Feedstock For Biogas Production Research Articles

N fertilization strategies for the use of P-rich organic amendments in the restoration of soil productivity—short-term responses in two soils

To facilitate nutrient management and the use of manure as a feedstock for biogas production, manure is often separated into a solid and a liquid fraction. The former fraction is usually high in P and low in N, so when incorporated in the soil as fertilizer, it needs to be supplemented by N from, e.g., mineral fertilizers or nitrogen-fixing species. To explore strategies to manage N with solid-separated manure, we examined how the amount of digestate and the N:P ratio of pig digestate, i.e., manure that had partially undergone anaerobic digestion, affected the productivity of Westerwolds ryegrass and red clover in a pot experiment with one soil which was rich and another which was poor in plant nutrients. The soil and plant species treatments were combined with four doses of digestate, which gave plant available phosphorus (P) concentrations of 2, 4, 8, or 16 mg P100 g−1 soil. Ammonium nitrate was dosed to obtain factorial combinations of digestate amount and N:P ratios of 1.8, 4, 8, and 16. Clover was harvested once at the beginning of flowering (15 weeks after seeding), while Westerwolds ryegrass was allowed to regrow three times after being cut at the shooting stage (in total, 4 cuts, 6, 9, 12, and 15 weeks after seeding). Ryegrass yield increased by up to 2.9 times with digestate dosage. Interactions with the N:P ratio and soil type were weak. Hence, the effect of increasing the N:P ratio was additive across digestate dosages. Red clover biomass also increased by up to 39% with digestate dosage. Residual nutrients in the soil after red clover cultivation were affected by the initial differences in soil characteristics but not by digestate treatment or biomass of harvested red clover. A targeted N management is required to benefit from the P-rich digestate in grass cultivation, while the long-term effects of red clover culture on N input need further investigation.

Animal Manure as an Alternative Bioenergy Resource in Rural Sub-Saharan Africa: Present Insights, Challenges, and Prospects for Future Advancements

Energy availability is a pivotal driver in fostering sustainable socio-economic development. However, sub-Saharan Africa (SSA) grapples with paradoxes headlined by abundant energy resources but with the world’s lowest access to clean energy index per capita. Faced with a lack of access to clean energy sources like electricity, rural areas in the majority of SSA countries almost exclusively depend on biomass-fuels, mostly fuelwood, leading to heightened respiratory health risks as well as environmental degradation and accelerated climate change. As an alternative, this review investigates the potential of animal manure as a sustainable energy resource for rural SSA households, emphasising its utilisation as a feedstock for biogas production using anaerobic digestor technology. Results show that despite the abundance of literature that reports on successes in lab-scale bioreactor optimisation, as well as successes in the initial rollout of biogas biodigester technology in SSA with the help of international collaborators, the actual uptake of biogas bioreactor technology by rural communities remains low, while installed bioreactors are experiencing high failure rates. Resultantly, rural SSA still lags significantly behind in the adoption of sustainable clean energy systems in comparison to rural communities in other regions. Among some of the hurdles identified as driving low technology assimilation are onerous policy requirements, low-level government involvement, high bioreactor-instalment costs, the lack of training and awareness, and water scarcity. Prospects for success lie in innovative technologies like the low-cost portable FlexiBiogas system and private–public partnerships, as well as flexible energy policy frameworks. Bridging the knowledge-implementation gap requires a holistic approach considering cultural, technological, and policy aspects.

The Advantage of Citrus Residues as Feedstock for Biogas Production: A Two-Stage Anaerobic Digestion System

