Drying behavior and thermo-gravimetrical kinetic analysis of foam-pretreated sewage sludge

Abstract

An innovative pretreatment technology, in which CaO was jointly added with NaOH followed by appropriate mechanical whipping, was investigated for the foaming and drying of sewage sludge (SS). Foaming efficiency, appropriate density of the best drying performance and drying temperature were examined. Considering high foaming efficiency and low energy consumption, the optimal mixture was found to be 1.0 wt% NaOH with 1.0 wt% CaO, which takes only 50% of the foaming time to reach the appropriate density (0.6 g mL⁻¹) compared to that with 2.0 wt% CaO. When compared with SS, the optimal mixture also saved 20%–26% drying time to reach 40% moisture content. Non-linear regression techniques (Nonlinear Curve Fit (Dose Resp)) were applied to simulate the drying process of S_2:2. The kinetics of sludge was studied by thermogravimetry analysis using the Starink method with three heating rates (10, 20 and 50 K min⁻¹). Different trends in apparent activation energy support the conclusion that differences appear in the chemical compositions of sludge samples that have different ratios of additives. Moreover, the TG analysis results provide referable combustion data for the sludge samples in this research.