Decrease the effective temperature of hydrothermal treatment for sewage sludge deep dewatering: Mechanistic of tannic...

Area of Science:

• Environmental Engineering
• Water Treatment
• Materials Science

Background:

• Hydrothermal treatment (HT) for sludge dewatering faces challenges with refractory compounds and high nitrogen concentrations in filtrates.
• These issues limit the efficiency and environmental friendliness of conventional HT processes.

Purpose of the Study:

• To develop a novel tannic acid (TA)-aided hydrothermal treatment (HT) process to address limitations in sludge dewatering.
• To investigate the mechanisms by which TA improves dewaterability and reduces refractory nitrogenous compounds.

Main Methods:

• Sludge samples were treated using hydrothermal treatment with varying concentrations of tannic acid.
• Dewaterability, hydrophobicity, and the characteristics of soluble extracellular polymeric substances (S-EPSs) were analyzed.
• Protein secondary structure and TA-protein interactions were examined to elucidate the underlying mechanisms.

Main Results:

• TA addition significantly improved sludge dewaterability across tested HT temperatures by increasing relative hydrophobicity.
• The effective HT temperature was reduced from 180 to 160 °C, with optimal TA dose (0.15 mmol/g TS) reducing filtrate total organic nitrogen by 47.27%.
• TA-HT enhanced protein precipitation by disrupting protein structure and creating hydrophobic binding sites for TA.

Conclusions:

• Tannic acid-aided hydrothermal treatment is an effective strategy for simultaneous sludge dewatering and reduction of refractory nitrogenous compounds.
• The improved dewaterability is linked to TA's interaction with S-EPSs, specifically high-molecular-weight proteins, promoting precipitation.
• Understanding TA-EPS interaction mechanisms can guide further optimization of HT for sludge management.