Phosphorus removal from municipal wastewater by hydrous ferric oxide reactive filtration and coupled chemically enhanced secondary treatment: part I--performance.

This work examines the performance of a hydrous ferric oxide (HFO) reactive filtration (RF) process with coupled chemically enhanced secondary treatment (RECYCLE) for phosphorus removal from municipal wastewater (HFO-RF-RECYCLE). A 3-month, 0.95-ML/d (0.25-mgd) demonstration of HFO-RF-RECYCLE was performed at a municipal wastewater treatment plant equipped with oxidation ditches and secondary clarifiers. Influent to the plant averaged 6.0 mg/L phosphorus, with a tertiary effluent average of 0.011 mg/L phosphorus. Iron doses to the plant were low, at 5 mg/L. Inline recycling of HFO solution rejects to the plant influent resulted in a maximum 90.3%, dose-dependent reduction of phosphorus in the secondary effluent at 4.5 ML/d (1.2 mgd). Other results included reduction of total suspended solids and turbidity. A mass balance analysis was performed. We conclude that HFO-RF-RECYCLE may allow very low levels of phosphorus discharge from municipal wastewater treatment plants with a ferric-iron-based tertiary filtration process and residual recycling.