Agricultural Biogas Research Articles

Influence of the Parameters of Used Biochar on the Dark Fermentation Process

The aim of the work was to analyze the impact of biochar produced under various production conditions on the course of the dark (hydrogen) fermentation process. A series of experiments were planned, in which the starting material was digestate from a functioning agricultural biogas plant. Changes in the physicochemical properties and microstructure of biochar obtained in the manufacturing process with different parameters were also analyzed. Another issue analyzed was the size and dynamics of the gas production during dark fermentation with the use of various types of auxiliary material. This work showed that increasing the temperature and holding time during the production of biochar from digestion pulp improved the dynamics of biohydrogen production during the process of dark fermentation. The results of this research can be used in industrial research to optimize the process of biohydrogen production using biochar.

Assessment of the flow of substrate and agricultural biogas through the adhesive skeleton bed in phenomenological and numerical terms

Assessment of the flow of substrate and agricultural biogas through the adhesive skeleton bed in phenomenological and numerical terms

An Agricultural Biogas Plant as a Thermodynamic System: A Study of Efficiency in the Transformation from Primary to Secondary Energy

Using a wide range of organic substrates in the methane fermentation process enables efficient biogas production. Nonetheless, in many cases, the efficiency of electricity generation in biogas plant cogeneration systems is much lower than expected, close to the calorific value of the applied feedstock. This paper analyses the energy conversion efficiency in a 1 MWel agricultural biogas plant fed with corn silage or vegetable waste and pig slurry as a feedstock dilution agent, depending on the season and availability. Biomass conversion studies were carried out for 12 months, during which substrate samples were taken once a month. The total primary energy in the substrates was estimated in laboratory conditions by measuring the released heat (17,760 MWh·year−1), and, in the case of pig slurry, biochemical methane potential (BMP, (201.88 ± 3.21 m3·Mg VS−1). Further, the substrates were analysed in terms of their chemical composition, from protein, sugar and fat content to mineral matter determination, among other things. The results obtained during the study were averaged. Based on such things as the volume of the biogas, the amount of chemical (secondary) energy contained in methane as a product of biomass conversion (10,633 MWh·year−1) was calculated. Considering the results obtained from the analyses, as well as the calculated values of the relevant parameters, the biomass conversion efficiency was determined as the ratio of the chemical energy in methane to the (primary) energy in the substrates, which was 59.87%, as well as the electricity production efficiency, as the ratio of the electricity produced (4913 MWh·year−1) to the primary energy, with a 35% cogeneration system efficiency. The full energy conversion efficiency, related to electricity production, reached a low value of 27.66%. This article provides an insightful, unique analysis of energy conversion in an active biogas plant as an open thermodynamic system.

Utilization of Digestate from Agricultural and Food Waste for the Production of Biochar Used to Remove Methylene Blue

The treatment of waste or by-products from the agri-food industry in agricultural biogas plants results in the production of biogas. After anaerobic digestion, digestate remains and is often used for soil fertilization. The solid digestate (SD) can also be used for the production of biochar, a material with specific properties and many applications. Such a model of operation fits perfectly into the concept of a circular economy, because the waste material can be used to produce an adsorbent that can be used to treat industrial wastewater. The research assumption of this study was to investigate selected properties of biochar prepared at variable temperatures in the pyrolysis process from solid. The potential of biochar for methylene blue (MB) sorption was also initially investigated in terms of biochar’s suitability for immobilizing metals in degraded soils. Biochar was produced at temperatures between 400–900 °C, with a temperature gradient of 50 °C. The efficiency of the production was in the range of 51–40% and decreased with the increasing temperature. The rising process temperature was also accompanied by a decrease in the nitrogen and hydrogen content of biochar. The produced biochar had an alkaline pH ranging from 11.40 to 12.69 and it increased as the temperature increased. The rise in the pyrolysis temperature effected a significant increase in the specific surface area BET (Brunauer–Emmett–Teller) in the case of biochar BSD750, BSD800, and BSD850 (BSD—biochar solid digestate). When analyzing the C content of individual biochar variants, there was no clear downward or upward trend, just as in the case of TOC (total organic carbon) value for the produced biochar. The greatest potential for removing MB (methylene blue) from solutions was demonstrated by biochar produced at 650–900 °C. The ability to remove MB rose along with the production temperature of the biochar.

