Higher Methane Production Rate Research Articles

Combined mesophilic anaerobic and thermophilic aerobic digestion process for high-strength food wastewater to increase removal efficiency and reduce sludge discharge.

In this study, a process that combines the mesophilic anaerobic digestion (MAD) process with thermophilic aerobic digestion (TAD) for high-strength food wastewater (FWW) treatment was developed to examine the removal of organic matter and methane production. All effluent discharged from the MAD process was separated into solid and liquid portions. The liquid part was discarded and the sludge part was passed to the TAD process for further degradation. Then, the digested sludge from the TAD process was recycled back to the MAD unit to achieve low sludge discharge from the combined process. The reactor combination was operated in two phases: during Phase I, 40 d of total hydraulic retention time (HRT) was applied; during Phase II, 20 d was applied. HRT of the TAD process was fixed at 5 d. For a comparison, a control process (single-stage MAD) was operated with the same HRTs of the combined process. Our results indicated that the combined process showed over 90% total solids, volatile solids and chemical oxygen demand removal efficiencies. In addition, the combined process showed a significantly higher methane production rate than that of the control process. Consequently, the experimental data demonstrated that the combined MAD-TAD process was successfully employed for high-strength FWW treatment with highly efficient organic matter reduction and methane production.

Assessment of two-phase olive mill solid waste and microalgae co-digestion to improve methane production and process kinetics

Olive mill solid waste (OMSW) is a pollutant waste coming from olive oil elaboration by the two-phase centrifugation system. OMSW has a high organic matter content and unbalanced carbon to nitrogen (C/N) ratio, 31/1, which avoids obtaining high methane yields in the anaerobic digestion of this waste. In the present study a microalgae, Dunaliella salina, was employed as co-substrate for the OMSW anaerobic digestion in order to decrease the C/N ratio and increase its biodegradability. Different co-digestion mixtures (C/N ratios) were studied. The increase of D. salina from 25% to 50% in the co-digestion mixture clearly increased the biodegradability of the sole substrates. The highest biodegradability was found for the co-digestion mixture 50% OMSW-50% D. salina. Nevertheless, the maximum methane production, 330mLCH4/gVSadded, and the highest methane production rate were obtained for the co-digestion mixture 75% OMSW-25% D. salina, keeping a C/N ratio near to 26.7/1.

Methanosaeta dominate acetoclastic methanogenesis during high‐rate methane production in anaerobic reactors treating distillery wastewaters

AbstractBACKGROUNDAnaerobic treatment of vinasses wastewater can result in high methane production rates, which depends on the ability to maintain a high specific methanogenic activity in the reactor. Here, it was investigated whether methane production could be increased by optimizing (1) temperature and (2) organic loading rate. It was expected that by maintaining high residual acetate concentrations, due to systematic overloading, anaerobic sludge with higher methanogenic activity would develop.RESULTSA pilot‐scale experiment of 180 days showed that Methanosarcina were unable to dominate acetoclastic methanogenesis in an upflow anaerobic sludge bed (UASB) reactor, despite the favorable conditions. This could be attributed to their reduced tendency to incorporate into sludge granules. Conversion rates of 40 to 50 kg COD m−3 d−1 were obtained for vinasses in mesophilic UASB reactors.CONCLUSIONThese high methane production rates open the possibility to achieve electricity production of more than 2 kW m−3 reactor, with concomitant economic perspectives. © 2013 Society of Chemical Industry

Influence of thermophilic aerobic digestion as a sludge pre-treatment and solids retention time of mesophilic anaerobic digestion on the methane production, sludge digestion and microbial communities in a sequential digestion process

