Water treatment residuals
What is it?
Water Treatment Residuals (WTR) are primarily sediment, metal (alumunium, iron, or calcium) oxide/hydroxides, activated carbon, and lime removed from raw water during the water purification process. The effectiveness of WTR in reducing soluble phosphorus depends on several factors, including source water characteristics, water treatment methods, and length of residual storage time prior to land application. Different water treatment facilities create different physical and chemical compositions and phosphorus sorption capability of WTR.
How is it being used?
No projects in Ontario.
Past research done on the efficiency of the use of WTR for phosphorus reduction is promising. Laboratory studies have shown that WTRs adsorb large amounts of phosphorus and increase the phosphorus-sorbing capacity of soils. This decreases phosphorus losses in runoff and leaching. Surface application of WTRs showed an 88% reduction in runoff and leachate dissolved phosphorous. Agyin-Birikorang et. al. also state that phosphorous sorption by aluminum-based WTRs is practically irreversible.  Results from another study state that WTR can be used for phosphorous removal in engineered wetlands and it carries the benefits of reuse of a by-product that promotes sustainability.  It is estimated that the phosphorous adsorptive capacity of amended media, which was mixed with 4% of WTR, was 4 times as high as the traditional media under the same conditions. 
- Agyin-Birikorang S, O’Connor G, Obreza T. Drinking Water Treatment Residuals to Control Phosphorus in Soils. UF/IFAS Extension. 2016.
- Babatunde AO, Zhao YQ, Burke AM, Morris MA, Hanrahan JP. Characterization of aluminum-based water treatment residual for potential phosphorus removal in engineered wetlands. Environmental Pollution 157 (2015) 2830-2836. doi: 10.1016/j.envpol.2009.04.016
- Wang JJ, Li T, Zhang Y. Water treatment residual as a bioretention media amendment for phosphorus removal. Huan Jing ke xue: Huanjing kexue 12:35 (2014) 4642-4647.