Biogas Methane Research Articles

The effect of Fenton sludge on anaerobic digestion of papermaking wastewater in an upflow anaerobic sludge blanket reactor

An upflow anaerobic sludge blanket (UASB) reactor was used to investigate the effect of adding Fenton sludge (FS) on the anaerobic digestion of actual papermaking wastewater. The results showed that a one-time addition of 10 g/L FS could sustainably promote the performance of UASB for more than 40 days. The organic matter removal efficiency increased by 15.56%, and the biogas production increased by 24.52%. The proportion of methane in biogas increased by 12.87%. Adding FS increased the capacitance values of sludge extracellular polymeric substances and the electron transfer system activity in reactor increased by 1.76 times. The dehydrogenase activity and coenzyme F420 of the sludge increased by 1.54 and 2.11 times, respectively. Adding FS enriched the iron-reducing bacteria (Thermodesulfobacteriota) and hydrolytic acid-producing bacteria (Chloroflexota and Synergistota), thereby promoting the hydrolysis and acidification process. Adding FS was beneficial to the enrichment of methanogen, especially Methanosaeta, significantly increasing the methane production.

Management of Tanning Waste from Leather Processing by Anaerobic Digestion Using a Dynamic Method on a Semi-Technical Scale

In the context of climate policy, measures are being taken around the world to reduce pollution. These have been intensified in the areas of transport, industry, and energy, with the goal of zero emissions. The role of the biogas plant in energy transition and as a waste treatment plant for disposal is very important. This article describes research on a dynamic anaerobic digestion (AD) process plant. The subject of this study was leather shavings, which is a problematic waste. The research presented here is intended to demonstrate the decomposition of the flesh in the process, to confirm its biogas yield, and to evaluate the biological and technical parameters of the process. High biochemical stability was achieved for each of the tests evaluated, and no specific technical requirements were demonstrated. The only technical aspect to be addressed during operation was sedimentation, which can be solved by preparing the mixture earlier or by changing the mixing method. This made it reasonable to investigate the material further in the context of an industrial project. The characteristics of protein degradation in the AD process resulted in a high methane content in the biogas, above 65%. It was also observed that the long conditioning time of biogas in the gas cushion favourably affected the proportion of methane in biogas. Analytical results confirmed 77.5% methane content, which was a very good result. This paper presents the results of a surprising effect of chromium, primarily Cr (III), on the performance of anaerobic digestion.

Testing the ability of water hyacinth for wastewater treatment and methane biogas production

This study aims to assess the potential of water hyacinth (WH) in treating wastewater and its viability for co-digestion with municipal solid waste to achieve zero waste treatment by generating methane biogas. A batch flow reactor treated wastewater, evaluating nine parameters (NO3, PO4, BOD5, Turbidity, Chromium, Cadmium, Lead, Calcium, and Magnesium). The highest removal efficiencies were observed for NO3 (94.13%), PO4 (75.85%), BOD5 (100%), Turbidity (93.86%), Chromium (94.3%), Cadmium (94.93%), Lead (91.33%), Calcium (41.42%), and Magnesium (43.13%). The pH ranged from 7.82 to 7.44. Methane biogas production was examined using anaerobic digesters with varying ratios of carbon-based waste and WH, along with pH, temperature, and total solid content variations. The optimal methane biogas production ratio was found to be 1:3 for WH and solid waste at 35°C, 10% total solids, and a pH of 7.5, resulting in the highest cumulative methane generation of 1039.80 mL/gm vs. The Gompertz model accurately described methane biogas generation with a yield of 1083.088 mL/gm vs., supported by a coefficient of determination (R2) of 0.999. The kinetics of the biodegradation process were evaluated using a first-order kinetic model. The negative value of k (-0.2364) suggests a rapid solid waste biodegradation, with a high correlation coefficient (R2) of 0.9971. Numerous correlations were employed to enhance the production of methane, yielding a correlation coefficient of 91.36%.