In this study, the changes in sludge reduction, methane production and microbial community structures in a process involving two-stage thermophilic aerobic digestion (TAD) and mesophilic anaerobic digestion (MAD) under different solid retention times (SRTs) between 10 and 40 days were investigated. The TAD reactor (RTAD) was operated with a 1-day SRT and the MAD reactor (RMAD) was operated at three different SRTs: 39, 19 and 9 days. For a comparison, control MAD (RCONTROL) was operated at three different SRTs of 40, 20 and 10 days. Our results reveal that the sequential TAD–MAD process has about 42% higher methane production rate (MPR) and 15% higher TCOD removal than those of RCONTROL when the SRT decreased from 40 to 20 days. Denaturing gradient gel electrophoresis (DGGE) and real-time PCR results indicate that RMAD maintained a more diverse bacteria and archaea population compared to RCONTROL, due to the application of the biological TAD pre-treatment process. In RTAD, Ureibacillus thermophiles and Bacterium thermus were the major contributors to the increase in soluble organic matter. In contrast, Methanosaeta concilii, a strictly aceticlastic methanogen, showed the highest population during the operation of overall SRTs in RMAD. Interestingly, as the SRT decreased to 20 days, syntrophic VFA oxidizing bacteria, Clostridium ultunense sp., and a hydrogenotrophic methanogen, Methanobacterium beijingense were detected in RMAD and RCONTROL. Meanwhile, the proportion of archaea to total microbe in RMAD and RCONTROL shows highest values of 10.5 and 6.5% at 20-d SRT operation, respectively. Collectively, these results demonstrate that the increased COD removal and methane production at different SRTs in RMAD might be attributed to the increased synergism among microbial species by improving the hydrolysis of the rate limiting step in sludge with the help of the biological TAD pre-treatment.

Methanogenic capabilities of ANME‐archaea deduced from 13C‐labelling approaches

Anaerobic methanotrophic archaea (ANME) are ubiquitous in marine sediments where sulfate dependent anaerobic oxidation of methane (AOM) occurs. Despite considerable progress in the understanding of AOM, physiological details are still widely unresolved. We investigated two distinct microbial mat samples from the Black Sea that were dominated by either ANME-1 or ANME-2. The (13) C lipid stable isotope probing (SIP) method using labelled substances, namely methane, bicarbonate, acetate, and methanol, was applied, and the substrate-dependent methanogenic capabilities were tested. Our data provide strong evidence for a versatile physiology of both, ANME-1 and ANME-2. Considerable methane production rates (MPRs) from CO2 -reduction were observed, particularly from ANME-2 dominated samples and in the presence of methane, which supports the hypothesis of a co-occurrence of methanotrophy and methanogenesis in the AOM systems (AOM/MPR up to 2:1). The experiments also revealed strong methylotrophic capabilities through (13) C-assimilation from labelled methanol, which was independent of the presence of methane. Additionally, high MPRs from methanol were detected in both of the mat samples. As demonstrated by the (13) C-uptake into lipids, ANME-1 was found to thrive also under methane free conditions. Finally, C35 -isoprenoid hydrocarbons were identified as new lipid biomarkers for ANME-1, most likely functioning as a hydrogen sink during methanogenesis.

Biogas production from wheat straw in batch and UASB reactors: The roles of pretreatment and seaweed hydrolysate as a co-substrate

This research evaluated biogas production in batch and UASB reactors from pilot-scale acid catalysed steam pretreated and enzymatic hydrolysed wheat straw. The results showed that the pretreatment was efficient and, a sugar yield of 95% was obtained. The pretreatment improved the methane yield (0.28m3/kg VSadded) by 57% compared to untreated straw. Treatment of the straw hydrolysate with nutrient supplementation in a UASB reactor resulted in a high methane production rate, 2.70m3/m3.d at a sustainable OLR of 10.4kg COD/m3.d and with a COD reduction of 94%. Alternatively, co-digestion of the straw and seaweed hydrolysates in a UASB reactor also maintained a stable anaerobic process and can thus reduce the cost of nutrients addition. We have shown that biogas production from wheat straw can be competitive by pretreatment, high methane production rate in UASB reactors and also by co-digestion with seaweed hydrolysate.

