To reduce coliform levels in a facultative pond discharging to surface water (flow and temperature constant), which action is appropriate?

• A. Increase chlorine to the effluent to bring residual up
• B. Raise water temperature and detention time of biological treatment
• C. Adjust pump station controls to produce shorter, more frequent run times
• D. Install an aerator in the pond to increase both mixing and DO

Answer: (A)

Directly reducing the number of coliforms in the discharged water comes from disinfection, not just from how the pond operates biologically. With a constant flow and temperature, increasing the chlorine residual in the effluent provides immediate, measurable disinfection that inactivates coliform bacteria as the water leaves the plant. This is the most reliable way to meet surface-water discharge limits, because it adds a sanitizing step before the water enters the environment.

Raising temperature or increasing detention time would try to improve the pond’s biological treatment, but those factors aren’t being adjusted in this scenario, and they don’t guarantee the level of disinfection needed. Shorter, more frequent pump run times don’t address the pathogen content in the effluent. An aerator can improve mixing and oxygen, which helps overall pond health, but it doesn’t reliably achieve the required pathogen reduction on its own.

So, increasing the chlorine residual directly targets coliform reduction at the point of discharge. Just be sure to manage chlorine dosing to meet regulatory limits and consider any dechlorination needs before releasing into the environment.