The Challenge

Mount Pleasant Waterworks in South Carolina, a private utility, was planning a plant expansion to better serve its customers when an emergency short-term need arose. With the spring high-flow season approaching, the plant faced a shortfall in treatment capacity. Management considered two options: renting a unit or building a temporary, disposable unit. Both options would be costly, an estimated $30,000-$40,000 per month for a rental unit or $160,000 or more for a temporary, disposable one. Moreover, neither option would necessarily deliver the dependability Mt. Pleasant needed. The assumption that these were the only two options may have been right for other companies but not for Harn R/O. Based on its working knowledge of water treatment plants and the unique needs of their owners and operators, Harn came up with an innovative solution that was less costly, more dependable and delivered long-term value.

The Solution

Harn R/O Systems built a new unit in less than three months and installed it outside the plant on railroad ties under a protective tent. Connected directly to the well, it was intended to run for six months but ran for two years as Harn worked with Mt. Pleasant on the overall plant expansion. Once the new plant was built, Harn moved the “temporary” skid in as it built and installed another new unit to meet Mt. Pleasant’s overall needs. Most importantly, this innovative solution enabled Mt. Pleasant Water Works to serve its customers’ needs with no shortfalls or problems.

The Result

“Harn’s solution was not only innovative but it saved our utility a significant amount of money,” said Greg Hill of Mt. Pleasant Water Works. “The one-time capital expense for a unit that will run for 20 years or more cost less than it would to rent a temporary unit for six months. Plus, the unit could then be incorporated into our permanent installation. Harn’s knowledge, experience and commitment to quality delivered far more than just equipment for our plant. They were a partner in ensuring quality and service to our customers.”

Brief R/O System Specification

Owner: Mount Pleasant Waterworks
Engineer: Thomas Hutton
Application: Potable drinking water
Startup: 2001/ 2004
Capacity: 1.7 MGD
Array: 10:5, 7-element vessels, 2 trains
Pretreatment: Scale inhibitor, cartridge filter
Low Pressure Piping: Sch. 80 PVC
High Pressure Piping: 316 Stainless Steel
Membrane Type: Hydraulics ESPA2
Operating Data
Feed TDS: 1,600 mg/l
Permeate TDS:
200 mg/l
R/O Feed Pressure: 120 psi
Recovery: 80%
System Features:
  • Raw water cooling and high temperature alarm control
  • Interstage boost pumping maintains adequate flux in second stage
  • VFDs on pumps modify pressures to accommodate varying raw water temperatures while maintaining constant production and recovery