Manure-based Biogas Research Articles

Estimation of biogas potential from poultry manure to 2040 in Türkiye using time series and the artificial neural network (ANN)

The number of poultry in Türkiye constituted approximately 24 % of Europe’s total in 2020. Although Türkiye has a significant number of poultry animals, it has been relatively unsuccessful in terms of managing the associated poultry waste. The present study focuses on poultry manure-based biogas potential (PMBP), which represents an alternative means of poultry manure management in Türkiye. PMBPs were calculated for each year from 2003 to 2021, for which it was found that for 2021, Türkiye's PMBP had increased by 40 % since 2003, reaching 3469 GWh. The possible electrical energy savings that PMBP could provide for lighting, habitation, business, government offices, and industry throughout Türkiye were calculated, with PMBP spatial distribution maps for 2021 created according to geographical region and province. The province with the highest PMBP was found to be Manisa, at 390 GWh. The projected PMBPs were calculated to 2040 using the artificial neural network (ANN) and autoregressive integrated moving average (ARIMA). According to ARIMA, the PMBP for 2040 could potentially be increased by as much as 32 % from that of 2021, while according to ANN predictions, this same increase could be as much as 72 %. The ability to reduce greenhouse gas emissions resulting from poultry manure management in Türkiye through biogas production was calculated. Investors may need to prepare a feasibility study for the establishment of a biogas plant in a suitable region within Manisa province, as it has the highest PMBP among the regions evaluated.

Forecasting of biogas potential using artificial neural networks and time series models for Türkiye to 2035

Being among the developing countries, Türkiye's electrical needs are increasing day by day with its increase in population. To address this need, consideration should be given to bovine manure-based biogas potential (BMBP), which is a renewable energy source, particularly as one of Türkiye's national livelihoods – which is dependent on foreign countries for energy – is livestock farming. Although there are significant numbers of bovine stock distributed across the various geographical regions of Türkiye, there are no studies to date that have attempted to determine the BMBPs of these regions, either for past or future years. The aim of the current study was to calculate for the first time the BMBP for seven different regions of Türkiye between 2004 and 2021 and to estimate these for 2022 to 2035 using Artificial Neural Networks (ANN), autoregressive integrated moving averages (ARIMA) from time series, and linear regression models. Türkiye's BMBP for 2021 has been calculated to be 14,262 GWh/year, which corresponds to approximately 3.2 % of the total renewable energy used by Türkiye in 2021. For 2035, Türkiye's BMBP has been forecast to be 19,905 GWh/year according to ANN's Levenberg-Marquardt algorithm, 16,862 GWh/year according to the Bayesian Regularization algorithm, 19,329 GWh/year according to ARIMA, and 19,897 GWh/year according to the Linear Regression method. All the models proposed for predicting the BMBPs for different geographical regions in Türkiye for the coming years of interest were found to perform extremely well (MSE = 205–7917 and MAPE = 0.919–4.430). When evaluated on a regional basis, the highest BMBP for 2021 was forecasted to be 3163 GWh/year for the Central Anatolia region, which corresponded to approximately 7 % of its total electricity consumption. Considering these values, it is clear that BMBP can provide significant savings with regard to the volume of electrical energy Türkiye will require in the coming years.

Methane emission rates averaged over a year from ten farm-scale manure storage tanks

