Forward osmosis-integrated granular anaerobic MBR: enhancing filterability and reducing mass transfer limitations

Area of Science:

• Environmental Engineering
• Water Treatment Technologies
• Membrane Science

Background:

• Submerged forward osmosis (FO) systems integrated with anaerobic membrane bioreactors (AnMBRs) face challenges with membrane fouling and mass transfer limitations.
• Operational conditions significantly impact the performance of these integrated systems.

Purpose of the Study:

• To systematically investigate the influence of draw solution (DS) type, gas sparging, and granular sludge fractions on FO filtration performance.
• To understand and overcome limitations in FO-integrated AnMBRs.

Main Methods:

• Experimental investigation of different draw solutions (e.g., sodium acetate vs. sodium chloride).
• Evaluation of continuous and intermittent gas sparging effects on water flux and external concentration polarization (ECP).
• Analysis of granular sludge size impact on fouling and membrane surface foulant composition using 3D excitation-emission fluorescence spectroscopy.

Main Results:

• Sodium acetate as DS resulted in lower reverse solute flux (RSF) and reduced salinity accumulation compared to sodium chloride.
• Continuous gas sparging (0.25 m³/m²h) effectively mitigated ECP and fouling; intermittent sparging caused flux fluctuations.
• Larger granular sludge (>0.63 mm) exhibited lower fouling potential. Proteins were identified as key foulants on the membrane surface.
• Membrane flushing with deionized water successfully restored initial flux, indicating reversible fouling.

Conclusions:

• Optimizing DS type, employing continuous gas sparging, and utilizing larger sludge granules are crucial for mitigating fouling in FO-AnMBRs.
• Understanding foulant composition (proteins) and hydrodynamic conditions aids in enhancing long-term system performance.
• These findings offer practical strategies for improving the efficiency and stability of integrated FO-AnMBR systems.