The role of organic matter in the removal of emerging trace organic chemicals during managed aquifer recharge
Introduction
Managed aquifer recharge (MAR) systems, such as riverbank filtration (RBF) and soil aquifer treatment (SAT), are widely used natural processes for drinking water augmentation projects using source water that might be impaired by wastewater discharge. Previous studies have demonstrated that MAR systems are effective in dampening and reducing the concentrations of dissolved organic carbon (DOC) as well as various trace organic contaminants (TOrC) that might be present in impaired source waters (Drewes and Fox, 1999, Brauch et al., 2000, Grünheid et al., 2005). The presence of TOrC has become a key concern for drinking water augmentation projects during the past decade (Kolpin et al., 2002, Heberer, 2002, Focazio et al., 2008). Although adverse human health effects caused by these compounds at concentrations commonly observed in impaired water resources are very unlikely (Schwab et al., 2005), minimizing exposure of wastewater derived contaminants in these projects is desired. Previous research on the fate of TOrC during MAR has primarily focused on collecting anecdotal and site specific information on their occurrence and removal (Drewes et al., 2002, Montgomery-Brown et al., 2003, Grünheid et al., 2005, Dillon et al., 2008). Studies delineating the mechanisms and boundary conditions for the transformation of wastewater derived TOrC during MAR are lacking.
Previous studies demonstrated that the type and bioavailability of effluent organic matter (EfOM) controls the extent of soil biomass growth in MAR systems (Rauch and Drewes, 2004, Rauch and Drewes, 2005). EfOM may consequently effect the degradation of TOrC by serving as a co-substrate in microbiologically facilitated transformations (Stratton et al., 1983). The diversity and expression of the soil microbial community also depends on composition and concentration of the organic carbon substrate controlling trophic cycles in the subsurface (Preuß and Nehrkorn, 1996, Szewzyk et al., 1998). The composition of EfOM (i.e. in terms of its bioavailability) is primarily determined by the degree of wastewater treatment employed (Drewes and Fox, 1999), which can vary widely from primary to conventional to advanced wastewater treatment. As a result, effluent qualities fed to MAR systems can vary in biodegradable dissolved organic carbon (BDOC) concentrations from less than 1 up to 15 mg/L or more. As a consequence, soil microbial communities growing on different levels of BDOC can differ widely in total biomass and diversity.
The objectives of this research were to investigate the role of 1) abiotic vs. biotic conditions, 2) BDOC and 3) the type of organic carbon matrices on the removal of select TOrC, such as pharmaceutical residues, personal care products, and household chemicals, during MAR.
Section snippets
Target organic contaminants
Compounds selected for this study represent small molecular weight organic chemicals (180 to 360 Dalton) that are hydrophilic at neutral pH regimes as indicated by an octanol/water partition coefficient at pH 7 (log DpH=7 of less than 2.6). TOrC with these properties have a high potential to migrate into groundwater and are not expected to be adsorbed onto porous media. The molecular structures and physicochemical properties of the target compounds chosen for this study are presented in Table 1.
Adsorption behavior of target TOrC
In order to assess whether physical retardation would be a contributing factor in the removal of select TOrC in the column experiments, an abiotic column experiment was conducted to study sorption of the compounds onto the virgin porous media used in the columns. None of the six TOrC included in this experiment exhibited significant retardation during flow through porous media as compared to the conservative tracer bromide (indicated by Rd values very close to 1, Table 3). These findings reveal
Conclusions
Hydrophilic, small-molecular size TOrC can survive conventional and advanced wastewater treatment processes and are one of the key concerns in drinking water augmentation projects using impaired source waters. More research is needed to better understand the trophodynamic role of organic carbon on the removal of TOrC in MAR applications. In this study we conducted column experiments to illuminate key factors for the metabolic removal of twelve TOrC during soil infiltration. Experiments were
Acknowledgments
Partial funding for this study was provided by the Gwangju Institute of Technology in Korea. We are thankful for analytical support during this study provided by Dr. Thomas Heberer at the Technical University in Berlin, Germany, Matt Oedekoven, and Stephan Wagner.
References (48)
- et al.
A general model for multiple substrate biodegradation. Application to co-metabolism of structurally non-analogous compounds
Water Research
(2003) - et al.
Behaviour of pharmaceuticals, cosmetics and hormones in a sewage treatment plant
Water Research
(2004) - et al.
Carbamazepine as a possible anthropogenic marker in the aquatic environment: investigations on the behaviour of carbamazepine in wastewater treatment and during groundwater infiltration
Water Research
(2004) - et al.
The solids retention time – a suitable design parameter to evaluate the capacity of wastewater treatment plants to remove micropollutants
Water Research
(2005) - et al.
Fate of natural organic matter (NOM) during groundwater recharge using reclaimed water
Water Science and Technology
(1999) - et al.
A national reconnaissance for pharmaceuticals and other organic wastewater contaminants in the United States–II untreated drinking water sources
Science of the Total Environment
(2008) - et al.
Removal of bulk dissolved organic carbon (DOC) and trace organic compounds by bank filtration and artificial recharge
Water Research
(2005) Occurrence, fate and removal of pharmaceutical residues in the aquatic environment: a review of recent research data
Toxicology Letters
(2002)- et al.
Elimination of COD, microorganisms and pharmaceuticals from sewage by trickling through sandy soil below leaking sewers
Water Research
(2003) - et al.
Behavior of alkylphenol polyethoxlate metabolites during soil aquifer treatment
Water Research
(2003)