Biogas Production Plants Research Articles

A Methodological Approach for the Characterization of Hazardous Zones due to Potentially Explosive Atmospheres: a Case Study

The biogas role is becoming crucial in the panorama of sustainable development. In fact, Countries of the European Union have agreed on a new 2030 Framework for climate and energy, which includes targets aimed at achieving a more competitive, secure and sustainable energy system. A specific target has established that at least a 27% share of renewable energy consumption must be achieved. Biogas sector is quickly developed in Italy, which is the second biogas producer in Europe, after Germany, and by the end of 2017 about 1,900 plants were operating. One of the main hazards, associated with the biogas production, is the formation of potentially explosive atmospheres (methane is present in biogas composition), deriving from accidental biofuel releases. Indeed, in the industrial plants there are several potential sources, such as valves, flanges, compressors, etc.. The paper illustrates a case study, referred to a biogas production plant. In particular, the paper describes a methodological approach aimed at classifying the places (zone 0 or zone 1 or zone 2 or non-hazardous zone), where potentially explosive atmospheres could occur, and characterizing explosive atmosphere geometry in terms of extent and volume. This topic plays a very important role in order to ensure a safer operation of the plants, because classification of hazardous areas allows to choose equipment and protective systems (according to Atex Directive 2014/34/EU) intended for use in potentially explosive atmospheres. The classification has been carried out in accordance with Atex Directive 99/92/EC, which states the minimum requirements for improving the safety and health protection of workers exposed to potentially explosive mixtures.

Synthesis of biogas supply networks using various biomass and manure types

This contribution presents a developed generic mixed integer linear programming (MILP) model for optimizing biogas supply network to generate electricity over monthly time-periods by maximizing the economic performance. Dry matter content and methane yield for each feedstock are included, which more accurately represents a realistic network. The model is applied to an illustrative case study of an agricultural biogas production plant in Slovenia. Optimal results show poultry manure and bedding and corn silage as the selected feedstocks to meet the production of 999 kW of electricity. Technologies selected include anaerobic digester, press-based dewatering and combined heat and power plant (CHP), while water, and heat required for the anaerobic digestion plant itself are “recycled”. A profit after tax of about 254,625 $/y is obtained. Furthermore, sensitivity analysis in terms of prices of electricity and digestate, dry matter content and utilization of crop residues is performed.

Recent trends in biogas value chains explained using cooperative game theory

In Denmark, since 2014, it has been possible to upgrade biogas to a gas grid and achieve support in line with biogas-based heat and power production. Since then, most new biogas production plants have chosen to upgrade their biogas. In this study, a mixed integer programming model is used to find the optimal biogas value chain, and cooperative game theory is used to understand real world observations compared to this study's results. Specifically, three profit allocation mechanisms are applied to allocate the profit between the heterogeneous owners in the value chain. It is found that Danish biogas plants should use large shares of manure combined with deep litter. Furthermore, it is found that input suppliers have relatively poor bargaining power in the profit allocation negotiations due to poor alternatives. This may explain why livestock farmers tend to receive little payment for their manure, and why they are hesitant to join biogas projects.Finally, it is found that biogas plants prefer to upgrade their biogas for several reasons. First, if the natural gas price is expected to be high, it is preferable to upgrade biogas than to use it directly in a local combined heat and power plant (CHP). Second, if the natural gas price is expected to be low, it is preferable to upgrade because the CHPs have better alternatives and therefore better bargaining power before investments (ex ante). Third, when the value chain contains an upgrading plant, the biogas plant has a greater bargaining power—in particular ex post.

