Demonstration and theoretical basis of energy-efficient high recovery small-scale brackish reverse osmosis system
Schuetze, Bryan David
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An innovative small-scale reverse osmosis (RO) system was developed for energy-efficient brackish desalination at high-recovery. The small-scale RO system used such features as closed (pressurized) circulation of concentrate, parallel single membrane configuration and operating pressure based on constant (operator-specified) target permeate flux. Tests were conducted to determine energy consumption for desalination of NaCl solutions at various concentrations. In addition, tests were conducted to determine the impact of crossflow velocity on severity of colloidal membrane fouling and an assessment was made of the effectiveness of concentrate circulation to optimize crossflow velocity for the mitigation of colloidal fouling. In the last phase of testing, the small-scale system was field tested to determine energy consumption for desalination of brackish groundwater from three wells, representing a wide range of chemical compositions, levels of total dissolved solids and scaling potentials. Test results indicated that a system with this design could achieve specific energies comparable to those of conventional large-scale brackish RO configurations for desalination of NaCl solutions at concentrations up to 5,000 milligrams per liter (mg/L) and for desalination of brackish groundwater with moderate to high scaling potential, when operated within the range of permeate flux recommended by the membrane manufacturer for desalination of brackish groundwater. Tests also indicated that concentrate circulation is an effective means to optimize crossflow velocity for mitigation of colloidal fouling.