Efficiency of the first stage French system on a combined sewerage system

Efficiency of the first stage French system on a combined sewerage system

Abstract

The study investigates the influence of sludge layer thickness on pollutant removal efficiency in the first stage of French vertical flow constructed wetlands connected to a combined sewer system. A pilot scale experiment was established using three vertical filter columns with identical composition but different sludge layer thicknesses. One of the columns was equipped with a geotextile layer. The system operated under real conditions with direct inflow of municipal wastewater. Monitored parameters included NH₄⁺-N, NO₃⁻-N, total phosphorus, COD, suspended solids, dissolved oxygen, ORP, conductivity, and pH. Preliminary results indicate that when the sludge layer is sufficiently saturated, it develops a “sponge effect”. Reduced hydraulic conductivity prolongs the hydraulic retention time and significantly improves pollutant removal compared to mineralized sludge layers. The findings suggest that maintaining a minimum sludge layer thickness is critical to sustaining biological treatment functions. Furthermore, effective pollutant removal in the first stage supports the long-term performance of the second stage by preventing clogging and extending system lifetime.

The study investigates the influence of sludge layer thickness on pollutant removal efficiency in the first stage of French vertical flow constructed wetlands connected to a combined sewer system. A pilot scale experiment was established using three vertical filter columns with identical composition but different sludge layer thicknesses. One of the columns was equipped with a geotextile layer. The system operated under real conditions with direct inflow of municipal wastewater. Monitored parameters included NH₄⁺-N, NO₃⁻-N, total phosphorus, COD, suspended solids, dissolved oxygen, ORP, conductivity, and pH. Preliminary results indicate that when the sludge layer is sufficiently saturated, it develops a “sponge effect”. Reduced hydraulic conductivity prolongs the hydraulic retention time and significantly improves pollutant removal compared to mineralized sludge layers. The findings suggest that maintaining a minimum sludge layer thickness is critical to sustaining biological treatment functions. Furthermore, effective pollutant removal in the first stage supports the long-term performance of the second stage by preventing clogging and extending system lifetime.

constructed wetland, sludge, French system, first stage

constructed wetland, sludge, French system, first stage

SEMRÁDOVÁ, T.; ZEDNÍK, O.; KRIŠKA-DUNAJSKÝ, M.; ŠKARPA, P.; TŮMOVÁ, T.

22.10.2025