Anaerobic digestion (AD) is an important step in waste recovery. In Colombia, the production of citrus food significantly contributes to environmental impact via waste generation. In 2021, the waste produced, specifically citrus rind, amounted to 725,035 tons/year. During degradation, wastes generate leachate and greenhouse gases (GHGs), which negatively impact water sources (leachate), soil, and human and animal health. This article describes the design of a two-phase biodigestion system for the degradation of organic matter and biogas production. The system uses citrus waste to produce biogas with neutral emissions. The biodigestion process begins with the stabilization of the methanogenesis reactor (UASB), which takes approximately 19 days. During this period, the biogas produced contains approximately 60% methane by volume. Subsequently, the packed bed reactor operates for 7 days, where hydrolytic and acetogenic bacteria decompose the citrus waste, leading to the production and accumulation of volatile fatty acids. The final step involves combining the two phases for 5 days, resulting in a daily biogas production ranging from 700 to 1100 mL. Of this biogas, 54.90% is methane (CH4) with a yield of 0.51 LCH4gSV−1. This study assesses the methane production capacity of citrus waste, with the process benefiting from the pH value of the leachate, enhancing its degradability. Consequently, this approach leads to a notable 27.30% reduction in solids within the digestion system. The two-phase anaerobic biodigestion system described in this article demonstrates a promising method to mitigate the environmental impact of citrus waste while concurrently producing a renewable source of energy.

Impact of Thermal Pretreatment on the Physicochemical Characteristics and Biomethane Yield Potential of Solid Slaughter Waste from High-Throughput Red Meat Abattoirs Valorized as a Potential Feedstock for Biogas Production

Rapid urbanization worldwide results in high demand for meat products, which in turn result in high numbers of animals being slaughtered for human consumption to meet food security demands, especially in low-income countries such as South Africa. The waste produced during slaughtering can serve as feedstock for biogas production. This study aims to determine the impacts of pasteurization and sterilization pre-treatments on high-throughput red meat abattoir solid slaughter waste’s physicochemical properties and biomethane yield when used as a feedstock for biogas production. Abattoir solid slaughter waste was collected from 45 high-throughput red meat abattoirs across South Africa and the various physicochemical properties were determined using standard methods, along with the impact of sterilization and pasteurization on red meat abattoir waste. Biomethane yield analysis was performed using AMPTS II with a hydraulic retention time of 40 days. Pasteurization and sterilization pretreatment was seen to increase physicochemical parameters such as pH, volatile solids, total solids, carbon, and nitrogen analyzed in all samples. Pasteurization and sterilization were also seen to increase biomethane yield, where methane production ranged from 610.67 Nml to 1756.30 Nml, 1592.20 Nml to 3319.30 Nml, and 949.57 Nml to 3297.87 Nml for untreated, sterilized, and pasteurized samples, respectively. There was no significant difference (p < 0.05) observed in the effect pasteurized and sterilized samples had on physicochemical properties and biomethane yield. It can be concluded that pasteurization and sterilization enhance the bioavailability of the physicochemical properties and biomethane yield of red meat solid slaughter waste when valorized as feedstock for biogas production.

NUTRIENT CHARACTERIZATION, BIOGAS AND ELECTRICITY GENERATION POTENTIALS OF ROOT AND TUBER WASTES

Rapid population growth and increasing food demand have led to a significant rise in organic waste generation, which has had a negative impact on the environment. However, these wastes can be utilized as substrates for anaerobic digestion (AD) biogas production, providing a sustainable and environmentally friendly waste management solution. The aim of this study was to evaluate the nutrient composition, biogas potential, and electricity generation capacity of root and tuber waste as a feedstock for biogas production. Waste samples were collected from various restaurants in Malumfashi. The nutrient composition of the waste samples was analyzed using standardized AOAC methods, and the biogas potential was estimated using the Baserga model equations. The results revealed that the waste samples had a total solid content of 94.70%, a volatile solid content of 87.60%, a crude protein content of 0.10%, a nitrogen-free extract of 5.1%, a crude fiber content of 5.04%, a crude fat content of 7.1%, and an ash content of 5.3%. The estimated biogas yield from complete degradation of fresh organic matter from roots and tubers was 501m3/ton, with a methane content of 52%. Based on the calorific value of biogas and the efficiency of electrical conversion, the estimated electrical potential was determined to be 1072 kWh/ton. The study recommends the utilization of root and tuber waste as a valuable resource for biogas generation and renewable energy production. Additionally, further research should be conducted to determine the specific biogas production outputs of root and tuber wastes.

