A mathematical approach to find long-term strategies for the implementation of resource-orientated sanitation

Abstract

In the present discussion of sustainability centralised water infrastructures are exposed to new challenges, which may cause a conceptual alteration in urban water management. If technologies for closing urban water and nutrient cycles are to at least partially replace existing systems, then intensive reconstruction work becomes essential. The paper presents the development and implementation of a mathematical approach to minimise environmental impact and economic costs on the way to more source-controlled future states in urban water management. To find an optimal transformation strategy, a simultaneous project scheduling and network flow problem was defined as a bi-criteria mixed-integer program. An optimal solution is found by minimising two objective functions concurrently - the economic costs and 'ecologic costs' for the period of consideration. This paper discusses the influence of the weighting of these two costs on optimal transformation strategies for a real catchment in Germany. The results show that the approach can very well support decision makers when showing all impacts of transformation processes in detail. All in all, the developed model can be seen as a first step in strategy-finding for transformations in existing urban water systems.

A Simplified Sanitary Sewer System Generator for Exploratory Modelling at City-Scale

“…This adaptation involves not only technical aspects, but also resource efficiency, resilience and sustainability. Recent research suggests a transition towards more decentralised schemes (e.g., on-site, cluster or community-level infrastructure for treating, dispersing or reusing wastewater at or near its source) that align better with development scenarios (Kaufmann Alves 2013, Larsen et al 2013, Baron et al 2016, Bakhshipour et al 2019, Hoffmann et al 2020, Elmqvist et al 2021) and changing goals (Hering et al 2012). Their 'degree of centralisation', defined as the ratio of sinks and sources (Eggimann et al 2015) can vary from fully centralised (e.g., all sources are connected to one centralised wastewater treatment plant) to fully decentralised (every source has its own local sink) (Larsen et al 2013, Eggimann et al 2015, Poustie et al 2015.…”