Characterization of soluble molecules from thermochemically pretreated sludge

Soluble molecules generated during the thermochemical pretreatment of an industrial microbial biomass were characterized by a dark color and a poor anaerobic biodegradability. Fractionation of this thermochemically pretreated microbial biomass has been investigated in order to identify inhibitory or refractory fractions. An adsorbent resin (Amberlite XAD 7HP) was selected for its ability to partially remove color from the pretreated substrate. Resin treatment or acid precipitation (pH = 3) were both effective in increasing biodegradability and removing biotoxicity from the pretreated microbial biomass. The increase in biodegradability was found to be the consequence of elimination of high-molecular-weight compounds through resin treatment or pH precipitation.