Methane (CH4) emissions from animal manure stored in outdoor tanks are difficult to predict because of several influencing factors. In this study, the tracer gas dispersion method (TDM) was used to quantify CH4 emissions from ten manure storage tanks, along with the collection of supporting information, in order to identify its emission drivers. The dataset included two tanks storing dairy cattle manure, six holding pig manure, and two with digestate from manure-based biogas plants. CH4 emissions from the tanks were measured six to 14 times over a year. Emissions varied from 0.02 to 14.30 kg h−1, or when normalised by the volume of manure stored, emission factors (EFs) varied from 0.05 to 11 g m−3 h−1. Annual average CH4 EFs varied greatly between the tanks, ranging from 0.20 to 2.75 g m−3 h−1. Normalised EFs are similar to literature values for cattle and digested manure, but at the high end of the interval for pig manure. The averaged manure temperature for all tanks varied from 10.6 to 16.4 °C, which was higher than reported in a previous Danish study. Volatile solids (VS) concentration was in average higher for cattle manure (ranging from 3.1 and 4.4 %) than pig manure (ranging from 1.0 to 3.6 %). CH4 emission rates were positively correlated with manure temperature, whereas this was not the case for VS concentration. Annual average EFs were higher for pig than for cattle manure (a factor of 2.5), which was greater than digested manure emissions (a factor of 1.2). For the pig manure storage tanks, CH4 emissions were higher for covered tanks than for uncovered tanks (by a factor of 2.3). In this study, manure storage tanks showed a large disparity in emission rates, driven not only by physical factors, but also by farm management practices.

Sustainable Biofuel Production from Animal Manure and Crop Residues in Ghana

Renewable energy is predicted to play a crucial role in the energy sector as transitioning from fossil fuels to biofuels is key to achieving carbon neutrality. The comprehensive utilization of livestock manure and crop residues as a viable source of biofuels can play a significant role in Ghana’s future energy system. This current study aims to examine and predict the biofuel potential in Ghana from animal manure and crop residues. The biogas-biomethane potential of animal manure is determined using anaerobic digestion technology, whereas crop residues’ bioethanol potential is assessed using computational and analytical approaches. The findings demonstrate that animal manure biogas potential is 237.72 normal million cubic meters (NMm3). The highest manure-biogas potential per animal is from cattle (27.15 Nm3) and pigs (18.15 Nm3), while the least contribution is from chickens (1.80 Nm3). In addition, the annual bioethanol production is 3.74 gigaliters (GL), and residues from maize (0.88 GL), yams (0.82 GL), and plantains (0.47 GL) had the largest share per annum. By 2100, Ghana has the potential to produce 1288.56 NMm3 of manure-based biogas which can offset 13.88% of liquefied petroleum gas (LPG) consumption. The biogas potential positively correlates with the biomethane potential of 901.99 NMm3. Furthermore, 91.85% of the 14.76 GL of bioethanol will be from food crop residues. This study provides critical information to lawmakers and energy planners with strategies to achieve energy security and minimize the ecological footprint in an optimistic scenario.

Not all sites are created equal – Exploring the impact of constraints to suitable biogas plant locations in Sweden

Biogas production from manure is attractive to support plans towards a circular economy as it allows for renewable energy production and nutrient recycling in agriculture. Finding optimal locations for biogas plants, which minimize transport distances to and from farms, while accounting for multiple feasibility constraints, remains a challenge. We developed 1 km2 spatially-explicit datasets for known feasibility constraints such as distance to housing, compatible land-use zoning, and the presence of roads with sufficient weight bearing capacity. These datasets were used to improve the realism of an optimization model designed to minimize transportation costs in Sweden. At a national level, the presence of durable enough roads most limited the number of suitable locations for a plant. We further focused our analysis on a case study region where a company wanted to invest in a new manure-based biogas plant. In contrast to the national level, the constraint for remaining at least 500 m from housing/buildings had the greatest limiting impact, excluding 71% of grids in the Sjöbo or Tomelilla municipalities of Southern Sweden. Still, we identified 105 suitable locations for a new biogas plant. The most suitable location, accounting for feasibility and minimized transportation costs, changed when simultaneously accounting for another proposed plant in a neighboring municipality. Our results indicate that utilizing both local and national datasets can help narrow down potential biogas development sites and that long-term planning is necessary for actors with ambitions to build several plants to minimize costs and maximize energy and nutrient recycling benefits.

