Sludge from the sewage stations is regularly added to the land round 'by 'ere, although more as a soil conditioner than a fertiliser: By the time they dig it out of the tanks most of the goodness has been washed out AIUI
Big issue is parasite cycles. If you can separate the location where you dump yer dung from the one where you grow yer food by a fair bit, the chance of a build up of parasites is reduced. So we need to take french shit and sell them ours. Really.