Sanitation systems

Abstract

Hybrid wastewater systems can be defined as the co-existence of centralized and modular systems in the same catchment. Currently, we have no explicit knowledge if such hybrid systems can be longterm stable or if modular systems always will be a stopgap solution.The current evidence indicates that depending on the settlement structure, centralized systems can have diseconomies of scale and modelling studies show that there are conditions where hybrid systems are cost-effective. Decisive factors are the costs of modular systems and the heterogeneity of urban areas. Overall, there are good reasons to believe that fortifying centralized systems with modular systems enables overcoming some of the critical weaknesses of the one fits all centralized systems approach.However, centralized systems show strong path dependencies. Besides a wide range of institutional and organizational barriers, the current engineering economic and planning methodologies also need to be improved and adapted. From a purely engineering perspective, the following research needs can be identified: (i) Long-term transition planning tools that are spatially explicit and can consider a wide range of modular technologies; (ii) Cross-sectoral integration methodologies; (iii) Better methods to integrate multi-criteria decision analysis (MCDA) to consider the broader range of benefits hybrid systems can provide; and (iv) Improved engineering economic methodologies considering uncertainties, unused capacity and the value of adaptability.This document is the accepted manuscript version of the following article: Maurer, M. ( 2023). Sanitation systems. Are hybrid systems sustainable or does winner takes all? In T. Bolognesi, F. Silva Pinto, & M. Farrelly (Eds.), Routledge environment and sustainability handbooks. Routledge handbook of urban water governance (pp. 134-144).