Selecting a locally appropriate and sustainable sanitation system for a given case within a city is a complex multi-criteria decision-making problem. It involves
- A continuously growing number of technology options and corresponding system configurations;
- Multiple criteria from all sustainability dimension including health and hygiene, environmental protection, appropriate technology, operation and maintenance, financial and economic viability, socio-cultural and institutional acceptance;
- And many stakeholders with sometimes conflicting interests.
The problem is particularly challenging in expanding urban areas of developing countries, where most of the current population growth is taking places. In these areas, conventional sanitation systems are often not viable because they depend on expensive sewer systems, large quantities of water and energy, and stable institutions.
Moreover, the sustainable development goals challenge us to come up with better solutions that close cycles at the lowest possible level in order to protect natural resources and people downstream.
This has led to the development of many novel technologies and system configurations such as urine diversion toilets, container-based sanitation, or decentralized wastewater treatment systems. These options are more appropriate for developing urban areas because they are independent from sewers, energy, or water and often also require less space. The innovations are also potentially more sustainable because they allow for the recovery of nutrient, water, energy resources and are more flexible to changing socio-demographical or environmental conditions. This potential has also been recognized in high-income countries like Switzerland, where the focus is on optimising aging infrastructure.
While novel technologies potentially are more appropriate and enhance resource efficiency, they also increase planning complexity. How appropriate are different technologies in a specific case ? How can they be assembled into entire systems ? And how do these systems perform for different sustainability indicators at the scale of an urban settlement ?