Utilização de carvão ativado obtido a partir de lodo da indústria de polpa celulósica para tratamento de efluente industrial

Abstract

Pulp mills generate substantial quantities of primary sludge (PS) and secondary sludge (SS), whose management continues to pose technical, environmental, and economic challenges. This thesis investigated the conversion of these residues into activated carbon and its application to industrial effluent treatment, with emphasis on waste valorisation and material-cycle closure. The study encompassed sludge characterisation, production of activated carbons via pyrolysis followed by chemical activation with sodium hydroxide (NaOH), screening and optimisation of operating conditions using the Plackett–Burman design (PB) and the central composite rotatable design (CCRD), physicochemical and textural characterisation of the resulting adsorbent, and evaluation of adsorption performance using methylene blue and real pulp-mill effluent. Under the optimised conditions, sample LPLS-08 achieved a yield of 83.35%, an iodine number of 301.02 mg I₂∙g⁻¹, and a BET surface area of 311.11 m²∙g⁻¹. In experiments conducted with industrial effluent collected from the primary clarifier of an extended-aeration activated-sludge treatment plant, colour removal ranged from 64.89 to 92.25%, whilst chemical oxygen demand (COD) removal ranged from 33.29 to 44.31%. Kinetic modelling revealed that the pseudo-second-order model provided the most robust description of colour adsorption and remained the most reliable model for COD, although the Elovich model yielded a marginally superior overall fit for that response. Weber–Morris analysis indicated that adsorption proceeded through multiple stages, with concurrent contributions from external mass-transfer resistance and intraparticle diffusion, suggesting a higher affinity of the adsorbent for chromophoric and aromatic fractions than for the bulk organic load. Equilibrium modelling further demonstrated that the statistically best-fitting model did not necessarily correspond to the most physically defensible choice. Although the Redlich–Peterson model produced the best numerical indicators for both colour and COD, its estimated parameters lacked the physicochemical coherence required to support its conclusive adoption. For colour, the Freundlich and Temkin models offered more consistent mechanistic interpretations, whereas for COD the Temkin model proved most defensible. Collectively, these results establish not only the technical feasibility of converting pulp-mill sludge into activated carbon, but also its strategic valorisation potential as an integrated solution for simultaneous waste management and industrial effluent treatment.