Brackish Water RO and NF Operation on High TDS Feed Waters

An increasing number of brackish water RO (Reverse Osmosis) and NF (Nanofiltration) systems are being designed and operated on high salinity feed water sources which can range from 2,000 to 10,000 mg/l TDS (Total Dissolved Solids). Increased feed TDS can dramatically impact the design of the RO/NF in terms of hydraulic design, feed pressure requirements and in permeate quality. Two case studies with high feed TDS feeds are described in detail, including how well design correlates with actual operations. The 1st case study is the 16-mgd 75% recovery North Miami Beach Norwood Oeffler water treatment plant which includes a 6-mgd hybrid RO system whose feed source is the 2900 mg/l Floridan Aquifer. The 2nd case study is El Paso Water Utilities, the world’s largest inland desalination plant, has a rated plant output at 27.5-mgd with a 15-mgd 81% recovery RO system whose feed source is the 2000 ppm mg/l Hueco Bolson Aquifer. Hybrid RO and NF systems which can use a number of different membrane types can be used to roduce the most energy efficient systems, can produce the best permeate quality, and can improve system flux distribution that may reduce the rate of fouling. The use of turbine-type energy recovery devices in a esign can improve the energy efficiency, improve permeate quality, and improve flux distribution and reduce the rate of fouling.

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