Role of syntrophic microbial communities in high-rate methanogenic bioreactors

Anaerobic purification is a cost-effective way to treat high strength industrial wastewater. Through anaerobic treatment of wastewaters energy is conserved as methane, and less sludge is produced. For high-rate methanogenesis compact syntrophic communities of fatty acid-degrading bacteria and methanogenic archaea are essential. Here, we describe the microbiology of syntrophic communities in methanogenic reactor sludges and provide information on which microbiological factors are essential to obtain high volumetric methane production rates. Fatty-acid degrading bacteria have been isolated from bioreactor sludges, but also from other sources such as freshwater sediments. Despite the important role that fatty acid-degrading bacteria play in high-rate methanogenic bioreactors, their relative numbers are generally low. This finding indicates that the microbial community composition can be further optimized to achieve even higher rates.

Estimating evolution of δ13CH4 during methanogenesis in the boreal peatland ecosystems based on stoichiometric chemical reactions, microbial dynamics and stable carbon isotope fractionation

A change in natural isotopic composition of products may be used to reveal metabolic pathways of substrate transformation by microbial community (Vavilin, 2012). In this study, data of δ13CH4 obtained during methanization of organic material from three boreal peatland ecosystems, previously measured and evaluated by Galand et al. (2010), was used to describe mathematically a system dynamics of peat transformation. In the system of differential equations, both stoichiometric chemical reactions and an equation for the 13C isotope accumulation in products including isotope fractionation and microbial dynamics were considered. The model confirm that acetoclastic and hydrogenotrophic methanogenesis occurred with high methane production rates during cellulose methanization in the mesotrophic fen (MES) while hydrogenotrophic methanogenesis happened without intermediate acetate production during non-canonical cellulose methanization in the nutrient-poor peat (OLI – oligotrophic fen, OMB – ombrotrophic peat). This was in agreement with Galand et al. (2010). The model showed that a value of δ13CH4 depended on acetoclastic and hydrogenotrophic methanogenesis rates and on coefficients of stable carbon isotopes fractionation. A strong kinetic fractionation factor (1.064–1.087) was used for hydrogenotrophic methanogenesis. The produced volumes of CH4 and CO2 were about 1:1 (MES) and 1:2 (OLI, OMB) which was in accordance with stoichiometric chemical reactions. Inhibition of methanogenesis by methyl fluoride (CH3F) was described in the model assuming exponential decrease of methane production rate in time which was about 3.6 times higher for acetoclastic methanogenesis when compared to hydrogenotrophic methanogenesis. It was confirmed that CH3F resulted in a strong decrease of δ13CH4 in MES only.

Study on Anaerobic Digestion Performance of Kitchen Wastes: Inhibition of Ammonia Nitrogen and Volatile Acid on the <i>Anaerobic methanogenesis</i>

The inhibition of ammonia nitrogen and volatile acid on anaerobic methanogenesis during the anaerobic digestion of kitchen wastes by way of digest fluid backflow was studied. The experiment was conducted at 35°C, and used kitchen wastes as organic carbon source .The results shows that the ammonia nitrogen inhibition concentration is 1400-1700 mg/L. When the ammonia nitrogen concentration rises to 2000 mg/L, the anaerobic methanogenesis efficiency decreased obviously, along with the accumulation of volatile acid. At the feeding organic load of 3.5-4.0kgVS/(m3.d), the anaerobic methanogenesis system was stable operation, the higher VS reduction (72.17%) and the higher methane production rate were obtained..

A numerical study on optimization of multilateral horizontal wellbore patterns for coalbed methane production in Southern Shanxi Province, China

China's southern Shanxi Province contains thick, gassy coals of anthracite rank. These high-methane-content (higher than 500 ft3/ton) coals necessitate pre-mining methane drainage to enhance the health and safety of underground coal workers. Both traditional vertical wells and multilateral horizontal wells, which were shown to perform better, have been drilled in the area in order to effectively reduce the gas content of coals. However, optimization of well drilling patterns is crucial to improve the gas drainage by boosting well performance and resulting in significant additional recovered gas in a cost-effective manner. In this study, exploration borehole data from an undeveloped coalbed methane field in China's Qinshui Basin was obtained where permeability is expected to range from 0.1 to 10 md. Reservoir modeling conducted in this study concludes that in the presence of low permeability coals (less than 1.0 md) well patterns can be optimized to maintain high-methane production rates. In this work, relationships to determine combinations of horizontal lateral spacing and permeability that yield similar production curves were developed in order to maximize production. Pinnate wells with laterals spaced at 600-ft intervals in reservoirs with 2.0 md permeability performed similar to those with 200-ft lateral intervals in 0.5 md reservoirs. Additional similar relationships were drawn for reservoirs ranging from 0.1 to 8.0 md. Furthermore, because of the Qinshui Basin's potential high stress regime, Pitchfork and Pinnate horizontal well patterns were analyzed based on their potential for catastrophic wellbore failure at well junctions and producing well branches. Analyses concluded that Pitchfork wells had a significantly lower risk for significant wellbore loss due to borehole collapse, while providing the opportunity for higher gas recovery in reservoirs exhibiting directional permeability.

