The degradation of emerging contaminant coumarin was separately investigated in anodic, electro-Fenton and
subcritical water oxidation processes. With respect to the anodic and electro-Fenton oxidation, the influence of
constant current, treatment time and initial concentration of coumarin was studied. Regarding subcritical water
oxidation, the effect of the oxidant concentration, temperature, treatment time and initial coumarin concentration was investigated. In anodic and electro-Fenton oxidation processes, coumarin degradation proceeded in a
similar manner, achieving 99% degradation, after 180 min at a constant current of 200 mA. In both set-ups,
further increasing the applied current lowered the degradation efficiency due to the formation of by-products
and the increasing occurrence of side-reactions. The highest degradation of 88% was achieved in subcritical
conditions, specifically at 200 ◦C, using 150 mM H2O2 and after 37.5 min of treatment. Under subcritical conditions, temperature was the most prominent parameter, followed by the H2O2 concentration. Under all methodologies, increasing treatment time had a small positive effect on coumarin degradation, indicating that time is
not the most influential parameter. A comparison of the three methodologies in terms of performance as well as
energy consumption and simplicity of operation highlighted the advantages of subcritical water oxidation.