Investigation of micropollutants in two laboratory-scale constructed wetlands: experimental data and modeling
In recent years, new types of water contaminants have emerged. More and more focus is notably set on pharmaceuticals, personal care products or pesticides, as it has been observed that these substances are commonly found in surface water. This contamination notably results from direct input by runoff, improper disposal, leaks or sewer overflows. Moreover, these substances are also usually weakly removed in conventional wastewater treatment plants. As an alternative, constructed wetlands are very promising because they allow the use of a combination of various degradation processes and are therefore likely to be efficient for a larger spectrum of compounds. This study aimed to investigate the removal efficiency of two small‐scale sand constructed wetlands for various micropollutants. The two wetlands differed by the addition of a UV lamp and an aeration system in separate compartments in one of the system. The hydraulics of both wetlands was investigated using sodium salt and resazurin tracer tests. The development of two models revealed that both resazurin and to a lesser extent sodium salt were affected by sorption and cation exchange processes retarding the observed concentration breakthrough curves. In addition, the monitoring of the resazurin front progression through the wetlands was made possible by an image acquisition system and image processing. This has clearly shown the heterogeneity of the porous medium and the development of preferential flow paths. Finally, micropollutants degradation tests were conducted in order to assess the removal efficiency of the two systems. Ibuprofen, naproxen ketoprofen and triclosan were well degraded by both wetlands, whereas diclofenac, irgarol, diuron, terbutryn and mecoprop seemed to be especially sensitive to UV as their degradation is considerably higher in the compartmented wetland. Two other substances, carbamazepine and IPBC are more recalcitrant since no degradation was observed in both systems. These data were expected to be used to calibrate a simple degradation model; however, the hydraulic model is still unsatisfactory and needs to be further developed.