Improved Methane Yield Research Articles

Influence of mix ratio of potato peel and pig manure on reaction kinetics and methane recovery from anaerobic co-digestion

The potential improvement in methane recovery and reaction kinetics from different mixes of potato peel (PP) and pig manure (PM) in a single stage anaerobic co-digestion/mono-digestion process was investigated in a laboratory study. The highest methane yield of 231 mL/g TCODadded was observed in the 50:50 mix of potato peel and pig manure. Compared to the mono-digested substrates, co-digestion of PP and PM at 75:25, 50:50, and 25:75 synergistically improved methane yield by 17%, 25%, and 11%, respectively. The co-digested mixes also produced methane at a faster rate, with the fastest methane production rate occurring at the 50:50 mix. Thus, co-digestion of potato peel and pig manure enhanced the methane yield and reaction kinetics. Hence, co-digestion rather than mono-digestion should be actively considered when a carbon rich waste (such as potato peel) and nutrient rich waste (such as pig manure) are available within reasonable proximity.

Multicomponent nanoparticles as means to improve anaerobic digestion performance

Sufficient quantity of trace metals is essential for a well performing anaerobic digestion (AD) process. Among the essential trace elements in active sites of multiple important enzymes for AD are iron and nickel ions. In the present study, iron and nickel in the form of Fe2O3 and NiO were coated on TiO2 nanoparticles to be used in batch and continuous operation mode. The effect of TiO2, Fe2O3–TiO2, and NiO–TiO2 nanoparticles on each step of AD process was assessed utilizing simple substrates (i.e. cellulose, glucose, acetic acid, and mixture of H2–CO2) as well as complex ones (i.e. municipal biopulp). The hydrolysis rate of cellulose substrate increased with higher dosages of the coated TiO2 with both metals. For instance, the hydrolysis rate was increased up to 54% at Fe2O3–TiO2 and at a concentration of 23.5 mg/L for NiO–TiO2 it was increased up to 58%, while higher dosage suppressed the hydrolytic activity. Experimental results revealed that low dosages of NiO–TiO2 increased the accumulated methane production up to 24% probably by increasing the enzymatic activity of acetoclastic methanogenesis. NiO–TiO2 showed positive effect on batch and continuous AD of biopulp and improved methane yield up to 8%.

The impact of immersed liquid circulation on anaerobic digestion of rice straw bale and methane generation improvement

Immersed liquid circulation is assumed to improve solid-state anaerobic digestion (SS-AD) with digestate flow convection on the surface of solid-state bed (SSB), which depends on SSB concentration and circulation rate (CR). In this study, the impact of CR on rice straw SS-AD was investigated within a 30 L pilot digester. Results showed that SSB threshold concentration for efficient biogas conversion was 10%–12% TS, achieving the methane yield of 185.3 mL/g VS. Within the threshold, methane production progress and VFAs release could be enhanced simultaneously by rational CR increasing, but no significant methane yield improvement was observed; above, the rapid and stable biogas generation could be acquired with a competitive methane yield of 174.7 mL/g VS (150% CR). No matter within or above the threshold, efficient lingo-cellulosic degradation was always accompanied by the moderate CR for effective methane generation. SSB was proposed to be above threshold for industrial application.

Syntrophic metabolism facilitates Methanosarcina-led methanation in the anaerobic digestion of lipidic slaughterhouse waste

Different inoculum to slaughterhouse waste (SHW) ratios (Ino/SHW) influences the digester performance, substrate utilization, and methane yield through microbial shift and their metabolic syntrophy. Acetoclastic Methanosarcina (68–87%) was dominant in the exponential phase, overpowering the initial abundance of Methanosaeta (86% of methanogens) in the SHW digesters. Positive interactions among acetogenic and acetate-oxidizing species of Clostridium (11%) with Methanosarcina (84% of methanogens) improved the methanogenic activity (292 mL g−1 VSinitial d−1) and final VS utilization (90%) at the highest Ino/SHW loading. In contrast, significant improvement of methane yield (152% higher than the control) at the lowest Ino/SHW loading was attributed to strong syntrophy among Methanosaeta (24% of methanogens) and its exoelectrogenic partners, Bythopirellula (0.52%) and Mariniphaga (0.08%) and the acetogenic Cloacimonas (0.16%) and Longilinea (0.32%). These syntrophic interactions among the core microbiota induced major metabolic activities, including butanoate, glycine, serine and threonine, methane, propanoate, and pyruvate metabolism, and quorum sensing.

