Potential for biofuels from the biomass of prickly pear cladodes: Challenges for bioethanol and biogas production in dry areas

Prickly pear is a term used to refer to several species of cactus belonging primarily to the genus Opuntia. In general, these species present an exceptional ability to produce biomass in soil and climate conditions unfavorable for most plant species, in part due to their high water use efficiency. Given the current increase demand for renewable energy and the future prospect of more limited water resources, the potential use of prickly pear cladodes for biofuel production deserves to be investigated. The objectives of this study were to gather information on the chemical composition of prickly pear biomass from the most cultivated varieties in NE Brazil, discuss the potential of processing biomass for ethanol and biogas production and to point out gaps in know-how and priorities for research on this topic. We quantified in the tree varieties studied significant amounts of uronic acids (10.7%) and oxalic acid (10.3%), confirming the reports of high amounts of pectin and calcium oxalate in cladodes of prickly pear. The estimated potential of ethanol production for prickly pear (1490–1875 L ha⁻¹ yr⁻¹) was low when compared to traditional biomass sources (sugarcane and sugar beet, for example). However, it appears that prickly pear stands out as a biomass with potential for high production rates of methane (3717 m³ ha⁻¹ yr⁻¹), being comparable to traditional energy crops. Further studies are needed to assess more consistently both the sustainability of biomass production as the potential for ethanol, and biogas production, specially for newly released varieties of prickly pear.     

Performance evaluation of biogas upgrading systems from swine farm to biomethane production for renewable hydrogen source

Biogas upgrading to biomethane is a necessary process for biohydrogen production from renewable source. In this work, absorption processes using water and diethanolamine (DEA) as absorbent were modeled in Aspen Plus software. The purpose was to find the optimal operating condition for sustainable production of biomethane using multi-criteria perspective considering technical, environmental and economic aspects. The absorption system was modified by including one additional absorber unit for improving biogas upgrading efficiency. The performance of the biogas upgrading system was evaluated and compared in terms of methane recovery, methane content in biomethane, and energy consumption. Effects of operating conditions such as operating pressure in absorber, concentration, and total flow rate of absorbents were investigated. The results revealed that the performance of the modified absorption system was superior to the conventional system. The methane content in biomethane, methane recovery, and energy consumption increased with the increase of operating pressure in the absorbers. Increasing concentration and total flow rate of absorbents increased the methane content in biomethane and the energy consumption but decreased the methane recovery. The optimal operating condition could achieve 96%v/v of methane content in biomethane with methane recovery of higher than 95%v/v in the modified water absorption system. The optimum operating pressures of absorber Units 1 and 2, and total absorbent flow rates were at 13 and 5 bar and 16,000 kmol/h, respectively.     

Life Cycle Energy Assessment of biohydrogen production via biogas steam reforming: Case study of biogas plant on a farm in Serbia

The aim of this paper is to demonstrate and to quantify energy flows in a life cycle of biogas to biohydrogen production, starting from feedstock materials via anaerobic digestion, biogas upgrading, biohydrogen production, to the end of biogas system (application of digestate as fertilizer in agriculture). The performance of the biogas plant of Mirotin dairy farm in Serbia has been assessed. According to Life Cycle Energy Assessment approach, results obtained in this study have shown that biohydrogen production via biogas steam reforming has negative energy balance (with ?16,837 GJ). It has also been demonstrated that this process is energy unsustainable in an environmental context. In future analysis it would be necessary to consider the other aspects of sustainability, e.g. the economical and social factors in order to estimate the overall sustainability of the biogas utilization pathways, especially having in mind that the technology of converting biogas to hydrogen is still in the development phase.     

Optimization of the production and quality of biogas in the anaerobic digestion of different types of biomass in a batch laboratory biodigester and pilot plant: Numerical modeling,kinetic study and hydrogen potential

The study aims to evaluate the biogas production and quality from four biomasses (microalgae (MB), sorghum (S), corn stubble (CS), rapeseed oil (RO)) in a digestion process carried out in two batch reactor (6 L) and pilot plant (1.5 m³) agitated mechanically.The substrates were characterized and anaerobic digestion was carried out as batch tests in mesophilic conditions for 30–35 days. Inoculum/substrate ratio was 1:1–2:1. Gas composition and total gas volume produced were monitored. Methane yields of 306, 345, 419, and 740 NL kg VS^?1 were obtained for MB, CS, S, and RO, respectively, in laboratory tests, while in pilot plant tests were 182, 151, 397 and 655 NL kg VS^?1. CH₄ percentage in biogas was 49–60%. The yield of H₂ generated for the four biomasses in the two types of biodigesters has been estimated, obtaining values between 16 and 39 mL g VS^?1.First-order, Modified Gompertz, and Cone models have been applied to evaluate the kinetic parameters on the methane produced in the batch and pilot plant tests, obtaining an excellent fit. ADM1 model with 19 biological processes (disintegration of biomass composite, enzymatic hydrolysis, and digestion of soluble materials mediated by organisms), acid-base equilibria, kinetic study, and liquid-gas transference has been used to fit the cumulative methane volume.     

