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.
Highlights
Almost 7% of the world population currently live in areas where the water demand exceeds the capacity of local water resources and two thirds of the population are exposed to water stress at least for one month a year [1]
Travel time estimations of recharged water during subsurface passage were based on breakthrough curves (BTC) of electrical conductivity measured in PZ6 and PZ7
Normalized BTCs measured in PZ6 and PZ7 from infiltration basin 2 are illustrated in Figure S3
Summary
Almost 7% of the world population (about 500 million people) currently live in areas where the water demand exceeds the capacity of local water resources and two thirds of the population are exposed to water stress at least for one month a year [1]. Water sources in arid and semi-arid areas are subject to significant pressure especially during spring and summer months, when water demand rises exorbitantly due to tourism and irrigation needs. Recycled water is mainly applied in agriculture and landscape irrigation; due to the limited freshwater resources, the implementation of planned potable reuse to augment drinking water supplies is increasing worldwide [6,7,8,9]. In addition to mixing with other sources and provision of buffer in case of emergency, the recharge into aquifers can result in additional attenuation of many contaminants [10,11]
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