Science: Reusing treated effluent to combat water shortage: predicting the fate and risk of contaminants

Areas facing periods of drought constantly struggle with a stable water supply for agriculture and nature. With a changing climate, these draught periods might increase, resulting in even more water shortage. This poses an even bigger challenge to guarantee a sufficient water supply to the agricultural sector and nature areas. Reusing effluent water is one of the Possible solutions that can be considered to combat water deficiency. This unexploited water source can be used for irrigation, to enlarge ground water reservoirs, and supplying water to nature, like streams and wetland areas. Not only non-food crop production and desert greening programs can utilize effluent, but also irrigation of food crops is a possibility. However, despite wastewater treatment, effluent may still contain the so-called ‘contaminants of emerging concern’ (CEC), like pharmaceutical residues and the notorious PFAS. These may pose a risk to crops or human health. Such risks should be understood and quantified to allow for a safe use of such unused water sources.

Gas extraction

Qatar, partner in the project faces a special situation. This country continuously struggles to get enough fresh water. Currently, most fresh water is generated by desalination of sea water, a relatively expensive technology. At the same time, in addition to municipal effluent, Qatar has a lot of waste water available due to gas extraction. This extraction water is treated in wastewater plants, but besides CECs, also large amounts of salts remain after treatment. This poses an additional problem for reuse in, for example, agriculture or desert regreening projects. But despite these problems, the potential of this large effluent reserve is large, especially since the waste water treatment process also results in a large amount of bio-sludge. ‘This might be a bonus, since it can possibly be used as a fertilizer on the nutrient-poor soils’, Soedarso says.

Safe option

To make effluent water safe for reuse, ETE, together with Dutch and international partners, has started a project to understand CEC behavior in soils and effluent and possible risks for agriculture. Within the framework of the new Aquaconnect project ‘Assessing the fate of contaminants of emerging concern in effluents during irrigation’, Soedarso and her colleagues are addressing potential problems and solutions regarding the use of effluent in agriculture. To understand if CECs pose a risk to crops or human health, and if using effluent in agriculture is a safe option, the team aims to better understand how CECs present in effluent behave when used for irrigation. ‘We specifically want to find out how, and to what degree, CECs bind to soil and how much end up in the groundwater’, Soedarso explains. ’If we understand the interaction between soil, water and CECs, we can develop simulation models to predict the effects of effluent irrigation on soil and groundwater quality, as well as the exposure to crops and humans. This helps us to assess and manage associated risks.’ During their research, scientists will establish a link between the Dutch and Qatar casus and develop an overall evaluation for safe effluent reuse.

Best economical value

As a first step to better understand the fate of CECs in effluent when used for irrigation, Soedarso focuses on experimental studies. ‘We will perform experiments to study how CECs bind to soil and how much end up in groundwater’, Soedarso explains. ‘For example, we aim to quantify to what degree CECs adsorb or chemically react or bind to components in soil.’ In the Netherlands, the scientists have planned a series of lab and pilot field experiments, to better understand how CEC bind and migrate through different soils. In Qatar, also experiments are carried out to follow the CECs during their migration through different sandy soil types, using large square soil-filled containers, of 3x3x1 meter in size. By applying effluent on top of the soil, the flow of CECs through the soil, as well as their binding to soil can be followed and quantified. By collecting the water that has percolated through the soil, scientists can evaluate how much of the CECs end up in groundwater. Based on these experiments, simulation models will be developed, to predict how the CECs may behave in different soils in a real-life situation, and assess the associated exposure risks.

But the study will also include how different crops perform growing on effluent. In addition, water use as well as associated costs and the final crop value will be quantified by Soedarso’s project partners. Soedarso: ‘Initial experiments conducted last year have shown that cotton does very well. My colleagues in Qatar will experiment with more different crops to see what plant species delivers the best economical value.’ In addition, Soedarso’s PhD colleague, Alaadin Elozeiri, will develop a good salt removal technology to reduce the high salt concentrations from the gas extraction-related effluent, so this water stream can safely be reused in addition to municipal effluent.

At ETE, experiments will start soon and the initial focus will be on the CEC adsorption to the soil. ‘Developing the method is definitely a challenge’, Soedarso says. ‘The advantage is that we can do these first experiments at a small lab scale, while each test can also be performed rather quickly, within one to two days. That will allow us to experiment a lot of options in a relatively short time!’

The project “Regreening Deserts’ is carried as an international outreach within the framework of Aquaconnect.

Associated partners are Shell, The University of Qatar, Texas A&M Qatar, Texas A&M, HKUB, Qatar Ministry of Environment and Agriculture. Within AquaConnect, partners related to the Dutch case study are UvA, KWR, Water Agency Vechtstromen.