Search Results (72)

This review relates the kinetics of anaerobic digestion (AD) to energy outcomes, including typical ranges of methane yields and volumetric methane productivities (down to hourly g L⁻¹ h⁻¹ scales relevant for industrial plants). It further translates these relationships into practical control principles that support stable, high methane productivity. Evidence spans substrate selection and co-digestion with emphasis on carbon/nitrogen (C/N) balance, pretreatment strategies, and reactor operation, linking process constraints with operating parameters to identify interventions that raise performance while limiting inhibition. Improving substrate accessibility is the primary step: pretreatment and co-digestion shift limitation beyond hydrolysis and allow safe increases in organic loading. Typical mesophilic operation involves hydraulic retention times of about 10–40 days for food waste and 20–60 days for different types of livestock manure and slowly degradable energy crops, with stable performance achieved when the solids retention time (SRT) is maintained longer than the hydraulic retention time (HRT). Stability is further governed by sustaining a low hydrogen partial pressure through hydrogenotrophic methanogenesis. Temperature and pH define practicable operating ranges; meanwhile, mixing should minimise diffusion resistance without damaging biomass structure. Early-warning indicators—volatile fatty acids (VFAs)/alkalinity, the propionate/acetate ratio, specific methanogenic activity, methane (CH₄)% and gas flow—enable timely adjustment of loading, retention, buffering, mixing intensity and micronutrient supply (Ni, Co, Fe, Mo). In practice, robust operation is generally associated with VFA/alkalinity ratios below about 0.3 and CH₄ contents typically in the range of 50–70% (v/v) in biogas. The review consolidates typical feedstock characteristics and biochemical methane potential (BMP) ranges, as well as outlines common reactor types with their advantages and limitations, linking operational choices to energy yield in combined heat and power (CHP) and biomethane pathways. Reported pretreatment effects span approximately 20–100% higher methane yields; for example, 18–37% increases after mechanical size reduction, around 20–30% gains at 120–121 °C for thermal treatments, and in some cases nearly a two-fold increase for more severe thermal or combined methods. Priorities are set for adaptive control, micronutrient management, biomass-retention strategies, and standardised monitoring, providing a coherent route from kinetic understanding to dependable energy performance and explaining how substrate composition, pretreatment, operating parameters, and kinetic constraints jointly determine methane and energy yield, with particular emphasis on early-warning indicators. Full article

Biomethane plays a key role in the green transition, offering a renewable, carbon-neutral substitute for natural gas while enabling the storage and use of intermittent renewable energy. This work presents a techno-economic assessment of biomethane production through the Power-to-Biomethane concept, which combines electrolytic hydrogen from renewable electricity with the direct catalytic methanation of raw biogas from anaerobic digestion. The main objective of this study is to identify the optimal plant size and configuration, taking into account the different operational management strategies of the system’s constituting units. The analysis integrates thermochemical modeling with a techno-economic optimization procedure. Three different configurations for renewable energy production, photovoltaic-based, wind-based, and hybrid photovoltaic–wind, were evaluated for a case study in Southern Italy. Results show that the hybrid configuration provides the best techno-economic balance, achieving the highest annual biomethane output (≈2288 t) and the lowest levelized cost of biomethane (EUR 97.4/MWh). While current biomethane production costs exceed natural gas prices, the proposed pathway represents a viable long-term solution for renewable integration and climate-neutral gas supply. Full article

