Biomethane Potential Research Articles

Measuring Biomethane Potential of Food Scrap Waste Anaerobically Co-Digested with Waste-Activated Sludge Using Respirometry.

The use of respirometry to study the biokinetics of microbiota treating wastewater or digesting wastewater sludges has become more prevalent over the last few decades. The use of respirometry to examine the biokinetics of anaerobic microbiota co-digesting organic waste streams such as wastewater sludge and food scrap is an area of active research. To date, no visualized protocol has been published on the topic. Accordingly, in this protocol, we configured a respirometer to measure methane production and flow rate over time using three different food-to-microorganism (F:M) ratios and food scrap waste and waste-activated sludge as substrates. The resulting data, coupled with substrate utilization measurements, provides the basis for understanding how different substrate concentrations influence the rate at which anaerobic microbiota produce methane. Additionally, this protocol presents a method to develop biokinetic parameters (e.g., methane production rate constant and yield). Others can use this respirometry protocol to examine organic degradation under anaerobic conditions and develop microbial parameters.

Assessment of the in situ biomethanation potential of a deep aquifer used for natural gas storage.

The dihydrogen (H2) sector is undergoing development and will require massive storage solutions. To minimize costs, the conversion of underground geological storage sites, such as deep aquifers, used for natural gas storage into future underground hydrogen storage sites is the favored scenario. However, these sites contain microorganisms capable of consuming H2, mainly sulfate reducers and methanogens. Methanogenesis is, therefore expected but its intensity must be evaluated. Here, in a deep aquifer used for underground geological storage, 17 sites were sampled, with low sulfate concentrations ranging from 21.9 to 197.8µM and a slow renewal of formation water. H2-selected communities mainly were composed of the families Methanobacteriaceae and Methanothermobacteriaceae and the genera Desulfovibrio, Thermodesulfovibrio, and Desulforamulus. Experiments were done under different conditions, and sulfate reduction, as well as methanogenesis, were demonstrated in the presence of a H2 or H2/CO2 (80/20) gas phase, with or without calcite/site rock. These metabolisms led to an increase in pH up to 10.2 under certain conditions (without CO2). The results suggest competition for CO2 between lithoautotrophs and carbonate mineral precipitation, which could limit microbial H2 consumption.

Evaluation of traditional and machine learning approaches for modeling volatile fatty acid concentrations in anaerobic digestion of sludge: potential and challenges.

This study evaluates models for predicting volatile fatty acid (VFA) concentrations in sludge processing, ranging from classical statistical methods (Gaussian and Surge) to diverse machine learning algorithms (MLAs) such as Decision Tree, XGBoost, CatBoost, LightGBM, Multiple linear regression (MLR), Support vector regression (SVR), AdaBoost, and GradientBoosting. Anaerobic bio-methane potential tests were carried out using domestic wastewater treatment primary and secondary sludge. The tests were monitored over 40days for variations in pH and VFA concentrations under different experimental conditions. The data observed was compared to predictions from the Gaussian and Surge models, and the MLAs. Based on correlation analysis using basic statistics and regression, the Gaussian model appears to be a consistent performer, with high R2 values and low RMSE, favoring precision in forecasting VFA concentrations. The Surge model, on the other hand, albeit having a high R2, has high prediction errors, especially in dynamic VFA concentration settings. Among the MLAs, Decision Tree and XGBoost excel at predicting complicated patterns, albeit with overfitting issues. This study provides insights underlining the need for context-specific considerations when selecting models for accurate VFA forecasts. Real-time data monitoring and collaborative data sharing are required to improve the reliability of VFA prediction models in AD processes, opening the way for breakthroughs in environmental sustainability and bioprocessing applications.

A comparative assessment of biomethane potential of fresh fecal matter and fecal sludge and its correlation with malodor.