Agricultural Biogas Production—Climate and Environmental Impacts

Livestock manure is a major source of the greenhouse gases (GHGs) methane (CH4) and nitrous oxide (N2O). The emissions can be mitigated by production of biogas through anaerobic digestion (AD) of manure, mostly together with other biowastes, which can substitute fossil energy and thereby reduce CO2 emissions and postdigestion GHG emissions. This paper presents GHG balances for manure and biowaste management as affected by AD for five Danish biogas scenarios in which pig and cattle slurry were codigested with one or more of the following biomasses: deep litter, straw, energy crops, slaughterhouse waste, grass–clover green manure, and household waste. The calculated effects of AD on the GHG balance of each scenario included fossil fuel substitution, energy use for transport, leakage of CH4 from biogas production plants, CH4 emissions during storage of animal manure and biowaste, N2O emissions from stored and field applied biomass, N2O emissions related to nitrate (NO3−) leaching and ammonia (NH3) losses, N2O emissions from cultivation of energy crops, and soil C sequestration. All scenarios caused significant reductions in GHG emissions. Most of the reductions resulted from fossil fuel substitution and reduced emissions of CH4 during storage of codigestates. The total reductions in GHG emissions ranged from 65 to 105 kg CO2-eq ton−1 biomass. This wide range showed the importance of biomass composition. Reductions were highest when straw and grass–clover were used as codigestates, whereas reductions per unit energy produced were highest when deep litter or deep litter plus energy crops were used. Potential effects of iLUC were ignored but may have a negative impact on the GHG balance when using energy crops, and this may potentially exceed the calculated positive climate impacts of biogas production. The ammonia emission potential of digestate applied in the field is higher than that from cattle slurry and pig slurry because of the higher pH of the digestate. This effect, and the higher content of TAN in digestate, resulted in increasing ammonia emissions at 0.14 to 0.3 kg NH3-N ton−1 biomass. Nitrate leaching was reduced in all scenarios and ranged from 0.04 to 0.45 kg NO3-N ton−1 biomass. In the scenario in which maize silage was introduced, the maize production increased leaching and almost negated the effect of AD. Methane leakage caused a 7% reduction in the positive climate impact for each percentage point of leakage in a manure-based biogas scenario.

Organic Waste-Based Fertilizer in Hydroponics Increases Tomato Fruit Size but Reduces Fruit Quality.

In regions with intensive agricultural production, large amounts of organic waste are produced by livestock animals. Liquid digestate from manure-based biogas production could potentially serve as fertilizer if integrated with closed horticultural irrigation systems. The aim of this experiment was to investigate how fertilizer based on liquid biogas by-products of pig manure digestion can affect the growth and production of tomato plants. Integration of a nitrification bioreactor presumes a significantly lower concentration of nutrient solutions and a higher level of oxygenation than classical mineral cultivation. Therefore, additional controls were included. We compared plant growth and fruit quality traits of tomato plants grown in a hydroponic solution with organic fertilizer with two levels of mineral fertilizer. The tomatoes grown with organic waste-based liquid fertilizer showed reduced growth rates but increased mean fruit size, resulting in no significant change in total yield compared with high-mineral cultivation. The growth rate was similarly reduced in plants cultivated with low-mineral fertilizer. Plants cultivated with organic waste-based fertilizer had high Cl− concentration in xylem sap, leaves, and, ultimately, fruits. The leaves of plants cultivated with organic waste-based fertilizer contained higher concentrations of starch and soluble carbohydrate and low concentrations of phosphorous (P) and sulfur (S). The plants grown with organic waste-based or low-mineral medium showed significantly poorer fruit quality than the plants cultivated with the high-mineral solution. The low-mineral treatment increased xylem sap contribution to fruit weight because of higher root power. The organic waste-based fertilization did not change the root power but increased fruit size. In conclusion, organic waste-based cultivation is a possible solution for sustainable plant production in greenhouses. However, additional adjustment of nutrient supply is required to improve fruit quality.

