Biogas Reactor Research Articles

Portable biogas as alternative energy by utilizing durian peel

In the Magelang district, Candimulyo is well known as a durian center. During the harvest season, durian peel waste is piled up in several places. Through a portable biogas reactor, this community service attempts to use durian peel waste as an alternative energy source. Participatory Rural Appraisal (PRA) is the methodology employed to incorporate the community's active role in the implementation of program. As a result, portable biogas innovation can be used to light a stove, in an average of 20-40 minutes.

Yak rumen fluid inoculum increases biogas production from sheep manure substrate

Hydrolytic bacteria are essential for the degradation of lignocellulose to produce biogas and organic fertilizers. In this study, sheep manure was used as substrate, and sheep manure slurry, yak rumen fluid and slurry from a biogas reactor (SBR) were used as inocula in single-stage anaerobic digestion. The SBR and rumen fluid inocula increased biogas production by 23% and 43%, respectively, when compared to solely sheep manure in the single-stage anaerobic digestion. The two-stage anaerobic digestion, with yak rumen fluid as inoculum in the hydrolytic reactor, increased the biogas production by 59, 86, and 58% compared with the control. Microbial analysis of the effluent revealed that yak rumen fluid contained hydrolytic bacteria such as Proteiniphilum, Jeotgalibaca, Fermentimonas, and Atopostipes to enhance the degradation of sheep manure and increase biogas production. It was concluded that yak rumen fluid, rich in hydrolytic bacteria, increases the degradability of sheep manure and improves production of volatile fatt acids and biogas.

Integrating metagenomic binning with flux balance analysis to unravel syntrophies in anaerobic CO2 methanation

BackgroundCarbon fixation through biological methanation has emerged as a promising technology to produce renewable energy in the context of the circular economy. The anaerobic digestion microbiome is the fundamental biological system operating biogas upgrading and is paramount in power-to-gas conversion. Carbon dioxide (CO2) methanation is frequently performed by microbiota attached to solid supports generating biofilms. Despite the apparent simplicity of the microbial community involved in biogas upgrading, the dynamics behind most of the interspecies interaction remain obscure. To understand the role of the microbial species in CO2 fixation, the biofilm generated during the biogas upgrading process has been selected as a case study. The present work investigates via genome-centric metagenomics, based on a hybrid Nanopore-Illumina approach the biofilm developed on the diffusion devices of four ex situ biogas upgrading reactors. Moreover, genome-guided metabolic reconstruction and flux balance analysis were used to propose a biological role for the dominant microbes.ResultsThe combined microbiome was composed of 59 species, with five being dominant (> 70% of total abundance); the metagenome-assembled genomes representing these species were refined to reach a high level of completeness. Genome-guided metabolic analysis appointed Firmicutes sp. GSMM966 as the main responsible for biofilm formation. Additionally, species interactions were investigated considering their co-occurrence in 134 samples, and in terms of metabolic exchanges through flux balance simulation in a simplified medium. Some of the most abundant species (e.g., Limnochordia sp. GSMM975) were widespread (~ 67% of tested experiments), while others (e.g., Methanothermobacter wolfeii GSMM957) had a scattered distribution. Genome-scale metabolic models of the microbial community were built with boundary conditions taken from the biochemical data and showed the presence of a flexible interaction network mainly based on hydrogen and carbon dioxide uptake and formate exchange.ConclusionsOur work investigated the interplay between five dominant species within the biofilm and showed their importance in a large spectrum of anaerobic biogas reactor samples. Flux balance analysis provided a deeper insight into the potential syntrophic interaction between species, especially Limnochordia sp. GSMM975 and Methanothermobacter wolfeii GSMM957. Finally, it suggested species interactions to be based on formate and amino acids exchanges.AQaLxbUWFz91qWxiAB1_X5Video

Small-Scale Biogas Reactors Converting Organic Waste to Energy and Ferlilizer: A Case Study of Sam Ratulangi University Green Campus Project

