A solar photo-Fenton process combined with a biological nitrification and denitrification system is proposed for the decontamination of a landfill leachate in a pilot plant using photocatalytic (4.16 m(2) of Compound Parabolic Collectors - CPCs) and biological systems (immobilized biomass reactor). The optimum iron concentration for the photo-Fenton reaction of the leachate is 60 mg Fe(2+) L(-1). The organic carbon degradation follows a first-order reaction kinetics (k = 0.020 L kJ(UV)(-1), r(0) = 12.5 mg kJ(UV)(-1)) with a H(2)O(2) consumption rate of 3.0 mmol H(2)O(2) kJ(UV)(-1). Complete removal of ammonium, nitrates and nitrites of the photo-pre-treated leachate was achieved by biological denitrification and nitrification, after previous neutralization/sedimentation of iron sludge (40 mL of iron sludge per liter of photo-treated leachate after 3 h of sedimentation). The optimum C/N ratio obtained for the denitrification reaction was 2.8 mg CH(3)OH per mg N-NO(3)(-), consuming 7.9 g/8.2 mL of commercial methanol per liter of leachate. The maximum nitrification rate obtained was 68 mg N-NH(4)(+) per day, consuming 33 mmol (1.3 g) of NaOH per liter during nitrification and 27.5 mmol of H(2)SO(4) per liter during denitrification. The optimal phototreatment energy estimated to reach a biodegradable effluent, considering Zahn-Wellens, respirometry and biological oxidation tests, at pilot plant scale, is 29.2 kJ(UV) L(-1) (3.3 h of photo-Fenton at a constant solar UV power of 30 W m(-2)), consuming 90 mM of H(2)O(2) when used in excess, which means almost 57% mineralization of the leachate, 57% reduction of polyphenols concentration and 86% reduction of aromatic content.