Status and potential of biogas energy from animal wastes in Turkey

Biogas is a potentially important energy source that can be used for the production of heat, electricity and fuel. It can be produced at wastewater treatment plants, landfills, food and other industrial operations throughout the world. There is largely untapped potential in agricultural operations where animal waste is often land applied or otherwise disposal of without conversion to energy. According to the last agricultural census (2009) in Turkey; there are a total of 3,076,650 agricultural enterprises and approximately 70% of these enterprises are running livestock farming. 10,811,165 of total animal is cattle, 26,877,793 of total animal is small ruminant and 234,082,206 is poultry. The amount of wet waste of these animals is about 120,887,280 t. These wastes could be a major problem for enterprises and cannot be utilized properly. The best way to utilize waste is to produce biogas. In this study, biogas amount which will be obtained from animal waste was calculated for all provinces by using the number of livestock animals and also considering various criteria such as the rate of dry matter and availability. Animal origin waste map of Turkey was also produced with these calculated values. The biogas energy potential of Turkey was found to be 2,177,553,000 m³ (2.18 Gm³) by using the animal numbers in the last agricultural census (2009). The total biogas potential is originated from 68% cattle, 5% small ruminant and 27% poultry. Biogas energy equivalence of Turkey is approximately 49 PJ (1170.4 ktoe). When the prepared waste map is examined; provinces that have more than 1 GJ of biogas energy potential are found to be; Bolu, Bal?kesir, ?zmir, Sakarya, Konya, Manisa, Erzurum, Afyon, Kars and Ankara respectively.     

Preliminary design of a small-scale system for the conversion of biogas to electricity by HT-PEM fuel cell

In this work a novel concept for the decentralized conversion of biogas to electricity is introduced. It consists of five segments: gas supply, gas treatment, gas reforming, gas usage and post-combustion. The system was designed in a regional project called GREEN-FC. The project is dealing with a design study for the conversion of 1 m³ h⁻¹ biogas to electricity, based on equilibrium calculations for steam reforming and water–gas shift reaction in combination with CFD simulations. The simulation results revealed that the system converts methane fully and delivers a maximum yield of hydrogen with a low concentration of carbon monoxide, thus making it suitable for a high-temperature polymer–electrolyte membrane (HT-PEM) fuel cell. The calculated electrical efficiency of the novel process is approximately 40%. Another important result of this work is the modular prototype design, because the individual components of the prototype can be replaced. For example alternative reactors that convert biogas into hydrogen and other technologies that use hydrogen can be included.     

Planning land use for biogas energy crop production: The potential of cutaway peat production lands

Each year, thousands of hectares of peatland that had been harvested are being released in Finland, which can offer an opportunity to increase energy crops and attain the bioenergy targets for non-agriculture lands. In this study, the Geographic Information System (GIS) method was used to improve the assessment of decentralized renewable energy resources. The amount of peat production lands and future cutaway areas for energy crop production was calculated as a case study by using ArcGIS and the Finnish Topographic database. There are almost 1000 km² of peat production lands in Finland, and theoretically, approximately 300 km² of cutaway peatlands could be used for energy crops after 30 years. The dry biomass yield of reed canary grass (Phalaris arundinacea) or timothy-fescue grass (mix of Phleum pratense and Festuca pratensis) could be higher than 100 Gg a⁻¹ in these lands indicating methane potential of approximately 300 GWh. The exhausted peat production areas in the western region of Finland have significant potential for use for energy crops; North and South Ostrobothnia account for almost 45% of the total peat production land. A future goal could be to use the cutaway peat production lands more efficiently for bioenergy to mitigate climate change. Since the use of wastelands (including peatlands) are being considered in Europe as a way to avoid competition with food production, the GIS method used in the study to identify suitable peat lands could be applicable to biomass resource studies being conducted in many countries.     