Organic Waste Management (OWM) has been a major problem worldwide in most of the cities among developing countries such as Indonesia. Sam Ratulangi University (UNSRAT) is located in the rural setting of the medium city of Manado, North Sulawesi, Indonesia, was committed to achieving minimum waste across all campus locations, by averting some waste through reduced consumption and diverting the rest through recycling, composting, or reusing. A large amount of yard waste such as grass, leaves, and branches is produced on campus in UNSRAT, which is a problem that needs to be effectively solved. Composting is a sustainable OWM practice that converts organic waste into valuable products such as liquid organic fertilizer and biogas. OWM and bioenergy production are complementary to each other, because the application of compost back into the soil can contribute to sustainable soil health, and biogas is the principal renewable energy source that manages potentially harmful organic wastes. Thus, in the present article, recycling of organic waste has recently become an important topic and the intensification of organic waste conversion strategies was elaborated and analyzed frequently. The result indicated that creating a small-scale biogas reactor is more cost-effective, eco-friendly, and presents a sustainable waste treatment method within UNSRAT campus into valuable products that promote the university as a green campus. Keyword: bioenergy; biogas reactor; organic waste; organic liquid fertilizer

Effect of Phase Change Materials and Phase Change Temperature on Optimization of Design Parameters of Anaerobic Reactor Thermal Insulation Structure.

Direct-absorption anaerobic reactors can maintain the fermentation process of microorganisms by utilizing solar absorption and scattering media in the biogas reactor to improve the slurry temperature. Direct-absorption heating alone can save the corresponding electric energy and ensure the normal fermentation process of the biogas slurry in the reactor, but there is still the problem of temperature fluctuation. In order to improve the stability of the fermentation process, it is proposed to optimize the design of this kind of reactor by adding paraffin phase change material. This article mainly studies the influence of paraffin phase change material added on the top and side of the reactor in the fermentation process and gives the corresponding design parameters for different climatic conditions, which lays a theoretical reference for the design process of this kind of reactor.

Viability of Wildflower Seeds After Mesophilic Anaerobic Digestion in Lab-Scale Biogas Reactors.

The use of wildflower species as biogas feedstock carries the risk that their seeds survive anaerobic digestion (AD) and cause weed problems if spread with the digestate. Risk factors for seed survival in AD include low temperature, short exposure and hardseededness (HS). However, it is not possible to predict how AD will affect seed viability of previously unstudied species. In laboratory-scale reactors, we exposed seeds of eight species from a mixture of flowering wild plants intended as biogas feedstock and three reference species to AD at two mesophilic temperatures. Half of the species were HS, the other was non-HS (NHS). Viability was determined using a combination of tetrazolium and germination tests. Viability and germinability were modeled as functions of exposure time using a dose-response approach. Responses to AD varied considerably among species, and none of the considered influencing factors (time, temperature, HS) had a consistent effect. Seed lots of a species differed in inactivation times and seed-killing efficacy. The HS species Melilotus officinalis, Melilotus albus, and Malva sylvestris were particularly AD-resistant. They were the only ones that exhibited biphasic viability curves and tended to survive and germinate more at 42°C than at 35°C. Viability of the remaining species declined in a sigmoidal curve. Most NHS species were inactivated within a few days (Cichorium intybus, Daucus carota, Echium vulgare, and Verbascum thapsus), while HS species survived longer (Malva alcea). AD stimulated germination in the HS species A. theophrasti and its AD-resistance overlapped with that of the most resistant NHS species, C. album and tomato. In all seed lots, germinability was lost faster than viability, implying that mainly dormant seeds survived. After the maximum exposure time of 36 days, seeds of HS species and Chenopodium album were still viable. We concluded that viability responses to mesophilic AD were determined by the interplay of AD-conditions and species- and seed-lot-specific traits, of which HS was an important but only one factor. For the use of wildflowers as biogas feedstock, we recommended long retention times and special care with regard to HS species.

