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The design of solid oxide fuel cells (SOFC) using biogas for distributed power generation is a promising alternative to reduce greenhouse gas emissions in the energy and waste management sectors. Furthermore, the high efficiency of SOFCs in conjunction with the possibility to produce hydrogen may be a financially attractive option for biogas plants. However, the influence of design variables in the optimization of revenues and efficiency has seldom been studied for these novel cogeneration systems. Thus, in order to fulfill this knowledge gap, a multi-objective optimization problem using the NSGA-II algorithm is proposed to evaluate optimal solutions for systems producing hydrogen and electricity from biogas. Moreover, a mixed-integer linear optimization routine is used to ensure an efficient heat recovery system with minimal number of heat exchanger units. The results indicate that hydrogen production with a fuel cell downstream is able to achieve high exergy efficiencies (65–66%) and a drastic improvement in net present value (1346%) compared with sole power generation. Despite the additional equipment, the investment costs are estimated to be quite similar (12% increase) to conventional steam reforming systems and the levelized cost of hydrogen is very competitive (2.27 USD/kgH2).

Lignocellulosic biomass is considered a key resource for the future expansion of biogas production through anaerobic digestion (AD), and research on the development of pretreatment technologies for improving biomass conversion is an intensive and fast-growing field. Consequently, there is a need for creating tools able to predict the efficiency of a certain pretreatment on different biomass types, fast and accurately, and to assist in selecting a pretreatment technology for a specific biomass. In this study, seven different types of raw lignocellulosic biomass of industrial relevance were systematically analyzed regarding their composition (carbohydrates, lignin, lipids, ash, extractives, etc.) and subjected to a common pretreatment. The aim of the study was to identify the most important characteristics that make a biomass good receptor of the specific pretreatment prior to AD. A simple ammonia pretreatment was chosen as a case study and partial least squares regression (PLS-R) was used for modeling initially the ultimate methane yield of raw and pretreated biomass. In the sequel, PLS-R was used for modeling the efficiency of the pretreatment on increasing the ultimate methane yield and hydrolysis rate as a function of the biomass composition. The fit of the models was satisfactory, ranging from R2 = 0.89 to R2 = 0.97. The results showed that the most decisive characteristics for predicting the efficiency of the pretreatment were the lipid (r = −0.88), ash (r = +0.79), protein (r = −0.61), and hemicellulose/lignin (r = −0.53) content of raw biomass. Finally, the approach followed in this study facilitated an improved understanding of the mechanism of the pretreatment and presented a methodology to be followed for developing tools for the prediction of pretreatment efficiency in the field of lignocellulosic biomass valorization.

Due to rapid movement of rural population to new regions and countries in order to find work and for better living conditions, population growth and economic development, there is gradual increase in production of waste and demand of electricity worldwide. According to World Bank statistics, the global Municipal Solid Waste generated was 1.3 billion tons in year 2012 and this is expected to increase above 2.2 billion tons per year by 2025. Due to lack of sites for waste disposal, it has become a serious environmental as well as health issue. Now various methods have been adopted for waste disposal. Among this, energy accessed from municipal solid waste is the most common practice adopted by developing countries. In addition, Waste to Energy and Energy from Waste technologies are used which include thermal and biological technologies. Gasification, pyrolysis and incineration are thermal technologies used in conversion of waste to energy. During these processes, syngas is produced which is used in combustion engine or turbines to generate electricity. Apart from this, biomethanation is also used in which biogas is produced. In this review article, we have discussed all the environmental and green methods used for the generation of energy from Municipal Solid Waste their advantages and drawbacks.

In this study, a two-stage biohythane production system was used to treat swine manure to solve the high Chemical Oxygen Demand (COD) concentration and verify the total energy recovery between the two-stage and a traditional single-stage system. Experiments were carried out in single-stage methane production, two-stage biohythane production in long Hydraulic Retention Time (HRT), and short HRT. The COD removal efficiency and energy recovery were finally compared between single-stage (CH4 fermenter) and two-stage (H2+ CH4 fermenter) systems. The results showed that the methane production rate of 53.2 ± 2.7 mL/d.L, the COD removal efficiency of 29.6 ± 5.8%, and total energy recovery of 2.9 ± 0.1 kJ/L.d was obtained in the single-stage of methane production system with HRT 11.08 d, pH 7, and temperature 55 °C, respectively. In the two-stage of hydrogen and methane productions system, the hydrogen production rate of 1.8 ± 0.7 mL/d.L, the methane production rate of 65.7 ± 2.5 mL/d.L, the COD removal rate was 97.8 ± 1.7%, and the total energy recovery of 3.6 ± 0.1 kJ/L.d was obtained and stabilized when the sugary wastewater content gradually reduced to 0%. This study shows that the methane production rate increases 20%, COD removal efficiency increases to 97.8 ± 1.7%, and total energy recovery increases 30%. At the same time, the single-stage (CH4 fermenter) switched to a two-stage (H2+ CH4 fermenter) system. The two-stage anaerobic biohythane production system successfully treated the high organic swine manure and obtained a higher energy recovery against the traditional single-stage of the biomethane production system.

Solar and wind energy technologies, due to their nature of weather dependency, have been recognized as not the complete solution for the renewable energy transition. Creating a solution for the short fall is empirical if we are to remove the dependency on fossil fuels and reach net zero targets. The production of hydrogen, biogas and other gases can be produced sustainably, which can also allow for the utilization of waste materials or the ability to store energy and allow a greater positive impact on our environment. However, production of these gases is not always as transparent or environmentally friendly as perceived, so with the aid of certification and blockchain, we can create a system that can guarantee their environmentally positive origin, and ultimately help assist the transition to a greener future. This paper explores the varying production methods, with consideration to their environmental impact, and the implications of the use of certificates and blockchain to monitor production, trade and usage.

