Economics and greenhouse gas balance of biogas use systems in the Finnish transportation sector

Energy decisions play an essential role in reducing greenhouse gas (GHG) emissions in the transportation sector. Biogas is a renewable energy source and can be used as an energy source for gas-operated cars or for electric cars. This paper compares different ways to use biogas, which is produced on a medium scale anaerobic digestion plants, as an energy source for transportation. The research is conducted from an economic and environmental point of view, and the option to deliver upgraded biogas via a natural gas grid is taken into account. Different processes for the use of biogas for transportation purposes are compared using life cycle assessment (LCA) methods in the Finnish operational environment. It seems that the most economical way is to use biogas in gas-operated cars due to the high price of methane for vehicle fuel use. A new feed-in tariff for electricity produced with biogas will, however, have highly positive economic effects on electricity production from biogas. From the environmental point of view, the highest CO₂ reductions are gained when biogas is used in gas-operated cars or in CHP plants for power and heat production. During the transition stage, it might be reasonable to use biogas in gas-operated cars and most importantly in heavy vehicles to reduce GHG and local pollutants rapidly. If biogas production is located near a natural gas grid, the biogas can be delivered effectively via the natural gas grid. The use of biogas in gas-operated cars is an effective way to reduce carbon dioxide significantly in the transportation sector.     

Environmental assessment of electricity generation from an Italian anaerobic digestion plant

A standard ISO Life Cycle Assessment study was carried out to evaluate the environmental sustainability of electricity production from an anaerobic digestion (AD) plant using a mixture of dedicated energy crops, agricultural residues and livestock effluents as input materials. The functional unit was 1 MJ of electricity. System boundaries were from cradle to grave and covered all the phases from energy crops cultivation to the production of biogas and its use in a Combined Heat and Power plant to produce electricity. Liquid and solid digestate storage and spreading on agricultural land were included. Primary data were collected from the AD plant for all the above phases. Since heat produced is used only internally, no allocation was applied in the study. As regards digestate management, CH₄ emissions were calculated from literature, whereas four literature methods were applied for calculation of nitrogen emissions with the goal to perform a sensitivity analysis on LCA results. ILCD Handbook impact assessment methodologies were used. Results show that the main hotspots are energy crops cultivation and the management of digestate, mainly because of both nitrogen and methane emissions, affecting Global Warming, Acidification, Marine and Freshwater Eutrophication. Finally, a detailed Monte Carlo analysis, was carried out to evaluate the results uncertainty. The study represents the state of the art about the environmental performance of the AD plant with the use of sensitivity and uncertainty analysis, which both improve the reliability of results, and allows drawing general conclusions on how to mitigate the environmental impacts of AD process.     

Environmental systems analysis of biogas systems—Part II: The environmental impact of replacing various reference systems

This paper analyses the overall environmental impact when biogas systems are introduced and replace various reference systems for energy generation, waste management and agricultural production. The analyses are based on Swedish conditions using a life-cycle perspective. The biogas systems included are based on different combinations of raw materials and final use of the biogas produced (heat, power and transportation fuel). A general conclusion is that biogas systems normally lead to environmental improvements, which in some cases are considerable. This is often due to indirect environmental benefits of changed land use and handling of organic waste products (e.g. reduced nitrogen leaching, emissions of ammonia and methane), which often exceed the direct environmental benefits achieved when fossil fuels are replaced by biogas (e.g. reduced emissions of carbon dioxide and air pollutants). Such indirect benefits are seldom considered when biogas is evaluated from an environmental point of view. The environmental impact from different biogas systems can, however, vary significantly due to factors such as the raw materials utilised, energy service provided and reference system replaced.     