Biochar enhanced bioaugmentation provides long-term tolerance under increasing ammonia toxicity in continuous biogas reactors

Bioaugmentation of ammonia-tolerant methanogens into inhibited anaerobic digestion (AD) reactors was demonstrated as an in-situ remediation strategy to alleviate ammonia toxicity. This study investigated the long-term performance of a novel bioaugmentation strategy, using gel-immobilized ammonia tolerant methanogens (biogel) enhanced with biochar to alleviate ammonia toxicity in thermophilic continuous anaerobic systems. Three ammonia shocks were applied in four continuous stirred-tank reactors, namely by adding biogel (R2), biochar (R3), both biogel and biochar (R4) and control reactor (R1), respectively. The results showed R1, R2, R3 and R4 suffered 31.3%, 28.6%, 26.0% and 17.1% methane production loss, respectively at 5.5 g NH4+-N L−1. R4 achieved 100% methane production recovery compared to 13% of R1. R3 and R4 successfully acclimatized to 6.5 g NH4+-N L−1 with 71.7% and 61.8% original methane yield compared to 36.9% and 35.6% for R1 and R2, respectively. The introduced Methanoculleus thermophilus sp. along with syntrophic partners was protected by the biochar, and its relative abundance in R4 was tenfold than R2. Bioaugmentation developed a long-term ammonia resistance due to the synergistic interaction between biogel and biochar on alleviating ammonia inhibition, securing an additional gross profit of 11.8 $ ton−1 feedstock for the continuous biogas reactor.

Flows and budgets of nutrients and potentially toxic elements on four Swedish organic farms using digestate from agricultural residues

Few fertilizers are permitted for organic farming, which is a challenge when securing nutrient availability, particularly of nitrogen (N). Digestate from biogas production could be a valuable fertilizer for increasing crop yields, through its high content of plant-available nitrogen (NH4-N), but is rarely used in practice. This study evaluated how anaerobic digestion of manure and use of digestate affected inflows and outflows of nutrients and potentially toxic elements on four organic farms with different solutions for digestate production. Mass flows and element concentrations were documented 3 years on three dairy farms and one crop farm and used for calculating farm budgets. Nitrogen and phosphorus (P) budgets were also calculated for biogas reactor and storage pits on three farms. Nitrogen surplus exhibited large variation (18–87 kg N ha−1 year−1) at farm level, with purchased digestate or poultry manure giving major N inputs. The risk of process losses was high, with up to 40% of N and P in feedstock entering farm biogas reactors not recovered in digestate. The proportion of NH4-N in total N in digestate was slightly higher (2–9%) or lower (37%) than in feedstocks entering farm biogas reactors. Improved stirring in farm biogas reactors and storage pits to decrease N and P sedimentation, particularly when digesting poultry manure, would directly increase digestate value. Two farms purchasing digestate from central biogas plants received a digestate causing significant cadmium inputs. Keeping records on element flows can help to tailor the use of digestate for organic farms to achieve a sustainable use of nutrients.

Serial anaerobic digestion improves protein degradation and biogas production from mixed food waste

Optimization of the biogas generation process is important to achieve efficient degradation and high methane yield, and to reduce methane emissions from the digestate. In this study, serial digester systems with two or three biogas reactors were compared with a single reactor, with the aim of improving degree of degradation and methane yield from food waste and assessing adaptation of microbial communities to different reactor steps. All systems had the same total organic load (2.4 g VS/(L d)) and hydraulic retention time (55 days). Serial systems increased methane yield by >5% compared with the single reactor, with the majority of the methane being obtained from the first-step reactors. Improved protein degradation was also obtained in serial systems, with >20% lower outgoing protein concentration compared with the single reactor and increasing NH4+-N concentration with every reactor step. This resulted in separation of high ammonia (>384 mg NH3-N/L) levels from the main methane production, reducing the risk of methanogen inhibition. Methanosarcina dominated the methanogenic community in all reactors, but increases in the hydrogenotrophic genera Methanoculleus and Methanobacterium were observed at higher ammonia levels. Potential syntrophic acetate-oxidizing bacteria, such as MBA03 and Dethiobacteraceae, followed the same trend as the hydrogenotrophic methanogens. Phylum Bacteroidota family Paludibacteraceae was highly abundant in the first steps and then decreased abruptly, potentially linked to an observed decrease in degradation in the last-step reactors. Nevertheless, the results indicated a trend of increasing relative abundance of the potentially proteolytic genera Proteiniphilum and Fastidiosipila with successive reactor steps.

