Sustainable engineering of sewers and sewage treatment plants for scenarios with urine diversion

Urine diversion (UD) has been studied for decades as a way to enable distributed sanitation and to recycle nutrients onto land to fuel circular economies. No study to date has attempted a quantitative technical and economic analysis of the downstream effects of UD on sewage transport and treatment. This work used the SeweX model to reveal for the first time that through UD, hydrogen sulfide concentration in sewer headspaces can be reduced, and consequently sewer corrosion can be reduced. For a long rising main of 5 km, sewer headspace H2S can be reduced from 280 ppm to 200 ppm by diverting 75% of the urine. The same scenario enables the reduction of sewer corrosion from 12 to 10 mm/yr. Modeling sewage treatment plants with BioWin showed that sewage treatment responds to UD with a sharp reduction of the anoxic volume and a decrease of energy requirement by up to 50% at 75% UD. An upgrade of bioreactors to increase capacity by 20% can be completely avoided if 7% of the catchment’s urine is diverted. Reductions in upgrade expenditure by up to 75% can provide the economic incentive for the uptake of UD.