Methanogenic Process Research Articles

Process contribution evaluation for COD removal and energy production from molasses wastewater in a BioH2-BioCH4-MFC-integrated system.

In this study, a three-stage-integrated process using the hydrogenic process (BioH2), methanogenic process (BioCH4), and a microbial fuel cell (MFC) was operated using molasses wastewater. The contribution of individual processes to chemical oxygen demand (COD) removal and energy production was evaluated. The three-stage integration system was operated at molasses of 20g-COD L-1, and each process achieved hydrogen production rate of 1.1±0.24 L-H2 L-1 day-1, methane production rate of 311±18.94mL-CH4 L-1 day-1, and production rate per electrode surface area of 10.8±1.4gm-2 day-1. The three-stage integration system generated energy production of 32.32kJg-COD-1 and achieved COD removal of 98%. The contribution of BioH2, BioCH4, and the MFC reactor was 20.8, 72.2, and, 7.0% of the total COD removal, and 18.7, 81.2, and 0.16% of the total energy production, respectively. The continuous stirred-tank reactor BioH2 at HRT of 1 day, up-flow anaerobic sludge blanket BioCH4 at HRT of 2 days, and MFC reactor at HRT of 3 days were decided in 1:2:3 ratios of working volume under hydraulic retention time consideration. This integration system can be applied to various configurations depending on target wastewater inputs, and it is expected to enhance energy recovery and reduce environmental impact of the final effluent.

Latitudinal distribution of microbial communities in anaerobic biological stabilization ponds: effect of the mean annual temperature.

SummaryConsidering wide utilization and high methane fluxes from anaerobic biological stabilization ponds (ABSPs), understanding the methanogenesis in ABSPs is of fundamental importance. Here we investigated the variation and impact factors of methanogenesis in seven ABSPs that spanned from the north to the south of China. Results showed that methanogen abundance (7.7 × 109–8.7 × 1010 copies g−1 dry sediment) and methanogenic activities (2.2–21.2 μmol CH 4 g−1 dry sediment h−1) were considerable for all sediments. Statistical analysis demonstrated that compared with other factors (ammonium, pH, COD and TOC), mean annual temperature (MAT) showed the lowest P value and thus was the most important influencing factor for the methanogenic process. Besides, with the increasing MAT, methanogenic activity was enhanced mainly due to the shift of the dominant methanogenic pathway from acetoclastic (49.8–70.7%) in low MAT areas to hydrogenotrophic (42.0–54.6%) in high MAT areas. This shift of methanogenic pathway was also paralleled with changes in composition of bacterial communities. These results suggested that future global warming may reshape the composition of methanogen communities and lead to an increasing methane emission from ABSPs. Therefore, further research is urgently needed to globally estimate methane emissions from ABSPs and re‐examine the role of ABSPs in wastewater treatment.

Two-stage thermophilic fermentation and mesophilic methanogenic process for biohythane production from palm oil mill effluent with methanogenic effluent recirculation for pH control

Two-stage thermophilic fermentation and mesophilic methanogenic process with methanogenic effluent recirculation to hydrogen reactor for biohythane production from palm oil mill effluent (POME) was investigated. Maximum hydrogen (4.1 L H2/L-POME) and methane production (16.6 L CH4/L-POME) from POME in batch tests were achieved at 30% recirculation rate of methanogenic effluent. Continuous hydrogen production of without and with recirculation phase was 2.2 and 3.8 L H2/L-POME, respectively. Continuous methane production of without and with recirculation phase was 12.2 and 14 L CH4/L-POME, respectively. Both reactor effluents were effective to keep at optimal pH with 2 times increasing in hydrogen production. The hydrogen and methane yield were 135 mL H2/gVS and 414 mL CH4/gVS, respectively. Biohythane gas composition was composed 13.3% of hydrogen, 54.4% of methane and 32.2% carbon dioxide. Two-stage process with methanogenic effluent recirculation flavored Thermoanaerobacterium sp. in the hydrogen reactor and efficiently for energy recovery from POME.

