Pay Drechsel’s research while affiliated with International Management Institute and other places

Globally, the use of untreated, but often diluted or partially treated wastewater in agriculture spans approximately 30 million hectares (ha). This far exceeds the area of planned use of well-treated (reclaimed) wastewater, which is estimated to cover at best 2 million ha (Qadir et al. Forthcoming). This gap has likely widened over the last decade despite significant investments in treatment infrastructure and capacity, due to the rapid population growth and the consequent increase in water consumption and wastewater generation. As a result, millions of small-scale farmers in urban and peri-urban areas of developing countries depend on wastewater or wastewater- polluted water sources to irrigate high-value edible crops for urban markets, often lacking alternative sources of irrigation water (Raschid-Sally and Jayakody 2008; Drechsel et al. 2022; UNEP 2023). While (undiluted) wastewater can contain high amounts of crop nutrients that farmers value, the water will also contain various chemical, biological and physical pollutants, such as organic and inorganic compounds, pathogens (bacteria, viruses and parasites), heavy metals, hazardous chemicals, emulsions, pharmaceutical residues, nanoparticles, etc. The composition of wastewater can vary widely depending on its source, such as domestic, industrial or agricultural activities, as well as its treatment level and any dilution that occurs if channeled into existing water bodies. In those bodies, the water can cause significant ecological damage and, if reused, public health problems (Qadir et al. 2010; Khalid et al. 2018).

Reducing greenhouse gas emissions from organic waste is a key pillar in advancing the circular bioeconomy. In the Global South, efforts have primarily focused on waste management regulations, with varying enforcement in these countries. These have focused mainly on human and environmental health without considering waste as a resource. For a genuine shift towards a circular bioeconomy, regulations must evolve to ensure environmental safety, promote resource recovery, and foster private sector engagement. This can be achieved through targeted policies, subsidies, financial incentives, and the development of public-private partnerships that open new market opportunities. Countries like Singapore, Brazil, China, Japan, South Korea, Ghana, and South Africa are leading the way with forward-thinking regulatory frameworks. These nations have built robust ecosystems by empowering statutory agencies to oversee waste management, engaging the private sector, and implementing financial mechanisms to support reuse and recovery. These innovative models are setting a precedent for successful circular bioeconomy implementation. Policymakers should take note of these approaches to craft impactful strategies that drive sustainable economic growth while addressing environmental challenges.

In low- and middle-income countries, inadequate sanitation results in faecal contamination of the water used by urban farmers for irrigation. Consumers of raw contaminated vegetables run the risk of developing diarrhoeal diseases and helminth infections, which are a leading cause of under-five mortality and impact the well-being and productivity of millions of adults. This review identifies the evidence base for assessing which factors determine the success and/or failure of interventions that aim to manage the risk of faecal contamination in the urban irrigated vegetable value chain. We carried out a systematic search of the literature from the perspective of the COM-B behaviour framework (Capability + Opportunity + Motivation = Behaviour). Our results reveal that most interventions address stakeholders’ opportunity or capability to adopt safe practices without adequately considering their motivation. Interventions often focus on one sector rather than on the whole value chain (sanitation, agriculture, trade, consumption). To effectively change hygiene and food safety practices in the urban irrigated vegetable value chain, stakeholders’ intrinsic motivations need to be identified. Where WHO's multi-barrier approach is the best option, we recommend building on local multistakeholder platforms and adopting a behaviour change framework to support the largely technical change from farm to fork.

Safely managed wastewater is critical to water-related sustainable development. With a focus on the domestic wastewater component of SDG 6.3.1, this study reports that household activities worldwide generate 267.5 billion m ³ yr − 1 of wastewater, of which 63% (168.8 billion m ³ yr − 1 ) is collected in sewers and septic tanks, and 54.7% (146.3 billion m ³ yr − 1 ) is treated. In comparison, 45.3% (121.2 billion m ³ ) is released to the environment in untreated form, either uncollected (98.7 billion m ³ yr − 1 ) or collected but untreated (22.5 billion m ³ yr − 1 ). The monitoring of and progress on safely managed wastewater remain strongly uneven between the Global North and Global South and between geographic regions and income groups. While there is clear progress in the agricultural reuse of treated wastewater, untreated water reuse requires more attention. Considerable challenges remain because of terminology, informal irrigation, and the usefulness of reporting reuse volumes or areas for health-based targets.

Gaining insight into the food sourcing practices of cities is important to understand their resilience to climate change, economic crisis, as well as pandemics affecting food supply and security. To fill existing knowledge gaps in this area food flow data were collected in four West African cities - Bamako (Mali), Bamenda (Cameroon), Ouagadougou (Burkina Faso), and Tamale (Ghana). The data cover, depending on the city, road, rail, boat, and air traffic. Surveys were conducted for one week on average during the peak harvest, lean, and rainy seasons, resulting in a dataset of over 100,000 entries for 46 unprocessed food commodities. The data collected includes information on the key types of transportation used, quantity, source, and destination of the food flows. The data were used to delineate urban foodsheds and to identify city-specific factors constraining rural-urban linkages. The data can also be employed to inform academic and policy discussions on urban food system sustainability, to validate other datasets, and to plan humanitarian aid and food security interventions.

Urban and peri-urban agriculture (UPA) is widely distributed throughout the Global South. Despite urban population growth and diversifying food habits, UPA delivers an important part of urban food supply, as well as other types of services to cities, such as employment and waste reuse. Nevertheless, the extent and importance of UPA varies between different urban areas, while challenges like limited recognition, land conversion, and water pollution and competition threaten the potential of UPA to contribute to urban resilience. Key investment priorities for research and innovation for overcoming current challenges include incentivized peri-urban zoning, urban allocation of productive lands, and increasing capacities for controlled environment agriculture (CEA). Innovative repositioning of food marketing can help to strengthen supply of healthy food from UPA production, increase decent employment, and turn food markets into nutrition hubs. Priority innovations for contributing to the circular bioeconomy of cities include scaling the safe use of wastewater for irrigation through investments in the adoption of multiple risk-barrier approaches and scaling UPA-based ecosystem services for valorising solid waste and environmental management. Innovations in urban governance are required to support these processes by bringing food systems into urban planning through food mapping and the multisectoral platforms for dialogue and policy formulation across city regions and with vertical levels of government.

In West Africa, rampant urbanization is changing food systems, including the magnitude and composition of food flows and the length of supply chains. An increasing body of literature discusses pathways to sustainable transformation of urban food systems taking into account links between urban and rural spaces. Research and policy have focused on the role of cities as consumption centers receiving food from local, regional, and global hinterlands. This study aims at widening the perspective on the role of cities in food distribution, by bringing into focus a city's function as a consumption, aggregation, and disaggregation center. The analysis is based on a comprehensive set of primary data on food flows collected in four West African cities across different seasons. The analysis shows that the investigated cities are integrated into multi-scale urban and market networks. Their position within these networks interacts with their reliance on other territories for food supply and with their functions, such as the aggregation of goods. The capital cities of Ouagadougou (Burkina Faso) and Bamako (Mali) relied more on lower-rank urban settlements further away, while Tamale, a secondary city in Ghana, acted as an assembly market for local rural producers and in turn supplied larger urban centers. Bamenda, a secondary city in Cameroon, acted as a consumption center sourcing mainly from its hinterland. Beyond that, city functions were context-specific and varied according to type of product and season. Extending the perspective on the role of cities has implications for policy, including bringing into focus and strengthening midstream segments, such as market and transport links.