Supplement to the depleting energy resources and the stringent environmental laws regarding the atmospheric emissions of greenhouse gases, the development of clean and renewable sources of energy has been a great issue. Worldwide, energy usage is steadily increasing and would continue to increase in the coming years; the effects of global warming are also becoming more and more prevalent. Biogas holds a promising future in the sustainable supply of low-cost energy that will minimize greenhouse gas emissions. Unlike solar and wind, biogas does not rely on weather conditions. It can also be stored and transported making it easily adaptable to changes in demand. This study would utilize membrane technology for the upgrading of biogas to a clean and useful fuel replacing fossil fuels and consider the limiting factors of the process found in literature which is the trade-off between gas permeability and selectivity. In doing so, we analyse the factors that affect permeability and selectivity of ceramic membranes and then introduce methods of optimisation. Biogas components are passed through the membrane as feed gas to observe the flow characteristics at various operating conditions for membranes with different pore sizes. It was observed that for all pore sizes studied, there was a proportional rise in flowrate as the feed pressure was increased from 0.2 to 3 bar. Also, an increase in temperature from 20 °C to 100 °C favoured the membrane selectivity. In general, methane gas showed a higher flux than carbon dioxide irrespective of the operating conditions indicating that the permeation of the gases is related to their molecular weight, for example, using 15 nm membrane at 20 °C and 3 bar, a flux of 3.59 and 2.27 L/min was obtained for CH4 and CO2 respectively with the same trend recorded using other pore sizes, temperature and pressure ranges. It must also be noted that the pore size plays a vital role in the optimisation of membrane process as the 15 nm membrane, being the lowest mean pore size studied showed the highest separation factor of 1.60 which is close to the ideal Knudsen value. Overall, it was found that the behaviour of gases through these membranes is determined by an interplay of factors – dynamic size and diffusion rate.

Low quality and yield of methane severely hindered the industrial application of straw biogas fermentation and there has been no effective solution found so far. In this study, a novel method has been developed to improve the quality and yield of methane during biogas fermentation. We coupled microbial electrolysis cell (MEC) with normal anaerobic fermentation to enhance the yield and purity of methane. This novel fermentation process achieved the methane purity of more than 85%, which was critically higher than those of previously published reports. With the stimulation from microorganisms and electric current, the degradation of fiber has been greatly enhanced. The MEC system significantly improves the yield and purity of biogas, bringing a new path to synthesize the methane by the carbon dioxide and hydrogen ions in solution under the electron. Electrochemical index analysis showed the extra methane synthesis which was mainly led by the external circuit electron transfer. The result of the gas chromatograph and solid degradation rate showed that the carbon source of extra methane was CO2 produced in normal fermentation and extra volatile solid degradation. These results show that MEC significantly enhanced the quality and yield of methane in a straw fermentation process, giving insights for normal anaerobic fermentation.

Massive amounts of biogas slurry are produced due to the development of biogas plants. The pollution features and the risk of biogas slurry were fully evaluated in this work. Thirty-one biogas slurry samples were collected from sixteen different cities and five different raw materials biogas plants (e.g. cattle manure, swine manure, straw-manure mixture, kitchen waste and chicken manure). The chemical oxygen demand (COD), ammonia nitrogen ( NH 4 + - N ), anions (e.g. Cl−, SO 4 2 - , NO 3 - and PO 4 3 - ), antibiotics (e.g. sulphonamides, quinolones, β2-receptor agonists, macrolides, tetracyclines and crystal violet) and heavy metals (e.g. Cu, Cd, As, Cr, Hg, Zn and Pb) contents from these biogas slurry samples were systematically investigated. On this basis, risk assessment of biogas slurry was also performed. The concentrations of COD, NH 4 + - N and PO 4 3 - in biogas slurry samples with chicken manure as raw material were significantly higher than those of other raw materials. Therefore, the biogas slurry from chicken manure raw material demonstrated the most serious eutrophication threat. The antibiotic contents in biogas slurry samples from swine manure were the highest among five raw materials, mostly sulphonamides, quinolones and tetracyclines. Biogas slurry revealed particularly serious arsenic contamination and moderate potential ecological risk. The quadratic polynomial stepwise regression model can quantitatively describe the correlation among NH 4 + - N , PO 4 3 - and heavy metals concentration of biogas slurry. This work demonstrated a universal potential threat from biogas slurry that can provide supporting data and theoretical basis for harmless treatment and reuse of biogas slurry.

Fruit and vegetable waste (FVW) contains rich resources that can be recovered by methods such as incineration, anaerobic digestion to generate heat energy, biogas, and preservation by ensiling. However, a horizontal comparison of the resource potential and environmental impact of different recycling methods employed for FVW has not been conducted. This study quantifies and computes the recycling potential and global warming potential (GWP) of anaerobic digestion, ensiling, and incineration of the FVW generated during primary production in China. First, a gray model was employed to estimate the FVW output in 2030, based on the FVW produced between 2002 and 2017. Next, the resource potential and GWP of anaerobic digestion, incineration, and ensiling were evaluated. Finally, an optimization method was utilized to analyze possible strategies of FVW recycling in 2030. Results indicate that FVW output in China is expected to increase to 170 Mt by 2030, highlighting the need for efficient treatment options. Further, the resource potential and GWP of different waste treatment strategies were notably different. The recycling potential of ensiling was the highest at 1950 MJ/t; while the GWP of anaerobic digestion was the lowest at −31 kg CO2eq. An optimization analysis suggested that the optimal target of 100% would be attained if all FVW is ensiled in 2030. The study provides a basis for informed technical decision-making related to FVW recycling options in the future.

Reactivity-controlled compression ignition (RCCI) combustion involves in-cylinder fuels blending of varying reaction rates to enhance the combustion magnitude by stratification. Nitrogen oxides (NOx) and soot control techniques increase carbon monoxide (CO) and unburned-hydrocarbon (UHC) emissions in RCCI at low loads. A modified injection and proper Biogas mixing may reduce further CO, UHC, and trade-off with other emissions. The effects of loads (5.5 and 6.5 bar IMEP), port mixing distances (0–100%), swirl ratios (0–80%), and biogas pressures (1–4 bar) on the mixture distribution and emissions were evaluated experimentally, at 1600 rpm. Exergy analysis and combustion kinetics were applied for more understanding of emissions attributes. The process at 5.5 bar IMEP improves mixture homogeneity, uniform fuel stratification and reduces emissions across the mixing intervals. Injection at valve reduces CO, UHC, and NOx emissions by 11.54%, 9.38%, and 33.75% at 5.5 bar IMEP. Operating at the valve, 80% swirl ratio and 1 bar pressure further reduce the UHC (115.77 ppm), NOx (3.89 ppm), and PM (5.29 ppm) emissions by 1.94%, 49.94%, and 77.42%, than normal airflow. Thus, injecting biogas of low pressure at the valve amidst a stream of swirling air contributes to trade-off reduction techniques at low load.

