Search

Cotton stalks (CS) are lignocellulosic agricultural by-products, a potential source for biogas production, but pretreatment must be considered since hydrolysis is the rate-limiting stage for lignocellulosic biomass substrates. This study investigates the feasibility of mechanical pretreatment of CS to enhance methane production. Batch anaerobic digestion of CS samples with particle sizes ranging from 0.5 to 65 mm was carried out in 1 L eudiometer batch digesters for 48 days at 37°C. Results showed that methane yield was inversely proportional to particle size, and the quality of biogas was good (54.0–55.2% CH4). Significant increases in methane yield were observed with 20.3% and 26% for samples with a particle size of 3 mm and 0.5 mm, respectively, compared to untreated CS. The coefficient of anaerobic energy turnover was relatively low (20.2–25.5%). Reduction of the CS particle size to 3 mm or less is recommended to achieve effective methane conversion and decrease the retention time in an anaerobic digester from 31 to about 25 days. However, to offset the high energy demand required for grinding, further research should be conducted in combining size reduction with chemical and physicochemical pretreatment.

It is urgent to determine suitable municipal sludge treatment solutions to simultaneously minimize the environmental negative impacts and achieve sustainable energy benefits. In this study, different sludge pretreatment techniques were applied and investigated to enhance the sludge solubility and, subsequently, facilitate the anaerobic biodegradation performance of the mixed sludge under different sludge concentrations and pretreatment techniques. The sludge characteristics before and after pretreatment and batch experiments of anaerobic digestion of sludge samples under different conditions were analyzed and discussed. The results showed that the mechanical pretreatment method, alone and in combination with low-temperature heat treatment, significantly improved the sludge solubility, with the highest solubility at 39.23%. The maximum biomethane yield achieved was 0.43 m3/kg after 10 d of anaerobic digestion of a 3% sludge sample subjected to mechanical and thermal pretreatment prior to anaerobic biodegradation. In comparison, it took more than 28 d to achieve the same biomethane production with the unpretreated sludge sample. Mechanical pretreatment and subsequent heat treatment showed a high ability to dissolve sludge and, subsequently, accelerate anaerobic digestion, thereby providing promising prospects for increasing the treatment capacity of existing and new sludge treatment plants.

In the transition to a climate neutral future, the transportation sector needs to be sustainably decarbonized. Producing advanced fuels (such as biomethane) and bio-based valorised products (such as pyrochar) may offer a solution to significantly reduce greenhouse gas (GHG) emissions associated with energy and agricultural circular economy systems. Biological and thermochemical bioenergy technologies, together with power to gas (P2G) systems can generate green renewable gas, which is essential to reduce the GHG footprint of industry. However, each technology faces challenges with respect to sustainability and conversion efficiency. Here this study identifies an optimal pathway, leading to a sustainable bioenergy system where the carbon released in the fuel is offset by the GHG savings of the circular bio-based system. It provides a state-of-the-art review of individual technologies and proposes a bespoke circular cascading bio-based system with anaerobic digestion as the key platform, integrating electro-fuels via P2G systems and value-added pyrochar via pyrolysis of solid digestate. The mass and energy analysis suggests that a reduction of 11% in digestate mass flow with the production of pyrochar, bio-oil and syngas and an increase of 70% in biomethane production with the utilization of curtailed or constrained electricity can be achieved in the proposed bio-based system, enabling a 70% increase in net energy output as compared with a conventional biomethane system. However, the carbon footprint of the electricity from which the hydrogen is sourced is shown to be a critical parameter in assessing the GHG balance of the bespoke system.

Macroalgae have recently attracted attention as a possible feedstock for energy as well as for biogas. Macroalgae have higher productivity than terrestrial plants, and do not compete with crops for arable land but insight is still necessary on the biogas yield for an overall sustainable evaluation. The objective of this study was addressed to evaluate the effect mechanical pre-treatment (MW) on anaerobic digestion (AD) conversion of the brown algae Fucus vesiculosus washed ashore in the Gulf of Riga. The AD were carried out in batch tests at 37 °C, over an incubation time no longer than 21–25 days, in order to evaluate the biological methane potential (BMP). Two mechanical pre-treatment methods were tested including a biomass washing with TAP water and a further manual chopping up to a maximum size of 5 mm. Total solids (TS) and volatile solids (VS) tests were defined according to EPA standards [1] . The batch test-based BMP was further compared with the theoretical biological BMP from Buswell's formula. The results show the BMP is doubling up to 200 l CH 4 /kg TS if any pre-treatments method is applied. The thicker cell walls of the brown marine algae respect other macro algae types and as well respect fresh water macroalgae which inhibit the activity of fermentative bacteria during the hydrolysis process.