Spatial Differentiation of Agricultural Biomass Potential in Polish Voivodeships

The main aim of the article is to assess the potential of agricultural biomass and the possibility of its use for energy purposes in Polish voivodeships. Five sources of agricultural biomass were analyzed: straw, hay, waste wood from orchards, perennial energy crops, and natural fertilizers. For the purposes of the research, the theoretical and technical potential of agricultural biomass was estimated. The potential of agricultural biomass was estimated for Polish voivodeships based on the data of the 2020 Agricultural Census. The conducted research shows that Polish voivodeships have a significant theoretical potential for agricultural biomass. However, due to the fact that biomass is widely used in plant production (as a natural fertilizer) and animal production (as fodder or bedding), only about 40% of the identified theoretical potential can be used for energy purposes. The research also shows that the dominant source of agricultural biomass that can be used in Poland is straw from cereal crops. Moreover, a significant part of the identified potential is located in the western part of Poland (Wielkopolskie, Dolnośląskie, Kujawsko-Pomorskie, Zachodniopomorskie voivodships) and partly in the east (Lubelskie voivodship). Although the possibility of using natural fertilizers for energy purposes has not been identified, the theoretical potential of which is very high, an increase in the importance of renewable energy from agricultural biogas plants should be expected in the near future. This is due to the changes taking place in the storage and management of natural fertilizers.

Analysis of Voltage Distortions in the Power Grid Arising from Agricultural Biogas Plant Operation

Agricultural biogas plant operations are energy sources that fit well with rural land use. The continuous increase in cattle and pigs creates the need to manage animal waste, especially slurry. Using it for energy production in biogas plants offers the possibility of obtaining electricity, heat, and highly efficient manure. The thermal energy generated in an agricultural biogas plant is used to heat the substrate in the fermentation process and can also be used to heat buildings, dry fodder, or wood. Electricity can be used to cover the farm’s needs and sold to an energy company. However, the energy generated in the biogas plant must be of the right quality. One of the main factors describing the quality of electricity is the voltage distortion from the sinusoidal waveform. This paper presents the results of a study of the impact of biogas plant operation on the course of voltage and current in the grid. The theoretical analysis of the voltage distortion mechanism at the point of connection of an agricultural biogas plant was based on a simplified power system model consisting of a voltage source and the equivalent impedance of the power system. According to the theoretical analyses, agricultural biogas plant operation should reduce the voltage distortion factor. In order to confirm this statement, field tests were carried out at three agricultural biogas plants, based on which an analysis was made of the impact of the power generated in the biogas plants on the value of voltage distortion occurring at the point of their connection. However, the field tests did not confirm the conclusion of the theoretical analysis. Only in one case (where the biogas plant was connected near a substation and there was the highest short-circuit power) could it be seen that an increase in generation affected the voltage distortion factor. In the other two cases, generation did not significantly affect the shape of the voltage waveform. However, in each of the biogas plants studied, as the generation power increased, the current distortion factor decreased, suggesting that agricultural biogas plants should operate as close to the rated power as possible.

Perception of biogas plants: A public awareness and preference - A case study for the agricultural landscape

The energy transition and the EU's ambitious policies require member countries to find socially acceptable solutions. One possible solution is agricultural biogas plants. However, research on public acceptance of biogas plants has been a small part of the research on renewable energy sources. The aims of the article were to (I) examine the public awareness of agricultural biogas plants, (II) analyze the public opinion on the perception of biogas plants in a diverse landscape, and (III) perform visual assessment of the landscape with an existing biogas plant based on investments from Poland. A combination of methodological approaches was used to achieve the aims: survey research and visual assessment. Survey research was used to investigate the public awareness and perception of biogas plants in a diverse landscape. Visual assessment of operating biogas plant in the rural landscape was performed using the JAR-WAK landscape evaluation method. The conducted research showed that, according to the respondents, the biggest disadvantage of biogas plants is odors, and the greatest benefit is the production of energy and heat. The surveyed people also negatively perceived landscapes with biogas plants. However, the visual assessment for operating a biogas plant indicated no negative impact on the landscape.

