Adsorption of phenolic compounds and color from bleached Kraft mill effluent using allophanic compounds

Synthetic and natural allophanic compounds were used to evaluate the phenolic compounds and color removal capacity from a biological treated softwood bleached Kraft mill effluent. Kinetics studies and solid/solution relationship using synthetic allophanic compounds were studied and compared with powder activated carbon adsorption. On the other hand, the pH effect (4 to 9) on allophanic compounds adsorption was studied. The adsorption capacity of three allophanic soil profiles (10-20, 20-40 and 40-60 cm) activated by washing the soil with H2SO4, 0.1 M, and by calcination at 550 degrees C was also evaluated. Kinetics studies showed that the adsorption hall-time was 2 min in both activated carbon and synthetic allophanic compounds and more than 90 and 70% removal occurred in the first 5 min, respectively. The adsorption of color and phenolic compounds increased with decreasing solid/solution ratio in both activated carbon and synthetic allophanic compounds. pH plays an important role in adsorption phenomena. Phenolic compounds and color removal increased with the decreasing of suspension-efffuent pH, obtaining the optimum at pH 5.0 with 87 and 96% removal, respectively. Phenolic compounds and color removal were near 90 and 75% when 20-40 cm acidified and calcinated soil profile was used, respectively. The organic matter content in the 10-20 cm soil profile and the low content of the fine colloidal fraction in the 40-60 cm profile reduced the removal capacity of the allophanic soil. (C) 1998 Elsevier Science Ltd. All rights reserved.