Thermophilic Methane Fermentation Research Articles

PH buffering additives mitigate the inhibition of thermophilic dry methane fermentation

pH buffering additives mitigate the inhibition of thermophilic dry methane fermentation

Improvement of coffee grounds high solid thermophilic methane fermentation by co-digestion with in-situ produced waste activated sludge: Performance and stability

The feasibility of in-situ stabilization in the co-digestion of coffee grounds (CG) and waste activated sludge (WAS) was investigated. Two lab-scale thermophilic continuous stirred tank reactors (CSTR), R1 and R2 were operated with substrates that contained different WAS ratios, S1 (WAS% = 20%) and S2 (WAS% = 30%). During the whole process, there was no external supply of ammonia and trace elements. The volatile solid (VS) removal efficiency of R1 and R2 was comparable, and the biogas yield of R1 (0.467 ± 0.100 L/g-VSin) was slightly higher than R2 (0.408 ± 0.020 L/g-VSin). The total ammonia nitrogen (TAN) of R1 and R2 was 482 ± 32 and 884 ± 24 mg/L, respectively. The stoichiometry formulas of co-digestion were established to calculate the theoretical microbial yield coefficients and the requirements of microorganism reproduction. A comparison between the theoretical requirements and experimental values showed that co-digestion with WAS could avoid supply for an external supply of minerals. For the net energy production, R1 and R2 could generate 6342 and 5069 kWh of electricity daily, respectively.

Batch-Mode Analysis of Thermophilic Methanogenic Microbial Community Changes in the Overacidification Stage in Beverage Waste Treatment.

Biogasification by methane fermentation is an important and effective way to utilize beverage wastes. Beverage wastes are good feedstocks for methane fermentation because of their richness in sugars and proteins, although overacidification and inhibition of methane production caused by high substrate loading often become problematic. This study investigated changes in microbial communities in the overacidification state of the thermophilic methane fermentation process with beverage waste by establishing a simulated batch culture. We assessed 20 mL-scale batch cultures using a simulant beverage waste mixture (SBWM) with different amounts of addition; high cumulative methane production was achieved by adding 5 mL of SBWM (11358 mg—chemical oxygen demand—COD/L of organic loading), and overacidification was observed by adding 10 mL of SBWM (22715 mg—COD/L of organic loading). The results of 16S rRNA amplicon sequence analysis using nanopore sequencer suggested that Coprothermobacter proteolyticus, Defluviitoga tunisiensis, Acetomicrobium mobile, and Thermosediminibacter oceani were predominantly involved in hydrolysis/acidogenesis/acetogenesis processes, whereas Methanothrix soehngenii was the major acetotrophic methane producer. A comparison of microbial population between the methane-producing cultures and overacidification cultures revealed characteristic population changes especially in some minor species under 0.2% of population. We concluded that careful monitoring of population changes of the minor species is a potential indicator for prediction of overacidification.

Acclimation Improves Methane Production from Molasses Wastewater with High Salinity in an Upflow Anaerobic Filter Reactor: Performance and Microbial Community Dynamics.

This study evaluated the performance of an upflow anaerobic filter (UAF) reactor in the thermophilic methane fermentation of hypersaline molasses wastewater. The high salinity (~ 45mS/cm) of the undiluted wastewater completely inhibited the biogas production. An acclimation strategy involving gradient dilution of the molasses wastewater was implemented to gradually increase the salt stress. Consequently, the biogas production was recovered, inhibited only slightly by the high salinity of the undiluted wastewater. The reactor steadily achieved a high total organic carbon (TOC) loading rate of 5g/L/day, with approximately 60% TOC removal efficiency. Acclimation to the gradually increased salt stress leads to a relative abundance of some halotolerant microbes, such as bacteria from Arcobacter, Tissierella, and Ruminococcaceae, which increased as their hydrolytic and acidogenic abilities adjusted to the incremental increase in salinity. Additionally, hydrogenotrophic methanogens, especially Methanoculleus, showed greater resistance to hypersalinity than aceticlastic methanogens. These results suggest that acclimation of the fermentation microbial community to hypersalinity is an effective strategy to improve methane production from hypersaline molasses wastewater in thermophilic UAF reactors.

