Crushed Autoclaved Aerated Concrete (CAAC), a Potential Reactive Filter Medium for Enhancing Phosphorus Removal in Nature-Based Solutions—Preliminary Batch Studies

• Main Authors: Joana América da Cunha Castellar, Joan Formosa, Josep Maria Chimenos, Joan Canals, Montserrat Bosch, Joan Ramon Rosell, Heraldo Peixoto da Silva, Jordi Morató, Hans Brix, Carlos Alberto Arias
• Format: Article
• Language: English
• Published: MDPI AG 2019-07-01
• Series: Water
• Subjects: phosphorus; recycled concrete; tobermorite; kinetics; wastewater; reuse; calcium silicate hydrates
• Online Access: https://www.mdpi.com/2073-4441/11/7/1442

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 (P_i; 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 P_i, with the combination of its main effects stronger on P removal than each one separately. Intriguingly, we noticed that the higher the concentration of P_i, the faster and higher the removal of P. Contrary to expectations, PS 5 mm showed 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.