Life cycle assessment of large-scale and household biogas plants in northwest China

Abstract In northwest China, large-scale (modern) and household biogas production (conventional) plants are the two main methods of biogas fermentation, a promising means of livestock waste disposal and effective agricultural recycling. Differences in the operating mechanisms of the two systems result in differences in their environmental performance. In this study, detailed life cycle assessments of large-scale and household biogas production were conducted to compare their environmental performance in terms of energy use and environmental impact potential per function unit (2136 tonne/yr of manure flowing into the biogas plant). Data were collected over a two-year period (2014–2016). The results showed that the total biogas output from the large-scale digester was 1.88 times that of the household digester. Net energy output did not differ much between the two systems, due to the high energy consumption of the large-scale plant during production. The energy-use efficiency of the large-scale plant was 1.29 times that of the household plant due to the use of co-products. Higher carbon dioxide and volatile organic compound emissions from the burning of biogas in the large-scale plant caused a higher potential for global warming and photochemical oxidation. However, higher ammonia and sulfur dioxide emissions occurred in the household plant, resulting in a higher potential for eutrophication, acidification and human toxicity. In conclusion, the waste of extra biogas for heat in large-scale biogas production, and undeveloped management, emissions through poor air-tightness and lack of technical biogas purification in household biogas production are the main hotspots to improve the environmental performance.

Evaluation of biogas potential from livestock manures and rural wastes using GIS in Iran

Abstract The increasing demand of energy, fossil resource limitation and environmental pollution due to fuels combustion has motivated researchers to study about renewable sources of energies. Biogas is a renewable energy resource which is produced through decomposing organic waste under anaerobic conditions and is mainly composed of methane (60%) and carbon dioxide (35–40%). Anaerobic digestion of livestock manure and rural waste, which need to be managed properly to prevent pollution, can be used for sustainable biogas production, reduction of unpleasant odors and microbial pathogens and production of rich fertilizers. This study addresses on how utilization of information such as rural and livestock population, land-use maps and geographic information system (GIS) can be employed to develop a model for evaluation of biogas production from livestock manure and rural household waste, in Iran. The model can be used to identify the appropriate locations for construction of biogas production plants. Moreover, the analysis process used in the current study relies on more spatially detailed information about the available biomass and suitable sites for biogas plant construction, compared to the previous studies conducted in Iran. The results showed that 2740 million m3/year of methane can be annually produced using livestock manure and rural wastes.

Biogas production plants; existing classifications and proposed categories

Production of biogas from anaerobic digestion has the potential to be part of the transition to a renewable based energy system. However, diverse classifications may obstruct knowledge sharing within and between countries, thus potentially hindering development of biogas solutions, as part of an environmentally sustainable renewable based energy system. The aim of this study is to present an approach to categorize biogas production plants and to investigate and compare some country-specific classifications of biogas production plants. The study shows that there are differences between the country-specific classifications studied, both in the terminology and in the underlying descriptions when the terminology is the same. It is also shown that the biogas plants studied do not fit into all of the in-depth country specific European classifications studied. A Framework for Categorization that includes seven categories is proposed. When the biogas plants studied are inserted into the framework, similarities between different plants are shown. These similarities are not found when using the existing European biogas plant classifications. It has also been shown that only three of the proposed categories are included in any of the four in-depth European classifications studied. The Framework, developed in this study, shows the complexity of common categories for biogas production plants, and it is an attempt towards finding a common classification for biogas plants.

Dynamic Simulation of Disturbances Triggering Loss of Operability in a Biogas Production Plant

In the recent years, the biogas industry is rapidly growing, but the sector has been affected by several major accidents related to its supply chain, which pointed out the need to perform a detailed process safety analysis. Hazards and operability analysis (HazOp) is one of the most used and efficient technique for the identification of potential accidents, but its main limitation is the qualitative nature of the results. This study aims to override this limitation by supporting HazOp study using a dynamic simulator, which is able to reproduce deviations and operational failures in a typical biogas production plant, in order to help in the quantification of HazOp results and to improve safety and reliability of the process. The main result of the study is the maximum biogas production rate that can be safely handled by the system under normal conditions and then the maximum rate that can be allowed if some safety barrier (though correctly designed) should fail has been evaluated too. The most critical failure identified is a malfunctioning in the pressure relief system of the digester, because under this condition, the maximum biogas production rate that can be reached is about 2/3 of the corresponding value for a properly working system.

