Some machines and designs have been perfected for centuries. The toilet however is not one of them! Because it took us so long to discover how germs make us sick, our toilets were really horrible things.
In fact, it has taken us so long to understand sanitation, composting, and the environmental impact of using fresh-water flushing toilets, that the entire human race has become used to an activity (flushing toilets) that is astoundingly wasteful (you're not only wasting drinking water, but you're wasting excellent nutrients in your own shit which is then lost to sewage sludge, which itself takes huge resources to purify)
The thing is, you can totally recycle all human (and food) waste without much of an inconvenience and really no smell at all. Yes, let me repeat that - no smell at all. You crap in a bucket of sawdust, cover it completely with more sawdust, and the bucket does not smell.
The fact that our civilization has taught itself that flushing our shit away with drinking water is "the right thing to do" is really very troubling and wrong once you realize the vast resources that could be saved by some very, very basic stuff like sawdust toilets and composting.
I am aware that achieving this on an urban scale would be a challenge, but it can certainly be solved.....
Most importantly, smell is not the only reason you might want to get rid of shit quickly, systematically and far from the hands of humans and animals. It is a major carrier of disease.
> I am aware that achieving this on an urban scale would be a challenge, but it can certainly be solved.....
It probably can - but can it be solved to a degree that gives a better net result than the current system? Water is expensive, but so are the trucks required to ship sawdust in and shit out of the urban areas that most people live in (>80% in the US) and the rest of the infrastructure required to safely turn it into compost.
1: In some places. In many places water is really quite abundant.
Edit: Also, a cursory reading of https://en.wikipedia.org/wiki/Sewage_treatment suggests that there are several paths for processed sewage to be either, indeed, composted or turned "into fertilizer pellets. This product is then sold to local farmers and turf farms as a soil amendment or fertilizer".
Any solution that displaces the modern toilet will need to be at least as easy and thoughtless to operate as the current setup. I think a half-way solution is to outfit houses with a greywater circuit that could be used for the toilets. That would make a tremendous cut into the amount of drinking water that toilets are using.
Yes they're not very good in dry climates, but they were never designed to be.
Same with sanitation, whatever your toilet is you can't really get rid of disease without running water. Having running water it is straightforward to build sewerage using same underground collectors.
It too much reminds me of futile attempts of commies 100 years ago to build communism by killing all capitalists: there is no shortcut here, you've got to have per capita GDP high enough to have communism first (so far, 100 years later, we're still not there), then it comes naturally and you don't have to kill anyone.