The current work focuses on biohythane (biohydrogen + biomethane) production from waste biomass by utilising CaO2+CaCO3 and NaOH as additives and purification in a novel purification and mixing column with water and NaOH scrubbing. The production process indicates an enhanced hydrogen content of 33.85% with CaO2+CaCO3 as an additive from the fermentative reactor. The methanogenic reactor produces an improved methane content of 67.24% by utilising NaOH as the alkali reagent. During purification, NaOH scrubbing results in the highest purification of 87.43% hydrogen and 91.27% methane. In contrast, the water scrubbing system produces a maximum purity of 76.18 and 82.36%, respectively. Further, the variation of gas flow rate illustrates improved biohydrogen and biomethane purity up to 97.85 and 98.39%, with a gas flow rate of 0.12 m3 h−1. While producing biohythane, a gas flow rate of 0.12 m3 h−1 produces the optimum concentration of hydrogen and methane at 31.08 and 66.17%, respectively.

China has been placing a substantial focus on biogas for reducing energy consumption and carbon dioxide (CO2) emissions. The operation mode of biogas systems may make the CO2 reduction target over-optimistic. There is limited research to investigate the influential factors that may be causing the gap between the actual and theoretical CO2 reduction costs of biogas systems in China. In this research, by using field survey data of 209 biogas users and 489 non-biogas users from 19 villages in 2015, the gap between actual and theoretical unit CO2 reduction cost is quantified at approximately 156 USD/t CO2. By employing the Logarithmic Mean Divisia Index I (LMDI) model, it is found that both the cost effect (48%) and the reduction effect (52%) contribute to the unit CO2 reduction cost gap. Four influential factors–household labor, accessibility to the energy resource, acceptance of biogas technology, and subsidy–significantly narrow the gap between actual and theoretical CO2 reduction costs, while the levelized subsidy contributes to widening the gap. On average, biogas systems should be operated for at least four years and the substitution rate should be more than 67% in order to keep the gap between actual and theoretical CO2 reduction costs under 50%.

A performance study was conducted with two 1 m3 capacity anaerobic digester for producing biogas from cow dung and kitchen waste. The entire structure was constructed of fiber-reinforced plastic. Following construction and assembly, the biogas digestion unit was checked for 30 days to ensure the digester's success for both biowastes. In each digester, 2.5 kg cow dung and kitchen waste was diluted with water in the ratio 1:1 and subjected to a fourty five days retention time to prepare a slurry of 15% and 20% total solid. Results presented an average per day gas yield of 0.35 m3 for cow dung and 0.20 m3 for the kitchen waste at an average substrate temperature of 32 °C while the daily ambient temperatures varied from 29 °C to 31 °C and a pH of 6.50 to 7.40 for the cow dung and 4.91 to 7.1 for the kitchen waste.

Energy enhancement and utilization of renewable energy sources have become inevitable solutions for the concerns of fossil fuel depletion and global warming. Two different cogeneration systems are proposed for cooling and power generation. A gas turbine and an ejector refrigeration cycle are employed in the configurations, in which gas turbine cycle uses biogas as the required fuel. First, these two configurations are analyzed from energy and exergy perspectives. A comprehensive parametric study is also performed by decision variables for the optimization. Results reveal that both energy and exergy efficiencies of conventional combined gas turbine/ejector refrigeration cycle can be improved up to 44.6% and 33.54%, respectively. Besides, the outcomes of the parametric study point out that the combustion chamber has a significant effect on energy and exergy efficiencies and can increased them about 10%. Also, it is found that the vapor generator accounts for the highest exergy destruction among all components. Moreover, by using a genetic algorithm as an optimization method, the thermal and exergetic efficiencies of the base system improves. In the best operating condition, the thermal and exergetic efficiencies of the system reach 57.11% and 36.68%, respectively.

In this work, a biomethane fuel was obtained from biogas, using a solid matrix of ashes obtained from a central heating plant fed by wood. Biomethane composition was studied in an experimental pilot plant that treats organic waste through dry anaerobic digestion. European limits were considered and respected for the biomethane injection into the gas grid. The process was able to completely remove carbon dioxide (CO2) during its initial phase. After 50 h of test CO2 concentration started to appear in the outlet gas. This behaviour is related to the ash content, reactive phases (e.g., Ca hydroxides) and fine particle size (

The main goal of this paper is to assess and compare three hybrid systems for the production of synthetic natural gas (biomethane) from biogas or process gas. Mathematical models were built to determine the main performance indicators and plant efficiency of the proposed solutions, such as mass and energy flows and gas composition in characteristic points of the systems, as well as the efficiencies of the full chains. The carbon footprint of the three approaches was calculated using a streamlined life cycle assessment. The results show that both methanation cases may be an interesting option for SNG production and energy storage. The energy efficiency of the solutions reaches a value of 84% for Case 1 (methanation from syngas) and 90% for Case 2 (methanation of biogas) and 3 (biogas upgrading), respectively. If the manure credit is accounted for emissions, the carbon footprint of biomethane from Case 3 is the lowest.

