Use of marine and engineered materials for the removal of phosphorus from secondary effluent

Constructed wetlands (CWs) require large area per population equivalent for the treatment of domestic wastewater. Hence, more compact CWs with equivalent or higher treatment efficiency per m2 than conventional CWs need to be developed. The aim of this study was to reduce the required area by enhancing the phosphorus removal through the use of marine (i.e., crushed coral, oyster-shells and mussel-shells (raw and pyrolyzed)) and engineered (i.e., nanoparticle–beads) materials. This was done in batch and column experiments. The pyrolyzed materials and the nanoparticle–beads showed a phosphorus removal capacity exceeding 99%, respectively through precipitation and adsorption. The conditions each material needed for the removal were different (e.g., contact times and material-to-solution ratios). Conversely, the raw marine materials did not achieve high removal efficiencies (12–59% after 7 days), unless the pH was increased to approximately 12. In general, all materials achieved phosphorus-removal levels beyond typical CW, the pyrolyzed materials and nanoparticle–beads being the most effective of the materials investigated. However, the high pH (
12) of the effluent after the treatment with pyrolyzed material can be a limitation of its application. A (separate) post-CW filter, packed with either pyrolyzed materials or nanoparticle–beads is proposed to increase the phosphorus removal efficiency thereby reducing the total space requirement of a CW. Recommendations for practical use are also included in this study.