Environmentally-friendly dewatering of sewage sludge: A novel strategy based on amphiphilic phase-transfer induced by recoverable organic solvent

Abstract

This study proposed a novel strategy for sludge dewaterability improvement by eliminating the solid-liquid affinity through the polarity regulation of liquid phase. Initial screening experiments with different types of organic amendments (e.g., polar solvents, low-pole solvents, cytolytic reagents) found that acetonitrile and acetone could reduce specific resistance to filtration of sludge by 83.9% and 76.8%, respectively, at the solvent-sludge mass ratio of 1:1. The vacuum distillation and atmospheric distillation were both examined for the solvent recovery from filtered sludge cake and filtrate. Also, by considering the sensible heat for feedstock heating and enthalpy of solvent evaporation, the theoretical energy consumption of acetonitrile/acetone-enhanced sludge dewatering process was estimated to be at least 1/3 lower than that of the thermal drying process with the same treatment capacity, which indicated the energy saving potential of solvent-enhanced sludge dewatering process. Mechanism investigation was conducted by analyzing the surface functional groups of residual solid phase and the phase-transfer characteristics of amphiphilic compounds based on high-resolution Fourier transform-ion cyclotron resonance-mass spectrometry. It was found that the polarity of liquid phase dominated the phase-transfer of sludge compositions. The sufficient decrease in liquid polarity (dielectric constant < 55) would significantly eliminate the affinity of polar functional groups with the low-pole liquid phases, which induced the precipitation of amphiphilic proteins and substantially enhanced the solid-liquid separation. These findings suggest a promising technology for sludge dewaterability improvement by modifying the physical properties of liquid phase, which exhibits the obvious advantages in saving energy and material consumption.