Methane–hydrogen fuel blends for SI engines in Brazilian public transport: Potential supply and environmental issues

In the last decades, the whole world has been feeling the effects of environmental pollution, especially air pollution in large cities, with the transport sector as a major contributor to this scenario. In this sense, Brazil presents 27 states with great potential for biogas generation from landfills through anaerobic digestion. Only in the year 2016, the calculations presented in this paper point to a methane production in landfills of 5.57E+09 m³. On the other hand, the high number of rivers and hydroelectric dams in the country makes possible the generation of electricity that reached 90.27 TWh in 2016. However, the water that is drained by the floodgates to control the level of the reservoirs becomes an interesting wasted energy source for other uses, such as the production of other clean fuel, hydrogen, through classical processes such as electrolysis. It is pointed out the possibility of producing 2.76E+06 tons of hydrogen only with the energy drained in these hydroelectric plants. These two fuels together can be used to fuel vehicles powered by the hydrogen–methane blends, like HBio95 and HBio60. The promise of harmful and CO₂ emissions by focusing on mixture of gases has recently attracted the interest of vehicle manufacturers and transport operators. In this scenario, this work presents an analysis on the use of mixture of gases in the urban bus fleet of the 27 Brazilian states, using as energy source derived from secondary energy from Brazilian hydroelectric plants and biogas from sanitary landfills, comparing this scenario with the use of only methane from landfills or only H₂ from hydroelectric plants, assessing issues such as pollutant emissions, engine performance and deployment facilities.     

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.     

Life cycle energy and environmental assessment of bio-CNG utilization from cassava starch wastewater treatment plants in Thailand

Global warming, energy security, and the rising costs of oil have added a greater driving force to the development of feasible alternatives to petroleum-based transportation fuels. In parallel, wastes and wastewater generated from various industries should be avoided or converted to energy more in the future in order to reduce environmental problems and provide additional sources of energy. In this aspect, biogas plant is an effective option where gas is produced biologically by the fermentation of animal dungs, sewage, and agricultural residues. To utilize biogas as a transportation fuel, raw biogas has to undergo two major processes: cleaning and upgrading, to achieve natural gas quality. The upgraded biogas (so called bio-methane or bio-CNG) is considered green fuel with respect to environment, climate, and human health. However, the resulting bio-CNG from the processes still needs to be evaluated in terms of greenhouse gas emissions and energy aspects. This paper presents the integrated life cycle energy and environmental assessment of compressed bio-methane gas (CBG or bio-CNG) generated from cassava starch wastewater treatment plant in Thailand. The functional units were set to be 1 MJ of bio-CNG and 1 km of vehicle driven. The system boundary covered six main steps: digestion, purification and upgrading, compression, distribution, refueling, and combustion. The energy analysis result showed that the net energy ratio was higher than one, indicating a net energy gain. For the greenhouse gases aspect, the results showed that the biogas production and biogas upgrading step had the highest impact due to methane loss and high energy consumption. Comparing with other fuels, the global warming potential of bio-CNG was lower than those of fossil-based CNG and gasoline.     

The potential role of hydrogen as a sustainable transportation fuel to combat global warming

Hydrogen is recognized as a key source of the sustainable energy solutions. The transportation sector is known as one of the largest fuel consumers of the global energy market. Hydrogen can become a promising fuel for sustainable transportation by providing clean, reliable, safe, convenient, customer friendly, and affordable energy. In this study, the possibility of hydrogen as the major fuel for transportation systems is investigated comprehensively based on the recent data published in the literature. Due to its several characteristic advantages, such as energy density, abundance, ease of transportation, a wide variety of production methods from clean and renewable fuels with zero or minimal emissions; hydrogen appears to be a great chemical fuel which can potentially replace fossil fuel use in internal combustion engines. In order to take advantage of hydrogen as an internal combustion engine fuel, existing engines should be redesigned to avoid abnormal combustion. Hydrogen use in internal combustion engines could enhance system efficiencies, offer higher power outputs per vehicle, and emit lower amounts of greenhouse gases. Even though hydrogen-powered fuel cells have lower emissions than internal combustion engines, they require additional space and weight and they are generally more expensive. Therefore, the scope of this study is hydrogen-fueled internal combustion engines. It is also highlighted that in order to become a truly sustainable and clean fuel, hydrogen should be produced from renewable energy and material resources with zero or minimal emissions at high efficiencies. In addition, in this study, conventional, hybrid, electric, biofuel, fuel cell, and hydrogen fueled ICE vehicles are comparatively assessed based on their CO₂ and SO₂ emissions, social cost of carbon, energy and exergy efficiencies, fuel consumption, fuel price, and driving range. The results show that when all of these criteria are taken into account, fuel cell vehicles have the highest average performance ranking (4.97/10), followed by hydrogen fueled ICEs (4.81/10) and biofuel vehicles (4.71/10). On the other hand, conventional vehicles have the lowest average performance ranking (1.21/10), followed by electric vehicles (4.24/10) and hybrid vehicles (4.53/10).     

