Characterisation by image analysis of anaerobic sludge from two EGSB reactors treating oleic acid: automatic detection of granules disintegration

Abstract

Suspended and granular sludge from two expanded granular sludge bed (EGSB) reactors fed with oleic acid at organic loads between 2 and 8 kg COD/m³.day was characterised by image analysis. The number, and the average length of free filaments in the dispersed fraction of biomass, and the morphologic changes of granular sludge when exposed to increasing oleic acid concentrations were quantified. Two methods to distinguish fine and non-fine solids by image analysis were validated by a method based on the ratio fine VSS/total VSS. Granules disintegration was detected by these methods. The adsorption of LCFA onto the sludge could be related to the morphology of the non-fine aggregates and to the number of free filaments. The number of free filaments and the average free filament length was significantly higher in the suspended than in the granular sludge. The degradation rate of the adsorbed LCFA decreased sharply as the size of fine aggregates increased, possibly due to internal diffusion limitations of intermediates such as acetate and products such as methane.