Synergistic integration of zeolite engineering and fixed-bed column design for enhanced biogas upgrading: Adsorbent synthesis, CO2/CH4 separation kinetics, and regeneration assessment

Biogas, a renewable energy vector derived from anaerobic digestion of organic waste, requires CO2 separation to enhance its calorific value for engine fuel. This study integrates CO2/CH4 separation in biogas using a novel approach integrating dual chemically-activated zeolites and fixed-bed column purification. Biogas produced via CSTR/ultrafiltration (69 % CH4, 30 % CO2, 14 ppm H2S) was further upgraded using HCl + NaOH and H2SO4 + NaOH activated zeolites. Optimal absorption capacity of 97.77 ± 0.01 % was achieved at 140 mesh, 60-minute H2SO4 + NaOH activation, 2-hour calcination (400 °C), and 200 mL/min flow rate. Breakthrough was observed at 18.12 min. Langmuir isotherm (R2 = 0.9992) and Elovich kinetics (R2 = 0.9846) best described the adsorption process. XRD analysis showed significant crystal size reduction post-activation (53.31 nm to 16.90 nm). Notably, BET analysis revealed enhanced surface properties surface area of 286.71 m2/g, pore volume of 0.213 cc/g, and pore diameter of 3.532 Å. An innovative dual-column system with non-isothermal TSA protocol optimized CO2 adsorption (30 mins) and desorption (17 mins, 40 °C, 100 mL/min), yielding superior near-pure methane biogas (99.29 % CH4, 0.66 % CO2, trace H2S). A methane loss of 2.75 % during upgrading demonstrated high CO2 selectivity. This synergistic approach presents a promising solution for sustainable biogas purification and engine fuel applications.

Impact of additives on syntrophic propionate and acetate enrichments under high-ammonia conditions

High ammonia concentrations in anaerobic degradation systems cause volatile fatty acid accumulation and reduced methane yield, which often derive from restricted activity of syntrophic acid-oxidising bacteria and hydrogenotrophic methanogens. Inclusion of additives that facilitate the electron transfer or increase cell proximity of syntrophic species by flocculation can be a suitable strategy to counteract these problems, but its actual impact on syntrophic interactions has yet to be determined. In this study, microbial cultivation and molecular and microscopic analysis were performed to evaluate the impact of conductive (graphene, iron oxide) and non-conductive (zeolite) additives on the degradation rate of acetate and propionate to methane by highly enriched ammonia-tolerant syntrophic cultures derived from a biogas process. All additives had a low impact on the lag phase but resulted in a higher rate of acetate (except graphene) and propionate degradation. The syntrophic bacteria ‘Candidatus Syntrophopropionicum ammoniitolerans’, Syntrophaceticus schinkii and a novel hydrogenotrophic methanogen were found in higher relative abundance and higher gene copy numbers in flocculating communities than in planktonic communities in the cultures, indicating benefits to syntrophs of living in close proximity to their cooperating partner. Microscopy and element analysis showed precipitation of phosphates and biofilm formation in all batches except on the graphene batches, possibly enhancing the rate of acetate and propionate degradation. Overall, the concordance of responses observed in both acetate- and propionate-fed cultures highlight the suitability of the addition of iron oxide or zeolites to enhance acid conversion to methane in high-ammonia biogas processes.Key points• All additives promoted acetate (except graphene) and propionate degradation.• A preference for floc formation by ammonia-tolerant syntrophs was revealed.• Microbes colonised the surfaces of iron oxide and zeolite, but not graphene.Graphical

Integrated microcontroller mq sensors for monitoring biogas: Advancements in methane and hydrogen sulfide detection

