Modern paper companies produce large quantities of sludge when using recycled fiber. These sludges are the residue leftover from the paper recycling process and consist of unusable short cellulose fibers inks and dyes, clay, glues and other residue along with any chemicals used in the recovery process. The main disposal routes for paper sludge are land-spreading as agricultural fertilizer or incineration in CHP plants at the paper mill. However, the shortage of landfill space and more restrictive environmental regulations have made disposal more costly and less desirable.
A recent analysis of the sludges from a carton paperboard mill and a tissue paper mill indicating the cellulose are composed of 50-65% of total dry weight of sludge, which can be an important fiber source for biofuel and biochemical feedstock. These fibers with low amount of lignin make them more digestible for enzyme and the process is much simpler compared with the one from biomass. Prior to hydrolysis, there is a need for pre-cleaning or separation of the contaminants through mechanical/chemical process.
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