Here is a link to a thread on another forum discussing issues with contaminated WVO. The main point of this thread is not to diss WVO, but rather to know what you are getting. It seems that some people collect WVO with some harsh cleaning chemicals improperly disposed in the oil. The result is injector failures in trucks running contaminated WVO or even home-brewed bio. The moral of the story is to talk to the people who are supplying your oil, and coach them on proper disposal methods to ensure your oil isn't tainted.
Valid concern. Most places do not use it though. Once ya know what it smells like, you'll know to avoid it if your dewatering/filtering/conversion (bio-d) process does not remove it.
Mist washing is effective at removing it because the acid is soluble in water - but not oil. We have made 100's of gallons of B100 using boil out 'contaminated' VO. The BioPro 190 utilizes a triple mist wash, effectively removing any that may remain at that stage...
It can be tested for by placing WVO or B100 in a container, adding water and agitating. After the water separates, test it for Ph using litmus paper.
I actually ended up burning some of this in my F350 (2 tank VO conversion) shortly before changing injectors. (we normally set it aside for bio-d) The Swamps crew later showed me where this affected my injectors - although no 'pitting' was present, some parts were 'polished' indicating early stages of damage!! They also indicated that of the MANY VO injectors they've evaluated - boil out had caused the only real damage they saw.
I would say those failures were more due to improper prep of the fuel by the user not the fault of the oil itself. Those problems could be taken care of it the oil was filtered, washed (if needed) and dried.