In 2015, the town of El Port de la Selva in Spain implemented soil-aquifer treatment (SAT) using tertiary treated wastewater effluents to replenish the local potable aquifer. This study evaluated the initial phase of this indirect potable water reuse system including a characterization of hydraulic conditions in the aquifer and monitoring of microbial contaminants and 151 chemicals of emerging concern (CECs). The combined treatment resulted in very low abundances of indicator bacteria, enteric viruses and phages in the monitoring wells after three days of infiltration and a reduction of antibiotic microbial resistance to background levels of local groundwater. After tertiary treatment, 94 CECs were detected in the infiltration basin of which 15 chemicals exceeded drinking water thresholds or health-based monitoring trigger levels. Although SAT provided an effective barrier for many chemicals, 5 CECs were detected above health-based threshold levels in monitoring wells after short hydraulic retention times. However, additional attenuation is expected due to dilution prior to abstraction via downstream drinking water wells and during granular activated carbon (GAC) filtration, which was recently installed to mitigate residual CECs. Overall, the results demonstrate that indirect potable water reuse can be a reliable option for smaller communities, if related risks from microbial and chemical contaminants are adequately addressed by tertiary treatment and subsequent SAT, providing sufficient hydraulic retention times for pathogen decay and CEC removal.

Probabilistic quantitative microbial risk assessment (QMRA) studies define model inputs as random variables and use Monte-Carlo simulation to generate distributions of potential risk outcomes. If local information on important QMRA model inputs is missing, it is widely accepted to justify assumptions about these model inputs by using external literature information. A question, which remains unexplored, is the extent to which previously published external information should influence local estimates in cases of nonexistent, scarce, and moderate local data. This question can be addressed by employing Bayesian hierarchical modeling (BHM). Thus, we study the effects and potential benefits of BHM on risk and performance target calculations at three wastewater treatment plants (WWTP) in comparison to alternative statistical modeling approaches (separate modeling, no-pooling, complete pooling). The treated wastewater from the WWTPs is used for restricted irrigation, potable reuse, or influences recreational waters, respectively. We quantify the extent to which external data affects local risk estimations in each case depending on the statistical modeling approach applied. Modeling approaches are compared by calculating the pointwise expected log-predictive density for each model. As reference pathogens and example data, we use locally collected Norovirus genogroup II data with varying sample sizes (n = 4, n = 7, n = 27), and complement local information with external information from 44 other WWTPs (n = 307). Results indicate that BHM shows the highest predictive accuracy and improves estimates by reducing parameter uncertainty when data are scarce. In such situations, it may affect risk and performance target calculations by orders of magnitude in comparison to using local data alone. Furthermore, it allows making generalizable inferences about new WWTPs, while providing the necessary flexibility to adjust for different levels of information contained in the local data. Applying this flexible technique more widely may contribute to improving methods and the evidence base for decision-making in future QMRA studies.

This paper presents the assessment of a planned scheme of indirect potable reuse (IPR) in the Vende´e region of France in its potential risks for human health and ecosystems, and also in its overall environmental impacts. Methods of risk assessment (quantitative microbial and chemical risk assessment) and life cycle assessment (LCA) are used to characterize the risk associated with the use of reclaimed water for IPR, but also the environmental benefits compared with other options for additional drinking water supply. The LCA results show that IPR is competitive with other options of water supply in its energy demand and greenhouse gas emissions. Pathogens as the main health hazard are controlled effectively by existing and planned preventive measures. For chemicals the number of potentially relevant substances could be reduced substantially by the assessment.

Soil aquifer treatment (SAT) is one of the most promising water reclamation and storage techniques in water reuse. This document summarizes the experiences gained in two full scale sites (Shafdan and El Port de la Selva) focused on overcoming the barriers associated with this low-cost technology.

