Reverse Osmosis Treatment Plant Expansion

South Island Public Service District, 
South Carolina

Reverse Osmosis Treatment Plant Expansion

Service Type: 
Project Highlights: 
  • Innovative design and operational strategies save capital and O&M costs.
  • Completed design and expansion of a RO water treatment plant.
  • Innovated design modifications offered by Carollo including the redesign of the existing three RO trains increased the production capacity by 20%.
  • Carollo’s innovation in technologies improves permeate water quality, reducing fouling potential and increasing the useful life of membranes.
South Island RO Treatment Plant
Carollo designed the upgrades and expansion of the South Island PSD’s RO WTP from 1.5 to 3 mgd.

The South Island Public Service District (SIPSD) hired Carollo to provide engineering design and construction services related to the expansion of their reverse osmosis (RO) treatment plant located in Hilton Head, South Carolina. The SIPSD has been operating their RO treatment plant since 2001 and due to recent limitations on use of fresh Floridan Aquifer water imposed by the state, the SIPSD decided to expand the RO plant from 1.5 to 3 mgd, maximizing the use of their deep, geothermal and brackish Cretaceous well supply. The initial process consisted first of a plate and frame heat exchanger/cooling tower process, followed by RO. The heat exchanger/cooling tower process reduces the Cretaceous well temperature from 122 degrees Fahrenheit to 104 degrees Fahrenheit. The RO process operates at a recovery rate of 80 percent.

Prior to expanding the RO treatment plant, Carollo was first required to negotiate a new NPDES permit for discharging additional RO by-product water into the environmentally sensitive Calibogue Sound. Toxicity testing had proven troublesome to the SIPSD and Carollo demonstrated to the State that the past toxicity test failures were due to naturally occurring constituents that are not regulated (i.e., common ion toxicity, or ion imbalance toxicity). Additionally, CORMIX modeling was performed that demonstrated infinite dilution at the point of discharge.

In concert with the permitting effort, Carollo completed the design services related to the expansion of the plant capacity. Additional heat exchanger and cooling tower capacity was required for redundancy. Carollo also evaluated the maximization of the use of the existing RO equipment. Plant electrical and mechanical audits were prepared to determine if the existing infrastructure required additional support for the expanded capacity.

Carollo prepared design drawings, specifications, and contract documents for the equipment related to the expanded capacity. Construction-phase services were also provided.

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