Methane Production from a Rendering Waste Covered Anaerobic Digester: Greenhouse Gas Reduction and Energy Production

Livestock wastes can serve as the feedstock for biogas production (mainly methane) that could be used as an alternative energy source. The green energy derived from animal wastes is considered to be carbon neutral and offsetting the emissions generated from fossil fuels. In this study, an evaluation of methane production from anaerobic digesters utilizing different livestock residues (e.g., poultry rendering wastewater and dairy manure) was carried out. An anaerobic continuous flow system (15 million gallons, polyethylene-covered) subjected to natural conditions (i.e., high flow rate, seasonal temperatures, etc.) containing poultry rendering wastewater was set up to evaluate methane potential and energy production. A parallel pilot-scale plug-flow anaerobic digestion system (9 m3) was also set up to test different feedstocks and operating parameters. Biogas production was sampled and monitored by gas chromatography over several months of operation. The results showed that methane production increased as the temperature increased as well as depending on the type of feedstock utilized. The covered rendering wastewater lagoon achieved an upward of 80% (v/v) methane production. The rates of methane production were 0.0478 g per g of COD for the poultry rendering wastewater and 0.0141 g per g of COD for dairy manure as feedstock. Hence, a poultry processing plant with a rendering wastewater flow rate of about 4.5 million liters per day has the potential to capture about two million kilograms of methane for energy production per year from a waste retention pond, potentially reducing global warming potential by about 50,000 tons of CO2 equivalent annually.

Environmental impact assessment of producing frozen spinach in central Italy

Europe has increased its production, processing, and export of vegetables in recent decades due to changing dietary patterns supporting a greater consumption of vegetables high in nutrition. The growing interest in environmental issues has led to advocacy for sustainable vegetable production and consumption. Thus, this study assessed the ecological impacts of producing 1 kg of frozen spinach (functional unit) by a food processor in central Italy (cradle-to-factory gate approach). We evaluated the global warming potential (GWP) for distributing the final to different destinations. We also compare the potential environmental credits for different spinach residue management strategies, residue reduction through improved process efficiency, and as a feedstock for biogas production (avoided maize silage) based on the total volatile solids content. The life cycle assessment was used following the CML_IA impact assessment method based mainly on primary data related to 2019/2020. The GWP was 1.55 kg CO2eq. with respect to the functional unit. Excluding the dominant cultivation phase, packaging, particularly corrugated board boxes, electricity, and wastewater treatment were significant contributors across the midpoint impact categories assessed. The GWP for distributing the packaged frozen to Australia was 24 times more impactful than regional inland distribution. When spinach residue is reduced to 20% and 10%, total impacts for all impact categories also decrease by 12% and 22%, respectively. The benefit of using the current amount of spinach residue to produce biomethane was less than 7% across all impact categories except terrestrial ecotoxicity (13%). Therefore, reducing spinach waste along the processing line and efficient end-of-packaging life management through recycling and reuse by the manufacturer can considerably reduce the environmental impacts of frozen spinach.

Biowaste as a feedstock for biogas production – a case study

ABSTRACT The use of biowaste and its diversion from landfill aims to reduce the negative impact on the environment and contribute to increasing material recycling and renewable energy production. It has been proven that biogas technology is capable of converting large amounts of biowaste into renewable energy in an economical and sustainable way, replacing unsustainable fossil energy sources, and reducing dependence on fossil fuels. This paper presents the possibility of biogas production in Croatia from separated biowaste as input material. The paper analyzed current bio waste volumes in Croatia and their potential for renewable energy, as well as the advantages and disadvantages of such waste treatment for renewable energy production. The results of the analysis provide data and information for policymakers, planners, and operators in order to sufficiently address management of the separately collected organic fraction of municipal solid waste. They also clearly present environmental benefits associated with the use of digestate derived from this waste fraction.

Co‐Digestion of Water Hyacinth and Duck Manure for Potential Low‐Cost Biogas Production by Rural Communities

AbstractLeftover harvested water hyacinth biomass and duck manure can create waste management issues. As they are readily abundant and available, potential co‐digestion of both waste sources for biogas production is explored as a waste‐to‐energy approach for a rural fishermen community. Seven 19‐L do‐it‐yourself bioreactors are constructed with four different feedstock mixing ratios. The mixing ratios of water hyacinth to duck manure are varied at 70:30, 50:50, and 30:70, and are conducted in duplicate. One reactor utilizing 100% water hyacinth as feedstock acts as the control. Biogas production is measured daily for 50 days through the water displacement method. Variations in pH and chemical oxygen demand levels are monitored weekly. The results show that the highest biogas production is from the mixture of water hyacinth to duck manure at a 70:30 ratio (p < 0.05), with a volume of cumulative gas produced at 4.27 L that can be well simulated through the logistic function kinetic model (R2 = 0.965). The biogas produced consists of methane, carbon monoxide, and hydrogen sulfide. The findings prove the potential of water hyacinth and duck manure as feedstocks for biogas production as one of the waste management solutions that can be practiced by the community.

