Constructed wetlands and waste stabilization ponds for small rural communities in the United Kingdom: A comparison of land area requirements, performance and costs

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 similar to 480 percent more land than a secondary facultative pond and an aerated rock filter. Its estimated 2005 cost is E1100-2600 p.e.(-1), whereas that of a primary facultative pond and rock filter is similar to 400 pound 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.