Search Results (102)

Today, there is considerable interest in creating artificial microbial consortia to solve various biotechnological problems. The use of such consortia allows for the improvement of process indicators, namely, increasing the rate of accumulation of target products and enhancing the conversion efficiency of the original substrates. In this work, the prospects for creating artificial consortia based on anaerobic sludge (AS) with cells of different yeasts were confirmed to increase the efficiency of methanogenesis in glucose- and glycerol-containing media and obtain biogas with an increased methane content. Yeasts of the genera Saccharomyces, Candida, Kluyveromyces, and Pachysolen were used to create the artificial consortia. Their concentration in the biomass of consortium cells was 1.5%. Yeast cells were used in an immobilized form, which was obtained by incorporating cells into a cryogel of polyvinyl alcohol. The possibility of increasing the efficiency of methanogenesis by 1.5 times in relation to the control (AS without the addition of yeast cells) was demonstrated. Using a consortium composed of methanogenic sludge and yeast cells of the genus Pachysolen, known for their ability to convert glycerol into ethanol under aerobic conditions, the possibility of highly efficient anaerobic conversion of glycerol into biogas was shown for the first time. Analysis of the metabolic activity of the consortia not only for the main components of the gas phase (CH₄, CO₂, and H₂) and metabolites in the cell culture medium, but also for the concentration of intracellular adenosine triphosphate (ATP), controlled by the method of bioluminescent ATP-metry, showed a high level of functionality and thus, prospects for using such consortia in methanogenesis processes. The advantages and the prospect of using the developed consortia instead of individual AS for the treatment of methanogenic wastewater were confirmed during static tests conducted with several samples of real and model waste. Full article

The global production of brewers’ spent grains (BSG) is 37 million tons yearly. Composting represents an eco-friendly method to manage and valorize organic by-products in a circular economy model. This project aims to compare two BSG bin-composting mixtures (BSG and wheat straw with pig slurry solid fraction, MIX1, or sheep manure, MIX2) and approaches (manual turning, MT, and static composting, ST). The two mixtures’ physicochemical characteristics and greenhouse gas (GHG) emissions were assessed during the process. The evolution of physicochemical properties is reported in detail. Headspace samples of GHG emissions were collected and analyzed with gas chromatography coupled with specific detectors. Carbon dioxide (CO₂) emissions were 34.3 ± 0.03 and 31.0 ± 0.06 g C kg⁻¹ fresh matter (FM) for MIX1-MT and MIX2-MT, and 28.8 ± 0.01 and 31.2 ± 0.02 g Ckg⁻¹ FM for MIX1-ST and MIX2-ST. Methane emissions were negligible (all conditions < 0.086 ± 0.00 mg C kg⁻¹ FM). Nitrous oxide (N₂O) emissions from composting are affected by the substrate, bulking material, pile dimension, and manure. Particularly, the total emissions of N₂O, estimated as CO₂ equivalents, were 45.8 ± 0.2 and 63.0 ± 0.4 g CO₂ eq kg⁻¹ FM for MIX1-MT and MIX1-ST, respectively. In both composting approaches, MIX2 showed a low CO₂ equivalent (1.8 ± 0.02 and 9.9 ± 0.05 g CO₂ eq kg⁻¹ FM for MT and ST), likely due to incomplete decomposition. The bin-composting process represents a solution for recycling and reusing organic waste and livestock manure in small to medium-sized breweries. The solid fraction of the pig slurry resulted in the most suitable manure. Full article

