CONSTRUCTED WETLANDS AND WASTE STABILIZATION PONDS FOR SMALL RURAL COMMUNITIES IN THE UNITED KINGDOM: A COMPARISON OF LAND AREA REQUIREMENTS, PERFORMANCE AND COSTS

摘要

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.