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City outlines tertiary treatment upgrades at water reclamation facility to meet DEQ limits
Summary
Utilities manager Craig Vorpahl briefed the Post Falls City Council on startup of new tertiary clarifiers and membrane filtration at the water reclamation facility, saying the facilities must remove additional phosphorus to meet a DEQ permit limit and that optimization is underway.
POST FALLS, Idaho — City utilities staff on Dec. 17 outlined the start-up and purpose of new tertiary treatment equipment at the Post Falls water reclamation facility and explained why facilities beyond the city's long-standing secondary treatment system are required.
"We're going to be giving a staff update on tertiary treatment," utilities manager Craig Vorpahl told the council, using a seasonal analogy: while secondary systems remove the bulk of contaminants, "to get to that last little bit, that's where we're going to have to call upon something additional." Vorpahl said a pilot study informed a two-step approach: tertiary clarification to chemically bind and remove phosphorus, followed by membrane filtration to reach the city's permit limit.
Vorpahl reported that existing treatment removes about 96% of total phosphorus but the discharge remains above the permit. The transcript shows staff describing incoming and discharged phosphorus with a symbol that appears inconsistent ('about a £190 per day' incoming, '£7 per day' discharge, permit limit '£3.19 per day'); staff said the tertiary clarification plus membrane filtration approach is intended to meet the stated permit limit. Vorpahl described membrane pore size as 0.3 microns and said the new facilities can treat about 5,200,000 gallons per day while current flows are about 3,100,000 gallons per day. He said staff are now optimizing chemical dosing and the split of flow through clarification versus membrane filtration so the system meets limits without unnecessary extra cost or energy use.
During questions, Vorpahl clarified that river discharge permits focus primarily on phosphorus, while land-application permits emphasize nitrogen and that the two permit types have different requirements. He said the new tertiary equipment will also enable expanded recycled-water land-application options in the future. Vorpahl closed by noting staff will continue optimization during start-up and offered further briefings for council and staff.
What happens next: Staff will continue start-up optimization, confirm permit compliance in operational testing and report progress to the council.
