A REVIEW OF CURRENT AND FUTURE BRINE DISPOSAL OPTIONS AND MEMBRANE RECOVERY OPTIMIZATION TECHNOLOGIES FOR INLAND REVERSE OSMOSIS PLANTS

Population pressures have strained the capacity of drinking water sources in some regions of the United States. Consequently, water agencies have had to consider other sources for potable water including brackish and saline waters. With the rapid advances in membrane technology over the past few decades, the use and treatment of these poorer quality water sources is now possible. Although membrane processes are becoming more competitive economically, in the case of reverse osmosis applications, a major concern is still the disposal of the concentrated brine in an environmentally responsible manner. While the disposal of brine from plants near the ocean often involves rerouting back to the ocean, the disposal of concentrated brines at inland sites poses a much greater challenge.The past 5 years has shown the increasing occurrence of larger production Reverse Osmosis (RO) facilities, i.e. greater than 10 MGD capacity. The general question is how to dispose of brine for larger reject streams. For example, a typical brackish RO plant producing 50 MGD and operating at 85% recovery would have a brine reject stream of almost 9 MGD. Though this is a large amount of reject water to process, one positive fact is that inland sites would presumably use river or brackish water as a feed source. Assuming a feed water salinity of 1,500 mg/L and an overall salt rejection of 85%, the resulting brine stream would have a salinity of around 9,500 mg/L; about a third the salinity of seawater.In most cases at inland sites, the disposal of brine involves either the dilution of the waste stream in another receiving body or the concentration of brine solutions (Truesdall et al., 1995). There is also a trend towards the mixing of brine with sewage wastewater. However, these options may not be viable if TDS limits are exceeded or if there is no adequate receiving body available. Therefore, other options such as deep well injection, solar ponds, evaporative ponds, land application, or mechanical concentration must be considered.