It is well documented that excess phosphorus in source waters is a major contributor to harmful algal bloom formation. While there are many approaches to controlling algal populations in reservoirs, including a variety of phosphorus reduction approaches (e.g., sequestration of legacy phosphorus with alum or clay products), addressing physical phosphorus loading upstream is considered less often. Water treatment residuals (WTR) containing alum, a common waste product of conventional surface water treatment, have been shown to retain the ability to capture phosphorus even after the WTR ‘sludge’ is formed and removed from the sedimentation process. This research designed and tested a refillable, reusable in-stream phosphorus cartridge system which beneficially reutilizes WTR ‘sludge’ to sequester instream phosphorus and remove it from the water when spent media is replaced. This reduces in-stream phosphorus entering into the reservoir without permanently adding additional materials to the waterbody and provides measurable results as to the amount of phosphorus removed. The ten sampling events during the first year’s field assessment indicated that the gates removed a total of 556.31 g of reactive phosphorus (PO43−) and it is anticipated that the actual phosphorous removal was even greater. Other watershed managers can implement the same approach using their own WTR to capture in-stream phosphorus.

Numerous drinking water plants and agricultural wastewaters generate water treatment residuals (WTR) during coagulation processes. These WTRs may be effective at reducing nutrients entering waterways, thereby decreasing the potential formation of algal blooms. Of the WTRs used in this study, Al-based WTR (Al-WTR) was the most effective achieving a 20 °C cumulative adsorbed concentrations (q e ) after 28 days of desorption of 63–76 mg PO 4 /kg Al-WTR depending on the initial spiked concentration. When the isotherm temperature was 5 °C, Al-WTR effectiveness decreased. Ferric chloride WTR (Fe-WTR) was only effective when 0.6 mg/L of PO 4 was spiked to surface water with 0.01 mg/PO 4 stored at 20 °C yielding a 28 day cumulative q e 5.67 mg PO4/kg Fe-WTR. At 5 °C, the cumulative q e after extended desorption was 1–4.63 mg/kg Fe-WTR. Ferrous sulfate based WTR (Fe2-WTR) was not capable of adsorbing any additional PO 4 regardless of the spiked concentration or temperature.

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