Is it possible to combine two or more Biquads? I've wrote a Equalizer, and now it apply the Biquads in serie (cascade), I was just thinking if i can combine the biquads it will more efficient than applying one-per-one.

Is that possible?
Possible, yes.  But higher-order IIR filters tend to be less stable and more susceptible to various numerical problems (lost precision, underflow, overflow, etc.), compared to a cascade or bank of suitable partitioned biquad filters.