Which waste category's key contaminants include COD, Oil & Grease, Heavy Metals and Cyanide?

• A. Metal Plating
• B. Cannery
• C. Oil Refinery
• D. Steel Mill

Answer: (A)

Wastewater from metal finishing processes carries a distinctive mix of contaminants tied to the plating operations. Plating baths often introduce heavy metal ions into the effluent as parts of the coating metals (such as chromium, nickel, copper, zinc, cadmium, etc.). Many plating setups also use organic cleaners and degreasers, which raise the oxidizable organic load measured as COD, and lubricants or oils used in processing can contribute Oils and Grease to the wastewater. In some plating lines, cyanide is used in the plating baths (for example in various gold and silver plating processes), leaving cyanide as a key contaminant in the effluent. When you see COD, Oil & Grease, Heavy Metals, and Cyanide listed together, it points to metal finishing waste streams, where this combination of organics, oils, metals, and cyanide is characteristic of the processes involved. The other industries listed typically have different dominant contaminants (for example, cannery waste emphasizes organic matter and fats/oils but not cyanide; oil refineries focus on hydrocarbons; steel mills have metals and process chemicals but cyanide is not a defining contaminant).