Cyanide and hexavalent chromium are specified as harmful substances. From this volume, we will see how they are actually detoxified. Let's start with cyanide detoxification.

(1)Treatment of constant effluent containing cyanide

A method called alkaline chlorination is adopted for detoxification. This process alkalifies cyanide effluent and dissolves it into carbon dioxide and nitrogen by the action of chlorine. This process is usually performed in the following three stages:

(2)Highly concentrated effluent

For highly concentrated cyanide effluent, including old plating solution, plating film detachment solution, and exhaust gas cleaning solution, disposal is handled by an industrial waste treatment facility, instead of each plant detoxifying the effluent. Such companies are required to fully comply with the specified procedures after detoxifying the industrial waste by designated methods, such as the high-pressure hydrolysis method and electrolytic oxidation method.

(3)Incidents

From time to time, there are incidents where the cyanogen level exceeds the effluent standards. Most of such incidents are caused by incomplete separation of drainage, resulting in such effluent mixed into unintended drainage, not because of the inadequate cyanogen treatment.