Energy recovery technologies such as the pressure exchanger (PX), have previously focused on seawater RO applications due to the rather quick payback. This leaves brackish water RO (BWRO) facilities to turbochargers that yield less efficient transfer of energy than their PX counterparts. Recently, the first municipal BRWO application of a PX energy recovery device was designed for the City of North Port, Florida’s Southwest Water Treatment Plant and will be started up in 2nd quarter 2022. This greenfield facility currently has a raw water TDS of about 3,500 mg/L and is anticipated to experience raw water quality degradation based on predictive groundwater modeling. The City’s vision for facility includes long-term resiliency and longevity which drove the team to design a wide range of TDS from the aquifer supply including future TDS levels of nearly 13,000 mg/L. This anticipated increase in TDS levels drives careful design, operations, and equipment considerations. More specifically, the energy load for the facility jumps dramatically over the degradation of water quality. The design team sought out opportunities to reduce overall operation expense through PX integration in the high salinities and the first of its kind, low TDS early stages of the facility. These complexities will be identified in the paper as well as a large focus on the PX integration at both low brackish water and into seawater salinities. With feed pressures ranging from 200 psi to 520 psi, the PX offered a significant energy saving opportunity. An overview of the PX operation will be included to orient the audience with the benefits and drawbacks identified for both seawater and this brackish water application. The integration into a BWRO process varies significantly from the seawater application. Accordingly, the paper will describe the challenges of implementing PX devices into brackish systems and functionality required to ensure the system will achieve the proper operation. A detailed dive into the instrumentation, connectivity of the hydraulics and water quality relationship will be discussed as it varies dramatically from the traditional seawater application. Once the hydraulics and instrumentation items are addressed, the paper will tackle the major benefits of integrating the PX into a BWRO system including:• Approximately 20% (or more) reduction in membrane feed pump flow, resulting in reduced feed pump horsepower and total dynamic head • Reduced energy requirements • Reduced capital and operating costs This will be the first Brackish Water municipal installation of the Brackish pressure exchanger within the U.S. This paper will present and discuss the design considerations and key parameters including impacts to RO system operation and water quality, energy saving considerations, and data from the facility startup in 2nd quarter 2022. Municipalities with brackish-water supplies will be shown the way to reduce operating costs and maintain water quality from their RO treatment facility.
This presentation is available to AMTA Members only.
- Lance Littrell
- AMTA/AWWA Membrane Technology Conference, Las Vegas
- AMTA/AWWA Membrane Technology Conference
- BWRO, Seawater RO, Brackish Water