The central objective is nutrient reduction in eutrophic coastal waters of the Baltic Sea, in marine aquaculture facilities and in saline wastewater from land-based facilities. Vascular plants with different salt tolerances are used for taking up nutrients, including a wastewater treatment plant for saline wastewater. For the produced biomass, further potential uses will be designed. Halophytes, i.e. vascular plant species that otherwise only occur in salt marshes and other coastal habitats, such as the European pickleweed (Salicorna europaea agg.) as well as marsh plants used for medicinal purposes, such as water mint (Mentha aquatica), will be used in the food and natural medicine sectors to expand the product range in the BaMS region.
Newspaper article in the Kieler Nachrichten newspaper dated April 2, 2022
Halophytes, i.e. salt-tolerant coastal plants, are cultivated in diverse locations with the help of nutrient-rich wastewater, and the biomass is thus refined into high-quality food. Halophytes, or vascular plant species, such as the European pickleweed (Salicorna) and marsh plants such as watercress (Nasturtium officinale) can also be used to great effect in natural medicine.
Other coastal plants such as sea kale (Crambe maritima) have even become rare. In the past, it was highly valued as a vegetable. Due to its high nutrient content and good taste, it easily passes for a "superfood" these days.
Examples of halophytes:
European pickleweed (Salicornia europaea) is characterized by a slightly peppery taste and can be served raw, blanched or as a side dish. Here, only the tips of the pickleweed are consumed. In the past, the ashes of the pickleweed were used for soap production.
European pickleweed (Salicornia europaea)
Photo: Martina Mühl
Sea aster (Tripolium pannonicum) tastes spicy to slightly salty and is milder overall than samphire. The young leaves are excellent as raw vegetables or cooked vegetables. The plant stores excess salt in older leaves and later discards them.
Sea aster (Tripolium pannonicum) in the horizontal filter of the constructed wetland (photo: Martina Mühl).
The sea-side aster (Tripolium pannonicum), on the other hand, tastes slightly salty and spicy and is excellent suitable as a raw food or vegetable. The sea-side aster regulates its salt balance by dropping old leaves containing surplus salt; replacing them by fresh and new leaves.
Sea-side aster (Tripolium pannonicum)
Photo: Martina Mühl
Land-based aquaculture facilities with marine species have so far been complex and cost-intensive due to the high technical effort required for wastewater treatment. The use of flow-through systems with seawater or saline groundwater requires the efficient treatment of the resulting wastewater, for which no conclusive concepts exist yet. The development of a wastewater treatment plant for saline wastewater based on constructed wetlands and the reduction of nutrients in surface waters are therefore important elements for the sustainable development of aquaculture technology.
The aim of the wastewater treatment plant is to clean nutrient-rich and saline wastewater and enable land-based aquaculture becoming independent of sewage treatment plants. To achieve this, the wastewater from shrimp farming is first fed into an eddy current separator, where the sludge sinks and is pumped off. The treated wastewater is thus almost free of solids and reaches a bottom shaft, from where it flows in a controlled manner into the two vertical filters, where it passes through the bed from top to bottom. At this point, the plant roots are able to take nutrients such as nitrogen from the wastewater and subsequently nitrify them.
In the following process, the wastewater enters a horizontal filter with a natural gradient. Here, the plants again extract nutrients from the water and decompose them via bacterial processes. In the denitrification process, the nitrate present is reduced to nitrogen and can leak back into the atmosphere. The now cleaned water enters a drainage shaft and can be transported back into the Baltic Sea.
left: full view of the wastewater treatment plant in Bülk, right: horizontal filter of the wastewater treatment plant
Photos: Martina Mühl
Newspaper article in the Kieler Nachrichten newspaper dated June 26, 2021
The Kiel Sea Farm represents a site where various halophytes (pickleweed, sea arrow-grass, sea kale, sea-side aster) are tested. The aim is to determine the conditions under which halophytes can be grown efficiently and in an eco-friendly approach on the water. At the same time, it is important that these are not only suitable for nutrient removal, but also for further treatment as food. Regional beach litter can be used as a substrate, since it is often considered only a waste product on beaches, contains many nutrients, and consequently can enable the pickleweed to grow faster.
left: floating greenhouses, right: blooming sea-side aster
Photos: Kiel Sea Farm
Floating wetlands for bioremediation of aquatic systems are already established in Germany, but the materials of the islands are based on artificial polymers. The objective in this project is to produce floating wetlands from completely biodegradable materials that originate from regional, sustainable development. In addition, the pre-cultivated plant mats have so far been made of coconut fibers, which will be replaced here by hemp fibers and bulrushes. For this purpose, Hanffaser Uckermark is testing various island modules. In addition, not only the commonly used halophytes are to be cultivated on the mats, but also other medicinal plants such as buckbean (Menyanthes trifoliata) or meadowsweet (Filipendula ulmaria).