In the past decade, agricultural biogas plants have become one of the key tools driving the energy transition in rural areas. Nevertheless, their development in Poland still lags behind that in Western European countries, suggesting the existence of barriers that go beyond technological or regulatory issues. This study aims to examine how Polish farmers perceive the risks and expected benefits associated with investing in biogas plants and which of these perceptions influence their willingness to invest. The research was conducted in the second quarter of 2025 among farmers planning to build micro biogas plants as well as owners of existing biogas facilities. Geographic Information System (GIS) tools were also used in selecting respondents and identifying potential investment sites, helping to pinpoint areas with favorable spatial and environmental conditions. The findings show that both current and prospective biogas plant operators view complex legal requirements, social risk, and financial uncertainty as the main obstacles. However, both groups are primarily motivated by the desire for on-farm energy self-sufficiency and the environmental benefits of improved agricultural waste management. Owners of operational installations—particularly small and medium-sized ones—tend to rate all categories of risk significantly lower than prospective investors, suggesting that practical experience and knowledge-sharing can effectively alleviate perceived risks related to renewable energy investments. Full article

A three-year optimization study was conducted at a mechanical biological treatment plant with the aim of enhancing organic fractions recovery from mechanically separated fine fractions (MSFF) of residual waste using a screw press. The study aimed to optimize key operating parameters for the employed screw press, such as pressure, liquid-to-MSFF, feeding quantity per hour, and press basket mesh size, to enhance volatile solids and biogas recovery in the generated press water for anaerobic digestion. Experiments were performed at the full-scale facility to evaluate the efficiency of screw press extraction with other pretreatment methods, like press extrusion, wet pulping, and hydrothermal treatment. The results indicated that hydrolysis of the organic fractions in MSFF was the most important factor for improving organic extraction from the MSFF to press water for fermentation. Optimal hydrolysis efficiency was achieved with a digestate and process water-to-MSFF of approximately 1000 L/ton, with a feeding rate between 8.8 and 14 tons per hour. Increasing pressure from 2.5 to 4.0 bar had minimal impact on press water properties or biogas production, regardless of the press basket size. The highest volatile solids (29%) and biogas (50%) recovery occurred at 4.0 bar pressure with a 1000 L/ton liquid-to-MSFF. Further improvements could be achieved with longer mixing times before pressing. These findings demonstrate the technical feasibility of the pressing system for preparing an appropriate substrate for the fermentation process, underscoring the potential for optimizing the system. However, further research is required to assess the cost–benefit balance. Full article

Mechanical–biological treatment plants face challenges in effectively separating organic fractions from residual municipal solid waste for biological treatment. This study investigates the optimization measures carried out at the Erbenschwang MBT facility, which transitioned from solely aerobic treatment to integrated anaerobic digestion using a screw press. This study focused on evaluating the efficiency of each mechanical pretreatment step by investigating the composition of the residual waste, organic fraction recovery rate, and screw press performance in recovering organic material and biogas to press water. The results showed that 92% of the organic material from the residual waste was recovered into fine fractions after shredding and trommel screening. The pressing experiments produced high-quality press water with less than 3% inert material (0.063–4 mm size). Mass balance analysis revealed that 47% of the input fresh mass was separated into press water, corresponding to 24% of the volatile solids recovered. Biogas yield tests showed that the press water had a biogas potential of 416 m³/ton VS, recovering 38% of the total biogas potential. In simple terms, the screw press produced 32 m³ of biogas per ton of mechanically separated fine fractions and 20 m³ per ton of input residual waste. This low-pressure, single-step screw press efficiently and cost-effectively prepares anaerobic digestion feedstock, making it a promising optimization for both existing and new facilities. The operational configuration of the screw press remains an underexplored area in current research. Therefore, further studies are needed to systematically evaluate key parameters such as screw press pressure (bar), liquid-to-waste (L/ton), and feed rate (ton/h). Full article

