Valorisation of paper waste sludge via fermentation and pyrolysis

RIDOUT, A.; BOSHOFF, S.; HAIGH, K.; CARRIER, M.; VAN RENSBURG, E.; GÖRGENS, J.:
Cellulose Chemistry and Technology, 50, 439-442 (2016).

Abstract

The pulp and paper industry produces large quantities of paper waste sludge (PWS), typically 100 to 500 kg PWS per ton of paper, usually disposed of by landfill. This material has a high organic content and can thus be used as a feedstock for fermentation and pyrolysis or a combination of the two processes. Low and high ash PWSs (8.5 and 46.7 wt%) were subjected to fast pyrolysis conversion to maximise the bio-oil yield by optimising the reactor temperature and pellet size. Maximum bio-oil yields of 44.5 ± 1.7 daf, wt% at 400 oC, and 59.9 ± 4.1 daf, wt% at 340 oC, for an intermediate pellet size of 4.84 ± 0.15 mm, were attained from the conversion of the low and high PWS, respectively. A thermogravimetric study found that the observed increase in non-condensable gas yield, which corresponded to a decrease in the bio-oil yield, was due to the promotion of exothermic reactions for high heating rates using smaller pellet sizes. PWSs with low and medium ash content were utilized for the production of ethanol via simultaneous saccharification and fermentation. The two samples were screened for fermentation efficiency with different enzyme cocktails and yeast strains and found to vary significantly between different enzymes, but not between different yeast strains. The two samples were further investigated in a fed-batch culture, which indicated that medium ash PWS was a better feedstock for bioethanol production compared to low ash PWS. It is expected that the fermentation residue will be suitable for pyrolysis.

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