Biogas production by anaerobic digestion (AD) of organic wastes is important for the transition to fossil free fuelsin both the transport sector, industries and shipping. The aim of this study was to target the residual organicmatter in the outgoing residue from the AD process, so called digestate, with different thermal treatmentmethods in order to improve digestate degradability and biogas potential upon post-digestion. The thermaltreatment was performed at 55 ◦C in 24 h, 70 ◦C in 1 h and by thermal hydrolysis process (THP; 165 ◦C, 8 bar in0.33 h), and were carefully selected to offer a simultaneous possibility for pasteurization of the digestate accordingto the regulations in Sweden. Digestates from ten full-scale biogas plants were collected, with differentsubstrate profiles including wastewater treatment plant (WWTP), food waste digestion, agriculture digestion andmanure digestion. The results showed that all thermal treatment methods caused increased dissolved organiccarbon concentration (DOC). Four of the thermal treated digestates with the highest increase in DOC weresubsequently tested for the bio-methane potential. Thermal treatments at 70 ◦C and THP, respectively, resulted inthe highest increase in bio-methane potentials, with an increase of 15–39% for one WWTP, 38 – 40% fordigestate from an agriculture digestion plant and 20 – 22% for digestate from a co-digestion plant treating foodwaste. Interestingly, the bio-methane potential from digestate treated with the energy-intense THP method, didnot show any significant difference compared to thermal treatment at 70 ◦C for 1 h. The outcomes of this studysuggest that placing a pasteurization unit between a main digester and a post digester, when applying two-stepdigestion allows for a combined pasteurization and increased biogas production. Funding: Swedish Energy AgencySwedish Energy AgencyMaterials & Energy Research Center (MERC) [35624-2]; Tekniska verken i Linkoping AB

In this study, adsorbents were self-assembled using CuO-loaded hollow microspheres. Adsorption tests for H2S in biogas were performed at room temperature under dry atmosphere. The specific surface area of the adsorbent is 270 m2/g, with an adsorption capacity as high as 51.87 mg H2S/g, attributed to the well-developed adsorbent pore volume of 0.932 cm3/g, wherein mesopores and macropores accounted for 99.14%. In addition, nano-CuO, with a particle size of 5.34 nm, is evenly dispersed on the whiskers of the hollow spheres. These factors provide a good environment for H2S adsorption from biogas. The regeneration rate of the adsorbent after the third and fifth regenerations was approximately 80% and 60%, respectively, suitable for the removal of H2S from biogas at room temperature under dry atmosphere.

Hydrogen is currently receiving attention as a possible cross-sectoral energy carrier with the potential to enable emission reductions in several sectors, including hard-to-abate sectors. In this work, a techno-economic optimization model is used to evaluate the competitiveness of time-shifting of electricity generation using electrolyzers, hydrogen storage and gas turbines fueled with hydrogen as part of the transition from the current electricity system to future electricity systems in Years 2030, 2040 and 2050. The model incorporates an emissions cap to ensure a gradual decline in carbon dioxide (CO2) levels, targeting near-zero CO2 emissions by Year 2050, and this includes 15 European countries. The results show that hydrogen gas turbines have an important role to play in shifting electricity generation and providing capacity when carbon emissions are constrained to very low levels in Year 2050. The level of competitiveness is, however, considerably lower in energy systems that still allow significant levels of CO2 emissions, e.g., in Year 2030. For Years 2040 and 2050, the results indicate investments mainly in gas turbines that are partly fueled with hydrogen, with 30–77 vol.-% hydrogen in biogas, although some investments in exclusively hydrogen-fueled gas turbines are also envisioned. Both open cycle and combined cycle gas turbines (CCGT) receive investments, and the operational patterns show that also CCGTs have a frequent cyclical operation, whereby most of the start-stop cycles are less than 20 h in duration.

The effects of organosolv, hydrothermal, combined organosolv, and hydrothermal processes followed by enzyme pretreatment on Napier grass and silage were evaluated for their efficacy in enhancing methane production. The pretreatment of Napier grass and silage by organosolv followed by enzymatic hydrolysis significantly improved methane yields by 1.9–2.0 times compared with untreated Napier grass and silage. In addition, organosolv-treated Napier grass followed by enzymatic hydrolysis yielded 7.8% more methane (410 mL/g-volatile solidadded (VSadded)) than organosolv-treated silage followed by enzymatic hydrolysis (378 mL/g-VSadded). Organosolv pretreatment enhanced lignin removal, while hydrothermal pretreatment effectively hydrolyzed hemicellulose. Delignification and reduction of crystallinity during organosolv improve the degradability of Napier grass and silage, resulting in their significantly higher energy recovery of 14.8 and 13.6 kJ/g-VSadded, respectively, which were higher than the energy recovery attained from the hydrothermal process.

Upgrading CO2/CH4 enriched biogas effluents, especially from landfills, is a viable route towards simultaneously generating renewable methane for energy production and purified carbon dioxide for industries like oil and gas, whose main use is enhanced oil recovery. Pelletized basic immobilized amine sorbents (BIAS) previously utilized for post-combustion CO2 capture are prime candidates for CO2 removal from landfill gas (inherent CH4 enrichment) because of the pellets' high CO2 selectivity and tunability for optimized performance at different temperatures and gas compositions. This work examines the process parameters and material properties that are key in the production scale-up of our previously developed polychloroprene latex-polyethylenimine (PEI, MW = 25,000) binder/silica-fly ash pellet supports. Thicker pastes with aqueous binder solution/powder ratios between 2.9/1 and 3.24/1 exhibited average storage moduli of G' ≥ 9.5 × 106 ± 1.2 × 105 Pa and were easily prepared then transformed into separable cylindrical ropes via a lab-scale mixer-extruder machine. The dried supports displayed good crush strength and a > 98% efficient amine impregnation. Pellets containing 32 wt% PEI800/N-N-diglycidyl-4-glycidyloxyaniline crosslinker (1/0.13 wt. ratio) showed a high 1.95 mmol CO2/g capture from simulated landfill gas (60% CO2/39% CH4/1% O2) at 75 °C that dropped

Anaerobic digestion is one of the most preferred methods for sludge treatment in wastewater treatment plants. Though it is widely used because of its potential to generate renewable energy (biogas), there are some limitations in its efficient operation. The solubilization of sludge is identified as a very slow rate reaction and because of that higher volume of sludge digester is required for sludge treatment and is been identified as one of the main problems. This problem has been addressed by various pre-treatment methods. Nano materials-based pre-treatment was also attempted to enhance the solubilization of sludge and ultimately to improve the bio-methanation efficiency of sludge digesters. Recent studies have shown that nano particles of metallic oxides have aided in enhancing the methane generation and nano particles of iron oxides and hydroxides have shown a positive effect on the methane generation rate. This mini-review aims to summarize the recent advancements in nano particles of iron oxides and hydroxides as an additive, elucidate the various effects of parameters affecting the sludge treatment and thereby enhance the bio-methanation. This article is also supported with a preliminary study to examine the effect of granulated nanoscale oxyhydroxides of Fe (GNOF) in the sludge solubilization rate and overall effect on the sludge digestibility of a lab scale anaerobic reactor fed with waste activated sludge. The study was conducted for hydraulic retention time (HRT) of 40 days and 20 days. The treated samples were analyzed for pH, volatile fatty acids (VFA), alkalinity, and SCOD. The results showed a positive impact of GNOF in the sludge solubilization and subsequent anaerobic digestion. The work presented in this review would help to advance the knowledge and ultimately helps in improving the bio-methanation efficiency of anaerobic digesters.