Improvement of solid-state anaerobic digestion of broiler farm-derived waste via fungal pretreatment

Fungus, Trichoderma longibrachiatum, was used for the pretreatment of broiler farm derived-lignocellulosic bedding material (rice husk) to enhance the subsequent solid-state anaerobic digestion (SS-AD). Fungal pretreatment efficacy was evaluated through a series of batch studies with respect to carbon-to-nitrogen (C/N) ratio and pretreatment time. Lignocellulosic outer layer structure disruption of the rice husk was prominent under the best fungal pretreatment condition evaluated (C/N ratio of 18.9 and pretreatment time of 7 days). Consequently, the resulting methane yield of 438.1 ± 20.0 NmL/gVSadded was obtained which was ~2.0-folds higher than that of the control (without pretreatment). Furthermore, in semi-continuous SS-AD, fungal pretreatment could significantly enhance digestibility of organic substance in high solid loading (30% total solids) AD process by 3.2-folds and improve microbial kinetic parameters with subsequent daily methane yield improvement by 2.4-folds. Thus, fungal pretreatment could be an environmentally-friendly and effective low-cost approach for broiler farm-derived waste management to enhance SS-AD efficacy.

Improvement of methane production at alkaline and neutral pH from anaerobic co-digestion of microalgal biomass and cheese whey

Over the past decades, biofuels from microalgae have gained increasing attention. In the present work, methane production from mono-digestion of thermochemical microalgal hydrolysate and co-digestion with cheese whey was evaluated in an anaerobic sequencing batch reactor. The reactor was fed with 5 g total chemical oxygen demand (TCOD)/L and operated either at alkaline or neutral pH. The average methane content in the biogas was higher at alkaline pH (83 %) than at neutral pH (61 %), whereas the methane yield from co-digestion was similar at alkaline (233 N mL/g TCOD) and neutral pH (226 N mL/g TCOD), being 1.8-fold higher than the mono-digestion of the microalgal hydrolysate. After increasing stepwise the organic load up to 12 g TCOD/L, the methane production rate reached peaks around 1000 N mL/L-d, being between 200−800 mL/L-d in those stages with lower organic loads. The methane production from the particulate fraction of the microalgal hydrolysate and its co-digestion with cheese whey demonstrated that the particulate fraction was indeed used to produce methane, but co-digestion did not improve methane yield. The results showed that microalgal hydrolysate could be efficiently co-digested with a carbon-rich substrate enhancing methane production.

Dry mesophilic anaerobic co-digestion of vegetable wastes with animal manures using leach bed reactor

Anaerobic digestion is an environmentally sustainable technology for converting a variety of organic solid feedstocks to energy in the form of methane. To improve methane yield, the digestion of more than one waste is commonly applied. This study aimed to investigate the dry anaerobic co-digestion (TS of 20%) of vegetable wastes (VW) and animal manures (cow manure (CM) and poultry manure (PM)) through conducting biochemical methane potential (BMP) assays at different substrate to inoculum (S/I) ratio. Fractionation and fluorescence analyses showed that organic matter of VW was less accessible and less complex compared to that of CM and PM. The highest methane yields of mono-digestion experiments were registered with S/I 0.5. Best results of methane yield were observed by the co-digestion of VW and CM (284 mL/g VS), which was about 2.3-fold higher than that of VW mono-fermentation. This finding was confirmed at a laboratory-scale leach bed reactor. Result showed an increase of biogas yield from 220 to 445 mL/g VS, during mono and co-digestion, respectively. The co-digestion of VW and CM mixture led to the enhancement of both methane yield and digestate quality in comparison to mono-digestion.

