CH4 Content In Biogas Research Articles

Viscosity influence on kinetics parameters in dry anaerobic digestion

The viscosity that governs mass exchanges is a determining parameter of dry digestion kinetics. This observation leads to the measurement of viscosity influence on key kinetic parameters of digestion such as microbial growth, degradation of COD, biogas production and its CH4 quality. Thus, for limit viscosities at the beginning of digestion in batch mode at 37 °C and 55 °C of potato residues of 18–35 % TS content, the evolution of kinetic parameters is observed. The results show strong microbial growth for 4.39 × 10−2 Pa s and 7.5 × 10−2 Pa s in digestion at 37 °C and 4.12 × 10−2 Pa s in digestion at 55 °C. The reduction of COD is optimal for 7.50 × 10−2 Pa s at 37 °C and 6.57 × 10−2 Pa s at 55 °C. Biogas production is higher for 7.5 × 10−2 Pa s at 37 °C and 4.12 × 10−2 Pa s at 55 °C. Finally, the CH4 content of biogas is higher for 4.39 × 10−2 Pa s and 4.12 × 10−2 Pa s at 37 °C and 55 °C, respectively. These results show that optimal conditions for microbial growth and CH4 production are obtained with the 22 % TS scenario giving a viscosity of 4.39 × 10−2 Pa s at 37 °C and 4.12 × 10−2 Pa s at 55 °C. These results confirm the importance of the viscosity in biochemical kinetics in dry digestion.

Responses of applied voltages on the archaea microbial distribution in sludge digestion

As the development of urban population led to the increase of domestic water consumption, consequently the generation of surplus sludge (SS) produced increasingly during sewage treatment processes. In order to enhance the SS resource utilization efficiency, an electricity-assisted anaerobic digestion (EAAD) system was employed to examine the alterations in the digestion broth and the characteristics of gas production. Additionally, the response of applied voltages on the distribution of archaeal community near various electrodes within the sludge was explored. The results revealed that the application of high voltages exceeding 3.0 V hindered the CH4 production but stimulated the CO2 generation. Subsequently, both CH4 and CO2 production were impeded by the applied voltages. Furthermore, the increased voltages significantly decreased the abundance of Methanomicrobia, Methanosaeta, and Methanosarcina, which were crucial determinants of CH4 content in biogas. Notably, the excessively high voltages intensities caused the AD process to halt and even inactivate the microbial flora. Interestingly, the distribution characteristics of archaeal community were influenced not only by the voltages intensity but also exhibited variations between the anode and cathode regions. Moreover, as the applied voltage intensified, the discrepancy of responses between the cathode and anode regions became more pronounced, offering novel theoretical and technical foundations for the advancement of electricity-assisted with AD technology.

Succinic Production from Source-Separated Kitchen Biowaste in a Biorefinery Concept: Focusing on Alternative Carbon Dioxide Source for Fermentation Processes

This study presents sustainable succinic acid production from the organic fraction of household kitchen wastes, i.e., the organic fraction of household kitchen waste (OFHKW), pretreated with enzymatic hydrolysis (100% cocktail dosage: 62.5% Cellic® CTec2, 31%% β-Glucanase and 6.5% Cellic ® HTec2, cellulase activity of 12.5 FPU/g-glucan). For fermentation, A. succinogenes was used, which consumes CO2 during the process. OFHKW at biomass loading > 20% (dry matter) resulted in a final concentration of fermentable sugars 81–85 g/L and can be treated as a promising feedstock for succinic production. Obtained results state that simultaneous addition of gaseous CO2 and MgCO3 (>20 g/dm3) resulted in the highest sugar conversion (79–81%) and succinic yields (74–75%). Additionally, CH4 content in biogas, used as a CO2 source, increased by 21–22% and reached 91–92% vol. Liquid fraction of source-separated kitchen biowaste and the residue after succinic fermentation were successfully converted into biogas. Results obtained in this study clearly document the possibility of integrated valuable compounds (succinic acid) and energy (biogas) production from the organic fraction of household kitchen wastes (OFHKW).

