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The Influence of Temperature on Rheological Parameters and Energy Efficiency of Digestate in a Fermenter of an Agricultural Biogas Plant
This investigation specifically aims to enhance the understanding of digestate flow and mixing behavior across typical temperatures in bioreactors in agricultural biogas plants, facilitating energy-efficient mixing. Experimental tests confirmed that digestate exhibits non-Newtonian characteristics, allowing its flow behavior to be captured by rheological models. This study validated that digestate rheology significantly varies with temperature, which influences flow resistance, mixing efficiency and overall energy requirements. Two rheological models—the Bingham and Ostwald models—were applied to characterize digestate behavior, with the Ostwald model emerging as the most effective for Computational Fluid Dynamic (CFD) simulations, given its balance between predictive accuracy and computational efficiency. Specifically, results suggest that, while three-parameter models, like the Herschel–Bulkley model, offer high precision, their computational intensity is less suitable for large-scale modeling where efficiency is paramount. The small increase in the accuracy of the shearing process description does not compensate for the significant increase in CFD calculation time. Higher temperatures were found to reduce flow resistance, which in turn enables increased flow rates and more extensive mixing zones. This enhanced mass transfer and mixing potential at elevated temperatures are especially pronounced in peripheral areas of the bioreactor, farthest from the agitators. By contributing a model for rheological behavior under realistic bioreactor conditions, this study supports the optimization of energy use in biogas production. These findings emphasize that temperature adjustments within bioreactors could serve as a reliable control strategy to maintain optimal production conditions while minimizing operational costs.
Use of Shredded Recycled Plastic as Filter Bed Packing in a Vertical Flow Filter for Onsite Wastewater Treatment Plants: Preliminary Findings
Household wastewater is a problem, especially in areas with a dispersed settlement where there is no wastewater collection system or wastewater treatment plant. In this case, it is necessary to build a local or onsite wastewater treatment plant. This paper is an attempt to analyse the possibility of using recycled shredded ABS plastic (acrylonitrile butadiene styrene) as packing media in an experimental vertical flow filter for use in on-site wastewater treatment plants. Studies have shown that shredded recycled ABS is a promising filtration material that has several features important in the treatment process, like a large surface area, high mechanical strength and chemical inertness. The system was operated with a hydraulic load of 50 dm3/m2 (3 months). BOD5 (biochemical oxygen demand), COD (chemical oxygen demand), and total suspended solids (TSS) reduction efficiency in the primary effluent was high; 94.4%, 77.8%, and 92.8%, respectively.
Preparation of Samples for the Study of Rheological Parameters of Digested Pulps in a Bioreactor of an Agricultural Biogas Plant
The studies of the rheology of digested pulp from agricultural biogas plants have often been fragmentary and non-standardised due to their complexity and time-consuming nature. As a result of measurements, it was possible to develop a procedure and range of measurements for the correct determination of the parameters of the carrier substance. The applicability of the coaxial cylinder measurement system was demonstrated for assessing the rheological parameters of digested pulp from a fermenter that utilises agricultural biomass. To determine the characteristics of solid particles, the Zingg diagram was used, inter alia, allowing the comparison of particles from each fraction. The analysis of the shape and size of solid particles may help to describe the onset of motion of this phase, flow type, or sedimentation type. The authors propose a completely new research approach to obtain an appropriate, repeatable test conditions of medium, which is the carrier liquid from the biogas plant reactor. The proposed methodology and the scenario of the entire study make it possible to achieve scalable and comparable test results in any laboratory. The proposed solution eliminates the influence of most external factors on the sample and rheological measurements, and the effectiveness of the presented procedure was confirmed in tests.
Energy and Economic Balance between Manure Stored and Used as a Substrate for Biogas Production
The aim of the study is to draw attention to the fact that reducing methane and nitrous oxide emissions as a result of traditional manure storage for several months in a pile is not only a non-ecological solution, but also unprofitable. A solution that combines both aspects—environmental and financial—is the use of manure as a substrate for a biogas plant, but immediately—directly after its removal from the dairy barn. As part of the case study, the energy and economic balance of a model farm with dairy farming for the scenario without biogas plant and with a biogas plant using manure as the main substrate in methane fermentation processes was also performed. Research data on the average emission of ammonia and nitrous oxide from 1 Mg of stored manure as well as the results of laboratory tests on the yield of biogas from dairy cows manure were obtained on the basis of samples taken from the farm being a case study. The use of a biogas installation would allow the emission of carbon dioxide equivalent to be reduced by up to 100 Mg per year. In addition, it has been shown that the estimated payback period for biogas installations is less than 5 years, and with the current trend of increasing energy prices, it may be even shorter—up to 4 years.
The Impact of Manure Use for Energy Purposes on the Economic Balance of a Dairy Farm
The use of methane fermentation in mesophilic conditions for the energy use of cow manure and additional co-substrates from the farm can bring a small dairy farm (140 dairy cows) financial benefits of up to EUR 114,159 per year. Taking into account the need to pay for emissions calculated as carbon dioxide equivalent, this profit could be reduced to EUR 81,323 per year. With the traditional direct use of manure, this profit would drop by as much as 60% to the level of EUR 33,944 per year. Therefore, the introduction of fees for emissions may significantly burden current dairy farms. As has already been shown, just compacting and covering the manure (which costs approx. EUR 2000 per year for 140 cows) would give almost twice as much profit—EUR 64,509 per year. Although an investment in a small biogas plant with a cogeneration unit on a family dairy farm may have a payback period of less than 6.5 years and a return of capital employed of 16%, most small farms in the world will not be able to afford its construction without external subsidies. At the same time, it would make it possible to reduce emissions by almost 270 times—from 41,460 to 154 tons of CO2eq per year—and the possibility of preserving valuable nutrients and minerals and supporting soil properties in the digestate. Therefore, it seems necessary for Europe to introduce a support system for small- and medium-sized farms with this type of investment in the near future in a much larger form than it has been so far.
