Search Results (12)

The agricultural industry produces a substantial quantity of organic waste, and finding a suitable method for disposing of this highly biodegradable solid waste is a difficult task. The utilisation of anaerobic digestion for agricultural waste is a viable technological solution for both renewable energy production (biogas) and waste treatment. The primary objective of the study was to assess the composition of biogas, namely the percentages of methane, carbon dioxide, ammonia, and hydrogen sulphide. Additionally, the study aimed to quantify the amount of biogas produced and determine the methane yield (measured in NmL/g VS) from different agricultural substrates. The biochemical methane potential (BMP) measurements were conducted in triplicate using the BPC Instruments AMPTS II instrument. The substrates utilised in the investigation were chosen based on their accessibility. The substrates used in this study comprise cattle manure, chicken manure, pig manure, tomato plants, tomatoes, cabbage, mixed fruits, mixed vegetables, dog food, and a co-digestion of mixed vegetables, fruits, and dog food (MVMFDF). Prior to the cleaning process, the makeup of the biogas was assessed using the BIOGAS 5000, a Geotech Analyser. The AMPTS II flow cell automatically monitored and recorded the volume of bio-methane produced after the cleaning stage. The data were examined using the Minitab-17 software. The co-digestion of mixed vegetables, mixed fruits, and dog food (MVMFDF) resulted in the highest methane level of 77.4%, followed by mixed fruits at 76.6%, pig manure at 72.57%, and mixed vegetables at 70.1%. The chicken manure exhibited the greatest levels of ammonia (98.0 ppm) and hydrogen sulphide (589 ppm). Chicken manure had the highest hydrogen sulphide level, followed by pig manure (540 ppm), tomato plants (485 ppm), mixed fruits (250 ppm), and MVMFDF (208 ppm). Ultimately, the makeup of biogas is greatly affected by the unique qualities of each substrate. Substrates containing elevated quantities of hydrogen sulphide, such as chicken manure, require the process of biogas scrubbing. This is because they contain substantial amounts of ammonia and hydrogen sulphide, which can cause corrosion to the equipment in biogas plants. This emphasises the crucial need to meticulously choose substrates, with a specific focus on their organic composition and their capacity to generate elevated methane levels while minimising contaminants. Substrates with a high organic content, such as agricultural waste, are optimal for maximising the production of methane. Furthermore, the implementation of biogas scrubbing procedures is essential for efficiently decreasing carbon dioxide and hydrogen sulphide levels in biogas. By considering and tackling these problems, the effectiveness of biogas generation can be enhanced and its ecological consequences alleviated. This strategy facilitates the advancement of biogas as a sustainable energy source, hence contributing to the attainment of sustainable development goals (SDGs). Full article

One of the byproducts of sugarcane bagasse combustion in sugarcane mills is sugarcane bagasse ash (SCBA), which contains up to ~40 mass% of organic matter. Currently, SCBA is partially used as a soil fertilizer. However, SCBA’s poor content of minerals, which are required by soils, restricts its use in soils, resulting in the disposal of large amounts of SCBA in landfills. Alternatively, SCBA has shown promise for some environmental applications such as wastewater treatment, but its use in gas cleaning deserves further study. The objective of this work was to assess the use of as-received SCBA to remove hydrogen sulfide (H₂S) from biogas, thus, to add value to the ash. The experimental procedure consisted of passing biogas containing H₂S through a column with SCBA and monitoring the H₂S content inline by employing a gas chromatograph until the concentration of H₂S, measured after the column, was ~10% of the original concentration. The breakthrough time of the SCBA adsorption curve was ~75% the breakthrough time observed with activated carbon, showing that SCBA could be a cheap alternative to commercial materials that are currently used for biogas scrubbing. This result could positively impact ethanol sugarcane mills that need to clean biogas produced from vinasses, as part of a strategy to integrate biogas production and cleaning operations using low-value residues (i.e., vinasses and ash). SCBA’s capacity for removing H₂S from biogas results from the presence of K-compounds (e.g., K₂SiO₃ and K₂Si₂O₅) on the ash’s surface and its relatively high porosity. Additionally, S-enriched SCBA (due to H₂S retention) can expectedly be more beneficial to soils than directly adding the ash since S is an essential nutrient for the growth of plants. Full article

