Analysis for Trivalent and Hexavalent Chrome in wastewater

Hi. We are a tannery processing hides using chrome powder (as Cr2O3, trivalent) as the main tanning agent. So our wastewater would naturally contain chrome, I think in its trivalent form still. A brief background on the tanning process - we pickle the hides to a pH of 2.8 using formic and sulfuric acids, add the chrome powder in, the lastly basify or neutralise the bath to fix the chrome onto the collagen structure using alkali such as magnesium oxide, sodium bicarbonate or sodium carbonate / washing soda [affil. link to info/product on Amazon] to a pH of around 3.8-4.0.

Our government regulation for discharge of wastewater is for hexavalent chrome and not for trivalent chrome. But the laboratory analysis they use to determine the amount of chrome in the wastewater is for total chrome, which I think is not fair for us. Total chrome would mean discharge of both tri and hex chrome, am I correct? I would like to ask if there are separate procedures for analysing tri and hex chrome? Also, with the process I gave above, is there a chance that the tri chrome are converted to hex chrome? How are the tri chrome converted to hex chrome? Is it easily converted?

HACH makes test kits for Hex-Chrome, Tri-Chrome and Total Chrome. You can run all 3 tests and see what the difference is. I do not think you will get a permit change for total chrome to trivalent chrome. You can oxidize the tri-chrome back to hex-chrome, but from what I can tell you are not adding oxidizers into your process. If you are concerned that you may be, add a hex-chrome reduction step into the wastewater treatment plan.