Optimizing Potable Water Reuse Systems: Chloramines or Hydrogen Peroxide for UV-Based Advanced Oxidation Process?

Area of Science:

• Environmental Science
• Water Treatment Engineering
• Photochemistry

Background:

• Municipal wastewater reuse is crucial for water security in arid regions.
• Ultraviolet advanced oxidation processes (UV-AOP) are vital for removing trace organic contaminants in recycled water.
• Chloramines, used for biofouling control, interfere with UV-AOP efficiency by acting as competing photo-oxidants.

Purpose of the Study:

• To evaluate the treatment efficiencies of UV-AOP using monochloramine (NH2Cl) and hydrogen peroxide (H2O2) as photo-oxidants.
• To investigate the impact of varying NH2Cl and H2O2 doses on the degradation of indicator contaminants.
• To determine optimal UV fluence for effective and efficient water reuse treatment.

Main Methods:

• A pilot-scale reactor was used to assess UV-AOP treatment of real recycled water.
• Six indicator contaminants were monitored under different combinations of NH2Cl, H2O2, and UV fluence.
• Reactive species, including hydroxyl radicals (HO•) and reactive chlorine species, were identified.

Main Results:

• Photolysis of NH2Cl alone generated reactive species that removed indicator compounds, with efficiency increasing with UV fluence.
• Addition of H2O2 boosted hydroxyl radical formation and enhanced contaminant removal.
• Above 2 mg L−1 (as Cl2) background NH2Cl, adding H2O2 yielded minimal additional treatment benefits.

Conclusions:

• Both NH2Cl and H2O2 contribute to contaminant degradation in UV-AOP, with NH2Cl acting as a primary photo-oxidant.
• Optimizing UV fluence is critical for maximizing treatment efficiency regardless of oxidant combination.
• Balancing NH2Cl and H2O2 doses is essential for energy-efficient and cost-effective potable water reuse.