Evaluation of energy efficiency of various biogas production and utilization pathways

The energy efficiency of different biogas systems, including single and co-digestion of multiple feedstock, different biogas utilization pathways, and waste-stream management strategies was evaluated. The input data were derived from assessment of existing biogas systems, present knowledge on anaerobic digestion process management and technologies for biogas system operating conditions in Germany. The energy balance was evaluated as Primary Energy Input to Output (PEIO) ratio, to assess the process energy efficiency, hence, the potential sustainability. Results indicate that the PEIO correspond to 10.5–64.0% and 34.1–55.0% for single feedstock digestion and feedstock co-digestion, respectively. Energy balance was assessed to be negative for feedstock transportation distances in excess of 22 km and 425 km for cattle manure and for Municipal Solid Waste, respectively, which defines the operational limits for respective feedstock transportation. Energy input was highly influenced by the characteristics of feedstock used. For example, agricultural waste, in most part, did not require pre-treatment. Energy crop feedstock required the respect cultivation energy inputs, and processing of industrial waste streams included energy-demanding pre-treatment processes to meet stipulated hygiene standards. Energy balance depended on biogas yield, the utilization efficiency, and energy value of intended fossil fuel substitution. For example, obtained results suggests that, whereas the upgrading of biogas to biomethane for injection into natural gas network potentially increased the primary energy input for biogas utilization by up to 100%; the energy efficiency of the biogas system improved by up to 65% when natural gas was substituted instead of electricity. It was also found that, system energy efficiency could be further enhanced by 5.1–6.1% through recovery of residual biogas from enclosed digestate storage units. Overall, this study provides bases for more detailed assessment of environmental compatibility of energy efficiency pathways in biogas production and utilization, including management of spent digestate.     

Evaluation of annual bioenergy crops in the boreal zone for biogas and ethanol production

Three annual plant species, maize, hemp and faba bean were tested for suitability as dedicated biomass crops in Boreal conditions. Biomass yields were 10-15 t ha^-1. The crops were analyzed for their composition and tested as raw materials for conversion to methane and to fermentable sugars. The methane yield was 379 ± 16 Ndm³ kg⁻¹ VS⁻¹ from maize, 387 ± 20 Ndm³ kg⁻¹ VS⁻¹ from faba bean and 239 ± 9 Ndm³ kg⁻¹ VS⁻¹ from hemp. Based on the yield per hectare, maize proved to be the most potential raw material source for methane production. Analogous to methane production, maize was the most productive raw material also in standard hydrolysis tests, with a conversion yield of about 80% of the theoretical sugars. Based on the amount of carbohydrates, the highest theoretical yield per hectare was obtained with hemp. However, considering all parameters, including the need for weeding and fertilizers, all three crops studied proved to be attractive options for cultivation in boreal conditions as well as being used as energy crops in boreal climate.     

An evaluation of the policy and techno-economic factors affecting the potential for biogas upgrading for transport fuel use in the UK

Gaseous biofuels including biomethane, which has been shown to be more environmentally beneficial than liquid biofuels, should contribute to meeting the challenging UK targets set for the supplying of biofuels to the road transport fuel market. Under the Renewable Transport Fuel Obligations the financial incentives for the supply of biofuels have been volatile, e.g. 2008/2009 saw Renewable Transport Fuel Certificate values fall to zero. Any shortfall from the maximum value has significant implications for all biofuels. It is demonstrated that biomethane can be produced at a cost which is competitive with liquid biofuels and fossil fuels within the UK. Technologies such as water scrubbing, pressure swing adsorption and physical and chemical absorption are available to upgrade biogas generated by anaerobic digestion of organic wastes to transport fuel quality, and technologies such as membrane separation and cryogenic distillation are being modified for such an application. The manufacture and sale of biomethane as a transport fuel is also financially competitive with Combined Heat and Power. One limiting factor may be the additional cost of purchasing and maintaining biomethane fuelled vehicles. Support in this area could lead to the rapid expansion of biomethane transport fuel infrastructure and bring significant long term environmental and economic advantages.     

A study of a greenhouse concept on conventional biogas systems for enhancing biogas yield in winter months

A new concept is introduced of using a greenhouse for enhancing the biogas yield from a conventional biogas system in the winter months. If a conventional biogas system is glazed, the trapped solar energy can be used to raise the temperature of the slurry which normally goes low enough to reduce the gas yield appreciably. Numerical calculations have been performed corresponding to the meteorological data on a typical winter day, i.e. 19 January 1981, at New Delhi (India). A comparative study of the performances of conventional and solar-assisted biogas plants using the concept of a greenhouse indicates that the ambient temperature of the slurry can be raised from 18°C to about 37°C, the optimal temperature for anaerobic fermentation.     

