New Hampshire Municipal Wastewater Treatment Facility
Re-engineering a 6.0 MGD municipal wastewater treatment plant to provide biological phosphorus removal was accomplished by turning off aeration to the first cell of the multi-celled aeration tank and mixing the contents with mechanical mixers.
Chemicals – PAC, poly-aluminum chloride – are added to treated wastewater at the splitter box that directs the flow leaving the aeration tanks and directs it to the plants secondary clarifiers. An in-line ortho-phosphate monitor tracks and records the final effluent concentration.
The combination of biological and chemical treatment produces and effluent with a total-phosphorus concentration that averages less than 0.2 mg/L. Without filtration.
Using this approach, the municipality has avoided a multi-million dollar investment in new anaerobic tanks, additional clarifiers, and final effluent filtration. Because chemical addition is necessary to precipitate copper, plant staff considers the chemical phosphorus removal to be a beneficial side benefit of copper removal. In other words, it costs almost nothing more for the plant to produce an effluent with 0.2 mg/L than it did to discharge more than 1.0 mg/L total-P prior to the process changes.
The pre-anaerobic zone creates VFAs (volatile fatty acids). As the VFA rich flow moves into the aeration tanks, phosphorus accumulating organisms (PAOs) use the VFAs as a fuel source to take ortho-phosphorus out of solution and convert the soluble phosphorus to cellular phosphorus. The chemicals added for copper removal, precipitate what little soluble phosphorus remains after aeration.
By re-engineering the use of the existing plant, City personnel are getting better treatment at the same cost with multi-million dollar savings, more sustainably.