Predicting steady-state biogas production from waste using advanced machine learning-metaheuristic approaches

This research offers a fast and accurate method for measuring the biogas production rate throughout biogas production. An agricultural biogas plant's measurement of eight process variables served as the source of experimental data used to create the models. Biomass type, reactor/feeding, volatile solids, pH, organic load rate, hydraulic retention time, temperature, and reactor volume were utilized in this context. Artificial neural networks (ANN) were developed to evaluate the biogas production rate. The variable selection was carried out using the cuckoo optimization algorithm (COA), multi-verse optimization algorithm (MVO), leagues championship algorithm (LCA), evaporation-rate water cycle algorithm (ERWCA), stochastic fractal search (SFS), and teaching–learning-based optimization (TLBO). In this study, the model's size decreased, the important process variables were highlighted, and the ANN models' potential was enhanced for prediction. The proposed COA, MVO, LCA, ERWCA, SFS, and TLBO and ensembles are the outcome of using the abovementioned approaches to synthesize the multi-layer perceptron (MLP). To evaluate the effectiveness of the used models, we have developed a scoring system in addition to employing mean absolute error, mean square error, and coefficient of determination as accuracy criteria. Implementing the COA, MVO, LCA, ERWCA, SFS, and TLBO algorithms enhances the accuracy of the MLP. It is found that some of the used hybrid techniques could provide better prediction outputs than traditional MLP rankings. Additional investigation indicated that the ERWCA is better than the three other algorithms. The biogas production rate was estimated with the greatest precision with R2 = 0.9314 and 0.9302, RMSE of 0.1969 and 0.24925, and MAE of 0.1307 and 0.19591.

Positioning a Measurement System for Determining the Mixing Quality in Biogas Digesters

AbstractMixing quality in agricultural biogas plants is crucial for nutrition supply to the microorganisms and needs to be ensured by an energy‐efficient mixing strategy. Various approaches have been proposed to determine the mixing quality in biogas digesters. Among them are magnetic‐inductive or force sensors brought into vertical digesters through the concrete wall. This article presents an approach to locating these sensors effectively around the circumference of the digester to avoid positioning in dead zones and maximize information quality regarding flow and mixing behavior. Particle image velocimetry is used to measure flow fields in a transparent model digester. Finally, optimum measurement locations considering three widely used agitator geometries are suggested.

Effect of Reactive and Non-Reactive Additive Treatment on the Recovery of Phosphorus from Biogas Digestate

The annual phosphate (PO43−) utilization has increased, leading to a depletion of existing sources of phosphorus (P). To overcome this, digestate as a source to recover P is being investigated. Due to the abundance of nutrients, the digestate from an agricultural biogas plant is used as fertilizer for crops. The separation of solids and liquids from the digestate by a screw press is the simplest form of concentrating, therefore, recovering PO43−. This is the most commonly employed method in existing biogas plants. However, the separation is not very efficient as only 20–30% of P is recovered in the solid phase. The goal of this study is to increase the separation efficiency and recover more P into the solid phase, in order to improve the transportability. For this, separation trials at a laboratory scale were performed for five experimental groups, with biochar and straw flour as non-reactive additives and kieserite as a reactive additive. In addition, untreated digestate was studied as a control. The control and the treatment with biochar and straw flour were carried out at 25 °C, while the treatment with kieserite was performed at 25 °C and 50 °C. The separation trails were performed at treatment times of 0 h, 1 h, 2 h, 8 h, and 20 h. The results showed that the treatment with additives had a beneficial effect on the recovery of P. It was noted that kieserite treatment at 25 °C and 50 °C bound about 61% of the total P present in the digestate to the solid phase. A sequential extraction was performed to study the effect of additives on the recovery of different P species. The results concluded that, compared to biochar and straw flour, kieserite was efficient in recovering the non-labile fractions (NaOH-P and HCl-P) of P, which act as slow-release fertilizers. This study shows that the use of additives, especially kieserite, has a positive influence on recovering P from digestate, and further research to optimize the recovery process would be beneficial.

