In many areas of France, especially in rural areas where access to mains drainage is limited, sewage has to be treated on site using a “fosse septic” or similar treatment system. There are many different types of sewage treatment but the purpose of each and every one is to safely treat the effluent water that is discharged from properties. There are several stages involved in this proces.
- Collection – In 1992 a new law was passed handing responsibility for overseeing and regulating old and new waste water installations to the local communes. The law stipulated that all household waste liquids had to be processed in the correct manner, by means of a Fosse Toutes Eaux (a septic tank that accepts all waste waters) and a filtration system (previously households had been allowed to drain the water from the kitchen and bathrooms directly into the surrounding soil or nearby ditch).
- Pre-Treatment – As a result of the law all waste water now had to flow directly into the septic tank where separation of the solid matter and the treatment of the water could begin. Once in the tank the waste starts to divide itself, with the lightest parts of the waste (fat, oil, grease) floating to the surface and forming a crust (suspended solids), and the heavier solids dropping and settling at the bottom of the tank (sludge). The pre-treatment involves the waste being consumed by bacteria, with the suspended solids being digested by aerobic bacteria and transformed into carbon dioxide and water, whilst the sludge is digested by anaerobic bacteria.
- Treatment – With a conventional “fosse septic” the effluent would then need to pass through a large filter bed, or filtered land drain, where further treatment takes place, removing many more waste and toxic particles. However, the approval of compact filter systems and microstations for use in France has now removed the need for a filter bed as treatment takes place within a sealed compact unit where the anaerobic digestion is intensified.
- Evacuation – Finally the treated liquid is either allowed to soak away into the soil or siphoned off into a nearby ditch, or similar.