Assessing the Potential of Reclaimed Wastewater as a Resource for Sustainable Agricultural Practices

Can reclaimed wastewater (RW) emerge as a transformative solution for sustainable agriculture, reshaping the way we manage water sources in farming? 

It is in response to this pivotal question that ASAP-WATER project was designed, based on the awareness that freshwater sources are under increasing pressure and that innovative and sustainable approaches are needed to maintain agricultural productivity and guarantee food security. Agriculture stands out as the sector that has the largest needs for water, using huge amounts for irrigation to ensure crop growth and food production. In fact, agriculture accounts for about 70-80% of global freshwater withdrawals. The challenges we face due to water shortage, climate change, rapid urbanisation and population growth demand a comprehensive approach for water resources management. Climate change, with its erratic rainfall patterns, is exacerbating water scarcity by causing droughts in some regions and intense rainfall in others. 

In the midst of this problematic scenario, the potential of RW is emerging as a way to address water scarcity in a sustainable way. This approach not only helps to reduce pressure on freshwater sources, but also promotes a reduction in the use of inorganic fertilisers, as these waters typically contain nutrients essential for crops (e.g., N, P, K). However, the use of RW in agriculture continues to raise environmental/public health concerns, particularly regarding the presence of pollutants. Despite wastewater treatment processes, micropollutants (e.g., pharmaceuticals, personal care products, etc.) and microorganism, including pathogens, can persist in RW and if not carefully monitored and managed, these pollutants can pose risks to soil health, plant growth and ultimately food safety. Although there is legislation in Europe setting minimum safety requirements for water reuse (Regulation EU 2020/741), these are essentially based on microbiological and physicochemical parameters and micropollutants are still under review. Indeed, this remains a critical issue and a major barrier to the diffusion of this practice among stakeholders and the public. Balancing the potential benefits of RW with these inherent risks requires a comprehensive approach that includes robust monitoring and strategic implementation practices to ensure the safe and responsible integration of this alternative water source into agricultural systems. 

The project will rely on a multidisciplinary team with the complementary skills needed to carry out the proposed tasks. It will bring together 3 R&D units from the Faculty of Engineering (LEPABE, LSRE-LCM – FEUP) and the Faculty of Science (GreenUPorto - FCUP) of the University of Porto, and will also be supported by SIMDOURO, a wastewater management company, with which the team has previously worked.

#1. Study the quality of RW to ensure its compliance with agricultural standards

Establishment of a monitoring plan in wastewater treatment plants (WWTPs) of different sizes and receiving different types of effluents, trying to get a seasonal snapshot of the physicochemical and potential agronomic parameters of these waters (e.g. pH, total organic carbon, COD/BOD5, total suspended solids, nutrient, heavy metal and emerging contaminants levels, microbial indicators). In this study, it will be included pollutants listed in the Urban Wastewater Treatment Directive, the Water Framework Directive Watch List and other compounds that have been commonly identified in WWTP effluents.

#2. Investigate the impact of RW on soil/substrate

Monitor changes in soil/substrate properties and composition due to RW irrigation and compare results with data from irrigation with conventional water supply, study the persistence/fate of selected emerging contaminants in the irrigated soils/substrates using sorption assays, column leaching studies, dissipation (volatilisation, aerobic/anaerobic degradation, photodegradation) and toxicity tests.

#3. Evaluate crop uptake of emerging contaminants under different production systems and irrigation practices

Conduct plant uptake experiments with an economically relevant horticultural crop used as model systems (lettuce) grown in soil/substrate and irrigated with RW or produced under hydroponic conditions (worst-case scenario for contaminant exposure). Crop yield and nutritional content will be monitored. Studies analysing the effect of irrigation practice (drip/sprinkler) on both contaminant uptake and irrigation infrastructure (e.g. biofouling causing nutrient depletion, contaminant/pathogen accumulation and clogging of the irrigation water lines) will be conducted.

#4. Estimate the risks and assess differences in crop yield and production viability for each condition tested

These activities will integrate the information gathered in the previous ones (occurrence of emerging contaminants in RW, occurrence/behaviour/fate of pollutants on irrigated growing media, plant uptake) with data on their effects on soil/human (literature data complemented by toxicity tests performed during the project, including biofilm and pathogen monitoring results). In addition, a comparative study will be conducted between the different production systems tested and conventional agriculture in terms of economic/environmental/social benefits and costs.