The concern for sustainability, understood as the responsible use of natural resources to ensure the well-being of future generations, has grown across various sectors. One of the main drivers of environmental degradation is the use of fossil-fuel-based transportation, which produces pollutant emissions and contributes to climate change. In this context, electric cars have emerged as a smart and sustainable alternative, as they do not emit polluting gases and, when powered by renewable energy sources such as photovoltaics, can significantly reduce the carbon footprint. Based on this concept, it is noted that electric cars are an intelligent alternative to reduce the degradation caused by fossil fuels. The generation of electricity from renewable sources, such as photovoltaics, biogas and others, combined with the low maintenance costs and long service life of these technologies, represents an extremely sustainable solution. In this work, methodologies are applied for sizing and analysis of the cost of electricity generation through photovoltaic energy. The operational cost of the electric car being fueled by electricity provided by this source and by energy from the utility grid compared to the operational cost of an internal combustion engine car is also considered. The (CO₂)eq emitted by the use of the photovoltaic plant, energy from the grid and the gasoline used in the internal combustion engine car is also determined. It is concluded that the return on investment for the energy generated by photovoltaic energy is approximately 5 years. The annual cost for an electric car is 76.49% lower when using electricity provided by energy concessionaires in Brazil and 81.35% lower for energy from photovoltaic plants compared to an internal combustion engine vehicle, also considering that the harm to the environment is low for this technology. These data emphasize the importance of looking for technological and sustainable solutions that adapt energy production systems, reduce costs and, above all, help to mitigate the impact on the environment, reflecting a commitment to the future of our planet and the quality of life of future generations. Full article

The energy efficiency of water treatment plants (WTPs) plays a key role in the sustainable management of water resources. In the face of increasing water demand, climate change, and increasingly stringent environmental regulations, optimising the energy consumption of treatment processes is becoming a priority for water system operators and decision-makers alike. Water treatment plants, depending on the type of water source served (groundwater, infiltration, surface water), vary considerably in terms of their technological design, which directly affects their energy efficiency and operating costs. According to the International Water Association, the water sector accounts for approximately 4% of global electricity consumption, a significant proportion of which is consumed by water treatment and distribution processes. Electricity is used in many process steps, such as water pumping, aeration, filtration, disinfection, and filter flushing. The energy consumption of a System for Upgrading Water (SUW) depends not only on the quality of taken raw water, but also on the size of the station, used technologies, and operation organisation. This study shows that implementing high-efficiency pumping systems and AI-based optimisation can reduce energy consumption in WTPs by 20–30%. The introduction of membrane filtration in surface water plants has demonstrated a reduction in energy use by up to 50%, while the use of biogas from sludge treatment has cut external energy demand by 15–25%. The results emphasise the potential to reduce CO₂ emissions by 10–20% compared to conventional treatment methods. However, achieving significant reductions in energy consumption in SUW requires a comprehensive understanding of the diversity of water facilities, technological processes, and specific energy requirements. Full article

The development of plant-growth-promoting bacteria (PGPB) is one of the important research topics in agricultural microbiology. Four bacterial isolates that exhibited nitrogen fixation, phosphate and potassium solubilization, as well as indole-3-acetic acid (IAA) and siderophore production abilities, were selected from biogas residue, namely BR-1, BR-16, BR-17, and BR-44. According to morphological and molecular biological identification, BR-1, BR-16, BR-17, and BR-44 belonged to Bacillus subtilis, Bacillus cereus, Bacillus megaterium, and Bacillus subtilis, respectively. The four functional strains were combined into a composite microbial community. The optimal media were peptone (15 g/L), sucrose (10 g/L), and KCl (2 g/L); the optimal incubation conditions were an initial pH of 7.0, a volume of 47 mL/250 mL, an inoculum size of 6% v/v, an incubation temperature of 31 °C, a shaking speed of 205 r/min, and an incubation period of 20 h, as determined through a single factor test and the response surface methodology (RSM). In the optimized process, a liquid bacterial inoculant with an OD₆₀₀ of 1.866 was obtained, with an effective viable count of 8.955 × 10⁹ CFU/mL. A solid bacterial inoculant was prepared by using bran as a substrate, and its effective viable count was 1.11 × 10⁹ CFU/g. The application of the bacterial inoculants promoted the growth of watermelon, increased the photosynthetic efficiency and yield, and improved fruit quality. This study provides a theoretical basis and technical support for the development and application of microbial inoculants. Full article

