Urban wastewater systems: From disposal to reuse. A study of different systems with focus on water and nutrients flows.

Urban wastewater systems are currently exposed to a major rethink dictated by new demands on resource management. It is postulated that next to providing efficient sanitation (preventing spread of pathogenic microorganisms) these systems should support resource reuse. It remains uncertain of what will be the sanitation of the future; the understanding of technical performances of various alternatives towards possibilities to improve resource management is a necessary background for choosing design alternatives of wastewater systems to be used in the future.

This thesis consists of a number of studies all with an aim to better understand the performance of the current and alternative urban wastewater systems as applied in industrialized countries and their influence on the environment. The objective is to quantify the differences in performance of existing (conventional and alternative) as well as other possible systems. Technical performances of wastewater systems are quantified mainly with respect to nutrients and water flow. Waste/resource reuse possibilities and interaction with existing infrastructure is also investigated. The alternative systems studied are mainly urine separation systems and extensive vegetated roofs for storm water retention and disposal. The interconnection and inter-influence of urban wastewater systems with other technical and non-technical systems/sectors of society is also investigated, which is done in both a conceptual and quantitative way.

The results prove the potential of a change in urban wastewater management towards source control and reuse. Wastewater systems based on source control can potentially support water savings, water reuse and nutrients reuse. When the alternative systems are implemented on a small scale only, their influence on the environment (positive or negative) is negligible; however the effects will be more and more significant as more and more systems coming into operation. The results from the studies performed in this thesis showed that to achieve desired changes, technical developments of new systems are crucial, but there is also a need of institutional adjustments to support novel systems with legal and economic means.