Major steps towards better, sustainable and affordable food production free of environmental challenges have been taken, with the "world's first farm to grow indoor, vertically farmed berries at scale" opening in Richmond, VA. It's backed by an international team of scientists that see this new…
Human waste could be used. It requires more processing to keep it safe, however.
There is also the complecating factor of chemicals. Night soil needs relatively little work. Toilet cleaner, however, needs more processing.
It’s currently nowhere close to viable to do in a city environment, that could be changed in future.