Comparison of Performance, Ageing and Eco Balance Data from Four Types of Constructed Wetlands Treating Raw Sewage

Abstract

Seven filtration systems treating raw wastewater planted with helophytes and designed by Atelier Reeb between 1996 and 2003, have been closely monitored by the appropriate authorities. The most basic system, not including sequential feeding, and the most sophisticated system involving pumps, are compared with regard to their filtering capacities (the first being less efficient), their ageing (in general, vegetated systems have a long life and they age well) and their eco balance (the more basic systems are of interest here). The filters are grouped into four types of system according to feeding method, flow type within the filter and the number of stages of filtration. The three batch-fed systems have performed well with respect to French standards. The most basic system, with gravitational feeding, requires more careful monitoring and an additional treatment phase with a wooded buffer zone in order to obtain satisfactory results. Its very low costs of operation nevertheless make it a viable system in many cases, on condition that the design has been properly adapted.