Abstract

Allophanic soil, natural and activated by acidification or calcination was used to adsorb organic recalcitrant compounds (lignin and chlorophenols) from biologically pre-treated kraft mill effluent. A synthetic non crystalline aluminosilicate like allophane coated with iron oxide (Al-Si-Fe) was used as control for comparison purposes. It was observed that the adsorption capacity of the allophanic soil increased at higher solid/solution ratio, and at lower pH values. The highest total phenolic compounds removal was obtained between pH 4.0 and 4.5 for natural and activated soil using a solid/solution ratio of 1:5, and for synthetic aluminosilicate using 300 mg in 30 mL of effluent solution. Soil activated by calcination procedure presented the highest total phenolic compounds adsorption capacity (71–85%) for untreated and aerobic or anaerobic pre-treated effluent. The specific chlorophenols analysis indicated that pentachlorophenol (PCP) was almost completely adsorbed onto the allophanic soil (>99%), and that over 79% of the 2,3,4,6-tetrachlorophenol (TeCP) was adsorbed, independent of the biological pre-treatment type and the soil activation procedure. On the other hand, 2,4-dichlorophenol (DCP) coming from both aerobic and anaerobic treated effluent was poorly removed (24–30%) when natural soil was used for adsorption; whereas in calcinated and acidified soil DCP removal was more than 71%.