Methane production from lignocellulosic residues
MetadataShow full item record
Aims: Biochar production by intermediate pyrolysis of renewable lignocellulosic biomass to replace traditional carbon material as a reducing agent and energy source in the metallurgical industries produces carbon rich waste streams viz., hemicellulose hydrolysate from hot water extraction (HWE) and aqueous pyrolysis liquid (APL) from pyrolysis requiring efficient treatment before discarding to enhance energy recovery and avoid environmental problems. Anaerobic digestion (AD), a robust biological process, was considered to treat these challenging organic waste streams individually or as co-digestion for enhanced energy recovery in the form of methane. AD of hydrolysate and APL, both individually and as co-digestion, was performed to study the effect of HWE and pyrolysis temperatures and biomass types on the methane yield. Effect of AD temperature and organic load (OL) on methane yield from Norway spruce hydrolysate was also studied. Materials and methods: Air-dried wood chips of Norway spruce and birch were hot water extracted in two different conditions of 140 °C for 300 min and 170 °C for 90 min to produce hemicellulose rich hydrolysate to use as AD substrate. The wood chips (with or without HWE) were pyrolyzed at 550 °C or 400 °C to produce APL which was used as AD substrate. Both hydrolysate and APL were prepared and supplied by RISE-PFI, Trondheim, Norway. The hydrolysates from HWE and the APL from pyrolysis were tested for bio-methane potential (BMP) during batch AD in an Automatic Methane Potential Test System II (AMPTS II, Bioprocess Control® Sweden AB). Syringe batch reactors were used to study the effect of OL on methane yield. Simplified lab scale up flow anaerobic sludge bed (UASB) reactors of 345 mL working volume were used for mesophilic continuous AD of Norway spruce hydrolysates. Results and discussions: Hydrolysate of Norway spruce and birch showed good biodegradability (ranging from 69 to 79 %) in batch AD reactors. The HWE hydrolysates from pretreatment temperature of 170 °C gave a 13 % lower methane yield for birch compared to hydrolysates pretreated at 140 °C (not significant decrease for Norway spruce) in batch AD, while it was 9 % lower for Norway spruce in continuous AD compared to hydrolysates pretreated at 140 °C. This is due to higher concentration of inhibitors (furans and soluble lignin) and possible extraction and formation of higher concentration of recalcitrant compound (soluble lignin) at higher temperature. Birch (hardwood) hydrolysate pretreated at 140°C resulted in higher methane yield (8 %) than Norway spruce (softwood) as hemicellulose extraction is better in hardwood. Hydrolysate of Norway spruce pretreated at 140 °C gave higher methane yield and improved production rate during mesophilic AD (35 °C) compared to thermophilic AD (55 °C) as thermophilic mixed cultures are more susceptible and sensitive to furan inhibitors. However, the result of hydrolysate pretreated at 170 °C was not consistent despite having higher concentration of furan inhibitors. Methane yield of hydrolysate pretreated at 170 °C decreased with increase in OL during the mesophilic AD while hydrolysate pretreated at 140 °C had similar methane yield at all OLs suggesting better performance of hydrolysate pretreated at 140 °C during higher OLs due to lower concentration of inhibitors compared to hydrolysate pretreated at 170 °C. During thermophilic condition, both hydrolysates pretreated at 140 °C and 170 °C were affected negatively with increasing OLs. APL of birch from pyrolysis temperature at 400 °C and 550 °C had a methane yield of 44 % and 49 %, respectively, while a large decrease in methane yield from 59 % to 32 % was observed from the APL of Norway spruce with the increase in pyrolysis temperature from 400 °C to 550 °C, respectively, suggesting that increase in pyrolysis temperature might have increased the concentration of phenols in APL of softwood compared to hardwood as softwood has a higher concentration of lignin, which resulted in lower methane yield. Methane yield from APL of hot water extracted birch at 140 °C and 170°C before pyrolysis (400 °C) improved compared to APL from non-hot water extracted birch and can be attributed to the removal of inhibitors while increasing sugar concentration during HWE. However, HWE at 140 °C before pyrolysis gave lower methane yield from Norway spruce APL had inconsistent result while HWE at 170 °C had no significant effect. A co-digestion ratio of 3:1 (Hydrolysate:APL) improved the methane yield by 40 % and 6 % in Norway spruce and 26 % and 59 % in birch pretreated at 140 °C and 170 °C, respectively, compared to the 1:1 ratio suggesting that adding APL only as an additive is beneficial in terms of methane yield, rate and digestion time than considering as sole AD feed.
Has partsArticle 1: Ghimire, N., Bakke, R. & Bergland, W.H.: Thermophilic Methane Production from Hydrothermally Pretreated Norway Spruce (Picea abies). Applied Sciences 10(14), (2020), 4989. https://doi.org/10.3390/app10144989
Article 2: Ghimire, N., Bakke, R. & Bergland, W.H.: Mesophilic Anaerobic Digestion of Hydrothermally Pretreated Lignocellulosic Biomass (Norway Spruce (Picea abies)). Processes 9(2), (2021), 4989. https://doi.org/10.3390/pr9020190
Article 3: Wijst, C.v.d., Ghimire, N., Bergland, W.H., Toven, K., Bakke, R. & Eriksen, Ø.: Improving Carbon Product Yields in Biocarbon Production by combining Pyrolysis and Anaerobic Digestion. Manuscript submitted to BioResources
Article 4: Ghimire, N., Wijst, C.v.d., Toven, K., Eriksen, Ø., Bakke, R. & Bergland, W.H.: Methane Production in Cascade Processing of Woody Biomass. Manuscript submitted to Science of the Total Environment
Article 5: Ghimire, N., Bakke, R. & Bergland, W.H.: Applied Liquefaction of Lignocellulosic Biomass for Methane Production: A Review. Manuscript submitted to Bioresource Technology