Treatment and nutrients recovery with Constructed Wetlands: closing the cycle of urban wastewater and agricultural drainage/runoff - exploration of novel setups, technologies and application

Constructed wetlands (CWs) applied to municipal wastewater and agricultural drainage water (ADW) treatment were studied to remove and recover both water and nutrients within contained. In PRIMA FIT4REUSE and H2020 WATERAGRI research projects, novelties within the field as hybrid CWs, biochar as substrate, biomass revalorisation and aeration were explored. The reportedly promising properties of CWs were profitably applied both in urban and agricultural context, confirming such technology as a convenient and efficient choice for tackling the circularity challenges. The application of CWs after an upflow anaerobic sludge blanket reactor granted considerable enhancement of the municipal wastewater treatment process: hybrid CWs granted increased performance in N and P removal, indicating that such NBSs can reach high removal rates without further intensification. Continuous CW aeration did not increase the performances, whereas partial and intermittent aeration granted a slight removal boost, arguably due to an enhancement of biotic metabolism, thus increasing the uptake by such components. When applied to ADW, the best performing CW were identified as the surface-flow for N and P removal; biochar applied within horizontal flow CWs did not seem to influence the system performance, but further experiments are required. In the same agricultural context, it was assessed that by regular harvesting the CW biomass (common reed) it is possible to exploit its nutrients uptake capacity providing soil with important nutrients. Composting the reed biomass can yield a valuable substance to be applied as soil amendment, with the potential to increase its properties, C pool and both nutrients content and availability, while decreasing the mineral fertiliser need. It was however assessed that reed should be mixed with additional substances, such as potato cuttings, to provide better properties. Further experiments should be performed to fully assess the potentials of agricultural waste recycling.