Modular efficient biological nutrient removal (BNR) solution to help make every drop of fresh water count
Key West is one of America’s most scenic locales. Situated in the Florida Keys southwest of Miami, it is visited by millions of people each year and is home to more than 30,000 year-round residents. While there’s plenty of ocean, potable water is a precious commodity which is piped 125 miles from the mainland. Restrictions are not uncommon during drought season so every drop counts, and reuse is a key part of the island’s conservation strategy.
Challenge
Water scarcity poses unique challenges to KW Resort Utilities Corp. (KWRU) the utility firm that provides wastewater management, wastewater recovery, and wastewater treatment in the region. KWRU began operation in the late 1960s and has worked hard over the decades to keep up with wastewater needs as population and tourism have boomed, spurred by land reclamation and development.
In 1983, KWRU began a relationship with Evoqua Water Technologies, which provided a 250,000-gallon-per-day (GPD) Davco™ field-erected extended aeration treatment plant. Evoqua was chosen because their field-erected tanks can be set up quickly and adapted easily to meet changing needs — a good fit with KWRU’s step-by-step strategy for managing growth. “The advantage is that you’re able to incrementally increase the size of your plant with the growth of your community,” says KWRU president Chris Johnson, “and still you’re able to maintain an operational environment that’s familiar and uniform.” By 1995, outgrowing the capacity of the initial plant, KWRU added a Davco field-erected treatment plant. By the late 2000s, the utility was not only outgrowing capacity again, but also facing a new challenge with tighter treatment limits of 5 ppm suspended solids, 5 ppm BOD, 3 ppm nitrogen, and 1 ppm phosphorous.
Solution
To meet this challenge, KWRU added a 56,000 GPD standalone clarifier in 2007 which facilitated the conversion of the entire plant operation to a three-stage Biological Nutrient Removal (BNR) process. The overhaul was completed ahead of the adoption of the new standards, however by the middle of the 2010s, the facility once again needed more capacity. “We were starting to exceed 90% of capacity,” says Johnson. To address this issue, KWRU expanded the treatment capacity of the existing Davco Field-Erected Biological Treatment system to 849,000 GPD by adding a new three-stage 350,000 GPD plant to augment the existing plant capacity of 499,000 GPD.
The DAVCO™ Field-Erected Treatment Plant was selected because their ability to be constructed quickly and adapted easily to meet changing needs — a good fit with KWRU’s strategy for managing growth.
Key West Resort Utilities selected Evoqua Water Technologies and sales partner Heyward Florida Incorporated for this turnkey project. The three-stage BNR activated sludge plant includes steel outer walls 90 feet in diameter and 20.5 feet high. Evoqua supplied steel tanks, walls for the wastewater plant, field erection, field painting and commissioning labor.