One way of coping with water shortness is through reusing wastewater. In order to enhance potable water production in sites dealing with water shortness, treated wastewater can be fed into an intermediate storage system, generally a natural water reservoir from which drinking water is produced. This procedure is called indirect potable reuse. Although this technique may be an innovative way of coping with water shortness, little is known about the effect of this procedure concerning environmental and human health. In order to find more about the environmental and health human risks arising from indirect potable reuse technologies a risk assessment was carried over in the French Department of Vendée. This site deals with water shortness from May to October through a significantly enhanced water consumption in the coastal aera of this department caused by the increase of tourism activities and intensified crop irrigation. To achieve this task 35 different organic micropollutants, in its majority pesticides and pharmaceuticals were studied. Therefore, a risk assessment on water reuse technologies was performed at the site of concern. Furthermore, the impact of two tertiary treatments developed within the framework of the European DEMOWARE project on minimising arising risks was also taken into account. Results showed that 16 substances present a potential risk to the environment and/or to human health at the WWTP effluent. Similar results were achieved in fresh water, in this case 14 compounds have a risk quotient higher than 1 indicating a risk for both, health and environment. Furthermore, outcomes from the tertiary treatments risk characterisation showed that none of the studied tertiary techniques is cappable of reducing environmental and health risks for all substances to acceptable levels (RQ < 1). Same results were achieved for the risk characterisation in fresh water.

Nutrients, phosphorus and nitrogen, from municipal and industrial water streams contribute to the pollution or reduce the ecological potential of receiving water bodies. Recovering or reducing the nutrient content of waste streams, thus reducing the amounts of phosphorous and nitrogen that ends up in the water bodies, will contribute to a better environment. The first part of this report describes two tests performed to treat the concentrate of the reverse osmosis process at the Torreele facility. The first test used a natural system based on willows; the second test was based on post-denitrification MBBR. The willows proved able to remove nutrients for more than 30%, resulting in a substantial cost benefit for discharge which could make it economical feasible when installed at full-scale to treat the total volume of RO concentrate. Contrary to the willows, that even remove part of the nitrogen in winter, the post-denitrification MBBR was only efficient when N-NO3- exceeded 30 mg/L. The variable N-NO3- N-NO3- concentration and salinity of RO concentrate seemed to be limiting factors for a good performance. The second part of this report summarizes the activities regarding the optimization of water and nutrient (nitrogen and phosphorus) management at the reuse site Braunschweig, Germany. A detailed analysis of supply and demand of both, water and nutrients, for the reuse site was conducted. The optimization potential is especially high for nitrogen management, since the simultaneous supply via the Braunschweig wastewater treatment plant and additional conventional nitrogen fertilizer application by farmers result in an oversupply of nitrogen, losses to environment and a low efficient reuse compared to the total potential of renewable nitrogen in wastewater or sludge. Following this analysis, two possible solutions are discussed (fertigation and technical nutrient recovery), which are practically relevant for the Braunschweig reuse scheme in mid- and long-term timescale. Results indicate a high potential to increase the efficiency of nitrogen recycling. Simultaneously irrigation adopted on water demand of plants can be achieved.

This report describes different options for tertiary treatment of secondary effluent from municipal wastewater treatment plants for the purpose of water reuse. For each of the treatment trains, associated environmental impact (represented by energy demand and related global warming potential) and risk reduction potential (i.e. removal of chemical and microbial contaminants) are described based on the results of the DEMOWARE case studies. This should inform water professionals about impacts and benefits of different options for producing reclaimed water, enabling an informed decision on an adequate treatment train depending on the water quality targets for the respective reuse purpose.

This report summarizes the results of Life Cycle Assessment, Water footprinting, and quantitative microbial and chemical risk assessment for selected demosites of water reuse in Europe, measuring the potential impacts of different types of water reuse on environment and human health. The case studies show that water reuse is often preferable from an environmental point of view in areas with water scarcity problems if compared to other alternatives such as water import or seawater desalination. Potential risks of water reuse for ecosystems or human health can be adequately managed if suitable processes for reclaimed water treatment are used and operated correctly. However, the study also shows the trade-offs between a higher level of reclaimed water treatment and increased environmental impacts from associated efforts in energy, chemicals and infrastructure. This inherent trade-off requires a site-specific assessment of reuse schemes to choose an adequate treatment scheme for risk management with reasonable global environmental impacts.

This report presents the assessment of the planned water reuse scheme at Le Jaunay reservoir (Vendée) in its potential risks for human health and ecosystems, and also in its overall environmental impacts. Methods of risk assessment (quantitative microbial and chemical risk assessment) and Life Cycle Assessment are used to characterize the potential hazards associated with the use of reclaimed water, but also the environmental benefits compared to other options for additional drinking water supply. The assessments show that water reuse can be operated without unacceptable risks for humans and the environment, and that it is competitive to other options of water supply in its energy demand and greenhouse gas emissions. Data quality should be improved in a demonstrator phase to validate the outcomes of this first assessment.