Comprehensive and proper management of fecal sludge (FS) is an ongoing concern in many nations.Decentralizedfecal sludge treatment plants (FSTPs) are effective in this regard; however, many have experienced strong public opposition based partly on suspicion of malodor. Fecal sludge and freshly generated fecal matter (FM) samples from various FSTPs were collected, characterized, and investigated for biomethane potential. The homogenized samples were anaerobically digested for 28days. Digestion successfully reduced total suspended solids, biochemical oxygen demand, and threshold odor number values of 97,350-97,420mg/l, 43,230-43,260mg/l, and 130-150 for FM, to 49,500-49,650mg/l, 23,760-23,850mg/l, and 3338, respectively, for FS samples. The comprehensive gas yield from Bhongir, Boduppal, and Shadnagar FS samples was 40, 55, and 31ml, respectively. In contrast, cumulative gas generation from the FM was 26,361ml. Digestion of FS samples also reduced concentrations of volatile solids and coliforms by 66-72% and 99%, respectively. Characterization of gas samples revealed methane and carbon dioxide concentrations as 56% and 22% for FM, and 0.4% and 61% for FS samples, respectively. Hydrogen sulfide and ammonia gas were absent in FS samples, dispelling common societal misconceptions of FSTPs being associated with malodor.

Optimizing alkali-pretreatment dosage for waste-activated sludge disintegration and enhanced biogas production yield

The rapid transition towards modernization and industrialization led to an increase in urban population, resulting in paramount challenge to municipal sewage sludge management. Anaerobic digestion (AD) serves as a promising venue for energy recovery from waste-activated sludge (WAS). Addressing the challenge of breaking down floc structures and microbial cells is crucial for releasing extracellular polymeric substances and cytoplasmic macromolecules to facilitate hydrolysis and fermentation process. The present study aims to introduce a combined process of alkaline/acid pre-treatments and AD to enhance sludge digestion and biogas production. The study investigates the influence of alkali pretreatment at ambient temperature using four alkali reagents (NaOH, Ca(OH)2, Mg(OH)2, and KOH). The primary goal is to provide insights into the intricate interplay of alkali dosages (0.04–0.12 g/gTS) on key physic-chemical parameters crucial for optimizing the pre-treatment dosage. Under the optimized alkaline/acid pre-treatment condition, the TSS reduction of 18%–30% was achieved. An increase in sCOD concentration (24%–50%) signifies the enhanced hydrolysis and solubilization rate of organic substrate in WAS. Finally, the biomethane potential test (BMPT) was performed for pre-treated WAS samples. The maximum methane (CH4) yield was observed in combination A1 (244 mL/g) and D1 (253 mL/g), demonstrating the pivotal role of alkali optimization in enhancing AD efficiency. This study serves as a valuable resource to policymakers, researchers, and technocrats in addressing challenges associated to sludge management.

Enhancing the Fermentation Process in Biogas Production from Animal and Plant Waste Substrates in the Southeastern Region of Bulgaria

Annually, a huge amount of waste from plant biomass and animal manure is produced from agriculture and animal farming. Many studies provide information on the biomethane potential of agricultural and livestock wastes, but only a few studies have investigated the application of the substrates in combination. The objective of the study is to enhance the fermentation process in the digester for biogas production, obtained from animal and plant waste substrates. In four batch processes for three months, the temperatures and the residence time of the substrates in the fermenter were analyzed. Simultaneously, electricity and thermal energy were produced via cogeneration units, which were exported to the public grid and city heating network. The plant substrate is a silage mixture of corn and wheat waste. The animal substrate is a mixture of beef and pig manure. Animal and vegetable waste raw materials are collected and transported to the site, located in the region of southeastern Bulgaria. The total annual consumption of animal and plant waste is 17,971 t/year. The enhancement of the process leads to the production of 1,506,000 Nm3 CH4/a of methane, the generation of which requires 299.63 MWh/a of electricity and 649.09 MWh/a thermal energy.

