How to remove the baseline of sensor output?
If you always want to subtract the same value just use an op-amp and 4 resistors as a difference amplifier.  If you want more precision you can buy difference amplifier chips with well matched resistors inside it already.  An instrumentation amplifier could also be a good choice here because it will have high input impedance.

Put your sensor on the non-inverting side of the instrumentation amplifier.  Attach a 30mV reference to the inverting input of the instrumentation amplifier.  

You will probably have to construct the 30mV reference from a 1.25V reference and a voltage divider.  If you need to make the 30mV offset adjustable then use a potentiometer instead of a fixed divider.