Farmer's willingness to adopt private and collective biogas facilities: An agent-based modeling approach

Manure-based biogas may make an important contribution both to the energy transition and to the reduction in greenhouse gas emissions. Despite these benefits, in Switzerland the use of manure as an energy source is still very limited. The engagement of farmers in biogas production is low and the barriers to their participation are not well known. This study investigates the behavior of Swiss farmers towards anaerobic digestion and the potential impact of changing incentives. Based on a comprehensive survey, including a choice experiment, their willingness to participate in manure-based biogas production is investigated at different levels. An Agent-Based Model (ABM) is designed and used to simulate the development of biogas facilities under different framework conditions. The agent's' properties are derived from the farmers’ survey. Simulation results show that revenue for produced energy is the main driver. An increase of 0.10 CHF/kWh energy revenues (compared to 0.45 CHF/kWh today) would enable the establishment of 10 additional biogas facilities (10% more than today) enabling the manure of an additional 4285 livestock units to be mobilized for biogas, (<1% of the total available manure). The influence of the availability of additional material (co-substrate) for digestion is visible but with even less impact, while a one-time remuneration grant has barely any influence. In this context, the mobilization of the full resources potential involves substantial changes at the technological, organizational, institutional, political, economic, and socio-cultural levels.

Microbiome Diversity and Community-Level Change Points within Manure-based small Biogas Plants.

Efforts to integrate biogas plants into bioeconomy concepts will lead to an expansion of manure-based (small) biogas plants, while their operation is challenging due to critical characteristics of some types of livestock manure. For a better process understanding, in this study, three manure-based small biogas plants were investigated with emphasis on microbiome diversity. Due to varying digester types, feedstocks, and process conditions, 16S rRNA gene amplicon sequencing showed differences in the taxonomic composition. Dynamic variations of each investigated biogas plant microbiome over time were analyzed by terminal restriction fragment length polymorphism (TRFLP), whereby nonmetric multidimensional scaling (NMDS) revealed two well-running systems, one of them with a high share of chicken manure, and one unstable system. By using Threshold Indicator Taxa Analysis (TITAN), community-level change points at ammonium and ammonia concentrations of 2.25 g L−1 and 193 mg L−1 or volatile fatty acid concentrations of 0.75 g L−1were reliably identified which are lower than the commonly reported thresholds for critical process stages based on chemical parameters. Although a change in the microbiome structure does not necessarily indicate an upcoming critical process stage, the recorded community-level change points might be a first indication to carefully observe the process.

The fertilising potential of manure-based biogas fermentation residues: pelleted vs. liquid digestate

Spreading of manure on agricultural soils is a main source of ammonia emissions and/or nitrate leaching. It has been addressed by the European Union with the Directives 2001/81/EC and 91/676/EEC to protect the environment and the human health. The disposal of manure has therefore become an economic and environmental challenge for farmers. Thus, the conversion of manure via anaerobic digestion in a biogas plant could be a sustainable solution, having the byproducts (solid and liquid digestates) the potential to be used as fertilizers for crops.This work aimed at characterizing and assessing the effect of digestates obtained from a local biogas plant (Biogas Wipptal, Gmbh), either in the form of liquid fraction or as a solid pellet on: (i) the fertility of the soils during an incubation experiment; (ii) the plant growth and nutritional status of different species (maize and cucumber). Moreover, an extensive characterization of the pellet was performed via X-ray microanalytical techniques.The data obtained showed that both digestates exhibit a fertilizing potential for crops, depending on the plant species and the fertilizer dose: the liquid fraction increases the shoot fresh weight at low dose in cucumber, conversely, the solid pellet increases the shoot fresh weight at high dose in maize. The liquid digestate may have the advantage to release nutrients (i.e. nitrogen) more rapidly to plants, but its storage represents the main constraint (i.e. ammonia volatilization). Indeed, pelleting the digestates could improve the storability of the fertilizer besides enhancing plant nutrient availability (i.e. phosphate and potassium), plant biomass and soil biochemical quality (i.e. microbial biomass and activity). The physical structure and chemical composition of pellet digestates allow nutrients to be easily mobilized over time, representing a possible source of mineral nutrients also in long-term applications.

