Civil Engineering PE

Answer: A - Wastewater treatment plant effluent may need to be dechlorinated to reduce the toxicity due to chlorine residuals. High levels of chlorine residuals are toxic to certain kinds of aquatic life. Chlorine residuals may react with organic materials found in certain receiving waters and form carcinogenic compounds that may not be removed by conventional water treatment plants. Many times, regulatory agencies require municipalities to add dechlorination facilities to existing treatment plants and set specific design criteria. The type of dechlorination system selected is based on the following criteria: type of chemical storage required, amount of chemical needed, ease of operation, compatibility with existing equipment, and safety.