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•Energy storage via biomethanisation may benefit from previous H2 injections.•Low CO2 levels may inhibit hydrogenotrophic methanogens.•Acetate may act as storage during conditions ...unfavorable for biomethanisation.•The reactor inorganic carbon level was an indicator of reactor stability.
Surplus electricity from fluctuating renewable power sources may be converted to CH4 via biomethanisation in anaerobic digesters. The reactor performance and response of methanogen population of mixed-culture reactors was assessed during pulsed H2 injections. Initial H2 uptake rates increased immediately and linearly during consecutive pulse H2 injections for all tested injection rates (0.3 to 1.7LH2/Lsludge/d), while novel high throughput mcrA sequencing revealed an increased abundance of specific hydrogenotrophic methanogens. These findings illustrate the adaptability of the methanogen population to H2 injections and positively affects the implementation of biomethanisation. Acetate accumulated by a 10-fold following injections exceeding a 4:1 H2:CO2 ratio and may act as temporary storage prior to biomethanisation. Daily methane production decreased for headspace CO2 concentrations below 12% and may indicate a high sensitivity of hydrogenotrophic methanogens to CO2 limitation. This may ultimately decide the biogas upgrading potential which can be achieved by biomethanisation.
China has a long history of utilizing biogas technology for the treatment of waste and the production of energy. This paper reviews the development and technology of the three types of biogas ...digesters used in China: household-scale digesters, biogas septic tanks, and biogas plants for the treatment of municipal, industrial, and agricultural waste. The structure of household-scale digesters is simple and practical; the basic type is the fixed-dome digester, also called the hydraulic digester. The biogas septic tank for sewage treatment is a combination of the traditional digester, an anaerobic filter, and a facultative filter.
Biogas plants apply several different processes depending on the type of waste treated. The treatment of municipal waste biogas is conducted using the completely stirred tank rector (CSTR). The upflow anaerobic sludge blanket (UASB) is the most common technology used in the anaerobic treatment of industrial wastewater, followed by the CSTR and the anaerobic contact (AC) process. The treatment of agricultural waste mainly employs traditional hydraulic digesters, while newer biogas plants use advanced anaerobic processes such as CSTR and UASB as well as upflow solids reactors (USR) and upflow blanket filter (UBF) reactors. Biogas plants for agricultural waste are classified as small, medium, large and super large based on the scale of biogas production and digester volume.
Although small-scale biogas plants are the most common, large-scale biogas plants produce the largest biogas output. With the changes associated with socio-economic development, the growth of household-scale digesters will slow down in the future. As central sewage treatment networks become more widespread, biogas septic tanks will be confined to villages and small towns. The development of biogas plants holds the most growth potential for the future.
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•Plasma biogas reforming over K-, Ce- and Mg-promoted catalysts was carried out.•Plasma-alone, catalysis-alone and plasma-catalysis modes were evaluated.•Plasma-catalytic coupling ...showed a synergy in conversion and energy efficiency.•Adding promotors to Ni catalyst enhanced the conversion of reactants.•The promoted Ni catalysts increased carbon deposition on the catalysts.
Plasma-catalytic biogas reforming over Ni-X/Al2O3 catalyst (X=K, Mg and Ce) has been carried out in a coaxial dielectric barrier discharge (DBD) plasma reactor at 160°C. Three different process modes: plasma-alone, catalysis-alone and plasma-catalysis have been investigated to get new insights into the synergistic effect resulted from the interaction of the plasma with the promoted Ni catalysts. Compared to the biogas reforming using either plasma-alone or catalysis-alone mode at the same temperature (160°C), the combination of the plasma with the Ni-based catalysts exhibited a low temperature synergistic effect, as evidenced from the much higher reforming performance of the plasma-catalytic process compared to that of the sum of the individual processes (plasma-alone and catalysis-alone). The addition of promoters (K, Mg and Ce) into the Ni/Al2O3 catalyst enhanced the conversion of CH4, the yield of H2 and the energy efficiency of the plasma process. In this study, the behaviour of K, Mg and Ce promoters in the low temperature plasma-catalytic biogas reforming was clearly different from that in high temperature thermal catalytic process in terms of the conversion of CH4 and carbon deposition, which could be ascribed to the temperature-dependent character of the promotors. In the plasma-catalytic biogas reforming, the Ni-K/Al2O3 catalyst showed the best performance, enhancing the conversion of both CO2 and CH4, the yield of H2, CO and C2–C4 alkanes and the energy efficiency of the plasma process. The highest conversion of CO2 (22.8%) and CH4 (31.6%) was achieved by placing the K-promoted catalyst in the plasma reforming process. The Mg-promoted catalyst remarkably increased the H2/CO molar ratio in the gas products (up to 2.2) due to the decreased CO2 conversion. In addition, compared to the un-promoted Ni/Al2O3 catalyst, although the use of the promoted catalysts increased the carbon deposition on the surface of the spent catalysts by 22%–26%, the total amount of deposited carbon was still less than that reported in high temperature catalytic dry reforming processes. More than 80% of the increased carbonaceous species was in the form of reactive carbon species, which can be easily oxidized by CO2 and O atoms and maintain the stability of the catalysts during the reforming reaction.
