Removal Mechanisms for Organic Micropollutants during Artificial GroundwaterRecharge

摘要

One of the major concerns regarding the use of surface water sources of impaired quality forrndrinking water supply is the survival and accumulation of organic micropollutants, such asrnendocrine disruptors (EDCs), pharmaceutical residues, personal care products, or disinfectionrnby-products (DBPs). Riverbank filtration (RBF) or soil-aquifer treatment (SAT) have beenrnrecognized as potential barriers for these compounds. However, some organic micropollutantsrnare not efficiently attenuated during soil passage by physical adsorption and have affectedrnproduction wells at groundwater recharge facilities. The purpose of this study was to investigaternthe role that biological metabolism and adsorption play in the removal of selected hydrophilicrntrace organic contaminants in artificial groundwater recharge systems. Specifically, werninvestigated how different source water qualities and recharge operations promote the microbialrnbreakdown of trace organic contaminants. The working hypothesis for this study was that therncomposition and concentration of organic carbon in recharged water introduced into an aquiferrnhas a major impact on establishing soil biomass activity and a soil microbial community tornenable the metabolic breakdown of certain trace organic contaminants. Several emergingrnmicropollutants (representing pharmaceutical residues and personal care products) were selectedrnfor this study that differed in terms of physico-chemical properties such as molecular size andrnhydrophobicity (indicated by KOW), and their reported biodegradability. Removal of theserncompounds was studied in different soil column systems representing different redox regimesrn(anoxic vs. oxic). Column system influents were spiked with the selected micropollutants atrnenvironmental concentrations and different organic carbon fractions (bulk water, hydrophobicrnacids (HPO-A), hydrophilic carbon (HPI) and colloidal carbon). Column performances werernmonitored twice a week in terms of soil biomass activity (measured as phospholipids extractionrnand dehydrogenase activity), organic carbon removal, pH, conductivity, and trace compoundrnremoval. In parallel, the adsorption behavior of selected compounds was evaluated in abioticrncolumn and batch tests under addition of sodium azide. Results of this study indicated thatrndifferent organic carbon fractions were able to support different soil biomass activities andrnpromoted different removal behavior for certain micropollutants. Oligotrophic conditions, whichrnestablished in systems fed with more recalcitrant organic carbon fractions (HPO-A, HPI), led to arnhigh degree of removal pointing to a highly diverse biocommunity responsible for removal.rnFindings of this study suggest that an effect of organic matter on sorption of intermediaternhydrophobic organic micropollutants in RBF is not expected.