Enzymatic treatment of deinking sludge – effect on fibre and drainage properties

Abstract

This work focused on the enzymatic treatment of deinking sludge (DS), a waste stream arising from German deinked pulp mills. Three industrial DS samples were characterised with respect to chemical composition and fibre morphology. In this study, four cellulase enzyme preparations were tested under neutral pH conditions and one cellulase was identified as suitable for DS conditioning with no need of pH adjustment. Additionally, our approach shows that inorganic particles contained in the DS samples do not negatively affect cellulase activity, as illustrated by respectable hydrolysis yields of up to 61%. Enzymatic treatment of DS led to fibre shortening and fibre fines generation with increasing enzyme dose and incubation time. The dewaterability of enzyme-treated DS samples was tested and the results showed that high amounts of fibre fines enhanced filter cake consolidation during dewatering, resulting in higher cake solids. A 10-14 percentage point increase in cake solids was obtained depending upon the enzyme dose applied, the origin of the DS sample, and the exposure period. Through the enzymatic treatment the annually generated amount of DS in Germany could be reduced by up to 20%, which would mean considerable disposal cost savings.

Enzymatic Hydrolysis of Softwood Derived Paper Sludge by an In Vitro Recombinant Cellulase Cocktail for the Production of Fermentable Sugars

“…The hydrolysis yields by Opt CelMix and the different commercial cellulase preparations were then evaluated after 48 h. Comparable yields of about 90% were obtained by the Opt CelMix, Cellic CTec2 ® and Celluclast ® 1.5 L, while Viscozyme ® L displayed a yield of 26.4% (Figure 7B). High yields from the conversion of paper sludge by the commercial enzymes were expected as a recent study showed that Celluclast ® 1.5 L displayed a hydrolysis yield of 76.8% with the hydrolysis of deinking paper sludge [47]. Comparison of (A) hydrolytic rates after 6 h and (B) glucose yields obtained after 48 h from the hydrolysis of 2% (w/v, dry mass basis) paper sludge for 48 h at 50 °C using the Opt CelMix, Celluclast ® 1.5 L, Cellic ® CTec2 and Viscozyme ® L at a protein loading of 7.5 mg/g biomass.…”

“…The hydrolysis yields by Opt CelMix and the different commercial cellulase preparations were then evaluated after 48 h. Comparable yields of about 90% were obtained by the Opt CelMix, Cellic CTec2 ® and Celluclast ® 1.5 L, while Viscozyme ® L displayed a yield of 26.4% (Figure 7B). High yields from the conversion of paper sludge by the commercial enzymes were expected as a recent study showed that Celluclast ® 1.5 L displayed a hydrolysis yield of 76.8% with the hydrolysis of deinking paper sludge [47].…”

Valorisation of deinking sludge as a substrate for lignocellulolytic enzymes production by Pleurotus ostreatus

“…Breaking down of cellulose fibres in DIS by enzymes has been shown to not only add value to the feedstock, but also significantly reduce the water content and bulk of the sludge that has to be discarded (Steffen et al 2017a). Williams (2017) has studied three different types of paper sludge for ethanol production and has reported that usage of enzymes and break down of cellulose has significantly reduced the water holding capacity and increased the bulk density of all the three types of paper sludge.…”

“…Enzyme performance at high pH values (8.6 in case of our substrate), typically associated with high amounts of mineral fillers present in DIS, is advantageous for many applications in the paper industry, as most of the current commercial cellulases perform best in weakly acidic conditions (pH 5-7) (Steffen et al, 2017a). Other factors that may affect stability and activity of enzymes produced on DIS are remaining organic pollutants or heavy metals (originating from inks).…”