Hydrothermal Carbonization of Digestate Produced in the Biogas Production Process

In agricultural biogas plants, besides biogas, the by-product digestate is also produced. Due to its high moisture content and organic origin, it can successfully be applied in the hydrothermal carbonization process to avoid the fate of landfilling. This paper reviews the properties of agricultural digestate and its hydrothermal conversion (HTC) into hydrochar and process water. The type of feedstock and the parameters of the HTC process, such as temperature, pressure and residence time, affects the physical and chemical characteristics of hydrochar. Therefore, its possible application might be as a biofuel, fertilizer, soil improver, adsorber, or catalyst. In this paper, the properties of hydrochar derived from agricultural digestate are widely discussed.

Biochemical conditions for anaerobic digestion of agricultural feedstocks: A full-scale study linking elements concentration and residual methane potential

Agricultural biogas plants should operate at the highest biological efficiency, with a fast anaerobic conversion of organic feedstocks leading to a low Residual Methane Potential (RMP). Optimal biochemical conditions boost the metabolic activity of microorganisms, providing better process performances. In this study, RMP of 16 full scale agricultural biogas plants operating with different agri-based feedstock categories was used as indicator of biological efficiency and linked to their operational parameters such as Organic Loading Rate (OLR), Hydraulic Retention Time (HRT) and to chemical elements concentration in the digestate. RMP ranged between 1% and 26% of the total biomethane produced revealing a clear relation with HRT. The Principal Component Analysis (PCA) showed how specific trace elements supplementation, in the order Se > Mo > Co, and their concentration ratios (Ni/Co and Ni/Se) lead to RMP reduction in full-scale agricultural biogas plants with low HRT (<48 days) and high OLR (>3.61 kgVS m−3 day−1) mainly fed with manure and agro-industrial by-products.

Quantification of indicator and pathogenic bacteria in manures and digestates from three agricultural biogas plants over a one-year period

Interest in the conversion of manure in biogas via anaerobic digestion (AD) is growing, but questions remain about the biosafety of digestates. For a period of one year, we monitored the impact of three mesophilic agricultural biogas plants (BPs) mainly fed with pig manure (BP1, BP3) or bovine manure (BP2) on the physicochemical parameters, the composition of the microbial community and the concentration of bacteria (E. coli, enterococci, Salmonella, Campylobacter, Listeria monocytogenes, Clostridium perfringens, Clostridium botulinum and Clostridioides difficile). The BP2 digestate differed from those of the two other BPs with a higher nitrogen content, more total solids and greater abundance of Clostridia MBA03 and Disgonomonadacea. Persistence during digestion ranked from least to most, was: Campylobacter (1.6 to >2.9 log10 reduction, according to the BP) < E. coli (1.8 to 2.2 log10) < Salmonella (1.1 to 1.4 log10) < enterococci (0.2 to 1.2 log10) and C. perfringens (0.2 to 1 log10) < L. monocytogenes (-1.2 to 1.6 log10) < C. difficile and C. botulinum (≤0.5 log10). No statistical link was found between the reduction in the concentration of the targeted bacteria and the physicochemical and operational parameters likely to have an effect (NH3, volatile fatty acids and total solids contents, hydraulic retention time, presence of co-substrates), underlining the fact that the fate of the bacteria during mesophilic digestion depends on many interacting factors. The reduction in concentrations varied significantly over the sampling period, underlining the need for longitudinal studies to estimate the impact of AD on pathogenic microorganisms.