Distribution Characteristics of Methanogens in Urban Sewer System

A study was conducted through a 1200 m-PVC-pipe-reactor, which was used to simulate the urban sewer system. Gas chromatography, liquid chromatography and 454 high-throughput sequencing were utilized to study the variation of substrates during the methanogenic process and the distribution characteristics of methanogens in the sewer system. The results showed that the concentration of methane increased along the sewer system, which illustrated that methanogens existed in the sewer network. The methanogens mainly contained <i>Methanosarcina, Euryarchaeota</i>_unclassified and <i>Methanobacteriaceae</i>_unclassified. The distinct succession which <i>Euryarchaeota</i>_unclassified replaced <i>Methanosarcina</i> to be the first dominant microbial genus between 800-1000 m of the sewer system. Formic acid, methanol, methylamine, acetic acid and hydrogen were available substrates for methanogens. Among these substrates, acetic acid was the primary substrate for methanogen. The variation trends of these substrates were first increasing and then decreasing along the length of the sewer system, which led to the succession phenomenon of methanogens in the sewer system.

Improvement of methane production from rice straw with rumen fluid pretreatment: A feasibility study

To overcome the inherent recalcitrance of rice straw during anaerobic digestion process, effective pretreatment is required for promoting methane production. In the present study, a biological pretreatment using rumen fluid was proposed. The rice straw was pretreated with the rumen fluid at 39 °C for 120 h under anaerobic conditions. Various volatile fatty acids, especially acetic acid and propionic acid, were produced by the rumen fluid pretreatment. The methanogenic process was carried out over a 30-day anaerobic digestion. The results indicated that the optimal pretreatment time for anaerobic digestion was 24 h, resulting in a biogas production increase of 66.5%, a methane yield increase of 82.6% and a technical digestion time decrease of 40.0%, compared with the control. At the end of anaerobic digestion, degradation efficiency of total solid and volatile solid was respectively improved by 16.4–33.3% and 14.8–31.7% for rumen fluid pretreatment. The promoted methane production and organic matter degradation could be mainly attributed to the effective hydrolysis of rice straw by the mixed microorganisms in rumen fluid. Methane production could be well explained by modified Gompertz model rather than the first order model, and a higher methane production rate of 29.31 ml/(gVS·d), a rapider hydrolysis rate of 0.09 1/d, and a shorter lag phase of 1.62 d were obtained after 24 h pretreatment. Therefore, the rumen fluid pretreatment is promising for effective production of methane from rice straw and reduction of rumen fluid discharge from slaughterhouse.

Distribution and origin of dissolved methane, ethane and propane in shallow groundwater of Lower Saxony, Germany

More than 90% of Germany's domestic natural gas production and reserves are located in Lower Saxony, North Germany. Recently, research has been intensified with respect to unconventional shale gas, revealing a large additional resource potential in northern Germany. However, many concerns arise within the general public and government/political institutions over potential groundwater contamination from additional gas wells through hydraulic fracturing operations.In order to determine the naturally occurring background methane concentrations, ∼1000 groundwater wells, covering ∼48 000 km2, have been sampled and subsequently analyzed for dissolved methane, ethane and propane and the isotopic composition of methane (δ13C).Dissolved methane concentrations cover a range of ∼7 orders of magnitude between the limit of quantification at ∼20 nl/l and 60 ml/l. The majority of groundwater wells exhibit low concentrations (<1 μl/l), a small number of samples (65) reveal concentration in the range >10 ml/l. In 27% of all samples ethane and in 8% ethane and propane was detected. The median concentration of both components is generally very low (ethane 50 nl/l, propane 23 nl/l).Concentrations reveal a bimodal distribution of the dissolved gas, which might mirror a regional trend due to different hydrogeological settings. The isotopic composition of methane is normally distributed (mean ∼ −70‰ vs PDB), but shows a large variation between −110‰ and +20‰. Samples with δ13C values lower than −55‰ vs PDB (66%) are indicative for methanogenic biogenic processes. 5% of the samples are unusually enriched in 13C (≥25‰ vs PDB) and can best be explained by microbial methane oxidation.According to a standard diagnostic diagram based on methane δ13C values and the ratio of methane over the sum over ethane plus propane (“Bernard”-diagram) less than 4% of the samples plot into the diagnostic field of typical thermogenic natural gases. However, in most cases only ethane has been detected and the remaining less than 15 samples demonstrate an uncommon ratio of ethane to propane compared to typical thermogenic hydrocarbons. These data do not suggest a migration of deeper sourced gases, but a thermogenic source cannot be excluded entirely for some samples. However, ethane and propane can also be generated by microbial processes and might therefore represent ubiquitous background groundwater abundances of these gases. Nevertheless, our data suggest that due to the exceedingly low concentration of ethane and propane, respective concentration changes might prove to be a more sensitive parameter than methane to detect possible migration of deeper sourced (thermally generated) hydrocarbons into a groundwater aquifer.