Recent technological advances in microcontroller systems enable novel biogas monitoring capabilities. This study investigates microcontroller-based quantification of methane and hydrogen sulfide concentrations in biogas derived from anaerobic digestion. Anaerobic digesters were fed either 100% cow dung substrates or a 50:50 mixture of cow dung with municipal solid waste (MSW). Methane levels were monitored using an MQ-4 sensor, hydrogen sulfide via an MQ-136 sensor, and temperature with a K-type thermocouple, all integrated with an ATmega 2560 microcontroller system. The 100% cow dung digester produced biogas with maximum methane concentrations of 3488 ppm at 21 days, indicating improved methane production compared to the 50:50 mixture of cow dung with MSW. Hydrogen sulfide reached 195 ppm and 192 ppm for the 100% cow dung and mixed digesters. Mesophilic temperature conditions were maintained throughout the digestion process. Real-time quantification of biogas composition demonstrates the capabilities of microcontroller-based anaerobic digester monitoring to provide precise methane and hydrogen sulfide measurements.

Direct vs. indirect biogas methanation for liquefied biomethane production: A concept evaluation

Conventional liquefied biomethane (LBM) production plants consist of upgrading and liquefaction processes. Commonly, the captured CO2 during biogas upgrading is emitted into the atmosphere. One alternative, to produce more LBM, is to combine the conventional LBM production plant with the Power-to-Gas concept. Within this context, green H2 produced from renewable electricity can react with the CO2 in the biogas mixture, producing additional CH4. The present study evaluated the feasibility of integrating methanation with conventional LBM production plants. The performance of the proposed process designs was assessed through exergy and cost analysis considering detailed models. The results illustrated that integrated direct biogas methanation was superior to methanation of captured CO2. The integrated scheme with direct biogas methanation increased the LBM production by 52.2 % compared to the conventional LBM production plant but with lower exergy efficiency. It was indicated the feasibility of the integrated scheme through direct biogas methanation was highly dependent on the price of H2. A H2 price of 1.27 USD/kg H2 was required to produce LBM at a similar price as the conventional LBM production plant.

METHANE PRODUCTION FROM COW MANURE IN THE PRESENCE OF Bi(III) COMPLEX OF SULFAMIC ACID

The present study examines the process of biomethanization of cow manure in an anaerobic environment, in the presence of small amounts of Bi(III) complex of sulfamic acid. Since this complex has good antimicrobial activity, the purpose of adding the complex is to determine its effect on biogas and methane production. The reference samples (cow manure only) and mixtures of cow manure + 10 mg and cow manure + 20 mg of bismuth complex with a composition [Bi6O4(OH)4](NH2SO3)6 are subjected to biodegradation under the following conditions – duration of 33 days, nitrogen atmosphere and temperature of 34.5 ± 1°C. During the process, the volume of biogas and the percentage content of methane in biogas are measured in 2 - 3 days as well. The analyses performed reveal that until the 10th day, the amount of biogas produced increases constantly and is comparable both for the control samples and for the mixtures. Further, until the end of the experiment, a significant and constant increase in the volume of biogas produced by the mixtures is observed compared to the control samples.Regarding the percentage of methane produced by the reference samples and the mixtures, comparable relative amounts are found by the 7th day. From the 8th day to the 33rd day, the percentage of methane released by the mixtures is visibly greater than that by the reference samples.

Dimethyl Ether Biogas Reactivity-Controlled Compression Ignition for Sustainable Power Generation with Low Nitrogen Oxide Emissions

<div>Biogas (60% methane–40% CO<sub>2</sub> approximately) can be used in the reactivity-controlled compression ignition (RCCI) mode along with a high-reactivity fuel (HRF). In this work dimethyl ether (DME) that can also be produced from renewable sources was used as the HRF as a move toward sustainable power generation. The two-cylinder turbocharged diesel engine modified to work in the DME–biogas RCCI (DMB-RCCI) mode was studied under different proportions of methane (45–95%) in biogas since the quality of this fuel can vary depending on the feedstock and production method. Only a narrow range of biogas to DME ratios could be tolerated in this mode at each output without misfire or knock. Detailed experiments were conducted at brake mean effective pressures (BMEPs) of 3 and 5 bar at a speed of 1500 rpm and comparisons were made with the diesel–biogas dual-fuel and diesel–biogas RCCI modes under similar methane flow rates while the proportion of CO<sub>2</sub> was varied. The DMB-RCCI mode exhibited superior brake thermal efficiency (25.3% as against 22% and 31.5% as against 29% at the BMEPs of 3 and 5 bar) as compared to the other modes and was not sensitive to the concentration of methane. The NOx and soot emissions were also negligible and the lowest CH<sub>4</sub> emission levels were also attained. The cyclic fluctuations in IMEP were lower than 5% in this mode. Thus, DME can be used along with biogas to enhance its reactivity for sustainable power generation in the RCCI mode.</div>