Floating wetland with pre-cultivated plant mat in Born
The project reports of our individual project partners are available free of charge as PDF files from the Technical Information Library (TIB) in Hanover:
Could coastal herbs help solve environmental problems? What sounds like gourmet cuisine actually has a lot to do with fine dining while also representing an innovative approach to protecting our oceans. In the HaFF project, the BaMS network collaborated with partners to investigate how so called halophytes, salt loving plants such as samphire and sea aster, can contribute to the natural treatment of nutrient rich wastewater and surface waters. The project revealed major potential for aquaculture as well as climate and environmental protection.
Nitrogen and phosphorus are essential plant nutrients and therefore major components of fertilizers. However, excessive amounts can cause severe problems in aquatic ecosystems: algal blooms, oxygen depletion caused by decomposition processes, and a disrupted ecological balance. These effects are visible in many coastal regions of the Baltic Sea. HaFF developed solutions to naturally bind these nutrients using plants that thrive where most others cannot survive: in saline water.
The project was the first to successfully test a decentralized constructed wetland system for saline aquaculture wastewater under outdoor conditions, marking an innovative step within the blue bioeconomy. HaFF followed a holistic approach in which water treatment, biomass production, and product development were closely interconnected, making the project a model for extractive aquaculture.
One of Germany’s first outdoor constructed wetlands for saline wastewater was established in Kiel. On the site of a shrimp farm, halophytes such as sea clubrush and sea aster were specifically cultivated to remove nutrients from process water while simultaneously generating biomass for product development.
The combined filter bed system achieved a nitrogen reduction of around 60 percent, a remarkable efficiency under real world conditions. Sea aster produced biomass yields of 2–13 kg/m², while sea arrowgrass reached up to 6 kg/m². Both plants show strong potential for use as coastal vegetables or in cosmetic applications.
Additional subprojects focused on cultivating coastal herbs in floating greenhouses and on floating islands. In the greenhouses, beach wrack was used as a cultivation substrate, providing a consistently good nutrient supply for salt tolerant plants irrigated with Baltic Sea water. Under these conditions, samphire and sea aster demonstrated the best performance among the cultivated coastal herbs.
The floating islands, made from biodegradable materials, were deployed in the nutrient rich and sheltered lagoon waters of Mecklenburg Western Pomerania. Here too, sea aster showed the strongest growth alongside softstem bulrush. During the course of the project, floating islands made from recycled glass aggregate were also tested very successfully. Glass aggregate represents an innovative material for ecological water management because it eliminates the need for plastics and does not contribute to eutrophication.
The harvested coastal herbs from the haloponic systems can be marketed directly as gourmet vegetables. However, the project also explored further applications. Initial fermented extracts from samphire and sea arrowgrass have shown potential for use in natural cosmetics and dietary supplements. Sea arrowgrass in particular contains compounds relevant for skincare applications. The close integration of applied research and product development made HaFF a true pioneer of the blue bioeconomy.
Events, tastings, and media coverage significantly increased public interest in halophytes and contributed to the acceptance of alternative food products. The project also opened new perspectives for regional value chains in coastal areas.
The approach is convincing from an ecological perspective as well. Using beach wrack as a cultivation substrate creates value from a previously underutilized material. Cultivating protected species such as sea arrowgrass within controlled systems enables their legal use for the first time without interfering with sensitive natural habitats.
HaFF was part of a German Federal Ministry of Education and Research funding program focused on the blue bioeconomy. The solutions developed within the project are practical and scalable, with strong application potential for land based marine aquaculture. Furthermore, the experience gained throughout the project can be expanded to many additional areas of application.
