Impact of separate urine collection on wastewater treatment systems

Wastewater treatment should not only be concerned with urban hygiene and environmental protection, but development of a sustainable society must also be considered. This implies a minimisation of the energy demand and potential recovery of finite minerals. Urine contains 80% of the nitrogen (N) and 45% of the phosphorus (P) in wastewater. Separate collection and treatment would improve effluent quality and save energy in centralised biological nutrient removal (BNR). BNR processes are not optimal to treat water with very low N concentration resulting from separate urine collection. Relying on nutrient removal through sludge production, methanation of the sludge, subsequent nutrient removal from the digestion effluent results in optimised and more sustainable wastewater treatment. This paper quantitatively evaluates this option and discusses the potential.