Autoclaved aerated concrete grains as alternative absorbent and filter media for phosphorus recovery from municipal wastewater: A case study in Hanoi, Vietnam

Abstract

Construction and demolition wastes, especially autoclaved aerated concrete (AAC), increase with the expansion of construction. AAC is a high-porosity material with a surface rich in metal hydroxides, which promotes both biofilm growth and phosphate binding. This study assessed the efficiency of using AAC grains for the recovery of phosphorus (P) and biological treatment of municipal wastewater (MWW). Batch adsorption tests using synthetic phosphate-rich wastewater determined the affinity of P for 3–5 mm and 5–10 mm AAC grains, and P adsorption profiles were obtained. AAC grains adsorbed P well with maximum adsorption of 1.1 mg P/g based on the Langmuir isotherm model and a P removal efficiency of >96% (initial P concentration 30 mg/L). Biofiltration through three reactor tanks with AAC particles (30–50 mm and 3–5 mm) was performed by circulating MWW with retention times of 19–40 h to evaluate the elimination efficiency (E) of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in each reactor tank. The biofiltration system effectively removed the target pollutants, with E values ranging from 80% to 90% for COD, 38% to 70% for TN, and 80% to 92% for TP. The high E values led to P recovery from MWW, resulting in a P content of 1.33 g/kg of AAC in the biofiltration system. This study demonstrated that AAC waste can serve as an inexpensive and easily recyclable P recovery material in the biofiltration system used to treat MWW.