Laboratory column experiments on options for redox control in infiltration ponds for artificial recharge


The redox environment is of utmost importance for the removal of organic compounds during artificial recharge. Within the research project OXIRED-2 five laboratory sand column experiments with natural sediments from the Lake Tegel infiltration pond and with microsieved surface water from Lake Tegel (Berlin) were performed to study the possibility to control the redox environment. Special emphasis was given to the sediments, the set-up of the column experiments, and the contact time within the column. The sediment was used either untreated or heated to 200°C or 550°C to study the effect of activation of organic carbon at 200°C and the effect of at least partial removal of natural organic carbon at 550°C. Additionally, an artificially produced iron coated sand was used for a two-layer experiment to increase the residence time of compounds susceptible to sorption within a given redox zone. Results reveal an immediate decrease of oxygen content at the outflow of the column in every experiment. Likewise, the redox potential also dropped significantly and immediately after the experiments started. However, the redox potential was significantly lower (approximately – 200 mV) in the experiments with the untreated or slightly heated sediments, and higher (about + 300 mV) for the experiment with the sediment heated up to 550°C. The redox zones known in natural environments developed also within the experiments even down to sulfate reduction at experiment No. 2. Ozonation of the influent water did not change the redox environment at the outflow of the column indicating a high reduction capacity of the natural sediment in the column within the duration of the experiments of up to 19 days. A constant input of ozone and an extended duration of the experiments might lead to a depletion of organic carbon in the sand column which could increase the redox potential. However, a complete depletion of organic carbon is very unlikely for managed aquifer recharge systems. The two-layer experiment with natural sand and artificially produced iron coated sands revealed that the iron coated sands had no influence on the redox system and only slight effect on the transport of ions. However, combining layers with different functionality might show great opportunities for designing and controlling redox systems especially with specific residence times in different redox zones for certain compounds in mind.

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