Showing papers on "Biogas published in 2015"
TL;DR: A comprehensive review of research achievements on anaerobic digestion developments for biogas production is presented in this article, which includes a discussion of factors affecting efficiency (temperature, pH, C/N ratio, OLR and retention time).
Abstract: With the rising demand for renewable energy and environmental protection, anaerobic digestion of biogas technology has attracted considerable attention within the scientific community. This paper presents a comprehensive review of research achievements on anaerobic digestion developments for biogas production. The review includes a discussion of factors affecting efficiency (temperature, pH, C/N ratio, OLR and retention time), accelerants (greenery biomass, biological pure culture and inorganic additives), reactors (conventional anaerobic reactors, sludge retention reactors and anaerobic membrane reactors) and biogas AD processes (lignocellulose waste, municipal solid waste, food waste, livestock manure and waste activated sludge) based on substrate characteristics and discusses the application of each forementioned aspect. The factors affecting efficiency are crucial to anaerobic digestion, because they play a major role in biogas production and determine the metabolic conditions for microorganism growth. As an additive, an accelerant is not only regarded as a nutrient resource, but can also improve biodegradability. The focus of reactor design is the sufficient utilization of a substrate by changing the feeding method and enhancing the attachment to biomass. The optimal digestion process balances the optimal digest conditions with the cost-optimal input/output ratio. Additionally, establishment of theoretical and technological studies should emphasize practicality based on laboratory-scale experiments because further development of biogas plants would allow for a transition from household to medium- and large-scale projects; therefore, improving stability and efficiency are recommended for advancing AD research.
1,149 citations
TL;DR: A review of the worldwide history, current status, and predictable future trend of bioenergy and bio-fuels can be found in this paper, with a focus on the development and utilization of renewable energy such as bioenergy.
Abstract: The recent energy independence and climate change policies encourage development and utilization of renewable energy such as bioenergy. Biofuels in solid, liquid, and gaseous forms have been intensively researched, produced, and used over the past 15 years. This paper reviews the worldwide history, current status, and predictable future trend of bioenergy and biofuels. Bioenergy has been utilized for cooking, heating, and lighting since the dawn of humans. The energy stored in annually produced biomass by terrestrial plants is 3–4 times greater than the current global energy demand. Solid biofuels include firewood, wood chips, wood pellets, and wood charcoal. The global consumption of firewood and charcoal has been remaining relatively constant, but the use of wood chips and wood pellets for electricity (biopower) generation and residential heating doubled in the past decade and will increase steadily into the future. Liquid biofuels cover bioethanol, biodiesel, pyrolysis bio-oil, and drop-in transportation fuels. Commercial production of bioethanol from lignocellulosic materials has just started, supplementing the annual supply of 22 billion gallons predominantly from food crops. Biodiesel from oil seeds reached the 5670 million gallons/yr production capacity, with further increases depending on new feedstock development. Bio-oil and drop-in biofuels are still in the development stage, facing cost-effective conversion and upgrading challenges. Gaseous biofuels extend to biogas and syngas. Production of biogas from organic wastes by anaerobic digestion has been rapidly increasing in Europe and China, with the potential to displace 25% of the current natural gas consumption. In comparison, production of syngas from gasification of woody biomass is not cost-competitive and therefore, narrowly practiced. Overall, the global development and utilization of bioenergy and biofuels will continue to increase, particularly in the biopower, lignocellulosic bioethanol, and biogas sectors. It is expected that by 2050 bioenergy will provide 30% of the world’s demanded energy.
641 citations
TL;DR: In this paper, the authors systematically review the state-of-the-art of biogas cleaning and upgrading technologies, including product purity and impurities, methane recovery and loss, upgrading efficiency and the investment and operating costs.
