Phosphorus removal by wollastonite: A constructed wetland substrate

Wollastonite, a calcium metasilicate mineral mined in upstate New York, is an ideal substrate for constructed wetland ecosystems for removing soluble phosphorus from secondary wastewater. Design parameters, required for designing a full-scale constructed wetland, were measured in vertical upflow columns with hydraulic residence times varying from 15 to 180 h. Secondary wastewater was pumped vertically upward through eleven soil columns, 1.5 m in length and 15 cm in diameter and influent and effluent concentrations of soluble phosphorus were monitored for up to 411 days. Greater than 80% removal (up to 96%) was observed in nine out of 11 columns and effluent concentrations of soluble phosphorus ranged from 0.14 to 0.50 mg/l (averaging 0.28 mg/l) when the residence time was > 40 h. Columns with a decreased residence time averaged 39% removal. A direct relationship between residence time and soluble phosphorus removal was established. (C) 2000 Elsevier Science B.V. All rights reserved.