Effects of multiple inhibitory components on anaerobic treatment processes in municipal solid waste incineration leachate.

This study served to investigate the comparative and combined effects of calcium, ammonia nitrogen, and aquatic humic substances (AHS) on specific methanogenic activity (SMA) in municipal solid waste leachate at mesophilic conditions. Using orthogonal experiments, anaerobic granular sludge was cultured with different concentrations combinations of the three added components for 13days. The combination of 6000mg/L calcium, 400mg/L ammonia nitrogen, and 4000mg/L AHS was the most inhibitory combination on the SMA of granular sludge, with a calculated 4.49mL (standard temperature and atmospheric pressure) (STP) CH4/(gVSS·d) of SMA. The SMA with the addition of the inhibitory components was much lower than the control group's (1000mg/L calcium, 200mg/L ammonia nitrogen and 2000mg/L AHS) with a calculated 12.97mL (STP) CH4/(gVSS·d) of SMA. Calcium was the major inhibitor among the three components followed by AHS. High concentrations of calcium significantly inhibited the utilization of propionate and butyrate in the substrate and further affected the methanogenic process.

Effect of control of pH in anaerobic digestion of organic fraction of municipal solid waste

Anaerobic digestion often encounters the problem of higher population of the acid-forming bacteria relative to the slower growing methanogenic bacteria which inhibits the methanogenic process leading to problems such as low gas yield and process instability. In this study, anaerobic digestion of organic fraction of municipal solid waste has been carried out in two identical model laboratory-scale single stage anaerobic digesters simultaneously; one without the control of pH and other with the control of pH, with same substrate keeping all other conditions identical. Results indicated that the hydraulic retention time of AD reaction could be reduced by at least seven days and the overall efficiency of gas production of the digester could be increased by more than 21.95% (at 50 days time) by the control of pH in the digester.

Distinctive non-methanogen archaeal populations in anaerobic digestion.

Methanogens define the archaeal communities involved in anaerobic digestion. Recently, non-methanogen archaeal populations have been unexpectedly identified in anaerobic digestion processes. To gain insight into the ecophysiology of these uncharacterized archaeal populations, for the first time, a phylogenetic analysis was performed on a collection of non-methanogen archaeal 16S rRNA gene sequences from anaerobic digesters of broad geographic distribution, revealing a distinct clade formed by these sequences in subgroup 6 of the Miscellaneous Crenarchaeotal Group in the newly proposed archaeal phylum Bathyarchaeota. This exclusive phylogenetic assemblage enabled the development of a real-time quantitative PCR (qPCR) assay specifically targeting these non-methanogen archaeal populations in anaerobic digestion. Application of the qPCR assay in continuous anaerobic digesters indicated that these archaeal populations were minor constituents of the archaeal communities, and the abundance of these populations remained relatively constant irrespective of process perturbations. Analysis of the archaeal populations in methanogenic communities further revealed the co-occurrence of these non-methanogen archaea with acetoclastic methanogens. Nevertheless, the low abundance of non-methanogen archaea as compared with acetoclastic methanogens suggests that the non-methanogen archaeal populations were not major players in animal waste-fed methanogenic processes investigated in this study and the functions of these archaeal populations remain to be identified.

