Enhanced removal of emerging contaminants during managed aquifer recharge using optimized operating conditions

Abstract

The challenge of safe drinking water lies at the nexus of population growth, climate change, and environmental degradation due to pollution. To ensure potable water within the foreseeable future, robust, sustainable, and effective water treatment systems are essential. Managed aquifer recharge (MAR), including riverbank filtration (RBF) and artificial recharge and recovery (ARR), offers an effective and promising means for providing safe drinking water. However, in order to reduce the physical footprint of these installations, an improved performance for removal of key constituents, including chemicals of emerging concerns (CECs) is needed. The objectives of this study were to determine the role of sorption to clays in CEC removal during MAR, identify the effect of biodegradable dissolved organic carbon (BDOC) and its relationship with redox states on CEC attenuation, and determine how a sequence of optimal conditions can improve CEC removal in full-scale MAR. These objectives were achieved through a combination of bench-, laboratory-, and field-scale experiments. BDOC is both a driver of microbial diversity and redox state, and therefore is an essential parameter affecting MAR performance. The results suggest that an oxic, low-BDOC (<0.5 mg/L BDOC) environment seems to be optimal for CEC-removal performance. Under suboxic conditions, a low-BDOC environment is more efficient than a high-BDOC (>2 mg/L BDOC) environment. A low-end threshold has been observed, where too little dissolved organic carbon (<0.26 mg/L DOC) is present to promote effective CEC attenuation. In addition, clays were shown to effectively sorb a variety of CECs. In combination, these results provide valuable insight that will allow design of performance-enhanced MAR systems such as hybrid RBF/ARR schemes.