Experimental investigation of energy consumption for the process of initial heating of a substrate for the use of electric heat-mechanical system

Purpose. Experimental determination of energy consumption for the process of initial heating of the substrate to the temperature of anaerobic digestion in a biogas reactor using an electrothermal-mechanical system with automatic control to assess the energy efficiency of the process of heating the substrate and the profitability of further processing of the resulting biogas into thermal and electrical energy.
 Methodology. Experimental studies of the dynamics of temperature changes in an heating cable placed in an electrothermal-mechanical system, determining the duration of the process and the energy consumed by the initial heating of the substrate, processing and analysis of the obtained data arrays, summarizing the results obtained.
 Findings. Biogas technologies play an important role in the formation of a modern energy system, the profitability of which directly depends on the energy efficiency of anaerobic digestion intensification. The process of digestion of waste is long, so one of the main methods of intensification of biogas production is the mixing of waste in the process of anaerobic fermentation. There is a need to improve the energy efficiency of anaerobic digestion intensification and the profitability processing of biogas into heat and electricity. Ways to improve energy efficiency mainly consist in reducing the time of heating the substrate in a biogas reactor, reducing the consumption of electrical energy for the process of thermal stabilization of anaerobic digestion, structural combination of energy-efficient systems for mixing and heating raw materials in reactors, and introducing automatic production systems. The implementation of these actions will make it possible to establish the optimal geometric dimensions of an electrothermal-mechanical system with automatic control for mixing and heating the substrate in a biogas reactor and significantly increase the energy efficiency of biogas plants and the subsequent processing of the resulting biogas into thermal and electrical energy.
 Originality. As a result of the experimental study and analysis of the data obtained, it was found that with the same power of the heating sections, the change in the temperature of the electric cable in each blade does not occur in the same way. The authors found that the average value of the temperature of the sections of the electric heating cable of the lower blades is 12.9% higher compared to the upper blades of the electrothermal-mechanical system. In the course of experimental studies, the authors found that when using a heating system made of an electric heating cable mounted in the blades of a two-tier paddle mixer, it consumes J, on the process of initial heating of the substrate from before °С in a biogas reactor with a volume of 40 liters. The duration of the heating itself is 300 minutes. In the course of experimental studies, the authors established the energy efficiency from dividing the electrothermal-mechanical system into heating sections, when each blade is a separate section with its own automatic temperature control of the electric heating cable mounted in the corresponding section, while the consumption of electrical energy is reduced by 27.9%.
 Practical value. The results obtained can be used in the design, construction and modernization of biogas production intensification systems, namely, mixing and heating of the substrate in biogas plants. This will improve the energy efficiency of the biogas formation process and the profitability of its processing into heat and electricity.

Nature‐based solutions in soil restoration for improving agricultural productivity

AbstractSoil is a living and dynamic body, which is prone to degradation under conventional agricultural practices. Healthy soil is one of the most important pillars of sustainability as it delivers several ecosystem services along with its control on microbial activity, nutrient recycling, and decomposition. Nature‐based solutions can play an important role in restoring soil quality for enhanced agricultural productivity and sustainability. This article discusses various nature‐based options available for improving soil quality. Indigenous practices such as sheep penning, tank silt application, green manuring, and refuse from croplands and households have the potential to restore and maintain soil fertility. Biofertilizers can add nutrients (N fixers), fixe up to 300 kg N ha through biological nitrogen fixation (BNF) and facilitate (nutrient solubilizer and mobilizers) nutrient availability in the soil. Biochar, a commonly used product, can increase soil moisture availability by 8%–10% and aids in mitigating climate change through C‐sequestration. Biochar may have a climate change mitigation potential of 1.8 Pg CO2‐C equivalent per year. When added to the soil, it not only acts as a nutrient source; but also acts as a soil amendment. Biogas slurry, the effluent from biogas reactors, contains various nutrient elements that can enrich soil fertility. The holistic approach in a farming system, through integration of different enterprises, reduces dependence on off‐farm resources. Soil management through nature‐based options will maintain crop productivity and sustainability in the long run without any adverse effects on the environment.

