Dissolved Phosphorus Retention of Light-Weight Expanded Shale and Masonry Sand Used in Subsurface Flow Treatment Wetlands

• Published in: Environmental science & technology 2004-02, Vol.38 (3), p.892-898
• Main Authors: Forbes, Margaret G., Dickson, Kenneth R., Golden, Teresa D., Hudak, Paul, Doyle, Robert D.
• Format: Article
• Language: English
• Subjects: Applied sciences; Biodegradation, Environmental; constructed wetlands; Construction Materials; Ecosystem; Environmental Monitoring; Exact sciences and technology; Geologic Sediments - chemistry; Masonry; Natural water pollution; Other wastewaters; Phosphorus; Phosphorus - analysis; Phosphorus - chemistry; Phosphorus - isolation & purification; Pollution; Rainwaters, run off water and others; Retention; Sand & gravel; Sediments; Silicon Dioxide; Soils; Solubility; sorption isotherms; Studies; wastewater; Wastewaters; Water Purification - methods; Water treatment and pollution; Wetlands
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es034341z

Using surface flow constructed wetlands for long-term phosphorus (P) retention presents a challenge due to the fact that P is stored primarily in the sediments. Subsurface flow wetlands have the potential to greatly increase P retention; however, the substrate needs to have both high hydraulic conductivity and high P sorption capacity. The objective of our study was to assess the P retention capacity of two substrates, masonry sand and light weight expanded shale. We used sorption/desorption isotherms, flow-through column experiments, and pilot-scale wetlands to quantify P retained from treated municipal wastewater. Langmuir sorption isotherms predicted that the expanded shale has a maximum sorption capacity of 971 mg/kg and the masonry sand 58.8 mg/kg. In column desorption and column flow-through experiments, the masonry sand desorbed P when exposed to dilute P solutions. The expanded shale, however, had very little desorption and phosphorus did not break through the columns during our experiment. In pilot cells, masonry sand retained (mean ± standard deviation) 45 ± 62 g P/m2/yr and expanded shale retained 164 ± 110 g P/m2/yr. We conclude that only the expanded shale would be a suitable substrate for retaining P in a subsurface flow wetland.