Energy driven technologies and enhanced per-capita waste production have led to the establishment of novel technologies to simultaneously produce fuels as well as treat the wastes. Anaerobic digestion is cost-effective and sustainable process to produce biogas. Biogas is a mixture of CO₂, CH₄, H₂S, is an eco-friendly and inexpensive renewable biofuel. This mixture of gases restricts biogas utilization in vehicular fuel, CHPs, therefore, biogas upgradation becomes a necessary step. Conventional upgradation technologies for example water scrubbing, physical adsorption, chemical adsorption, amine scrubbing, etc. are cost intensive and require high maintenance. Novel technologies like biological methods of biogas upgradation are being investigated and new improvements are made in the conventional methods. This review aims to give a close insight about various technologies of upgradation including, pressure swing, amine scrubbing, membrane separation, cryogenic separation, biological methods, etc., along with the major challenges and limitations. The study also intends to provide an overview about the future perspective and scope of these technologies. Full article

One of the methods of municipal waste disposal and energy production is anaerobic digestion. This study investigates the effect of thermal and chemical pretreatment on the anaerobic digester’s biomethane production. The optimal condition was evaluated using RSM in two modes: maximum and minimum use of H₂O₂. The optimal state was obtained in the first case under 110.8 °C, 4.63% NaOH, 8% H₂O₂, and 111.9 °C, 4.47% NaOH, 2% H₂O₂ in the second case. Experimental results obtained 77%, 76.6% VS (volatile solid) reduction, and 89.1%, 88.7% SCOD (soluble chemical oxygen demand) reduction in the two optimum conditions, respectively. Experiment results were extrapolated to dry industrial digesters using a factor of 0.89% and durations including 30 days and 25 days. Then, the processes of biogas improvement were simulated. After biogas improvement, the economic analysis of the process was conducted with the definition of various scenarios. It was determined that, at current prices, pretreatment is not economically viable and that, with an increase in electricity prices to 0.09 $/kWh and 0.145 $/kWh, the digestion process with a NaOH 4.47% 112 °C pretreatment, chemical scrubbing, and digestion with NaOH 4.47% 112 °C, 2% H₂O₂ are sequentially economically viable. Full article

A proper exploitation of biogas is key to recovering energy from biowaste in the framework of a circular economy and environmental sustainability of the energy sector. The main obstacle to widespread and efficient utilization of biogas is posed by some trace compounds (mainly sulfides and siloxanes), which can have a detrimental effect on downstream gas users (e.g., combustion engines, fuel cells, upgrading, and grid injection). Several purification technologies have been designed throughout the years. The following work reviews the main commercially available technologies along with the new concepts of cryogenic separation. This analysis aims to define a summary of the main technological aspects of the clean-up and upgrading technologies. Therefore, the work highlights which benefits and criticalities can emerge according to the intended final biogas application, and how they can be mitigated according to boundary conditions specific to the plant site (e.g., freshwater availability in WWTPs or energy recovery). Full article

This work analyses the two most diffused technologies for biogas upgrading, namely water scrubbing and membrane separation. In order to carry out such analysis, these two technologies are coupled with photovoltaic panels and an electric energy storage system. The optimal water scrubbing renewable plant achieves a primary energy saving of 5.22 GWh/year and an operating cost saving of 488 k€/year, resulting in the best plant. It was compared to a reference system based on a cogenerator unit, directly supplied by biogas, producing thermal and electric energy, and delivered to the district heating network and to the electric grid. The profitability of both plants depends on the electric energy and biomethane exporting price. The proposed bigas upgrading plant achieves a payback period lower than 10 years with a biomethane selling price greater than 0.55 €/Sm³ and a primary energy saving index around 25–30% with a null share of thermal energy exported by the cogeneration plant. Full article

