) reduction in water has been receiving increasing attention in water treatment due to its carcinogenic and endocrine-disrupting properties. This study employs a novel advanced reduction process, the UV/oxalic acid/ferric iron systems (UV/C2
systems), in reducing NO3−
due to its high reduction efficiency, excellent selectivity, and low treatment cost. The UV/C2
process reduced NO3−
with pseudo-first-order reaction rate constants of 0.0150 ± 0.0013 min−1
, minimizing 91.4% of 60 mg/L NO3−
and reaching 84.2% of selectivity for gaseous nitrogen after 180 min at pHini.
7.0 and 0.5 mg/L dissolved oxygen (DO). Carbon dioxide radical anion (CO2•−
) played a predominant role in reducing NO3−
. Gaseous nitrogen and NH4+
, as well as CO2
, were the main nitrogen- and carbon-containing products, respectively, and reduction pathways were proposed accordingly. A suitable level of oxalic acids (3 mM) and NO3−
(60 mg/L) was recommended; increasing initial iron concentrations and UV intensity increased NO3−
reduction. Instead, increasing the solution pH decreased the reduction, and 0.5–8.0 mg/L DO negligibly affected the process. Moreover, UV/C2
systems were not retarded by 0.1–10 mM SO42−
or 0.1–1.0 mM HCO3−
but were prohibited by 10 mM HCO3−
and 30 mg-C/L humic acids. There was a lower reduction of NO3−
in simulated groundwater (72.8%) than deionized water after 180 min at pHini.
7.0 and 0.5 mg/L DO, which meets the drinking water standard (<10 mg/L N-NO3−
). Therefore, UV/C2
systems are promising approaches to selectively and efficiently reduce NO3−
in drinking water.