Ferric Chloride in Wastewater Treatment

Wastewater Treatment Facilities have been built to remove biological and chemical waste from water as it is used. These facilities maintain a healthy environment for organisms as well as people because it removes potentially harmful material and kills pathogens that would easily spread through cities. Phosphorus is a compound of interest because a high concentration of it at discharge will eventually lead to eutrophication and hypoxia in local waterways. For these reasons, the Environmental Protection Agency has reduced the allowable concentration of phosphorus in effluent from 1.0 ppm to 0.1 ppm. Ferric chloride is used in wastewater treatment facilities to precipitate phosphorus to remove it from the system. The question is whether ferric chloride can continue to remove phosphorus at a steady rate or will it reach a point at which it is no longer effective? I hypothesize that at the facility level the ferric chloride will have a significant effect on the amount of phosphorus in the effluent as it is discharged into the lake. In the lab I hypothesis that as more ferric chloride is added to a standardized solution more phosphorus will be precipitated out. Ferric chloride has a significant effect on the removal phosphorus at facility levels because as more ferric chloride is added into the effluent the phosphorus is precipitated out of the effluent and the final concentration of phosphorus is less than 1.0 ppm. In the lab, phosphorus concentrations at one ppm behave as expected with more phosphorus precipitated at greater doses of ferric chloride. At greater initial phosphorus levels, it seems to be less effective and precipitates less phosphorus as ferric chloride doses increase.