The Effect of The Combination of Zeolite and Activated Biochar-Based Sugarcane Bagasse on The Increase of CH4 in Biogas with A Different Time Variation

This study aimed to determine the effect of variation in biogas purification time on methane (CH4) content, heating value, and combustion efficiency. The statistical analysis used was a one-way ANOVA analysis. The purification used activated bagasse biochar and zeolite. The variations of purification time were divided into three treatments, which are 10 minutes, 20 minutes, and 30 minutes. The contents of CH4 in biogas with purification times, respectively, were 281201,45 ppm, 313563,05 ppm, and 339112,92 ppm. The biogas field heat value results with purification times were 242.79 kJ, 248.37 kJ, and 255.35 kJ. The biogas’ heat value with purification time was 515.60 kJ, 890.07 kJ, and 849.50 kJ. The results of combustion efficiency with purification times of 10 minutes, 20 minutes, and 30 minutes, respectively, were 47,95%, 28,20%, and 30,84%. Based on the results, it can be concluded that biogas purification using a combination of activated bagasse biochar and zeolite absorbent with different purification times has better values than biogas purification using an adsorbent not activated. It can increase the CH4 content in biogas and biogas field heat value, but it reduces the heat value and biogas combustion efficiency due to incomplete combustion.

Performance of a percolation reactor integrated to solid-state anaerobic garage-type digesters with leachate recirculation for organic fraction of municipal solid waste treatment

Solid-state anaerobic digestion (SSAD) systems have been used for the sustainable treatment of the organic fraction of municipal solid waste (OFMSW). Unlike previous reports considering lab-scale SSAD systems as a unique system, the present study aims to deeper evaluate only the complementary percolation reactor (PR) integrated into the first semi-industrial scale SSAD system in Latin America. An innovative methodology was developed based on the probability function analysis of the monitoring data with target values reported in the literature and a linear correlation matrix to address the relation between different operating parameters. The results indicate that under a maximum organic loading rate of 1.9 kg VS.m−3.d−1, PR achieved a VS removal efficiency of 56 %, producing a highly stabilized inoculum (VS/TS ratio of 0.43). A maximum methane yield of 0.06 m3 CH4.kg VS−1removed and biogas CH4 content up to 76.5 % were reached during the long-term operation of 730 days.

In-situ biogas upgrading with H2 addition in an anaerobic membrane bioreactor (AnMBR) digesting waste activated sludge

Biological in-situ biogas upgrading is a promising approach for sustainable energy-powered technologies. This method increases the CH4 content in biogas via hydrogenotrophic methanogenesis with an external H2 supply. In this study, an anaerobic membrane bioreactor (AnMBR) was employed for in-situ biogas upgrading. The AnMBR was operated in semi-batch mode using waste activated sludge as the substrate. Pulsed H2 addition into the reactor and biogas recirculation effectively increased the CH4 content in the biogas. The addition of 4 equivalents of H2 relative to CO2 did not lead to appreciable biogas upgrading, although the acetate concentration increased significantly. When 11 equivalents of H2 were introduced, the biogas was successfully upgraded, and the CH4 content increased to 92%. The CH4 yield and CH4 production rate were 0.31 L/g-VSinput and 0.086 L/L/d, respectively. In this phase of the process, H2 addition increased the acetate concentration and the pH because of CO2 depletion. Compared with a continuously-stirred tank reactor, the AnMBR system attained higher CH4 content, even without the addition of H2. The longer solid retention time (100 d) in the AnMBR led to greater degradation of volatile solids. Severe membrane fouling was not observed, and the transmembrane pressure remained stable under 10 kPa for 117 d of continuous filtration without cleaning of the membrane. The AnMBR could be a promising reactor configuration to achieve in-situ biogas upgrading during sludge digestion.

CO2 sequestration mediated by wollastonite in anaerobic digestion of sewage sludge: From sequence batch to semi-continuous operation

This study investigated the mechanisms involved in CO2 sequestration under the sequence batch and semi-continuous operation using wollastonite in sludge anaerobic digestion. Wollastonite substantially elevated CH4 content in biogas and played a role in CO2 capture. It increased biogas yield of the glucose due to pH buffering effect but did not increase that of the hydrolysate from thermal alkali pretreated sludge. Under the semi-continuous operation, wollastonite improved the CO2 sequestration, but decreased the biogas yield from 166 to 24 mL/g soluble chemical oxygen demand, since seemingly wollastonite residues inhibited microbes in the sludge. However, the use of dialysis bags to wrap wollastonite offset the negative impact of the wollastonite residues in the sludge, thereby increased biogas yield. The present study is conducive to understanding the mechanisms involved in and proving the feasibility of the CO2 sequestration using wollastonite in sludge anaerobic digestion and its impacts on long-term operation. Consequently, the findings of the study provide key parameters and useful guidelines for scaling up and wollastonite application in anaerobic digestion of sewage sludge.

