The advantages of the use by a major UK water utility serving 8 million people in central England of constructed subsurface flow reed beds for secondary, tertiary and storm water treatment at small sewage treatment works is placed in context with improved permit compliance to more stringent standards and a continuing downward pressure on operating costs. Capital and energy costs are compared with the competing tertiary treatment process of recirculating sand filtration. Further economic advantage is gained by combining tertiary treatment and stormwater treatment.
With over 160 sites in operation by mid 1997 the success of the strategy has given confidence to allow for the early or emergency installation of reed beds to improve or maintain effluent quality before replacement, or in one case the provision, of secondary treatment. Use of constructed reed beds is now being extended to larger facilities where only a proportion of the flow needs to be treated to achieve standards. For tertiary treatment reed beds there is an additional environmental benefit with the typical removal of 10.7 mg/l of total nitrogen.