Crushed autoclaved aerated concrete (CAAC), a potential reactive filter medium for enhancing phosphorus removal in nature-based solutions preliminary batch studies

Phosphorus (P) is a limited resource and can promote eutrophication of water streams and acidification of oceans when discharged. Crushed autoclaved aerated concrete (CAAC), a by-product from demolition, has shown great potential for recovering P. The potential of CAAC to be used in nature-based solutions as a P-reactive filter medium was evaluated by performing preliminary batch essays. Here, we evaluated the interactions and main effects of the initial concentration of P (Pi; 5, 10 or 20 mg L-1), particle size (PS; 4 or 5 mm) and contact time (CT; 60, 180, 360, 720 and 1440 min) upon the removal. We performed physical and chemical characterization to understand the removal processes. Data collected were fitted in adsorption kinetic models. The statistical analysis showed a significant interaction between CT and Pi, with the combination of its main effects stronger on P removal than each one separately. Intriguingly, we noticed that the higher the concentration of Pi, the faster and higher the removal of P. Contrary to expectations, PS 5mmshowed higher removal rates than PS 4 mm, indicating that besides adsorption, other unidentified chemical processes are in place. Further studies using columns/pilots with real wastewater are recommended for a future follow-up.