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HaFF - Constructed wetlands for the bioremediation of saline waters and wastewaters

The main objective of the project is the reduction of nutrients in eutrophic coastal waters and in the wastewater of marine aquaculture facilities. Nutrient reduction is achieved through biomass production of vascular plants. Various flood-tolerant species of different salt tolerances are tested.

Sustainable utilization of nutrient surpluses

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.

With HaFF, the first saltwater plant-based wastewater treatment in Germany was developed.

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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.

A halophyte is a salt-tolerant plant that grows in soil or waters of high salinity, coming into contact with saline water through its roots or by salt...

To Wikipedia about Halophytes

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

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

Wastewater treatment plant

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