Evaluation of Stability Factors in the Anaerobic Treatment of Slaughterhouse Wastewater

The main environmental factors that assured the stability of an anaerobic batch process for the treatment of slaughterhouse wastewater were evaluated. The reactor was inoculated with anaerobic sludge from a distillery wastewater treatment plant. The volume of produced CH4 was proportional to the quantity of organic matter removed matter (measured as Chemical Oxygen Demand, COD). The overall organic matter removal was 75%. The acetic, propionic and butyric acids concentration profiles were similar, where acetic acid had the highest concentration throughout the study period. The response time recorded between the acetogenic and methanogenic stages in this study was two days. The process showed an elevated acidogenic activity of 1.62 g of VFA/g of COD removed and a high Methane Production Rate (MPR) of about 450 ml of CH4/g of COD removed. The anaerobic treatment of slaughterhouse wastewater generated a buffer system which produced sufficient alkalinity to neutralize the effects of Volatile Fatty Acids (VFA) generated during the process.

Activities and distribution of methanogenic and methane‐oxidizing microbes in marine sediments from the Cascadia Margin

We investigated methane production and oxidation and the depth distribution and phylogenetic affiliation of a functional gene for methanogenesis, methyl coenzyme M reductase subunit A (mcrA), at two sites of the Integrated Ocean Drilling Program Expedition 311. These sites, U1327 and U1329, are respectively inside and outside the area of gas hydrate distribution on the Cascadia Margin. Radiotracer experiments using (14)C-labelled substrates indicated high potential methane production rates in hydrate-bearing sediments [128-223 m below seafloor (mbsf)] at U1327 and in sediments between 70 and 140 mbsf at U1329. Tracer-free experiments indicated high cumulative methane production in sediments within and below the gas hydrate layer at U1327 and in sediments below 70 mbsf at U1329. Stable tracer experiments using (13)C-labelled methane showed high potential methane oxidation rates in near-surface sediments and in sediments deeper than 100 mbsf at both sites. Results of polymerase chain reaction amplification of mcrA in DNA were mostly consistent with methane production: relatively strong mcrA amplification was detected in the gas hydrate-bearing sediments at U1327, whereas at U1329, it was mainly detected in sediments from around the bottom-simulating reflector (126 mbsf). Phylogenetic analysis of mcrA separated it into four phylotype clusters: two clusters of methanogens, Methanosarcinales and Methanobacteriales, and two clusters of anaerobic methanotrophic archaea, ANME-I and ANME-II groups, supporting the activity measurement results. These results reveal that in situ methanogenesis in deep sediments probably contributes to gas hydrate formation and are inconsistent with the geochemical model that microbial methane currently being generated in shallow sediments migrates downward and contributes to the hydrate formation. At Site U1327, gas hydrates occurred in turbidite sediments, which were absent at Site U1329, suggesting that a geological setting suitable for a gas hydrate reservoir is more important for the accumulation of gas hydrate than microbiological properties.

