Effect of climate, wastewater composition, loading rates, system age and design on performances of French vertical flow constructed wetlands: A survey based on 169 full scale systems

The main objective of our work was to study the efficiency of the 2 stages French vertical flow constructed wetland system and its compact version by compiling data of 169 full scale systems in operation for up to 12 years. Design parameters and treatment performances, mostly based on 24 h composite samples performed by independent local authorities, have been compared to see how climate, wastewater composition, loading rates, system age and design were influencing the treatment performances. A bit more than 97% of the samples analysed at outlet of the plants were fulfilling the most common French discard limits (in mg/L 125 COD, 25 BOD). Removal efficiencies were not affected by factors including hydraulic and organic loads (until 60 cm/d), defect of maintenance and temperature within the ranges observed. Age of treatment plants had an effect only during start-up, but after 0.5–2 years of operation, performance was constant. Similarly, the feedback from 5 years of data obtained with “compact VFCWs” showed that this system met French standards and outperformed the first stage of “classical VFCWs”. This survey of 169 full scale systems represents a confirmation of the good performance and the robustness of the French VFCWs.