Evaluation of stainless steel cathodes and a bicarbonate buffer for hydrogen production in microbial electrolysis cells using a new method for measuring gas production

Microbial electrolysis cells (MECs) are often examined for hydrogen production using non-sustainable phosphate buffered solutions (PBS), although carbonate buffers have been shown to work in other bioelectrochemical systems with a platinum (Pt) catalyst. Stainless steel (SS) has been shown to be an effective catalyst for hydrogen evolution in MECs, but it has not been tested with carbonate buffers. We evaluated the combined using of SS cathodes and a bicarbonate buffer (BBS) at the applied voltages of 0.5, 0.7 and 0.9 V using a new inexpensive method for measuring gas production called the gas bag method (GBM). This method achieved an average error of only 5.0% based on adding known volumes of gas to the bag. Using the GBM, hydrogen production with SS and a BBS was 26.6 ± 1.8 mL which compared well to 26.4 ± 2.8 mL using Pt and BBS, and 26.8 ± 2.5 mL with a Pt cathode and PBS. Electrical energy efficiency was highest with a SS cathode and BBS at 159 ± 17%, compared to 126 ± 14% for the Pt cathode and BBS, and 134 ± 17% for a Pt cathode and PBS. The main disadvantage of the SS was a lower gas production rate of 1.1 ± 0.3 m³ H₂-m⁻³ d⁻¹ with BBS and 1.2 ± 0.3 m³ H₂-m⁻³ d⁻¹ with PBS, compared to 1.7 ± 0.4 m³ H₂-m⁻³ d⁻¹ with Pt and PBS. These results show that the GBM is an effective new method for measuring gas production of anaerobic gas production processes, and that SS and bicarbonate buffers can be used to effectively produce hydrogen in MECs.     

New sustainable bioconversion concept of date by-products (Phoenix dactylifera L.) to biohydrogen,biogas and date-syrup

The dates production is usually accompanied by considerable loss of fruit byproducts. The chemical analysis showed that ‘Deglet Nour’ discarded flesh is rich in soluble sugars (79.8% ± 0.8%) and fibers (12.3% ± 0.4%). A processing approach was implemented to permit the production of biohydrogen from the flesh and biogas from the crude fiber fraction after soluble sugars extraction. This approach showed interesting results since the obtained biochemical hydrogen potential and the maximum methane yield were 292 mL H₂/gVS _initial and 235 mL CH₄/gVS _fibers respectively. Parallelly, the “hot water” soluble sugar fraction (date syrup) was of interest for agro-alimentary applications and showed a high sucrose, glucose and fructose content of 33.5%, 11.8% and 13.17% respectively. This study presents a proof of concept allowing an efficient sustainable energetic conversion of the date by-products biomass to biohydrogen via dark fermentation or to soluble sugars fraction and biogas via a biorefinery approach.     

A review of the biogas industry in China

This article presents an overview of the development and future perspectives of the Chinese biogas industry. The development of the industry has the potential to improve the rural environment and produce significant amounts of sustainable energy for China. Barriers to the development are the relatively weak environmental policies, imperfect financial policies and lack of long-term follow-up services. The rapid economic development of China has also seen a development in the scales of biogas plants constructed. Although the technology has been improved, this review has identified problems in the construction and operation of Chinese biogas plants, particularly in the efficiency of household systems. All levels of China's government acknowledge this and recent biogas projects have more focus on quality and less on the quantity. The intention is to gradually introduce stricter environmental policies, to provide better service systems, improve the financial policies that support the construction and follow-up service of biogas projects, promote the use of standardized engineering equipment and materials and standards for plant construction and production. This will promote the development of biogas projects at various scales further, and reduce the dependency on fossil fuels and emissions of greenhouse gases.     

Evaluation of methods for estimating energy performance of biogas production

This study focused on identifying various system boundaries and evaluating methods of estimating energy performance of biogas production. First, the output–input ratio method used for evaluating energy performance from the system boundaries was reviewed. Secondly, ways to assess the efficiency of biogas use and parasitic energy demand were investigated. Thirdly, an approach for comparing biogas production to other energy production methods was evaluated. Data from an existing biogas plant, located in Finland, was used for the evaluation of the methods. The results indicate that calculating and comparing the output–input ratios (R_pr1, R_pr2, R_ut, R_pl and R_sy) can be used in evaluating the performance of biogas production system. In addition, the parasitic energy demand calculations (w) and the efficiency of utilizing produced biogas (η) provide detailed information on energy performance of the biogas plant. Furthermore, R_f and energy output in relation to total solid mass of feedstock (F_O/TS) are useful in comparing biogas production with other energy recovery technologies. As a conclusion it is essential for the comparability of biogas plants that their energy performance would be calculated in a more consistent manner in the future.     

