This work reports on pulp mill wastewater (PMW) tertiary treatment by Fenton (Fe2+/H2O2) and solar photo-Fenton (Fe2+/H2O2/UV) processes in a pilot plant based on compound parabolic collectors (CPCs). Solar photo-Fenton reaction is much more efficient than the respective dark reaction under identical experimental conditions. It leads to DOC mineralisation, COD and total polyphenols (TP) removal higher than 90%. The solar photo-Fenton experiment with 5 mg Fe L-1 reaches 90% of DOC mineralisation with 31 kJ L-1 of UV energy and 50 mM of H2O2. The initial non-biodegradability of PMW, as shown by respirometry assays and BOD5/COD ratio, can be changed after a solar photo-Fenton treatment. Experiments with 20 and 50 mg Fe L-1 revealed that solar photo-Fenton can reach the same DOC degradation (90%), however, consuming less H2O2 and time. Diluting the initial organic load to 50% also diminishes the dosage of H2O2 and the necessary reaction time to achieve high DOC removals. Accordingly, solar photo-Fenton can be considered an alternative or complementary process to improve the performance of a biologic treatment and, subsequently, achieve legal limits on discharge into natural waters. (C) 2012 Elsevier B.V. All rights reserved.