An integrated metagenome and -proteome analysis of the microbial community residing in a biogas production plant

To study the metaproteome of a biogas-producing microbial community, fermentation samples were taken from an agricultural biogas plant for microbial cell and protein extraction and corresponding metagenome analyses. Based on metagenome sequence data, taxonomic community profiling was performed to elucidate the composition of bacterial and archaeal sub-communities. The community’s cytosolic metaproteome was represented in a 2D-PAGE approach. Metaproteome databases for protein identification were compiled based on the assembled metagenome sequence dataset for the biogas plant analyzed and non-corresponding biogas metagenomes. Protein identification results revealed that the corresponding biogas protein database facilitated the highest identification rate followed by other biogas-specific databases, whereas common public databases yielded insufficient identification rates. Proteins of the biogas microbiome identified as highly abundant were assigned to the pathways involved in methanogenesis, transport and carbon metabolism. Moreover, the integrated metagenome/-proteome approach enabled the examination of genetic-context information for genes encoding identified proteins by studying neighboring genes on the corresponding contig. Exemplarily, this approach led to the identification of a Methanoculleus sp. contig encoding 16 methanogenesis-related gene products, three of which were also detected as abundant proteins within the community’s metaproteome. Thus, metagenome contigs provide additional information on the genetic environment of identified abundant proteins.

Diagnostic concept for dynamically operated biogas production plants

With today's growing focus on on-demand energy production, the dynamic operation of biogas plants is becoming more and more important. Detecting unacceptable load changes and so preventing process failures is vital. In the present contribution, we propose an operating scheme that includes the detection of disturbances and intervention. This is then evaluated systematically with the help of a mathematical model for step changes in the organic loading rate. We summarize the qualitative results for each diagnosis variable in an operation diagram, enabling an intuitive, comprehensive comparison. Of the diagnosis variables analyzed, we find that the most promising for identifying incipient process failures in biogas plants are the volatile fatty acids to total alkalinity ratio (VFA/TA), followed by the ratio of methane to carbon dioxide γ in the biogas. In addition, the combination of the online measured variables pH value and gas composition can reveal disturbances early on in a wide range of different conditions.

Resource recycling with algal cultivation: environmental and social perspectives

Efficient use and recycling of resources by utilizing nutrients of waste water and CO2 from flue gases are considered through comparing two conceptual systems: a conventional small scale waste water treatment plant (base case) and a waste water treatment plant combined with algae cultivation unit (algae case). The used algae case concept is based on interviews of experts working with algae cultivation in Finland. Hotspots related to the algae case are assessed from environmental perspectives. According to model calculations, in high latitudes effective algae production may be achieved, although the areal production rates are very low in winter. In the algae case concept nutrients of waste water can be more effectively recycled using bio-based chitosan as flocculant. Also energy is produced in the biogas production plant, which increases the resource recycling of the algae case. When considering the energy balance, a positive net energy ratio (NER) >1 is possible to achieve with maximum methane production potential of algal biomass.

Eubacteria and archaea communities in seven mesophile anaerobic digester plants in Germany

BackgroundOnly a fraction of the microbial species used for anaerobic digestion in biogas production plants are methanogenic archaea. We have analyzed the taxonomic profiles of eubacteria and archaea, a set of chemical key parameters, and biogas production in samples from nine production plants in seven facilities in Thuringia, Germany, including co-digesters, leach-bed, and sewage sludge treatment plants. Reactors were sampled twice, at a 1-week interval, and three biological replicates were taken in each case.ResultsA complex taxonomic composition was found for both eubacteria and archaea, both of which strongly correlated with digester type. Plant-degrading Firmicutes as well as Bacteroidetes dominated eubacteria profiles in high biogas-producing co-digesters; whereas Bacteroidetes and Spirochaetes were the major phyla in leach-bed and sewage sludge digesters. Methanoculleus was the dominant archaea genus in co-digesters, whereas Methanosarcina and Methanosaeta were the most abundant methanogens in leachate from leach-bed and sewage sludge digesters, respectively.ConclusionsThis is one of the most comprehensive characterizations of the microbial communities of biogas-producing facilities. Bacterial profiles exhibited very low variation within replicates, including those of semi-solid samples; and, in general, low variation in time. However, facility type correlated closely with the bacterial profile: each of the three reactor types exhibited a characteristic eubacteria and archaea profile. Digesters operated with solid feedstock, and high biogas production correlated with abundance of plant degraders (Firmicutes) and biofilm-forming methanogens (Methanoculleus spp.). By contrast, low biogas-producing sewage sludge treatment digesters correlated with high titers of volatile fatty acid-adapted Methanosaeta spp.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0271-6) contains supplementary material, which is available to authorized users.

