DARE COUNTY REVERSE OSMOSIS DESALINATION DRINKING WATER PLANT

Dare County Water Department
600 Mustian Street
Kill Devil Hills NC 27948
TEL: 252-441-7788
TEL: 919-473-1101 ext. 303
FAX: 252-441-2239
EMAIL: BobO@co.dare.nc.us
Web site: http://208.11.168.2/waterhome/
Robert (Bob) Oreskovich, Director
C. Randy McPhee, Assistant Water Director

Thomas Missimer
Missimer International Inc.
8140 College Parkway, Suite 202
Fort Myers FL 33919
TEL: 941-432-9494
FAX: 941-432-9453

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WELCOME!

Hi. Welcome to the Dare County Water Department Home Page. We hope you have found us on the Internet to learn more about our water system located on the Outer Banks of North Carolina.

My name is Bob Oreskovich. Those of you native to the Outer Banks will not recognize this name. I moved to Kill Devil Hills during the summer of 1988 from southwest Florida. At that time, we were beginning the construction of our first Reverse Osmosis (R.O.) water treatment plant in Dare County located in Kill Devil Hills. As you will see from our home page, we have expanded our water service area to below Oregon Inlet on Hatteras Island with our second RO Plant in Rodanthe. We have since continued southward on Hatteras Island with renovations to the former Cape Hatteras Water Association system as well as constructing our third RO Plant in 1998 on Water Association Road in Frisco. The RO Plant is scheduled to begin producing desalted water by November 1999.

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1. anti-scalant: Argo Scientific Hypersperse 120
2. 1st Pass RO: Fluid Systems Model 8821-FSD-TFCL 8" spiral wound brackish water membranes
3. 2nd Pass RO: Hydranautics 8040-LSZ-CPA2 8" spiral wound brackish water membranes
4. average feed pressure: 285psi
5. pumps: 8"x6" submersible, 6-stage, vertical turbine Afton pumps with 250 hp U.S. motors
6. computer contol: Allen Bradley Programmable Logic Controller (PLC)
7. major operating cost: the electricity used to generate the RO pressure needed to push the feedwater through the RO membranes -- 2.981 kilowatt hours per thousand gallons (ptg) with cost of $0.134 ptg and the electrical cost is 30.5% of the total cost to produce the water
8. water lab: Hach DR/3000 Spectophotmeter

KILL DEVIL HILLS RO PLANT LAB

The Dare County KDH RO Plant lab is certified by the State of North Carolina for bacteriological analysis of drinking water using state of the art lab equipment. This certification is for three different types of bacteriological analysis. Two methods are qualitative presence/absence for total and fecal coliform bacteria. The third method is a quantitative heteratrophic plate count method. These three methods are recognized by the state as acceptable in determining if water is safe to drink from a bacteriological viewpoint.

Compliance samples must be taken from throughout our distribution system each month and analyzed for bacteria content. The number of analyses required depends on the size of the system. Dare County's water system serves a population approximately 25,000, therefore, we are required to run 30 bacteriological analyses per month. The Dare County KDH RO Plant lab also performs numerous physical and chemical analysis on different waters that we are concerned with. Analyses are performed on raw well water, finished and distributed waters. We also monitor our discharge waters according to a NPDES (National Pollution Discharge Elimination System) permit.

The RO Plant has two discharge streams: a concentrate stream of 200 to 600 GPM and a feed water instrument stream of .7 GPM. These discharge waters are monitored weekly for turbidity, pH, Total Suspended Solids (TSS) and settable matter. The TSS and turbidity tests are sent to a lab that is certified by the State of North Carolina to run those tests. The results are then forwarded to the North Carolina Division of Environmental Management.

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(source: http://208.11.168.2/waterhome/waterd~1/whtrev~1.htm)

What Is Reverse Osmosis?

Reverse Osmosis, simply expressed, is a specific process which employs the use of semipermeable membranes for the desalting/deminerlizing of water.

Nature applies semipermeable membranes in many ways from the osmosis phenomenon occurring in plants to the the various functions in the human body. These membranes are selective in purpose such as the lungs which separate gases from gases to the digestive tract which separates liquids from liquids. Membrane processes, in the generic sense, are quite broad and little agreement exists on the actual physics involved associated with the transport of materials through these membrane walls.

The phenomenon of osmosis was discovered in 1748 and is described as the transport of a fluid, the solvent (such as water), through a semipermeable membrane to a solution of higher concentration, the solute. However, it has been only since the late 1950's that scientists have been able to develop synthetic membranes which can duplicate some of what nature does so well.

Out of the research has evolved the specific process known as REVERSE OSMOSIS where the natural occurring phenomenon is reversed by applying pressure to the fluid on the solute side of the semipermeable membrane. The Reverse Osmosis process is also used in systems producing high quality water for a vast range of users; the medical community, pharmaceutical industry, electronic manufacturers, and power utilities, to mention a few.

A well known example of OSMOSIS is illustrated in the drinking of sea water. Salt water is consumed which increases the salt concentrate of the fluids surrounding the body cells. Water "transports" across the cell walls by osmosis, trying to dilute the salt water. In doing so, the cells dehydrate and the cell actually "dessicates" or dies from lack of water.

Osmosis is described as the transport of a fluid (water) or solvent in which a solute (salt) is dissolved across a semipermeable membrane from the side of lower concentration (milligrams per liter) to the side of higher concentration. Each and every solution has its own inherent characteristic "osmotic pressure" dependent on the concentration of salts in the solution. The application of a pressure higher than the osmotic pressure applied to the opposite side forces the solvent in the opposite direction across the membrane, i.e., from the side of higher concentration to the side of lesser concentration. This is called "REVERSE OSMOSIS".

The theories of water transport through membranes are many, with little organized agreement amongst the researchers. It is generally accepted that porosity of the membrane is very tight with holes (if you want to call them that) of 5 to 20 angstroms (.00000002 inches in diameter). The membranes are several mils thick with most consisting of an asymmetric layer (active membrane) with the balance a more porous substrate, spongy in nature that serves as the support for the asymmetric portion. For more information on Reverse Osmosis click here Water Quality Association - What Is....Reverse Osmosis

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