Valorization of brown macroalgae Sargassum plagiophyllum for biogas production under different salinity conditions

This study investigates the biogas production from Sargassum plagiophyllum under different salinity using a semi-continuous reactor. Inoculum preparation was conducted by mixing the two prepared S. plagiophyllum juice (deionized and saline water) with the cow manure using a ratio of 1:1. Once every two days, 5 % of the substrate was replaced with 5 % of fresh macroalgae juice continuously. The results found that cumulative biogas production in deionized water was 3.7 times higher than in saline water after 30 days. It could be attributed to anaerobic bacteria growth inhibited by salt. The maximum cumulative methane and biogas yields in the deionized water digester were 266.18 mL/g-VS and 371.76 mL/g-VS, respectively. The kinetics of the methane production was also determined, and the experimental data fitted well with the modified Gompertz model. These results indicate that S. plagiophyllum, under low salinity conditions, can be developed as a feedstock for biogas production.

Production of Biogas from Food Waste Using the Anaerobic Digestion Process with Biofilm-Based Pretreatment

The production of biogas from food waste is a good approach to the minimization of food waste and increase in the production of renewable energy. However, the use of food waste as a feedstock for biogas production currently poses a difficulty due to an ineffective hydrolysis process, which is a pretreatment procedure and the initial step of the biogas conversion process. This restriction results from the food waste polymers’ solubilization and breakdown. This has an impact on the volume of biogas produced during the methanogenesis stage. It is essential to increase the biodegradation of organic compounds (OC) during the hydrolysis process to increase biogas generation. This study focuses on the enhancement of biogas production by the anaerobic digestion (AD) of food waste (FW). FW was hydrolyzed by the immobilized biofilm and digested anaerobically in a semi-continuous digester. Four different digesters including the control were prepared. The control digester composed of no hydrolyzed food waste had no immobilized biofilm while the other three digesters had immobilized biofilm-hydrolyzed food waste with inoculum concentrations of 10%, 30%, and 50%. The results showed that the 50% digester had the highest biogas yield of about 2000 mL/500 mL. The 10%, 30%, and control digesters had a biogas yield of 1523 mL, 753 mL, and 502 mL respectively. Thus, the analysis of total volatile solid (TVS) reduction in the digesters with 10%, 30%, and 50% inoculum and the control have increased to 43.4% for the digesters with 30% and 10%, 60% for the digester with 50% inoculum, and only 29% for the control. Total chemical demand (TCOD) removal increased to 29%, 33%, 43%, and 56% for the control, and 10%, 30%, and 50%, respectively for the inoculum-to-feed ratio. From these results, the 50% inoculum-to-feed ratio has shown the highest biogas production and highest degradation based on TVS reduction and TCOD reduction. Based on this study, the biofilm pretreatment method can be considered a promising method for the enhancement of biogas volume and biodegradation. Biogas production was high (2000 mL) for hydraulic retention time (HRT = 20) days but the HRT = 15 days was also able to produce a significant amount (1400 mL) of biogas and the 50% inoculum-to-feed ratio has shown the highest volume of biogas production.

