title: Column studies to assess the effects of climate variables on redox processes during riverbank filtration.
abstract: Riverbank filtration is an established technique used world-wide to produce clean drinking water in a reliable and cost-efficient way. This practice is, however, facing new challenges posed by climate change, as already observed during past heat waves with the local occurrence of anoxic conditions. In this study we investigated the effect of direct (temperature) and indirect (dissolved organic matter (DOM) concentration and composition, flow rate) climate change variables on redox processes (aerobic respiration, denitrification and Mn(III/IV)/Fe(III) reduction) by means of column experiments. Natural river water, modified river water and river water mixed with treated wastewater effluent were used as feed waters for the columns filled with natural sand from a river-infiltration system in Switzerland. Biodegradable dissolved organic matter was mainly removed immediately at the column inlet and particulate organic matter (POM) associated with the natural sand was the main electron donor for aerobic respiration throughout the column. Low infiltration rates (≤0.01 m/h) enhanced the oxygen consumption leading to anoxic conditions. DOM consumption did not seem to be sensitive to temperature, although oxygen consumption (i.e., associated with POM degradation) showed a strong temperature dependence with an activation energy of ∼70 kJmol(-1). Anoxic conditions developed at 30 °C with partial denitrification and formation of nitrite and ammonium. In absence of oxygen and nitrate, Mn(II) was mobilized at 20 °C, highlighting the importance of nitrate acting as a redox buffer under anoxic conditions preventing the reductive dissolution of Mn(III/IV)(hydr)oxides. Reductive dissolution of Fe(III)(hydr)oxides was not observed under these conditions.
authors.affiliation: EAWAG, Swiss Federal Institute of Aquatic Science and Technology, Water Resources & Drinking Water, Überlandstrasse 133, 8600 Dübendorf, Switzerland; ETH Zürich, Institute of Biogeochemistry and Pollutant Dynamics, Universitätstrasse 16, 8092 Zürich, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Rudolf von Rohr
authors.affiliation: EAWAG, Swiss Federal Institute of Aquatic Science and Technology, Water Resources & Drinking Water, Überlandstrasse 133, 8600 Dübendorf, Switzerland; ETH Zürich, Institute of Biogeochemistry and Pollutant Dynamics, Universitätstrasse 16, 8092 Zürich, Switzerland; Ecole Polytechnique Fédérale de Lausanne (EPFL), School of Architecture, Civil and Environmental Engineering (ENAC), 1015 Lausanne, Switzerland.
authors.forename: Janet G
authors.initials: JG
authors.lastname: Hering
authors.affiliation: EAWAG, Swiss Federal Institute of Aquatic Science and Technology, Water Resources & Drinking Water, Überlandstrasse 133, 8600 Dübendorf, Switzerland; ETH Zürich, Institute of Biogeochemistry and Pollutant Dynamics, Universitätstrasse 16, 8092 Zürich, Switzerland.
authors.forename: Hans-Peter E
authors.initials: HP
authors.lastname: Kohler
authors.affiliation: EAWAG, Swiss Federal Institute of Aquatic Science and Technology, Water Resources & Drinking Water, Überlandstrasse 133, 8600 Dübendorf, Switzerland; ETH Zürich, Institute of Biogeochemistry and Pollutant Dynamics, Universitätstrasse 16, 8092 Zürich, Switzerland; Ecole Polytechnique Fédérale de Lausanne (EPFL), School of Architecture, Civil and Environmental Engineering (ENAC), 1015 Lausanne, Switzerland. Electronic address: urs.vongunten@eawag.ch.
authors.forename: Urs
authors.initials: U
authors.lastname: von Gunten
mesh_terms: D000693:Anaerobiosis; D057231:Climate Change; D005296:Ferrous Compounds / Q000032:analysis; D005374:Filtration; D006812:Humic Substances / Q000032:analysis; D008345:Manganese / Q000032:analysis; D010084:Oxidation-Reduction; D045483:Rivers / Q000737:chemistry; D013696:Temperature; D014872:Water Movements; D018508:Water Purification
chemical_list: D005296:Ferrous Compounds; D006812:Humic Substances; D008345:Manganese
keywords: BDOM; Climate change; Microbial respiration; POM; Redox milieu; Wastewater effluent