As a type of high-water-content agricultural waste, vegetable waste (VW) is extremely prone to spoilage and environmental pollution. Anaerobic digestion (AD) technology can accelerate the degradation of VW; however, its direct reaction might encounter the risk of termination due to excessive acidification. How to effectively prevent excessive acidification and further accelerate the degradation and maturity of VW remains a significant challenge at present. This paper employed the methods of AD of biogas and aerobic treatment (AT) of biogas slurry (BS) to develop a set of three groups of coupled devices for thermostatic anaerobic and aerobic processes with temperature control by solar collectors. The reaction process was further facilitated by adopting a mixture of raw materials and exogenous additives. In Lanzhou, a comparative experiment was carried out to examine the impacts of a blank group (BG) (additive-free), a 1 g/L urea group (UG), and a 1 g/L plant ash group (PG) on the decomposition process of the mixture of cow dung and tomato stems and leaves. The thermostatic batch wet AD stage of the mixed raw materials at (26 ± 2 °C) lasted for 49 days. The substrate after digestion underwent aerobic aeration treatment for 8 h at different temperatures and different aeration rates. The results show that the system could be initiated smoothly and maintain stable operation in winter under the temperature control of the solar collector; adding additives during AD significantly boosted biogas and methane production during the first 28 days, with urea being the most effective. During the subsequent aerobic phase, UG demonstrated the highest bio-effectiveness under optimized conditions of (30 ± 1 °C) and an aeration rate of 12 L/min. Comprehensive analysis revealed that the optimal operation strategy was identified as the use of UG with a 29-day reaction cycle. The research results have significant referential value for the rapid decomposition of high-water-content agricultural and livestock waste in cold regions. Full article

Marine cold seeps are unique ecological niches characterized by the emergence of hydrocarbons, including methane, which fosters diverse microbial communities. This study investigates the diversity and distribution of hydrocarbon-degrading genes and organisms in sediments from the Caspian and Mediterranean Seas, utilizing 16S rRNA and metagenomic sequencing to elucidate microbial community structure and functional potential. Our findings reveal distinct differences in hydrocarbon degrading gene profiles between the two seas, with pathways for aerobic and anaerobic hydrocarbon degradation co-existing in sediments from both basins. Aerobic pathways predominate in the surface sediments of the Mediterranean Sea, while anaerobic pathways are favored in the surface sediments of the anoxic Caspian Sea. Additionally, sediment depths significantly influence microbial diversity, with variations in gene abundance and community composition observed at different depths. Aerobic hydrocarbon-degrading genes decrease in diversity with depth in the Mediterranean Sea, whereas the diversity of aerobic hydrocarbon-degrading genes increases with depth in the Caspian Sea. These results enhance our understanding of microbial ecology in cold seep environments and have implications for bioremediation practices targeting hydrocarbon pollutants in marine ecosystems. Full article

This study endeavors to develop an economical and user-friendly biological sulfide oxidation system and explore its mechanism for generating biological elemental sulfur under micro-aerobic conditions using psychrophilic anaerobically digested media (liquid/solid inoculums obtained from agricultural livestock wastes) for sulfide-free biogas production. With an initial hydrogen sulfide concentration of 5000 ppm, a biogas flow rate ranging from 0.9 to 1.8 L/h-L_inoculum-mix, and an air injection rate of 0.6–1% (oxygen concentration in biogas), a remarkable biodesulfurization efficiency of 99–100% was attained using solid inoculum as the biodesulfurization medium. This efficiency was achieved without compromising the methane quality in the treated biogas. Compared to liquid inoculum, solid inoculum requires less than half the volume and no mixing equipment, such as bubble column reactors. The biodesulfurization reactor requires only 1 m³, which is approximately 1.5% of the volume of a wet anaerobic digester and 3% of a dry anaerobic digester, while processing cow manure (Total Solids: 20%) at 1.03 m³ of manure per day. Moreover, it can be operated at (19–20 °C), leading to substantial reductions in cost and footprint. Full article

