Fragmented limestone wastes as a constructed wetland substrate for phosphorus removal

This study investigated the potential of fragmented Moleanos limestone (FML) as substrate in constructed wetlands for phosphorus removal. Being a waste material which results from industries of extraction and production of decorative stones for construction activities, FML is quite inexpensive. Laboratory experiments were performed in a packed bed column with recycle to test the FML's capacity to sorb phosphorus from a phosphate solution. The experimental data were found to follow the Langmuir model better than the Freundlich model. From the isotherm parameters obtained it can be concluded that the sorption capacity of FML is similar to those quoted in the literature for mineral materials. A subsurface flow constructed wetland filled with FML and planted with Phragmites australis was monitored during 20 months, at a mean hydraulic load of 40 ± 4 L/(m2 day). Results demonstrated that average phosphorus removal efficiencies of 61% ± 7 can be achieved during the trial period, and a global first order kinetic constant of 0.062 ± 0.001 m/day was fitted to experimental data using the well mixed serial tanks model. Morphological aspects of reed growth were also studied and indicated high plant yield. The use of FML as a substrate media in constructed wetlands can be a promising solution in developing a cost effective, environmental friendly and sustainable technology for phosphorus removal, particularly where this material is readily available.

► A limestone rock (Moleanos) was verified suitable as a constructed wetland substrate. ► Phosphorous adsorption is well modelled by the Langmuir isotherm. ► The phosphorous removal efficiency of pilot wetland is higher than 60%. ► Wetland efficiency was well predicted by the tanks-in-serial model with N = 2. ► Moleanos limestone can be a promising low cost solution for phosphorous removal.