Biodegradability and methane fermentability of polylactic acid by thermophilic methane fermentation

Polylactic acid (PLA) is considered to be a promising polymer to replace petroleum-based plastics. The aim of this study was to evaluate the biological decomposability of PLA by thermophilic methane fermentation (TMF) and to analyse the microorganisms involved in PLA decomposition. Small- and large-scale batch tests were carried out using disposable cutlery as PLA products and pure poly L-lactic acid (PLLA) pellets. It was found that 70–77% of PLA was decomposed by TMF, based on weight changes. The yield of CH4 was 321–343 mL CH4/g PLA consumed. The addition of bacteria doubled the physicochemical degradation rate of PLA. It was determined that PLA decomposition by TMF was efficient, and that it was enhanced by microbial activity. In particular, lactic acid-consuming bacteria were found to play an important role in PLA decomposition by TMF. Thus, we can conclude that TMF is potentially suitable for PLA treatment and biofuel generation.

Effect of organic loading rate on thermophilic methane fermentation of stillage eluted from ethanol fermentation of waste paper and kitchen waste

Thermophilic methane fermentation was a valid approach for handling the stillage eluted from ethanol fermentation of waste paper and kitchen waste. The wide organic loading rate (OLR) range (2-14g VTS/(L d)) for stable performance and relatively high energy recovery efficiency (79.0%) were achieved, and OLR of 8g VTS/(L d) was optimum for achievement of highest biogas evolution and VTS removal efficiency. Microbial community analysis revealed that hydrolysis of cellulose was the critical step for methane production from the stillage.

Fermentation inhibition of thermophilic methane fermentation with coffee grounds and its mitigation methods

Fermentation inhibition of thermophilic methane fermentation with coffee grounds and its mitigation methods

Thermophilic Dry Methane Fermentation of Distillation Residue Eluted from Ethanol Fermentation of Kitchen Waste and Dynamics of Microbial Communities.

Thermophilic dry methane fermentation is advantageous for feedstock with high solid content. Distillation residue with 65.1% moisture content was eluted from ethanol fermentation of kitchen waste and subjected to thermophilic dry methane fermentation, after adjusting the moisture content to 75%. The effect of carbon to nitrogen (C/N) ratio on thermophilic dry methane fermentation was investigated. Results showed that thermophilic dry methane fermentation could not be stably performed for >10weeks at a C/N ratio of 12.6 and a volatile total solid (VTS) loading rate of 1g/kg sludge/d; however, it was stably performed at a C/N ratio of 19.8 and a VTS loading rate of 3g/kg sludge/d with 83.4% energy recovery efficiency. Quantitative PCR analysis revealed that the number of bacteria and archaea decreased by two orders of magnitude at a C/N ratio of 12.6, whereas they were not influenced at a C/N ratio of 19.8. Microbial community analysis revealed that the relative abundance of protein-degrading bacteria increased and that of organic acid-oxidizing bacteria and acetic acid-oxidizing bacteria decreased at a C/N ratio of 12.6. Therefore, there was accumulation of NH4+ and acetic acid, which inhibited thermophilic dry methane fermentation.

Production of biofuels from sweet sorghum juice via ethanol–methane two-stage fermentation

Sweet sorghum juice is rich in fermentable sugar. Combining ethanol fermentation with methane fermentation to convert sweet sorghum juice to biofuels not only maximizes the energy recovery, but also reduces the environmental load. A two-stage fermentation, consisting of continuous ethanol fermentation and thermophilic methane fermentation, was developed to convert sweet sorghum juice to productions of ethanol and methane. The results of batch ethanol fermentation indicated that it was essential to supplement the feedstock with nutrients in order to improve the ethanol yield. Continuous ethanol fermentation could be performed at 35°C without decreasing the ethanol yield at a dilution rate of 0.3h−1, and ethanol yield and productivity of 88.5% and 20.3g/L/h were obtained, respectively. In contrast, the productivity was improved to 27.4g/L/h by increasing the dilution rate to 0.4h−1 at a fermentation temperature of 33°C. The stillage eluted from the ethanol production process was subjected to thermophilic methane fermentation. After adjusting the C/N ratio of the stillage to 40, a total organic carbon (TOC) removal efficiency of 87.0% and gas evolution rate of 1200mL/g-TOC were achieved, even at a high TOC loading rate of 10g/L/d by adding (NH4)2SO4 of 0.1g/L-stillage.