Biogas generation through anaerobic digestion of orange peel waste and crude glycerol in single‐stage and two‐stage batch system

AbstractOrange peel waste (OPW) and crude glycerol (CG) can be used in anaerobic processes. To avoid inhibition due to D‐limonene from OPW, the process can be carried out in two stages. Thus, this work aimed to evaluate the generation of methane in biogas through the anaerobic digestion of OPW and CG, individually and mixed, in a single‐stage and two‐stage batch system. For this purpose, the biochemical methane potential (BMP) of the wastes, separately and mixed, was determined in a single‐stage system (methanogenic phase) and in a two‐stage system (acidogenic and methanogenic), following the German standard VDI 4630. The results obtained were statistically analyzed using Shapiro−Wilk and non‐parametric tests. For OPW, the BMP value found was 160.5 m3 CH4. tonSV−1. For CG, the result for BMP was 344.8 m3 CH4. tonVS−1. The result of these mixed wastes was equivalent to 501.3 m3 CH4. tonSV−1, for BMP. Through the statistical tests used, it was found that the use of OPW and CG, separately and mixed, in the two‐stage system does not present a statistically significant difference in the production of biogas when using the same wastes in a single‐stage system. However, it was found that the co‐digestion of these wastes is promising for biogas generation and contributes to managing these agro‐industrial wastes.

An upcycling bioprocess for sustainable aviation fuel production from food waste-derived greenhouse gases: Life cycle assessment and techno-economic analysis

Biogas generated from food waste through anaerobic digestion is typically utilized for heat and electricity. However, recent developments in synthetic biology have enabled the conversion of carbon dioxide (CO2) and methane (CH4) in biogas into desired products by microorganisms. This study introduced a novel bioroute for the production of sustainable aviation fuel (SAF) using food waste in a carbon–neutral and cost-effective manner. Both CO2 and CH4 derived from food waste are sequentially bioconverted into lipids by photosynthetic and methanotrophic microorganisms, which are then upgraded into SAF. A comparative life cycle assessment was conducted, revealing that this proposed bioroute has a lower environmental impact than a thermo-route involving hydrothermal liquefaction. Furthermore, a techno-economic analysis of the bioroute was also performed to evaluate both the capital and operating costs, showcasing the feasibility of this concept with current cutting-edge technologies. With potential food waste disposal subsidies taken into consideration, the bioroute-based SAF could yield an internal rate of return of up to 38%, demonstrating its economic viability in the market. By leveraging food waste and innovative biotechnology, this bioroute has the potential to contribute to a more eco-friendly and economically sustainable aviation industry.

Magnetic porous microspheres enhancing the anaerobic digestion of sewage sludge: Synergistic free and attached methanogenic consortia