Thermochemical Pretreatment for Improving the Psychrophilic Anaerobic Digestion of Coffee Husks

Psychrophilic anaerobic digestion emerges as an appealing integrated solution for the management of agricultural waste, particularly for farmers in regions where the average temperature does not exceed 26 °C, as seen in coffee cultivation. Therefore, this study seeks to assess the biomethane potential of thermochemical-treated coffee husk through psychrophilic anaerobic digestion (C3-20 °C-w/pretreatment). To examine its viability, outcomes were compared with reactors operating at both mesophilic (C1-35 °C) and psychrophilic (C2-20 °C) conditions, albeit without the use of pretreated coffee husk. The C3-20 °C-w/pretreatment test demonstrated a 36.89% increase (150.47 NmL CH4/g VS; 161.04 NmL CH4/g COD), while the C1-35 °C test exhibited a 24.03% increase (124.99 NmL CH4/g VS; 133.77 NmL CH4/g COD), both in comparison to the C2-20 °C test (94.96 NmL CH4/g VS; 101.63 NmL CH4/g COD). Notably, the C3-20 °C-w/pretreatment trial yielded superior outcomes, accompanied by an associated energy output of 3199.25 GWh/year, sufficient to meet the annual energy demands of 494 residences. This marks an increase of 83 and 182 million residences compared to the mesophilic and psychrophilic AD of CH without pretreatment, respectively.

Assessment of the biomethane potential of commingled farm residues with sewage sludge and its techno-economic viability for rural application

Assessment of the biomethane potential of commingled farm residues with sewage sludge and its techno-economic viability for rural application

Enhancing BMP and digestibility of DAF sludge via hydrodynamic cavitation

This study addresses fats, oils, and grease bioconversion challenges in dissolved air floatation (DAF) sludge from dairy processing waste streams. A hydrodynamic cavitation (HC) based pre-treatment method was developed for enhanced anaerobic digestion of DAF sludge. Bench-scale pre-treatment experiments were carried out using a vortex-based HC device at 20 L/min and 250 kPa pressure drop. Influence of severity of the pre-treatment (number of passes through HC device) and substrate concentration on biomethane potential (BMP) was quantified. The study revealed that soluble chemical oxygen demand (sCOD) increases with number of passes (34 % after 80 passes). Higher sludge concentration was found to increase the lag time observed in the BMP data. It was possible to tolerate 3 % VS sludge. The pre-treatment showed a notable increase in BMP, exceeding 82 % of theoretical BMP, with VS removal surpassing 73 %. The highest methane yield achieved was 756 mL/gVS of sludge. The net energy gain (after subtracting energy required for pre-treatment) was found to be more than 100 kWh/ton of sludge. The developed pre-treatment process and presented results provide a basis for the effective valorisation of DAF sludge, promoting a circular economy approach.

Relation of organic fractions in fresh and stored fecal sludge and foodwaste to biogas production

Abstract There is limited understanding of the potential for anaerobic digestion and biogas production from fecal sludge. In this study, biomethane potential (BMP) tests from fresh, stored, and dewatered fecal sludge, together with co-digestion with fresh foodwaste, revealed that fresh fecal sludge produced similar cumulative biogas (CBG) to fresh foodwaste (615–627 mL/gVS), while stored fecal sludge showed a wide range of gas production (13–449 mL/gVS). Co-digestion significantly enhanced the CBG production of fresh (1.2×), dewatered (1.5×), and stored (29–36×) fecal sludge. In BMP tests with the higher range of gas production, a biphasic CBG production was observed, with degradation of readily biodegradable organics occurring during the first week. The first-order rate coefficients indicated hydrolysis limitation, which was also confirmed by the presence of slow-growing methanogens (Halobacterota). Priming with co-digestion significantly enhanced CBG from stored fecal sludge. The physical–chemical metrics VS/TS and TOC/TN were not predictors of biogas production, while BOD/COD and sCOD were better indicators, suggesting that metrics of stabilization representing biologically available fractions are more representative than metrics of entire pools of organic matter. This study suggests that biogas production from anaerobic digestion is viable for fresh fecal sludge, whereas for stored fecal sludge it requires co-treatment or pretreatment.

