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A research group at Aalborg University have investigated pollutant removal by sand filtration and different sorption technologies; e.g., sorption by granular media, sorption by suspended flocs and sorption by bottom sediments. Both sand filtration and sorption are applied in all the demonstration facilities. The initial investigations included both bench and pilot scale testing of the above-mentioned technologies. The picture below illustrates an experimental setup for testing different types of sand filters.

One of the key issues with regard to the sand filters is to quantify how the hydraulic performance is affected by adsorption of particles in the filter. The investigations on pollutant removal by granular media sorption will focused on sorption of dissolved phosphorus by various materials such as crushed marble rock, crushed shells from marine organisms and limestone. The experiments on sorption by suspended flocs tested different types and concentrations of aluminum salts and the experiments on pollutant sorption by bottom sediments focused on phosphorus removal by iron (oxy)hydroxide enriched bottom sediments. The picture below shows a macro shot of crushed shells with a particle size of 0-2 mm. The shells are extracted from marine sediments and consist primarily of calcite (crystalline CaCO3), which has a high capacity for binding phosphorus.

Some the results of the laboratory investigations are shown below. The figure shows how the phosphorous concentration decreases during the different stages of the treatment in a system with sedimentation, sand filtration and fixed media filtration. The experiment was conducted at different loadings. The results clearly demonstrate that the sorption filter enhances the phosphorus removal.

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