Which is the preferable biogas utilisation technology for anaerobic digestion of agricultural crops in Ireland: Biogas to CHP or biomethane as a transport fuel?

The utilisation of anaerobic digestion to produce biogas as an energy source is a mature technology in many European countries but is yet to be developed in Ireland. In 2009, the EU issued the Renewable Energy Source Directive 2009/28/EC which requires a 20% share of renewable energy sources (heat and electricity) in final energy consumption for all member states, respectively, including a 10% share of biofuels in the transport sector by 2020. The introduction of biogas to produce power and electricity in the form of CHP technology and biomethane as a transport fuel can help Ireland achieve the mandatory targets set by the directive. The key focus of the paper is to determine the optimum small to medium scale biogas technology and the impact the introduction of that technology infrastructure will have on renewable energy targets for Ireland. In terms of feedstock, agricultural sources such as energy crops and slurry offer a sustainable input to the anaerobic digestion process. The crop rotations under consideration consist of different arrangements of grass silage, maize silage and barley. Grass silage is found to be the most suitable crop for biogas energy production while biogas upgrading to biomethane as a transport fuel has the optimum technology potential in Ireland. To fuel a car operating on biomethane, 0.22 ha of grass land is required annually. Full scale national development of 5% of the area under grass in Ireland will contribute 11.4% of renewable energy to the total final transport energy demand by 2020, surpassing the target set by the Renewable Energy Source Directive 2009/28/EC.     

Biogas (a promising bioenergy source): A critical review on the potential of biogas as a sustainable energy source for gaseous fuelled spark ignition engines

Increasing demand for energy accompanied by environmental concerns has raised the requirement for limiting the use of fossil fuels in energy generation and transportation applications. Among the green and renewable energy-based solutions, biogas is quite promising since it could be implemented for power generation applications (engines driving generators and pump sets) in rural areas, at domestic and industrial scales with lower capital investment and production cost by using the agricultural crop residues and other domestic biomass sources as raw materials. However, the composition of biogas varies depending on the raw materials, and higher concentration of carbon dioxide in biogas results in combustion variations affecting engine durability. This review focuses on the role of biogas in achieving sustainable development goals with an emphasis on its utilization in gaseous fuelled spark-ignited engines. Recent progress in biogas production and upgradation techniques are also detailed. Challenges related to the stability and characteristics of biogas fuelled spark-ignited engines could be addressed by either modifying the physical parameters of the engine or by enhancing the fuel quality (upgradation to biomethane or blending with hydrogen). A comprehensive review on the effects of these approaches on the performance, combustion, and emission characteristics of biogas-fuelled engines is discussed in detail with a note on engine operating parameters.     

Sustainability of algal biofuel production using integrated renewable energy park (IREP) and algal biorefinery approach

Algal biomass can provide viable third generation feedstock for liquid transportation fuel. However, for a mature commercial industry to develop, sustainability as well as technological and economic issues pertinent to algal biofuel sector must be addressed first. This viewpoint focuses on three integrated approaches laid out to meet these challenges. Firstly, an integrated algal biorefinery for sequential biomass processing for multiple high-value products is delineated to bring in the financial sustainability to the algal biofuel production units. Secondly, an integrated renewable energy park (IREP) approach is proposed for amalgamating various renewable energy industries established in different locations. This would aid in synergistic and efficient electricity and liquid biofuel production with zero net carbon emissions while obviating numerous sustainability issues such as productive usage of agricultural land, water, and fossil fuel usage. A ‘renewable energy corridor’ rich in multiple energy sources needed for algal biofuel production for deploying IREPs in the United States is also illustrated. Finally, the integration of various industries with algal biofuel sector can bring a multitude of sustainable deliverables to society, such as renewable supply of cheap protein supplements, health products and aquafeed ingredients. The benefits, challenges, and policy needs of the IREP approach are also discussed.     

