Adsorventes a partir do lodo de esgoto para remoção de compostos lipofílicos de madeira de eucaliptos

Abstract

Sewage sludge is a byproduct of the wastewater treatment and its final disposal can become an environmental problem. The preparation of adsorbents is considered an attractive method of reuse of this byproduct. Adsorbents obtained from sewage sludge have not yet been used in removing of lipophilic compounds of the wood. These compounds are precursors of the pitch, resinous materials that, when formed, cause economic losses to the pulp and paper industries. Sewage sludge was used to prepare adsorbents from calcination at seven temperatures (400, 500, 600, 700, 800, 900 e 1000 ° C) for five hours. The properties of morphology and specific surface area of the adsorbents were evaluated. The adsorbents were used on the adsorption study of lipophilic compounds of the wood and the results were compared to talc. The observation of photographs of the surface obtained by scanning electron microscopy revealed the presence of pores and cavities on the surface of the adsorbents. The adsorption isotherms were classified, according to the IUPAC, as type IV and H3 hysteresis, corroborating the presence of mesopores. The correlation between calcination temperature and the BET surface area, which ranged from 0,73 to 23,4 m2g-1, was evidenced, and with an increase in calcination temperature promoted a decrease in the surface area values. Adsorbents obtained by calcination between 400 and 800 ºC presented SBET values higher compared to talc (5,25 m2 g-1) and those produced at 600 and 700 ºC presented greater adsorption potential (94%), while talc removed 11.8% of extractives. The adsorbent produced at 700 ° C was used on the adsorption study of four compounds that represent the major chemical classes present on wood extractives (dodecan-1-ol, hexadecanoic acid, tetracosane, -sitosterol). The adsorption time, adsorbent quantity and the adsorbat initial concentration were optimized. The optimal conditions were used in order to evaluate the adsorbent preparation time, and,after that, the condition with the best result was used for the calcination of sewage sludge samples from ten cities (Bambuí, Belo Horizonte, Bom Despacho, Claro dos Poções, Corinto, Curvelo, Janaúba, Montes Claros, Porteirinha e Taiobeiras). For contact time were optimized 30 minutes of stirring and to the adsorbent dosage of 0.2 g. The adsorption isotherms presented classification H, according to Giles (1960), indicating high affinity of the compounds by the adsorbent. The decrease in the calcination time of the adsorbing did not cause reduction in adsorption efficiency, besides reducing the energetic costs of production. The percentage removal of compounds adsorbents produced from sludege from ten cities was above 70%, except for the adsorption of tetracosane by the adsorbent concerning to the city Claro dos Poções. The best adsorption rates (greater than 85 %) were obtained by adsorbents from sewage sludge of the cities in Belo Horizonte, Bom Despacho, Corinto, Curvelo and Montes Claros. The obtained results evidenced the efficiency of the adsorbent in removal of lipophilic compounds present in wood extractives and, consequently, pitch.