The addition of exogenous materials is a commonly reported method for promoting the anaerobic digestion (AD) of sludge. However, most exogenous materials are nano-sized and their use encounters problems relating to a need for continuous replenishment, uncontrollability and non-recyclability. Here, magnetic porous microspheres (MPMs), which can be controlled by magnetic forces, were prepared and used to enhance the methanogenesis of sludge. It was observed that the MPMs were spherical particles with diameters of approximately 100 µm and had a stable macroporous hybrid structure of magnetic cores and polymeric shells. Furthermore, the MPMs had good magnetic properties and a strong solid–liquid interfacial electron transfer ability, suggesting that MPMs are excellent carriers for methanogenic consortia. Experimental results showed that the addition of MPMs increased methane production and the proportion of methane in biogas from AD by 100.0 % and 21.2 %, respectively, indicating the MPMs notably enhanced the methanogenesis of sludge. Analyses of variations in key enzyme activities and electron transfer in sludge samples with and without MPMs in AD revealed that the MPMs significantly enhanced the activities of key enzymes involved in hydrolysis, acidification and methanation. This was achieved mainly by enhancing the extracellular electron transfer to strengthen the proton motive force on the cell membrane, which provides more energy generation for methanogenic metabolism. A careful examination of the variations in the morphology, pore structure and magnetism of the MPMs before and after AD revealed that the MPMs increased the prevalence of many highly active anaerobes, and that this did not weaken the magnetic performance. The microbial community structure and metatranscriptomic analysis further indicated that the acetotrophic methanogens (i.e., Methanosaeta) were mainly in a free state and that CO2-reducing methanogens (i.e., Methanolinea and Methanobacterium) mainly adhered to the MPMs. The above synergistic metabolism led to efficient methanogenesis, which indicates that the MPMs optimised the spatial ecological niche of methanogenic consortia. These findings provide an important reference for the development of magnetic porous materials promoting AD.

Changes in Microbiota Composition during the Anaerobic Digestion of Macroalgae in a Three-Stage Bioreactor.

The use of microalgae as a raw material for biogas production is promising. Macroalgae were mixed with cattle manure, wheat straw, and an inoculant from sewage sludge. Mixing macroalgae with co-substrates increased biogas and methane yield. The research was carried out using a three-stage bioreactor. During biogas production, the dynamics of the composition of the microbiota in the anaerobic chamber of the bioreactor was evaluated. The microbiota composition at different organic load rates (OLRs) of the bioreactor was evaluated. This study also demonstrated that in a three-stage bioreactor, a higher yield of methane in biogas was obtained compared to a single-stage bioreactor. It was found that the most active functional pathway of methane biosynthesis is PWY-6969, which proceeds via the TCA cycle V (2-oxoglutarate synthase). Microbiota composition and methane yield depended on added volatile solids (VSadded). During the research, it was found that after reducing the ORL from 2.44 to 1.09 kg VS/d, the methane yield increased from 175.2 L CH4/kg VSadded to 323.5 L CH4/kg VSadded.

Results from the operation of an efficient and flexible large-scale biogas methanation system

This study reports a comprehensive analysis of the operation of a biogas methanation system with a total 240 kW SNG output.

Comparative evaluation of the effect of ultrasonic pretreatment at different temperatures on enhancing anaerobic digestion of rumen wastes

The aim of this study was to determine the most appropriate treatment for the duration of ultrasonic pretreatment at two different temperatures in the process of anaerobic digestion (AD) of ruminal contents in the slaughterhouse. The experiments were performed at the Golshan industrial slaughterhouse in Lorestan province. In this study, after homogenizing the rumen contents of different animals, the effect of ultrasonic pretreatment time at three different intervals of 10, 20, and 30 min at two different temperatures of 30 °C and 40 °C was investigated to determine the effect of variables related to the trend of changes in methane, total biogas, and daily biogas production. The Taguchi L18 method was used to investigate the process conditions and achieve optimal production conditions for biogas methane. The results showed that with an increase in pretreatment time up to 30 min and the temperature up to 40 °C, the production of biogas and methane also increased. The highest amount of methane, total biogas, and daily biogas produced was related to the use of ultrasonic pretreatment for 30 min at 40 °C with 50.66 % methane, total biogas production of 332.66 mL/gVS, and the best performance compared to other treatments in the shortest possible time. Therefore, the use of ultrasonic pretreatment over longer periods and at higher temperatures improves the AD process and produces more total methane and biogas. Finally, this research presented equations for the production of biogas and methane at a time of 10–30 min and a temperature of 30–40 °C, which showed high accuracy.

