A Journey towards Sustainable Small Wastewater Treatment Systems in Low and Lower–Middle Income Countries

Doctoral thesis, 2020

The sustainability of small wastewater treatment systems (WWTSs) in low and lower-middle income countries represents a challenge in terms of functionality and optimal performance in the ongoing effort to treat wastewater sufficiently to enable safe discharge or reuse. The reuse of wastewater is a common practice in these countries, especially where water resources are scarce. However, current practice does not always ensure that public health risks are avoided. The sustainable development goals (SDGs) include the target of halving the proportion of untreated wastewater by 2030 (SDG 6.3). To achieve this, it is crucial to identify and understand the challenge of having sustainable WWTSs that operate optimally, and to support the formulation of effective strategies for implementing more sustainable systems. In this thesis, a case study approach was used to investigate nine small WWTSs in Cochabamba, Bolivia. A WWTS consists of the collection system, i.e. the sewer network, and the wastewater treatment plant (WWTP). Quantitative data was collected in the field from the WWTPs and qualitative data was collected regarding the sewer network and the users. A body of knowledge was built up dealing with the specific difficulties experienced at these WWTSs in achieving optimal performance and how the actual performance impacts on human health and ecological risks in areas where wastewater irrigation is practised. This body of knowledge was used to acquire a greater understanding of how the sustainability of small WWTSs can be assessed. Systematization of standard sustainability indicators was used and contextualized further with the aid of participatory methods involving local stakeholders. A key finding was that a lack of institutional capacity to implement adequate treatment systems and provide local technical expertise, along with a lack of financial resources, prevented the WWTPs from performing optimally. The performance of the WWTPs was also affected by issues in the sewer network resulting from design problems or inadequate use. In this context there were five relevant sustainability dimensions for assessment of small WWTSs: institutional, social, economic, technical, and environmental. The list of contextualized sustainability indicators and the knowledge acquired led to the development of a sustainability assessment tool, EVAS (Evaluation of Sustainability/Evaluación de Sostenibilidad), for small WWTSs during the operational stage. The aim of the EVAS tool is to enable managers of small WWTSs and local decision-makers to assess the current status of their WWTSs and support the formulation of strategies to improve their sustainability.