The present study tested the performance of coagulation after wet oxidation (WO) as a way to improve water quality, namely colour, and establish its viability as a secondary treatment process for water cycle closing. The experiments were carried out with model TMP (Thermomechanical Pulp) water concentrated by nanofiltration. The WO runs were conducted at a temperature of 453 K and p(O-2) of 1 MPa. Fe-2(SO4)(3) was chosen as the coagulant for the coagulation experiments. The experimental results showed that coagulation allowed 83% colour removal and 75% lignin reduction with a coagulant dose of 0.86 g Fe3+/L. Recirculation of sludge to the WO system improved the performance of the WO process. The dose needed to achieve the same results for the coagulation after the recirculation loop, i.e. coagulation after wet oxidation with coagulation sludge recycled to the WO system, was 0.78 g Fe3+/L. The Fe ion concentration remaining after coagulation was observed to be 0.91-0.95 mg/L, which could permit sludge-free water reuse in paper mills.