Phosphorus can be removed by which methods?

• A. Chemical removal
• B. Biological removal
• C. Biological or chemical removal
• D. Physical filtration

Answer: (C)

Phosphorus removal relies on two main approaches: biological removal and chemical removal.

Biological removal uses phosphorus-accumulating microorganisms that take up phosphorus from the water and store it as polyphosphate. In enhanced biological phosphorus removal (EBPR) processes, alternating anaerobic and aerobic conditions encourage these bacteria to release and then take up phosphorus, reducing its concentration in the final effluent.

Chemical removal adds precipitating chemicals, such as iron, aluminum, or lime, to bind phosphorus into insoluble compounds that settle out in clarifiers. This method is effective at reducing dissolved phosphorus that biological processes might not remove.

Some plants use both methods to meet stringent discharge limits or to handle varying loads. Physical filtration mainly removes solids and the phosphorus bound to those solids, but it does not reliably remove dissolved phosphorus by itself, so it isn’t considered a primary method for phosphorus removal.