The role of biodegradable dissolved organic carbon on the degradation of pharmaceuticals and personal care products during soil aquifer treatment

As human populations continue to grow and global climate changes occur, the water required to sustain arid regions is becoming scarce. One option to increase future water supplies in arid regions is to store water in aquifers, and one potential source is reclaimed municipal wastewater. This reuse of reclaimed water could drastically reduce the incidence of water crises expected in arid regions in coming decades. While municipal wastewater treatment plants efficiently remove many wastewater constituents such as total organic carbon and nutrients, some residual contaminants remain in trace quantities following treatment. Pharmaceuticals and personal care products (PPCPs) are an example of trace contaminants often inefficiently removed during conventional wastewater treatment and reclamation. One strategy to manage these residual contaminants might be to further degrade or remove them during soil aquifer treatment (SAT), making this treatment process a desirable and effective addition to the water reclamation system. Unfortunately, factors that control the degradation of PPCPs during SAT, such as the effluent organic matter composition and concentration, are largely unknown. The objective of this study was to assess the ability of the biologically available portion of effluent organic matter to affect the degradation of PPCPs during simulated subsurface transport. This required analysis of a surrogate set of PPCPs, representative of major pharmacological classes and personal care products frequently used and development of an analytical method to measure the selected PPCPs. To verify that the developed analytical method was capable of detecting PPCPs in real water samples, PPCPs were measured in two municipal wastewater reclamation facility effluents. PPCPs were detected in both effluents, although the concentrations of some studied PPCPs were highly variable in the effluents. Samples were also collected from the Truckee River at likely discharge locations for the Truckee, CA municipal wastewater treatment facility, which incorporates SAT as part of the treatment process. Among the seven PPCPs analyzed, carbamazepine and benzotriazole were in Truckee River samples downstream of the infiltration zone, suggesting that these compounds persist during SAT. Next, a column experiment was conducted were BDOC concentrations in the soil column feed waters were manipulated, while measuring PPCP concentrations. Unfortunately, little PPCP degradation was observed under conditions used in this study and future research is required to better understand the factors affecting the degradation of these compounds during SAT and subsurface flow.