In this research, a traditional waste material that has been costly to handle will be used for beneficial purposes. Alum (i.e., hydrated aluminum sulfate—Al2(SO4)3⋅14–18H2O) is a common coagulant in drinking water treatment (DWT). The coagulation treatment inevitably generates large quantities of alum sludge, or water treatment residuals (WTR). The most common practices for WTR management are landfilling and agricultural application. Out of the concern of deteriorated soil quality, many producers are reluctant to apply WTR on their farms, whereas hauling the large quantities of WTR to landfills is also costly. Recognizing the major constituents in WTR, such as SiO2, Al2O3, Fe2O3, and mono-/di-valent metal elements (e.g., Na+, K+, Ca2+, and Mg2+), as well as WTR’s own physical and chemical properties, this “waste” can be transformed into valuable products, such as construction materials (e.g., concrete and bricks) and ceramic materials. As a preliminary research attempt, we are using WTR-based ceramsites as an adsorbent material for pollutant removal from water matrices. They have demonstrated a good 24 h water absorption capability (9–63%), bulk density (438.79–829.80 kg/m3), and apparent density (720.83–1592.86 kg/m3). In this preliminary study, WTR-based ceramsite can successfully remove phosphate (PO43−) through adsorption process, achieving 90.05% removal in 69 h. More detailed studies are currently in progress to further investigate the possibility of WTR-based ceramsite to remove other pollutants, such as per-/poly-fluoroalkyl substances (PFAS). The preliminary experiments suggest the ceramsites have a potential to be used as a lightweight water filter media, particularly counting the benefits of solid waste repurposing. Our study will help the water sector reduce its operating expenses and generate new revenue opportunities and enhance its environmental stewardship.
