Ceramsite Made with Water and Wastewater Sludge and its Characteristics Affected by SiO2 and Al2O3

To solve the disposal problems of residual sludges, wastewater treatment sludge (WWTS) and drinking-water treatment sludge (DWTS) were tested as components for production of ceramsite. SiO2 and Al2O3 were the major acidic oxides in WWTS and DWTS, so their effect on characteristics of ceramsite was also investigated to optimize the process. Results show that WWTS and DWTS can be utilized as resources for producing ceramsite with optimal contents of SiO2 and Al2O3 ranging 14-26% and 22.5-45%, respectively. Ceramsite within the optimal SiO2 and Al2O3 contents ranges was characterized using thermal analysis, X-ray diffraction (XRD), morphological structures analyses, and compressive strength measurements. Significant weight loss below 600 °C is through the release of structural water and gases. Bloating and crystallization in ceramsite above 900 °C are caused by the oxidation and volatilization of inorganic substances. Higher strength ceramsite with less Na-Ca feldspars and amorphous silica and more densified surfaces can be obtained at 18% ≤ Al2O3 ≤ 26% and 30% < SiO2 < 45%, while porous ceramsite with complex crystalline phases and lower strength can be obtained at 14% ≤ Al2O3 < 18% and 22.5% ≤ SiO2 < 30%. This revolutionary technology of utilization of WWTS and DWTS can produce high performance ceramsite, in accordance with the concept of sustainable development.