Overlap/Chunk processing possible with Zero-phase?
If you apply a zero-phase IIR (for instance, by filtering both forwards and backwards) to a segment of a signal that has been zero-padded on both sides, and the two zero-padding lengths are equal or greater than the length of the IIR filter's impulse response (until that response drops below your desired noise floor), then you can sum non-overlapping segments, but you have to keep and include the zero-padded tails in the sum (similar to overlap add).  The error will be related to the (infinite length) ends of the IIR tails that have been cut off by finite length zero-padding.