Abstract:
Deinking sludge (DS) is a residue from the waste paper recycling industry. It is a by-product originating
from the deinking process which is designed to remove inks and other impurities from waste papers to
recover usable fibers. The aim of this study was to investigate the possibility of anaerobic digestion (AD)
of DS in order to produce methane (CH4) by degrading organic matter. DS differs clearly from common AD
substrates due to its specific composition. The focus was laid on comparing various inocula in order to
find appropriate microbial consortia. Three inocula from different origins were investigated. After sludge
and inocula characterization, batch AD at a mesophilic (37 C) condition was performed for 21 days to
determine biogas and CH4 potentials as well as sludge biodegradability in comparison to cellulose. The
highest average CH4 yield achieved in the 21 days of the batch experiment was 167 NmL/g organic dry
matter (oDM). However, the CH4 potentials from all experiments did not have a wide range (average
160 NmL/g oDM; standard deviation ±5.0 NmL/g oDM). The highest organic matter degradation achieved
was 31%. It can be stated that conventional AD inocula are usable to degrade DS, but that a significant part
of the oDM was anaerobically not degradable. The overall CH4 yields were lower compared to top AD substrates
such as energy crops, but in a similar range like residue-based AD substrates such as manure.
Since actual DS management is cost-intensive and affecting the profitability of waste paper industry significantly,
AD as a management option with an energetically valuable output is a very promising option