Energy recovery from wastewater microalgae through anaerobic digestion process: Methane potential, continuous reactor operation and modelling aspects

A mixture of piggery slurry and algal species (mainly composed of Nannochloropsis limnetica), grown in municipal wastewater, were used as substrates for biogas production. Mono- and co-digestion experiments were performed at batch and continuous reactor operation. The mono-digestion of wastewater microalgae led to the highest methane yield (408 ± 34 N mL/gVS). However, for manure-based biogas plants, a 60:40 v/v piggery slurry to wastewater microalgae ratio in terms of organic matter was identified as the most efficient mixture in batch assays (355 ± 27 N mL/gVS). The advantage of co-digestion was also evidenced under continuous reactor operation, which had markedly higher biogas production (23%, p < 0.05) compared to the mono-digestion of livestock manure. Moreover, it was demonstrated that the co-digestion process resulted in a more robust process as indicated by lower accumulation of acetate (i.e. presented during mono-digestion of piggery slurry) and propionate (i.e. recorded during mono-digestion of wastewater microalgae). The experimental data were compared with dynamic modelling (BioModel). A new set of biodegradability parameters was estimated and employed to improve the simulations of mono-digestion scenarios. Subsequently, the co-digestion scenario was used for model validation. Results obtained from simulations showed that the co-digestion can lead to relatively high methane productivity and prevent process instabilities.

A spatial analysis of biogas potential from manure in Europe

Anaerobic digestion is increasingly used worldwide to generate energy from biogas, bringing significant economic and environmental benefits. In particular, in the European Union (EU), biogas can contribute significantly in several countries to reach the renewable energy targets. This study provides an assessment of the spatial distribution of the biogas potential of farm manure from livestock and poultry in Europe, which is a key issue for the location and economic performances of a bioenergy plant. Biogas estimates provided in this study are computed through a spatial analysis algorithm that uses data of livestock and poultry, manure production and collection, leading to the evaluation of the spatial distribution of biogas potential at 1 km spatial resolution. Following this analysis, the theoretical biogas potential of manure was estimated at 26 billion m3 biomethane in Europe (23 billion m3 biomethane in the EU) and the realistic biogas potential, counting on collectible manure, was assessed at 18 billion m3 biomethane in Europe (16 billion m3 biomethane in the EU). Several maps provide the suitable locations and capacity of manure-based biogas plants in two different scenarios. Between 13,866 and 19,482 biogas plants could be built in Europe, with a total installed capacity between 6144 MWe and 7145 MWe, and an average capacity between 315 kWe and 515 kWe.

Economic sustainability of biogas production from animal manure: a regional circular economy model

Purpose This paper aims to understand the implementation of a circular economic business where animal manure is used to produce biogas and alternative fertilizer in a regional network of manure suppliers and biogas producers and to reveal the impacts of five variables (manure quantity, transportation distance, manure dry content, manure price and manure discharge price) on the economic sustainability of manure-based biogas supply chains. Design/methodology/approach An enterprise input-output approach is used to model physical and monetary flows of the manure-based biogas supply chain. Computational experiments are performed on all variables to identify under which conditions the cooperation is beneficial for all actors. Findings The cooperation is profitable for a large-scale farm (>20,000 t/year) if biogas producer (b) pays farmer (f) to receive its manure (5 €/t) or if f sells manure for free and manure disposal costs are >10 €/t. Cooperation is always profitable for b if f pays b to supply its manure (5€/t). If b receives manure for free, benefits are always positive if b is a medium-large-scale plant (>20,000 t/year). For a small-scale plant, benefits are positive if manure dry content (MDC) is ≥12 per cent and transportation distance is ≤10 km. Originality/value The paper adds value to the biogas production research, as it makes holistic analysis of five variables which might change under different policy and geographical conditions. The investors in biogas production, suppliers and transportation companies can find correspondence to empirical findings for their own site-specific cases.

