The invention discloses a closed circulating membrane concentration 
system which comprises a membrane unit, a 
circulating pump, an electromagnetic three-way valve, an on-line 
sulfate radical concentration tester, a 
booster pump and a high-pressure pump. One end of the membrane unit is connected with a liquid inlet 
pipe, and the other end of the membrane unit is connected with a 
clear liquid drain 
pipe and a concentrated liquid pipeline; the liquid inlet 
pipe is sequentially provided with the 
booster pump and the high-pressure pump; the on-line 
sulfate radical concentration tester, the electromagnetic three-way valve and the 
circulating pump are sequentially arranged on the concentrated liquid pipeline, and the membrane unit, the on-line 
sulfate radical concentration tester, the electromagnetic three-way valve and the 
circulating pump form closed circulating. The closed circulating membrane concentration 
system is mainly used for separating 
sulfate radicals from high-concentration monovalent 
ion salt, the membrane 
feed pressure is regulated by testing the concentration of 
sulfate radical ions in the concentration process of 
saline water, concentrated liquid drained by the 
system is supersaturated liquid, therefore, the draining volume is greatly decreased, 
energy consumption is at least reduced by 20% compared with an existing concentration system, and the number of applied membranes is also decreased by 20%.