You clearly have not been exposed to the joys of the Clean Water Act and ammendments. The biggest problem with your suggestion is the daily volume of water involved. It would be impractical to transport several hundred thousand gallons per day. Also, there are strict regulations in place for land irrigation in order to avoid runoff. Second, its illegal to irrigate crops for human or animal consumption with treated wastewater without jumping through mucho hoops first (if even then).
But aren't the byproducts 99.9999% pathogen free.?
They seem to be doing it in WI.Your'e problem may be in the amount of water coming from pig effluent as opposed to cow. Is there a way to evaporate the majority of the water to leave a usable product?