Biological sludge stabilisation Part 2: Influence of the composition of waste activated sludge on anaerobic stabilisation

Abstract

An experimental investigation was carried out to establish a relationship between the composition of the organic material of waste activated sludge and the extent of its transformation into biogas in an anaerobic digester. The volatile fraction of waste activated sludge was considered to be composed of an active fraction, formed by live material, and an inactive fraction, which does not exhibit metabolic activity in an aerobic environment. Five different sludges were generated with active fractions varying from 76 to 16% of the volatile sludge mass. The active fractions were calculated from the measured specific utilisation rates. The results of the investigation showed that the conversion efficiency of the organic material in waste activated sludge depended strongly on the sludge composition. In an anaerobic digester operating at 25°C, 53% of the active fraction and 15% of the inactive fraction were digested. The digestion efficiency of the active sludge fraction corresponded to the value obtained for primary sludge.

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