The Influence of CO2 Injection into Manure as a Pretreatment Method for Increased Biogas Production

Manure is considered a by-product or organic waste in cattle, pig, chicken or other animal breeding farms, which can be a valuable product as compost or feedstock for biogas production. The production of biomethane from biogas always copes with the formation of carbon dioxide (CO2) as a by-product. This CO2 may be recycled through the feedstock as a pretreatment to maximize homogeneity, and improve biogas yield and biogas quality. The CO2-pretreatment process of cow manure (CoM), chicken manure (ChM) and pig manure (PM) was performed in the continuously fed agitated reactor at 25 °C temperature and ambient barometric pressure. Biogas yield and composition exploration were performed in an anaerobic continuous feeding digester with controlled mesophilic (37 °C) environmental conditions. The CO2 pretreated PM, CoM and ChM yielded 234.62 ± 10.93 L/kgVS, 82.01 ± 3.19 L/kgVS and 374.53 ± 9.27 L/kgVS biomethane from feedstock volatile solids, respectively. The biomethane yield from CO2 pretreated CoM, ChM and PM achieved was higher over untreated manure by +33.78%, +28.76% and +21.78%, respectively. The anaerobic digestion process of tested feedstocks was stable, and the pH of the substrate was kept steady at a pH of CoM 7.77 ± 0.02, PM 8.07 ± 0.02 and ChM 8.09 ± 0.02 during all the experiment. The oxidation-reduction potential after pretreatment was within the optimal range (−255 ± 39.0 to −391 ± 16.8 mV) for anaerobic digestion. This process also had a positive effect on the energy generated from the feedstock, with ChM showing the greatest increase, from 2.38 MJ/kg to 3.06 MJ/kg.

Characterization and analysis of fish waste as feedstock for biogas production

Abstract Fish waste (FW) is biodegradable waste that remains underutilized and causes a problem to the environment since the existing disposal techniques result in health risks and environmental pollution. FW has significant potential for producing biogas that decreases the reliance on fossil fuels because it contains easily biodegradable organic matter. The physicochemical analysis of the FW such as moisture content of 61.78%, volatile solids (VS) of 93.94%, total solids of 38.21%, ash content (AC) of 0.52%, total organic carbon of 54.2%, total Kjeldahl nitrogen of 9.2% and carbon to nitrogen (C/N) ratio of 5.89% were considered and analyzed in this research. In addition, the methane potential was determined and obtained using gas detector. The results shown that the methane (CH4) content in FW was 50.12%, which was the potential feedstock of FW for biogas production. Nevertheless, the VS of FW was high, which was good for this feedstock to be easily digested as the sign of producing biogas and demonstrates 99.9985% of performance rate. Finally, the FW had a lower C/N ratio compared with other biogas production waste. Future work needs to consider co-digestion with higher C/N ratio feedstocks.

Advancements in Giant Reed (Arundo donax L.) Biomass Pre-Treatments for Biogas Production: A Review

Giant reed is a non-food, tall, rhizomatous, spontaneous perennial grass that is widely diffused in warm-temperate environments under different pedo-climatic conditions. In such environments, it is considered one of the most promising energy crops in terms of economic and environmental sustainability, as it can also be cultivated on marginal lands. Owing to its complex and recalcitrant structure due to the lignin content, the use of giant reed as a feedstock for biogas production is limited. Thus, pre-treatment is necessary to improve the methane yield. The objective of this review was to critically present the possible pre-treatment methods to allow the giant reed to be transformed in biogas. Among the studied pre-treatments (i.e., hydrothermal, chemical, and biological), alkaline pre-treatments demonstrated better effectiveness in improving the methane yield. A further opportunity is represented by hybrid pre-treatments (i.e., chemical and enzymatic) to make giant reed biomass suitable for bio-hydrogen production. So far, the studies have been carried out at a laboratory scale; a future challenge to research is to scale up the pre-treatment process to a pilot scale.

Increasing Biowaste and Manure in Biogas Feedstock Composition in Luxembourg: Insights from an Agent-Based Model

