Application fuzzy DEMATEL methodology to investigate some technical parameters of biochemical methane potential (BMP) test produced vegetable waste anaerobic biogas

As the transition to renewable energy systems is accelerating, anaerobic digestion, which is one of the methods of energy recovery from organic substrates, continues to be studied with great interest by scientists. Anaerobic digestion research and applications are mostly carried out with biochemical methane potential (BMP) tests to decide the methane potency of sewage sludge, energy crops, and organic wastes. Unlike long and costly continually reactor experiments, actually, BMP tests are cumulative and can be performed with a relatively low investment of materials, technical labor, and also time. For the BMP to give accurate results, the effect of all the tools and technical parameters used in the implementation of the BMP should be well understood. In such situations, it is very useful to apply fuzzy logic methods in multi-criteria decision-making stages when more than one parameter changes at the same time. Therefore, in this study, fifteen parameters were determined and analyzed with the fuzzy DEMATEL (decision-making trial and evaluation laboratory) method to understand the cause-effect mechanism of the technical parameters of BMP. As a result of these analyses, it was seen that the material of the reactor (r_i-c_j value of 0.55), the particle size (r_i-c_j value of 0.43), the effect of mixing (r_i-c_j value of 0.32), and the amount of the total solids (TSA) (r_i-c_j value of 0.25) had a high effect in the causal sense. It was observed that the first-order parameter (material of reactor) was 27% stronger than the second-order (the particle size) parameter in terms of causality. Likewise, the second-order parameter is 34% stronger than the third-order parameter (the effect of mixing) in terms of cause effect. In addition, it was understood that the most effective parameters in the mechanism of effect were pH (r_i + c_j value of 3.41), C/N ratio (r_i + c_j value of 3.26), and temperature (r_i + c_j value of 3.07), respectively. Besides, high methane yield is seen in mesophilic conditions. The average cumulative biogas yield of the reactor is 282.1 NmL/g VS. The highest percentage of methane formed in the biogas occurred on the 21st day. Briefly, this study is important to provide a facilitating way for researchers working on BMP to understand the cause-effect mechanism of system technical requirements.

Quantitative Analysis of Core Lipid Production in Methanothermobacter marburgensis at Different Scales

Archaeal lipids have a high biotechnological potential, caused by their high resistance to oxidative stress, extreme pH values and temperatures, as well as their ability to withstand phospholipases. Further, methanogens, a specific group of archaea, are already well-established in the field of biotechnology because of their ability to use carbon dioxide and molecular hydrogen or organic substrates. In this study, we show the potential of the model organism Methanothermobacter marburgensis to act both as a carbon dioxide based biological methane producer and as a potential supplier of archaeal lipids. Different cultivation settings were tested to gain an insight into the optimal conditions to produce specific core lipids. The study shows that up-scaling at a constant particle number (n/n = const.) seems to be a promising approach. Further optimizations regarding the length and number of the incubation periods and the ratio of the interaction area to the total liquid volume are necessary for scaling these settings for industrial purposes.

Biomethanation of Carbon Monoxide by Hyperthermophilic Artificial Archaeal Co-Cultures

Climate neutral and sustainable energy sources will play a key role in future energy production. Biomethanation by gas to gas conversion of flue gases is one option with regard to renewable energy production. Here, we performed the conversion of synthetic carbon monoxide (CO)-containing flue gases to methane (CH4) by artificial hyperthermophilic archaeal co-cultures, consisting of Thermococcus onnurineus and Methanocaldococcus jannaschii, Methanocaldococcus vulcanius, or Methanocaldococcus villosus. Experiments using both chemically defined and complex media were performed in closed batch setups. Up to 10 mol% CH4 was produced by converting pure CO or synthetic CO-containing industrial waste gases at a high rate using a co-culture of T. onnurineus and M. villosus. These findings are a proof of principle and advance the fields of Archaea Biotechnology, artificial microbial ecosystem design and engineering, industrial waste-gas recycling, and biomethanation.

Hyperthermophilic methanogenic archaea act as high-pressure CH4 cell factories

Bioprocesses converting carbon dioxide with molecular hydrogen to methane (CH₄) are currently being developed to enable a transition to a renewable energy production system. In this study, we present a comprehensive physiological and biotechnological examination of 80 methanogenic archaea (methanogens) quantifying growth and CH₄ production kinetics at hyperbaric pressures up to 50 bar with regard to media, macro-, and micro-nutrient supply, specific genomic features, and cell envelope architecture. Our analysis aimed to systematically prioritize high-pressure and high-performance methanogens. We found that the hyperthermophilic methanococci Methanotorris igneus and Methanocaldococcoccus jannaschii are high-pressure CH₄ cell factories. Furthermore, our analysis revealed that high-performance methanogens are covered with an S-layer, and that they harbour the amino acid motif Tyr^α444 Gly^α445 Tyr^α446 in the alpha subunit of the methyl-coenzyme M reductase. Thus, high-pressure biological CH₄ production in pure culture could provide a purposeful route for the transition to a carbon-neutral bioenergy sector.

Methods for quantification of growth and productivity in anaerobic microbiology and biotechnology

Anaerobic microorganisms (anaerobes) possess a fascinating metabolic versatility. This characteristic makes anaerobes interesting candidates for physiological studies and utilizable as microbial cell factories. To investigate the physiological characteristics of an anaerobic microbial population, yield, productivity, specific growth rate, biomass production, substrate uptake, and product formation are regarded as essential variables. The determination of those variables in distinct cultivation systems may be achieved by using different techniques for sampling, measuring of growth, substrate uptake, and product formation kinetics. In this review, a comprehensive overview of methods is presented, and the applicability is discussed in the frame of anaerobic microbiology and biotechnology.