Mesophilic and thermophilic anaerobic biodegradability of water hyacinth pre-treated at 80 °C

Water hyacinth ( Eichornia crassipes) is a fast growing aquatic plant which causes environmental problems in continental water bodies. Harvesting and handling this plant becomes an issue, and focus has been put on the research of treatment alternatives. Amongst others, energy production through biomethanation has been proposed. The aim of this study was to assess the anaerobic biodegradability of water hyacinth under mesophilic and thermophilic conditions. The effect of a thermal sludge pre-treatment at 80 °C was also evaluated. To this end, anaerobic biodegradability tests were carried out at 35 °C and 55 °C, with raw and pre-treated water hyacinth. According to the results, the thermal pre-treatment enhanced the solubilisation of water hyacinth (i.e. increase in the soluble to total chemical oxygen demand (COD)) from 4% to 12% after 30 min. However, no significant effect was observed on the methane yields (150–190 L CH 4/kg volatile solids). Initial methane production rates for thermophilic treatments were two fold those of mesophilic ones (6–6.5 L vs. 3–3.5 L CH 4/kg COD·day). Thus, higher methane production rates might be expected from thermophilic reactors working at short retention times. The study of longer low temperature pre-treatments or pre-treatments at elevated temperatures coupled to thermophilic reactors should be considered in the future.

A methodology for optimising feed composition for anaerobic co-digestion of agro-industrial wastes

An optimisation protocol for maximising methane production by anaerobic co-digestion of several wastes was carried out. A linear programming method was utilised to set up different blends aimed at maximising the total substrate biodegradation potential (L CH 4/kg substrate) or the biokinetic potential (L CH 4/kg substrate d). In order to validate the process, three agro-industrial wastes were considered: pig manure, tuna fish waste and biodiesel waste, and the results obtained were validated by experimental studies in discontinuous assays. The highest biodegradation potential (321 L CH 4/kg COD) was reached with a mixture composed of 84% pig manure, 5% fish waste and 11% biodiesel waste, while the highest methane production rate (16.4 L CH 4/kg COD d) was obtained by a mixture containing 88% pig manure, 4% fish waste and 8% biodiesel waste. Linear programming was proved to be a powerful, useful and easy-to-use tool to estimate methane production in co-digestion units where different substrates can be fed.

Strategies for optimizing recovery of the biogas process following ammonia inhibition

Strategies for recovery of ammonia-inhibited thermophilic biogas process, were evaluated in batch and lab-scale reactors. Active methane producing biomass (digested cattle manure) was inhibited with NH 4Cl and subsequently, 3–5 days later, diluted with 50% of water, or with 50% digested manure, or with 50% fresh manure or kept undiluted. Dilution with fresh cattle manure resulted in the highest methane production rate during the recovery period while dilution with digested cattle manure gave a more balanced recovery according to the fluctuations in volatile fatty acids. Furthermore, the process recovery of a 7600 m 3 biogas plant suffering from ammonia inhibition was observed. The ammonia concentration was only gradually lowered via the daily feeding with cattle manure, as is the normal procedure at Danish full-scale biogas plants. Recovery took 31 days with a 40% methane loss and illustrates the need for development of efficient process recovery strategies.

Methane in pristine and impaired mangrove soils and its possible effect on establishment of mangrove seedlings

Pristine and impaired mangrove soils (from road construction, aquaculture, and sewage) in Baja California Sur, Mexico were investigated for methane dynamics, related soil properties, and their impact on initial establishment of black mangrove propagules. All soils (Salic Fluvisols and Histosols) had neutral to alkaline pH, were saline, and had variable organic carbon content, and redox potentials. Most pristine mangrove soils showed low methane concentration, low methane production rates, and no methane emission. Impaired mangrove soil (from aquaculture) and mangrove soil affected by sewage water showed high methane concentration, high methane production rates, and high methane emission, thus acting as a methane source. Elevated methane concentrations, similar to levels detected in the impaired mangrove soil, reduce the growth of seedlings under closed chamber conditions. Addition of sulfate to the soil reversed the trend. These results indicate that impaired mangrove soils in dry climatic regions produce and emit methane and that elevated methane concentration in the vicinity of propagules may affect establishment of mangrove seedlings in impaired mangrove soils.

