The revised version of the European Urban Wastewater Directive has tightened the limits for the discharge of nutrients (nitrogen and phosphorus) and micropollutants from wastewater treatment plants into the environment. In order to meet the requirements, existing technology must be upgraded or an additional treatment stage added. In addition to investment costs, this also means a considerable increase in operating costs for municipal wastewater treatment plants. This is where the AbWiFaser project comes in.
The aim of the project is to develop a plant-based wastewater post-treatment process that combines the hydroponic cultivation of fiber nettles with further nutrient reduction of already pre-treated municipal wastewater as an energetically advantageous method. The aim is to create a cost-effective, energy-efficient and nutrient- and pollutant-reducing alternative to a conventional further treatment stage.
WATER PROTECTION AND RESOURCE-CONSERVING USE OF WATER
The revised European Urban Waste Water Directive specifically promotes the reuse of water in agriculture and thus supports sustainable management approaches. Especially in regions affected by water scarcity, the reuse of treated wastewater can make a significant contribution to meeting water requirements in crop cultivation.
At the same time, the remediation potential of some crops can help to reduce nutrient surpluses and micropollutants and improve water quality.
NETTLE FIBERS AS A LINK IN WASTEWATER RECYCLING
Nettles are known as nitrogen-loving, fast-growing plants that thrive in moist locations. In horticultural folklore, they are regarded as indicator plants for nitrogen-rich soils. The fiber nettle (Urtica dioica L. convar. fibra) is a variety of the common nettle that has been selected for its high fiber content. Against the background of the negative effects of global textile production, in particular the high water consumption of cotton production, alternative fiber plants are becoming increasingly important.
This is where the AbWiFaser project comes in. With the innovative solution approach of combining nature-based “polishing” (with regard to the required effluent values of the UWWTD) of already well pre-treated wastewater with a hydroponic cultivation process for fiber nettle cultivation, the effluent values of the amended municipal wastewater directive can be complied with and valuable renewable raw materials can be produced regionally and in a resource-saving manner.
DEVELOPMENT OF A FIBER NETTLE SOIL FILTER
The starting point is the third treatment stage or secondary clarification of a municipal wastewater treatment plant. At the end of this stage, the water leaves the treatment plant and is released into the environment via the receiving water. Thanks to a regular monitoring program, it is known what quantities of nutrients are still contained in the water. These quantities are sufficient to cover the needs of the nitrogen-loving fiber nettles. The innovative approach of AbWiFaser is to direct this nutrient-rich water to flooded areas of a soil filter where the fiber nettles are planted. Automated irrigation and drainage of the areas enables the maximum water treatment rate and at the same time creates ideal growing conditions for the plants.
As part of the research project, the efficiency of the new water treatment step is being investigated, taking into account various influencing factors such as substrate type, retention time and plant density. The filter performance will be monitored and continuously optimized over a period of 18 months. At the same time, the extent to which the developed filter meets the requirements of the amended municipal wastewater directive and which business and operator models would be suitable for widespread implementation will be evaluated.