If appropriate landfill utilisation technologies were implemented, landfills on the African continent could be a source of energy for domestic and commercial use instead of their current status as environmental and health hazards. The present study reviewed 59 research publications authored from 2004 to 2021 on existing landfills technologies. These technologies are currently implemented in some African countries and are considered viable for developing landfill-based biogas generators. It emerged from the review that very little waste to energy conversion is happening in African landfills. The current technologies are too expensive for most African countries. However, it is clear that there is potential to develop landfill-based biogas generators that are optimal for the peculiarities of African landfills and dumpsites.

In the present work, effect injection timing (IT) on the modified dual fuel (DF) engine performance with effective utilization of biodiesel and gaseous fuel combinations is reported. Biodiesel prepared Ceiba Pentandra oil called Ceiba Pentandra oil methyl ester (CPNTOME) and its B20 blend (CPNTOME B20) are used as pilot injected fuels while the biogas (raw and purified) is used as the inducted fuel in the modified DF engine. Hence, the present research focus on the study of DF engine performance fuelled with liquid and gaseous fuel combinations. Meanwhile, the effect of IT on modified DF engine performance is investigated. Brake thermal efficiency (BTE), carbon monoxide (CO), hydrocarbon (HC) and smoke emissions were found to be less besides higher emissions of NOx were observed. Combustion parameters such as ignition delay (ID), and peak pressure (PP) are analysed. The DF engine operated on renewable fuel combinations in DF mode can cover the way for partial substitution of fossil fuel along with reduction in greenhouse gas emissions. Advancing the IT improves the DF engine performance and reduces the smoke, CO and NOx emissions.

In this study, a thermodynamic and economic analysis of a synthetic fuel production facility by utilizing the hydrogenation of CO2 captured from biogas is carried out. It is aimed to produce methanol, a synthetic fuel by hydrogenation of carbon dioxide. A PEM electrolyzer driven by grid-tie solar PV modules is used to supply the hydrogen need of methanol. The CO2 is captured from biogas produced in an actual wastewater treatment plant by a water washing unit which is a method of biogas purification. The required power which is generated by PV panels, in order to produce methanol, is found to be 2923 kW. Herein, the electricity consumption of 2875 kW, which is the main part of the total electricity generation, belongs to the PEM system. As a result of the study, the daily methanol production is found to be as 1674 kg. The electricity, hydrogen and methanol production costs are found to be $ 0.043 kWh−1, $ 3.156 kg−1, and $ 0.693 kg−1, respectively. Solar availability, methanol yield from the reactor, and PEM overpotentials are significant factors effecting the product cost. The results of the study presents feasible methanol production costs with reasonable investment requirements. Moreover, the efficiency of the cogeneration plant could be increased via enriching the biogas while emissions are reduced.

Over the last few years, a paradigm shift has emerged towards a circular economy that seeks to return to the process as many material/energy flows as possible to increase the sustainability of products, reducing waste and pollution. The citrus industry is not an exception hence one way to apply this approach is through the re-use of certain outflows to produce bioproducts and bioenergy. The objectives of this work are, first, to present the environmental profile of lemons and derivatives in Argentina through the Life Cycle Assessment methodology, and second, to unveil environmental implications of shifting from traditional industries to biorefineries which apply circular economy principles. To do that, the current production scheme for manufacturing essential oil, concentrated juices and dehydrated peel is studied (baseline), to then consider new products, i.e., ethanol, limonene and biogas, through several scenarios with different degrees of biogas recirculation. We find that for lemon production, agrochemicals represent more than 60% in eleven of the twelve impact categories. For processed products, agriculture contributes with more than 50% in all the categories, followed by natural gas and electricity consumption. It also results that adding value to wastes and implementing circular economy strategies do not ensure a better environmental performance of the system. When comparing the current situation with biorefinery schemes, the most promising scenario is the one in which all the biogas is used to produce electricity, causing the least impact in eight of the twelve categories analyzed.

A novel single-reactor system having entrapped anaerobic microorganisms has been developed to co-produce H2 and CH4. pH is one of the key operating and environmental parameters affecting the performance of a bio-system. This work aimed to investigate the pH shock effects on the novel biohythane system. The experiments were suddenly changing the original cultivation pH value of 6 into 4, 5, 7 or 8 for 4 h. The results indicate that a short pH shock could be used to regulate H2/CH4 composition without notably affecting biogas yield and chemical oxygen demand (COD) removal. Peak biohythane production was obtained after the pH shock to 8, having H2/CH4 yields of 11.5 ± 1.6/44.8 ± 3.1 mL/g COD. During pseudo steady-state conditions of effective cultivation periods, the values of H2 content in biohythane and COD removal efficiency were in ranges of 20–39% and 71–79%, respectively. The significances and applications of the experimental results have been discussed. The novelty of this work is elucidating a less-discussed field-operation problem of pH perturbances for a newly-developed biohythane system.