Influence of enclosure filled with phase change material on photo-thermal regulation of direct absorption anaerobic reactor: Numerical and experimental study

Direct absorption methane reactor can maintain the fermentation process of microorganism by utilizing solar absorption and scattering of media in biogas reactor to improve the slurry temperature. However, direct absorption heating alone can save the corresponding electric energy and ensure the normal fermentation process of the biogas slurry in the reactor, but there are still problems of big temperature fluctuation and low solar heat absorption efficiency. In order to improve the stability of the fermentation process, it is proposed to optimize the design of this kind of reactor by filling paraffin PCM (phase change material). In this paper, a novel transient model for simulating the photo-thermal transfer process of the reactor with PCM structure was proposed. Experimental and numerical methods were utilized to analyze the effect of PCM parameters on photo-biochemical transformation process and solar heat absorption efficiency. The results show that filling paraffin phase change material in the enclosure of direct absorption reactor can effectively improve its thermal insulation and thermal storage performance, so as to improve the rate of volatile fatty acids (VFA) and gas production by anaerobic fermentation by maximum 31.1%. The average solar heat absorption efficiency of reactor equipped with PCM is bigger than 50%. Thicknesses of 4 cm and 2 cm for side and top structure were selected, respectively.

Multi-omics joint analysis of the effect of temperature on microbial communities, metabolism, and genetics in full-scale biogas reactors with food waste

Due to the diversity of microbiota and the high complexity of their interactions that mediate biogas production, a detailed understanding of the microbiota is essential for the overall stability and performance of the anaerobic digestion (AD) process. This study evaluated the microbial taxonomy, metabolism, function, and genetic differences in 14 full-scale biogas reactors and laboratory reactors operating under various conditions in China. This is the first known study of the microbial ecology of AD at food waste (FW) at a regional scale based on multi-omics (16S rRNA gene amplicon sequencing, metagenomics, and proteomics). Temperature significantly affected the bacterial and archaeal community structure (R2 = 0.996, P = 0.001; R2 = 0.846, P < 0.002) and total inorganic carbon(TIC) slightly changed the microbial structure (R2 = 0.532, P = 0.005; R2 = 0.349, P = 0.016). The Wood-Ljungdahl coupled with hydrogenotrophic methanogenic pathways were dominant in the thermophilic reactors, where the acs, metF, cooA, mer, mch and ftr genes were 10.1-, 2.8-, 16.2-, 1.74-, 4.15-, 1.04-folds of the mesophilic reactors (P < 0.01). However, acetoclastic and methylotrophic methanogenesis was the primary pathway in the mesophilic reactors, where the ackA, pta, cdh and mta genes were 2.2-, 3.2-, 14.3-, 1.88-folds of the thermophilic group (P < 0.01). Finally, the Wilcoxon rank-sum test was applied to explain the cause of the temperature affecting AD microbial activities. The findings have deepened the understanding of the effect of temperature on AD microbial ecosystems and are expected to guide the construction and management of full-scale FW biogas plants.

Modeling of a bio-methane solar system driven by solar energy and heat pump

The paper presents a novel thermodynamic modeling approach of a pilot solar biomass system for bio-methane energy production and wastewater treatment by creation of two packages (STSB and MHPB) modeling platform under TRNsys studio software. Indeed, several newly developed mathematical schemes using the communicating elements: a new Multi-stage air to water Heat Pump, a new Vacuum Tube solar Collector (VTC), thermodynamic storage, and a biogas reactor) have been validated by experiment. The work presents and discusses two scenarios (packages), the first one –STSB- concerns the pilot solar-biomass system, and uses only renewable energy for the bio-methane production by anaerobic digestion mechanism under the mesophilic conditions (±35 °C to ±42 °C), The second scenario consists of a modeling Multi-stage Heat Pump Biomass reactor (MHPB). The packages developed have been tested for industrial case study. A validation process of two scenarios with experimental tests of a 500 L reactor -for the biomass of the cardboard paper-proves a good agreement, where the errors band is about 1% for STSB and 1.5% for the MHPB package. The biogas reactor treats about 900 (m3/year) liquid biomass (3 m3/day). The prediction results indicate that the biogas production attaint 51 (m3) per year. According to the biogas composition analysis, the bio-methane represents 74%, leading to prediction results of 38 (m3) per year of bio-methane for the case study. . Further, the extended results from the modeling packages platform indicate that for this installation type of 700 m3, the bio-methane (CH4) production is estimated of 52 836 (m3) per year, representing 64% of the total fuel consumption for the current case of cardboard recycling and packaging company.

