Enzymatic Hydrolysis of Recovered Office Printing Paper with Low Enzyme Dosages to Produce Fermentable Sugars

Abstract

The use of recovered paper and paper manufacturing wastes are a potentially large, concentrated, and convenient raw material for ethanol production via enzyme hydrolysis and fermentation. However, many previous studies in the area have investigated impractically high enzyme charges. In this research, low dosages of enzymes on copy paper (CP) were investigated for the conditions of 5% consistency (w/v) and 50 °C for 48 h. The removal of inorganic filler (mainly calcium carbonate) by washing prior to hydrolysis led to higher sugar yields than the unwashed CP as well as CP acidified to remove the ash. Enzyme adsorption measurement showed that both acid-soluble ash and acid-insoluble ash adsorb enzymes with a greater affinity than fibers. Drying of the fibers (termed hornification) decreased the efficiency of enzyme hydrolysis, confirming previous results. The mechanical refining at 10% consistency in a laboratory refining mill of previously dried fibers improved the sugar recovery to similar or higher levels as never-dried fibers. By plotting water retention value (WRV) versus corresponding sugar recovery, it was shown that WRV is more useful at low enzyme charges reflecting the use of refining and the reversal of hornification. For de-ashed and refined copy paper, the sugar recovery was determined to be 82% and 97% with enzyme dosages of 4 and 8 Filter Paper Unit (FPU)/g oven-dried (OD) substrate.