Abstract: Biogas is experiencing a period of rapid development and biogas upgrading is attracting increasing attention. Consequently, the market for biogas upgrading is facing significant challenges in terms of energy consumption and operating costs. Selection of upgrading technology is site-specific, case-sensitive and dependent on the biogas utilisation requirements and local circumstances. Therefore, matching the technology selected for use to specific requirements is significantly important. This paper systematically reviews the state-of-the-art of biogas cleaning and upgrading technologies, including product purity and impurities, methane recovery and loss, upgrading efficiency and the investment and operating costs. In addition, the potential utilisation of biogas and the corresponding requirements on gas quality are investigated in depth. Based on the results of comparisons between the technical features of upgrading technologies, the specific requirements for different gas utilizations and the relevant investment and operating costs, recommendations are made regarding appropriate technology.
610 citations
TL;DR: This review critically presents and discusses the state of the art of biogas upgrading technologies with special emphasis on biotechnologies for CO2, H2S, siloxane and halocarbon removal.
Abstract: The lack of tax incentives for biomethane use requires the optimization of both biogas production and upgrading in order to allow the full exploitation of this renewable energy source. The large number of biomethane contaminants present in biogas (CO2, H2S, H2O, N2, O2, methyl siloxanes, halocarbons) has resulted in complex sequences of upgrading processes based on conventional physical/chemical technologies capable of providing CH4 purities of 88–98 % and H2S, halocarbons and methyl siloxane removals >99 %. Unfortunately, the high consumption of energy and chemicals limits nowadays the environmental and economic sustainability of conventional biogas upgrading technologies. In this context, biotechnologies can offer a low cost and environmentally friendly alternative to physical/chemical biogas upgrading. Thus, biotechnologies such as H2-based chemoautrophic CO2 bioconversion to CH4, microalgae-based CO2 fixation, enzymatic CO2 dissolution, fermentative CO2 reduction and digestion with in situ CO2 desorption have consistently shown CO2 removals of 80–100 % and CH4 purities of 88–100 %, while allowing the conversion of CO2 into valuable bio-products and even a simultaneous H2S removal. Likewise, H2S removals >99 % are typically reported in aerobic and anoxic biotrickling filters, algal-bacterial photobioreactors and digesters under microaerophilic conditions. Even, methyl siloxanes and halocarbons are potentially subject to aerobic and anaerobic biodegradation. However, despite these promising results, most biotechnologies still require further optimization and scale-up in order to compete with their physical/chemical counterparts. This review critically presents and discusses the state of the art of biogas upgrading technologies with special emphasis on biotechnologies for CO2, H2S, siloxane and halocarbon removal.
464 citations
TL;DR: In this paper, the barriers, gaps, and challenges in deploying biogas production technology are identified, and the issues are classified as economic, technical, social or regulatory issues.
Abstract: Recently the United States Environmental Protection Agency qualified biogas from landfills and anaerobic digesters as a cellulosic transportation biofuel under the expanded Renewable Fuel Standard (RFS2). Biogas is a renewable fuel that can generate Renewable Identification Number credits for the producer. The wastewater industry may not be able to keep pace with this opportunity. Less than 10% of WWTPs in the US have currently produced biogas for beneficial use. Supporting growth of the biogas industry requires implementation of new practices and policies. In this review, the barriers, gaps, and challenges in deploying biogas production technology are identified. Issues are classified as economic, technical, social or regulatory issues. Some of the critical challenges to the economics of digester operations are the slow rate of biogas generation, the low energy content of the biogas, and the costs to upgrade the biogas. Currently there is little biogas utilization at US WWTPs. Most biogas is flared while some is used for onsite process heat and power production. Case studies of co-digestion of biosolids with organic wastes at field-scale show the use of co-digestion could overcome significant economic challenges including higher methane yield, more efficient digester volume utilization and reduced biosolids production. These findings could provide guidance in retrofitting existing facilities or in designing new biogas production and utilization systems. The RFS2 ruling increases market certainty, hence reduces risk. The evaluation of applications of co-digestion at WWTP scales ranging from 1 million gallons per day (MGD) to 375 MGD determined its potential feasibility for different types of digester operation, organic waste and loading rate as well as effectiveness of providing energy self-sufficiency at the WWTPs. This work could improve economics of anaerobic digestion at WWTPs, enabling viable and sustainable biogas industry and offsetting costs for wastewater management.
