Hello and welcome P.Tony.

I don't know the answer to your question, but i found a brief reference to the pH of swine manure in the following article:

http://www.cals.ncsu.edu/waste_mgt/smithfield_projects/phase2report05/cd,web%20files/A2.pdf

pH is mentioned on the table found on page 13 of the report above. It doesn't mention if the the pH they measured is optimal.

I did a quick search on BioSystems Design's website but I didn't find the answer. That site is usually the first place I look for specific data about BSF.

http://biosystemsdesign.wordpress.com/

Good luck!