Metagenome approaches revealed a biological prospect for improvement on mesophilic cellulose degradation.

Improvement on the bioconversion of cellulosic biomass depends much on the expanded knowledge on the underlying microbial structure and the relevant genetic information. In this study, metagenomic analysis was applied to characterize an enriched mesophilic cellulose-converting consortium, to explore its cellulose-hydrolyzing genes, and to discern genes involved in methanogenesis. Cellulose conversion efficiency of the mesophilic consortium enriched in this study was around 70%. Apart from methane, acetate was the major fermentation product in the liquid phase, while propionate and butyrate were also detected at relatively high concentrations. With the intention to uncover the biological factors that might shape the varying cellulose conversion efficiency at different temperatures, results of this mesophilic consortium were then compared with that of a previously reported thermophilic cellulose-converting consortium. It was found that the mesophilic consortium harbored a larger pool of putative carbohydrate-active genes, with 813 of them in 54 GH modules and 607 genes in 13 CBM modules. Methanobacteriaceae and Methanosaetaceae were the two methanogen families identified, with a preponderance of the hydrogenotrophic Methanobacteriaceae. In contrast to its relatively high diversity and high abundance of carbohydrate-active genes, the abundance of genes involved in the methane metabolism was comparatively lower in the mesophilic consortium. A biological enhancement on the methanogenic process might serve as an effective option for the improvement of the cellulose bioconversion at mesophilic temperature.

Sulfur Poisoning of the Reverse Water Gas Shift Reaction (RWGSR) on Anode Supported SOFCs

SOFCs have the advantage of being able to operate with fuels other than hydrogen due to their high operation temperatures. Among these, biogas from anaerobic digestion is considered to be carbon neutral and highly underused for power generation. Methane-free biogas, which can be produced by inhibition of the methanogenic process, is an alternative high quality fuel, consisting mainly of CO2 (70 to 50%), H2 (30 to 50%) and traces of CO and H2S. The impact of H2S in the ppm range on the performance of anode supported Ni-YSZ SOFC at 750°C is evaluated. An initial voltage drop is observed when the cell is exposed to H2S but the voltage recovers after a few hours of exposure to the impurity. Impedance spectroscopy revealed an increase in the polarization resistance even though the cell voltage was increasing. Furthermore, it was found that this behavior is due to deactivation of the reverse water gas shift reaction (RWGSR); a mathematical model confirmed this conclusion. The poisoning effect is partly reversible under the applied operating conditions. Figure 1

Effect of pretreatment techniques on food waste solubilization and biogas production during thermophilic batch anaerobic digestion

The purpose of this study was to optimize the alkaline, ultrasonication, and thermal pretreatment in order to enhance the solubilization of food waste (FW) for the production of volatile fatty acids, hydrogen, and methane in thermophilic batch anaerobic digestion. Initially, the effect of pretreatment techniques in the acidogenic phase was studied, and the optimal combinations of different conditions were determined. It was found that each pretreatment technique affected food waste solubilization differently. Alkaline pretreatment increased hydrogen yield in the acidogenic sludge by four times over control. COD solubilization was increased by 47 % when FW pre-heated at 130 °C for 60 min. Ultrasonication at 20 kHz and 45 min reduced processing time to 38 h from the 60–80 h needed in normal operation. Response surface methodology (RSM) was used to optimize a combination of alkaline, ultrasonication, and thermal pretreatment. Optimized conditions were applied to methanogenic single-stage thermophilic AD process, and their impact on biogas production was monitored. Results showed that FW heated at 130 °C for 50 min geminates biogas production compared to control experiment. In conclusion, a short thermal pretreatment regime could significant affect biogas production in single-stage thermophilic AD.

