Biogas production is the most important and promising alternative for replacing fossil fuels in an environmentally friendly manner. Along with the many renewable energy sources available, biogas production occupies an irreplaceable position due to the undeniable availability of biomass and the need to manage agro-commercial waste. The article reviews the current state of technology used in the production of biogas for selected European examples in terms of methane fermentation efficiency and actual energy production. The novelty of the article is its description of innovative trends that have great potential to play an important role in this field in the near future. The development of the biogas industry in Europe is evident, although the dynamics vary from country to country. Different models are presented, which are based on the different types of feedstock used for biogas production and the proportion of substrates used in co-digesters. Of course, Germany is the undisputed pioneer in the use of this renewable energy source. Nevertheless, the efforts to improve energy self-reliance and environmental impacts are reflected in the growing number of operational biogas plants in other European countries, which provides hope for rapid progress toward the complete abolition of the conventional exploitation of fossil fuels.

The main idea of a circular economy (CE) is to separate economic growth from resource consumption and environmental impacts. The characteristic approach of a CE assumes the minimisation of the amount of waste generated at the design level and, as a standard, includes innovations throughout the value chain. From an agricultural point of view, agricultural biogas plants are particularly important because they enable the management of all waste biomass and its conversion into useful energy and agricultural fertiliser. This paper presents methods for assessing the economic effectiveness of an investment in an agricultural biogas plant. The research goal was to develop a financial model. The authors of this study used available examples of the profitability of commercial ventures. We considered the investment aspects of agricultural biogas plants. Exemplary solutions are discussed, allowing the reader to become acquainted with various methods and proposals for thus far estimated investments. It may seem chaotic, but this is how the biogas market is characterised in the context of the implementation of biogas projects. Guidance is given regarding how to understand investing in this sensitive private farming sector. It is admirable that the renewable energy market has been systematised, and we hypothesise that it is necessary to develop an investment model in Polish conditions.

The aim of this study was to perform a comparative analysis of the unit gas emission value in the exhaust of a dual fuel diesel engine. The results of the effects of a diesel engine’s applications in biogas plants and the method for calculating mass gas emissions per unit of produced electricity are shown. The test was performed using a two-cylinder, naturally aspirated, liquid-cooled diesel engine. The diesel engine powered a generator connected to the grid. The engine was fed with liquid fuels—waste cooking oil methyl ester (UCOME) and diesel fuel (DF)—and with a gas fuel, biogas (BG). The engine ran at a constant rotational speed (2000 rpm ± 30 rpm) with variable load. The gas analyzer measured the amount of CO, NO, NO₂, and PM (particulate matter) in exhaust gas. This gas content share was then converted to mass per engine generated energy unit. This experiment showed the effect of BG introduced to the intake manifold on fuel combustion, as well as an increase in CO and NO₂ emission and decrease in NO and PM. In terms of dependence of exhaust emissions on the type of liquid fuel used, the use of UCOME as opposed to diesel fuel resulted in PM reduction and increase of NO emissions.

The article reviews selected systems and technological variants of biogas production. Biogas installations and methods of biogas production were characterized in terms of control and measurement. The required technical and technological criteria for biogas production and treatment were indicated. The conditions of biorefining in the context of the generation of new products were analysed. Based on the amount of manure produced in pig production, the potential of biogas production in Poland was indicated based on the visualization of the biogas production potential by poviats in Poland. The substrate in the form of slurry, manure and other agricultural waste for the production of agricultural biogas in Poland was analysed quantitatively. The economic aspects in the agricultural biogas plant sector were revealed, indicating the operation of the economies of scale for this industry sector. An example of a pilot biogas production for anaerobic digestion using pig slurry is presented. The paper presents pre-liminary results of experimental studies on the course of changes in the biogas volume flow for the average daily production of agricultural biogas and the qualitative composition of agricultural biogas produced from pig slurry. The results of the measurements show a clear influence of the hydrodynamic mixing system of the substrate for the evaluation of the biogas flow through the adhesive bed in the context of agricultural biogas production in the range (1–14) m3 d–1.

Biohydrogen production is a promising alternative to replace fossil fuels in an environmentally friendly way. In addition to the many available renewable energy sources, the production of “colored” hydrogen and biohydrogen occupies an irreplaceable position due to the undeniable availability of biomass and the need to manage food waste (FW). This article presents the current state of biohydrogen production technology—examples on continents (America, Africa, Asia, Australia and Oceania) and in Europe in terms of the efficiency of dark methane fermentation (CH₄). Biophotolysis processes leading to the production of biohydrogen are indicated: directly and indirectly. The mechanism of the fermentation process of obtaining hydrogen and two-stage hydrogen fermentation are presented. The novelty of this article is the development of innovative trends in the development of the biohydrogen industry in Europe. Various models of the biohydrogen process are presented for different raw materials and proportions of substrates used in co-fermenters. Researchers from China are the undisputed pioneers in the use of renewable energy sources. However, improved energy self-sufficiency and environmental impacts are reflected in the growing number of pilot installations operating in European countries. This also gives hope for rapid progress towards full animal and FW management also in Poland.

This paper describes examples of energy crops that are profitable to burn, and whose cultivation is not complicated or expensive. Rapid growth of biomass, especially the green mass of energy crops, is indicated, which means that, in relation to fossil fuels, energy crops are considered renewable raw materials. An assessment of Polish non-food energy agriculture was conducted in the context of the prospects of a renewable energy source, namely, biomass. Recommendations for crop cultivation, the size of possible yields and the most important parameters of the obtained biomass, which have the greatest impact on the suitability of energy use, are presented. Materials of biological origin for combustion are divided into three groups: wood waste, by-products and plant products for the energy industry. It is indicated that 2 tons (Mg) of dry wood or straw is energetically equivalent to 1 Mg of coal, and 1 m³ of biogas is energetically equivalent to 1 kg of Polish coal. A novelty of this article is the interpretation of obtaining primary energy, including energy from renewable sources, in the European Union and Poland, taking into account the production of wood waste, straw, cereals and energy crops. The mechanism of the impact of the production parameters of energy crops was revealed during the prepared analysis of the prospects of Polish energy agriculture. Additionally, we conducted an analysis of the potential of biomass as a source of energy in the context of: obtaining primary energy, including energy from renewable sources, in the European Union and Poland; the number of biogas plants in Poland; and the area of agricultural land that is potentially useful for the cultivation of energy crops.