Formaldehyde is a carcinogen compound and one of the most important pollutants contained in wastewaters. Three different treatments were evaluated in a high-pressure batch reactor for the total organic carbon (TOC) degradation of formaldehyde solutions: thermolysis, noncatalytic wet oxidation, and catalytic wet oxidation over a CuO-ZnO/Al2O3 catalyst. The absence of the catalyst leads to a predominant induction period (30 min) without changes in TOC concentrations, while the catalytic treatment leads to significant enhancement in TOC reduction. In the catalytic experiments, an asymptotic behavior was observed with a final TOC reduction of approximately 80%, with the remaining nonoxidizable TOC being due to methanol, a refractory compound contained in the formaldehyde solution that is resistant to oxidation even with increasing temperature and pressure. Formic acid was identified as an intermediary compound, and a new kinetic model was developed, designed as the modified generalized kinetic model, to account for refractory and nonoxidizable compounds. Moreover, leaching of the catalyst in the liquid phase was not significant, and the carbon adsorption capacity was not detected.