Phage Genome Diversity in a Biogas-Producing Microbiome Analyzed by Illumina and Nanopore GridION Sequencing.

The microbial biogas network is complex and intertwined, and therefore relatively stable in its overall functionality. However, if key functional groups of microorganisms are affected by biotic or abiotic factors, the entire efficacy may be impaired. Bacteriophages are hypothesized to alter the steering process of the microbial network. In this study, an enriched fraction of virus-like particles was extracted from a mesophilic biogas reactor and sequenced on the Illumina MiSeq and Nanopore GridION sequencing platforms. Metagenome data analysis resulted in identifying 375 metagenome-assembled viral genomes (MAVGs). Two-thirds of the classified sequences were only assigned to the superkingdom Viruses and the remaining third to the family Siphoviridae, followed by Myoviridae, Podoviridae, Tectiviridae, and Inoviridae. The metavirome showed a close relationship to the phage genomes that infect members of the classes Clostridia and Bacilli. Using publicly available biogas metagenomic data, a fragment recruitment approach showed the widespread distribution of the MAVGs studied in other biogas microbiomes. In particular, phage sequences from mesophilic microbiomes were highly similar to the phage sequences of this study. Accordingly, the virus particle enrichment approach and metavirome sequencing provided additional genome sequence information for novel virome members, thus expanding the current knowledge of viral genetic diversity in biogas reactors.

Experimental Investigation of Energy Consumption for the Process of Initial Heating of a Substrate to the Fermentation Temperature

The aim of the work is to experimentally study the energy consumption for the process of initial heating of the substrate to the fermentation temperature in order to increase the energy efficiency of the biogas formation process. To achieve the goals set, a preparation and a series of experimental studies of the indicators of energy consumption for the process of initial heating of the substrate to the fermentation temperature were carried out. The working hypothesis is that the use of a heating cable built into the stirrer paddles reduces the energy costs for the process of initial heating of the substrate, increasing thus the energy efficiency of the biogas production. The most important result of the study was to obtain the dependences of the temperature change in the heating cable, substrate, reactor walls and energy consumption for heating and mixing during the initial heating of the substrate. The significance of the research results presented in the work lies in the fact that when using a heating cable built into the stirrer paddles, the process of initial heating of the substrate to the fermentation temperature occured faster on average by 16 minutes, and the amount of energy spent was also decreased on average by 6.6% for heating and 5.3% for mixing the substrate in a 40-liter biogas reactor. The implementation of the data obtained experimentally increased the energy efficiency of biogas production and the profitability of further processing of biogas into heat and electricity.

Pengembangan ternak Ruminansia terintegrasi di Desa Koto Simandolak Kabupaten Kuantan Singingi: Pemanfaatan kotoran ternak untuk biogas dan pupuk organik

Kuantan Singingi Regency is one of the ruminant-producing districts in Riau Province. Koto Simandolak Village, located in Benai District, Kuantan Singingi Regency, the majority of the people work as farmers. Generally, farmers in Koto Simandolak Village cultivate livestock traditionally, namely by releasing them to the wild. This condition causes several problems including livestock manure, pollution of the village environment, and conflicts with residents. This problem can be solved if the farmer wants to keep the cattle. By holding cattle, the manure will be collected directly in the cage. Animal manure can be processed and used in biogas and organic fertilizer. The Research and Community Services Team of Universitas Riau saw the potential for utilizing livestock manure waste in Koto Simandolak Village. The Team conducts training and assistance in the installation of biogas reactors as well as training and mentoring in the biogas production process using livestock manure. Another output of biogas production is organic fertilizer. The ultimate goal of this service activity is to increase the income of the target community, namely through increasing livestock production, biogas production, and organic fertilizer production.

Mesophilic and Thermophilic Anaerobic Digestion of Wheat Straw in a CSTR System with 'Synthetic Manure': Impact of Nickel and Tungsten on Methane Yields, Cell Count, and Microbiome.