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•Membrane contactors with renewable CO2 absorbents are used for biogas upgrading.•Mass transfer resistance in the membrane contactor for biogas upgrading is studied.•Temperature has ...little effect on CO2 absorption rates of the renewable absorbents.•Biogas upgrading performance is highly dependent on the gas and liquid flow rates.•This study paves a new way to use renewable absorbents for carbon minimization.
This study employs novel renewable absorbents derived from biogas slurry (BS) for biogas upgrading via membrane contactors. CO2 absorption capacity of biogas slurry can be enhanced by adding alkali solutions, vacuum regeneration or vacuum membrane distillation (VMD). These methods are used to produce four types of renewable CO2 solvents, including vacuum regenerated BS, recovered aqueous ammonia (RAA) from BS by VMD, calcium oxide treated BS and potassium hydroxide treated BS. These renewable absorbents for CO2 capture from biogas by membrane contactors are investigated. CO2 removal efficiency reduces but absorption rates increase with the rise in CO2 volume fraction in the feed gas stream. Absorption temperature has a limited effect on CO2 absorption rates of the renewable absorbents. RAA shows the best CO2 absorption performance among the four types of renewable absorbents in the membrane contactor. RAA flowing on the tube side leads to a 50% higher CO2 removal efficiency compared with RAA on the shell side. At low gas flow rates, partial absorbents and hollow fibers may not be utilized. Thus, selection of membrane module parameters, including the length of module, the number of hollow fibers, biogas flow rates and absorption performance, should be carefully considered when using membrane contactors for biogas upgrading.
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•Digestate fertilizing-value typology was established from a big digestate database.•Dry matter and nitrogen content appear as first driver of digestate variability.•Raw digestates ...are classed/grouped according to anaerobic digestion feedstock and process.•Liquid and solid fractions are classed/grouped according to feedstock and separation equipment.•The digestate typology is compared to the latest European Union regulation proposal on fertilizers.
Defined as the residue from anaerobic digestion (AD), digestate refers to a set of materials with varied biochemical compositions. The objective of this study was to establish a digestate typology according to its fertilizing-value with data from literature and internal unpublished databases. To establish a relatively big database allowing the application of advanced statistics, usual fertilizing-value parameters were used: dry matter, volatile solids, C/N, C/Organic-N, total N (TN), total ammoniacal nitrogen (TAN), TAN/TN, total P and total K. Statistical analysis was performed on a dataset of 91 raw digestates, 34 solid fractions and 25 liquid fractions after separation. The resulting typology outlined that fertilizing-values are linked to AD feedstock and process. As case study regulations, no digestate (without any post-treatment) fulfilled French standards and the latest European Union regulation proposal on fertilizers. Options to reach regulations’ product categories were discussed according to the typology. For the first time, a digestate typology was established based on fertilizing value, which can be a useful tool enhancing digestate management and policy making.
