1). While holding the pH at 2.0- 2.5 with sulfuric acid, bisulfite (sodium, calcium or meta) needs to be added to reduce the ORP value by a shift of 50mV. When the change in ORP value is noted, this indicates the reaction is complete. This change happens quickly so it is crucial that the pH of the water be held tightly so as not to mistake a rise in pH for the completion of the reduction reaction. Once this drop in ORP has occurred the color will also change from orange to blue and the pH can then be adjusted up using caustic soda to 8.5-8.8 for the best removal of the trivalent chrome.
2). If you are at a pH > than 2.5 and don’t want to add acid, reduction of hexavalent chrome can be done by the addition of Aquapure™ I-300 wastewater treatment chemicals. Typical additions are 1-3 mls/gallon of rinses contaminated with hexavalent chrome but may require more. Jar testing should be done to determine the best dosing.
In all cases, water needs to meet local, state and federal guidelines for chrome removal.