Hydroponic materials improve organic micropollutant removal in vertical flow constructed wetlands treating wastewater

Unconventional substrata like activated carbon or clay beads can enhance micropollutant removal in constructed wetlands. However, hydroponic materials widely used in horticulture have not yet been investigated for their potential to remove micropollutants. In addition, potential effect of plant species other than reeds on micropollutant removal has not been sufficiently investigated. Therefore, a nature-based, post-treatment technology called improved vertical flow constructed wetlands (CW) with hydroponic (H) materials (CWH) was designed by employing cocopeat and mineral with ornamental plant species syngonium and periwinkle. A mesocosm CWH system was tested in a climate-controlled greenhouse for 550 days for its potential to remove frequently found micropollutants in wastewater, namely sulfamethoxazole, trimethoprim, diclofenac, erythromycin, carbamazepine, pyrimethanil, tebuconazole, pymetrozine, atrazine and DEET from wastewater effluent. The main focus was to understand the contribution of sorption, microbial degradation and phytoremediation on the removal of those micropollutants. It was found that cocopeat showed a capacity for sorbing micropollutants, ranging between 80 and 99% of the compounds added while less than 10% sorption was observed for mineral wool. Additionally moderate to high biological removal (25-60 μg of compound/kg dry weight of substratum/day) for most of the studied compounds was observed in all the cocopeat biotic groups. Furthermore, it could be stated that plants appear not to be an important factor for micropollutant removal. The observed differences in removal between the cocopeat and mineral wool systems could be explained by the difference in physico-chemical properties of the substrata, where cocopeat has a higher water holding capacity, moisture content, nutrient and organic matter content, and a higher intraparticle porosity and surface area. This study revealed notable removal of persistent and mobile micropollutants in cocopeat CWH, namely carbamazepine (80-86%) and diclofenac (97-100%). These results demonstrate the potential beneficial use of hydroponic materials as substratum in more advanced constructed wetlands designed to remove micropollutants.