Lignocellulosic residues, such as straw, are currently considered as candidates for biogas production. Therefore, straw fermentations were performed to quantitatively estimate methane yields and cell counts, as well as to qualitatively determine the microbiome. Six fully automated, continuously stirred biogas reactors were used: three mesophilic (41 °C) and three thermophilic (58 °C). They were fed every 8 h with milled wheat straw suspension in a defined, buffered salt solution, called ‘synthetic manure’. Total reflection X-ray fluorescence spectrometry analyses showed nickel and tungsten deficiency in the straw suspension. Supplementation of nickel and subsequently tungsten, or with an increasing combined dosage of both elements, resulted in a final concentration of approximately 0.1 mg/L active, dissolved tungsten ions, which caused an increase of the specific methane production, up to 63% under mesophilic and 31% under thermophilic conditions. That is the same optimal range for pure cultures of methanogens or bacteria found in literature. A simultaneous decrease of volatile fatty acids occurred. The Ni/W effect occurred with all three organic loading rates, being 4.5, 7.5, and 9.0 g volatile solids per litre and day, with a concomitant hydraulic retention time of 18, 10, or 8 days, respectively. A maximum specific methane production of 0.254 m3 CH4, under standard temperature and pressure per kg volatile solids (almost 90% degradation), was obtained. After the final supplementation of tungsten, the cell counts of methanogens increased by 300%, while the total microbial cell counts increased by only 3–62%. The mesophilic methanogenic microflora was shifted from the acetotrophic Methanosaeta to the hydrogenotrophic Methanoculleus (85%) by tungsten, whereas the H2-CO2-converter, Methanothermobacter, always dominated in the thermophilic fermenters.

EXPERIMENTAL INVESTIGATION OF ENERGY LOSSES OF A BIOGAS REACTOR IN THE ENVIRONMENT FOR MESOPHILIC MODE OF FERMENTATION

The aim of the work is an experimental study of energy losses to the environment for the mesophilic mode of fermentation in order to increase the duration of substrate cooling and reduce energy costs for the process of biogas formation. To achieve the goals set, the following tasks have been solved: a methodological approach has been developed for conducting experimental studies; an experimental plant for a biogas reactor with an electrothermal-mechanical system with automatic control for mixing and heating the substrate was made; experimentally investigated energy losses to the environment for the mesophilic mode of fermentation; processing, analysis and comparison of the obtained experimental data were carried out. The working hypothesis of the research was that the use of an heating cable built into the stirrer paddles would provide a longer process of cooling the substrate to the heating switch-on temperature, which would reduce energy costs for the biogas formation intensification process. The most significant result of the study is to obtain the dependences of the change in the temperature of the heating cable, the substrate in the lower, middle and upper tiers of the reactor and the duration of the substrate cooling to the heating switch-on temperature in the operating biogas plant. The significance of the results of experimental studies lies in the fact that when placing a heating cable built into the stirrer paddles, the process of cooling the substrate to the heating switch-on temperature occurs later, on average, by 35 minutes, when the substrate is fermented in a biogas reactor with a volume of 40 liters. The implementation of the data obtained will increase the energy efficiency of the processes of intensification of biogas production and the profitability of further processing of biogas into heat and electricity.

Impact of Granular Activated Carbon on Anaerobic Process and Microbial Community Structure during Mesophilic and Thermophilic Anaerobic Digestion of Chicken Manure

In this work, the impact of granular activated carbon (GAC) on the mesophilic and thermophilic anaerobic digestion of chicken manure and the structure of microbial communities was investigated. These results demonstrated that GAC supplementation effectively enhanced the consumption of produced organic acids in the mesophilic and thermophilic batch tests, accompanied by faster biomethane production in the presence of GAC than from reactors without GAC. However, since the free ammonia level was 3–6 times higher in the thermophilic reactors, this led to the instability of the anaerobic digestion process of the nitrogen-rich substrate at thermophilic temperatures. Bacteroidia and Clostridia were the two main bacterial classes in the mesophilic reactors, whereas the class Clostridia had a competitive advantage over other groups in the thermophilic systems. The archaeal communities in the mesophilic reactors were mainly represented by representatives of the genera Methanosarcina, Methanobacterium, and Methanotrix, whereas the archaeal communities in the thermophilic reactors were mainly represented by members of the genera Methanosarcina, Methanoculleus, and Methanothermobacter. New data obtained in this research will help control and manage biogas reactors in the presence of GAC at different temperatures.