374 citations
TL;DR: Analysis and optimisation of the anaerobic digestion of the organic fraction of municipal solid waste and its role in bioreactor landfills.
Abstract: 1.Fundamentals of the anaerobic digestion process 2.Reactor sizing, process kinetics, and modelling of anaerobic digestionof complex waste 3.Analysis and optimisation of the anaerobic digestion of the organicfraction of municipal solid waste 4.Anaerobic digestion of the organic fraction of municipal solid waste:a perspective 5.Types of anaerobic digester for solid wastes 6.Characteristics of the OFMSW and behaviour of the anaerobic digestionprocess 7.Co-digestion of the organic fraction of municipal waste with otherwaste types 8.Pretreatments for the enhancement of anaerobic digestion of solidwastes 9.Use of hydrolysis products of the OFMSW for biological nutrientremoval in wastewater treatment plants 10.Products, impacts and economy of anaerobic digestion of OFMSW 11.Anaerobic digestion of organic solid waste in bioreactor landfills
368 citations
TL;DR: In this paper, the authors focus on the different alternatives of digestate valorisation, apart from land applications, such as the use of the digestate liquor for replacing freshwater and nutrients in algae cultivation, and the conversion of solid digestate into added-value products (char or activated carbons) through a pyrolysis process.
Abstract: In the agricultural sector of many European countries, biogas production through anaerobic digestion (AD) is becoming a very fast-growing market. AD is a simple and robust process that biologically converts an organic matrix into biogas and digestate, the latter corresponding to the anaerobically non-degraded fraction. So far, digestate has been mostly used at farm-scales for improving soils. However, its ever-increasing production induces problems related to transport costs, greenhouse-gas emissions during storage and high nitrogen content that constrains its use to land application only. Consequently, research on alternative valorisation routes to reduce its environmental impact and to improve the economical profitability of AD plants should draw increasing interest in the future. This review therefore focuses on the different alternatives of digestate valorisation, apart from land applications: (I) the use of the digestate liquor for replacing freshwater and nutrients in algae cultivation; (II) the use of solid digestate for energy production through biological (i.e. AD, bioethanol) or thermal processes (i.e. combustion, hydrothermal carbonization and pyrolysis); (III) the conversion of solid digestate into added-value products (char or activated carbons) through a pyrolysis process.
359 citations
TL;DR: In this paper, a review of various operating parameters and their effects on anaerobic digestion (AD) is presented, and different pretreatment methods including mechanical, thermal, chemical and biological methods to improve the effectiveness of AD of municipal solid waste (MSW) management.
Abstract: Municipal solid waste (MSW) management is becoming a serious issue in all over the world. Anaerobic digestion (AD) is one of the technologies to convert that waste into useful form of energy. But megacities like Singapore having limited resources, cannot fulfill the cow dung or other animal manure requirements in AD. Therefore there is a need to study critically the operating parameters and also the pretreatment technologies available for treating the substrate so that one can get the maximum output with limited input. To fulfill the need, the present paper deals with the review of various operating parameters and their effects on AD. This paper also reviews different pretreatment methods including mechanical, thermal, chemical and biological methods to improve the effectiveness of AD of MSW.
334 citations
TL;DR: In this paper, the authors present the actual context of anaerobic digestion within the sugarcane ethanol production in Brazil, presenting the main obstacles for its full application and the directions to promote it as well.
