Assessment of enhanced soil aquifer treatment through experiments with a long-column and small-diameter wells

Jana Sallwey1, Fritz Kalwa1, Felix Barquero1, Christian Konrad2, Liedl Rudolf1
1 Institut für Grundwasserwirtschaft, TU Dresden
2 G.U.B. Ingenieur AG

9.4 in Artificial and natural groundwater recharge (co-organized by IAH-D)

26.03.2020, 14:30-14:45, Händel-Saal

Soil Aquifer Treatment (SAT) systems, utilizing the soil passage via the unsaturated zone as a tertiary treatment option, are used worldwide to achieve economical and low-tech treatment for water reuse. As the mostly targeted contaminants are degraded better under aerobic conditions, the waste water is typically infiltrated in intermittent cycles of flooding and drying. With decreasing land availability in urban regions, SAT practitioners are looking to maximize the infiltration capacity of schemes while maintaining the remediation potential of the unsaturated zone. This requires finding a balance between long residence times, to achieve the best aerobic degradation possible and high hydraulic loading rates (HLR).

To assess the optimization potential at the infiltration basins of the SHAFDAN-treatment plant in Tel Aviv, Israel, experiments were conducted with a 6 m long column, filled with material from the site. The simulation of different wetting-/drying cycles showed that higher oxygen saturation in the soil leads to higher degradation rates of dissolved organic carbon, ammonium and trace compounds. To increase the HLR by holding the same treatment quality, drying phases had to be prolonged. Nevertheless, shorter wetting and drying cycles (less than 1 day per cycle) allowed to increase both HLR compared to most common loading cycles (more than a week per cycle) without compromising  oxygen availability. Furthermore, stabilization of the aerobic conditions through airsparging was tested. Injection of air into the vadose zone during the drying cycle proved to increase the oxygen saturation as well as the degradation rates immediately.

Another option to increase the infiltration capacity is the use of vadose zone wells. They require little land and shift part of the treatment into deeper strata, thereby enhancing recharge performance. Biological clogging at these wells was simulated by feeding six identical well-aquifer models with different well setups. The experiments showed that biological clogging, as it is expected during the infiltration of treated waste water, is much less influenced by the setup of the well as physical clogging. Further experiments were conducted to assess regeneration possibilities.

This study presents results from different laboratory experiments assessing three promising measures for the enhancement of the infiltration capacity of SAT basins: 1) improved operational dynamics, 2) additional airsparging and 3) integration of vadose zone wells. Insights obtained from the experiments will be used to increase geohydraulic and biogeochemical knowledge on SAT processes. This is beneficial for the optimal operational management of existing SAT plants and effective planning of new SAT schemes. A better understanding will also be valuable to promote SAT and its benefits to increase its acceptance among political and administrative actors.

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