Granular waterworks sludge-biochar composites: Characterization and dye removal application

Development of composite adsorbents from waste materials has the potential to build circular economies to meet environmental sustainability goals. This study investigates granular waterworks sludge-biochar composites, which combine the high carbon and surface area of biochar with the clay properties of waterworks sludge in a synergy to increase the composite’s functions on dye removal. The sorption ability of methylene blue (MB) dye onto two composite adsorbents; (1) rice husk biochar sludge composite (BSC) and (2) raw rice husk sludge composite (RSC) is investigated as compared to a control of unmodified raw materials including rice husk biochar (RHB) and waterworks sludge (sludge). The composite materials exhibit surface properties inherited from both raw materials; however, their chemical compositions are more comparable to sludge. As compared to sludge, higher surface area and MB removal capacity are noticed from both composites. Both BSC and RSC exhibit a similar adsorption isotherm to RHB, which is better described by a Langmuir model, while a Freundlich adsorption isotherm model is better fit for sludge. BSC possesses the highest MB sorption capacity of 16.949 mg/g, followed by RHB, RSC, and sludge with the capacity of 14.493, 13.966, and 8.576 mg/g, respectively.