Using plants to remediate wastewater produced from the cleaning process of blasted rock materials

Sammanfattning: Water pollution is one of society’s most crucial issues which has a negative impact on water quality. The cleaning of blasted rock materials is a process which produces wastewater containing nitrogen and other pollutants such as heavy metals due to explosives residue from blasting. The release of this wastewater to a recipient could have a negative impact on water quality. In order to counteract contamination of recipients, wetlands can be used. However, there is little knowledge and research of their efficiency in removing such contaminants from wastewater of blasting operations. Therefore, the aim of this report is to study plant’s remediation of pollutants, which is one of the processes involved in wetland treatment systems. This is examined through studying the effectiveness of different wetland-plant combinations’ ability to remove nitrogen and heavy metals in the wastewater. Another aim is to examine the silicon concentrations in the wastewater since silicon can be found from blasted rocks. This is of interest since elevated levels of silicon can act as a beneficial nutrient for crops and could then increase the value of the wastewater. The removal of the aforementioned substances has been studied after one, four and 24 hours through water analysis. Reed canary grass (Phalaris arundinacea), slender tufted sedge (Carex acuta) and yellow iris (Iris pseudacorus) were paired together in three different combinations for the study; A, B and C. The result from the water analysis was that the wastewater contained in average 64 mg N L-1, which is considered to be extremely high. For the nitrogen remediation the plant combinations containing I. pseudacorus removed the most nitrogen, 12 %, after 24 hours. Although, the nitrogen reduction was significantly lower compared to other studies. The heavy metal content was more than ten times lower in comparison to the upper limit values and was not reduced significantly by different systems. Regarding the silicon content, it was the same as found naturally in soil and water. The plants did not absorb any silicon, which indicates that the silicon was in a particular chemical form which is hard for plants to absorb. Sedimentation is mentioned as a major remediation process in wetlands, however in this study when plants were not present the result illustrated that the sedimentation probably did not function optimally. This could then demonstrate the importance of plants for other remediation processes. The conclusion of this study is that plants’ reduction of nitrogen in wastewater constitutes of a small part and could affect the function of sedimentation. In addition, according to this study yellow iris could be added to plant combinations to increase the treatment potential of wastewater produced from the cleaning process of blasted rock material, though further studies are recommended.