Abstract: The replacement of fossil fuels by biofuels has been extremely important worldwide to stimulate the growth of economies based on the sustainability through the use of renewable resources. Anaerobic digestion for biogas production is recognized as a clean technology that allies the suitability of wastes with energy generation, fulfilling the requirements for a sustainable alternative to provide the optimization of the biofuels production. This alternative is especially interesting for the sugarcane ethanol production in Brazil, in which the generation of vinasse, the main liquid waste, is very expressive. Nevertheless, the use of vinasse for anaerobic digestion has been finding some challenges to its establishment in the Brazilian sugarcane biorefineries. This paper reviews the actual context of anaerobic digestion within the sugarcane ethanol production in Brazil, presenting the main obstacles for its full application and the directions to promote it as well. Alternatives for biogas use are also presented and compared, highlighting the environmental and energy advantages of applying anaerobic digestion in the sugarcane biorefineries. This scenario is envisaged as a suitable way to achieve the future biorefineries model, based on the use and recovery of renewable resources with economic, social, and environmental benefits.
320 citations
TL;DR: A discussion on the different materials used to produce membranes for gas separation is given in this paper, including inorganic, organic and mixed matrix membranes, as well as polymer of intrinsic microporosity (PIM).
Abstract: Biogas is a renewable energy source like solar and wind energies and mostly produced from anaerobic digestion (AD). The production of biogas is a well-established technology, but its commercial utilization is limited because on-site purification is needed before its transport or use. Biogas composition varies with the biomass digested and contains mainly methane (CH4) and carbon dioxide (CO2), as well as traces of hydrogen sulfide (H2S), ammonia (NH3), hydrogen (H2), nitrogen (N2), carbon monoxide (CO), oxygen (O2). In some cases dust particles and siloxanes are present. Several purification processes including pressurized water scrubbing, amine swing absorption, pressure swing adsorption, temperature swing adsorption, cryogenic separation and membrane technologies have been developed. Nevertheless, membrane technology is a relatively recent but very promising technology. Also, hybrid processes where membranes are combined with other processes are believed to have lower investment and operation costs compared with other processes. In this report, a discussion on the different materials used to produce membranes for gas separation is given including inorganic, organic and mixed matrix membranes, as well as polymer of intrinsic microporosity (PIM). Advantages and limitations for each type are discussed and comparisons are made in terms of permeability and diffusivity for a range of operating conditions.
310 citations
TL;DR: In this article, a review summarizes the challenges in SS-AD of lignocellulosic biomass and discusses the mechanisms and feasibility of potential strategies for resolving them, including pretreatment of feedstock, improvement of inoculation efficiency, co-digestion of multiple feedstocks, and upgrading biogas to higher value transportation fuels.
Abstract: Solid-state anaerobic digestion (SS-AD) has gained increasing attention in recent years, especially for digesting lignocellulosic biomass Compared to liquid anaerobic digestion (L-AD), SS-AD handles feedstocks with higher total solids content, and therefore, performs more effectively at higher organic loading rates and has higher volumetric biogas productivity Challenges facing SS-AD of lignocellulosic biomass are primarily related to its relatively low methane yield, potential instability, and low value end-products These challenges are either due to the inherent limits of SS-AD (eg retarded mass transfer caused by high solid content) or can be attributed to the nature of lignocellulosic biomass (eg components recalcitrant to biodegradation) To address these challenges, a variety of methods, including pretreatment of feedstock, improvement of inoculation efficiency, co-digestion of multiple feedstocks, and upgrading biogas to higher-value transportation fuels, have been examined to enhance the performance of SS-AD and increase the value of the end products This review summarizes these challenges in SS-AD of lignocellulosic biomass and discusses the mechanisms and feasibility of potential strategies for resolving them
TL;DR: In this article, the authors provide a comprehensive study on algal biomass as feedstock for biogas production, which is one of the most promising solutions to mitigate climate change and as alternative to fast depleting of fossil fuels and oil reserves.