Effect of the co‐digestion of agricultural lignocellulosic residues with manure from South American camelids

AbstractThis study aims to evaluate the effects of the co‐digestion of agricultural residues with manure from camelids from the Andean zone. Different combinations of llama manure (LM) and vicuñas (VM) were made with amaranth (AS), quinoa (QS), and wheat (WS) residues. They were fermented using sewage sludge as inoculum. The co‐digestion was evaluated under mesophilic conditions for 40 days. The ratios of volatile substances of substrate / co‐substrate evaluated were 0:100; 25:75; 50:50, 75:25, and 100:0. Two substrate / inoculum ratios (SIR 1:1 and SIR1:2) were also evaluated. The results indicate that the maximum methane accumulation rate is obtained in SIR 1:1 for a VM‐AS ratio (25:75) with 540 mL/g volatile solid (VS). In general, the results did not increase with the increase in inoculum; rather, the tendency to improve methane yield is associated with an increase in the amount of agricultural residues, mainly AS. Regarding the kinetic modeling, the transfer model is the one that best adjusted the predicted values to those observed with an r2 between 0.991 and 0.999, and an RMSE value between 2.06 and 13.62 mL/g (volatile solid) VS. Finally, all the trials presented synergistic effects in their co‐digestion except the digesters formed by LM‐AS, LM‐QS and LM‐WS of SIR 1:2. These presented antagonistic effects in which the addition of the co‐substrate generated competition with the substrates, reducing methane production. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd

The impact of single step ozonation of antibiotics-contaminated waste sludge to biogas production

Antibiotics contamination of the environment is a growing public health concern, due to their persistency, possible chronic effects and spread of antibiotics resistance genes. The aim of the study was to determine efficiency of ozonation of waste biological sludge, contaminated by various antibiotics (400 mg L−1 of Tiamulin, Amoxicillin and Levofloxacin) in terms of inreased biogas production potential. It was confirmed that contaminated waste sludge inhibits overall biogas production in further anaerobic stabilization for 10–30% resulting also in lower methane yield in the gas mixture (14–45%). Ozonation of waste biological sludge was accomplished in batch system for 10 (22–24 mgO3 gvss−1) or 20 (36–69 mgO3 gvss−1) minutes. The impact to biogas production potential was measured for untreated, contaminated, ozonated untreated and ozonated contaminated sludge after its addition to anaerobic sludge in closed system at 37 °C. Ozone at applied doses simultaneously removed antibiotics related inhibition of biogas production and in some cases enhances biogas production (13–18%) with improved methane yield (22–32%). The highest improvement in biogas production potential was determined for Tiamulin while ozonation of Levofloxacin contaminated sludge was less efficient. It was concluded, that proposed ozone doses resulted in removal of inhibition due to the antibiotics but did not lead to economically feasible increase of biogas production and methane yield.

Methane Production from Propionate Enhanced by Met@Fe3O4 via Increasing Microbe–Material Attachment in a Direct Interspecies Electron-Transfer Process

Propionic acid is an important metabolic intermediate of anaerobic digestion, but its biotransformation to methane is difficult. Although Fe₃O₄ was reported to benefit the direct interspecies electron transfer (DIET) in propionate digestion, the poor attachment of Fe₃O₄ to microbes limited further improvement of methane yield. In this study, the use of methionine-modified Fe₃O₄ (Met@Fe₃O₄) aiming at increasing the attachment of Fe₃O₄ to microbes and enhancing the electron transfer to boost methane production from propionate was reported, and its role was explored. It was observed that in the presence of Met@Fe₃O₄, the methane yield and the maximal methane production rate were, respectively, 81.2 and 152.1% greater than those of the control and 37.6 and 82.7% higher than those of Fe₃O₄. The investigation of the mechanism indicated that the lower electrochemical impedance of Met@Fe₃O₄ made it more effective for promoting not only the intracellular electron transfer of acetoclastic methanogenesis but also extracellular DIET mainly rather than Fe₃O₄, resulting in the improvement of enzyme and microbial activities involved in anaerobic propionate degradation. Further studies demonstrated that the protein on the cell surface was more likely to bind to Met@Fe₃O₄ because of the enhanced hydrophilic nature, and the attachment of Met@Fe₃O₄ to microbes was increased, leading to a faster extracellular electron-transfer efficiency. This study provided an alternative method to improve propionate biodegradation for efficient energy recovery.