Biowaste and manure are resources readily available as feedstock for biogas production. Possible scenarios with increased use of biowaste and manure for biogas production in the Grand Duchy of Luxembourg are investigated in this study using an Agent-Based Model (ABM) coupled with Life Cycle Assessment (LCA). ABMs are particularly suitable to simulate human-natural systems, since they allow modelers to consider behavioral aspects of individuals. On the other hand, when it comes to the assessment of a system’s environmental sustainability, LCA is largely recognized as a sound methodology and widely used in research, industry, and policy making. The paper simulates three different scenarios that reproduce 10 years and can help policymakers building emission mitigation strategies. The aim is to increase the number of biogas plants or change the feedstock composition for anaerobic digestion in Luxembourg whilst observing the expected environmental impacts generated by these changes. The first scenario (Scenario A) is the baseline scenario, which simulates the current situation, with 24 operating biogas plants. The results of Scenario A show that, on average, 63.02 GWh of electricity production per year is possible from biogas. The second scenario (Scenario B) foresees an increase in the manure share (which is initially 63%) in the biogas feedstock composition along with an increase in the number of biogas production plants. The third scenario (Scenario C) only concerns increasing the amount of manure in the feedstock composition without the introduction of new plants. The results of Scenario C show that an 11% increase in electricity production is possible if more farms contribute to the production by bringing their excess manure to the biogas plant. This value is even higher (14%) in Scenario D where more biowaste is made available. The aggregated life-cycle impact assessment (LCIA) single scores, calculated with the ReCiPe method, show that Scenario C has the lowest impacts (although by only around 7% compared to the worst performing scenario, i.e., Scenario D), while Scenario D allows the highest electricity production (71.87 GWh in the last year of the simulation). As a result, the inclusion of more livestock farms into already established biogas cooperatives (as in Scenario C) can pave the way for an increase in electricity production from renewables and can bring a reduction in environmental impacts (more than 35% for the Terrestrial Ecotoxicity impact category and more than 27% in categories such as Agricultural Land Occupation, Marine Eutrophication and Water Depletion), thanks to the exploitation of manure for biogas production.

Biogas catalytic methanation for biomethane production as fuel in freight transport - A carbon footprint assessment

The use of biomethane can help reduce greenhouse gas emissions (GHG) from road transport in trucks. To assess its potential contribution, two biomethane production pathways were analysed: conventional biogas upgrading and catalytic methanation of carbon dioxide from biogas, contained in biogas or separated via biogas upgrading. Pig manure was used as feedstock for biogas production. Throughout a life cycle assessment methodological approach, the total GHG equivalent emissions were calculated for each production pathway, considering the chemical absorption, pressure swing adoption and membrane separation technologies for biogas upgrading, and renewable sources of electricity (wind and photovoltaic) for hydrogen production further processed in methanation. Catalytic methanation via micro-structured reactors was selected as a reference process. The assessments show that emissions vary from 0.28 to 0.72 kg CO2-eq./m3 in biomethane production via biogas upgrading and from 0.36 to 1.04 kg CO2-eq./m3 via catalytic methanation. These values are comparable to those of natural gas conditioned as fuel for transportation, which lie between 0.038 and 0.55 kg CO2-eq./m3. Due to its emission neutrality, in the use phase of biomethane in trucks total emissions are substantially lower than those associated with fossil fuels (natural gas and diesel). For the investigated use cases, they range from 0.03 to 0.07 kg CO2 -eq./t km for biomethane, whereas for natural gas or diesel from 0.16 to 0.18 kg CO2 -eq./t km and 0.17–0.19 kg CO2-eq./t km. These results demonstrate the environmental benefits of biomethane in freight transport in terms of reduction in GHG emissions.

The potential for biogas production from autumn tree leaves to supply energy and reduce greenhouse gas emissions – A case study from the city of Berlin

Autumn tree leaves are residues that are generated annually and usually composted, but can also be used as a feedstock for biogas production. In this study, three scenarios were analysed to evaluate the utilization of tree leaves from the city of Berlin in Germany: a) composting (business-as-usual scenario); b) biogas production; and c) the pretreatment of leaves before biogas production. For these scenarios, greenhouse gas emissions and energy production potential were calculated using the biological resource utilization impacts (BIORIM) model and considering the location and capacity of existing agricultural biogas plants. A special focus was set on the decay of leaves before their entry into the biogas plant. The overall comparison showed that the biogas-related scenarios had a better performance in terms of greenhouse gas emissions (-140.1 kg of CO2eq per tonne of leaves for biogas and -167.4 kg of CO2eq for pretreatment before biogas) than the business-as-usual scenario (49.0 kg of CO2eq for composting). The pretreated leaves resulted in the lowest net emissions and highest energy production per tonne of feedstock. Measures to reduce the decay of leaves, such as increasing the loading to the biogas plant or ensiling, resulted in lower net emissions and higher energy output. However, further research is needed regarding costs and logistical feasibility for proper implementation. Using tree leaves for biogas production would represent an alternative energy source, which could reduce the share of fossil fuels and electricity imports for the city of Berlin, where about 7.5 metric ton of pretreated leaves would meet the average electrical energy consumption of one person in one year.

