BOOK OF ABSTRACTS 259 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Hall A Poster Session / Technologies and Applications P5.3 Long-Term Natural Organic Matter Removal in a Managed Aquifer Recharge Infiltration Pond Kristofer Hägg1, Christian Alsterberg2 1 Sydvatten AB, Hyllie Stationstorg 21, 215 32 Malmö, Sweden, Kristofer.hagg@sydvatten. 2 Sydvatten AB, Hyllie Stationstorg 21, 215 32 Malmö, Sweden. 2 Division of Water Resources Engineering, Faculty of Engineering LTH, Lund University, John Ericssons Väg 1, V-Hus, 221 00 Lund, Sweden Managed aquifer recharge (MAR) is a widely used method for producing drinking water worldwide.¹ In MAR systems, surface water is recharged into the aquifer by infiltrating it through infiltration ponds. During infiltration and subsequent percolation through the subsurface, natural organic matter (NOM), bacteria, and viruses are effectively removed.² Infiltration ponds are typically operated according to seasonal cycles. They are usually brought into operation during winter to allow the development of a mature biofilm before the onset of algae blooms in late summer and early autumn. In the initial phase of pond maturation, surface water infiltrates through a limited area at high rates. Once the pond is fully mature, water spreads across the entire pond surface and infiltration rates decline. This study assessed the long-term capacity of an infiltration pond to remove NOM from surface water. Water samples were collected from the incoming surface water and at 1 meter depth below the pond bottom. Cyanotoxin samples were also taken from the surface water and the extraction wells. The results showed an initial NOM removal efficiency of 25%, measured as UV254 absorbance. After one meter of infiltration, the NOM concentration in the percolating water closely followed the seasonal variation observed in the surface water. Removal efficiency increased significantly over time, demonstrating the positive effect of pond maturation. In response to several episodes of high bacterial loads in the surface water during the first year, infiltration to the ponds was intermittently halted. Following these events, NOM concentrations at one of the 1-meter sampling locations increased. This temporary deterioration was likely caused by repeated drying and rewetting cycles, which may have created fissures in the filter media, enabling preferential flow and rapid transport of water to the sampler. Cyanotoxin concentrations in the surface water peaked in late June, prior to the main seasonal algal bloom. However, no cyanotoxins were detected in the extraction wells. Overall, the results demonstrate the effectiveness of properly managed MAR systems in treating surface water and producing
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