Paddy fields are the main agricultural source of greenhouse gas methane (CH₄) emissions. To enhance rice yield, various fertilization practices have been employed in rice paddies. However, the key microbial and abiotic factors driving CH₄ emissions under different fertilization practices in paddy fields remain largely uncharted. This study conducted field experiments in a traditional double-cropping rice area in South China, utilizing five different fertilization practices to investigate the key factors influencing CH₄ emissions. High-throughput sequencing and PICRUSt2 functional prediction were employed to investigate the contributions of soil physicochemical properties, CH₄-metabolizing microorganisms (methanogens and methanotrophs), and key genes (mcrA and pmoA) on CH₄ emissions. The results showed that CH₄ emission fluxes exhibited seasonal variations, with consistent patterns of change observed across all treatments for both early- and late-season rice. Compared to the no-fertilization (NF) treatment, cumulative CH₄ emissions were lower in early-season rice with green manure (GM) and straw returning (SR) treatments, as well as in late-season rice with GM treatment, while rice yields were maintained at higher levels. High-throughput sequencing analysis revealed that potential methanogens were primarily distributed among four orders: Methanobacteriales, Methanocellales, Methanomicrobiales, and Methanosarcinales. Furthermore, there was a significant positive correlation between the relative abundance of the CH₄-related key gene mcrA and these microorganisms. Functional analysis indicated that these potential methanogens primarily produce methane through the acetoclastic and hydrogenotrophic pathways. Aerobic CH₄-oxidizing bacteria, predominantly from the genus Methylocystis, were detected in all the treatments, while the CH₄ anaerobic-oxidizing archaea ANME-1b was only detected in chemical fertilization (CF) and cow manure (CM) treatments. Our random forest analysis revealed that the relative abundance of two methanogens (Methanocellales and Methanosarcinales) and two environmental factors (pH and DOC) had significant impacts on the cumulative CH₄ emissions. The variance decomposition analysis highlighted the CH₄-metabolizing microorganisms explained 50% of the variance in the cumulative CH₄ emissions, suggesting that they are the key microbial factors driving CH₄ emissions. These findings provide guidance for the development of rational measures to reduce CH₄ emissions in paddy fields. Full article

The contribution of denitrifying anaerobic methane oxidation (DAMO) as a methane sink across different habitats, especially those affected by anthropogenic activities, remains unclear. Mining and industrial and domestic use of metals/metal-containing compounds can all cause metal contamination in freshwater ecosystems. Precipitation of metal ions often limits their toxicity to local microorganisms, yet microbial activity may also cause the redissolution of various precipitates. In contrast to most other studies that apply soluble metal compounds, this study investigated the responses of enriched DAMO culture to model insoluble copper compounds, malachite and covellite, in simulated sedimentary environments. Copper ≤ 0.22 µm from covellite appeared to cause immediate inhibition in 10 h. Long-term tests (54 days) showed that apparent methane consumption was less impacted by various levels of malachite and covellite than soluble copper. However, the medium-/high-level malachite and covellite caused a 46.6–77.4% decline in denitrification and also induced significant death of the representative DAMO microorganisms. Some enriched species, such as Methylobacter tundripaludum, may have conducted DAMO or they may have oxidized methane aerobically using oxygen released by DAMO bacteria. Quantitative polymerase chain reaction analysis suggests that Candidatus Methanoperedens spp. were less affected by covellite as compared to malachite while Candidatus Methylomirabilis spp. responded similarly to the two compounds. Under the stress induced by copper, DAMO archaea, Planctomycetes spp. or Phenylobacterium spp. synthesized PHA/PHB-like compounds, rendering incomplete methane oxidation. Overall, the findings suggest that while DAMO activity may persist in ecosystems previously exposed to copper pollution, long-term methane abatement capability may be impaired due to a shift of the microbial community or the inhibition of representative DAMO microorganisms. Full article