The impact of reduced graphene oxide (rGO) supplementation on cattle manure anaerobic digestion: Focusing on process performance and microbial syntrophy

At a time when there is a surge in demand for increasing renewable energy production, boosting biomethane production per unit organic matter/waste has become a big challenge and necessity. In this study, the effect of rGO addition on biomethane production from cow manure under mesophilic-batch conditions was investigated. Biomethane production was increased via rGO supplementation at appropriate concentrations. The highest biomethane production, which was 335 mL/gVSad (65 % increase), was obtained by adding 20 mg/L rGO (CM20) while rGO addition slightly increased (up to 5.4 %) the CH4 content of biogas. The microbial community analysis indicated that via rGO supplementation, the dominant bacteria changed from Levilinea to Candidatus Cloacamonas and a more diverse archaeal community was formed. According to this study results, rGO supplementation could be used at biogas plants to boost renewable energy production.

A novel two-stage process for biological conversion of syngas to biomethane

This study shows biomethane production in a novel two-stage syngas biomethanation consisting of the thermophilic anaerobic digestion of sewage sludge combined with an injection of syngas as the first stage. Since the syngas does not contain enough reducing equivalents, the produced biogas was connected to the second stage consisting of the trickle-bed reactor with the external H2 addition (ex-situ) to increase the CH4 content further. The aim was to evaluate the influence of different syngas compositions on the biomethane production in both stages. The results showed that H2 concentration in syngas is the main factor affecting the CH4 content in biogas. Moreover, the ex-situ reactor with H2 addition served to convert the residual CO and CO2, achieving the maximum CH4 content of 94.7% in the produced biomethane. In summary, the two-stage process enables biomethane production without any inhibitory effects on anaerobic sludge digestion.

Biomethanation processes: new insights on the effect of a high H2 partial pressure on microbial communities

BackgroundBiomethanation is a promising solution to upgrade the CH4 content in biogas. This process consists in the injection of H2 into an anaerobic digester, using the capacity of indigenous hydrogenotrophic methanogens for converting the injected H2 and the CO2 generated from the anaerobic digestion process into CH4. However, the injection of H2 could cause process disturbances by impacting the microbial communities of the anaerobic digester. Better understanding on how the indigenous microbial community can adapt to high H2 partial pressures is therefore required.ResultsSeven microbial inocula issued from industrial bioprocesses treating different types of waste were exposed to a high H2 partial pressure in semi-continuous reactors. After 12 days of operation, even though both CH4 and volatile fatty acids (VFA) were produced as end products, one of them was the main product. Acetate was the most abundant VFA, representing up to 94% of the total VFA production. VFA accumulation strongly anti-correlated with CH4 production according to the source of inoculum. Three clusters of inocula were distinguished: (1) inocula leading to CH4 production, (2) inocula leading to the production of methane and VFA in a low proportion, and (3) inocula leading to the accumulation of mostly VFA, mainly acetate. Interestingly, VFA accumulation was highly correlated to a low proportion of archaea in the inocula, a higher amount of homoacetogens than hydrogenotrophic methanogens and, the absence or the very low abundance in members from the Methanosarcinales order. The best methanogenic performances were obtained when hydrogenotrophic methanogens and Methanosarcina sp. co-dominated all along the operation.ConclusionsNew insights on the microbial community response to high H2 partial pressure are provided in this work. H2 injection in semi-continuous reactors showed a significant impact on microbial communities and their associated metabolic patterns. Hydrogenotrophic methanogens, Methanobacterium sp. or Methanoculleus sp. were highly selected in the reactors, but the presence of co-dominant Methanosarcinales related species were required to produce higher amounts of CH4 than VFA.