Domestic biogas technology is a promising source of renewable energy for cooking in developing countries. It is popular in Nepal's rural and peri-urban areas and can be scaled-up to replace solid fuel cookstoves. This study focused on the technical assessment of installed biogas plants such as structural components, pipelines and valves, stove and burner, biogas production and utilization, and effluent disposal system in 303 homes in Kavre district, Nepal. Furthermore, it evaluated the feedstock material's physical and chemical parameters to ascertain their implications on biogas production. The plants' problems were mainly due to faulty components and lack of proper operation and maintenance. About 18% of plants were nonfunctional, out of which 9% of the plants were damaged due to the 2015 mega-earthquake. The highest number of damages was found in the mixture of the inlet structure. About 55% of mixtures were nonfunctional. Almost 77% of users used cow dung and toilet waste either individually or in combination with animal urine as feedstock materials in the digester. The Carbon: Nitrogen (C: N) ratio of feedstock materials ranged from 5:1–24:1, with only 4% of samples measuring C: N greater than 20:1. Similarly, pH (7.7) levels were on the higher side.

This article presents some of the main findings from the SDEWES conferences of 2021 within the field of renewable energy. More specifically, results are summarized and contextualised within solar energy and thermal comfort, wind power resource assessment, and biogas and biomass resources and technology. The two last sections deal more broadly with energy systems and energy systems transition issues; the systems analyses used to design complex renewable energy systems and the investment strategies and barriers associated with the transition. This article presents some of the main findings from the SDEWES conferences of 2021 within the field of renewable energy. More specifically, results are summarized and contextualised within solar energy and thermal comfort, wind power resource assessment, and biogas and biomass resources and technology. The two last sections deal more broadly with energy systems and energy systems transition issues; the systems analyses used to design complex renewable energy systems and the investment strategies and barriers associated with the transition.

In this work, Ni-M-Al (M = K, Na, and Li) LDH-derived catalysts were evaluated for the biogas dry reforming. The catalysts were prepared by co-precipitation and characterized by SBET, XRD, TPR, NH3-TPD, CO2-TPD, SEM and TPO. Reactions were carried out in a fixed bed reactor with online GC analysis in step-wise mode in the range of 500–750 °C and the stability tests were performed at 700 °C. All prepared samples exhibited hydrotalcite-type structure. Differences in reducibility and in the acidity of oxides were observed. The acidity of the catalyst was in the order: NiLi > NiNa > NiK, which is in the opposite order of monovalent cation size. The NiLi catalyst showed the highest resistance to sintering during the reactions due to the higher reduction temperature of mixed oxides (Ni2AlO4 and NiAl2O4) which results in smaller Ni° crystallite size after reduction. The results at 700 °C showed that NiLi catalyst deactivation occurs mainly by carbon deposition, whereas the deactivation of NiK and NiNa catalyst occurs mainly by sintering. TPO results indicated different carbon species produced depending on how the reaction is performed. All the catalysts produced carbon nanotubes at 700 °C.

In this study, combined effect of ozonolysis (Oz) and temperature on rice straw (RS) hydrolysis was studied. At ozone dosage of 0.006 gO3/g RS, 19% disintegration in the RS fiber crystallinity was observed with 17% reduction in the total carbon content. Thermal (55 °C, 4d) treatment followed after Oz showed the generation of total volatile fatty acids (VFAs) and reducing sugars of 537.20 ± 17.09 mg/L/d and 1.18 ± 0.06 mg/L/d, respectively. Biomethane assays after pretreatment of RS showed 26% enhancement in the RS hydrolysis rate constant (k = 0.1885 d−1) with methane yield of 374 ± 6 ml CH4/g-VSsubstrate. The potential scale up feasibility was estimated by calculating net energy balance. A net positive gain of 0.5763 kWh/kg RS was obtained using this pretreatment.

In this paper, a hybrid renewable power plant with a storage system is designed. The benefits of sizing and energy management are assessed for a commercial building under eight different climatic conditions in the United States. In the considered system, photovoltaic panels are coupled to a unitized regenerative solid oxide fuel cell. The use of biogas to feed unitized regenerative solid oxide fuel cell is investigated, employing a detailed electrochemical model of electrolyzer and fuel cell modes. A battery pack is included in the plant as a secondary storage system, together with a diesel engine operating in backup mode. Four scenarios where biogas amount is varied together with the initial state of charge of the battery were evaluated. Results demonstrate that the power plant can operate with 100 % renewable procurement if the digester produces from 6000 to 9500 stdm3/y and the battery is completely charged at the beginning of the year. By reducing the biogas availability or starting with a low state of charge, the use of the diesel generator is inevitable. The study confirms that the proposed hybrid renewable power plant is technically feasible and can be considered a reliable and clean energy source in other areas and buildings.

This study investigated electrokinetic assisted anaerobic digestion of spent mushroom substrate supplemented with sugar mill wastewater for enhanced biogas production. Response surface method and artificial neural network tools were used to optimize the reactor performance. Findings showed that the best reactor performance was achieved at a temperature of 34.52 °C, a direct electric current of 1.61 V, and sugar mill wastewater loading of 59.61%, while the highest observed biogas yield and methane contents were 10344 mL and 63.05%, respectively. Moreover, amongst the different control parameters, sugar mill wastewater loading showed the most significant (P 117.588 and 97.253), and model efficiency (

The need for clean energy and fossil fuel depletion are the reasons behind the increasing tendency to utilize renewable energy resources. Biogas as the final product of anaerobic fermentation of some sources including animal waste, could be used in distributed electricity generation. This paper presents a mixed linear programming model for designing and planning of electricity production supply chain from animal manure. The proposed model determines the optimum locations for establishing facilities, optimum capacity level, and material flow throughout the supply chain. Multiple suppliers, collection centers and production centers, and multi-period conditions are considered in the proposed model. The proposed model is applied in a real case of Iran including all its 30 provinces for 10 years planning horizon. The achieved results confirm the capability of the proposed model in efficient design of electricity production chain network.

