An in-depth study on the deep-dewatering mechanism of waste activated sludge by ozonation pre-oxidation and chitosan re-flocculation conditioning.

At present, wastewater and sludge management departments are in urgent of the sludge deep-dewatering technique, which can substantially reduce sludge volume, enhance sludge calorific value and save costs. Ozonation pre-oxidation and chitosan (CT) re-flocculation conditioning have been verified to be an efficacious and environmental-friendly approach to realize sludge deep-dewatering. This paper focused on the novel insights into sludge properties under ozonation and CT conditioning. With 60 mg/gTS O and 20 mg/gTS CT, the water content of the conditioned sludge cake satisfied the deep-dewatering level (<60%). The ozone dosage of 60 mg/gTS effectually enhanced the release of soluble COD and retained the inherent organic matters simultaneously, and subsequently, CT could further reduce extracellular biopolymers, especially proteins. Fluorescence analysis indicated that the protein-like substances were largely decomposed into fulvic acid-like and humic acid-like substances after ozonation, and CT could further remove humic acid-like components. Macromolecules were observed to form by CT combining with ozonated extracellular polymers. Low-field NMR technique monitored sludge water states and suggested that water movability weakened after ozonation and enhanced again through CT conditioning. SEM images reflected that CT was available as junction link for ozonated polymers to aggregate into large flocs. Furthermore, the calorific value of conditioned sludge cake increased and sludge cake drying time was saved pronouncedly. The findings provided the systematic and comprehensive insights into the sludge properties in pre-oxidation and re-flocculation conditioning, which would aid in a better understanding of the in-depth dewatering mechanism and developing new dewatering technique.