Anaerobic co-digestion of winery wastewater

The operational performance of anaerobic batch reactors treating winery wastewater (WW) combined with waste activated sludge (WAS) in different proportions was investigated under mesophilic conditions. In these experiments it was shown that for anaerobic digestion of WW alone, methane production rate was lower than the rates achieved when WW and WAS were treated together. When WW was mixed with WAS at a concentration of 50% WW resulted in the highest methane production rates. A simplified anaerobic model was used to determine the main kinetic parameters; maximum COD reduction rate (q(DA)) and maximum methane generation rate (k(max)). The maximum values of q(DA) and k(max) were 16.50 kgCOD COD(-1) d(-1) and 14.34 kgCOD kgCOD(-1) d(-1), respectively.

Electrochemical promotion of catalytic reactions with Pt/C (or Pt/Ru/C)//PBI catalysts

The paper is an overview of the results of the investigation on electrochemical promotion of three catalytic reactions: methane oxidation with oxygen, NO reduction with hydrogen at 135 °C and Fischer–Tropsch synthesis (FTS) at 170 °C in the [CH4/O2(or NO/H2 or CO/H2)/Ar//Pt (or Pt/Ru)//PBI(H3PO4)/H2, Ar] fuel cell. It has been shown that the partial methane oxidation to C2H2 and the C2 selectivity were electrochemically promoted by the negative catalyst polarization. This was also the case in NO reduction with hydrogen for low NO and H2 partial pressures. In both cases the catalytic reactions have been promoted by the electrochemically produced hydrogen. It has been found that the NO reduction with hydrogen on the Pt/PBI strongly depends on NO and hydrogen partial pressures in the working gas mixture. At higher NO and H2 partial pressures the catalysis is promoted by the electrochemical pumping of H+ from the catalyst, i.e. at positive polarization. FTS demonstrated the highest methane production rate (11% of CO conversion) at zero fuel cell voltage.

Effects of bioaugmentation by an anaerobic lipolytic bacterium on anaerobic digestion of lipid‐rich waste

AbstractThe effect of bioaugmentation with an anaerobic lipolytic bacterial strain on the anaerobic digestion of restaurant lipid‐rich waste was studied in batch experiments with a model waste containing 10% lipids (triolein) under two sets of experimental conditions: (A) methanogenic conditions, and (B) initially acidogenic conditions in the presence of only the lipolytic strain biomass (4 days), followed by methanogenic conditions. The bioaugmenting lipolytic strain, Clostridium lundense (DSM 17049T), was isolated from bovine rumen. The highest lipolytic activity was detected at the beginning of the experiments. A higher methane production rate, 27.7 cm3 CH4(STP) g−1 VSadded day−1 (VS, volatile solids) was observed in experiment A with the presence of the bioaugmenting lipolytic strain under methanogenic conditions. The highest initial oleate concentration, 99% of the total oleate contained in the substrate, was observed in the experiments with the bioaugmenting lipolytic strain under treatment A conditions; the levels of palmitate and stearate were also higher until day 15, indicating that the bioaugmentation strategy improved the hydrolysis of the lipid fraction. In general, the results indicated that degradation of the long chain fatty acids (LCFAs) controlled the digestion process. Copyright © 2006 Society of Chemical Industry

Effect of Inoculum Addition Modes and Leachate Recirculation on Anaerobic Digestion of Solid Cattle Manure in an Accumulation System

The effect of both leachate recirculation (at 40 and 50 °C) and the mode of inoculum addition (at 50 °C) on the performance of a non-mixed accumulation (i.e. fed batch) system treating solid cattle wastes was investigated, using laboratory scale reactors at a filling time of 60 days. A relatively high methane production rate (MPR) and low stratification of intermediates occur with leachate recirculation. The leachate recirculation volume flow and methane production rate are smaller at 40 °C than at 50 °C: 0·31 and 0·7 l [CH4] l−1 [reactor] day−1, respectively. The increased MPR at higher temperature is at one hand caused by the increase of microbial activity, at the other hand by the lower viscosity causing the increased leachate recirculation volume. Dividing the inoculum in equal doses and distributing them with the feed positively affects the system behaviour as compared to adding the same inoculum amount at the reactor bottom at the start only. Without addition of inoculum a very poor system performance was observed. The average MPR was 0·2, 0·4 and 0·5 l [CH4] l−1 [reactor] day−1 for the reactor without inoculum, inoculum addition at the reactor bottom and inoculum addition in different equal doses, respectively.