Water. desalination + reuse

| 22 | Desalination & Water Reuse | February-March 2014 projects _________ Kelly Grieves, lead process engineer, Lauren Thomas, director of marketing, Seven Seas Water Corporation, USA ___ Editor's Note: Florida-based Seven Seas Water commissioned three desalination plants in the Caribbean in 2013. This article looks at the technical differences between the plants and the challenges in commissioning them. SEVEN SEAS Water, a private large-scale water service provider, successfully commissioned three seawater reverse osmosis (SWRO) water treatment plants in the Caribbean in 2013. The first facility, located within the Randolph E Harley Power Plant on St Thomas in the US Virgin Islands, was brought online on 5 June 2013, producing 3.3 MGD (12,500 m 3 /d). The plant was designed for a 20-year build, own, operate (BOO) contract, with the Virgin Islands Water & Power Authority ( WAPA). As a land- based permanent facility, it took advantage of an existing, concrete onshore intake structure that was refurbished. The second, fully commissioned on 29 August 2013, is at the Petrotrin Marine Terminal Facility in Point Fortin, Trinidad, and is a 5.5 MGD (20,833 m 3 /d) plant. It was designed for a 10-year BOO contract, with the Trinidad and Tobago Water & Sewerage Authority ( WASA), and was built in phases with modular electrical and mechanical design qualities. This design was intended for ease of installation and phased commissioning. The facility also required the construction of a new intake structure to be built 450 m offshore. The third, situated in the Estate Richmond Power Plant on St Croix in the US Virgin Islands, has been producing at its full capacity of 2.2 MGD (8,333 m 3 /d) since 6 September 2013. The facility was of similar design and build to its sister plant in the Randolph E Harley Power Plant on St Thomas. Housed in a permanent land based structure, and with the advantage of an existing intake chamber in place, this plant was also designed for a 20-year BOO contract with WAPA. This second-time-around design made for a successful installation and startup. Differences beTween The 3 sysTems Technical differences between each of these facilities brought unique design, construction and commissioning challenges. Although there are a number of differences that could be discussed, the focus will be on those that affected the approach to how the site was designed and constructed. Process DesiGn The SWRO facility in Point Fortin, Trinidad was a much more technically complex plant to design, construct and commission due to space constraints, site specific issues and raw water quality. The plant was built inside the Petrotrin facility in a compact 1.2 acre (0.5 ha) area, on top of an old abandoned industrial site. Complications arose when an aged oil well, capped in the 1940s, began to leak onsite. It was recapped, and the site layout design had to shift slightly to avoid the well. Due to the already tight space constraints, shifting the layout design proved to be difficult. Being presented with a space constraint challenge meant that the piping, pipe supports and equipment that could be elevated were placed above equipment and on top of containers. Installing pipelines and supports that are fixed high up is also more challenging for the construction team. Scaffolding, fall-arrest systems and all safety-related procedures were adhered to when working at heights. The feedwater for this site is drawn from the Gulf of Paria, which is well known for its seasonal salinity swings and wide suspended-solids range. The total dissolved solids (TDS), total suspended solids (TSS) Comparison of three 2013 Caribbean SWRO systems

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