Animal manure digestion is associated with limited methane production, due to the high content in fibers, which are hardly degradable lignocellulosic compounds. In this study, different mechanical and thermal alkaline pretreatment methods were applied to partially degradable fibers, separated from the effluent stream of biogas reactors. Batch and continuous experiments were conducted to evaluate the efficiency of these pretreatments. In batch experiments, the mechanical pretreatment improved the degradability up to 45%. Even higher efficiency was shown by applying thermal alkaline pretreatments, enhancing fibers degradability by more than 4-fold. In continuous experiments, the thermal alkaline pretreatment, using 6% NaOH at 55°C was proven to be the most efficient pretreatment method as the methane production was increased by 26%. The findings demonstrated that the methane production of the biogas plants can be increased by further exploiting the fraction of the digested manure fibers which are discarded in the post-storage tank.

Die zunehmende Nutzung von Energiepflanzen als Haupteinsatzstoff und der damit verbundende Flächenverbrauch ist der zentrale Kritikpunkt der Bevölkerung an der Biogasproduktion. Obwohl erhebliche energetische Potentiale an Abfällen und Reststoffen vorhanden sind, konnte sich die Verwertung dieser Materialien im Biogasprozess bis heute nicht flächendeckend etablieren. Wesentliche Hemmnisse sind hierbei die stark variierende Zusammensetzung dieser Stoffe und deren Substrateigenschaften. In der Regel beinhalten die Reststoffe einen hohen Faseranteil, der die vorhandene Verfahrenstechnik vor große Herausforderungen stellt. Daher war das Ziel dieser Arbeit, die Eignung und Verwertbarkeit des rohfasereichen Substrates Pferdemist als Beispielsubstrat zur Biogaserzeugung in kontinuierlich betriebenen landwirtschaftlichen Biogasanlagen zu untersuchen. Um dieses Ziel zu erreichen, wurde die vorliegende Arbeit in drei Abschnitte gegliedert: 1. Untersuchung der Zusammensetzung und Verwertbarkeit von Pferdemist mit verschiedenen Einstreumaterialien und Bestimmung der spezifischen Methanerträge unter Berücksichtigung des Alterungsprozesses des Pferdemistes; 2. Ermittlung der Effekte der mechanischen Substratvorbehandlung mit dem Querstromzerspaner auf den spezifischen Methanertrag und die Abbau-geschwindigkeit von nachwachsenden Rohstoffen und Pferdemist im Labormaßstab; 3. Untersuchungen zur Verwertbarkeit von Pferdemist im Praxismaßstab und den Einflüssen der mechanischen Aufbereitung auf den Biogasprozess an der Forschungsbiogasanlage „Unterer Lindenhof“. Eine Verwertung von strohhaltigem Pferdemist im Biogasprozess ist möglich. Allerdings muss eine Verunreinigung mit alternativen Einstreumaterialien aufgrund der geringen Abbaubarkeit vermieden werden. Zudem konnte ein erheblicher Verlust des Methanpotenzials durch eine Zwischenlagerung und der dadurch stattfindenden aeroben Rotte nachgewiesen werden. Aufgrund hoher Trockensubstanzgehalte und geringer Gehalte von essentiellen Mikro- und Makronährstoffen sollte der Einsatz von Pferdemist in Biogasanlagen nur mit geeigneten Co-Substraten erfolgen. Die mechanische Aufbereitung mittels Querstomzerspaner von Silagen und Pferdemist führte zu einer signifikanten Reduktion der Partikelgröße und Steigerung der Substratoberfläche. Es wurden jedoch keine signifikanten Veränderungen des spezifischen Methanertrages der untersuchten Silagen durch die Vorbehandlung festgestellt. Bedingt durch die Vergrößerung der Substratoberfläche wurde bei der Grassilage und der Getreide-Ganzpflanzensilage eine Steigerung der Abbaugeschwindigkeit nachgewiesen. Die mechanische Desintegration von Pferdemist resultierte in einer signifikanten Steigerung des spezifischen Methanertrags und einer deutlichen Verbesserung der Abbaukinetik. Bei der Betrachtung der Energiebilanz der Zerkleinerung konnte nur für die Aufbereitung der rohfasereichen Substrate ein positives Ergebnis erzielt werden. Dementsprechend ist eine vorherige Desintegration von Silagen für die Biogaserzeugung nicht zu empfehlen. Die Ergebnisse aus den Untersuchungen zur Verwertbarkeit von unbehandelten und mechanisch aufbereiteten Pferdemist im Praxismaxstab zeigen, dass der Einsatz von unzerkleinertem Pferdemist zu erheblichen verfahrenstechnischen Problemen führt und in unzureichenden Abbaugraden resultiert. Durch die mechanische Aufbereitung war ein störungsfreier Anlagenbetrieb möglich. Zusätzlich