Filamentous microalgae as an advantageous co-substrate for enhanced methane production and digestate dewaterability in anaerobic co-digestion of pig manure

This study aimed at exploring filamentous microalgae (Tribonema sp.) as an advantageous co-substrate for anaerobic digestion (AD) of pig manure. Its impacts on the AD performance were assessed in terms of methane yield, energy conversion efficiency, digestion kinetics, and digestate dewaterability. The microalgae substantially improved methane yield, AD kinetics, and digestate dewaterability of the AD process. The enhancement in methane yield ranged from 2 to 27.4%, with the maximum enhancement (corresponding to an energy conversion efficiency of 81%) occurring at a mixing ratio of 1:1 (VS basis). The AD kinetics was improved as indicated by the increased hydrolysis rate constants and diminished lag time. The specific resistance to filtration (SRF) of the digestate decreased significantly with the increasing proportion of the microalgae in the co-substrates, which would facilitate digestate processing and valorisation. Subsequently, the high biomass productivity of the microalgae (441 mg/L/d) in liquid digestate would enable sustainable bioenergy production through nutrient recycling.

Electric Field-Driven Direct Interspecies Electron Transfer for Bioelectrochemical Methane Production from Fermentable and Non-Fermentable Substrates

The bioelectrochemical methane production from acetate as a non-fermentable substrate, glucose as a fermentable substrate, and their mixture were investigated in an anaerobic sequential batch reactor exposed to an electric field. The electric field enriched the bulk solution with exoelectrogenic bacteria (EEB) and electrotrophic methanogenic archaea, and promoted direct interspecies electron transfer (DIET) for methane production. However, bioelectrochemical methane production was dependent on the substrate characteristics. For acetate as the substrate, the main electron transfer pathway for methane production was DIET, which significantly improved methane yield up to 305.1 mL/g chemical oxygen demand removed (CODr), 77.3% higher than that in control without the electric field. For glucose, substrate competition between EEB and fermenting bacteria reduced the contribution of DIET to methane production, resulting in the methane yield of 288.0 mL/g CODr, slightly lower than that of acetate. In the mixture of acetate and glucose, the contribution of DIET to methane production was less than that of the single substrate, acetate or glucose, due to the increase in the electron equivalent for microbial growth. The findings provide a better understanding of electron transfer pathways, biomass growth, and electron transfer losses depending on the properties of substrates in bioelectrochemical methane production.

Improving methane yield of oil palm empty fruit bunches by wet oxidation pretreatment: Mesophilic and thermophilic anaerobic digestion conditions and the associated global warming potential effects

Palm oil production is a significant agricultural industry in the South East Asia region and the empty fruit bunch by-product OPEFB is a lignocellulosic biomass left after palm oil recovery, which has shown to be recalcitrant to bioconversion. Pretreatment experiments were carried out in this study to mitigate the recalcitrance of this material using oxygen assisted hydrothermal pretreatment (with 3–9% oxygen loading in the form of H2O2) followed by batch anaerobic digestion at both mesophilic and thermophilic conditions. The optimal pretreatment for OPEFB was found to be with 6% oxygen at mesophilic condition resulting in 43% increase in methane yield over the control while at thermophilic conditions, the ultimate methane yield was ultimately lower, but received within a shorter time period. The gate-to-gate process was analyzed for global warming potential impacts and it was concluded that for the production of methane at the optimal condition resulted in the lowest greenhouse gas emissions (30% less than the control).

A two-stage anaerobic bioconversion of corn stover: Impact of pure bacterial pretreatment on methane production

Abstract Biological pretreatment is feasible for enhancing methane generation with crop residues. Improvement of the degradation efficiency of cellulose has always been the key to improve methane yield. The role of an anaerobic and thermophilic bacterium, Caldicellulosiruptor sp. F32, on the degradation of corn stalk was investigated. A pure bacterial pretreatment system (0.20 v/v), with 20 times CFU of 2.20 × 108 was verified to be beneficial to the deterioration of corn stalk residues and the increase of methane output. The highest methane yield was 250.2 mL/g volatile solid, which was 28% higher than that from the untreated group. In group 4, the concentrations of glucose and volatile fatty acids were higher than those in other groups. Furthermore, the assays by Fourier-transform infrared spectra and X-ray diffraction revealed that the crystallinity indexes of pretreated groups declined. Hence, biology-based pretreatment using pure bacterial system, Caldicellulosiruptor sp. F32, is a potentially effective approach to improve the degradation efficiency of lignocellulosic biomass.

