EcoStab

The vertical filters in the first stage where smaller than the French standard model. Therefore we were forced by the authorities to increase their number from three to five. This gave EcoStab the chance to conduct real size research. In cooperation with the University of Hannover we mounted 5 different filter designs. The results showed that there was no significant difference between the different designs. Only after some years one of the basins furnished with an industrial granulate showed higher growth of vegetation indicating that there is a difference in treatment. But this would not justify the five times higher price than natural material.

The receiving water course, La Largue, is a class 2 river ( SAGE 2012 ) with large trout populations. Because of this the municipality insisted in a nitrogen treatment even though French laws do not stipulate it for stations of this size.

Several particularities of the community sewerage system complicated the operation of the station. Most of the pit drain have not been deconstructed but just connected to the sewers. This results in a raised BOD/COD ratio which consequently leads to lower degree of purification. The community sewerage system was a combined sewer taking huge amounts of rainwater in the case of precipitation. In addition most of the system was built under the water table. Thus even small damaging resulted in more parasitic water. Thus, the station was object to several times the designed hydraulic charge for years.

The EcoStab constructed reed bed station was for years the most effective reed bed station in the Haut Rhin region following to the statistics of the administration for sanitary affairs.

During an accident in 2007 a high quantity of domestic fuel entered the station. It could be held back and treated by isolating the entry basin. Nevertheless part of the surfaces and vegetation had to be exchanged in the follow resulting in temporarily reduced purifying capacity.

Source: Agence de l'eau;  original publication