Understanding the potential and constraints of water reclamation is essential for the decision makers to design interventions that improve the process in a safely manner e.g. for Maputo, Mozambique. In this thesis i) the potential and constraints of using (partially) treated wastewater in irrigated agriculture for sub-Saharan Africa (SSA) was analysed; ii) the concentration of the indicator Escherichia coli (E. coli) in irrigation water, the lettuce (Lactuca sativa) produced in the irrigation fields in Infulene Valley, in Maputo, Mozambique, and the lettuce subsequently sold at local markets in Maputo was assessed; iii) and the potential contribution of wastewater-based nutrients to the supply of nitrogen (N), phosphorous (P), and potassium (K) for lettuce production in the Infulene Valley, in Maputo, Mozambique, was studied.

An extensive literature review was performed for existing examples of water reclamation in sub-Saharan Africa, followed by laboratorial analyses of water, soil and lettuce samples collected in the Infulene valley in Maputo. We analysed the faecal coliform contamination considering the E. coli as its indicator, the content of nutrients (Nitrogen, Phosphorous and Potassium), and the potential toxic elements (PTE) present in the samples.

Water reclamation is informally practiced in many SSA countries, with wide use of untreated reclaimed wastewater in agriculture. Wastewater quality in most of SSA countries is regulated by the 1989 WHO guidelines, instead of its more recent 2006 guidelines. The 1989 WHO guidelines are based on restrictive effluent criteria, which are more practical to use, compared to the 2006 WHO guidelines. However, the 1989 WHO guidelines are not effective for risk reduction of the farmers’ practices, based on the installed wastewater treatment capacity and the vulnerability of contamination along the supply chain. The 2006 WHO guidelines are more complex to implement for most of the SSA countries. The multiple barrier approach has been proposed for safe water reclamation combining the treatment and the critical points for quality control in the value chain to reduce the health risks. This requires the development of a water reclamation approach, which matches the required water quality at the point of use and the design of an affordable wastewater treatment, which reduces risks on the long term. Overall, it was concluded that there is a potential in SSA countries for water reclamation, although it requires the development of the relatively poor water and sanitation infrastructure to support its implementation.

We found that irrigation water is not the only potential source of faecal contamination in the value chain of lettuce produced at farms and sold at local markets of Maputo. The lettuce produced in the Infulene valley was also contaminated along the value chain, regardless of the irrigation source. The process of washing lettuce in the market presents a potential for re-contamination and it contributes little in risk reduction. Some measures for reducing the risk of contamination such as delaying harvest at the farm, and hygienic practices at the marketplace will impact the contamination levels of the lettuce, irrespective of the use of reclaimed wastewater or other water sources for irrigation in the Infulene Valley in Maputo.

Our analysis revealed further that wastewater is a viable alternative for nutrient supply in the Infulene Valley. It contains higher amounts of essential nutrients (N, P, and K) compared to groundwater. This highlights the potential of wastewater as an effective source to (1) re-plenish nutrients in agricultural systems to meet crop nutrient demands and (2) to reduce reliance on traditional fertilizers. However, careful nutrient management is crucial to avoid excessive nutrient dosing, which can lead to health and environmental hazards such as groundwater pollution, pollution of water ways, and soil degradation. Implementing strategies such as combined source control, frequent water monitoring, and appropriate treatment options can help for ferti-irrigation in peri-urban areas like the Infulene Valley.

Finally, our data showed that PTE were present at low concentrations in the irrigation water and soil. In plants, the concentration of chromium, aluminium, iron and sodium exceeded the recommended levels, suggesting sources unrelated to irrigation water. The high concentration of certain PTE when using river water and wastewater revealed the need for monitoring and understanding the elemental composition of crops, especially when different irrigation sources are used. Additionally, elevated sodium adsorption ratios and electrical conductivity levels across irrigation sources emphasize the need for cautious use of wastewater for irrigation. Monitoring activities are recommended for the Infulene valley, in order to prevent accumulation of Mn, Al, Fe, Cr and Na, which potentially have negative impacts on the crop production, environment, and food security.

Overall, it can be concluded that the promotion of safe water reclamation in SSA countries should be implemented applying a holistic approach, including water treatment and the entire agricultural value chain that includes crop producers (farms), crop handlers, market vendors, and end consumers. Planners should consider the ‘farm-to-market-consumer’ chain to implement local safety measures that mitigate risks. Change in social behaviour towards reclaimed wastewater also represents an important aspect for inclusion in activities towards the implementation of safe water reclamation. At policy level, persistent behaviours should also be changed to facilitate revisiting infrastructures and policies for reclaiming wastewater. In addition, initiatives for water reclamation should consider all potential end users, such as agricultural and industrial users, while embedding opportunities for a circular economy for a positive impact on farmers, society, and the environment.