Characterization of methanogenesis, acidogenesis and hydrolysis in thermophilic methane fermentation of chicken manure

The thermophilic methane fermentation of chicken manure (CM) with a total solids (TS) of approximately 10% was investigated with regard to ammonia inhibition. A gradual increase in total ammonia nitrogen to 6000mg/L was observed in the case of raw CM fermentation. A distinct rise in VFA accumulation combined with a low methane production of 0.29L/gVS occurred at a TAN of 4000∼5000mg/L. Biogas production completely ceased when TAN reached 8000mg/L after the addition of NH4HCO3. The high sensitivity of methanogenesis to TAN and free ammonia (FA) was quantitatively confirmed. The IC50 of TAN for methanogenesis, acidogenesis and hydrolysis was 5058, 5305 and 5707mg/L at a pH value of 8.1±0.2. Similar results but with a lower IC50 were obtained for FA inhibition during fermentation. The microbial community analysis revealed significant differences in hydrogenotrophic methanogens and aceticlastic methanogens before and after inhibition.

Microbial community shifts and biogas conversion computation during steady, inhibited and recovered stages of thermophilic methane fermentation on chicken manure with a wide variation of ammonia

The thermophilic methane fermentation of chicken manure (10% TS) was investigated within a wide range of ammonia. Microbiological analysis showed significant shifts in Archaeal and Bacterial proportions with VFA accmulation and CH4 formation before and after inhibition. VFA accumulated sharply with lower methane production, 0.29 L/g VS, than during the steady stage, 0.32 L/g VS. Biogas production almost ceased with the synergy inhibition of TAN (8000 mg/L) and VFA (25,000 mg/L). Hydrogenotrophic Methanothermobacter thermautotrophicus str. was the dominate archaea with 95% in the inhibition stage and 100% after 40 days recovery compared to 9.3% in the steady stage. Aceticlastic Methanosarcina was not encountered with coincided phenomenal of high VFA in the inhibition stage as well as recovery stage. Evaluation of the microbial diversity and functional bacteria indicated the dominate phylum of Firmicutes were 94.74% and 84.4% with and without inhibition. The microbial community shifted significantly with elevated ammonia concentration affecting the performance.

Trace metals requirements for continuous thermophilic methane fermentation of high-solid food waste

The amount of iron, cobalt and nickel required to perform thermophilic methane fermentation using high-solid food waste was examined in this study. To determine this, we devised and applied a theoretical consideration method. Three runs were performed using a completely stirred tank reactor. During the first run, start-up was carried out by decreasing the HRT from 100 to 50 and finally to 30days, which corresponds to a COD loading rate of 1.9, 3.8 and 6.3kgm−3day−1, respectively. Four typical operational parameters—the gas production rate, methane content, pH and total volatile fatty acid (VFA) concentration—were stable except a temporary rise in VFA was observed when the HRT was decreased from 50 to 30days, indicating that the system performed well with COD loading rate of 6.3kgm−3day−1. After day 57 (HRT: 30days, COD loading rate: 6.3kgm−3day−1), the reactor efficiency deteriorated due to the trace metals limitation. A combination of iron, cobalt and nickel (at 10, 1 and 1mgL−1, respectively) was added to the reactor approximately every 45days during the second run. The reduced gas production, methane content and pH were all restored to stable levels after regularly adding the trace metals. During the third run, trace metals were added to the substrate, and no limitation was noted at all. Based on the theoretical consideration and the experimental results, the most suitable values for Fe/COD, Co/COD, Ni/COD are 276, 4.96 and 4.43mgkg−1COD-removed, respectively, for high-solid thermophilic methane fermentation of food waste.

Reduction in environmental impact of sulfuric acid hydrolysis of bamboo for production of fuel ethanol

Fuel ethanol can be produced from bamboo by concentrated sulfuric acid hydrolysis followed by continuous ethanol fermentation. To reduce the environmental impact of this process, treatment of the stillage, reuse of the sulfuric acid and reduction of the process water used were studied. The total organic carbon (TOC) concentration of stillage decreased from 29,688 to 269mg/l by thermophilic methane fermentation followed by aerobic treatment. Washing the solid residue from acid hydrolysis with effluent from the biological treatment increased the sugar recovery from 69.3% to 79.3%. Sulfuric acid recovered during the acid–sugar separation process was condensed and reused for hydrolysis, resulting in a sugar recovery efficiency of 76.8%, compared to 80.1% when fresh sulfuric acid was used. After acetate removal, the condensate could be reused as elution water in the acid–sugar separation process. As much as 86.3% of the process water and 77.6% of the sulfuric acid could be recycled.

