Biological Water Filtration

We are working on a project for some folks where the need is for biological filtration of graywater for irrigation purposes. It’s a arid climate, and greenhouses are being set up for food production. The complex is being set up with composting toilets, eliminating blackwater, or sewage, but the graywater system needs to be reused, as freshwater is in short supply, and a typical sewage system will not work in the rocky ground conditions. The compost toilet material will eventually be used as fertilizer after being thoroughly composted and tested for fecal coliforms.