Conservative pollutants in wastewater are generally characterized by?

• A. Metals
• B. Nitrates
• C. Organic matter
• D. Pathogenic bacteria

Answer: (A)

Conservative pollutants are substances that resist biological breakdown in wastewater, so their concentrations don’t change much through the biological treatment steps. Metals fit this description well because they aren’t eaten or degraded by bacteria; they persist in the water and are removed mainly by physical-chemical methods (like precipitation, ion exchange, or adsorption) rather than by biodegradation.

In contrast, nitrates can be transformed by microbial processes (nitrification and denitrification), organic matter is readily consumed and oxidized by microbes, and pathogenic bacteria can be inactivated by disinfection. These behaviors mean nitrates, organic matter, and pathogens are not considered conservative.