Carbon dioxide and hydrogen sulfide are the main contaminants in biogas, which reduce its calorific value and cause wear on metallic appliances through corrosion. There are no comparative studies on the potential of dry adsorption and wet wood ash (carbonation) process on biogas upgrade. The current study for the first time investigates the effects of different process parameters on the use of wood ash for purification of biogas and compares the performance of the two processes. The chemical composition of wood ash was characterized using X-ray fluorescence (XRF) while biogas was analysed using gas chromatography and a digital biogas analyser. The effects of process parameters on biogas carbonation method were investigated. The highest CO2 uptake and methane increment achieved by use of wood ash slurry was 2.30 mmol/g-wood ash and 88%, respectively. This high CO2 uptake was possibly due to the high content of oxides (46% TS) in natural wood ash. The optimum conditions of adsorbent/water ratio and biogas flow rate for methane enhancement were 1:4, and 100 ml/min, respectively. In dry adsorption processes, an increase in mass of activated wood ash from 2.5 to 35 g increased CO2 removal from 8.9 to 67.9%. Furthermore, the evaluation of carbonation adsorption indicated that the process followed pseudo-first order kinetics. Activation of wood ash did not significantly improve its CO2 uptake by carbonation while the uptake by activated wood through dry adsorption was comparable to that of raw wood ash through carbonation process. Conclusively, raw wood ash by carbonation process is a good candidate recommendable for purifying biogas in household digesters.

To identify an early warning indicator for the anaerobic digestion of chicken manure and reveal a microbial mechanism of instability, a bench-scale digester with a working volume of 55 L was utilized by raising the organic loading rates (OLRs). Three characteristics were identified and posited as early warning indicators, namely: one-way changes, a longer early response time, and sudden variations. The core early warning indicator set was constructed, which included the oxidation-reduction potential (ORP), individual volatile fatty acids, and CH4/CO2. Considering the convenience, economic nature, and reliability of industrial biogas plants, the ORP was recommended as a final early warning indicator with an inhibition threshold of > −540 mV. The initial instability was caused by the accumulation of ammonia, which suppressed methanogenic activity, although it stimulated the growth of Methanosarcina. The accumulation of free volatile fatty acids, which inhibited both the growth and methanogenic activity of Methanosarcina, was responsible for the final collapse.

The aim of this study is to evaluate the most suitable operating conditions for anaerobic co-digestion processes with high replacement rates (64% on average) of dedicated crops (silage of maize and triticale) with residual biomass, represented by a mixture of whey (scotta), pitted olive pomace, olive mill wastewater, and sheep manure. Experimental trials were first carried out at pilot plant scale and then at industrial plant scale. Univariate and multivariate statistical analysis demonstrates that almost 70% of the dedicated crops, ordinarily used in industrial scale anaerobic digestion plants, can be replaced by a mixture of residual biomass, available on the territory, without a reduction in performance. Compared to the industrial plant, the pilot plant shows much higher values of biogas production rate and specific production rates for both biogas (about 0.64–0.86 Nm3/kgVS vs 0.35 Nm3/kgVS) and methane (about 0.30–0.43 Nm3/kgVS vs 0.20 Nm3/kgVS). With reference to a case-study of the Sardinia island, the use of all available biomass residues in existing and new anaerobic digestion plants can provide a production of more than 160 million Nm3/y of biogas, that corresponds to about 87 millions Nm3/y of biomethane, that is about 20% of the forecasted natural gas demand of the island.

The palm oil industry is gearing itself towards sustainability by implementing mandatory biogas capture for all palm oil mills in the effort to reduce greenhouse gases. This action also indicates that the anaerobic digestion of palm oil mill effluent (POME) will be one of the essential sources of biogas for energy generation. However, the availability of POME is limited during the low crop season due to the lower palm oil production. Concurrently, the solid wastes known as empty fruit bunches (EFB) are also produced from the oil mill. EFB has vast potential for power generation, though it is currently not being fully utilized. Therefore, this work aims to enhance the biogas production from anaerobic co-digestion (ACD) of EFB with POME by evaluating the effect of alkaline pretreatment of EFB, EFB-to-POME ratio, and temperature on the methane yield. The optimum EFB:POME ratio is 0.6:1 as the methane production of this ratio at both thermophilic and mesophilic conditions are relatively high (up to 74.02 ml CH4/g VS). Results show that ACD performs 2.36 times better than mono-digestion of POME at mesophilic conditions. The modified Gompertz model could predict the process behavior of the ACD of EFB with POME with high R2 (>0.95). Further investigation on other potential pretreatment methods and synergism analysis of co-digestion, which provides a balance between efficiency and economy could be carried out. The impact of this work will be towards a sustainable environment, which will significantly reduce the environmental impacts of palm oil production.

Renewable energy resources are critical for reducing poverty and addressing the energy shortage. Renewable energy technologies have been slow to gain traction in Bangladesh. This study examines the factors that influence biogas adoption and the effects on income and poverty levels. A total of 400 respondents were surveyed to achieve the objectives. The data were analysed using descriptive statistics and a set of econometric models. According to the results, approximately one-third of the respondents used biogas technology. Respondents’ perceptions of reduced cooking fuel costs and modern communication technologies such as internet connectivity and mobile phone use played a major role in their adoption decision. The likelihood of adoption is 11.9 per cent and 56.7 per cent higher for those who have access to the internet and mobile phone compared to their counterparts. Adopters of biogas have between 13 and 27 per cent higher per capita household income than non-adopters. Based on radius matching, the household poverty gap is approximately 16 per cent lower for biogas adopters than non-adopters. Modifying the extension approach through the use of modern communication techniques can help achieve widespread adoption. The availability of capital may play a vital role in adoption. There is a need to promote the role of biogas technology in anti-poverty programmes in Bangladesh.

The current paper illustrates the numerical study of the global combustion parameters. It mainly focused on the computational analysis that investigated the non-premixed combustion in the cylindrical burner. Therefore, we selected many fuels to supply the burner like Algerian biogas, CH4, C 3 H8, H 2 , natural gas, and diesel to compare their aerothermochemical characteristics variables. At first, we applied the numerical methods that confirm the solution convergence like combustion models and grid selection. After that, we resolved the aerothermochemical set equations of combustion using the coupled k- e turbulent dynamic model with the probability density function approach. These models are also used to surmount the closer in the set of combustion equations too. Moreover, we integrated the pollutant computation model based on the chemical reactions of NO production. Thus, we evaluated each considered fuel’s NO emission during all combustion fuels cases. Accordingly, the results show that Algerian biogas and hydrogen have special characteristics compared to other cases of fuels. The most prominent characteristics are: the high level of the mixture and burn relative to other fuels, their low pollutants emissions (CO and NO), and the proportional relationship between the OH and NO production. Consequently, biogas and H 2 conserve the impact on energy and the environment.

