Tennessee Wastewater Operator Practice Exam

After biological treatment is complete, most remaining phosphorus will be present as which form?

1. Polyphosphate

2. Organic phosphate

3. Orthophosphate

4. Phosphite

The correct answer is: Orthophosphate

After biological treatment, most remaining phosphorus will primarily be present as orthophosphate. This form of phosphorus is the simplest and most bioavailable, existing as inorganic phosphate ions (PO4^3-). During biological treatment processes, microorganisms typically uptake phosphorus in the form of orthophosphate, which is then incorporated into their cellular structures. As biological treatment proceeds, the complex organic forms of phosphorus, such as polyphosphates and organic phosphates, are often broken down or converted, leading to a predominance of orthophosphate in the effluent. Although some phosphorus may remain in other forms, orthophosphate is the most common state left after the biological treatment phase, making it a key parameter to monitor in the treatment process.