Experimental investigation on the production of biogas from waste food

The production of biogas has been a substantial target to be utilized globally, especially in the agricultural sector. Most organic waste that is being produced from other forms of renewable energy systems is mainly used to reduce greenhouse emission (GHG), which as well reduces the daily consumption of fossil fuels. Anaerobic Digestion (AD) has been studied widely in recent years where its implementation in the industry has seen a mitigating impact on greenhouse gases. Unrestricted discharge of the big amount of waste food (WF) has become the main effect of severe environmental pollution worldwide. Among the various treatment methods, anaerobic digestion (AD) of waste food allows its valorization and the biogas produced can be used as biofuel enhancing the gas supply. In this study, a mechanical pre-treatment with Hollander beater has been applied to break down the particle size of waste food in the way to increase feedstock specific surface areas in other to enhance biogas production. Following, the pre-treatment of waste food during 30 min beating time, the biogas yield achieved a value of about 610.33 ml/gTS. Accordingly, a response surface methodology (RSM) can be used to critically evaluate the effects of process parameter (beating time and temperature) to the output response (biogas production). Pre-treated waste food by Hollander beater at beating time of 30 min enhances biogas production by 80%. An optimum biogas yield was achieved with pre-treatment of waste food at a beating time of 30 min.     

Current state and environmental impact assessment for utilizing oil palm empty fruit bunches for fuel,fiber and fertilizer – A case study of Malaysia

This paper describes the trend of utilizing oil palm residue, i.e. the empty fruit bunches (EFB) left after extraction of the palm oil, using a case study of Malaysia, which is one of the world's major palm oil producers, and discusses the environmental performance of recycling technologies being developed in Malaysia for fuel, fiber, and fertilizer. Seven technologies are analyzed: ethanol production, methane recovery, briquette production, biofuel for combined heat and power (CHP) plants, composting, medium density fiberboard (MDF) production, and pulp and paper production. The life cycle assessment (LCA) method is used to discuss the environmental impacts of these technologies for adding value to this biomass. Sensitivity analyses are conducted to determine the land use effects for the various technologies utilizing EFB and to estimate the energy generation potential of raw EFB in CHP plants and methane production. Among the technologies for energy production, CHP plants have the best performance if the electricity generated is connected to the national grid, with superior benefits in the majority of impact categories compared to briquette, methane, and ethanol production. Overall, we find that methane recovery and composting are more environmentally friendly than other technologies, as measured by reduction of greenhouse gas emissions. Pulp and paper, and MDF production are favorable technologies for land use impacts; however, they have intense primary energy requirements, chemical use in the processes, and emissions from their waste treatment systems. Our results provide information for decision makers when planning for sustainable use of oil palm biomass.     

Technoeconomic analysis of an integrated microalgae photobioreactor, biodiesel and biogas production facility

As fossil fuel prices increase and environmental concerns gain prominence, the development of alternative fuels from biomass has become more important. Biodiesel produced from microalgae is becoming an attractive alternative to share the role of petroleum. Currently it appears that the production of microalgal biodiesel is not economically viable in current environment because it costs more than conventional fuels. Therefore, a new concept is introduced in this article as an option to reduce the total production cost of microalgal biodiesel. The integration of biodiesel production system with methane production via anaerobic digestion is proved in improving the economics and sustainability of overall biodiesel stages. Anaerobic digestion of microalgae produces methane and further be converted to generate electricity. The generated electricity can surrogate the consumption of energy that require in microalgal cultivation, dewatering, extraction and transesterification process. From theoretical calculations, the electricity generated from methane is able to power all of the biodiesel production stages and will substantially reduce the cost of biodiesel production (33% reduction). The carbon emissions of biodiesel production systems are also reduced by approximately 75% when utilizing biogas electricity compared to when the electricity is otherwise purchased from the Victorian grid. The overall findings from this study indicate that the approach of digesting microalgal waste to produce biogas will make the production of biodiesel from algae more viable by reducing the overall cost of production per unit of biodiesel and hence enable biodiesel to be more competitive with existing fuels.     

