Risks and opportunities associated with re-using domestic sewage treatment plants effluent for sub-surface irrigation in agriculture

Worldwide, fresh water scarcity is often caused by a high demand from the agricultural sector that globally accounts for 69% of fresh water withdrawal (Food and Agriculture Organization of the United Nations 2016). By 2050, the water demand of this sector is estimated to increase further by 19%, due to irrigational needs (UNESCO 2012). This is not only an issue for arid regions with low rainfall and high population density that are prone to increasing water stress; temperate areas with intense agriculture also suffer from frequent non-potable water shortages. The pressure on the availability of fresh water will continue to increase due to climate change, which will enhance prolonged dry periods (Chen, et al. 2017, Klijn, et al. 2012). Hence, it is crucial to explore alternative water resources. Re-using treated wastewater, which is currently discharged in large volumes on surface water, may provide an alternative freshwater source. Additionally, the load of contaminants of emerging concern (CECs) to surface water may be reduced due to soil passage and related biodegradation processes. Irrigation with treated wastewater is not a new phenomenon, as it is already used widespread, particularly in regions such as Middle East and North Africa (MENA) and other Mediterranean countries, where the availability of freshwater is limited (Food and Agriculture Organization of the United Nations 2016, Faour-Klingbeil en Todd 2018). However sub-irrigation via a controlled drainage system in comparison to sprinkling irrigation may have two major advantages: (i) there is no direct contact between fieldworkers and treated effluent, and (ii) it could make optimal use of soil processes that naturally minimize environmental occurrence and dispersion of CECs (Bartholomeus, et al. 2016, Nham, et al. 2015, van der Waals, et al. 2018, Hamann, et al. 2016). The extent to which the dispersion of the mixture of CECs, such as pharmaceuticals, metabolites, antibiotic resistant bacteria and resistance genes is diminished in sub-irrigation agricultural fields is not yet fully understood (Christou, et al. 2017, Greskowiak, et al. 2017). In addition, direct evidence on the effects of re-using treated effluent for sub-irrigation under real agriculture conditions for a broad selection of CECs is currently lacking (Bertelkamp, et al. 2014, Petrie, et al. 2018). Thus, this research aims at identifying the fate of a broad selection of CECs under real agricultural conditions and calculating the risks associated with reusing treated wastewater for sub-irrigation. To investigate such re-use, the CECs in the treated effluent of two field studies will be identified using broad suspect screening, and their fate (biodegradation, plant uptake, sorption, transport to groundwater and/or surface water) is assessed under different laboratory and field conditions. In the final step, risk analysis is performed and regionally scaled up using models. This presentation will discuss preliminary data.