Biodegradable organic waste offers significant opportunities for resource recovery within the frame of the circular economy. In this work, the effects of carbon-encapsulated iron nanoparticles and ozone pre-treatments in the mesophilic methanogenic stage of a temperature-phased an-aerobic digestion have been studied using biochemical methanogenic potential (BMP) tests and modeling simulation. To do that, digestates from a pre-treated thermophilic acidogenic reactor that co-digested sludge and wine vinasse were used. The addition of nanoparticles favored the removal of particulate matter, which increased by 9% and 6% in terms of total solids and volatile solids, respectively. When combined with ozone pre-treatment, these increases were 27% and 24%, respectively, demonstrating enhanced AD efficiency. The dose of iron nanoparticles encapsulated in carbon did not result in a statistically significant increase in methane production when sludge and vinasse were used as feedstock. The combination of nanoparticles with the ozone pre-treatment significantly improved the methanogenic phase of the second stage, increasing the methane production yield by 22% and reducing the lag phase from 10 days to 3 days, according to the modified Gompertz model. Full article

The high-temperature and high-humidity conditions arising from the biochemical degradation of landfill waste result in significant temperature gradients within the landfill cover. The effects of waste temperature on landfill gas transport and microbial aerobic methane oxidation are not fully understood. In this study, a fully coupled theoretical model was developed to simulate the interactions of moisture, heat, and gas transport within a capillary barrier cover. A series of parametric studies were carried out to investigate the influence of the combined effects of temperature gradient, initial soil moisture content, and landfill gas generation rate on methane transport, oxidation, and emissions. The simulated results indicated that increasing waste temperature intensified the temperature gradient, leading to higher surface evaporation rates and variations in methane oxidation efficiencies. Additionally, variations in initial soil moisture content and landfill gas generation rates were found to significantly impact gas migration and methane oxidation in the cover. This study demonstrates the critical role of waste temperature in landfill gas migration within landfill cover systems, providing technical methodologies for the optimized design of soil cover systems. Full article

The high externalized and still partly unknown costs of fossil fuels through air pollution from combustion, and their limited resources have caused mankind to (re)turn to renewable sources such as wind, solar, and biomass to meet its energy needs. Converting biomass to synthesis gas is advantageous since it can utilize a wide variety of (waste) feedstocks to obtain an energetic and versatile product at low cost in large quantities. Gasification is no new technology; yet in recent years, biomass gasification has attracted significant attention. Due to the non-depletable nature of agricultural waste and similar biomass side streams, which have little value and can bring environmental problems when mismanaged such as methane emissions, it is possible to obtain cheap electrical or thermal energy through the gas produced with high efficiencies. Combined heat and power (CHP) is the preferred use case, and recently the focus has moved to polygeneration, e.g., to make value-added products from the synthesis gas. Fischer–Tropsch synthesis from coal-derived syngas is now being complemented by the gas fermentation of biobased synthesis gas, where microorganisms yield materials from CO/H₂ (and CO₂) in an anaerobic process and from CH₄/O₂ in an aerobic process. Syngas methanation offers an alternative route to produce synthetic natural gas (SNG, or bio-SNG) as additional feedstock for gas fermentation. Materials made from syngas are decoupled from primary agricultural operations and do not compete with feed and food production. Due to the ample raw material base for gasification, which can basically be all kinds of mostly dry biomass, including waste such as municipal solid waste (MSW), syngas-derived products are highly scalable. Amongst them are bioplastics, biofuels, biobased building blocks, and single-cell protein (SCP) for feed and food. This article reviews the state-of-the-art in biomass gasification with a spotlight on gas fermentation for the sustainable production of high-volume materials. Full article