Biomethane production from different crop systems of cereals in Northern Italy

Global warming is linked to the reduction of green house gas emissions (GHG). The anaerobic digestion of animal manure and energy crops is a promising way of reducing GHG emissions.The increasing number of biogas plants involves a high consumption of energy crops and the needed of big agricultural area. In Italy, cereals silages are the main feedstock for biogas production and are commonly grown under two different crop systems: single crop (only maize) and double crops (maize later winter cereals).In this paper we present the results of experimental field tests carried out by monitoring the anaerobic biomethane potential (BMP) of different cereals silages commonly grown in the Padanian Plan.A laboratory device has been developed to measure the specific biomethane production of the different cereal silages. The different energy crops have been evaluated, in single and double crop systems, expressing the biomethane production per hectare.The maize hybrids show higher specific biomethane potentials respect to winter cereals. Maize FAO class 700 achieves the highest production per hectare as a single crop. Nevertheless, the highest biomethane productions per hectare are reached with double crop system in particular when maize FAO class 500 follows triticale (+12% respect the best single crop system).     

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.     

Sewage sludge-to-energy approaches based on anaerobic digestion and pyrolysis: Brief overview and energy efficiency assessment

Energy recovery from sewage sludge offers an opportunity for sustainable management of sewage sludge and energy. Anaerobic digestion and pyrolysis are among the most promising processes applicable for sewage sludge-to-energy conversion. Anaerobic digestion of sewage sludge forms methane-rich biogas, which can be utilized as fuel to offset heat and electricity consumption of the wastewater treatment sector. However, the digestion process has the limitation that it cannot sufficiently extract the energy in sewage sludge. The digested sludge is still energy profitable in that it contains considerable organic matter, but poor in biodegradability. Sludge pyrolysis is an innovative process that can convert both raw and digested sludge into useful bioenergy in the form of oil and gas, forming biochar as a byproduct that is environmentally resistant and holds potential for carbon sequestration and soil conditioning. It is expectable that sludge pyrolysis would step into practical deployment in the near future.This paper presents a brief overview of anaerobic digestion and pyrolysis in the application to bioenergy production from sewage sludge. An assessment of energy conversion efficiency of two parallel sludge-to-energy pathways is also presented. One pathway relies on an exclusive pyrolysis process (fed with raw sludge) while the other is based on anaerobic digestion followed by pyrolysis (fed with the digested sludge). The pathway via the combination of anaerobic digestion and pyrolysis could achieve higher energy efficiency compared to the pathway employing the pyrolysis alone.     

Photobiostimulation of anaerobic digestion by laser irradiation and photocatalytic effects of trace metals and nanomaterials on biogas production

Biogas generation from the latent energy in biomass is one of the most attractive renewable energy sources. This can be attributed to the environmental friendly nature of the process and its less energy requirements. This article reviews the anaerobic digestion of biomass (livestock manure and crop residues) for biogas and methane production as a source of renewable energy. Furthermore, this study investigates the enhancement of biogas and methane production using light and laser radiations. The laser radiation accelerates bacterial division and growth, where this process is termed as “photobiostimulation.” Additionally, laser radiation photoactivates the inactive enzymes. The results of this literature review showed that the irradiation of methanogenic bacteria with laser sources increased the biogas production by one and a half fold the traditional method of biogas production. The simultaneous irradiation of both nanomaterials and methanogenic bacteria using laser radiation increased the biogas volume by twofolds the biogas volume resulted from the traditional method of biogas production.     