Ecotoxicological assessment of residues from different biogas production plants used as fertilizer for soil

Residues from biogas production (RBP) are a relatively new materials, which may be an interesting resource for the improvement of soil fertility. Nevertheless, in spite of the potential benefits from the agricultural utilization of RBP, there is a need of comprehensive estimation of their toxicity. This information is needed to exclude potential negative environmental impacts arising from the use of RBP.Samples of RBP obtained from six biogas production plants with varied biogas production methods were analysed. The samples with and without separation on solid and liquid phases were investigated. The physicochemical properties of the RBP, heavy metals content (Cr, Cu, Ni, Cd, Pb i Zn) and toxicity on bacteria (Vibrio fischeri, MARA test – 11 different strains), collembolans (Folsomia candida) and two plant species (Lepidium sativum and Sinapis alba) was investigated. Toxicity of RBP was examined using Phytotoxkit F (root growth inhibition), collembolan test (mortality, inhibition of reproduction), Microtox® (inhibition of the luminescence of V. fischeri) and MARA test (growth of microorganisms).An especially negative effect on the tested organisms whereas was noted for the liquid phase after separation. In many cases, RBP without separation also showed unfavourable effects on the tested organisms. Liquid phase after separation and non-separated materials caused inhibition of root growth of L. sativum and S. alba at the level of 17.42–100% and 30.5–100%, respectively, as well as the inhibition of reproduction of F. candida with the range from 68.89 to 100%. In most cases, no ecotoxicological effect was observed for solid phase after separation for tested organisms. The solid phase after separation presented the most favorable properties between all investigated RBP. Therefore, it can be a potential material for the improvement of soil properties and for later use in agriculture.

Biodeterioration of cementitious materials in biogas digester

In biogas production plants, concrete structures suffer chemical and biological attacks during the anaerobic digestion process. The attack on concrete may be linked to the effects of (i) organic acids; (ii) ammonium and CO2 co-produced by the microorganisms’ metabolisms; and (iii) the bacteria’s ability to form biofilms on the concrete surface. In a context of biogas industry expansion, the mechanisms of concrete deterioration need to be better understood in order to propose innovative, efficient solutions. This study aims, firstly, to characterise the evolution of the biochemical composition of the biodegradable wastes during digestion so as to identify the compounds that are aggressive for concrete. Secondly, it aims to evaluate the mechanisms of concrete deterioration in anaerobic digesters. CEM I paste specimens were immersed in synthetic inoculated biowaste in anaerobic digestion conditions. The liquid fractions were analysed chemically. The alteration mechanisms of the cementitious matrices were investigated using XRD and SEM analyses. The maximal total concentration of organic acids was 65 mmol/L in the liquid fraction during the digestion process. The pH evolution showed two phases: acidification in the first few days and then a slow increase to pH 7–8. In only 4 weeks, an abundant biofilm developed on the cement paste surface. Biodeterioration leads to calcium leaching and carbonation of the cement paste.