Faecal contamination across the lettuce value chain was assessed in Maputo, Mozambique. Escherichia coli was used as an indicator of faecal contamination, with concentrations ranging from 3.4 to 5.7 log units/100 ml in groundwater, river water and partially treated wastewater. Municipal tap water used to wash lettuce heads in the markets had lower than 1 log unit/100 ml. Irrespective of the source of irrigation water, the lettuce heads were contaminated throughout the value chain, with concentrations ranging between 6.5 and 7.8 log units/100 g. Interventions and awareness raising should be applied at every stage of the value chain.

This research investigated the contribution of wastewater-based nutrient supply, viz., nitrogen (N), phosphorous (P), and potassium (K), for lettuce production in the Infulene Valley, Mozambique, from July to September 2019. The research was conducted in groundwater- and wastewater-irrigated agricultural plots. Water samples were collected weekly, soil samples were collected before planting and after harvest, and lettuce samples were collected at harvest time. The nutrient content (N, P, and K) was measured, and a mass balance method was applied. Wastewater had distinctly higher nutrient contents than groundwater, which guaranteed crop nutrition during the growing stage. Wastewater contributed 88%, 96%, and 97% to the N, P, and K requirements, respectively. The crop yield in the wastewater-irrigated areas was 43,8 ± 16 tons/ha, which was higher than 35 ± 8 tons/ha observed for the groundwater-irrigated areas, but results showed no statistically significant differences. Conclusively, wastewater led to reduced soil-nutrient gap and can be a source of nutrients. Therefore, wastewater is regarded as an alternative nutrient source of interest, and if properly applied, it might reduce environmental health hazards, resulting from run-off or leaching of excess nutrients

This review identifies the potentials and constraints of using (partially) treated or blended wastewater for irrigation in order to assess the potentials in the context of cities in sub-Saharan Africa, specifically Maputo, the capital of Mozambique. Less than 5% of the wastewater produced in the region is being treated. Nonetheless, untreated, partially treated, and/or blended wastewater is extensively being used for agricultural purposes. Despite the last updated WHO 2006 guidelines for ‘wastewater use in agriculture’, authorities only consider the different water quality parameters at the point of use. Other aspects such as irrigation type, crop management and post harvesting practices, which clearly influence the contaminant log reduction, are simply ignored. Those parameters, however, are considered alternatives to a classic contaminant log reduction, which may be very beneficial for developing countries. In a more holistic approach, trade-off is favoured between the required water quality for irrigation, use of affordable treatment technologies, and adequate post-harvest strategies to reduce the current health risks to acceptable levels. Such a trade-off makes use of multiple barrier approach, whereby wastewater treatment and critical point barriers throughout the supply chain are combined. Thus, there is a long way ahead to achieve proper water reclamation for productive use; the current paradigm has to change. Current restrictive guidelines are unrealistic given current practices, and approaches more appropriate to the location's situation still need to be developed. A multiple barrier approach in combination with master planning is recommended to consider wastewater treatment and critical point barriers throughout the supply chain.

The use of aquaculture is increasing to meet the growing global demand for seafood. However, the use of aquaculture for seafood production incurs potential human health risks, especially from enteric bacteria such as Salmonella spp. Salmonella spp. was the most frequently reported cause of outbreaks associated with crustaceans from 1998 to 2004. Among crustacean species, shrimp are the most economically important, internationally traded seafood commodity, and the most commonly aquaculture-raised seafood imported to the United States. To inform safe aquaculture practices, a quantitative microbial risk assessment (QMRA) was performed, incorporating stochastic variability in pathogen growth, industrial shrimp processing, and consumer shrimp preparation. Several scenarios including gamma irradiation and cooking time were considered in order to examine the relative importance of these practices in terms of their impact on risk. Median annual infection risks for all scenarios considered were below 10−4 and median disability adjusted life year (DALY) metrics were below 10−6 DALY per person per year, however, 95th percentile risks were above 10−4 annual probability of infection and 10−6 DALY per person per year for scenarios with improper cooking and lack of gamma irradiation. The greatest difference between microbiological risks for the scenarios tested was observed when comparing proper vs. improper cooking (5–6 orders of magnitude) and gamma irradiation (4–5 orders of magnitude) compared to (up to less than 1 order of magnitude) for peeling and “deveining” (removing the shrimp digestive tract) vs. peeling only. The findings from this research suggest that restriction of Salmonella spp. to low levels (median 5–30 per L aquaculture pond water) may be necessary for scenarios in which proper downstream food handling and processing cannot be guaranteed.