Sustainable use of crushed autoclaved aerated concrete (CAAC) as a filter medium in wastewater purification

Scrap material from the production of autoclaved aerated concrete (AAC) should be considered a valuable by-product and not a waste, as should residues from the demolition of houses built with AAC. This paper presents an innovative use of AAC that can contribute to environmental improvement. We tested crushed AAC (CAAC, 2-4 mm) for its phosphorus (P) removal efficiency by filtering a solution containing phosphate phosphorus (PO4-P) or pure wastewater in batch, bench-scale and field pilot-scale experiments. Slow phosphate removal kinetics of CAAC were demonstrated, but the removal efficiency was very high (93-99%). Mineralogical analyses (by ICP-OES) of the solid CAAC after contact with flowing wastewater yielded concentrations of 39.6 g P kg-1. Application of X-ray powder diffraction (XRPD) for mineral phase identification confirmed that the dominant mineral in AAC was tobermorite (Ca5Si6O16(OH)2 · 4H2O). Dissolution of this crystalline structure was followed by formation of calcium phosphates and the porous, tobermorite-rich material produced proved excellent in removal of P and organic matter from domestic wastewater. Only crushing and sieving to achieve a suitable particle size distribution is needed prior to application in different technical solutions.QC 20121016