Abstract
Drinking water treatment residuals (DWTRs) generated during drinking water treatment have been proposed for use in lake restoration as a solid-phase sorbent to inactivate phosphorus (P) in lake sediment. However, treatments that minimize leaching of nitrogen (N) and optimize P sorption capacity may be necessary prior to use. This study assessed seven different treatment methods, including washing and heat treatments at different temperatures and with and without oxygen limitation, among two DWTRs from Thailand. Results showed that oxygen-limited heat treatment at 600 °C substantially reduced N leaching (<0.2 mg/kg TKN) while also improving P sorption capacity (increase of 18–32% compared to untreated DWTR) to a maximum of 45.7 mg P/kg. Washing with deionized water reduced N leaching if a sufficient volume was used but did not improve P sorption. Heating at 200 °C with or without the presence of oxygen did not improve N leaching or P sorption. Regression of P sorption parameters from a two-surface Langmuir isotherm against physio-chemical properties indicated that oxalate-extractable (i.e., amorphous) aluminum and iron were significantly associated with total P sorption capacity (R2 = 0.94), but micropores and oxalate-extractable P modulated the P sorption from high-affinity to low-affinity mechanisms. In conclusion, this study confirmed the importance of amorphous aluminum in DWTRs for inactivating P, and the results suggest that high-temperature treatment under oxygen-limited conditions may be the most reliable way to optimize DWTRs for environmental remediation applications.
Highlights
Anthropogenic eutrophication of freshwater lakes as a result of excessive nutrient loading has contributed to the global proliferation of harmful cyanobacterial blooms and deterioration of ecological health of surface waters [1]
The metals Al, Fe, Mn, and Zn generally increased in concentration following treatment, with greater increases occurring at higher treatment temperatures
For this group of metals, washing had minimal effects on the contents. These compounds were relatively stable, and the changes observed in heat treatments were likely the result of a concentrating effect as other compounds were removed during treatment
Summary
Anthropogenic eutrophication of freshwater lakes as a result of excessive nutrient loading has contributed to the global proliferation of harmful cyanobacterial blooms and deterioration of ecological health of surface waters [1]. The most commonly used solid-phase sorbents for P immobilization in lakes are aluminum (Al) salts, including aluminum sulfate (alum), polyaluminum chloride (PAC), and aluminum chloride (AlCl3 ), having been applied to many hundreds of lakes worldwide [7]. While in-lake application of Al salts can be the most cost-effective measure to address eutrophication in lakes [8], limitations to the use of Al salts have been identified, including the possibility for transient toxicity to freshwater organisms from newly formed amorphous Al hydroxide [9] and reduced P adsorption effectiveness due to competing compounds [10] or crystalline aging of the newly formed, amorphous mineral [11]. Other P sorbents, such as iron (Fe) salts and lanthanum modified bentonites (LMBs), are limited by narrow physio-chemical conditions and cost, respectively [12,13]. The development of new and alternative P immobilizing materials is still needed [14]
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