Upgrading a horizontal surface flow constructed wetland with forest waste and aeration

Constructed wetlands (CWs) are regarded as sustainable wastewater treatment systems for small to medium-sized communities. However, ponds and horizontal surface flow CWs (SF-CWs) can be an ideal environment for mosquitoes to thrive. In the current context of climate change, this may pose serious health problems for the population, which may predispose authorities against their use. A possible solution for existing SF-CWs is to convert them into sub-surface flow by filling them with conventional media, i.e. gravel and/or sand. However, the mining of these materials poses an enormous environmental threat. Thus, alternative, sustainable filling materials for CWs should be tested. Another constraint of CWs is their large footprint, which in many cases (lack of expensive land) limits their applicability. This work studies the effects of filling a full-scale SF-CW with a forest residue (palm tree branches) and aeration. The results indicate that in terms of percentage removal, filling increased that of E. coli and Total Coliforms, while the combination of filling and aeration resulted in a significant improvement in BOD5, turbidity, and ammonium. However, the analysis of surface loads removed indicated significant increases in E. coli and TC with the filling alone, and of BOD5, turbidity, E. coli, Total Coliformis, and ammonium for the filling + aeration combination. Studies at full-scale level on the use of forest residues as CW substrate and aeration are scarce, thus this work can serve as a guide for more sustainable designs.