Acidogenic fermentation of biowaste coupled with nitrogen recovery using selective membranes to produce a VFA-rich liquid with a high C/N ratio

This research focuses on the production of a liquid stream rich in volatile fatty acids (VFAs) and low ammoniacal nitrogen content (<0.1 g N/L) from biowaste. The liquid stream was obtained by combining (i) mixed culture acidogenic fermentation to maximise VFA production and (ii) gas-permeable membrane (GPM) contactor to recover ammoniacal nitrogen. Three batch fermentation tests of biowaste collected in a full-scale mechanical-biological treatment plant provided high and stable VFA concentrations (37–39 g CODVFA/L). VFAs represented 73–81 % of the soluble chemical oxygen demand (sCOD) concentration, with a predominance of acetic, propionic and butyric acids. A highly specialized microbial community was observed in all batch tests, with Bacteroidota and Firmicutes as predominant phyla (>90 % of relative abundance). The GPM contactor recovered more than 99 % of the ammoniacal nitrogen in the fermentation liquid without VFA losses. The suitability of the produced fermentation liquid with a high C/N ratio for downstream applications was evaluated using biomethane potential tests (BMP) at different total ammonium nitrogen (TAN) concentrations (0.76–3.15 g N/L) and circumneutral pH. Despite achieving similar ultimate methane yields (279–314 NmL CH4/g CODfeed), lower TAN concentrations in the biowaste fermentation liquid improved anaerobic biodegradation kinetics, enhancing its potential applicability for methane production.

Enhancing the biomethane yield of groundnut shells using deep eutectic solvents for sustainable energy production

This study examined the influence of DES pretreatment using choline chloride and ethyl glycerol with the molar ratio of 1: 1 at different solid:liquid ratios and temperatures on groundnut shells’ microstructural arrangement and biomethane yield. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) were used to study the effects of pretreatment on microstructural arrangements, and the pretreated substrate was digested at mesophilic temperature to determine its biomethane potential. The result of SEM analysis indicated that DES pretreatment alters the microstructural arrangement of groundnut shells, and XRD analysis showed an optimum crystallinity index of 20.71% when the substrate with a solid:liquid ratio of 1:2 was experimented at 80°C. The highest theoretical biomethane yield of 486.81 mL CH4/gVSadded was recorded when the substrate with a 1:4 solid:liquid ratio was investigated at 100°C, and the highest biodegradability rate (84.87%) was observed from the substrate treated with a 1:2 solid:liquid ratio at 100°C. The optimum biomethane yield of 365.70 mL CH4/gVSadded, representing a 226.05% increase, was observed from 1:2 of solid:liquid ratios at 100°C. Therefore, DES pretreatment using choline chloride and ethyl glycerol is a bright, low-cost pretreatment method for enhancing the biomethane yield of lignocellulose feedstocks.

Optimization of biomethane production from lignocellulosic biomass by a developed microbial consortium

Biomethane production from lignocellulosic biomass via anaerobic digestion (AD) is a promising avenue for bioenergy. However, maximizing biomethane yield using developed microbial consortium (DMC) remains a complex challenge. This study aims to elucidate the comparative efficacy of a purposefully DMC under controlled conditions for AD of kallar grass (KG), rice husk (RH) and wheat residue (WR). The DMC encompasses Bacteroidetes, Firmicutes, Proteobacteria, Euryarchaeota, and Chloroflexi, with methanogens representing 14.6% of the community. Thorough physico-chemical characteristics and ultimate analyses provided comprehensive insights into compositions and bio-methane potentials prediction of biomasses. The digester revealed higher biomethane potentials (BMPs) with short lag phase and retention time and showed methane content of 61–64.6% during the first week of AD. The amount of volatile fatty acids (VFA) did not exceed the threshold levels, which facilitated the smooth operation of AD. The BMP was found highest in KG (289.7 mL/g VS), followed by RH (283.3 mL/g VS), and WR (269.7 mL/g VS) which is significantly higher than previously reported studies. The modified Gompertz model showed the best fit, followed by logistic and transference function models. The observed results signpost the tremendous potential of waste biomass particularly KG, RH and WR to produce biomethane by DMC. This study provides crucial insights for optimizing BMP emphasizing the promising prospects of KG, RH, and WR for sustainable bioenergy applications.