Counteracting foaming caused by lipids or proteins in biogas reactors using rapeseed oil or oleic acid as antifoaming agents

Foaming is one of the major operational problems in biogas plants, and dealing with foaming incidents is still based on empirical practices. Various types of antifoams are used arbitrarily to combat foaming in biogas plants, but without any scientific support this action can lead to serious deterioration of the methanogenic process. Many commercial antifoams are derivatives of fatty acids or oils. However, it is well known that lipids can induce foaming in manure based biogas plants. This study aimed to elucidate the effect of rapeseed oil and oleic acid on foam reduction and process performance in biogas reactors fed with protein or lipid rich substrates. The results showed that both antifoams efficiently suppressed foaming. Moreover rapeseed oil resulted in stimulation of the biogas production. Finally, it was reckoned that the chemical structure of lipids, and more specifically their carboxylic ends, is responsible for their foam promoting or foam counteracting behaviour. Thus, it was concluded that the fatty acids and oils could suppress foaming, while salt of fatty acids could generate foam.

Comparison of hematite-facilitated anaerobic digestion of acetate and beef extract

The effect of hematite with different specific surface areas (SSA) on anaerobic methanogenic process was investigated in this study using two different carbon sources (acetate or beef extract). Comparative analyses showed that methane generation rate, microbial growth and the starting-up duration were all significantly enhanced by hematite. The reduction rate of high SSA hematite was 2.5–3.5 times greater than that of low SSA hematite. This work indicated that low SSA hematite was superior to high SSA hematite in facilitating methanogenesis which was partially attributed to the lower affinity for the iron-reduction bacteria.

Two-stage thermophilic fermentation and mesophilic methanogen process for biohythane production from palm oil mill effluent

A two-stage thermophilic fermentation and mesophilic methanogenic process for biohythane production from palm oil mill effluent (POME) was investigated. The hydrogen and methane potential from POME were 170–200 L H2 kgCOD−1 and 210–292 L CH4 kgCOD−1, respectively. A continuous two-stage process with hydraulic retention time (HRT) of 2 d for hydrogen reactor and 15 d for methane reactor, obtained 34% higher energy yield than single stage methane production. The hydrogen and methane yields from two-stage were 210 L H2 kgCOD−1 and 315 L CH4 kgCOD−1, respectively with total energy yield of 15.34 MJ kgCOD−1. Mixed hydrogen and methane (biohythane) production rate was 4.4 L biogas L−1d−1 with containing of 51% CH4, 14% H2 and 35% CO2. Hydrogen reactor was dominated with hydrogen producing bacteria of Thermoanaerobacterium thermosaccharolyticum, while acetoclastic Methanoculleus sp. was the dominant methanogen in methane reactor. Two-stage process for biohythane production could efficiently for energy recovery from POME.

Single-stage fermentation process for high-value biohythane production with the treatment of distillery spent-wash

The current communication reports the development of a single-stage biosystem for biohythane production from wastewater treatment. A semi-pilot scale bioreactor with 34L capacity was used for this study. Maximum biohythane production of 147.5±2.4L was observed after five cycles of operation with production rate of 4.7±0.1L/h. The biohythane composition (H2/(H2+CH4)) varied from 0.60 to 0.23 during stabilized fifth cycle of operation. During each cycle of operation, higher H2 fraction was noticed within 12h of cycle period followed by CH4 production for rest of operation (36h). During biohythane production, COD removal efficiency of 60±5% (SDR, 29.0±1.9kg CODr/m3-day) was also achieved. The synergistic function of volatile fatty acids (VFA) production and consumption during process in hybrid biosystem played vital role on the composition of biohythane. The single-stage biosystem facilitates production of high valued and cost efficient biofuel (biohythane) with fewer controls than individual acidogenic and methanogenic processes.

Microbial methane formation in deep aquifers of a coal-bearing sedimentary basin, Germany.