Sugarcane bagasse (SCB) constitutes up to 28% of the weight of crushed sugarcane, with significant potential for bioenergy production. Solid-state anaerobic digestion with total solids (TSs) over 15% is an interesting technology that can be used to treat agricultural wastes such as SCB, resulting in smaller reactor sizes and lower water consumption. This study investigates methane production from SCB under wet (10% TS), hemi-solid (15% TS), and solid-state (20% TS) anaerobic digestion with substrate-to-inoculum ratios (SIR) of 1, 2, 3, and 4. Batch experiments were conducted under mesophilic conditions (37 °C) to evaluate methane yields, volumetric methane productivity, and kinetic parameters. Results revealed that the highest methane yields—125, 115, and 106 L CH₄ kg VS⁻¹—were achieved for wet, hemi-solid, and solid-state digestion, respectively. Despite similar methane yields across TS conditions, volumetric methane productivities increased by 118% and 128% from hemi-slid and solid-state digestion, demonstrating their potential for scaling up in commercial biogas plants. The first-order kinetic model best-predicted methane production (R² > 0.984), with hydrolysis identified as the limiting step (K_hyd ≤ 0.05 d⁻¹). These findings highlight the advantages of solid-state anaerobic digestion for lignocellulosic feedstocks like SCB, contributing to bioenergy sustainability and the circular economy. Full article

The size of a company is a fundamental factor that can influence its efficiency. In larger companies, economies of scale are a key consideration. The objective of this study was to evaluate the technical efficiency of agricultural biogas plants differentiated according to their capacity of power. The study included 43 agricultural biogas plants, which were divided into three groups according to their capacity power: group I, <0.5 MW; group II, 0.5–1 MW; group III, ≥1 MW. In order to assess the technical efficiency of agricultural biogas plants under the research, the Data Envelopment Analysis (DEA) method was applied. It was found that the largest biogas plants were the most efficient. However, the technical efficiency of the smallest biogas plants was not statistically significantly different from that of the largest biogas plants. This indicates that small entities can achieve the technical efficiency at a satisfactory level. For this reason, in the development policy of agricultural biogas plants, the optimal solution is the coexistence of large and small facilities. The smallest biogas plants were more sensitive to changes in the macroeconomic environment than other biogas plants. This may suggest a need to pay more attention to energy policy mechanisms to stabilize their performance in periods of disadvantageous macroeconomic conditions. Full article

Pig farms have been identified as one of the most important sources of greenhouse gas emissions. This study demonstrates the production of vehicle biomethane in a demonstration prototype plant based on photosynthetic upgrading technology, where the CO₂ and H₂S present in biogas are consumed by a microalgae culture. The information collected during the prototype construction allowed for an assessment of the capital and operating costs of this novel biogas upgrading technology with other conventional systems. With this objective, the costs of the equipment comprising the biogas cleaning and purification system were calculated considering a biogas flow rate of 5 m³ h⁻¹, corresponding to a small–medium biogas plant and an average pig farm size. The sustainability and competitiveness of the algae upgrading system and the low capital and operating costs vis à vis other upgrading technologies were proven. With a net energy production of 687 kWh day⁻¹ and an annual profit of €30,348 in a 3500 head pig farm, this technology can be easily installed in livestock farms, increasing the benefits and reducing the carbon footprint. Full article

Microplastics (MPs) are persistent, globally relevant pollutants that have thus far been rigorously studied in natural waters but have not been as extensively studied in industrial wastewaters. Samples were collected from the forestry industry, wastewater treatment plants and the biogas industry. An enzymatic treatment protocol for MPs’ detection was applied to an assortment of industrial samples ranging from wastewaters, effluents and condensates to sludges and digestates. The effects of selected enzymes were studied systematically to develop a basis for digestion protocols on industrial samples. Further, different methods of detection (micro FTIR and Raman) were compared to each other, and the samples were visually examined using SEM. The developed protocols in this study were then compared with blank samples, contamination controls and samples spiked with artificial microplastics. This research aimed to fill some of the gap in the knowledge regarding the analysis methods and especially in the type of samples screened for microplastics thus far and presents a systematic approach to MPs’ detection in industrial wastewaters. It highlights the issues with the used analytical methods (such as misidentification) and validates the analysis results with milled, random shape and wide-size-range reference MPs that represent real samples better than standardized, ideal round beads. This study provides the first-ever suggestion for an enzymatic digestion protocol for industrial sample analysis. Full article