Study on applicability and operation factor of thermophilic methane fermentation to garbage treatment in high concentration under once-a-day feeding condition

Study on applicability and operation factor of thermophilic methane fermentation to garbage treatment in high concentration under once-a-day feeding condition

Ecological Significance of Methanogenesis via Acetate Oxidation to Hydrogen Formation in Thermophilic Methane Fermentation Processes

Ecological Significance of Methanogenesis via Acetate Oxidation to Hydrogen Formation in Thermophilic Methane Fermentation Processes

Effect of the Influent TS Concentration on High Solid Thermophilic Methane Fermentation of Organic Fraction of Minicipal Solid Waste

Effect of the Influent TS Concentration on High Solid Thermophilic Methane Fermentation of Organic Fraction of Minicipal Solid Waste

THE ALFALFA PRODUCTIVITY UNDER CONDITIONS OF INSUFFICIENT WATER SUPPLY AND TREATMENT WITH PLANT GROWTH REGULATORS

The paper covers investigation of nitrogen fixation activity, growth processes and seed productivity of alfalfa inoculated with Sinorhizobium meliloti M6 under different water supply and treatment with synthetic and natural plant growth regulators. It was shown, that Polystimuline K, Polystimuline A-6 and Thermophilic Methane Fermentation Products have intensified nitrogen fixation activity of legume-rhizobial symbiosis. PS-K, PS-A-6 have essentially influenced on aboveground alfalfa mass under drought; both PS-K and TMFP under optimal water supply as well as PS-A-6 under limited water supply have intensified plant growth after cutting. It was showed that treatment of alfalfa with PS-K at budding stage partially reduce negative effect of water deficit on seed yield.

Comparison of organic matter degradation and microbial community during thermophilic composting of two different types of anaerobic sludge

Changes in organic matter degradation and microbial communities during thermophilic composting were compared using two different types of anaerobic sludge, one from mesophilic methane fermentation, containing a high concentration of proteins (S-sludge), and the other from thermophilic methane fermentation, containing high concentrations of lipids and fibers (K-sludge). The difference in the organic matter degradation rate corresponded to the difference in the organic matter constituents; the CO 2 evolution rate was greater in the composting of S-sludge than of K-sludge; moreover, the NH 3 evolution resulting from the protein degradation was especially higher in the composting of S-sludge. Then the differences in the microbial communities that contributed to each composting were determined by the PCR-DGGE method. Ureibacillus sp., which is known as a degrader with high organic matter degradation activity, was observed during the composting of S-sludge, whereas Thermobifida fusca, which is a well known thermophilic actinomycete that produces enzymes for lignocellulose degradation, were observed during the composting of K-sludge.

Comparison of thermophilic anaerobic digestion characteristics between single-phase and two-phase systems for kitchen garbage treatment

Lab-scale single-phase and two-phase thermophilic methane fermentation systems (SPS and TPS, respectively) were operated and fed with artificial kitchen waste. In both SPS and TPS, the highest methane recovery ratio of 90%, in terms of chemical oxygen demand by dichromate (CODcr), was observed at an organic loading rate (OLR) of 15 gCODcr/(l.d). The ratio of particle CODcr remaining to total CODcr in the influent was 0.1 and the ratio of NH(4)-N concentration to the input total nitrogen concentration was 0.5 in both SPS and TPS. However, the propionate concentration in the SPS reactor fluctuated largely and was 2 gCODcr/l higher than that in TPS, indicating less stable digestion. Regardless, efficient kitchen waste degradation can be accomplished in both SPS and TPS at an OLR of <20 gCODcr/(l.d), even though TPS may be more stable and easier to maintain. Bacillus coagulans predominated with an occupied ratio of approximately 90% in the acid fermentation reactor of TPS, and then a richer microbial community with a higher Shannon index value was maintained in the methane fermentation reactor of TPS than in the SPS reactor.

High-rate thermophilic methane fermentation on short-chain fatty acids in a down-flow anaerobic packed-bed reactor

In order to maximize the efficiency of methane fermentation on short-chain fatty acids, growth media containing acetic acid and butyric acid as major carbon sources were supplied to a thermophilic down-flow anaerobic packed-bed reactor. The organic loading rate (OLR) to the reactor ranged from 0.2 to 169 kg-dichromate chemical oxygen demand(CODcr)/m(3)-reactor/day, corresponding to a hydraulic retention time (HRT) of between 1.4 h and 20 days. Stable methane production was maintained at HRTs as short as 2 h (OLR=120 kg-CODcr/m(3)/day), with the short-chain fatty acids in the feed almost completely removed during the process. The apparent substrate removal efficiency, determined from the total CODcr values in the influent and effluent, was 75% at short HRTs. However, the actual substrate removal efficiency must have been greater than 75%, since a fraction of substrate was also utilized in microbial cell synthesis, and these cells were part of the measured total CODcr.