The combination of 1-octyl-3-methylimidazolium tetrafluorborate with TBAB or THF on CO2 hydrate formation and CH4 separation from biogas

Abstract [C8min] BF4 was used in this work to combine with TBAB or THF for the investigation about thermodynamic and kinetic additives on CO2 and CH4/CO2 hydrates. The results show that [C8min] BF4 has the inhibition effect on the equilibrium of hydrate formation. About the kinetic study, [C8min] BF4 could improve the rate of CO2 hydrate formation and increase the gas uptake in hydrate phase. At the same time, the combination of TBAB and [C8min] BF4 could increase the mole friction of CH4 in residual gas comparing with the data in THF solution. CH4 separation efficiency was strongly enhanced. Since that the size of CO2 and CH4 molecules are similar, CH4 and CO2 could form the similar hydrate, so the recovery of CH4 from biogas decreases lightly. The CH4 content in biogas can purified from 67 mol% to 77 mol% after one-stage hydrate formation. In addition, the combination of THF and [C8min] BF4 do not have obvious promoting effect on CH4 separation comparing with the gas separation results in pure THF solution.

Bioelectrochemically assisted anaerobic digestion system for biogas upgrading and enhanced methane production

The objective of this study was to evaluate the effect of biofilm and external voltage on the performance and microbial community composition of batch-fed, combined anaerobic digestion-bioelectrochemical cell (AD-BEC) systems under different operational conditions. A dextrin/peptone mixture was fed at a range of organic loading rates (0.34 to 1.37g COD/L-d). The hybrid system with both suspended biomass and biofilm without any external potential application achieved a substantially higher initial soluble COD consumption (53.7±2.3% vs. 39.7±3.7) and methane (CH4) production (331 vs. 225mL) within one day of feeding than the conventional AD system (suspended biomass only). Compared to the conventional AD system, the hybrid systems had higher resilience to shock organic loadings. A range of external potential (0.5 to 2.0V vs. Ag/AgCl) was applied to AD-BEC reactors, developed with two different start-up procedures. A potential of 2.0V resulted in water electrolysis leading to a higher CH4 production rate (105 vs. 84mL/L-d) and biogas CH4 content (88.5±1.4 vs. 64.5±1.9%) in the AD-BEC reactor (closed vs. open circuit condition, respectively). Application of external potential enriched putative exoelectrogens at the anode biofilm and hydrogenotrophic methanogens at the cathode biofilm, which may have contributed to the observed enhanced CH4 production in the AD-BEC system. A phylotype related to Methanobacterium formicicum, a hydrogenotrophic methanogen, dominated the archaeal community in the AD-BEC cathode biofilm.

Hydrogen and methane production in a two-stage anaerobic digestion system by co-digestion of food waste, sewage sludge and glycerol

In this study, hydrogen and methane production from co-digestion of food waste (FW), sewage sludge (SS) and raw glycerol (GL) was evaluated in a two-stage acidogenesis-methanogenesis anaerobic system under mesophilic conditions (35 °C). The effect of glycerol addition (1 and 3% v/v) as co-substrate was assessed in ternary mixtures (FW + SS + GL), with the concentration of all substrates kept at 10 g VS/L. Besides contributing to reduce the lag phase of the acidogenic bacterial culture, the presence of GL increased the hydrogen production in all tested conditions and the maximum hydrogen yield was obtained for the FW + SS + 3%GL mixture (179.3 mL H2/g VS). On the other hand, the highest methane production (342 mL CH4/g VS) was achieved in the test supplemented with 1% GL. At 3% GL, abrupt reductions in the biogas CH4 content and pH values resulting from instability in methanogenesis process were noticed over the experiment. By taking into account the hydrogen and methane production stages, the highest energy yield (i.e., 15.5 kJ/g VS) was obtained with the ternary mixture containing 1% GL. Overall, the results of this study demonstrate the feasibility of using glycerol as co-substrate to increase the H2 and CH4 production efficiency in a two-stage anaerobic co-digestion process, allowing simultaneous treatment of three residues (FW, SS and GL) and energy production.

