Sewer Water Harvesting to Support Urban Green Spaces

Abstract

This research has investigated how Sewer Water Harvesting (SWH) can be applied to provide a climate-proof fresh water source to support Urban Green Spaces (UGS) in Amsterdam. SWH is the process of extracting raw municipal sewage from the sewer and locally treating this to provide fit-for-purpose water in a dense urban environment while treatment residuals are discharged back into the sewer. SWH can help to meet the increasing water demand of UGS in Amsterdam, which experiences exacerbated dry periods as a result of climate change, while conventional water sources are unlikely to meet this demand.

The overall aim was to provide a conceptual design example of how SWH could be applied in the Amsterdam context to uncover what kind of impact can be achieved and advise on how SWH can be implemented From an analysis of potential applications, irrigation of UGS during dry periods was selected for the focus of the study. Suitable locations were identified, from which the Vondelpark was selected as study area for this research. Quality requirements for irrigation water and discharge of treatment residuals were determined. The water demand of the study area was determined by modelling the soil moisture balance using transformed weather data, taking into account climate change. Based on these requirements, a conceptual design of an SWH-unit comprised of fine screening, MF, NF and UV steps. To evaluate this potential impact for Amsterdam as a whole, the findings from the study area were extrapolated. The cost of SWH were compared to alternative water sources and the potential direct economic benefits. This demonstrated that costs of SWH are acceptable and can be further decreased. Furthermore, the potential impact on plant and soil health was
evaluated. Interviews with stakeholders identified barriers and opportunities of SWH and resulted in some recommendations for larger scale implementation.

The results of this research indicate that SWH can provide a new and reliable water source during dry periods to support UGS. SWH-units can be designed as mobile and modular units that can for a large part be operated and monitored remotely. The results further demonstrate that potential negative environmental effects can be prevented or mitigated and SWH can even improve the plant and soil health of UGS. From an engineering perspective, challenges related to the water quality are unlikely to be insurmountable. However, three aspects still require a significant amount of time and investment before SWH can be implemented on a larger scale. These are: (1) the lack of regulatory framework, (2) the unresolved responsibility for operation and (3) extensive water quality testing and environmental impact assessment. To accelerate innovation it is recommended to start as soon as possible with addressing these remaining issues. Commercial operation of SWH can provide an interesting opportunity, all the more so because SWH can also be used for household or industrial applications. The involvement of a wider variety of stakeholders can further help to overcome the remaining barriers.