The friction force at the EPDM liner/disc interface results in higher torque. How to reduce the torque?
Use a high-performance (double-offset) valve.  Once it rotates 2-3 degrees, the vane is clear of the seat so there is no torque due to seat friction.  Also the offset(S) are in the direction that reduces the dynamic torque. 
Triple offset butterfly valves would offer the same advantage, but they usually require a very high seating torque to achieve tight shutoff.
If for some reason you >MUST< use a lined valve, there are "undercut" valves with the O.D. of the disc reduced several thousandths.  These have reduced torque but are primarily offered for reduced scrubbing of the disc-edge against the liner in abrasive services. 

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