When reverse osmosis brines from potable wastewater reuse plants are discharged to
poorly-flushed estuaries, the concentrated organic contaminants are a concern for
receiving water ecosystems. UV/hydrogen peroxide (UV/H2O2) and UV/persulfate (UV/S2O8(2-))
advanced oxidation processes (AOPs) may reduce contaminant burdens prior to discharge,
but the effects of the high levels of halide, carbonate and effluent organic matter
(EfOM) normally present in these brines are unclear. On the one hand, these substances
may reduce process efficiency by scavenging reactive oxygen species (ROS), hydroxyl
(OH) and sulfate (SO4(-) radicals. On the other, the daughter radicals generated by
halide and carbonate scavenging may themselves degrade organics, offsetting the effect
of ROS scavenging. UV/H2O2 and UV/S2O8(2-) AOPs were compared for degradation of five
pharmaceuticals spiked into brines obtained from two reuse facilities and the RO influent
from one of them. For UV/H2O2, EfOM scavenged ∼75% of the OH, reducing the degradation
efficiency of the target contaminants to a similar extent; halide and carbonate scavenging
and the reactivities of associated daughter radicals were less important. For UV/S2O8(2-),
anions (mostly Cl(-)) scavenged ∼93% of the SO4(-). Because daughter radicals of Cl(-)
contributed to contaminant degradation, the reduction in contaminant degradation efficiency
was only ∼75-80%, with the reduction driven by daughter radical scavenging by EfOM.
Conversion of SO4(-) to more selective halogen and carbonate radicals resulted in
a wider range of degradation efficiencies among the contaminants. For both AOPs, 250
mJ/cm(2) average fluence achieved significant removal of four pharmaceuticals, with
significantly better performance by UV/S2O8(2-) treatment for some constituents. Accounting
for the lower brine flowrates, the energy output to achieve this fluence in brines
is comparable to that often applied to RO permeates. However, much higher fluence
was required for the least reactive pharmaceutical. Comparing AOP application to the
RO influent or brine, equal or greater removal was achieved for brine treatment for
comparable energy input. AOP treatment of brines could be applied to reduce, but not
eliminate, contaminant burdens prior to discharge.