Abstract: The objective of this work is to provide a comprehensive study on algal biomass as feedstock for biogas production. Algae-derived biofuels are seen as one of the most promising solutions to mitigate climate change and as alternative to fast depleting of fossil fuels and oil reserves. Microalgae and macroalgae underwent an intense academic and industrial research, thanks to their capability to overcome the drawbacks related to the first and second generations of biomass resources. Major advantages of algae are: no competition with food crops for arable land, high growth rates, low fractions of lignin which reduces the need for energy-intensive pretreatment and compatibility with biorefinery approach implementation. However, some disadvantages such as the presence of high water content, seasonal chemical composition and the occurrence of inhibitory phenomena during anaerobic digestion, make algal biofuels not yet economically feasible although they are more environment friendly than fossil fuels.
TL;DR: In this article, the authors provided up-to-date knowledge and information on macroalgae-based biofuels, such as biogas, bioethanol, biodiesel and bio-oils respectively obtained from anaerobic digestion, fermentation, transesterification, liquefaction and pyrolysis technique methods.
Abstract: Algae is a very promising source for renewable energy production since it can fix the greenhouse gas (CO2) by photosynthesis and does not compete with the production of food Compared to microalgae, researches on biofuel production from macroalgae in both academia and industry are at infancy for economically efficient and technological solutions This review provides up to-date knowledge and information on macroalgae-based biofuels, such as biogas, bioethanol, biodiesel and bio-oils respectively obtained from anaerobic digestion, fermentation, transesterification, liquefaction and pyrolysis technique methods It is concluded that bioethanol and bio-oils from wet macroalgae are more competitive while biodiesel production seems less attractive compared to high lipid content microalgae biomass Finally, a biorefinery concept based on macroalgae is given
TL;DR: Biological desulfurization methods are currently promoted to abiotic methods because they are less expensive and do not produce undesirable materials which must be disposed of.
TL;DR: In this paper, the authors suggest that these novel bioprocessing routes for conversion of low value feedstock to higher added value products will contribute to a sustainable future and will change the economic status of organic waste.
Abstract: Anaerobic digestion for the production of methane containing biogas is the classic example of a resource recovery process that combines stabilization of particulate organic matter or wastewater treatment with the production of a valuable end-product. Attractive features of the process include the production of a single end-product from a heterogeneous feedstock, and in-situ product separation of the gaseous end-product. Despite these intrinsic attractive properties of the process, the economic added value of the biogas produced is limited, enabling the development of alternative processes that yield higher-value end-products. Typically the production of higher value end-products from low value feedstock and industrial wastewater proceeds via intermediate production of organic acids (and carbon dioxide and molecular hydrogen). Optimization of organic acid production from particulate feedstocks and wastewater for development of the organic acid based resource recovery route receives significant research attention. The organic acid stream generated as such, has no economic value, but if organic acids can either be concentrated via membrane separation or (bio)converted to an end-product that can easily be separated from the liquid, an attractive biomass processing scheme can be developed. Attractive end-products of organic acid processing include polyhydroxyalkanoates, medium chain length fatty acids, or other organic molecules using bio-electrochemical systems. Overall we suggest that these novel bioprocessing routes for conversion of low value feedstock to higher added value products will contribute to a sustainable future and will change the economic status of organic waste.
TL;DR: An overview of the most recent advances pertaining to metabolic engineering of microbial methane utilization is presented and some ideas concerning metabolic improvements for production of acetyl-CoA and pyruvate, two main precursors for bioconversion, are presented.
TL;DR: The increase of hydrogenotrophic methanogens and syntrophic Desulfovibrio and the decrease of aceticlastic methanogen indicate a H2-mediated shift toward the hydrogenot microscopic pathway enhancing biogas upgrading.
