Optimized bimetallic ratios for durable membrane catalyst-film reactors in treating nitrate-polluted water

Area of Science:

• Environmental Engineering
• Catalysis
• Water Treatment

Background:

• Nitrate contamination poses a global water quality challenge.
• Conventional treatment methods create concentrated waste streams.
• Membrane Catalyst-film Reactors (MCfR) offer a novel denitrification approach without waste.

Purpose of the Study:

• To investigate the impact of indium-to-palladium (In:Pd) molar ratios on denitrification rates in MCfRs.
• To evaluate the long-term performance of optimized In-Pd catalysts in continuous-flow MCfRs.
• To identify factors affecting denitrification efficiency over time.

Main Methods:

• Evaluated eleven In-Pd bimetallic catalyst films with varying molar ratios (0.0029 to 0.28) in batch-mode MCfRs.
• Determined nitrate removal rates based on In:Pd ratios.
• Conducted continuous-flow experiments for over 60 days using optimized In:Pd MCfRs with nitrate-spiked tap water.

Main Results:

• Nitrate removal showed a volcano-shaped dependence on indium content, peaking at an In:Pd ratio of 0.045.
• The optimal In:Pd catalyst achieved a maximum nitrate removal rate of 0.19 mgNO3--N-min-1 L-1.
• Continuous-flow treatment revealed three stages: initial high efficiency, a decline, and stabilized denitrification.
• Catalyst loss (Pd and In) and elevated pH were identified as key factors in efficiency decline.

Conclusions:

• Optimized In:Pd bimetallic catalysts show promise for efficient nitrate removal in MCfRs.
• Long-term denitrification efficiency is limited by catalyst deactivation and pH increase.
• Further research is needed to mitigate catalyst loss and pH effects for sustained nitrate removal.