Automating Chemical Phosphorus Removal in Real Time

After receiving a new effluent permit with a 1.0 mg/L total phosphorus average monthly limit, the staff at the Hutchinson, MN wastewater plant concluded the only way to meet this limit was by using chemicals and precipitating the orthophosphate with their existing treatment system. Due to extreme swings in the influent phosphate concentration causing effluent values higher than the limit, the staff decided to implement an automatic chemical dosing system to react to the influent phosphate swings in real time. Before the real time control system was implemented, staff fed as much chemical as possible in order to meet their effluent target—sometimes as much as eight times the amount of chemical actually needed. After the system was installed, only the amount of chemical needed to achieve the set point was fed, reducing chemical consumption approximately 88%, and large swings in the effluent total phosphorus concentration have been eliminated