Ecotechnological methods for the treatment of waste water and sewage sludge using reed and pond biotopes in Lahstedt-Gadenstedt

Technical summary

The council of the municipality of Lahstedt has decided to renovate its remaining three conventional sewage treatment plants with sustainable and ecologically sound methods in order to limit the consumption of natural resources.

Artificial wetlands for waste water treatment, which have low operational costs, are established in various forms as a pilot project in the village of Gadenstedt (2.600 P.E.). The project is divided into three parts: polishing biotope (reed bed treatment system); combined waste water biotope (cascade of ponds and reed beds); reed planted dry beds for sewage sludge.

Polishing biotope

The processed sewage effluent from the existing trickling filter undergoes polishing treatment. The total area required is 1,1 ha. of which 7.300 m2 is covered by reeds (Phragmites) in four vertically percolated soil filters. These filters are sealed with a lining. When the existing trickling filter treatment plant becames dilapidated in years to come, the reed beds should function as the main biological purification step. This application will be piloted during the course of the project.

The purification performance of the existing sewage treatment plant is improved by advanced nitrification, phosphate elimination and reduction of pathogens, easily fulfilling the existing authority limits.

Combined waste water biotope

The impact on the receiving river from combined water discharge is reduced (in terms of pollutant load per hectare of paved area) far below the legal requirements. This will be achieved through an innovative cascade of unaerated ponds (8.820 m2 net )and a final soil filter planted with reeds (1.330 m2 net).

The construction and operational costs are below those of concrete storm water tanks with overflow.

A secondary wetland complex with valuable biotope functions has been created.

Sewage sludge dewatering and mineralization in reed beds

The scarcely known method of dewatering and stabilising sewage sludge in dry beds planted with reeds has been in practice in Lahstedt for nine years at two other treatment plants. Dry matter content of over 50 % is currently achieved. In the future, all of the sewage sludge deriving from the four treatment plants in the villages of Lahstedt will be dewatered and stabilised with the same energy- saving method.

A build-up of surplus sludge which cannot be put to agricultural use in the winter months is avoided. Transport costs are lowered by volume reduction  and new options for utilisation and recycling of this valuable nutrient source in landscaping, horticulture and recultivation can be explored.

The total project „Ecotechnological treatment of waste water and sewage sludge in Lahstedt“ will be presented as a registered and officially sponsored project at the world exhibition EXPO 2000 in Hanover.

Key-words:
* constructed wetlands for waste water treatment
* vertical subsurface flow reed bed treatment system
* advanced treatment of domestic waste water
* Phragmites australis
* open lagoons and planted soil filter basins for detention and treatment
   of combined sewer owerflows
* sewage sludge dewatering and mineralization in reed beds



Operation & Maintenance

Please click on the letter of recommendation for an increasing view.