I read the Humanure Handbook not long ago for the first time, so I'm perhaps behind the curve on this subject, but I've listened to all the podcasts, and have now read all the forums about poop beasts, and tree bogs, and that sort of thing, so, perhaps I've caught up.
There seems to be some concerns about smells, pathogens, and contaminating ground water.
Paul seems to say that the Humanure Handbook was good and informative, but perhaps is a starting point for advancing this conversation, and sees better methods to alleviate the aforementioned concerns,
Invariably, someone else will come along, and seemingly not read anything else written, and write, "You should read the Humanure Handbook! That's the ONLY WAY to manage it!"
What I find shocking is that very little is mentioned in this conversation about using Black Soldier Fly Larva. I've looked, and there ARE a few posts about them on permies, but in the critters forum. Nevertheless, those posts DO mention using BSFL for dealing with human excrement, and it seems nobody in the composting toilet forum has put the two thoughts together.
It's been close to two years since I first looked into BSFL, and I've never seen them in my area, so right now I'm working from memory, and it's all theoretical, at least in my own head, but, here are some interesting things:
1. BSFL can process nearly anything. It's not exactly a composting process, it's called bioconversion, because they convert waste into body mass.
2. The bioconversion process is quite rapid. I've seen videos of them eating whole cheese burgers, or whole fish, in less than 24 hours.
3. BSFL are sometimes called Latrine Flies because they have no problem with human excrement.
4. They are self-harvesting, when they have reached the final stage (or instar) of Larval form, their instinct is to get away from the food, and the swarm.
5. If I recall correctly, as they crawl away, they secrete an enzyme which disinfects their bodies before pupating, which means that it doesn't matter at all WHAT they've eaten.
There are a lot more interesting little features worth finding out, but off the top of my head, none really relevant to processing human excrement.
It's not adding nutrients to the soil, but it's kind of adding nutrients to the body mass of the soldier fly larva, which makes a great high-protein live feed for chickens, ducks, fish, and so on. I suppose they are also okay for human consumption, if you're into that, but to be on the safe side, I wouldn't feed BSFL to creatures who've been fed to them (byproducts included). I'd want to have at least one additional buffer in that process.
My grandmother has a lilac shrub that started growing like crazy one summer. We found out why when we took an auger to our malfunctioning toilet and a bunch of roots came out. They managed to get into the pipe at a joint. This was in the line before reaching the septic tank.
I'd like to chime in that American Elm seems to be a poop beast. I was throwing my dogs' poop into a buried rubbermaid container with holes drilled in it (was a worm bin). I am moving out of my place so I dug it up the other day, and I had a very difficult time removing it because the roots of the large american elm (well beyond it's dripline) had infiltrated the bin and formed a thick mat of roots digesting the poo.