Anaerobic digestion (AD) produces useful biogas and waste streams with high levels of dissolved methane (CH₄) and ammonium (NH₄⁺), among other nutrients. Membrane biofilm reactors (MBfRs), which support dissolved methane oxidation in the same reactor as simultaneous nitrification and denitrification (ME-SND), are a potential bubble-less treatment method. Here, we demonstrate ME-SND taking place in single-stage, AD digestate liquid-fed MBfRs, where oxygen (O₂) and supplemental CH₄ were delivered via pressurized membranes. The effects of two O₂ pressures, leading to different O₂ fluxes, on CH₄ and N removal were examined. MBfRs achieved up to 98% and 67% CH₄ and N removal efficiencies, respectively. The maximum N removal rates ranged from 57 to 94 mg N L⁻¹ d⁻¹, with higher overall rates observed in reactors with lower O₂ pressures. The higher-O₂-flux condition showed NO₂⁻ as a partial nitrification endpoint, with a lower total N removal rate due to low N₂ gas production compared to lower-O₂-pressure reactors, which favored complete nitrification and denitrification. Membrane biofilm 16S rRNA amplicon sequencing showed an abundance of aerobic methanotrophs (especially Methylobacter, Methylomonas, and Methylotenera) and enrichment of nitrifiers (especially Nitrosomonas and Nitrospira) and anammox bacteria (especially Ca. Annamoxoglobus and Ca. Brocadia) in high-O₂ and low-O₂ reactors, respectively. Supplementation of the influent with nitrite supported evidence that anammox bacteria in the low-O₂ condition were nitrite-limited. This work highlights coupling of aerobic methanotrophy and nitrogen removal in AD digestate-fed reactors, demonstrating the potential application of ME-SND in MBfRs for the treatment of AD’s residual liquids and wastewater. Sensor-based tuning of membrane O₂ pressure holds promise for the optimization of bubble-less treatment of excess CH₄ and NH₄⁺ in wastewater. Full article

When municipal solid waste (MSW) is placed in a landfill, it undergoes anaerobic decomposition, leading to the production of landfill gas, which primarily consists of methane (CH₄) and carbon dioxide (CO₂). Reducing methane emissions is essential in the fight against climate change. It must be implemented at global and European levels, as set out in 2030 in the impact assessment of the climate goal plan. This assessment states that to achieve the goal by 2030 and to reduce greenhouse gas emissions by at least 55%, the methane emissions must be reduced, considering the goals of the Paris Agreement. The Glasgow Climate Pact includes a global mitigation target of the year 2030: to reduce CO₂ emissions by 45%, and the emissions of methane and other greenhouse gasses. For that purpose, looking for new, more advanced ways of managing such waste is necessary. The main objective of this experimental study was to evaluate the influence of aeration, probiotic introduction, and water supply on the production of landfill gasses (CO₂, CH₄, N₂, H₂, etc.) in five different landfill models during the management of MSW and to propose the best solutions for reducing environmental pollution. The results of the research showed that the first and second models of landfills, using only anaerobic conditions, can be used for the treatment of MSW for the production of biogas (CH₄, CO₂), as up to 40–60% of it was released during the 120-experiment period. The third landfill model can be applied in old, already closed landfills, where the rapid stabilization and aeration of MSW are required to minimize pollutant emissions (N₂, etc.) and unwanted odors and shorten biodegradation processes. The results of the fourth and fifth landfill models, in which aerobic–anaerobic conditions were applied, showed that the developing nitrification–denitrification processes resulted in complete nitrogen removal (from 20% to 0%), and overall waste stabilization improved the biodegradation of the MSW. Later, relatively good (on average, 30%) results of biogas (CH₄, CO₂) emissions are achieved during anaerobic condition formation results. Summarizing all experiment results of all landfill models for the further evaluation of the processes, all models can be applied in real practice depending on where they will be used and what result they want to achieve. Full article