konnte eine sehr gute Substratausnutzung erzielt werden. Der zusätzliche Energieaufwand der mechanischen Intensivaufbereitung konnte durch den höheren Gasertrag weit mehr als ausgeglichen werden. Die Resultate der vorliegenden Arbeit zeigen, dass mit einer geeigneten Aufbereitungstechnik der Einsatz von Pferdemist und weiteren rohfaserreichen Strukturmaterialien in landwirtschaftlichen Biogasanlagen möglich ist. Eine vollständige Konversion des strohhaltigen Pferdemistes stellt ein Flächenäquivalent von bis zu 156.000 ha Maisanbaufläche dar. Damit liefert diese Arbeit einen wesentlichen Beitrag zur Steigerung der Nachhaltigkeit und Wirtschaftlichkeit der Biogaserzeugung und dem Erreichen der energiepolitischen Ziele. The increasing use of energy crops as the main feedstock and the resulting occupancy of arable land is the central point of criticism of the population in biogas production. Although waste and residues provide significant energy potentials, the conversion of these materials in the biogas process has not been established to date. Significant barriers are the widely varying composition of these materials and their substrate properties. In general, the residues contain a high percentage of fiber, which rises great challenges for the existing process technology. This work aimed to address these challenges by investigating the suitability and usability of the fiber-rich substrate horse manure for biogas production in continuously operated agricultural biogas plants. The study was divided into three consecutive 1. Investigation of the composition and usability of horse manure with different bedding materials and determination of the specific methane yields also taking into account the aging process degradation of horse manure; 2. Determination of the impact of mechanical pretreatment of the substrate with the cross-flow grinder on the specific methane yield and degradation kinetics of commonly used energy crops and horse manure in laboratory-scale; 3. Studies on the feasibility of horse manure in full-scale biogas processes and the effects of mechanical treatment at the research biogas plant "Unterer Lindenhof”. The use of straw-based horse manure in the biogas process is feasible. However, contaminations with alternative bedding materials due to their low degradability must be avoided. Furthermore, a substantial loss of methane potential could be detected due to the storage and meanwhile aerobic degradation. As a result of the high dry matter content and low levels of essential micro- and macro-nutrients, horse manure should only be utilized in biogas plants with suitable co - substrates. The mechanical treatment of silage and horse manure with the cross-flow grinder resulted in a significant reduction in particle size and increased substrate surface. However, no significant changes in the specific methane yield of the investigated silages were observed. Due to the increase of the substrate surface the degradation rate of the grass silage and whole crop silage accelerates. The mechanical disintegration of horse manure resulted in a significant increase of the specific methane yield and a significant improvement of the degradation kinetics. When considering the energy balance of the disintegration, a positive result could only be obtained for the processing of the fiber-rich substrates. Accordingly a previous disintegration of silage for biogas production is not recommended. The results from the investigation of the usability of untreated and disintegrated horse manure in the full-scale biogas process show that the use of horse manure without previous treatment causes serious procedural problems and results in insufficient degrees of degradation. The mechanical pretreatment guarantees a plant operation without failures during this trial. Additionally a complete substrate utilization can be achieved due to the treatment. The additional energy expenditure for the operation of the cross flow grinder was overcompensated by the higher gas yield. The results of this study show, that with a suitable treatment technology, the use of straw based horse manure and other high fiber structural materials in agricultural biogas plants is possible. A complete conversion of straw based horse manure provides an energy equivalent of up to 156,000 ha of maize. Thus, this study helps to improve the sustainability and profitability of biogas production and the achievement of the energy policy objectives.