Biomass from agriculture in small-scale combined heat and power plants - A comparative life cycle assessment

Biomass produced on farm land is a renewable fuel that can prove suitable for small-scale combined heat and power (CHP) plants in rural areas. However, it can still be questioned if biomass-based energy generation is a good environmental choice with regards to the impact on greenhouse gas emissions, and if there are negative consequences of using of agricultural land for other purposes than food production.In this study, a simplified life cycle assessment (LCA) was conducted over four scenarios for supply of the entire demand of power and heat of a rural village. Three of the scenarios are based on utilization of biomass in 100 kW (e) combined heat and power (CHP) systems and the fourth is based on fossil fuel in a large-scale plant. The biomass systems analyzed were based on 1) biogas production with ley as substrate and the biogas combusted in a microturbine, 2) gasification of willow chips and the product gas combusted in an IC-engine and 3) combustion of willow chips for a Stirling engine. The two first scenarios also require a straw boiler.The results show that the biomass-based scenarios reduce greenhouse gas emissions considerably compared to the scenario based on fossil fuel, but have higher acidifying emissions. Scenario 1 has by far the best performance with respect to global warming potential and the advantage of utilizing a byproduct and thus not occupying extra land. Scenario 2 and 3 require less primary energy and less fossil energy input than 1, but set-aside land for willow production must be available. The low electric efficiency of scenario 3 makes it an unsuitable option.     

Modeling & optimization of renewable hydrogen production from biomass via anaerobic digestion & dry reformation

There is a growing interest in the usage of hydrogen as an environmentally cleaner form of energy for end users. However, hydrogen does not occur naturally and needs to be produced through energy intensive processes, such as steam reformation. In order to be truly renewable, hydrogen must be produced through processes that do not lead to direct or indirect carbon dioxide emissions. Dry reformation of methane is a route that consumes carbon dioxide to produce hydrogen. This work describes the production of hydrogen from biomass via anaerobic digestion of waste biomass and dry reformation of biogas. This process consumes carbon dioxide instead of releasing it and uses only renewable feed materials for hydrogen production. An end-to-end simulation of this process is developed primarily using Aspen HYSYS® and consists of steady state models for anaerobic digestion of biomass, dry reformation of biogas in a fixed-bed catalytic reactor containing Ni–Co/Al₂O₃ catalyst, and a custom-model for hydrogen separation using a hollow fibre membrane separator. A mixture-process variable design is used to simultaneously optimize feed composition and process conditions for the process. It is identified that if biogas containing 52 mol% methane, 38 mol% carbon dioxide, and 10 mol% water (or steam) is used for hydrogen production by dry reformation at a temperature of 837.5 °C and a pressure of 101.3 kPa; optimal values of 89.9% methane conversion, 99.99% carbon dioxide conversion and hydrogen selectivity 1.21 can be obtained.     

Prospective application of farm cattle manure for bioenergy production in Portugal

Biogas is a promising renewable fuel, which can be produced from a variety of organic raw materials and used for various energetic purposes, such as heat, combined heat and power or as a vehicle fuel. Biogas systems implementation are, therefore, subjected to several support measures but also to several constraints, related with policy measures on energy, waste treatment and agriculture. In this work, different policies and policy instruments, as well as other factors, which influence a potential expansion of Portuguese biogas systems are identified and evaluated. The result of this analysis shows that the use of the cattle manure for biogas production is still far from its potential. The main reason is the reduced dimension of the Portuguese farms, which makes biogas production unfeasible. Various options are suggested to increase or improve biogas production such as co-digestion, centralized plants and modular plants. Horizontal digesters are the most suitable for the typical Portuguese plant size and have the advantage of being also suitable for co-digestion due to the very good mixing conditions. Mesophilic anaerobic digestion due to a more robustness, stability and lower energy consumption should be the choice. The recent increase in the feed-in tariffs for the electricity production based on anaerobic digestion biogas is seen as a political push to this sector.