ЭНЕРГЕТИЧЕСКИЙ ПОТЕНЦИАЛ И ОСОБЕННОСТИ БИОДЕГРАДАЦИИ ЗЕРНОВОЙ ПЫЛИ ПРИ ЕЕ ПЕРЕРАБОТКЕ В БИОГАЗ

The composition of the dust that is generated during the collection, transportation, processing and storage of grain is different and complex. The amount of grain dust can reach 26% by weight of the raw material. Due to the ability to ignite spontaneously, it is classified as a hazard class 3, and if it enters the human body, it can cause harm to health, therefore, grain processing enterprises take measures to reduce the concentration of grain dust in the air. On the other hand, the dust generated during grain processing is, due to its chemical composition, a valua- ble raw material, the loss of which is undesirable. The world literature describes such methods for processing aspiration grain dust as hydrolysis and the preparation of nutrient media for microorganisms, briquetting and combustion, use in composting, as well as conversion into biogas. The purpose of this work is to study the features of processing aspiration grain dusts of various agricultural crops into biogas and determine their energy potential and biodegradability. As a result of our laboratory studies, it was established that the specific biogas and methane yield from soybean grain dust was 186.37±58.89 – 230.30±21.90 and 95.54±36.95 – 122.17±15.39 ml/g VS respectively; from barley grain dust – 165.06±9.37 – 191.41±5.65 and 86.45±6.37 – 100.18±6.65 ml/g VS respectively. The concentration of methane in biogas in different variants ranged from 46.75±7.14 to 52.75±1.60%. When recycling 1 ton of these grain dusts at a biogas station, you can get from 278.70 to 382.25 kW of electrical energy and from 285.50 to 391.57 kW of thermal energy. The degree of decomposition of organic matter of substrates in our study is generally low – from 5.61±0.08 to 5.91±0.37%. Thus, it has been established that the grain dusts studied in this work can be considered as a promising cosubstrats for existing or planned biogas stations. The recommended processing time is no more than 35 days.

Enhancing kitchen waste minimization and energy generation at 20 °C: a psychrophilic anaerobic co‐digestion study

AbstractBackgroundIn developing countries, anaerobic digestion still represents an emerging technology for solid waste management, despite the great energy potential of methane in biogas for heating purposes, especially in low‐temperature regions. This research evaluated the effect of hydraulic retention time (40–120 days) on the anaerobic co‐digestion of 35% w/w waste activated sludge and 65% w/w organic kitchen waste at a low temperature (20 °C). The anaerobic co‐digestion was conducted in five 11‐L semicontinuous anaerobic digesters. Additionally, the expected energy production from organic kitchen waste was calculated.ResultsThe specific methane yield (SMY) ranged from 0.20 to 0.27 LCH4 g‐VSadd−1, comparable to the SMY reported for meso‐ and thermophilic anaerobic digestion. Moreover, the expected energy production was 1.06 MJ day−1 of equivalent liquefied petroleum gas, which could satisfy ≤6.6% of the daily water heating requirements of an average Mexican household. The hydraulic retention time in the range of 60–120 days did not seem to significantly affect the performance of the digesters.ConclusionsThese digesters could easily be installed in low temperature regions for domestic use. The waste activated sludge substrate can be replaced with other nitrogen‐rich substances for indoor use. The data shown in this research set the basis for further investigations and domestic applications. © 2023 Society of Chemical Industry (SCI).

