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 desig ning a full-scale constructed wetland, were measured in vertical upflow col umns with hydraulic residence times varying from 15 to 180 h. Secondary was tewater was pumped vertically upward through eleven soil columns, 1.5 m in length and 15 cm in diameter and influent and effluent concentrations of so luble phosphorus were monitored for up to 411 days. Greater than 80% remova l (up to 96%) was observed in nine out of 11 columns and effluent concentra tions of soluble phosphorus ranged from 0.14 to 0.50 mg/l (averaging 0.28 m g/l) when the residence time was > 40 h. Columns with a decreased residence time averaged 39% removal. A direct relationship between residence time an d soluble phosphorus removal was established. (C) 2000 Elsevier Science B.V . All rights reserved.