Determination of fluoroquinolones in cattle manure-based biogas residue by ultrasonic-enhanced microwave-assisted extraction followed by online solid phase extraction-ultra-high performance liquid chromatography-tandem mass spectrometry

The present work describes the development and application of an ultrasonic-enhanced microwave-assisted extraction (UEMAE) followed by online solid phase extraction (SPE)–ultra–high performance liquid chromatography–tandem mass spectrometry method for the analysis of 14 fluoroquinolones in cattle manure-based biogas residue (CMBBR). The UEMAE was performed using the mixed solution of sodium dihydrogen phosphate and disodium ethylenediamine tetraacetic acid, avoiding use of any organic solvent. The online SPE system employed two solid phase extraction columns in a parallel manner, and the extraction was performed by passing 1 mL of the extract through the column. Quantification was performed using standard spiked samples and structural analogue internal standard, which were indispensable to reduce the matrix effects. Validation parameters were performed and good linearity (R2 > 0.99 in all cases) and precision (inter- and intra-day relative standard deviations were lower than 12.8%) were obtained. Limits of detection were as low as 0.021 ng ∙ g−1 and lower limits of quantification were 0.5 ng ∙ g−1 for all fluoroquinolones. The overall extraction recovery, which was the product of the UEMAE recovery and the online SPE recovery, was assessed for three concentration levels (0.8, 40 and 400 ng ∙ g−1) and acceptable values (74.3–99.3%) were found. As a part of the method validation, the developed method has been used to analyze real CMBBR samples. Nine fluoroquinolones were found in the concentration range of 0.9–74.6 ng ∙ g−1, while five were not detected in the samples. The results showed the method could be adapted for screening the presence or the final fate of fluoroquinolones during fermentation of animal waste.

Anaerobic co-digestion of swine manure and crude glycerol derived from animal fat—Effect of hydraulic retention time

Crude glycerol (CG), an abundant by-product of bio-diesel production, has been identified as a suitable co-substrate for improving the biogas production of livestock manure through anaerobic digestion (AD). In this study, the potential of utilizing CG generated from the esterification of animal fats for biogas production was studied in both batch and continuous AD experiments, with emphasis on the importance of the hydraulic retention time (HRT). Batch experiments showed that the limiting step in the methane production rate during CG mono-digestion was the 1,3-propanediol uptake. Additionally, biochemical methane potential tests indicated that the addition of 1% w/w CG to swine manure-AD is more efficient in terms of percent of theoretical amount of methane obtained than the addition of 3% w/w. However, in continuous experiments, co-digestion of manure with 3% w/w CG did not exhibit any sign of inhibition within the HRTs tested (17–22 days). Moreover, a 222% increase of biogas productivity was observed with 3% CG supplementation at an HRT of 17 days, in contrast to a 146% increase at an HRT of 22 days. Based on this, and on the similar efficiency of soluble COD removal among the processes (ca. 93%), it was shown that it is possible to reduce the HRT without affecting negatively the efficiency of conversion of manure. Moreover, it was shown that CG from 2 nd generation biodiesel based on animal fat, is a suitable feedstock for boosting the methane production of manure-based biogas plants.

Cooperation in manure-based biogas production networks: An agent-based modeling approach

Biogas production from manure has been proposed as a partial solution to energy and environmental concerns. However, manure markets face distortions caused by considerable unbalance between supply and demand and environmental regulations imposed for soil and water protection. Such market distortions influence the cooperation between animal farmers, biogas producers and arable land owners causing fluctuations in manure prices paid (or incurred) by animal farmers. This paper adopts an agent-based modeling approach to investigate the interactions between manure suppliers, i.e., animal farmers, and biogas producers in an industrial symbiosis case example consisting of 19 municipalities in the Overijssel region (eastern Netherlands). To find the manure price for successful cooperation schemes, we measure the impact of manure discharge cost, dimension and dispersion of animal farms, incentives provided by the government for bioenergy production, and the investment costs of biogas plants for different scales on the economic returns for both actor types and favorable market conditions. Findings show that manure exchange prices may vary between −3.33 €/t manure (i.e., animal farmer pays to biogas producer) and 7.03 €/t manure (i.e., biogas producer pays to animal farmer) and thanks to cooperation, actors can create a total economic value added between 3.73 €/t manure and 39.37 €/t manure. Hence, there are cases in which animal farmers can profitably be paid, but the presence of a supply surplus not met by demand provides an advantage to arable land owners and biogas producers in the price contracting phase in the current situation in the Netherlands.

