| Wastewater activated sludge is produced during the biological treatment of wastewater. After treating the sewage, the sludge is allowed to settle. Part of the settled material is returned to the treatment process as return activated sludge and the excess is removed as waste activated sludge. The handling and disposal of the sludg e are energy and capital-intensive treatments, with a significant environmental impact.An innovative pretreatment technology, CaO joint add with NaOH following with appropriate mechanical whipping, was investigated for foaming and drying of sewage sludge(SS). Foaming efficiency, appropriate density of best drying performance and drying temperature were examined. Considering high foaming efficiency and low energy consumption, the optimal joint addition was found at 1.0 wt% Na OH with 1.0 wt% CaO, which costs only 50% of foaming time to reach the appropriate density(0.6 g/mL) comparing to that with 2.0 wt% CaO and saved 20% –26% drying time to reach 40% moisture content compared with SS. Non-linear regression techniques(Nonlinear Curve Fit(Dose Resp)) were applied to simulate the drying process of S2:2.The kinetics of sludge was studied by thermo-gravimetry analysis using the Starink method with three heating rates(10, 20 and 50K/min). Different trends in apparent activation energy supported the conclusion that difference appears in chemical compositions after foaming. The peak values of apparent activation energy(E) were prompted along with the development process of the transformation fraction. Finally the changeable trends of the reactor order(n) also illustrate the composition differences among the four sewage sludge samples. |
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