Centralized or decentralized? How to exploit Sweden’s agricultural biomethane potential

The agricultural sector holds great potential for contributing to European biomethane production, but how to best exploit it is still not clear. This study compares three technical solutions for producing liquefied biomethane from manure in Sweden: centralized biogas production and liquefaction, decentralized biogas production and centralized liquefaction, and decentralized biogas production and liquefaction. Technical and practical aspects of the three configurations are assessed through interviews with professionals, and the economic performance is compared through life cycle cost analysis. Depending on the conditions, the most cost-efficient alternative is either a gas pipeline from decentralized biogas production to a centralized liquefaction, or fully centralized production. The economic benefit of centralization increases with the number of farms involved but decreases with the biogas capacity of the system and the transport distance. The pipeline solution provides simple logistics and operation, although concession for pipe laying can be challenging. Moreover, a partly or fully centralized setup improves the delivery security of the system and reduces downtime. However, decentralized biomethane production can be an option for remote farms where centralization is not possible. For existing biogas plants, small-scale liquefaction or a pipeline to centralized liquefaction can be options for developing more biomethane production.

Processing of Agricultural Residues with a High Concentration of Structural Carbohydrates into Biogas Using Selective Biological Products

Biomass, particularly agricultural residues and biomass rich in structural carbohydrates, offers significant potential for sustainable biogas production. Biological pretreatment using microorganisms, particularly Trichoderma species, is discussed as a cost-effective and environmentally sustainable approach to improving the decomposition of structural carbohydrates into fermentable sugars. This study aimed to assess the impact of employing a selective biological product (BP) on the biogas production process and biomethane potential using winter wheat straw (WWS) as a representative feedstock. The biological product, consisting of microorganisms of the Trichoderma spp. genus, was introduced to enhance microbial activity. The biogas potential results showed that WWS treated with the BP exhibited a remarkable improvement in biogas production. Specifically, biogas yield increased from 364.1 L/kg of mass in untreated straw to 439.9 L/kg in BP-treated straw, representing a substantial 20.8% increase. Furthermore, in continuous loading tests, the steady-state biogas yield from BP-treated straw ranged from 553.6 to 582.0 L/kg VS, which was notably higher compared to untreated straw with a yield of 490.0 L/kg VS. Overall, the results of this study demonstrated that the application of selective biological products significantly enhanced biogas production and biomethane potential from structural carbohydrates containing biomass sources.

Fractional calculus as a generalized kinetic model for biochemical methane potential tests

This study presents a fractional calculus model as a generalized kinetic model for estimating the maximum methane yield and degradation kinetics in biomethane potential (BMP) assays, a key analytical method in anaerobic digestion research and application. The fractional model outperformed common first-order kinetic models by yielding superior data fitting and properly managing substrate heterogeneity. The fractional model showed robust performance in mono-digestion, co-digestion and pre-treatment BMP assays with or without presence of large tailing or sigmoidal patterns in the BMP curve. The main advantage of the fractional model over other models is its ability to capture the complexities of the methane production process without losing model accuracy. Assessment of the mathematical model revealed that for fractional orders greater than 0.8 the Mittag-Leffler sequence could be transformed into a more computationally efficient exponential function.

Catch and Cover Crops’ Use in the Energy Sector via Conversion into Biogas—Potential Benefits and Disadvantages

The development of civilization is related to an increase in energy demand, while its production is still based mainly on fossil fuels. The release of carbon into the environment, which disturbs the balance of the global system, is the consequence of using these fuels. One possible way to reduce the carbon footprint of the energy sector is the widespread use of cover crops’ biomass for energy production. The aim of this paper is to critically review the knowledge on the dissemination of catch and cover crops’ cultivation in different regions of the world, and the yield, chemical composition and biomethane potential of their biomass. Additionally, the environmental benefits, as well as the challenges and opportunities associated with this biomass use in the energy sector, are considered. The review showed that the aboveground biomass of cover and catch crops is a valuable source for the production of bioenergy in biogas plants. However, the key role of these crops is to prevent soil degradation. Therefore, changes in biomass target use must be preceded by a multi-aspect analysis that allows their impact on the environment to be assessed.

