if the water on your 50/50 test is not clear, then there is soap in your bio. In the medium to long term when it burns in your engine it leaves traces of ash which will abrade and damage the seats on the exhaust valves and if they dont close snug then you will lose compression. Not cheap to repair.
Interesting; is this from a scientific paper you've seen or from your experience?
True that valve seat recession happens, usually in petrol engine...and is a bad thing! Is it common with diesels?
In terms of the chemistry of soap, the only 'different' part of the make up compared to bio is the sodium or potassium, both metals that are very reactive, thus would burn well (?). Also metal additives were added to fuel for lubrication, lead being the best known.
One would expect that running on wvo might produce far more abrasive elements per volume from sub-micron particles of 'god knows what' along with sub micron carbon particulates (a.k.a. teeny BCBs).
Just my ramblings....discuss!