Organic micropollutants degradation from reverse osmosis concentrate
Anodic oxidation with a Magnéli (Ti4O7) reactive electrochemical membrane flow-through reactor towards drinking water production processes
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Abstract
Manmade
emergent contaminants are posing a big treat to the environment and human
health. Their accumulation in water resources threatens the ecosystem
equilibrium and challenges the current technologies to produce safe drinking
water. This research explores anode oxidation (AO) using a Magnéli phase
reactive electrochemical membrane (REM) flowthrough reactor as an alternative
to treat reverse osmosis concentrate (ROC) water containing a broad list of
organic micropollutants (OMPs). ROC water produced in two drinking water
treatment facilities in the Netherlands was used to test the technology. This
study searches for insights to manage ROC waste containing recalcitrant OMPs
and safely discharge effluent to surface water.
Throughout laboratory experimentation, the effectivity of degrading OMPs
(per-polyfluoroalkyl substances, pharmaceuticals, corrosion inhibitors, and
synthetic dyes) was investigated.
Main findings suggest that 100 mg/L Methylene blue (MB) spiked in an artificial
water matrix is completely mineralized after an applied charge dosage (CD) of
22.56 kC/L. Additionally, pharmaceuticals spiked in artificial water matrix and
ROC were degraded above 80% after applying a charge dosage of 5.64 kC/L.
Finally, PFOA and PFOS degradation for drinking water utilities 1 & 2 resulted
in an average of 49.5 and 76.90 % respectively after applying 120 kC/L.
Moreover, it was found that hardness in water inhibits the degradation capacity
reducing the effective area of the anode with scaling deposition. Besides, the
calcium and magnesium content slightly increases the energy consumption and the
frequency of chemical cleaning required to maintain the reactor. The Magneli
REM reactor has capabilities to degrade OMPs when treating ROC. Operational parameters
such as flowrate, and CD can be adjusted to obtain better degradation rates. However,
the treated water could contain byproducts with recalcitrant properties and
high toxicity (for instance, ultra and, short chain PFAS, bromate, chlorates
and perchlorates). For that reason, monitoring and further treatment is
recommended to safely discharge back to surface water.