Are ya from Milwaukee, then, Melani? I am and I too have wondered if Milorganite is still available. Milorganite stands for Milwaukee Organic Nitrate and not only was Milwaukee's sewage treatment plant able to produce a salable fertilizer but the plant (on Jones Island) was capable of pumping clean water back into Lake Michigan. Local sensibilities kept this from happening, unfortunately. I believe that the methane gas created was also used.
I have been researching composting toilets for use at a small self sustaining "vilage" being quietly assembled down in the Ozarks. There is a limit as to how many people may regularly use such a device and count on it producing a desirable product. Envirolet has a model that can handle the waste from a family of seven. They sell both a waterless version and one that requires water. The waterless version is the cheapest, around $2,000. Seems high until one realizes that it is a one time expense and the least intrusive ecologically speaking. Water is not a problem for the site but not having to use any is certainly a plus.