International audience; The increase in anaerobic digestion systems has profoundly affected the waste management of territories, particularly for agricultural systems. Changes in cultural practices and imports of organic waste modify the carbon (C) and nitrogen (N) fluxes on territories where anaerobic digestion is implemented. Successful anaerobic digestion can increase the economic and ecological efficiency of the waste management system. Conversely, poor anaerobic digestion leads to low economic and environmental efficiency due to greenhouse gas emissions and nutrient loss. Modeling the impact of anaerobic digestion on the systems integrating anaerobic digestion can improve the efficiency of these practices. The aim of this study was to develop, analyze, and evaluate a simple mass balance tool able to predict carbon and nitrogen fluxes in anaerobic digestion systems. The tool is composed of an exhaustive substrate database used by three models: (i) an anaerobic digestion model that predicts C and N contents in biogas and digestate; (ii) a phase separation model that predicts C and N content in liquid and solid phase digestates; and (iii) a storage model that predicts C and N content in raw, liquid phase, and solid phase digestates, as well as C and N emissions during storage. Sensitivity analyses were performed on the tool to determine critical inputs. Sensitivity analysis showed that outputs were highly sensitive to their respective inputs and to total inputs of solids. Performance evaluation showed that the tool can provide good quality predictions with R-2 correlations between observation and prediction varying from 0.72 to 0.99 with the best predictions obtained for raw digestate.

The main aim of anaerobic co-digestion of rice straw is to enhance volumetric methane yields and process stability to achieve synergetic effects. However, high carbon to nitrogen ratio of rice straw causes poor process stability for mono-digestion. This study investigated the co-digestion of rice straw and de-oiled rice bran, a nitrogen-rich by-product of the rice milling industry. The spent bio-slurry (having total solids concentration of 2.19%) from running de-oiled rice bran which inherently contains various types of microbes was used as an inoculum for process start-up. A series of experiments were conducted to optimise the methane yield in semi-continuous anaerobic digester operating at 30 days of hydraulic retention time at mesophilic temperature conditions. Co-digestion studies of rice straw and de-oiled rice bran with three different mixing ratios were conducted by maintaining a specific total solids concentration of 5.0, 7.5, and 10.0% total solids concentration for the designated digester. The biogas production, methane contents, volatile matter degradation efficiency were determined to evaluate the stability and performance of the system. The digester maintained at 5% and 7.5% TS showed nearly similar results in terms of methane yield and volatile matter conversion efficiency. During the entire experimentation the percentage of methane content in the produced biogas was in the range of 24.8–55.4%. The average methane yield of 0.169 and 0.173 L/g-VS was found for digester maintained at 5.0% and 7.5% TS respectively. However, the volatile solid mass removal efficiency of 40.13% and 37.94% was recorded for the digester maintained at 5% and 7.5% TS respectively. Since no chemical or thermal pre-treatment was adopted during the entire process it is highly economical and adaptable for concerned industries. Ultimately, the results of the present study were compared to the previous studies on anaerobic co-digestion of RS, which shows the promising result with no extra added input cost.

One of the important goals in today's world is sustainable power generation by using low or zero polluting fuels and energy conversion devices. In this context, utilization of gaseous fuels in internal combustion (IC) engines is focused more due to their better fuel mixing ability with air, higher combustion efficiency, easier transportation, and lower pollutant formation. Liquefied petroleum gas (LPG), compressed natural gas (CNG), hydrogen, and biogas are considered as commonly available alternative gaseous fuels for IC engines. Yet, a search for other possible alternative gaseous fuels is continuing in the world. In recent years, Oxy-hydrogen (HHO) also known as Brown's gas has been explored by many researchers in the world, for the possibility of using it for heat and power applications. Because of this, a comprehensive review of the production of HHO using different generators and its utilization in heat and power applications has been carried out, and the discussions are presented in this paper.

The main drawback of heating biogas digestion systems based on solar energy is its unavailability overnight and at different times (days and months). To circumvent this problem, a hybrid system(solar and electricity) powering the heat digester could provide the required mesophilic conditions. The present study aimed to evaluate the technical and design feasibility of using solar energy to assist in heating the digestion units. Also, measured and determined the contribution of solar energy to heat the system. This study was conducted in the central area of Coastal Delta, Egypt (30.5 ∘ N, 30.6 ∘ E; 8.5 m a.s.l.). Results show that the contribution of solar energy to biogas production was 75.21%, 60%, and 53.58% when using three settings temperature of (37, 40, and 45 °C) of the energy consumed via cattle dung solution heating. Furthermore, increasing the set temperature inside the horizontal and vertical digesters from 37 °C to 45 °C augmented their daily average volumetric biogas production by 87.12% and 59.45%, respectively. Finally, the current study says that solar energy has reduced energy consumption by 61.28%. Also, the economic analysis indicates that the estimated return profit was $ 177.41 (USD), which represents 45.15% of the total income per operation.

The accelerated chemical-industry has caused a rapid increase of calcium-containing alkali wastes, containing a large amount of calcium, magnesium, aluminum, and iron ions and caused a great risk to environment. Anaerobic digestion or dark fermentation is one of the most promising technologies to recover biogas, such as methane and hydrogen. Nevertheless, the hydrolysis processes of lignocellulosic biomass and waste activated sludge were the rate-limiting step of the biochemical reactions, which focused on pretreatment to improve the biodegradability of substrate. In addition, when some easily acidified wastes, such as kitchen residue, fruit and vegetable waste, and high concentration organic wastewater, are used as substrate to produce hydrogen and methane, volatile fatty acid accumulation often occurs, causing the process instability. Thus, this paper reviewed the main roles of calcium-based alkali materials such as calcium oxide, calcium peroxide and calcium hydroxide on the substrate pretreatment for obtaining high biodegradability, while others (e.g. calcium carbonate, lime and red muds) used as additives for maintaining process stability, thereby increasing biogas yield from anaerobic digestion and dark fermentation.