TtC:It's extremely feasible with flush toilets. I did a fully integrated system for an apartment complex in Canada back about three years ago. Worked wonders, too. I've made adjustments since then, and have an even better one now.
A lot of city people will be happy to hear that.
From the info I read, this is related to the required retention period for the waste to stay in the digester to carry out the process and the needed size of the container to do that.
/NS