Antimicrobial contaminant removal by multi-stage drinking water filtration

The fate of antimicrobials entering the aquatic environment is an increasing concern for researchers and regulators, and recent research has focused on antimicrobial contamination from point sources, such as wastewater treatment facility outfalls. The terraccumulation of antimicrobials and mobility in diffuse pollution pathways should not be overlooked as a contributor to the spread of bacterial resistance and the resulting threat to human drug therapy. This review critically examines recent global trends of bacterial resistance, antimicrobial contaminant pathways from agriculture and water treatment processes, and the need to incorporate diffuse pathways into risk assessment and treatment system design.; Slow sand filters are used in rural regions where source water may be subjected to antimicrobial contaminant loads from waste discharges and diffuse pollution. A simple model was derived to describe removal efficiencies of antimicrobials in slow sand filtration and calculate antimicrobial concentrations sorbed to the schmutzdecke at the end of a filtration cycle. Input parameters include water quality variables easily quantified by water system personnel and published adsorption, partitioning, and photolysis coefficients. Simulation results for three classes of antimicrobials suggested greater than 4-log removal from 1 mug/L influent concentrations in the top 30 cm of the sand column, with schmutzdecke concentrations comparable to land-applied biosolids. Sorbed concentrations of the antimicrobial tylosin fed to a pilot filter were within one order of magnitude of the predicted concentration.; To investigate the behavior of antimicrobial contaminants during multi-stage filtration, five compounds from four classes of antimicrobials were applied to a mature slow sand filter and roughing filter fed raw water from the Santiam River in Oregon during a 14-day challenge study. Antimicrobial removal efficiency of the filters was calculated from 0.2 mg/L influent concentrations using HPLC MS/MS, and sorption coefficients (Kd, Koc, Kom) were calculated for schmutzdecke collected from a mature filter column. Sulfonamides had low sorption coefficients and were largely unaffected by multi-stage filtration. Lincomycin, trimethoprim, and tylosin exhibited higher sorption coefficients and limited mobility within the slow sand filter column. The lack of a significant increase in overall antimicrobial removal efficiency indicated biodegradation is less significant than sorption in multi-stage filtration.