Coal-bearing sediments are major reservoirs of organic matter potentially available for methanogenic subsurface microbial communities. In this study the specific microbial community inside lignite-bearing sedimentary basin in Germany and its contribution to methanogenic hydrocarbon degradation processes was investigated. The stable isotope signature of methane measured in groundwater and coal-rich sediment samples indicated methanogenic activity. Analysis of 16S rRNA gene sequences showed the presence of methanogenic Archaea, predominantly belonging to the orders Methanosarcinales and Methanomicrobiales, capable of acetoclastic or hydrogenotrophic methanogenesis. Furthermore, we identified fermenting, sulfate-, nitrate-, and metal-reducing, or acetogenic Bacteria clustering within the phyla Proteobacteria, complemented by members of the classes Actinobacteria, and Clostridia. The indigenous microbial communities found in the groundwater as well as in the coal-rich sediments are able to degrade coal-derived organic components and to produce methane as the final product. Lignite-bearing sediments may be an important nutrient and energy source influencing larger compartments via groundwater transport.

Performance enhancement of leaf vegetable waste in two-stage anaerobic systems under high organic loading rate: Role of recirculation and hydraulic retention time

Abstract Continuous laboratory-scale experiments were conducted on two-stage anaerobic systems treating vegetable waste (VW) to improve CH 4 production. The acidogenic reactors were employed with a serial methanogenic reactor configuration with volume distribution ratios of 3 L/4 L and 3 L/7 L (acidogenic reactor/methanogenic reactor), as well as recirculation rates (RRs) of 0.8 and 1.6. Results showed that recirculation improved the performance of VW anaerobic digestion under an organic loading rate (OLR) of 2.6 g VS/L/d. The OLR increased from 2.6 g VS/L/d to 3.0 g VS/L/d to compare the stability of the processes and to study the behavior response of serial systems. System control without recirculation was susceptible to overloading and volatile fatty acids (VFAs) utilization was inhibited in the methanogenic reactor, which was implemented as a fixed-bed biofilm reactor with active carbon fiber textiles. These findings indicated overall process failure. The ratio of total volatile fatty acid (TVFA) and alkalinity gives a good indication of the process stability of anaerobic digestion. The TVFA/alkalinity ratio of the methanogenic reactor in the 3 L/4 L configuration, with RR of 1.6, increased to approximately 0.5, which indicates potential imminent failure of the methanogenic process. However, the methanogenic reactorin the 3 L/7 L configuration helped in utilizing the VFA produced by the overloading in the acidogenic reactor, which improved the CH 4 production and conversion efficiency of the system.

Methane and Carbon Dioxide in the Sediment of a Eutrophic Reservoir: Production Pathways and Diffusion Fluxes at the Sediment-Water Interface.

The estimated diffusion fluxes of methane (CH4) and carbon dioxide (CO2) at the sediment–water interface in the Rzeszów Reservoir in southeastern Poland are presented. The relevant studies were conducted during 2009, 2010, and 2011. Calculated fluxes ranged from 0.01 to 2.19 mmol m−2 day−1 and from 0.36 to 45.33 mmol m−2 day−1 for methane and carbon dioxide, respectively. While the values for calculated diffusion fluxes of methane are comparable with those reported for other eutrophic reservoirs, much higher values were obtained here for carbon dioxide. The resulting values of δ13C-CH4 and the fractionation coefficients between methane and carbon dioxide (αCH4-CO2) suggest that methane in the sediment of the Rzeszów Reservoir is produced by acetate fermentation, while the hydrogenotrophic methanogenic process is of successively greater importance with increasing depth. In the top layer of the sediment, 24–72 % of CO2 came from methanogenesis, while the contribution made by the degradation of organic matter by methanogenesis to CO2 was greater in the deeper layer.

Nitrogenase and homologs.

Nitrogenase catalyzes biological nitrogen fixation, a key step in the global nitrogen cycle. Three homologous nitrogenases have been identified to date, along with several structural and/or functional homologs of this enzyme that are involved in nitrogenase assembly, bacteriochlorophyll biosynthesis and methanogenic process, respectively. In this article, we provide an overview of the structures and functions of nitrogenase and its homologs, which highlights the similarity and disparity of this uniquely versatile group of enzymes.