Influence of processing conditions and biochemical composition on the hydrothermal liquefaction of digested urban and agricultural wastes

Hydrothermal liquefaction (HTL) of waste biomass is a promising technology to yield an energy dense biocrude oil and a nutrient rich solid phase. An abundant and problematic biomass waste stream potentially suited for HTL is digestate, the side stream of anaerobic digestion. HTL behavior of three digestates from urban and agricultural biogas plants has been studied using response surface methodology to investigate the influence of biochemical composition, temperature, and reaction time on biocrude yield and composition, energy recovery, as well as the mobility of nutrients (N, P, K) among the product phases using KOH as catalyst. A maximum energy recovery of up to 43% and a carbon recovery of 40% were achieved for the straw/manure digestate. Mass yields and biocrude composition by GC–MS analysis are shown to be heavily influenced by feedstock composition. High yields of > 80% for the main nutrients Ca, Mg, Fe, and P to the solid residue are observed.

The Effect of Agricultural Biogas Plants on the Quality of Farm Energy Supply

Agricultural biogas plants are among the renewable energy sources. While they have many advantages, they are less common than photovoltaic or wind power plants. One of the reasons for the lack of support for the construction of new agricultural biogas plants is the belief that biogas plants will affect the operation of consumers connected in its immediate vicinity through interference introduced into the grid. This article presents the possibilities a biogas plant built on a farm offers. The impact of an on-farm biogas plant on the voltage parameters of a farm specializing in barnless cattle rearing is analyzed in detail. As demonstrated by the authors’ research in one of the agricultural biogas plants (with an electrical capacity of 40 kW), these plants do not introduce significant disturbances to the power quality into the grid. The most significant changes in the parameters of the voltage supplying the farm under study were caused by the operation of the digester mixer installed in the fermenter. Thanks to the research, it was also possible to identify a problem with the effect of the digester mixer on the energy parameters produced in the biogas plant. This problem has so far not been noticed or corrected by biogas plant manufacturers.

Profitability of the agricultural biogas plants operation in Poland, depending on the substrate use model

The circular economy is one of the most critical challenges in the 21st century. By using waste, the consumption of valuable raw materials can be reduced. It will also reduce the amount of waste directed to landfill or incineration. Also, in biogas production terms, activities consistent with the circular economy are raised. They mainly consist of the use of waste in the anaerobic digestion process and the rational use of the digestate. For the owners of biogas plants, the essential issue is optimizing the anaerobic digestion process to produce as much biogas as possible. The work aimed to determine the profitability of the operation of agricultural biogas plants in Poland, depending on the substrate use model.The study analyzes two options for supplying agricultural biogas plants with substrates: Option I — traditional (maize silage and slurry) and Option II — waste (slaughterhouse waste and slurry). In both options, it was assumed that biogas plants would operate under the conditions of the auction system — one of the models in force in Poland. The investment balance can be significantly improved by using waste instead of maize silage. The profit for the biogas plant operating in Option I was estimated at PLN 628,360, and in Option II it was PLN 2,307,600. The conducted analysis showed that the operation of waste biogas plants is much more profitable than traditional ones. The positive impact on the natural environment will complement the economic benefits. It is because managing waste from the agri-food industry in controlled conditions will significantly contribute to energy production, considering the aspects of protection against climate change.

Development barriers of agricultural biogas plants in Poland

The article aims to identify barriers related to developing agricultural biogas plants in Poland. The secondary data was supplemented by primary data from a questionnaire conducted among employees of an enterprise whose biogas production is one of the elements of the circular economy. The results of the research revealed that the majority of respondents indicated external, systemic and developmental obstacles. The largest percentage of responses concerned the lack of stable legal regulations in the scope of renewable energy sources, including biogas plants, and the lack of programs financing the construction of agricultural biogas plants. Moreover, the respondents pointed to the proposals that could improve the development of agricultural biogas plants in the future. The respondents considered updating and ensuring the profitability of investments in the situation of significantly higher expenditures, growing costs of business and debt servicing through the reference price as a significant motivator, as well as inclusion in the support system of tariffs guaranteeing a stable income for at least 15 years. Barriers to developing agricultural biogas plants in Poland remain unchanged, and the awareness of the positive impact of agricultural biogas plants on many levels is still very low.