Microbial communities of terrestrial mud volcanoes are involved in aerobic and anaerobic methane oxidation, but the biological mechanisms of these processes are still understudied. We have investigated the taxonomic composition, rates of methane oxidation, and metabolic potential of microbial communities in five mud volcanoes of the Taman Peninsula, Russia. Methane oxidation rates measured by the radiotracer technique varied from 2.0 to 460 nmol CH₄ cm⁻³ day⁻¹ in different mud samples. This is the first measurement of high activity of microbial methane oxidation in terrestrial mud volcanos. 16S rRNA gene amplicon sequencing has shown that Bacteria accounted for 65–99% of prokaryotic diversity in all samples. The most abundant phyla were Pseudomonadota, Desulfobacterota, and Halobacterota. A total of 32 prokaryotic genera, which include methanotrophs, sulfur or iron reducers, and facultative anaerobes with broad metabolic capabilities, were detected in relative abundance >5%. The most highly represented genus of aerobic methanotrophs was Methyloprofundus reaching 36%. The most numerous group of anaerobic methanotrophs was ANME-2a-b (Ca. Methanocomedenaceae), identified in 60% of the samples and attaining relative abundance of 54%. The analysis of the metagenome-assembled genomes of a community with high methane oxidation rate indicates the importance of CO₂ fixation, Fe(III) and nitrate reduction, and sulfide oxidation. This study expands current knowledge on the occurrence, distribution, and activity of microorganisms associated with methane cycle in terrestrial mud volcanoes. Full article

Previous studies have shown that light quality and quantity affect methane emissions from plants. However, the role of photoperiod in plant-derived methane has not been addressed. We studied the effects of two photoperiods—long-day (16 h light/8 h dark), and short-day (8 h light/16 h dark)—on growth and methane emissions of lettuce (a long-day plant), mung bean (a short-day plant), and tomato (a day-neutral plant) under a temperature regime of 22/18 °C. All species were grown under both light durations. First, seeds were germinated in Petri dishes for one week, then plants were transferred to pots and randomly assigned to one of the two experimental conditions. Under each condition, twelve plants were grown for 21 days; at that time, plant growth and physiological traits, including plant dry mass, growth index, photosynthesis, chlorophyll fluorescence, total chlorophyll, nitrogen balance index, flavonoids, and anthocyanin, were measured. Lettuce plants under the short-day photoperiod had the highest methane emissions. Long-day plants that were exposed to short-day conditions and short-day plants that were exposed to long-day conditions were stressed; day-neutral plants were also stressed under short days (p < 0.05). All three species had decreased total dry mass under short-day conditions, most likely because of decreased photosynthesis and increased transpiration and stomatal conductance. Methane emission was positively correlated with shoot/root mass ratio, nonphotochemical quenching and anthocyanin; but was negatively correlated with stem height, dry mass, photosynthesis, water-use efficiency, total chlorophyll, and flavonoids (p < 0.05). This study revealed that, besides light intensity and quality, light duration can also affect methane emissions from plants. Full article

Waste management in large urban centers is one of the main challenges for public administration. Two of the most abundant wastes in cities are waste solid and municipal wastewater (MWW). Their management can be optimized if they are treated together. This work analyzed an anaerobic–aerobic system for the treatment of fruit and vegetable wastes (FVWs) and MWW. Firstly, FVWs were collected and characterized; once in the laboratory, they were placed in a tank with the MWW, aiming at transferring to the water those solids with a particle size below 105 µm; then, they were separated by sieving. The mixture of MWW and FVWs with a particle size below 105 µm was fed into an up-flow anaerobic sludge reactor (UASB); in the latter, dissolved and suspended organic matter was transformed into methane and carbon dioxide. The water that left the UASB was sent to be post-treated in an activated sludge reactor (ASR). The chemical oxygen demand (COD) was used as an evaluation parameter of the anaerobic–aerobic system; a removal efficiency higher than 80% was achieved, whereas it was 60% in the ASR. Another evaluation parameter was methane (CH₄) productivity, with an average of 3.0 L_CH4 L⁻¹ d⁻¹. VWF leaching achieved an average COD extraction of 7.68 kg∙m⁻³. The UASB efficiency was on average 70% for the assayed loads (2–8 kg COD·L⁻¹·d⁻¹). The energy potential calculated for the anaerobic–aerobic system was 510.2 kW∙h∙d⁻¹ Full article