When the Florida Keys Aqueduct Authority opens its upgraded desalination plant on Stock Island, Danfoss high-pressure pumps and energy recovery devices will radically improve the energy efficiency of a SWRO plant that plays a central role in the Florida Keys water supply strategy.

The Florida Keys Aqueduct Authority (FKAA) supplies 20 million gallons of potable water per day (75.7k m3/d) to its nearly 80,000 customers in the Florida Keys. While most of the water is normally sourced in aquifers, FKAA also operates two seawater reverse osmosis (SWRO) plants for emergency purposes and as a supplemental supply in periods of high demand.

FKAA initiated the upgrade of one of these plants, the Kermit H. Lewin Water Treatment Plant located on Stock Island, to increase its capacity, make it more resilient to hurricanes and rising flood levels, and improve its energy efficiency. Since opening in 1980, not only have guidelines for storm protection of such critical infrastructure changed significantly, so has the potential to save on the energy required by desalination.

Designed to withstand future floods and hurricanes

To improve resiliency to extreme weather events in the low-lying Florida Keys, the entire site and facility have now been upgraded to withstand Category 5 hurricanes, the most dangerous level of tropical storms. With sustained winds above 157 mph (252 kph), such storms can cause severe damage to everything in their path.

Accordingly, the refurbished facility lifts all electrical and mechanical equipment above the base flood elevation and expected sea-level rise anticipated by 2060, effectively placing the plant’s desalination operations on stilts to mitigate the risk of severe flooding.

Best-in-class energy efficiency reduces electricity consumption by 66%

Another key goal of the upgrade was to improve the plant’s energy efficiency at the same time as doubling its production capacity from 2 MGD (7,500 m3/d) to 4 MGD (15,000 m3/d).

To bring the refurbished plant up to date and reduce its financial and environmental costs, Carollo, a major U.S. engineering firm specializing in water and wastewater facilities, specified the latest axial-piston high-pressure pumps to replace legacy centrifugal pumps and swapped out old turbines for the newest active isobaric energy recovery technology.

This innovative high-pressure setup dramatically reduces the plant’s energy needs. In the new the Kermit H. Lewin Water Treatment Plant being built by Biwater, a world leader in water treatment, the RO process specific energy consumption will be slashed from 25.6 kW/kgal (6.77 kWh/m3) to 8.6 kW/kgal (2.27 kWh/m3). With this improvement the new plant will be among the most energy-efficient in its class, with significantly reduced electricity bills and greenhouse gas emissions.

The upgraded plant will consist of four RO trains, each of which includes two Danfoss APP 86 high-pressure pumps and three Danfoss iSave 70 ERDs. In addition to the dramatic improvement in energy efficiency, configuring each train with parallel high-pressure pumps provides additional resilience and other benefits: the smaller pumps are easier to lift and work on, and it is now affordable to keep a spare pump in stock.

The new improved plant will come online in Q4 2024

The new Kermit H. Lewin Water Treatment Plant is located just north of the existing plant.

Construction began in Q3 2021 and will be completed by Q2 2024. The plant is expected to be fully operational by Q4 2024.