Design and Construction of a Water Scrubber for the Upgrading of Biogas

This paper discusses the results of studies conducted on raw biogas produced from a prototypic biogas production plant located at the Teaching and Research Farm, University of Ibadan, Ibadan. This setup consists of a mixing chamber, a biogas digester and a stabilizing unit, locally designed and fabricated. It further discusses preliminary and detailed design coupled with the construction of an effective and efficient technology used in purifying raw biogas generated from the prototypic biogas production plant; this technology is otherwise known as the Water Scrubbing technology. The Scrubbing system consists of the Water scrubber with iron wool packed bed connected to a 500 litre water tank, and two tyre tubes which were used in storing the pre scrubbed (raw) biogas and the scrubbed (purified) biogas. The water scrubber has an inlet for the entry of the raw biogas and a discharge for the exit of the scrubbed biogas. Raw biogas from the plant was stored in a tyre tube and directly fed into the Water scrubber housing the iron wool packed bed, the purified biogas from the exit was also collected into another tyre tube. The samples of the gas mixture were taken before and after scrubbing and analyzed with Pascal Manometric Glass Tube technique. Results indicated that methane content of the scrubbed/ purified biogas was raised from 58% to 82% due to the reduction of Carbon dioxide and Hydrogen Sulphide. CO2 was reduced from 31% to 14% while H2S was reduced from 1% to 0.4%. The corresponding Energy content of the purified biogas was evaluated to be 41MJ/kg which is higher than that of the raw biogas which was evaluated to be 29MJ/kg.

Clostridium cluster I and their pathogenic members in a full-scale operating biogas plant.

A biogas production plant operating with main and secondary digesters (MD, SD) was analysed for the diversity of bacteria from Clostridium cluster I and its pathogenic members. The plant was run in two parallel lines, both receiving silages, and one, in addition, cattle manure (CM). Quantitative PCR of 16S rRNA genes from directly extracted DNA indicated that cluster I represented 0.2 to 5.6 % of the total bacterial communities. Its prevalence was particularly low in CM and also in SD compared to MD, indicating its decline during fermentation. In contrast, another highly abundant clostridial group, i.e. the "faecal" cluster XIVa, remained quantitatively unaffected during fermentation. A total of 85.1 % of 581,934 rRNA gene sequences gathered by group-specific PCR from the silages, CM and digesters could be assigned to cluster I. All remaining sequences fell into other clostridial groups. The three most dominant operational taxonomic units (OTUs) introduced with CM were from cluster I, and they declined during fermentation. Fermentation with CM significantly increased OTUs of clostridia outside of cluster I but not within. The only OTUs related to pathogens were detected for Clostridium botulinum with 0.18 % of all cluster I sequences in maize silage and less than 0.01 % in the other substrates and digester materials. These OTUs could be assigned to all four established C. botulinum groups, thus, potentially covering all seven neurotoxins. Mouse lethality tests of samples with suspected presence of C. botulinum, however, indicated no toxigenic potential and, thus, no risk associated with the rare occurrence of these OTUs.

BiogasAgriAtex, new methods of risk assessment explosion on biogas plants

In agricultural farms and biogas plants, the presence of produced greenhouse gases, vapors, mists that are mixed with air under atmospheric conditions may pose a risk of explosion. These possible mixtures are also defined as an explosive atmosphere. To cause an explosion it is necessary the occurrence of a so called ‘trigger’, which can be for example: a spark due to production processes, a breakdown of the electrical system, an inconsiderate use of open flames or a hot surface in contact with the explosive atmosphere. In absence of such ‘triggers’ the explosive atmosphere is no longer a possible risk. As specified in the ATEX (Atmosphere Explosible ) regulation, the presence of ‘triggers’ is expressed on a probabilistic basis. For this probability evaluation, it is necessary to consider the overall available historical data and perform a statistical survey. The aim of this study was to discuss explosion prevention during biogas production and to determine if inside agricultural biogas plants are present areas in which explosive atmospheres may occur. These risk areas should be classified determining several parameters such as the volume of explosive atmosphere (Vz), the risk distance (dz) and the dispersion time (t). For these evaluation was designed a software named BiogasAgriAtex developed in Microsoft Excel program following the CEI 31-35 2007 regulation (third edition), which applies the CEI EN 60079-10 (CEI 31-30) regulation. The main result of this study is a comprehensible program for agricultural companies that defines and manages critical points within biogas production plants.

