.