Renewable biogas production technology is an excellent method for eradication of greenhouse gas emission and thereby reducing global warming. This review discusses extensively on global biomass ...potential, energy need and method of satisfying the energy demand through sustainable techniques. One of the best alternative technological developments for the conversion of waste into useful energy is anaerobic digestion to produce biogas. It is recognized as one among leading green energy to manage the environmental and meet the current energy tasks to tackle globally. Generally, biogas can be utilized for cooking, heat and electricity generation. In order to extend the scope of application, traces of carbon dioxide, hydrogen sulphide has to be removed by several upgrading technologies to produce high purity methane (90%). This study discusses on biogas up-gradation using physical and chemical absorption, membrane separation, cryogenic separation, hybrid technology etc. Among the various up-gradation techniques, hybrid technology yields methane purity of 97%. In addition, this work reviews about benefits and problems in anaerobic integrated Solid Oxide Fuel Cell (SOFC) with latest real-world achievement in SOFC. Several SOFC systems with dynamic model development were reviewed based on efficiency of power generation. SOFC generates 45% more electricity than generator with heat engine. This review extends the scope for further research in biogas upgradation and global warming mitigation potential with carbon credits.
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•Waste to energy is the sustainable methodology to have unpolluted earth.•Biomass is found as best renewable source of energy for CH4 production.•Comparing with other upgrading methods, hybrid technology yields 97% pure CH4.•Upgraded biogas with >95% CH4 content increased SOFC efficiency.•Gradual increase in global electricity production due to renewable sources.
•Composting of biogas residues and spent mushroom substrate lasted 118 days.•Plant growth was used to evaluate the compost maturity.•Compost as tomato substrate showed better seedling quality than ...commercial seedling.•TOC, C/N, NH4+-N, NO3−-N, AK and lignocellulose can be used to evaluate compost maturity.
Recycling of BR and SMS are crucial for the development of biogas industry and commercial mushroom cultivation. The seed germination test is limited to examine the maturity of compost because of lacking the effect of insoluble part on plant growth. The aim of this study was to evaluate the maturity of compost by analysis the relationship between agronomic parameters of plant growth with physicochemical parameters of compost. The thermophilic period (over 50 °C) was lasted 52 days. TOC, C/N, AP and NH4+-N was decreased along with composting process, while TK, TP, AK and NO3−-N showed an opposite trend. As for seedling quality, the raw material (T0) showed the worst plant growth but the 100% compost (T1) showed better seedling quality compared with commercial seedlings. According to the analysis of Spearman correlation, the results indicated that TOC, C/N, NH4+-N, NO3−-N, AK and lignocellulose can be used to evaluate compost maturity.
The Renewable Energy Act 2023 (§39i) requires reducing corn silage in biogas plants from 40 % to 30 % in 2026. Since corn silage yields the highest biogas per weight unit of all biogas feedstocks, ...this poses new challenges for biogas plant operators. However, alternative biogas feedstocks not harvested directly from the field may contain siloxanes due to the use of care products and disinfectants. The conversion of siloxanes into silicon dioxide during the combustion process seriously threatens the lifetime and efficiency of the used gas engine, even in very low concentrations. Consequently, we present a highly sensitive measurement system for monitoring biogas. Detection limits down to 0.037 mg/m³ for the tested siloxanes have been reached. Furthermore, ketones can be detected down to 0.002 mg/m³, alcohols down to 0.001 mg/m³. The device combines an ultra-fast polarity switching ion mobility spectrometer with a switching time of 12 ms and a resolving power of RP = 70, a gas chromatographic pre-separation, and a non-dispersive infrared sensor for methane. In this context, we analyzed the biogas composition for volatile substances and siloxanes, whereby we only found the volatile substances. For demonstration, biogas was analyzed at three different stages during the gas purification process.
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Anaerobic digestion of renewable feedstocks has been known as a prospective technology for the production of clean energy in the form of biogas. Biogas is a sustainable energy carrier which is mainly ...composed of methane (60%) and carbon dioxide (35–40%). Among the raw substances, organic matters obtained from farm animal waste are pivotal sources for biogas production. In recent years, the number of animal husbandry has drastically grown in Malaysia. Accordingly, a large amount of animal waste including manure, blood and rumen content are produced which provide a tremendous source of biogas generation. This paper presents biogas potential from the organic waste obtained from the farm animals and slaughterhouses in Malaysia. The findings of this study indicated that biogas potential of 4589.49 millionm3year−1 could be produced from animal waste in Malaysia in 2012 which could provide an electricity generation of 8.27×109kWhyear−1.
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