Assainissement non collectif des habitations

Non-collective sanitation concerns around 13 million people in France, and the number of septic tanks in service is estimated at around 5 million. Between 100,000 and 150,000 new installations are carried out each year, while the total number of installations increases by around 50,000 a year [1] . The difference between the number of new installations and the increase is explained by the removal of old installations with connection to a sewage network, and by the rehabilitation of pre-existing installations. In the vast majority of cases, a septic tank is used for pre-treatment, while the soil in place, or a substitute filter bed, is used for treatment. Treated effluent is preferably infiltrated on the plot. Where the soil is unsuitable for infiltration, and if health and environmental constraints allow, effluent can also be discharged into the surface water environment, subject to a discharge level.

In the [W 6 601] file (reference [24] of the [doc. W 6 602]) document sheet), the evolution over time of the regulatory and normative context for non-collective sanitation was specified. This second part presents the hydraulic and biological operating principles of the various pretreatment and treatment techniques, as well as the associated sizing rules.