Giant cane (Arundo donax L.) for biogas production: The effect of two ensilage methods on biomass characteristics and biogas potential

Arundo donax L. is a perennial plant that can substitute for traditional energy crops to produce biogas, reducing costs because of its high biogas yield per Ha cultivated and low agronomic and energetic inputs. Nevertheless, Arundo donax biomass needs to be ensiled to be preserved and used. Because no full-scale data exist about A. donax ensilage and the effect of this process on potential biogas production, in this work two different ensiling techniques, i.e. trench and silo-bag ensiling, were performed at full scale, and the processes studied for 200 days. Results obtained indicated that A. donax could be successful ensiled by using the two approaches. Ensilage proceeded by fermentation of organic acids already present in the biomass, i.e. malic and oxalic acids that were degraded, giving volatile fatty acid accumulation. This was different from corn ensiling characterized by starch fermentation to lactic acids. Biological processes determined a loss of the potential biomethane production, namely −20.1% and −7.6% for trench and silo-bag, respectively. Taking into consideration biomethane yield per Ha and ensilage losses, potential biomethane losses of 5000 Nm³ CH₄ Ha⁻¹ for trench silage and of 2000 Nm³ CH₄ Ha⁻¹ for silo bag, were estimated, respectively. Nevertheless, taking into consideration the higher biomass and biomethane yields Ha⁻¹ in comparison with the other energy crops, A. donax still remained more efficient and cheaper than traditional energy crops in producing biogas.     

Local acceptance of existing biogas plants in Switzerland

After the Swiss government's decision to decommission its five nuclear power plants by 2035, energy production from wind, biomass, biogas and photovoltaic is expected to increase significantly. Due to its many aspects of a direct democracy, high levels of public acceptance are necessary if a substantial increase in new renewable energy power plants is to be achieved in Switzerland. A survey of 502 citizens living near 19 biogas plants was conducted as the basis for using structural equation modeling to measure the effects of perceived benefits, perceived costs, trust towards the plant operator, perceived smell, information received and participation options on citizens’ acceptance of “their” biogas plant. Results show that local acceptance towards existing biogas power plants is relatively high in Switzerland. Perceived benefits and costs as well as trust towards the plant operator are highly correlated and have a significant effect on local acceptance. While smell perception and information received had a significant effect on local acceptance as well, no such effect was found for participation options. Reasons for the non-impact of participation options on local acceptance are discussed, and pathways for future research are presented.     

Enhancement in daily production of biogas system

In this communication, a straightforward analysis of a conventional biogas system (KVIC) integrated with a greenhouse at the top of the dome has been presented. The effect of the use of movable insulation during off-sunshine hours has been included in the analysis. The use of night insulation reduces the heat losses from the top of the system, which causes an appreciable increase in the production of the biogas system. Numerical calculations have been made for a typical winter day in Delhi.     

A comparison of the drivers influencing adoption of on-farm anaerobic digestion in Germany and Australia

This review examines the drivers behind the adoption of on-farm anaerobic digestion in Germany where there were more than 4000 plants operating in 2009. In Australia, only one plant is operating, at a piggery in the State of Victoria. Germany’s generous feed-in-tariffs for renewable energy are typically given the credit for promoting investment in on-farm anaerobic digestion. But the particular biophysical and socio-economic character of farming in the country provided the fertile ground for these financial incentives to take root. Energy security has also been a major driver for the promotion of renewable energy in Germany since it imports over 60% of its energy needs. In contrast, Australia is a net energy exporter, exporting about two-thirds of its domestic energy. Although it has considerable potential for application in Australia, anaerobic digestion is unlikely to be widely adopted unless new incentives emerge to strongly encourage investment. Stronger Australian regulation of manures and effluent may serve as an incentive to a limited extent in the future. Yet the experience in Germany suggests that regulation on its own was not sufficient to encourage large numbers of farmers to invest in anaerobic digestion. Even with generous incentives from the German government, increasing construction costs and the rising cost of energy crops can put the financial viability of anaerobic digestion plants at risk. Unless improvements in efficiency are found and implemented, these pressures could lead to unsustainable rises in the cost of the incentive schemes that underpin the development of renewable energy technologies.