Thermophilic Methane Production from Hydrothermally Pretreated Norway Spruce (Picea abies)

Norway spruce (Picea abies) is an industrially important softwood species available in northern Europe and can be used to produce bio-methane after proper pretreatment to overcome its recalcitrant complex structure. Hot water extraction (HWE) pretreatment at two different conditions (170 °C for 90 min (severity 4.02) and 140 °C for 300 min (severity 3.65)) was applied to extract hemicellulosic sugars from Norway spruce for thermophilic anaerobic digestion (AD) of the hydrolysate. The methane yield of hydrolysate prepared at the lower pretreatment severity was found to be 189 NmL/gCOD compared to 162 NmL/gCOD after the higher pretreatment severity suggesting higher pretreatment severity hampers the methane yield due to the presence of inhibitors formed due to sugars and lignin degradation and soluble lignin, extracted partially along with hemicellulosic sugars. Synthetic hydrolysates simulating real hydrolysates (H170syn and H140syn) had improved methane yield of 285 NmL/gCOD and 295 NmL/gCOD, respectively in the absence of both the inhibitors and soluble lignin. An effect of organic loadings (OLs) on the methane yield was observed with a negative correlation between OL and methane yield. The maximum methane yield was 290 NmL/gCOD for hydrolysate pretreated at 140 °C compared to 195 NmL/gCOD for hydrolyate pretreated at 170 °C, both at the lowest OL of 6 gCOD/L. Therefore, both pretreatment conditions and OL need to be considered for efficient methane production from extracted hydrolysate. Such substrates can be utilized in continuous flow industrial AD with well-adapted cultures with stable organic loading rates.

Effects of Fe-Mn-modified biochar addition on anaerobic digestion of sewage sludge: Biomethane production, heavy metal speciation and performance stability

This study investigated the effects of MnFe2O4-biochar on sludge anaerobic digestion performance, methane production and heavy metal stabilization. The highest cumulative methane yield was achieved when the MnFe2O4-biochar dose was 1.50 g, which was 55.86% higher than control. A suitable dose of MnFe2O4-biochar stimulated methanogenic activities and improved methane yield, whereas excessive addition shows an inhibitory effect on anaerobic digestion. MnFe2O4-biochar addition significantly enhanced the biodegradation of organic matter, as the average volatile fatty acids degradation rate increased by 35.44%, compared to the control. Chemical speciation analyses demonstrated that MnFe2O4-biochar addition was more helpful for immobilization and risk reduction of heavy metals in sewage sludge. Simultaneously, microbial community analysis indicated that MnFe2O4-biochar obviously enriched acetoclastic methanogens Methanosarcina that capable of participating in direct interspecies electron transfer, which could accelerate substrate decomposition and methane production. These findings supply useful information for the resource utilization of sewage sludge.

Additives as a Support Structure for Specific Biochemical Activity Boosts in Anaerobic Digestion: A Review

Anaerobic digestion is an attractive technology for resource management of organic waste and stubble. State of biochemical reactions and activities in anaerobic digestion determines the process stability. Biochemical activities such as syntrophic, metabolic, catalytic and enzymatic activities regulate the anaerobic efficiency for improved methane yield. Inhibitors such as accesses volatile fatty acids, ammonia, sulphur and heavy metals may slow down the anaerobic digestion and may cause reactor failure. However, additives for various biochemical activities may help to diminish the effect of inhibitors as well as improving process stability for enhanced methane yield. This manuscript presents an overview of various additives for enhancing the biochemical activities. The overview consists application of (a) conductive material for improving syntrophic activity, (b) trace metals for metabolic activities, (c) nanoparticles for improving catalytic activity, metabolism and symbiosis during AD, (d) biological additives for enzymatic action and (e) application of zeolite for introducing cation exchange property in anaerobic digestion. Also, comparison of various additives as per biochemical activity has also been performed for a deeper insight of application of additives in anaerobic digestion.

