Dynamic reverse Cl^- driven integration of sludge conditioning and dewatering.

Area of Science:

• Environmental Engineering
• Water Treatment Technologies
• Membrane Science

Background:

• Gel fouling severely limits the efficiency of forward osmosis (FO) for dewatering waste activated sludge (WAS).
• Extracellular polymeric substances (EPS), particularly proteins and polysaccharides, are key contributors to gel fouling in FO systems.
• Existing methods struggle to effectively mitigate fouling, hindering sludge dewatering performance.

Purpose of the Study:

• To develop and evaluate a novel FO system integrated with in-situ ultraviolet/electrooxidation (UV/E-Cl) for simultaneous WAS conditioning and dewatering.
• To investigate the mechanisms by which UV/E-Cl treatment mitigates gel fouling by targeting EPS.
• To provide quantitative thermodynamic evidence for the effectiveness of the proposed system in reducing filtration resistance.

Main Methods:

• A novel FO system incorporating in-situ UV/E-Cl treatment driven by dynamic reverse chloride ions (Cl⁻).
• Density Functional Theory (DFT) simulations to analyze protein-polysaccharide interactions and network formation.
• Interfacial thermodynamics to quantify foulant adhesion energy and water occurrence states.
• Experimental evaluation of water flux and filtration resistance compared to a control group.

Main Results:

• The UV/E-Cl assisted FO system achieved a 614% increase in water flux compared to the control.
• Filtration resistance was reduced by orders of magnitude, attributed to the targeted breakdown of protein and polysaccharide fractions in EPS.
• DFT simulations revealed specific configurations driving cross-linked network formation, while interfacial thermodynamics showed a 97.51% decrease in foulant adhesion energy.
• A significant shift in water occurrence states from bound to free water within network pores was identified as the dominant factor in fouling mitigation.

Conclusions:

• The proposed UV/E-Cl assisted FO system offers a highly effective solution for simultaneous WAS conditioning and dewatering.
• Targeted disruption of EPS cross-links and alteration of water occurrence states are the primary mechanisms for fouling mitigation.
• This study provides crucial quantitative thermodynamic insights into overcoming gel fouling in FO processes.