PROJ00166

• Contract/PO #: C153311
• Contractor Name: Nunn, Town of
• Contract Type: Loan
• Water District: 0
• County: Weld
• Bill Number: SB 78-69
• Loan Projects - Doc Type: Feasibility Study

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Reverse Osmosis

Osmosis is defined as the spontaneous transport of a solvent
from a dilute solution to a concentrated solution across an ideal semi-

permeable membrane which impedes passage of solute but allows solvent flow,
Reverse osmosis (RO) is the reversing of the natural direction of transport
of a solvent by imposing a pressure greater than the osmotic pressure. In
the RO process, pressure is used to force fresh water through a selective
membrane which is capable of rejecting or intercepting the dissolved salts
and undesirable substances.

An RO system which could be used to reduce the nitrate content of the

Nunn water supply would remove about 80% of the nitrate with 25 to 50% of

the raw water needed for waste removal treatment depending on th~ specific
RO system used. In other words, depending on the specific RO system that
is selected, the quantity of treated water available for consumption would

be from 50 to 75% of the total quantity of raw water supplied.

The preliminary design of a RO system which would cdequately remove

nitrates to an acceptable level is described in Chapter VI. The construction

costs for the RO system described in Chapter VI are summarized in Chapter V.

Ion Exchange Process
Ion exchange is a process in which ions held by electrostatic
forces to charged groups on the surface of a solid are exchanged for ions
(such as the nitrate ion, N03-) of similar charge in a solution in which
the sol id is immersed. Ion e/:change is used extensively for removal of
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"hardness" ions (cA and MG ), and removal of iron and manganese from

water supplies. There have been resins developed which are fairly selective as
to the ions which are absorbed, However, at the present, ion exchange resins

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