Wastewater - Turning Problem to Solution

Action area 3: Sustainably managing wastewater for resource recovery and reuse

Wastewater must be adequately treated so that its safe circularity can be realized. To be treated it must first be collected. This action area presents some options for improving collection and treatment of wastewater to increase the potential for reuse. Approximately 63 per cent of global domestic and manufacturing wastewater is collected and 52 per cent of globally produced wastewater is treated. When looking at the domestic and manufacturing wastewater that is collected, 84 per cent is subject to some level of treatment (Jones et al. 2021). Estimates of wastewater treatment have shown some improvements since 2015 (UN-Habitat and WHO 2021), particularly for domestic wastewater. Despite these improvements, there is still a large variation between the percentage of wastewater collected, treated and reused in different regions (figure 3.4), with much of the progress occurring in developed countries. In countries where access to sanitation and wastewater services is low, a large percentage of wastewater cannot be collected and consequently cannot be treated.

sanitation systems. Both centralized and decentralized systems can vary in complexity. Once collected, wastewater can undergo various forms of treatment. UN-Habitat and WHO (2021) report that wastewater that is collected in centralized sewers is more likely to be treated than wastewater from decentralized systems. Treatment can also be managed centrally or through decentralized approaches that incorporate wide variety of solutions using physical, biological and ecological processes, or combinations of these. Wastewater treatment can range from the simple, such as screening and sedimentation (primary treatment), to the biological, such as using activated sludge (secondary treatment), and to more advanced technologies such as membrane filtration, disinfection and carbon adsorption (tertiary treatment) (figure 3.5). The degree to which treatment practices exist and reduce contaminant levels (Jones et al. 2021) and the proportion of (treated) wastewater relative to stream flow (Ehalt Macedo et al. 2022) are crucial determinants of how the recovered resources can be used as well as of the impact on the quality of receiving waters (Jones et al. 2021; Mateo-Sagasta, Raschid-Sally and Thebo 2015).

Collection infrastructure can either be centralized, with wastewater treated off-site, or in decentralized on-site

Water collection, treatment and reuse by region

Eastern Europe and Central Asia

North America

Western Europe

Middle East and North Africa

South Asia

Billion cubic metres per year Wastewater

Sub-Saharan Africa

50.0

Latin America and the Caribbean

1.5 10.0

Collection Treatment Reuse

No data

Source: Jones et al. 2021; GRID-Arendal/Studio Atlantis, 2023.

Figure 3.4: Water collection, treatment and reuse by region.

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