Selective Salt Recovery from Reverse Osmosis Brine - University of ...

CHAPTER 1
1.1 INTRODUCTION
Across the United States and the world, the issue of water scarcity is gaining
importance as communities struggle to provide water to their constituents. The Reverse
Osmosis (RO) treatment process removes dissolved salts from water, producing drinking
water from sources that cannot be treated conventionally. However, it is more wasteful
than conventional treatment and can only recover 50 % to 75% of the water diverted to
the treatment process. RO concentrate, as the waste volume is called, is difficult to treat
or dispose of because it contains high concentrations of dissolved salts. The National
Research Council identified concentrate management as an area in which significant
research is needed [1]. As water demand increases for limited water resources, RO
treatment will become more widespread, especially in arid areas where water resources
are already scarce.
Regulatory and economic constraints to traditional concentrate disposal methods
are driving research on alternate concentrate management strategies. This dissertation
describes development of a treatment process for RO concentrate to recover salts for
beneficial reuse and increase water recovery.
1.11 Background
The principle behind the RO process is that salt water and fresh water are
separated by a membrane that is more permeable to water than it is to salts. In a nonpressurized
system, fresh water would diffuse into the salt water solution. In the RO
process, pressure is applied to the salt water side of the membrane, overcoming the
osmotic pressure and forcing water through the membrane to the fresh water side. As a
result, the salt water becomes saltier and fresh water is recovered.
There are two main limitations to the RO process that limit recovery. First, as the
salt concentration in the RO feed water increases, more pressure is required to push fresh
water through the membrane. A mechanical limit exists at approximately 1200psi above
which the pressure differential will damage the membrane. This limit is significant in
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