Optimization of culturing conditions and selection of species for the use of halophytes as biofilter for nutrient-rich saline water

- Cultivation of halophytes was optimized to increase efficiency of a plant biofilter.
- A nitrate-N concentration of 10 mg l−1 is necessary for reasonable biomass production.
- Addition of iron in chelated form is necessary.
- Several tested species have potential to serve as biofilter and valuable co-products.
- Application: halophytic vegetable plants can be grown in marine aquaponic systems.

Salt-tolerant plants can be used as biofilters for nutrient-rich saline water such as aquaculture process water. Tripolium pannonicum (Jacq.) Dobrocz. was used to determine optimal culturing conditions for an efficient biofilter performance in terms of nutrient recycling by plant uptake. This performance was evaluated by taking different parameters into account, such as biomass production, plant nitrogen and phosphorus uptake as well as physiological parameters and decrease of nitrate-N and phosphate-P concentrations in the experimental fluid. Afterwards, additional plant species known as edible were studied to follow the idea of generating valuable co-products beside the use as biofilter. It was shown that a nitrate-N concentration of at least 10 mg l−1 is necessary for reasonable biomass production. A phosphate-P concentration of 0.3 mg l−1 is sufficient, but higher concentrations promote the uptake of phosphate-P. The addition of iron in chelated form is required for the growth of healthy plant biomass; the addition of manganese is beneficial but not implicitly necessary. Salt concentrations lower than seawater salinity promote biomass production and nutrient uptake. The use of a hydroponic culture system is more suitable than sand or expanded clay culture if controlled conditions and nutrient recycling are desired. The five weeks experiment to compare different halophyte species in 0.24 m2 tanks with nine plants each resulted in above ground fresh weight of 185 to 398 g and total uptake of nitrogen and phosphorus of 0.6 to 2.1 g and 0.1 to 0.4 g, respectively. All tested species have potential to serve as biofilter and source for valuable co-products. A promising application is the growth of halophytic vegetable plants in marine aquaponic systems.