Fostering renewable energy provision from manure in Germany – Where to implement GHG emission reduction incentives

Livestock production makes up a major share of agriculture sector and the manure it produces significantly contributes to greenhouse gas emissions. One option to lower these emissions significantly is using the manure to produce biogas which is used to generate power. Our model calculations show, that per kWh power from manure-based biogas –about 1.448kg of CO2 eq. of greenhouse gas (GHG) emission can be avoided due to the improved manure management and the substitution of electricity from the grid under actual German conditions. This form of utilization is supported under the German Renewable Energy Act; however, only the minor share of the manure is processed so far. Thus the question arises as to whether instruments in agricultural policy or instruments in energy policy are better to unlock this remaining potential. The elaborated allocation shows, that both sectors cause a comparable amount of GHG emissions reductions, at around 50% each. However, based on expected developments, the relevance of agriculture-related emissions is slated to increase. This leads to the conclusion that implementing instruments in both agricultural and energy policies would make sense.

Environmental performance of manure co-digestion with natural and cultivated grass – A consequential life cycle assessment

The aim of this study was to assess the environmental consequences of increased manure-based biogas production relying on grass as a co-substrate (from both unused and cultivated boreal grasslands). Through consequential life cycle assessment, three biogas scenarios were investigated: i) mono-digestion of dairy cow manure, ii) manure co-digestion with reed canary grass cultivated specifically for bioenergy production and iii) manure co-digestion with unused grass from semi-natural grasslands. A full balance of biogenic carbon was considered including soil carbon changes and indirect land use changes. Mono-digestion of manure showed a potential for an improved environmental performance for global warming and phosphorus-eutrophication, in comparison to conventional manure management, but yielded more than 2 times lower energy production compared to co-digestion. Co-digestion with grass from semi-natural grasslands showed an even 41% better potential to reduce global warming and resulted 2 times lower phosphorus-eutrophication compared to mono-digestion, provided that the grass would have otherwise been left un-harvested on land. Because of the indirect land use change associated with an additional demand for land, and the need for additional fertilizers, co-digestion with cultivated grass showed a 26% worse global warming, 2 times higher acidification, 4 times higher nitrogen-eutrophication and 36% worse phosphorus-eutrophication performance compared to natural grass. Results highlighted that grass co-digestion with manure does lead to an enhanced performance of the global warming and phosphorus-induced eutrophication impacts. This conclusion, however, did not apply for nitrogen-related impacts categories (acidification and nitrogen-induced eutrophication). Results were strongly affected by the choice of the indirect land use change factor for modelling and the energy source displaced. In a nutshell, this study highlighted the environmental relevance of considering energy grass and in particular semi-natural grasslands for the production of manure-based biogas, though it showed the necessity to improve the nitrogen balance of the supply chain of these scenarios, and to carefully consider the counterfactual use of the grass stream.

Effects of Biogas Substrate Recirculation on Methane Yield and Efficiency of a Liquid-Manure-Based Biogas Plant

Biogas plants are the most complex systems and are heavily studied in the field of renewable energy. A biogas system is mainly influenced by biological and technical parameters that strongly interact with each other. One recommended practice when operating a biogas plant is the recirculation of the substrate from the second fermenter into the first fermenter, which extends the recirculation amount (RA) and, in turn, the recirculation rate (RR). This technique should be applied to support and secure the biogas process. In this investigation, the RA was varied, starting with the recommended “best practice” of 10.0 m3/d (RR 40%). Every ten days, the RA was reduced in steps of 1.5 m3/d, with 5.5 m3/d (RR 27%) being the final value. The basic question to be addressed concerns to what extent the RR influences the methane yield and thereby influence the efficiency of a manure-based biogas plant in practice. Diverting the “best practice” to a RR of 27% stabilised the fermentation process and lead to significantly higher methane yields with smaller standard deviations. In addition, with a reduced RR, the standard optimal acid concentration within the biogas substrate was approximately reached.

Characterization of Spent Bleaching Earth and Its Utilization for Improving Manure-based Biogas Production

Characterization of Spent Bleaching Earth and Its Utilization for Improving Manure-based Biogas Production