Physiology and methane productivity of Methanobacterium thermaggregans

Accumulation of carbon dioxide (CO2), associated with global temperature rise, and drastically decreasing fossil fuels necessitate the development of improved renewable and sustainable energy production processes. A possible route for CO2 recycling is to employ autotrophic and hydrogenotrophic methanogens for CO2-based biological methane (CH4) production (CO2-BMP). In this study, the physiology and productivity of Methanobacterium thermaggregans was investigated in fed-batch cultivation mode. It is shown that M. thermaggregans can be reproducibly adapted to high agitation speeds for an improved CH4 productivity. Moreover, inoculum size, sulfide feeding, pH, and temperature were optimized. Optimization of growth and CH4 productivity revealed that M. thermaggregans is a slightly alkaliphilic and thermophilic methanogen. Hitherto, it was only possible to grow seven autotrophic, hydrogenotrophic methanogenic strains in fed-batch cultivation mode. Here, we show that after a series of optimization and growth improvement attempts another methanogen, M. thermaggregas could be adapted to be grown in fed-batch cultivation mode to cell densities of up to 1.56 g L-1. Moreover, the CH4 evolution rate (MER) of M. thermaggregans was compared to Methanothermobacter marburgensis, the CO2-BMP model organism. Under optimized cultivation conditions, a maximum MER of 96.1 ± 10.9 mmol L-1 h-1 was obtained with M. thermaggregans-97% of the maximum MER that was obtained utilizing M. marburgensis in a reference experiment. Therefore, M. thermaggregans can be regarded as a CH4 cell factory highly suited to be applicable for CO2-BMP.

High performance biological methanation in a thermophilic anaerobic trickle bed reactor

In order to enhance energy efficiency of biological methanation of CO₂ and H₂, this study investigated the performance of a thermophilic (55°C) anaerobic trickle bed reactor (ATBR) (58.1L) at ambient pressure. With a methane production rate of up to 15.4m³_CH4/(m³_{trickle bed}·d) at methane concentrations above 98%, the ATBR can easily compete with the performance of other mixed culture methanation reactors. Control of pH and nutrient supply turned out to be crucial for stable operation and was affected significantly by dilution due to metabolic water production, especially during demand-orientated operation. Considering practical applications, inoculation with digested sludge, containing a diverse biocenosis, showed high adaptive capacity due to intrinsic biological diversity. However, no macroscopic biofilm formation was observed at thermophilic conditions even after 313days of operation. The applied approach illustrates the high potential of thermophilic ATBRs as a very efficient energy conversion and storage technology.

Study of the performance of a thermophilic biological methanation system

This study investigated the operation of ex-situ biological methanation at two thermophilic temperatures (55°C and 65°C). Methane composition of 85-88% was obtained and volumetric productivities of 0.45 and 0.4LCH₄/Lreactor were observed at 55°C and 65°C after 24h respectively. It is postulated that at 55°C the process operated as a mixed culture as the residual organic substrates in the starting inoculum were still available. These were consumed prior to the assessment at 65°C; thus the methanogens were now dependent on gaseous substrates CO₂ and H₂. The experiment was repeated at 65°C with fresh inoculum (a mixed culture); methane composition and volumetric productivity of 92% and 0.46LCH₄/Lreactor were achieved in 24h. Methanothermobacter species represent likely and resilient candidates for thermophilic biogas upgrading.

Assessing the Ecophysiology of Methanogens in the Context of Recent Astrobiological and Planetological Studies

Among all known microbes capable of thriving under extreme and, therefore, potentially extraterrestrial environmental conditions, methanogens from the domain Archaea are intriguing organisms. This is due to their broad metabolic versatility, enormous diversity, and ability to grow under extreme environmental conditions. Several studies revealed that growth conditions of methanogens are compatible with environmental conditions on extraterrestrial bodies throughout the Solar System. Hence, life in the Solar System might not be limited to the classical habitable zone. In this contribution we assess the main ecophysiological characteristics of methanogens and compare these to the environmental conditions of putative habitats in the Solar System, in particular Mars and icy moons. Eventually, we give an outlook on the feasibility and the necessity of future astrobiological studies concerning methanogens.

A Critical Assessment of Microbiological Biogas to Biomethane Upgrading Systems

Microbiological biogas upgrading could become a promising technology for production of methane (CH(4)). This is, storage of irregular generated electricity results in a need to store electricity generated at peak times for use at non-peak times, which could be achieved in an intermediate step by electrolysis of water to molecular hydrogen (H(2)). Microbiological biogas upgrading can be performed by contacting carbon dioxide (CO(2)), H(2) and hydrogenotrophic methanogenic Archaea either in situ in an anaerobic digester, or ex situ in a separate bioreactor. In situ microbiological biogas upgrading is indicated to require thorough bioprocess development, because only low volumetric CH(4) production rates and low CH(4) fermentation offgas content have been achieved. Higher volumetric production rates are shown for the ex situ microbiological biogas upgrading compared to in situ microbiological biogas upgrading. However, the ex situ microbiological biogas upgrading currently suffers from H(2) gas liquid mass transfer limitation, which results in low volumetric CH(4) productivity compared to pure H(2)/CO(2) conversion to CH(4). If waste gas utilization from biological and industrial sources can be shown without reduction in volumetric CH(4) productivity, as well as if the aim of a single stage conversion to a CH(4) fermentation offgas content exceeding 95 vol% can be demonstrated, ex situ microbiological biogas upgrading with pure or enrichment cultures of methanogens could become a promising future technology for almost CO(2)-neutral biomethane production.