Clean Water Challenge
Reverse osmosis project aims to save energy, reduce labor, increase output
By PATRICIA KIME, Seapower Correspondent
The Next Generation
tridge filters that extract large particles (anything over 3 microns).
Then it passes through a membrane, usually made of a porous
thermoplastic polymer layered
with a dense polyamide separations layer (nylon, for example, is a
polyamide) that blocks additional
contaminants and dissolved molecules such as salt. During this second phase, the water must be pressurized (sometimes up to 800 to
1,000 pounds per square inch) to
overcome osmotic pressure and
provide a reasonable flow rate
through the membrane. The fresh
water is moved to a holding tank, where it is chlorinated to eliminate any bacterial contaminants that may
have survived the process. The briny wastewater is
flushed out to sea.
ONR aims to make new systems that would lengthen the lifetime of parts within it, including the cartridge filters, which currently last up to six weeks in
the open ocean, but just days in shallower littoral
waters, and the membranes, which break down from
exposure to chlorine after three to five years.
The Navy first experimented with desalination technology in the mid-1980s, starting with unsuccessful tests of
two commercial units. In 1988, however, the service
installed a Navy-developed reverse osmosis prototype
onboard the destroyer USS Fletcher and, after successful
sea trials, began using the system on a variety of platforms.
Today’s systems use basically the same technology
as that developed in the 1980s. ONR hopes its efforts
will unveil a new way of extracting the salt or tweak
the current technology, possibly by developing hardier,
more efficient reverse osmosis membranes.
Current desalination units are priced according to
output. For military use, a 2,000-gallon-per-day system
costs roughly $100,000, a 12,000-gallon-per-day unit
The Office of Naval Research (ONR) initiated a research and development program that will save energy while producing more clean
water for ships for the same amount of money as current systems.
■ Systems used today rely on basically the same technology as
that developed in the 1980s.
■ ONR wants to find a new way of extracting the salt or tweak
existing technologies to perform better.
■ Energy-efficient desalination technology is not simply a Navy
need; it’s a global concern.
The Office of Naval Research (ONR) is hoping industry will help the Navy overcome a long- standing challenge: ensuring ships have an
adequate supply of fresh water on board.
The service currently uses reverse-osmosis technology on most vessels to extract fresh water from the sea.
But according to ONR personnel, the present systems
are not energy efficient, are labor intensive and do not
keep up with demand.
To move reverse-osmosis technology into its next
iteration, ONR has initiated a research and development
program to build a reverse osmosis prototype that will
reduce energy usage, increase output and reduce maintenance requirements.
“Saving energy and producing clean water is a tacti-
cal issue for the Navy,” said J. Paul Armistead, ONR’s
manager of functional polymeric and organic materials
research. “We plan to build prototype desalination
units that will use 65 percent less energy and be 40 per-
cent smaller by weight and by volume, relative to cur-
rent Navy reverse osmosis systems. They should
require roughly 75 percent less maintenance.”
A reverse osmosis system works like this: Seawater
is pumped into the system where it first meets car-