This paper presents a simulation model for determining the most suitable type of microbiogas plant for small local communities on Slovenian farms, focusing on the efficient processing of organic waste. This model uses various input parameters, including different types and quantities of slurry and corn silage. Four different scenarios were developed to represent potential plant sizes, each evaluated using key economic indicators: net present value, breakthrough price, and internal rate of return. A scenario sensitivity analysis was conducted to assess the effects of changes in investment costs, fluctuations in energy prices, and the addition of corn silage to the anaerobic digestion process. The results highlight significant differences in economic viability across the scenarios, with some demonstrating positive financial outcomes and shorter payback periods and others indicating potential financial risks and longer recovery times under certain conditions. The analysis suggests that smaller micro biogas plants may struggle to achieve profitability without optimizing input ratios or reducing costs, whereas larger plants show more favorable economic indicators, provided certain conditions are met. Furthermore, the economic efficiency improves when adding maize silage to the fermentor mixture. Full article

The use of agricultural residues in biogas plants is becoming increasingly important, as they represent an efficient and sustainable substrate alternative. Pelletizing straw can have positive effects on transportation, handling, and biogas production. In this study, different grain straw pellets from mobile and stationary pelleting plants in Germany as well as the corresponding untreated straw were characterized and investigated for their suitability for anaerobic digestion (AD). Therefore, tests on the biochemical methane potential (BMP) and the chemical–physical characterization of unpelletized straw and straw pellets were carried out. The characterization of the pellets and the straw revealed a high average total solid content of 91.8% for the industrially produced straw pellets and of 90.8% for the straw. The particle size distribution within the tested pellet samples varied greatly depending on the pelleting process and the pre-treatment of the straw. In addition, a high C/N ratio of 91:1 on average was determined for the straw pellets, whereas the average higher heating value (HHV) content of the pellets was 17.58 MJ kg⁻¹. In the BMP tests, the methane production yields ranged from 260–319 normal liter (NL) CH₄ kg⁻¹ volatile solids (VS) for the straw pellets and between 262 and 289 NL CH₄ kg⁻¹ VS for the unpelletized straw. Overall, pelleting increases the methane yield on average from 274 to 286 NL CH₄ kg⁻¹ VS, which corresponds to an increase in methane yield of 4.3%. Based on the results, the feasibility of using straw pellets for AD could be confirmed, which can facilitate the possibility of increased biogas production from agricultural residues such as straw pellets and thus make the substrate supply more sustainable. Full article

In conditions of economic and political instability, when unpredictability affects business, the need for security, including financial security, becomes particularly important. In our study, we address this issue, with the main objective of comparing and evaluating the financial security of small and medium-sized renewable energy companies in Poland according to sustainable development goals. In order to study and describe relationships between selected groups of companies, financial ratios were used, including canonical variate analysis. The liquidity ratios of the surveyed companies indicated a low level of financial security in terms of the ability to meet short-term liabilities. The profitability of operations was low and did not contribute to the improvement of financial security in most of the companies. The lowest return on assets was found in the group of biogas plants. Higher profitability of assets was found in solar power plants, including those with system installations. Solar power plants were also characterized by a high level of total debt and a rapid turnover of assets in comparison to other studied companies. The results show that the financial security of small and medium-sized renewable energy enterprises in Poland is low, which may be a threat to sustainable development in the future. Full article