What is a selector?

• A. Part of the treatment system that selects a specific type of organism by providing an environment (Anaerobic, anoxic, or aerobic) that favors its growth.
• B. A device that removes solids from wastewater.
• C. A chemical used to precipitate metals.
• D. A pump in the plant.

Answer: (A)

A selector is a part of the wastewater treatment system that shapes which microorganisms dominate by creating specific environmental conditions, such as anaerobic, anoxic, or aerobic zones. By controlling the redox state and oxygen availability, it favors the growth of particular groups of microbes that perform desired processes—for example, promoting denitrifying bacteria in an anoxic zone or nitrifying bacteria in an aerobic zone, or supporting phosphorus-removing organisms in EBPR configurations. This targeted environment helps improve process stability, settling, and nutrient removal. It’s not a solids-removing device, a chemical used for precipitation, or a pump; it’s a zone that steers the microbial community through controlled conditions.