This paper explores the catalytic behaviour of different graphene-based nanostructures for the treatment of wastewater using Catalytic Wet Peroxide Oxidation (CWPO) processes. In a first stage, graphene-based nano-powders with distinct physical-chemical characteristics are tested in the CWPO of phenol using the following standard operating conditions: [Phenol](0) = 1 g center dot L-1, [H2O2](0) = 5g L-1 and 80 degrees C. Graphene nanoplatelets with the lowest oxygen content exhibit the highest catalytic activity. The typical phenol oxidation by-products are detected in the liquid phase while CO and CO2 appear in the gas phase. Afterwards, three dimensional (3D) porous graphene monoliths (D similar to 11.5 mm, H similar to 4 mm, D-open similar to 0.68mm and delta(w) = 0.36 cm, 75 cells center dot cm(-2), epsilon(graphene skeleton) = 41%) based on those nanoplatelets are additive manufactured using a direct ink writing technique and, then, tested under similar CWPO conditions. The results evidence that the 3D graphene-based structures are catalytically active, though they undergo a progressive deactivation due to the deposition of organic matter. The graphene-based monoliths can be regenerated by thermal treatments, allowing their use at industrial scale by means of reaction-thermal regeneration cycles.