Abstract: This study proposes an innovative setup composed by two stage reactors to achieve biogas upgrading coupling the CO2 in the biogas with external H2 and subsequent conversion into CH4 by hydrogenotrophic methanogenesis. In this configuration, the biogas produced in the first reactor was transferred to the second one, where H2 was injected. This configuration was tested at both mesophilic and thermophilic conditions. After H2 addition, the produced biogas was upgraded to average CH4 content of 89% in the mesophilic reactor and 85% in the thermophilic. At thermophilic conditions, a higher efficiency of CH4 production and CO2 conversion was recorded. The consequent increase of pH did not inhibit the process indicating adaptation of microorganisms to higher pH levels. The effects of H2 on the microbial community were studied using high-throughput Illumina random sequences and full-length 16S rRNA genes extracted from the total sequences. The relative abundance of archaeal community markedly increased upon H2 addition with Methanoculleus as dominant genus. The increase of hydrogenotrophic methanogens and syntrophic Desulfovibrio and the decrease of aceticlastic methanogens indicate a H2-mediated shift toward the hydrogenotrophic pathway enhancing biogas upgrading. Moreover, Thermoanaerobacteraceae were likely involved in syntrophic acetate oxidation with hydrogenotrophic methanogens in absence of aceticlastic methanogenesis.
TL;DR: In this article, the effects of a thermal hydrolysis process (THP) on the solubilization of main organics of sludge, as well as the performance of the followed biochemical methane potential (BMP) tests under mesophilic condition (35°C), were systematically evaluated.
TL;DR: In-depth analysis of operational and environmental parameters and bacterial community structure indicated the presence of three potential clusters in anaerobic digestion, determined by total ammonia concentration, free ammonia concentration and temperature, and characterized by an increased relative abundance of Bacteroidales, Clostridiales and Lactobacillales, respectively.
TL;DR: In this article, the experimental biochemical methane potentials (BMP) of typical food waste (FW) and straw from northern China were individually measured in a 1L enclosed reactor at 35°C, and were 0.26 and 0.16m 3 /kg-VS (volatile solids), respectively.
TL;DR: Anaerobic digestion of organic residues has the potential to significantly contribute to a shift from fossil to renewable energy as mentioned in this paper, but the byproduct, anaerobic slurry, does have properties that are different from the undigested material.
Abstract: Anaerobic digestion of organic residues has the potential to significantly contribute to a shift from fossil to renewable energy. The by-product, anaerobic slurry, does have properties that are different from the undigested material. There are concerns of soil organic matter depletion in soils, enhanced greenhouse gas and odour emissions, and pathogen spread upon production and use of biogas slurries as fertilizer. However, considering the pros and cons, anaerobic digestion of residues does have positive effects for the climate, the environment and for the farmer, compared to the use of undigested matter.
TL;DR: In this paper, a pipeline-quality biomethane was produced by anaerobic digestion of sludge with in-situ biogas cleanup and upgrading using corn stover biochar.
TL;DR: The anaerobic digestion process and its complexities are reviewed, the substrate used in the process, the relationship between the substrate and microorganisms and important operating parameters such as pH, temperature and loading rate are covered.
Abstract: The search for alternative energy and fuels has motivated researchers to focus on renewable and sustainable means of getting them instead of relying on the conventional way of energy and fuel production. Anaerobic digestion is a biochemical process during which complex organic matter is decomposed in absence of oxygen, by various types of anaerobic microorganisms. The process of Anaerobic digestion is appropriate for all waste water treatment systems given that the solid can be introduced to the system at an acceptable concentration. Biogas, the product of anaerobic digestion process is a clean and renewable form of energy which can be a substitute for conventional sources of energy which are causing ecological-environmental problems and at the same time depleting at a faster rate. This paper reviews the anaerobic digestion process and its complexities; it covers different stages involved in the process, the substrate used in the process, the relationship between the substrate and microorganisms and important operating parameters such as pH, temperature and loading rate.
TL;DR: In this paper, a review intended to critically evaluate the recent technological advances and promising prospects coupled with various aspects of biogas production such as sustainable feedstock utilization, microbial and enzyme dynamics, parameter optimization and process segregation, for enhancing this technology in outlook.
