CHAPTER 2 DESCRIPTION OF OPERATION
2-1 General. ROWPU barges are normally maintained in administrative or long-term storage in a logistics holding area.
When needed, ROWPU barges are removed from storage configuration and inspected and tested to ensure operational
readiness. Any deficiencies are corrected before the barge is towed by commercial or military tug to an operational site.
Once onsite and while anchoring is in progress, the chlorination system is started so chlorine will be available when the
ROWPU system is activated. As soon as barge anchoring is complete, the shore winch is moved to the beach and
securely anchored. The drinking water shore discharge hose is then deployed from the barge to the drinking water facility
on the beach. Next, water processing systems, with their auxiliary systems, are started.
2-1.1 To process seawater into drinking water, water is initially pumped through four filtering systems. The filtered
seawater is then pumped under high pressure into the RO pressure tubes. These tubes are the heart of the ROWPU
system where the reverse osmosis takes place. During this process, the filtered seawater is forced over a specially
fabricated membrane and the water that passes through the membrane is free of salt and other impurities. This product
water is further processed into drinking water by adding chlorine. The brine water that does not pass through the
membrane is pumped directly overboard.
2-1.2 During initial startup and checkout, drinking water is pumped overboard. When the quality of drinking water is
acceptable and sufficient time has elapsed to flush out piping, drinking water is then directed into the barge drinking water
storage tanks. Finally, the drinking water shore discharge system is started and drinking water is pumped to the water
storage facility ashore. Both ROWPU systems operate continuously and simultaneously. After about 10 hours of
operation, however, each system is normally shut down for 2 hours of scheduled maintenance. The amount of time
needed for this operational maintenance and the time between its performance will vary with the conditions of the water
2-2 Reverse osmosis process. The reverse osmosis process separates clean water from salt water. During the natural
osmosis process, pure water and salt water can be separated by a semipermeable membrane in a container at
atmospheric pressure (Figure 2-1). Because of the difference in salt concentration, pure water will naturally diffuse
through the membrane and raise the water level in the salt water side as though pressure were being applied to it. The
effective driving force causing the flow is called osmotic pressure. The magnitude of the osmotic pressure depends upon
the concentration of dissolved solids in the saltwater and the water temperature. The greater the concentration of salt in
the saltwater and the higher the water temperature, the higher the osmotic pressure.
2-2.1 To reverse the natural osmosis process, pressure is applied to the saltwater side (Figure 2-1). When the applied
pressure is greater than the osmotic pressure, purified water diffuses through the semipermeable membrane from the
saltwater side to the freshwater side, thus the term, reverse osmosis. The salt water side of the membrane becomes
more concentrated with salt and is called brine concentrate. The resulting purified water is called product water.
2-2.2 ROWPU is arranged so that water that has been filtered several times (pretreated) is pumped under pressure
across the semipermeable membrane, called the RO membrane. This membrane separates the pretreated feedwater
stream into product water that has passed through the membrane and a brine concentrate that has not passed through
the membrane. The product water flows to the drinking water storage tanks in the voids, and the brine concentrate flows