Optimization of Small Wastewater Treatment Plants with Constructed Wetlands

Constructed wetlands and soil filters provide stable biological treatment of municipal effluents, but mostly limited efficiency of denitrification. A promising approach to improve denitrification is the recirculation of filter effluent as operated in activated sludge systems.

Within a research project funded by the Bavarian Environment Agency (LfU), the treatment efficiency of a sewage treatment plant with constructed wetlands operated with filter effluent recirculation is investigated. The aim of the project is to identify optimum conditions for stable denitrification as well as existing problems, e. g. during operation in the winter months and to derive recommendations for a stable operation of constructed wetlands with denitrification.

Another project investigates the combination of sewage ponds and constructed wetlands. Two treatment plants with constructed wetlands as post-treatment for sewage ponds are monitored in this project. The major objective is to assess the potential of these systems to meet extended requirements for carbon and nitrogen removal. Problems with the operation of constructed wetlands as post-treatment for sewage ponds, such as possible colmation due to intensive algae bloom or adverse effects during mixed sewage treatment will be documented and recommendations for the design and construction of combined sewage ponds and constructed wetlands will be derived from these results.