Metal finishing industries can discharge wastewater with which features?

• A. High BOD with easy biodegradation
• B. Little BOD but may contain toxic pollutants; pH 1-12; may contain phosphates, chromate, cyanide, and metals; metals may concentrate in sludge and must be reported
• C. No heavy metals present
• D. High BOD and metals easily removed by treatment

Answer: (B)

Wastewater from metal finishing operations typically has a very low organic load but can carry hazardous inorganic pollutants. The critical concerns are the presence of heavy metals and other toxic substances, not a large amount of biodegradable organics. The pH can swing widely, from very acidic to very basic, and there may be contaminants such as phosphates, chromates, cyanide, and various metals. Because metals can concentrate in the sludge, the waste stream becomes a hazardous concern that must be properly reported and disposed of, often requiring pretreatment to precipitate metals and to bring pH to discharge limits.

This is why the option describing little BOD but potential toxic pollutants, extreme pH, presence of phosphates, chromate, cyanide, and metals, with metals concentrating in sludge and needing reporting, best matches what metal finishing wastewater typically contains. Other descriptions don’t fit the common profile—for example, metal finishing usually isn’t high in BOD, it often does involve heavy metals, and metals aren’t always easily removed by basic treatment methods.