An anaerobic-aerobic sequential batch process with simultaneous methanogenesis and short-cut denitrification for the treatment of marine biofoulings

Although combination of denitritation and methanogenesis for wastewater treatment has been widely investigated, an application of this technology to solid waste treatment has been rarely studied. This study investigated an anaerobic-aerobic batch system with simultaneous denitritation-methanogenesis as an effective treatment for marine biofoulings, which is a major source of intermittently discharged organic solid wastes. Preliminary NO2−-exposed sludge was inoculated to achieve stable methanogenesis process without NO2− inhibition. Both high NH4+-N removal of 99.5% and high NO2−-N accumulation of 96.4% were achieved on average during the nitritation step. Sufficient CH4 recovery of 101 L-CH4 kg-COD−1 was achieved, indicating that the use of NO2−-exposed sludge is effective to avoid NO2− inhibition on methanogenesis. Methanogenesis was the main COD utilization pathway when the substrate solubilization occurred actively, while denitritation was the main when solubilization was limited because of substrate shortage. The results showed a high COD removal efficiency of 96.0% and a relatively low nitrogen removal efficiency of 64.4%. Fitting equations were developed to optimize the effluent exchange ratio. The estimated results showed that the increase of effluent exchange ratio during the active solubilization period increased the nitrogen removal efficiency but decreased CH4 content in biogas. An appropriate effluent exchange ratio with high anaerobic effluent quality below approximately 120 mg-N L−1 as well as sufficient CH4 gas quality which can be used as fuel for gas engine generator was achieved by daily effluent exchange of 80% during the first week and 5% during the subsequent 8 days.

Fast Startup of Semi-Pilot-Scale Anaerobic Digestion of Food Waste Acid Hydrolysate for Biogas Production.

In this study, a fast startup of semi-pilot-scale anaerobic digestion of food waste acid hydrolysate for biogas production was carried out for the first time. During the period of fast startup, more than 85% of chemical oxygen demand (COD) can be degraded, and even more than 90% of COD can be degraded during the later stage of anaerobic digestion. During this anaerobic digestion process, the biogas yield, the methane yield, and the CH4 content in biogas were 0.542 ± 0.056 m3/kgCODconsumption, 0.442 ± 0.053 m3/kgCODconsumption, and 81.52 ± 3.05%, respectively, and these values were high and stable. Besides, the fermentation pH was very stable, in which no acidification was observed during the anaerobic digestion process (outlet pH was 7.26 ± 0.05 for the whole anaerobic digestion). Overall, the startup of this anaerobic digestion can be completed in a short period (the system can be stable 2 days after the substrate was pumped into the bioreactor), and anaerobic digestion of food waste acid hydrolysate is feasible and attractive for industrial treatment of food waste and biogas production.

Simultaneous carbon and nitrogen removal from anaerobic effluent of the cassava ethanol industry

This study investigated the simultaneous carbon and nitrogen removal from anaerobic effluent of cassava stillage using a lab-scale integrated system consisting of an upflow anaerobic sludge blanket (UASB) reactor and an activated sludge (AS) process. Simultaneous denitrification and methanogenesis (SDM) was observed in the UASB with nitrate recirculation. Compared with the blank reactor without recirculation, the overall chemical oxygen demand (COD) removal efficiencies in the combined system with nitrate recirculation were similar (80-90%), while the TN removal efficiencies were significantly improved from 4.7% to 71.0%. Additionally, the anaerobic COD removal efficiencies increased from 21% to 40% as the recirculation ratio decreased from 3 to 1. Although the influent nitrate concentrations fluctuated (60-140mgN/L), the nitrate removal efficiencies could be maintained at about 97% under different recirculation conditions. With the decreasing recirculation ratio from 3 to 1, the CH4 content in biogas improved from 2% to 40% while the N2 content reduced from 95.8% to 50.6%. The 16S rDNA sequencing results indicated that bacteria diversity in anaerobic SDM granular sludge was much higher than archaea. The effect of recirculation ratios on the bacterial and archaeal communities in SDM granular sludge could be further confirmed by the relative abundance of denitrifying bacteria.

