I have had similar thoughts. Our agency (A Florida County government department) treats wastewater to advanced waste treatment (AWT) standards thru biologic action followed by high level disinfection. The resulting effluent (we call it reclaimed water) is very good (meets State and Federal drinking water standards) and is used for landscape irrigation. We also did R&D for awhile with aquifer storage and recovery (ASR) of the same product. In so doing we had to pass our product thru dual in-line UV reactors to inhibit coliform, protozoa, and giardia (re)growth. This worked out quite well; alas, our geology was bad so our storage and recovery R&D did not work out.
The ultimate answer to your question depends upon what you are really looking for as a final product. How you get to the end depends upon what you start with.
Thank you all for your contributions.
As far as I found from the websites (not from trust worthy articles yet) greywater pasteurisation is a process using solar energy to heat the greywater up to more than 65-85 degree Celcius for a period of time to remove the pollutants (mostly germs I think). So I agree with Jim Casey about it. I don't think Urea/ammonia is a big problem if your purpose for recycling of greywater is for irrigation.
I think Yogibear1 is right saying the quality of treated greywater you can achieve depends on what's in the greywater. But I don't think we have a choice telling people to use the products that will not pollute the wastewater heavily so that our treatment can handle it.
Looks like greywater pasteurisation is not very feasible.