PM07 Pollutant Chemistry Transport, Cycling and Fate
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(PM087) Effect of biosolids on sorption and desorption of copper in chilean soils.

Garrido, T1, Mendoza, J1, Richter, P 1, 1 Universidad de Chile. Facultad de Ciencias Químicas y Farmacéuticas, Santiago, Chile

ABSTRACT- The high content of copper in some agricultural soils in the central zone of Chile may be accounted for either, by an abnormal geochemical content or by an intensive mining activity. On the other hand, biosolids application to soil may modify the sorptive properties of soil, thus modifying copper bioavailability. The purpose of the present study was to assess the effect of biosolids and their soluble fractions on copper mobility in soil. The study was carried out in soils from the central zone of Chile (Mapocho, Rancagua, and Colina series). Two sludges obtained from facultative stabilization ponds (FS) and two activated sludges (AS) were studied. Experiments on sorption of copper at pH 5 were performed in soils amended with 100 ton/ha incubated for 60 days. Assessment was done of the effect of the soluble sludge fraction (SSF) and subfraction of molecular weight >12,000 Da on copper desorption in the soils under study. Total copper contents in the Mapocho, Rancagua, and Colina soils were 474, 1,045, and 78 mg/kg, respectively. The Langmuir two-surface model turned out best to describe the sorption process. At beginning of incubation, the three sludge-amended soils showed an increase in maximum Cu sorption. This increase ranged from 12 to 65%. At 60 days of incubation sorption increase only in Rancagua soil. Mapocho soil with high content of geochemical copper, showed a strong retention of copper, regardless of type of sludge applied. Rancagua soil, instead, which contains copper of an anthropic origin, retain less copper, this effect being more pronounced with FS. The AS, which were obtained in a shorter digestion time, showed a higher content of soluble organic carbon. The amount of copper desorbed by SSF is directly related to the amount of organic carbon present. SSF of molecular weight >12,000 Da was mainly responsible for metal desorption. Funded by Doctorate Thesis Supporting Grant 2003 (Conicyt).

Key words: biosolids, copper sorption, langmuir model, dissolved organic matter

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