Abstract: A key strategy allied with today is to develop an alternative energy source instead of fossil fuels in order to compensate present energy need in addition to reduce environmental concerns owed by pollution and global warming. Energy generation in feasible manner without possessing environmental crash is a difficult task where alternative concepts were requisite to ensure sustainable development with accessible technologies. Further advances triggered renewed attention in biogas production technology while it has great impacts on diminishing major economic issues raised in the world. Since the light of these strategies, the present review intended to critically evaluate the recent technological advances and promising prospects coupled with various aspects of biogas production such as sustainable feedstock utilization, microbial and enzyme dynamics, parameter optimization and process segregation, for enhancing this technology in outlook. Appropriate selection, co-digestion, and biotransformation offers a great challenge that crafts substrate to become more energy efficient, besides to trim down the constraints behind principle biomass utilization. A basic framework for process stimulation with microorganisms and enzyme preparations explored that further experimental trials by means of identification of efficient microbes and standardization of enzyme dynamics would augment the feasibility of energy flow during anaerobic digestion. Accordingly, the optimization of various parameters is preferred to accelerate biogas production by resolving the problems occur during anaerobic digestion. Despite the development of multi-stage digester designs intend a breakthrough for process segregation and existing opportunities in this aspect needed further research interest to attain better performance of the system. Moreover, advance simulation approaches using projected prospects from this review would realize significant enhancement of biogas production in the predictable manner.
TL;DR: In this paper, the authors compared different process designs, each at a high level of technology readiness and suitable for large-scale conversion of CO2 into liquid hydrocarbon fuels, using biogas from sewage sludge as a source of CO 2.
Abstract: Utilising CO2 as a feedstock for chemicals and fuels could help mitigate climate change and reduce dependence on fossil fuels. For this reason, there is an increasing world-wide interest in carbon capture and utilisation (CCU). As part of a broader project to identify key technical advances required for sustainable CCU, this work considers different process designs, each at a high level of technology readiness and suitable for large-scale conversion of CO2 into liquid hydrocarbon fuels, using biogas from sewage sludge as a source of CO2. The main objective of the paper is to estimate fuel production yields and costs of different CCU process configurations in order to establish whether the production of hydrocarbon fuels from commercially proven technologies is economically viable. Four process concepts are examined, developed and modelled using the process simulation software Aspen Plus® to determine raw materials, energy and utility requirements. Three design cases are based on typical biogas applications: (1) biogas upgrading using a monoethanolamine (MEA) unit to remove CO2, (2) combustion of raw biogas in a combined heat and power (CHP) plant and (3) combustion of upgraded biogas in a CHP plant which represents a combination of the first two options. The fourth case examines a post-combustion CO2 capture and utilisation system where the CO2 removal unit is placed right after the CHP plant to remove the excess air with the aim of improving the energy efficiency of the plant. All four concepts include conversion of CO2 to CO via a reverse water-gas-shift reaction process and subsequent conversion to diesel and gasoline via Fischer–Tropsch synthesis. The studied CCU options are compared in terms of liquid fuel yields, energy requirements, energy efficiencies, capital investment and production costs. The overall plant energy efficiency and production costs range from 12–17% and £15.8–29.6 per litre of liquid fuels, respectively. A sensitivity analysis is also carried out to examine the effect of different economic and technical parameters on the production costs of liquid fuels. The results indicate that the production of liquid hydrocarbon fuels using the existing CCU technology is not economically feasible mainly because of the low CO2 separation and conversion efficiencies as well as the high energy requirements. Therefore, future research in this area should aim at developing novel CCU technologies which should primarily focus on optimising the CO2 conversion rate and minimising the energy consumption of the plant.
TL;DR: Overall, the application of emerging technologies is limited by AD effluent composition, especially the total solid content, which may lead to underutilization of AD for the treatment of agricultural and food wastes.
TL;DR: In this article, the effect of high and low-temperature thermal pretreatment (TPT) on sludge dewaterability, anaerobic digestion (AD), and biogas production efficiencies is summarized.
