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Item type:Publication, Access status: with files , Valorization of deinking sludges from wastepaper recycling: Biogas production and calcium carbonate recovery(2024); Deinking sludges are residues generated from deinking operation during wastepaper recycling. The common treatment option in Europe includes dewatering steps followed by incineration. Incineration of deinking sludge is capital intensive and not sustainable hence it was investigated if it can be valorized energetically by anaerobic digestion and materially by calcium carbonate recovery. Investigations were carried out by characterisation of substrates and execution of experiments. The dry matter of deinking sludges depends on the dewatering stage in treatment plant and is in the range of 2 to 40% fresh mass. The pre-dewatered deinking sludge has a dry matter content of 5 - 16% fresh mass. The organic dry matter of deinking sludges is in the range of 29 to 33% DM. Calcium carbonate and ash contents have the highest fraction of dry matter in deinking sludges and are 47 - 52% DM and 67 - 71% DM respectively. Deinking sludges showed good digestibility with common inocula and their biogas yield was observed to be about half of that of cellulose under similar anaerobic conditions. Pre-dewatered deinking sludge from the mixture of high and medium wastepaper grades showed the highest specific biogas yield (417 ± 0 NL/kg·oDM) followed by those with a mixture of medium wastepaper grades (275 ± 14 NL /kg·oDM) and lastly those from ordinary wastepaper grades (250 ± 21 NL /kg·oDM). A carbon to nitrogen ratio in the range of 29 and 34 is recommended to improve the efficiency of a semi-continuously operated anaerobic digestion of deinking sludge. Within the scope of this study, a hydraulic retention time of 19 days which corresponds to an organic loading rate of 1.6 ± 0.42 kg oDM/m3·d was observed as optimal for anaerobic digestion of deinking sludge using a semi-continuous system. Deinking sludge settles quickly in bioreactors, hence an efficient mixing mechanism during semi-continuous process is recommended. The two-step first order kinetics showed the best fitting for the anaerobic digestion of raw and pre-dewatered deinking sludges from ordinary wastepaper grades. The modified Gompertz model showed the best fit for pre-dewatered deinking sludges from high and medium wastepaper grades. The ashes of deinking sludges and its digestates are rich in calcium carbonate and contain some elements found in portland cement but in different proportion. The ashes contribute to flexural and compressive strength which make them suitable as supplementary building materials. Results obtained from the study show that biogas production from deinking sludges combined with calcium carbonate recovery is a sustainable approach.Publicationtype: Doctoral Thesis28 80 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Improving Methane Yields of Semi-continuous Anaerobic Digestion of Deinking Sludge from Wastepaper Recycling(2020-09-01); ; Purpose: The purpose of the study was to investigate the role of trace elements (TEs) supplementation in connection with the organic load rate (OLR) and the hydraulic retention time (HRT) on methane (CH4) yields in semi-continuous anaerobic digestion of deinking sludge (DS) in order to judge the possibility to use DS as alternative energy source in wastepaper recycling companies. Methods: After substrate characterization, a semi-continuous anaerobic digestion was performed for 74 days using 2-L stirred tank reactors at a mesophilic (37 °C) condition, whereas one of them was supplemented with a mixture of TEs (cobalt, nickel, molybdenum and selenium). The feeding periods had a duration of 4, 7 or 8 days. Results: The highest cumulative CH4 yield after a feeding period was found to be 151 NmL/g oDM after TE supplementation. The TEs-supplementation has resulted in 42% increase in CH4 yield compared to the non-supplemented variant. The increase took place at the end of the experiment. Earlier feeding periods with similar conditions regarding HRT and OLR, did not show an increase. This can be explained by the fact that TEs supplementation requires a longer adaption time for the microorganism. Conclusions: TEs addition has shown a strongly positive impact on CH4 yields. Our results showed that it is possible to receive the same yields in semi-continuous, more practice-close operation, compared to previous potential determination experiments under batch conditions. A further optimization potential is seen by optimizing TEs supplementation in connection with VOA level in the reactor, optimizing C/N ratio and lowering the duration of the feeding intervals. Graphic Abstract: [Figure not available: see fulltext.]Publicationtype: Journal Article29