Integrated role of algae in the closed-loop circular economy of anaerobic digestion

Following the surging demand for sustainable biofuels, biogas production via anaerobic digestion (AD) presented itself as a solution for energy security, waste management, and greenhouse gas mitigation. Algal-based biorefinery platform serves an important role in the AD-based closed-loop circular economy. Other than using whole biomass of micro- and macroalgae as feedstock for biogas production, the integration of AD with other bio- or thermochemical conversion techniques can achieve complete valorization of biomass residue after processing or valuable compounds extraction. On the other hand, anaerobic digestate, the byproduct of AD processes can be used for microalgal cultivation for lipid and pigments accumulation, closing the loop of resource flow. Furthermore, algae and its consortium with bacteria or fungi can be employed for combined biogas upgrading and wastewater treatment. Innovative strategies have been developed to enhance biogas upgrading and pollutant removal performance as well as minimize O2 and N2 content in the upgraded biomethane.

Multi-advantageous sorghum as feedstock for biogas production: A comparison between single-stage and two-stage anaerobic digestion systems.

Anaerobic digestion (AD) is a keystone in the circular economy concept . The produced biogas can be demand-driven controlled and regionally adaptable, but sustainable feedstocks are required. Sorghum is a valuable alternative considering its bioenergy potential and wide adaptability to different environmental conditions. In this study, AD of sorghum silage was performed in a single-stage continuously stirred tank reactor (CSTR) and in a two-stage leach-bed reactor (LBR) system. The two-stage LBR system revealed higher methane yields (434 L N kg VS −1 ) compared to the single-stage CSTR (308 L N kg VS −1 ). Methane content of biogas ranged from 53 to 59% in both systems. Only the CSTR exhibited acids accumulation, led by propionic acid concentration (2.0 g L −1 ). Buffer capacity of the two-stage LBR system was superior to the CSTR. Technical disruptions and constant ammonium content declination were shown in both systems, associated to inherent characteristics of fibrous sorghum. AD of sorghum biomass, however, can be effectively performed under controlled conditions, generating high methane yields in both types of systems. • Mesophilic AD of fibrous sorghum in a single- and in a two-stage digestion system. • Accumulation of volatile fatty acids occurred during experiments in CSTR. • Two-stage system produced higher methane yields and showed better process stability. • A constant declination of the ammonium-nitrogen content was observed. • Fibrous sorghum caused technical disruption in both types of system.

Methane Production Potential from Apple Pomace, Cabbage Leaves, Pumpkin Residue and Walnut Husks

Circular economy aims to eliminate organic waste through its transformation, composting and processing into other products or energy. The main aim of the study was to determine the specific methane yield (SMY) of anaerobic digestion (AD) of four different fruit and vegetable residues (FVR). In addition, the reduction in greenhouse gas (GHG) emissions was calculated based on the assumption that maize will be replaced by the FVR as a feedstock for biogas production. The SMY of four residues (apple pomace, cabbage leaves, pumpkin peels and fibrous strands and walnut husks) was measured in the biomethane potential test (BMP) in wet anaerobic digestion technology. The highest SMY (297.81 ± 0.65 NL kgVS−1) was observed for cabbage leaves while the lowest SMY (131.07 ± 1.30 kgVS−1) was found for walnut husks. The concentrations of two inhibitory gasses (NH3 and H2S) in biogas were low and did not affect the AD process. Only biogas produced from cabbage leaves was characterised by higher NH3 and H2S concentrations resulting from the highest protein concentration in this waste. FVR used as feedstock in biogas production may decrease the area of maize cultivation. Therefore, the GHG emissions from maize cultivation will be reduced. In Poland only, the use of four studied FVR as feedstock for biogas production would contribute to the reduction of GHG emissions by 43,682 t CO2 eq.