Consolidated bioprocessing of paper sludge to acetic acid by clostridial co-culture

Abstract

Thermophilic Clostridium thermocellum (CEL), Clostridium clariflavum (CLA) and Moorella thermoacetica (C. thermoaceticum, ACE) in co-culture were used to directly ferment paper sludge. The triculture system could greatly solubilize cellulose as well as hemicellulose and fermented them into acetic acid. Various microbial inoculum ratios were explored in 0.5-L fermenter and it was found that CEL to CLA to ACE inoculation volume ratio of 1:1:1 provided the highest product concentration and best efficiency. Scale-up to 5.0-L was carried out and resulted into 86.2% carbon conversion efficiency of all saccharides in paper sludge to acetic acid and 90.5% to total products. Such high efficiencies reached without pretreatment and without addition of expensive enzymes consist of a breakthrough towards cost-performant biorefinery. In addition, this work contributes to the yet limited knowledge on the combination of pure anaerobic bacterial cultures.