Exploring the efficacy and mechanism of tannic acid/Fe3+ conditioning for enhancing waste activated sludge dewaterability

Abstract

Waste activated sludge (WAS), as a kind of hydrophilic colloid substance, is still a major technical challenge in wastewater treatment industry. For enhancing WAS dewaterability, the approach of tannic acid (TA)/Fe3+ conditioning was verified to be feasible. During conditioning, sludge extracellular protein decreased pronouncedly. Fluorescence quenching analysis revealed that Fe3+ reduced the binding sites of extracellular polymeric substances available for TA, and the formed TA-Fe3+ complexes possibly promoted TA aggregates’ settlement and compression. Sludge supernatant viscosity, absolute value of zeta potential and pH value also decreased distinctly, and sludge particle size became larger than that of raw sludge or Fe3+-conditioned sludge. Scanning electron microscope suggested that sludge surface morphology became more compacted and denser after TA/Fe3+ conditioning, which was helpful for the release of water trapped in sludge bio-polymeric network. With 0.15 mmol/gTS TA and 0.9 mmol/gTS Fe3+ conditioning, sludge capillary suction time, specific resistance of filtration and water content of dewatered sludge cake were decreased by 76.3%, 94.7% and 13.5%, respectively. The findings not only shed new light on the means of applying natural plant organic polymer coupled with inorganic cation to promote WAS dewaterability but offered a potentially theoretical principle of the utilization of plant waste containing TA in WAS treatment.