No Chemical Treatments In Waste System?

First let me say Happy new Year to everyone out there, it's been a while since I have been on this great site,hope all is well with everyone! Now to my question, I recently visited one of sister company's plating facilities and their waste water facility. What struck me as odd was they did not put any chemical additions into their waste stream until it hit the floc, all they use is an anodic flock, they treat the Cn separately with chlorine gas and hypochlorite. Has anyone heard of this? the fellow that runs their waste room said that have great luck with it and it also reduces the sludge in their clarifier. I know in our system where I work we use calcium chloride and alum sulphate, that gets metered into our pre-treat tank at a ratio of 3:1. Like I said I never heard of this before and I was wondering if anyone else has heard of it--they plate Ni, Cu, Cn, tri-chrome & brass.

Best Regards

Since they treat the CN waste separately and they have no hexavalent chromium, it is not beyond the realm of possibility that the pH can naturally self-adjust to an acceptable range for good precipitation. I've never seen it do so consistently myself, but I have seen the condition exist in passing. With a large balancing tank and consistent production I suppose it's possible. Coagulant/coprecipitants like calcium chloride, alum, and ferrous sulfate ⇦ on eBay or Amazon [affil link] are usually beneficial in reducing dissolved and suspended heavy metals, but if they can comply with their permit without them, nothing wrong with that.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey