The availability of Cd in aerobically and anaerobically incubated sewagesludge amended by bentonite

摘要

During the evaluation of sewage sludge application on the agricultural land, the total content of potentially toxic elements usually plays a major role, but only available portion of element can be taken by plants, Main objective of the investigation was focused on determination of Cd availability in sewage sludge incubated under aerobic and anaerobic environment and amended by bentonite. Stabilised sludges from five different locations with different properties were incubated for eight month,.; with presence of air (aerated every other week) and without air (pressed into pot, covered and scaled) under controlled conditions (20 degreesC, 80% humidity). Each sludge was incubated as control treatment and with addition of two rates of bentonite in three replications. The available content of Cd was extracted by I mol.l(-1) NH4NO3 every other month and sequential extraction was made twice during incubation, Results showed great differences in Cd availability among tested sludges, Aerobically incubated sludges increased mean amount of mobile Cd in control as well as in bentonite treatments during incubation. Sludge incubated under anaerobic conditions released majority of Cd at the end of incubation. The application of bentonite decreased mean Cd availability under both conditions. Sequential analyses showed transformation of Cd bounds and Cd movement into labile exchangeable and oxide fractions in sludges incubated with presence of air and stable Cd distribution in sludge incubated under lack of air.