A critical review of pretreatment technologies to enhance anaerobic digestion and energy recovery

Biogas production from different waste resources still has limitations due to its complex structure and slowly biodegradable nature. To improve methane yield and anaerobic digestion performance, various substrate pretreatment methods have been suggested. This paper reviews the latest trends, progress, and research achievements about pretreatment technologies to improve anaerobic digestion efficiency. The pretreatment techniques are divided into four main groups which are physical, chemical, biological, and combined. The effect of inhibitor formation during the pretreatment process is discussed. The energy performance, economics, and environmental impact of these pretreatment technologies are revealed. This study concludes with future trends and emphasizes the necessity of pretreatment methods.

Quantitative visualization of subcellular lignocellulose revealing the mechanism of alkali pretreatment to promote methane production of rice straw

BackgroundAs a renewable carbon source, biomass energy not only helps in resolving the management problems of lignocellulosic wastes, but also helps to alleviate the global climate change by controlling environmental pollution raised by their generation on a large scale. However, the bottleneck problem of extensive production of biofuels lies in the filamentous crystal structure of cellulose and the embedded connection with lignin in biomass that leads to poor accessibility, weak degradation and digestion by microorganisms. Some pretreatment methods have shown significant improvement of methane yield and production rate, but the promotion mechanism has not been thoroughly studied. Revealing the temporal and spatial effects of pretreatment on lignocellulose will greatly help deepen our understanding of the optimization mechanism of pretreatment, and promote efficient utilization of lignocellulosic biomass. Here, we propose an approach for qualitative, quantitative, and location analysis of subcellular lignocellulosic changes induced by alkali treatment based on label-free Raman microspectroscopy combined with chemometrics.ResultsFirstly, the variations of rice straw induced by alkali treatment were characterized by the Raman spectra, and the Raman fingerprint characteristics for classification of rice straw were captured. Then, a label-free Raman chemical imaging strategy was executed to obtain subcellular distribution of the lignocellulose, in the strategy a serious interference of plant tissues’ fluorescence background was effectively removed. Finally, the effects of alkali pretreatment on the subcellular spatial distribution of lignocellulose in different types of cells were discovered.ConclusionsThe results demonstrated the mechanism of alkali treatment that promotes methane production in rice straw through anaerobic digestion by means of a systemic study of the evidence from the macroscopic measurement and Raman microscopic quantitative and localization two-angle views. Raman chemical imaging combined with chemometrics could nondestructively realize qualitative, quantitative, and location analysis of the lignocellulose of rice straw at a subcellular level in a label-free way, which was beneficial to optimize pretreatment for the improvement of biomass conversion efficiency and promote extensive utilization of biofuel.

Anaerobic Co-Digestion of Wastewater Sludge: A Review of Potential Co-Substrates and Operating Factors for Improved Methane Yield

Anaerobic digestion has been widely employed in waste treatment for its ability to capture methane gas released as a product during the digestion. Certain wastes, however, cannot be easily digested due to their low nutrient level insufficient for anaerobic digestion, thus co-digestion is a viable option. Numerous studies have shown that using co-substrates in anaerobic digestion systems improve methane yields as positive synergisms are established in the digestion medium, and the supply of missing nutrients are introduced by the co-substrates. Nevertheless, large-scale implementation of co-digestion technology is limited by inherent process limitations and operational concerns. This review summarizes the results from numerous laboratory, pilot, and full-scale anaerobic co-digestion (ACD) studies of wastewater sludge with the co-substrates of organic fraction of municipal solid waste, food waste, crude glycerol, agricultural waste, and fat, oil and grease. The critical factors that influence the ACD operation are also discussed. The ultimate aim of this review is to identify the best potential co-substrate for wastewater sludge anaerobic co-digestion and provide a recommendation for future reference. By adding co-substrates, a gain ranging from 13 to 176% in the methane yield was accomplished compared to the mono-digestions.