Global biomethane and carbon dioxide removal potential through anaerobic digestion of waste biomass

Anaerobic digestion is a bioenergy technology that can play a vital role in achieving net-zero emissions by converting organic matter into biomethane and biogenic carbon dioxide. By implementing bioenergy with carbon capture and storage (BECCS), carbon dioxide can be separated from biomethane, captured, and permanently stored, thus generating carbon dioxide removal (CDR) to offset hard-to-abate emissions. Here, we quantify the global availability of waste biomass for BECCS and their CDR and biomethane technical potentials. These biomass feedstocks do not create additional impacts on land, water, and biodiversity and can allow a more sustainable development of BECCS while still preserving soil fertility. We find that up to 1.5 Gt CO2 per year, or 3% of global GHG emissions, are available to be deployed for CDR worldwide. The conversion of waste biomass can generate up to 10 700 TWh of bioenergy per year, equivalent to 10% of global final energy consumption and 27% of global natural gas supply. Our assessment quantifies the climate mitigation potential of waste biomass and its capacity to contribute to negative emissions without relying on extensive biomass plantations.

Hydrogen and methane production through two stage anaerobic digestion of straw residues

Anaerobic digestion of agricultural waste can contribute to the European renewable energy needs. The 71% of the 20,000 anaerobic digestion plants in operation already uses these agro-waste as feedstock; part of these plants can be converted into two stage processes to produce hydrogen and methane in the same plant. Biomethane enriched in hydrogen can replace natural gas in grids while contributing to the sector decarbonisation. Straw is the most abundant agricultural residue (156 Mt/y) and its conventional final fate is uncontrolled soil disposal, landfilling, incineration or, in the best cases, composting. The present research work focuses on the fermentation of spent mushroom bed, an agricultural lignocellulosic byproduct, composed mainly from wheat straw. The substrate has been characterized and semi-continuous tests were performed evaluating the effect of the hydraulic retention time on hydrogen and volatile fatty acids production. It was found that all the tests confirmed the feasibility of the process even on this lignocellulosic substrate, and also, it was identified HRT 4.0 d as the best option to optimize the productivity of volatile fatty acids (17.09 gCODVFAs/(KgVS*d)), and HRT 6.0 d for hydrogen (7.98 LH2/(KgVS*d)). The fermentation effluent was used in biomethanation potential tests to evaluate how this process affects a subsequent digestion phase, reporting an increase in the energetical feedstock exploitation up to 30%.

The biogas upgrading from landfill leachate pretreated with low-frequency ultrasonic: anaerobic digestion performances and energy balance

The efficient biogas production from landfill leachate (LL) is one of hot topics in anaerobic digestion systems. Higher bioavailability of LL can be achieved by application a feasible and promising pretreatment technologies in order to utilize as a substrate for anaerobic reactors. Here, the enhanced bioavailabity of LL using the low-frequency ultrasonic process and energy balance in anaerobic digestion process was estimated within incubation period of 24 days. The optimal performance of low-frequency ultrasonic for LL biodegradability index: sCOD and TVFA were estimated under influencing parameters: ultrasonic density (UD) (0.02–0.14 W/mL) and Ultrasonic time (UT) (0–12 min). Moreover, the effects of low-frequency ultrasonic pretreatment process on biogas production in batch mode anaerobic reactors operated at 37 ± 1 °C were surveyed for daily and cumulative methane production, operational performance and energy balance. An increased sCOD (820 mg/L) and TVFA (659 mg/L) were observed under optimum codition: UD (0.1 W/mL) and UT (10 min). The highest methane production (430 mL) was found in reactor 4, where %15 volume ratio of LL pretreated with low frequency ultrasonic were feed in. Energy balance assessment indicated that output energy for anaerobic reactors assissted with ultrasonic in range of + 6.99 and + 7.98 kJ/g VS removed. Therefore, incorporation the low-frequency ultrasonic and digestion process revealed a promising and economic technique to improve biomethane potential and energy balance from LL.