Beth Kondro
Published: 2024
Total Pages: 0
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Excess nutrient loading to the Great Lakes Basin from agricultural runoff has negatively impacted water quality, resulting in harmful algal blooms. Best management practices, including constructed wetlands and sedimentation basins, can be used to reduce phosphorus losses from agricultural fields. Constructed wetlands are efficient in the removal of particulate phosphorus; however, removal of dissolved phosphorus is limited and requires further treatment to improve surface water quality. Several types of filter media (composed of Ca, Fe, and/or Al) can be used to further reduce the amount of dissolved phosphorus that enters surface water, and a media consisting of low-cost waste residual would be beneficial to adoption. Drinking water treatment residuals (DWTR) that often contain Al could be reused as an adsorbent for dissolved phosphorus. We evaluated the use of modified drinking water treatment residuals for removing dissolved phosphorus from wastewater. DWTR were mixed with binders, made into pellets to create an insoluble media with mechanical strength, and pyrolyzed to create a reactive media pellet. Pellets were evaluated using flow through columns and included experiments to determine the impact of pH (i.e. 6, 8, and 10), retention time (i.e. 1, 5, and 10 min), and field-collected agricultural runoff on dissolved P removal. Cement was found to be the best binding material to create an insoluble pellet with mechanical strength. The P removal capacity of the pellet consisting of the cement binder (1,397 mg P/kg) was within the range of previously evaluated steel slag (120-10,210 mg P/kg), a common reactive media for P removal. The addition of drinking water treatment residual and metals decreased the P removal capacity of the cement binder at pH 6-1 min retention at exhaustion. Increasing retention time increased the P removal capacity of the filter media tested. Wastewater pH has a minimal impact on the P removal capacity of all media except the pyrolyzed DWTR + cement binder media. Evaluated media was negatively impacted by real agricultural runoff with a measured decrease in P removal capacity (43-146 mg/kg decrease) compared to P-spiked distilled water at the same retention time. The pyrolyzed cement pellet was the most cost-effective reactive media, due to an increased P removal capacity. Pyrolyzed DWTR + cement binder would be more costly than the pyrolyzed cement binder alone but could provide a solution for the disposal of DWTR.
