Reactivity of inorganic sorbents in wetland conditions for organic micropollutant removal

The variety of contaminants entering the environment is constantly expanding. Their amounts, properties, and behaviour are highly individual, including their ability or rate of degradation, affinity for sorbents, etc. Constructed wetlands represent nature-based solutions, which have proven to be efficient for wastewater treatment and elimination of some of the emerging micropollutants. However, the current systems are not designed for the removal of slowly degradable compounds. On the other hand, reactive surfaces of Fe-based or Mn-based sorbents can be favourable for sorption of persistent pollutants or enhanced degradation of more complex organic compounds. Therefore, the main idea of our research is to increase the retention and degradation potential of the constructed wetlands for the compounds of emerging concern using appropriate inorganic amendments. During the development, optimisation, and testing of a model wetland treatment system we focused on the reactive solid-water(-plant) interfaces using the column experimental scale, both planted and unplanted. Iron hydroxides or manganese oxides were applied as amendments. Experimental vertical flow constructed wetlands, saturated and unsaturated, were supplied with artificial domestic wastewater containing 31 organic micropollutants at concentrations of 10 or 50 µg/L. The results showed that under unsaturated conditions, constructed wetlands exhibited total organic micropollutant removal ranging from 93 to 95%. Under saturated conditions, the total removal was lower: 63%, 61%, and 77% for the variants with sand, Mn oxides, and Fe hydroxides, respectively. Compared to sand-based wetlands, Fe and Mn amendments significantly enhanced compound removal under saturated and unsaturated conditions. In addition to pollutant removal efficiency, solid phase transformations under the given conditions were investigated using X-ray diffraction analysis and scanning electron microscopy combined with elemental analyses. Overall, investigating the reactive interface of inorganic sorbents in constructed wetland conditions is essential for understanding the underlying mechanisms and optimising the amendment use for appropriate stimulation of abiotic and biotic processes.