Advancements in CO2 methanation: A comprehensive review of catalysis, reactor design and process optimization

Renewable electricity, production/storage and distribution of green hydrogen and carbon dioxide emission reduction are just three of the practices needed for a net zero-emission world. The increasing amount of renewable energy produced requires the development of versatile technologies capable to store the excess renewable electricity produced. Hydrogen production through electrolysis, despite not being still economically viable, can be considered a mature technology. Different strategies to convert H2 into more volumetric dense fuel are under development through Power-to-Chemicals (PtC) process. Among these, CO2 methanation offers the advantage of a wide infrastructure available for the distribution and use of methane as chemical and fuel for both heat and power generation. The latter approach is also called Power-to-Gas (PtG) process. These technologies in the last year have been the focus of research, both public and private. In particular, direct methanation of biogas obtained from anaerobic digestors represents a challenge and an interesting opportunity due to the possibility to avoid the CO2 separation step at the moment needed for biogas purification to biomethane. Since CO2 separation is an additional cost, this route can be the key for economic sustainability of the process. In this review we focus on the main aspects involved in the design of a methanation plant, with a particular focus on the biogas methanation, starting from the reaction thermodynamics and kinetics. Afterwards, light is shed on the most interesting catalysts reported in the literature, with a focus on Ni-based catalysts and considering the support role in the reaction. Different kinetic approaches currently available and promising reactor types, including different simulation models, which are becoming increasingly fundamental in the reactor design and scale-up phase, are reported. Finally, the last chapter contains the most interesting and industrially relevant ongoing projects on direct biogas methanation.

Optimizing biogas methanation over nickel supported on ceria-alumina catalyst: Towards CO2-rich biomass utilization for a negative emissions society

Biogas methanation emerges as a prominent technology for converting biogas into biomethane in a single step. Furthermore, this technology can be implemented at biogas plant locations, supporting local economies and reducing dependence on large energy producers. However, there is a lack of comprehensive studies on biogas methanation, particularly regarding the technical optimization of operational parameters and the profitability analysis of the overall process. To address this gap, our study represents a seminal work on the technical optimization of biogas methanation obtaining an empirical model to predict the performance of biogas methanation. We investigate the influence of operational parameters, such as reaction temperature, H2/CO2 ratio, space velocity, and CO2 share in the biogas stream through an experimental design. Based on previous research we selected a nickel supported on ceria-alumina catalyst; being nickel a benchmark system for methanation process such selection permits a reliable data extrapolation to commercial units. We showcase the remarkable impact of studied key operation parameters, being the temperature, the most critical factor affecting the reaction performance (ca. 2 to 5 times higher than the second most influencing parameter). The impact of the H2/CO2 ratio is also noticeable. The response surfaces and contour maps suggest that a temperature between 350 and 450 °C and an H2/CO2 ratio between 2.5 and 3.2 optimize the reaction performance. Further experimental tests were performed for model validation and optimization leading to a reliable predictive model. Overall, this study provides validated equations for technology scaling-up and techno-economic analysis, thus representing a step ahead towards real-world applications for bio-methane production.

The Bioaugmentation of Electroactive Microorganisms Enhances Anaerobic Digestion

Direct interspecies electron transfer (DIET) between electroactive microorganisms (EAMs) offers significant potential to enhance methane production, necessitating research for its practical implementation. This study investigated enhanced methane production through DIET in an anaerobic digester bio-augmented with EAMs. A horizontal anaerobic digester (HAD) operated for 430 days as a testbed to validate the benefits of bioaugmentation with EAMs. Anaerobic digestate slurry, discharged from the HAD, was enriched with EAMs in a bioelectrochemical auxiliary reactor (BEAR) under an electric field. This slurry enriched with EAMs was then recirculated into the HAD. Results showed bio-augmentation with EAMs led to an increase in volatile solids removal from 56.2% to 77.5%, methane production rate from 0.59 to 1.00 L/L.d, methane yield from 0.26 to 0.34 L/g CODr, and biogas methane content from 59.9% to 71.6%. It suggests that bio-augmentation enhances DIET, promoting the conversion of volatile fatty acids to methane and enhancing resilience against kinetic imbalances. The enrichment of EAMs reached optimal efficacy under an electric field intensity of 2.07 V/cm with a mean exposure time of 2.53 days to the electric field in the BEAR. Bio-augmentation with externally enriched EAMs is a feasible and effective strategy to optimize anaerobic digestion processes.