Abstract: This review summarizes the effect of high- and low-temperature thermal pretreatment (TPT) on sludge dewaterability, anaerobic digestion (AD), and biogas production efficiencies. The AD of the TPT sludge has demonstrated the following observations: reduced sludge retention time, increased biogas generation, higher organics degradation, improved dewaterability, and lower digester volume than the conventional AD of sludge. Energy balance of the TPT process was energetically self-sustainable and produced surplus energy at solids concentration greater than 3%. Net energy and energy ratio of TPT and AD revealed that net energy and energy ratio are increased with increase in total solids concentration.
TL;DR: In this paper, a simple evaluation of energy consumption by pretreatments is made and it can be stated that unfortunately not all the pretreatment technologies have an energy self-sufficiency to be implemented in a WWTP, requiring many times a continuous energy investment.
TL;DR: The main findings are that the direct effects of anaerobic digestion on long-term sustainability in terms of soil fertility and environmental impact at the field level are of minor relevance, and potential cropping system-based changes induced by introduction of biogas plants are probably much more relevant for the overall performance and sustainability of the cropper system than thedirect effects triggered by application of digestates in comparison to the undigested feedstocks.
Abstract: Sustainability in agriculture means the inclusion of several aspects, as sustainable agriculture systems must not compromise not only their ability to satisfy future needs by undermining soil fertility and the natural resource base but also sustainable agriculture has had to address a range of other issues including energy use, efficient use, and recycling of nutrients, the effects on adjacent ecosystems including the effects on water bodies and climate change. Organic manures are an important factor to keep the soil fertility level of soils. However, their management is often related to large emissions. In this context, anaerobic digestion is—similarly to composting—a treatment option for stabilization of biogenic wastes leading to a residual product called digestates, enabling the sanitation and the recycling and use as fertilizer. It is also a means to obtain energy from wastes as well as from dedicated energy crops. Therefore, anaerobic digestion potentially addresses several aspects of agricultural sustainability. This review discusses the current state of knowledge on the effects of anaerobic digestion on organic compounds in digestates and the most important processes influencing N emissions in the field, as well as the possible long-term effects on soil microbial biomass and soil fertility. The main findings are that (1) the direct effects of anaerobic digestion on long-term sustainability in terms of soil fertility and environmental impact at the field level are of minor relevance. (2) The most relevant effects of anaerobic digestion on soil fertility as well as on N emissions will be expected from indirect effects related to cropping system changes such as changes in crop rotation, crop acreage, cover cropping, and total amounts of organic manures including digestates. Furthermore, (3) the remaining organic fraction after anaerobic digestion is much more recalcitrant than the input feedstocks leading to a stabilization of the organic matter and a lower organic matter degradation rate after field application, enabling a similar reproduction of the soil organic matter as obtained by direct application of the feedstock or by composting of the feedstock. (4) Regarding emissions, the main direct effect of anaerobic digestion on a farm level is the influence on gaseous emissions during manure or digestate treatment and handling, whereas the direct effects of anaerobic digestion on a field level on emissions (NH3
− and N2O− emissions, NO3
- leaching) are negligible or at least ambiguous. (5) The main direct effects of anaerobic digestion on the field level are short-term effects on soil microbial activity and changes in the soil microbial community. Therefore, in terms of the effects on agricultural sustainability, potential cropping system-based changes induced by introduction of biogas plants are probably much more relevant for the overall performance and sustainability of the cropping system than the direct effects triggered by application of digestates in comparison to the undigested feedstocks. Furthermore, to get the full potential advances from implementation of biogas plants in terms of improvement of the nutrient use efficiency and reduction of greenhouse gas emissions, there is the need to introduce more sophisticated techniques to avoid counteracting effects by pollution swapping, e.g., by gas-tight closure of the digestate stores and direct soil incorporation of the field-applied digestates.
TL;DR: In this article, the authors investigated the feasibility to combine anaerobic digestion and pyrolysis processes in order to increase the energy recovery from agricultural residues and the sustainability of an AD plant.