posted on 2019-11-01, 19:15authored byKiranmayi
P. Mangalgiri, Samuel Patton, Liang Wu, Shanhui Xu, Kenneth P. Ishida, Haizhou Liu
The
tapping of municipal wastewater for potable reuse significantly
enhances drinking water supply in drought-stricken regions worldwide.
Membrane-based potable reuse treatment trains commonly employ ultraviolet-based
advanced oxidation processes (UV-AOPs) to degrade trace organic contaminants
in water to produce high-quality recycled water. Hydrogen peroxide
(H2O2) is used as the default photo-oxidant.
Meanwhile, chloramines, which are added to prevent biofouling, pass
through the membranes and impact the treatment efficiency of UV-AOP.
Water reuse facilities therefore face the dilemma of optimizing H2O2 (an added photo-oxidant) and chloramines (a
carry-over photo-oxidant) doses. Utilizing a uniquely designed pilot-scale
reactor and real-time recycled water, we evaluated treatment efficiencies
of UV-AOP on six important indicator contaminants, with monochloramine
(NH2Cl) and H2O2 as photo-oxidants.
Hydroxyl radical (HO•) and reactive chlorine species,
such as the chlorine atom (Cl•) and chlorine dimer
(Cl2•–), were the major reactive
species. Overall, radicals generated from photolysis of NH2Cl alone achieved removal of indicator compounds, which can be further
improved by optimizing UV fluence, i.e., the UV dose. Furthermore,
the addition of H2O2 enhanced HO• formation and improved contaminant removal. However, the addition
of H2O2, when the background NH2Cl
level was above 2 mg L–1 (as Cl2), provided
limited improvement in treatment efficiency. These trade-offs between
chloramine and H2O2 as oxidants, and the recommended
optimization of the associated effective UV fluence, are critical
for energy-efficient and cost-effective potable reuse to address the
challenges of global water scarcity.