Bioreaktor ze złożem ruchomym, zwłaszcza do rekultywacji silnie zanieczyszczonych akwakultur i małych zbiorników wodnych
Thematic study of the BIOEAST thematic working group on bioenergy and new value added: Anaerobic digestion for renewable energy, carbon sink and organic fertilizers as an integral part of bioeconomy development
Leverage of Essential Oils on Faeces-Based Methane and Biogas Production in Dairy Cows
Currently, there is an ongoing intensive search for solutions that would effectively reduce greenhouse gas emissions (mainly methane) into the environment. From a practical point of view, it is important to reduce methane emissions from cows in such a way as to simultaneously trim emissions from the digestive system and increase its potential production from feces, which is intended as a substrate used in biogas plants. Such a solution would not only lower animal-based methane emissions but would also enable the production of fuel (in chemical form) with a high yield of methane from biogas, which would boost the economic benefits and reduce the use of fossil fuels. We tested the effect of administering an essential oil blend consisting of 5.5% oils and fats on methane and biogas production from dairy cow feces during fermentation. Three subsequent series (control and experimental) were conducted in dairy cows fed a total mixed ration (TMR) rich in brewer’s cereals and beet pulp, with 20% dry matter (DM) of the total diet. Cows from the experimental group received 20 g/cow/day of essential oil blend, namely a commercial additive (CA). The study showed that CA can increase the production of methane and biogas from dairy cow feces. It can be concluded that in the experimental groups, approx. 15.2% and 14.4% on a fresh matter basis and 11.7% and 10.9% on a dry matter basis more methane and biogas were generated compared to the control group, respectively. Therefore, it can be assumed that the use of CA in cow nutrition improved dietary digestibility, which increased the efficiency of the use of feces organic matter for biogas production.
The Biogas Potential of Oxytree Leaves
This article describes the characteristics of th Oxytree (Paulownia) plant, both in terms of its impact on GHG emissions and its potential use to produce biofuel, i.e., biogas. The described research involved the physico-chemical and elemental analysis of the Oxytree leaf composition and its biogas efficiency depending on the harvesting method. Three different scenarios were considered: the freshest possible leaves—processed immediately after stripping from the living tree; after the first day of collection from pruned or harvested wood; after the first week of collection from pruned or harvested wood. The best results were achieved for the harvest of the freshest leaves—on average 430 m3/Mg (biogas) and 223 m3/Mg (methane) per dry organic mass. The highest yield of biogas in terms of fresh mass (FM) was obtained for leaves fallen and collected after 1 day—123 m3/Mg FM, and 59 m3/Mg FM (methane). Processing Oxytree leaves through anaerobic digestion will contribute to reducing the carbon footprint of wood biomass production and is an additional source of renewable energy and fertilizer product.
Loss of Energy and Economic Potential of a Biogas Plant Fed with Cow Manure due to Storage Time
The aim of the publication was to analyze investments in biogas plants with a cogeneration unit for an average size dairy farm. The basis for the calculation was the use of cow manure as the only substrate in methane fermentation. The economic balance also includes ecological and service aspects. The study also shows how much energy and quality potential is lost due to improper manure management and what impact a single farm with dairy cows has on the emission of carbon dioxide equivalent. It has been estimated that as a result of improper storage of manure, even 2/3 of its fertilizing, energy and economic value can be lost, while causing damage to the environment. It has been estimated that for a single farm with 100 cows, without government mechanisms subsidizing investments in RES, the payback period exceeds 15 years, and the Return of Capital Employed is slightly more than 6%.
The energetic and economic analysis of demand-driven biogas plant investment possibility in dairy farm
Instalacja (urządzenie) do rewitalizacji stawów hodowlanych, zwłaszcza z grupy akwakultur słodkowodnych
Analysis of the Energy and Material Use of Manure as a Fertilizer or Substrate for Biogas Production during the Energy Crisis
The main goal of the publication was to show the differences in profit when using manure directly as fertilizer (after the storage period) or as a substrate for biogas plants with a cogeneration unit, and then using the digestate for fertilization purposes. The comparison covers the streams of costs, revenues and profits over the year between 14 October 2021 and 14 October 2022. This period was chosen due to the energy and fertilization crisis caused by the war in Ukraine. Profitability forecasts for biogas investments (including the payback period) are presented, with the reduction of greenhouse gas emissions, i.e., methane and nitrous oxide, taken into account. The performed economic, energy and ecological calculations of manure management can be used as guidelines when considering investing in biogas plants, as well as what is recently becoming a new trend: the carbon footprint of dairy production. Input substrate parameters, gaseous emissions and biogas yields were obtained from own research (manure samples were collected) and from literature data, including guidelines for international and national IPCC protocols.