Open Platform Low-Pressure Membrane System Procurement and Design – A Case Study from Post Falls, Idaho

The City of Post Falls, Idaho owns and operates a secondary treatment Water Reclamation Facility (WRF) utilizing enhanced biological phosphorus removal (EBPR) to treat municipal wastewater generated within its service area. The City’s WRF average daily flow (ADF) design capacity is 5 mgd with peak flow (PF) capacity of approximately 12 mgd. Reclaimed water from the Post Falls WRF is discharged year-round to the Spokane River under a NPDES Permit. New NPDES limits and a compliance schedule targeting reduced discharges of five-day carbonaceous biochemical oxygen demand (CBOD5) and total phosphorus (TP) are being driven by a total maximum daily load (TMDL) for dissolved oxygen (DO) in the receiving water body. To meet loading caps of 255 lbs/day CBOD5 and 3.19 lbs/day TP, concentration limits will decrease as future flows increase to eventual limits of <6 mg/L CBOD5 and <50 ?g/L TP, arguably some of the most stringent limits in the nation. The City undertook an 18-month pilot study in 2017 to test three microfiltration (MF)/ultrafiltration (UF) pressurized membrane modules in a tertiary filtration application targeting the new effluent requirements. During the pilot study, the City identified early on that the full-scale system would utilize an “Open Platform” membrane system to increase overall system reliability and long-term flexibility of their investment. Without a clear industry-wide definition for “Open Platform”, the City maintained the goal of targeting an Open-Platform membrane rack system that could accommodate a minimum of 2 of the 3 piloted (proven) modules, each with unique operating conditions. The City saw the Open Platform approach as a way of maintaining long-term flexibility to switch modules in the future (when replacing membranes) as well as provide a robust and competitive bidding environment for their initial installation. This paper presents the advantages and challenges associated with procurement and design of the Open Platform equipment and design approach for full-scale implementation. Overall, this paper highlights important elements, considerations and mitigation approaches for designers, system owners and equipment suppliers related to Open Platform system procurement and design.

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