Laboratory evaluation of alum, ferric and ferrous-water treatment residuals for removing phosphorous from surface...

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 PO₄/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 PO₄ was spiked to surface water with 0.01 mg/PO₄ 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 PO₄ regardless of the spiked concentration or temperature.