Adaptation of a Cogenerator with Induction Generator to an On/Off-Grid Operation Using a Power Electronic System

Cogeneration sources play a very important role in the power industry with dispersed renewable sources with forced generation (e.g., photovoltaics and wind generators). They also fit into the circular economy by increasing the efficiency of fuel use, including biogas from agricultural or livestock waste. The aim of our research was to develop an effective source of electricity powered by agricultural biogas. The most important features of such a source are: operation in on-grid and off-grid mode, as well as a low cost of the device and uncomplicated operation. In addition, in Europe, the source of electricity connected to the power grid must meet the technical requirements of the “Network Codes Requirements for Generators” (NC RfG) network code. The appropriate certificate is easier to obtain using a power converter system for the source. For this purpose, an induction generator with a converter system and a small battery was planned. A converter system was developed and built, and then tests were carried out in various operating modes. During the measurements, it was confirmed that the requirements for the quality of electricity for off-grid and on-grid operation modes were met. The assumed maximum time of voltage recovery after changing the operating mode, amounting to 40 ms, was not exceeded. Furthermore, the limit values of phase voltages with unsymmetrical load, amounting to ±10% of the rated voltage, were not exceeded. In the battery usage off-grid mode, the time after a step change in the load power was not longer than 2 s.

The Role of Biogas Production in Circular Economy Approach from the Perspective of Locality

The circular economy is an economic concept opposite to the current linear system. One of its main principles is to seek to minimise waste by reusing seemingly useless raw materials. Biogas plants are places where energy can be recovered from waste. In order to boost the environmental benefits of this concept, it is important to rely on local systems (including supply chains). Therefore, the aim of this study was to examine whether biogas plants in Poland operate in a circular manner from the perspective of locality. The analysis was based on questionnaire surveys concerning the nature of the facilities’ operations, divided into biogas plants located at sewage treatment plants, biogas plants based on municipal waste and agricultural biogas plants. On the basis of the data obtained, statistical and spatial analyses were carried out to verify the installed capacity of the facilities, the distance from which they obtain their substrate and the use of the biogas produced. The results of the study confirm that the functioning of biogas plants located in Poland is, in most cases, of a local character, fitting into the objectives of a circular economy. Biogas plants that are characterised by the lowest transportation needs are biogas plants located next to sewage treatment plants.

Study on the Effect of Dedicated Microelement Mixture (DMM) on the Kick-Off Phase of the Digester and Stabilization of the Methane Fermentation Process

The kick-off process is an important aspect of the proper operation of an agricultural biogas plant. At this stage, various operational problems may arise, mainly related to the stabilization of the fermentation process and reaching the full biogas production capacity. This paper presents the results of research on the kick-off of the fermentation process carried out on three selected biogas plants located in Poland. For the experiments, titration, potentiometric, and spectroscopic methods (ICP-MS) were used. The biogas plants during the kick-off period operated on the following substrates: a mixture of cattle and pig manure, corn silage, and whey liquor. Special attention was paid to the dosing process of the formulation developed by the authors (CMP-S1) containing Mo, Co, Ni, Se, and Mn for the fermentation chambers, to which the mixture of the selected microelements was not dosed. The study was carried out under real conditions on an engineering scale. The study showed that supplementing a dedicated mixture of microelements (DMM) in the first days of fermentation chamber kick-off has a positive effect on stabilizing the methane fermentation process and allows a faster and higher loading of fermenters with dry organic matter. The above translates into shortening the time (by more than half) of the kick-off process in the fermentation chamber, as well as brining about a significant reduction in costs.