Assessment of Full-Scale Indirect Potable Water Reuse in El Port de la Selva, Spain

Abstract

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.

Progress on legal and practical aspects on water reuse with emphasis on drinking water – an overview

“…• El Porto de la Selva is a small and tourist town with less than a thousand of inhabitants, in Spain. Nevertheless, during the summer months, the population increases by a factor of four, leading to rapid decline in groundwater levels of local aquifers with limited capacity (Fajnorová et al 2021). Current tertiary treatment and a non-potable reuse infrastructure was designed for street sweeping, non-agricultural irrigation, and infiltration via the dry riverbed to prevent saltwater intrusion in summer months (Frigola et al 2015).…”

“…Since 2015, El Porto de la Selva Groundwater Recharge (EPSGR), during winter months, has been testing regarding its potential to strengthen the local water reuse strategy. It was projected to infiltrate 200 m3 /d of tertiary treated effluent during 200-240 d/yr (outside of the tourism season, i.e., the period from October to May), resulting in 40,000-48,000 m3 /yr additional supply recharged to the groundwater (about 10% of the abstracted groundwater) (Frigola et al 2015;Fajnorová et al 2021). According to Fajnorová et al (2021), the conventional wastewater treatment in El Port de la Selva consists of biological nutrient removal with phosphorus precipitation and secondary clarification.…”

“…It was projected to infiltrate 200 m3 /d of tertiary treated effluent during 200-240 d/yr (outside of the tourism season, i.e., the period from October to May), resulting in 40,000-48,000 m3 /yr additional supply recharged to the groundwater (about 10% of the abstracted groundwater) (Frigola et al 2015;Fajnorová et al 2021). According to Fajnorová et al (2021), the conventional wastewater treatment in El Port de la Selva consists of biological nutrient removal with phosphorus precipitation and secondary clarification. The secondary effluent is further treated in a tertiary treatment plant equipped with dual media filtration and UV disinfection.…”

Characterization of a Shallow Coastal Aquifer in the Framework of a Subsurface Storage and Soil Aquifer Treatment Project Using Electrical Resistivity Tomography (Port de la Selva, Spain)

“…The average annual supply water abstraction in El Port de la Selva basin is about 400,000 m 3 , while the average annual volume of treated wastewater is in the range of 220,000 m 3 . Both abstraction and wastewater volumes have large fluctuations between summer and winter [36]. Furthermore, chloride concentrations in water abstracted from the municipal well were recurringly above the regional drinking water limit of 250 mg/L [37]-during the autumn months-probably triggered by saltwater intrusion after summer's high water demand period (Figure 2).…”