Efficient continuous biogas production using lignocellulosic hydrolysates as substrate: A semi-pilot scale long-term study

Traditional solid-state biogas production from lignocellulosic biomass has some issues such as relatively low methane yield, instability of fermentation system, etc., and these might be solved by changing solid-state mode to completely liquid-state mode using lignocellulosic hydrolysates as substrate for biogas production. However, the potential and possibility of this new technology for industrial application is still unclear. In this study, semi-pilot scale long-term biogas production using various lignocellulosic hydrolysates (acid hydrolysates of bagasse, rice straw, and corncob) as substrate was carried out in a 100L up-flow anaerobic bioreactor (internal circulation reactor, IC) for 76days. During operation, biogas was generated almost immediately when the substrate was pumped into bioreactor and the start-up can be finished in short period. Throughout the fermentation process, most COD (>85%) of lignocellulosic hydrolysates was utilized for biogas production. High biogas yield (0.549±0.058 m3/kg COD consumption), methane yield (0.381±0.043 m3/kg COD consumption) and CH4 content in biogas (69.6±5.6%) can be obtained respectively when the fermentation system was stable. Variations of inlet pH value and types of lignocellulosic hydrolysate showed little influence on the operation performance of this fermentation system. Overall, the fermentation scale, operation period, COD removal, biogas yield, CH4 content in biogas, and operation performance with various inlet pH value and different kinds of substrate shows that this technology has great potential and possibility of industrialization.

The influence of biomass agitation on biogas and methane production using the high-solids thermophilic anaerobic digestion

Abstract In this study, we tested the high-solids thermophilic anaerobic digestion of separated cattle slurry solids inoculated by liquid digestate collected from the 1st stage of the wet process operated in an agricultural mesophilic biogas plant. The process without batch agitation (stirring) was carried out in a barrel bioreactor located in the incubator, whereas the process with batch agitation was carried out in a rotating drum bioreactor (rotation speed: 0.1 min−1). In both cases, the biomass batch was non-liquid and the content of total solids was 18.8 wt%. The processes were conducted discontinuously without any addition for 21 days. The total solids content of both batches decreased to about 15 wt%, with only slight liquefaction. The bulk density increased from 500 to 750 kg m−3. The highest biogas production was achieved consistently on the 7th day. During the 21-day period, the unagitated batch produced 0.120 mN 3 of biogas, and the agitated batch produced 32.5% extra. The average CH4 content in biogas from the unstirred batch amounted to 47.7 vol.%, and biogas from the stirred batch reached 46.2 vol.%. The cumulative methane production rates from the unagitated and agitated batches were 0.095 and 0.121 mN 3 kgVS −1, respectively. Thus, the agitation resulted in 28.5% higher methane yield.

Anaerobic Digestion of Macrophytes Algae for Eutrophication Mitigation and Biogas Production

An economy based on biofuels requires production methods which are economically and technically competitive. The production of biogas from biomass by microorganisms is an attractive and ambitious possibility. Marine and lake algae represents a biomass source that could be used for biogas production and their extraction is of benefit for the aquatic environment reducing eutrophication. The goal of the experimental work is to evaluate the algae biomass naturally present in lagoon environment and analyze the biogas resulting from the anaerobic digestion. The Biomethane Potential (BMP) of macrophytes with inoculums from a sewage sludge treatment plant was measured at the University of Perugia. The CH4 content of biogas was approximately 52%, cumulative CH4 yield of 217 Nm3 /t SV was observed after 41 days of digestion.

Analysis of Biogas Produced from Switchgrass by Anaerobic Digestion

Material flow analysis (MFA) was applied to study the process of biogas production from switchgrass using a mid-temperature (35 ± 1 °C) batch anaerobic digestion process. The flow distributions of energy and material, including carbon (C) and nitrogen (N), were analyzed, as were the material and energy conversion efficiencies. The results showed that biogas and CH4 production were 268.80 and 135.31 NmLgVS-1 added, respectively, and the average CH4 content in biogas was 50.34%. Based on the MFA of the anaerobic digestion process, 30.6%, 3.6%, and 65.8% of C was converted into biogas, biogas slurry, and biogas residue, respectively; and 11.7% and 88.3% of N was converted into biogas slurry and biogas residue, respectively. The conversion efficiencies of the material and energy from switchgrass to biogas were 36.1% and 30.1%. Because of the low conversion efficiencies of matter and energy during biogas production, it is necessary to strengthen the secondary use of the fermentation residue. This study provides a basis for the optimization of the anaerobic digestion process and efficient utilization of resources and energy of energy-grass.