Waste activated sludge conditioning in a new Fe2+/persulfate/tannic acid process: Effectiveness and optimization study to enhance dewaterability

Fe 2+ /persulfate process can be used to improve sludge dewaterability significantly. However, a large dose of chemicals was always needed and it will cause filter cloth clogging, equipment corrosion and sludge calorific value reduction in practice. In this study, a new Fe 2+ /persulfate/TA (tannic acid) process was put forward, which could reduce the use of inorganic reagents and keep the outstanding conditioning capability. A Box-Behnken experimental design method based on response surface methodology (RSM) was selected to assess the roles of independent variables including SPS (sodium persulfate), Fe 2+ and TA, on sludge dewaterability characterized by capillary suction time, specific resistance of filtration, and water content of dewatered sludge cake. The optimized conditions were SPS dosage of 0.43 mmol/gTS (total solid), Fe 2+ dosage of 0.58 mmol/gTS and TA dosage of 0.14 mmol/gTS, at which the water content of dewatered sludge cake showed (75.89 ± 0.01)% highly close to the predicted minimum water content of dewatered sludge cake using the fitted equation. Moreover, in the new process, sludge properties altered distinctly with the elimination of extracellular protein, supernatant viscosity reduction and particle size increase. Further investigations were needed to explore the underlying mechanism and practical application for a better and comphrensive understanding of Fe 2+ /SPS/TA process.