Phyto extraction of heavy metals
In 2014 the Capital Region in Denmark carried out a test of the Chinese brake fern "pteris vittata" to examine its capability to accumulate arsenic and heavy metals from soil under Danish climatic conditions.
The test showed that the plant can uptake arsenic but it became also clear that the growing conditions are crucial for its efficiency and ability as soil cleaning method.
Based on the experience from the 2014 test it was decided to carry out a new test aimed at improved growing conditions within a realistic framework for a full scale project.
The objective of the 2015 project was to establish a controlled growth environment securing microbial activity and optimal conditions for nutrient uptake. Next it was the objective to investigate how big it is possible to develop the volume of the biomass per square unit. Finally, it was an objective to investigate the ferns ability to survive during a Danish winter under a cover of straw.
Results and perspectives
Despite a summer of unstable weather an excellent growth was achieved. The young plants developed fine and reached an average weight of 3.5 g (dry matter) or about one third of the plant weight achieved in 2014 on second season plants.
Given the achieved biomass per square meter and an average uptake of arsenic of 4 g/kg dry matter a total of 0.6 g As/m2 will be removed during a growth season. In the test the roots were measured to 20 cm and thereby the plants have removed 0.6 g arsenic from 300 kg soil.
An amount of 300 kg soil with an average concentration of arsenic at 40 mg/kg dry matter contains 12 g arsenic. Thus, the removal of the arsenic will last 20 years or the soil quality criterion will be met in ten years.
Based on the experiences from both 2014 and 2015 it is likely to believe that it is possible to increase the biomass and also increase the uptake of arsenic by adding phosphate rock to the soil.
Project type: Remediation
Project target: Soil