State-of-the-art small wastewater treatment plants usually consist of a mechanical treatment stage and a downstream biological wastewater treatment stage. The wastewater is first fed into a pit in which the solid substances settle; the dissolved organic substances are broken down by microorganisms in a downstream biological treatment stage. If further purification requirements have to be met in individual cases (e.g. nitrogen elimination, phosphorus elimination, wastewater hygienization), more complex small wastewater treatment plants must be constructed and operated.

Small wastewater treatment plants on your own property are usually built and operated by the house or property owner. In order to ensure good cleaning performance in the long term, it is necessary to regularly maintain and monitor the small wastewater treatment plants. This task is often assigned to specialist companies as part of a maintenance contract, especially in the case of technically complex systems. The faecal sludge from the mechanical treatment stage must be disposed of properly on a regular basis.

Every 2 years (4 years for systems without defects at the last inspection), small wastewater treatment plants must be inspected by a recognized private expert in water management (PSW); the inspection result must be certified to the lower water authority (district administrative authority).

• Test report by an expert (2 - 4 years)