Constructed Wetlands and Waste Stabilization Ponds for Small Rural Communities in the United Kingdom: A Comparison of Land Area Requirements, Performance and Costs

Abstract

Land area requirements for secondary subsurface horizontal-flow constructed wetlands (CW) and primary and secondary facultative ponds with either unaerated or aerated rock filters were determined for three levels of effluent quality: that specified in the Urban Waste Water Treatment Directive (UWWTD) (≤25 mg filtered BOD l−1 and ≤150 mg SS l−1 for waste stabilization ponds (WSP) effluents, and ≤25 mg unfiltered BOD l−1 for CW effluents (mean values); and two common requirements of the Environment Agency: ≤40 mg BOD l−1 and ≤60 mg SS l−1, and ≤10 mg BOD l−1, ≤15 mg SS l−1 and ≤5 mg ammonia-N l−1 (95-percentile values). A secondary CW requires 60 percent more land than a secondary facultative pond to produce an UWWTD-quality effluent, 38 percent more land than a secondary facultative pond and an unaerated rock filter to produce a 40/60 effluent and, were it to be used to produce a 10/15/5 effluent, it would require ∼480 percent more land than a secondary facultative pond and an aerated rock filter. Its estimated 2005 cost is £1100-2600 p.e.−1, whereas that of a primary facultative pond and rock filter is ∼£400 p.e.−1. On the basis of land area requirements, performance and cost, facultative ponds and unaerated or aerated rock filters are to be preferred to secondary subsurface horizontal-flow constructed wetlands.