Syntrophic acetate oxidation in industrial CSTR biogas digesters

The extent of syntrophic acetate oxidation (SAO) and the levels of known SAO bacteria and acetate- and hydrogen-consuming methanogens were determined in sludge from 13 commercial biogas production plants. Results from these measurements were statistically related to the prevailing operating conditions, through partial least squares (PLS) analysis. This revealed that high abundance of microorganisms involved in SAO was positively correlated with relatively low abundance of aceticlastic methanogens and high concentrations of free ammonia (>160mg/L) and volatile fatty acids (VFA). Temperature was identified as another influencing factor for the population structure of the syntrophic acetate oxidising bacteria (SAOB). Overall, there was a high abundance of SAOB in the different digesters despite differences in their operating parameters, indicating that SAOB are an enduring and important component of biogas-producing consortia.

Biogas Production from Thin Stillage on an Industrial Scale—Experience and Optimisation

With the increasing demand for renewable energy and sustainable waste treatment, biogas production is expanding. Approximately four billion litres of bio-ethanol are produced annually for vehicle fuel in Europe, resulting in the production of large amounts of stillage residues. This stillage is energy-rich and can be used for biogas production, but is a challenging substrate due to its high levels of nitrogen and sulphate. At the full-scale biogas production plant in Norrköping, Sweden (Svensk Biogas i Linköping AB), thin grain stillage is used as a biogas substrate. This paper describes the plant operation and strategies that have been implemented to digest thin stillage successfully. High ammonia concentrations in the digester have resulted in syntrophic acetate oxidation (SAO) becoming the major pathway for acetate degradation. Therefore, a long hydraulic retention time (HRT) (40–60 days) is used to allow the syntrophic acetate-oxidising bacteria time to grow. The high sulphate levels in thin stillage result in high levels of hydrogen sulphide following degradation of protein and the activity of sulphate-reducing bacteria (SRB), the presence of which has been confirmed by quantitative polymerase chain reaction (qPCR) analysis. To optimise biogas production and maintain a stable process, the substrate is diluted with tap water and co-digested with grain residues and glycerine to keep the ammonium nitrogen (NH4-N) concentration below 6 g L−1. Combined addition of iron, hydrochloric acid and cobalt successfully precipitates sulphides, reduces ammonia toxicity and supplies microorganisms with trace element. Mesophilic temperature (38 °C) is employed to further avoid ammonia toxicity. Together, these measures and doubling the digester volume have made it possible to increase annual biogas production from 27.7 TJ to 69.1 TJ.

Production of renewable energy in agriculture: current situation and future developments

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PRELIMINARY TRIAL APPLICATION OF BIOLOGICAL DESULFONATION IN ANAEROBIC DIGESTORS FROM PIG FARMS

This paper describes preliminary tests carried out in treatment plants serving two different pig farms in Northern Italy, in order to assess the feasibility of implementing biological sulphur removal from biogas produced by anaerobic digestion processes. This normally consists of mixture of CH4, CO2, and other gases; in the presence of sulphur, H2S is also formed, which must be removed prior to the gas use in thermal engines, to avoid corrosion phenomena. Sulphur removal in the plants considered is currently achieved by means of chemical filtration, however this adds costs to the process and generates a waste to be disposed of. As a process alternative, biological sulphur removal by means of Thiobacillus sp. bacteria can also be obtained. The process, however, requires specific conditions in the gas stream in order to achieve high process efficiency. Biological desulfonation was applied on a trial basis in two biogas production plants, with different layouts, and encouraging results. These confirms the validity of the process, although the maximum foreseen removal efficiencies were not achieved due to structural drawbacks of the tested facilities, that will have to be revamped in order to apply this process with full satisfaction and effectiveness.