RESUMO
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 (qe) 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 qe 5.67 mg PO4/kg Fe-WTR. At 5 °C, the cumulative qe 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.