The effluents of some pulp and paper processes are potentially pollutant, because of their large volume and their refractory nature. Biological processes generally are not capable to remove these compounds. Advanced Oxidation Processes (AOP) are characterized by the capability of exploiting the high reactivity of HO• radicals. AOP can produce a total mineralization, transforming recalcitrant compounds into inorganic substances (CO 2 and H 2 O 2), or partial mineralization, transforming them into more biodegradable substances. The high reactivity and low selectivity of these radicals are useful attributes that that make these processes in promising technologies. Due to the differences between pulping processes, the effluents from the various processes and operations of such industries also differ from each other, so that some oxidative processes should be combined to improve the removal efficiency. For the effective oxidation of refractory organic compounds, hydroxyl radicals should be generated continuously in situ due to its chemical instability. Generation of HO• is commonly accelerated by combining oxidizing agents. Among these treatments, UV radiation plus hydrogen peroxide (UV/H 2 O 2), Fenton's reagent (H 2 O 2 /Fe +2), photo-Fenton (UV/H 2 O 2 /Fe +2), and ozone in different combinations (O 3 /UV; O 3 /H 2 O 2) are considered to be effective for the oxidation of effluents from pulp and paper industries.

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Scale formation in the digester during kraft pulping represents a great problem in pulp mills. Scaling reduces pulping control and efficiency, increasing energy costs and leading to cleaning breakdowns, with subsequent losses in productivity. The kraft process promotes CaCO3 scaling due to high calcium ion and carbonate concentrations, as well as high alkalinity and temperature levels, which increase the speed with which liquors reach a state of supersaturation. This work examines the action of diethylene triamine penta(methylene phosphonic acid) (DTPMPA), either alone or combined with commercial anti-scaling agents, as an inhibitor of calcium carbonate precipitation in the kraft pulping of Pinus taeda. The theoretical amount of calcium deposited in the digester was obtained by mass balance. Soluble calcium was stable throughout cooking when using the phosphonates alone or combined with anti-scaling agents. When adding only DTPMPA, calcium stays in the pulp, rather than forming deposits.

The addition of a phosphonated chelant (DTPMPA) at different points of a TCF bleaching sequence and its effect on pulp properties were studied in this work. An industrial Eucalyptus grandis kraft pulp was submitted to a counter-ion exchange (Ca2+ or Na+ form) and was then bleached using DTPMPA in the washing or in the bleaching stages of two distinct sequences: OOpP and OQOpP (20 pulps). The counter-ion exchange affected fibre length, as well as the handsheets bulk and air permeability (higher for Na+-based pulps) and handsheet tensile strength, brightness, skeletal density, and total porosity based on Hg porosimetry (higher for Ca2+-based pulps). The hydrogen peroxide consumption in Op and P stages achieved the lowest values when the chelant was distributed rather than applied in a separate Q stage. The addition of chelant in the P stage provides pulps with higher ISO brightness (>85%). The chelant effects were always more noticeable in Ca2+-based pulps.

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