Biological characterization and treatment performances of a compact vertical flow constructed wetland with the use of expanded schist

The use of compact vertical flow constructed wetlands is becoming increasingly popular in France to treat raw domestic wastewater. This system enables the use of a single deep stage rather than two stages and therefore dramatically reduces the capital costs. A compact vertical flow constructed wetland known as Ecophyltre® was investigated. This system was partially filled with a light expanded schist (Mayennite®) designed to reduce the surface area to 1.2 m2 pe−1. The aim of this work was to highlight relationships between Mayennite® characteristics with biological activity and treatment performances. After 12 months of operation, the total accumulated dry matter quantity was around 5 kg m−2 (20% on the surface). Between 70% and 80% of the microorganisms respiration was principally measured in the top layer of Ecophyltre® during the first year of operation. However, biological activity was shared between the two Mayennite® layers over time. Results showed that Mayennite® retention enabled to kept around 15% water in mass enhancing microorganisms growing. Removal performances of this system met the French standards (35 mg TSS l−1; 25 mg BOD l−1; 125 mg COD l−1).