Biogas is one of the most important sources of renewable energy and hydrogen production, which needs upgrading to be functional. In this study, two methods of biogas upgrading from organic parts of municipal waste were investigated. For biogas upgrading, this article used a 3E analysis and simulated cryogenic separation and chemical scrubbing. The primary goal was to compare thermoeconomic indices and create hydrogen by reforming biomethane. The exergy analysis revealed that the compressor of the refrigerant and recovery column of MEA contributed the most exergy loss in the cryogenic separation and chemical scrubbing. The total exergy efficiency of cryogenic separation and chemical scrubbing was 85% and 84%. The energy analysis revealed a 2.07% lower energy efficiency for chemical scrubbing. The capital, energy, and total annual costs of chemical absorption were 56.51, 26.33, and 54.44 percent lower than those of cryogenic separation, respectively, indicating that this technology is more economically feasible. Moreover, because the thermodynamic efficiencies of the two methods were comparable, the chemical absorption method was adopted for hydrogen production. The biomethane steam reforming was simulated, and the results indicated that this method required an energy consumption of 90.48 $\frac{\mathrm{MJ}}{{\mathrm{kg}}_{{\mathrm{H}}_2}}$. The hydrogen production intensity equaled 1.98 $\frac{{\mathrm{kmole}}_{{\mathrm{H}}_2}}{{\mathrm{kmole}}_{\mathrm{biogas}}}$ via a 79.92% methane conversion. Full article

This study evaluates the effects of the varying substrate to inoculum ratios (S:I) of 0.5, 1, 2, 3, 4, 5, and 6 (volatile solids/VS basis) on the kinetics of biogas production during batch mesophilic (35 ± 1 °C) anaerobic digestion (AD) of simulated food waste (FW), using anaerobic digestate as the inoculum. Kinetic parameters during biogas production (scrubbed with NaOH solution) are predicted by the first-order and the modified Gompertz model. The observed average specific biogas yields are in descending order corresponding to the S:I ratios 1, 2, 4, 6, 3, 5, and 0.5, respectively, and the significant effect of the S:I ratio was observed. The tests with the S:I of 1 have the maximum average biogas production rates of 88.56 NmL/gVS.d, whereas tests with the S:I of 6 exhibited the lowest production rates (24.61 NmL/gVS.d). The maximum biogas yields, predicted by the first order and the modified Gompertz model, are 668.65 NmL/gVS (experimental 674.40 ± 29.10 NmL/gVS) and 653.17 NmL/gVS, respectively. The modified Gompertz model has been proven to be suitable in predicting biogas production from FW. VS removal efficiency is greater in higher S:I ratios, with a maximum of 78.80 % at the S:I ratio of 6, supported by the longer incubation time. Moreover, a significant effect of the S:I ratio is seen on kinetics and energy recovery from the AD of FW. Full article

Biogas is one of the most attractive renewable resources due to its ability to convert waste into energy. Biogas is produced during an anaerobic digestion process from different organic waste resources with a combination of mainly CH₄ (~50 mol/mol), CO₂ (~15 mol/mol), and some trace gasses. The percentage of these trace gases is related to operating conditions and feedstocks. Due to the impurities of the trace gases, raw biogas has to be cleaned before use for many applications. Therefore, the cleaning, upgrading, and utilization of biogas has become an important topic that has been widely studied in recent years. In this review, raw biogas components are investigated in relation to feedstock resources. Then, using recent developments, it describes the cleaning methods that have been used to eliminate unwanted components in biogas. Additionally, the upgrading processes are systematically reviewed according to their technology, recovery range, and state of the art methods in this area, regarding obtaining biomethane from biogas. Furthermore, these upgrading methods have been comprehensively reviewed and compared with each other in terms of electricity consumption and methane losses. This comparison revealed that amine scrubbing is one the most promising methods in terms of methane losses and the energy demand of the system. In the section on biogas utilization, raw biogas and biomethane have been assessed with recently available data from the literature according to their usage areas and methods. It seems that biogas can be used as a biofuel to produce energy via CHP and fuel cells with high efficiency. Moreover, it is able to be utilized in an internal combustion engine which reduces exhaust emissions by using biofuels. Lastly, chemical production such as biomethanol, bioethanol, and higher alcohols are in the development stage for utilization of biogas and are discussed in depth. This review reveals that most biogas utilization approaches are in their early stages. The gaps that require further investigations in the field have been identified and highlighted for future research. Full article

Hydrogen sulfide (H₂S) is a corrosive trace gas present in biogas produced from anaerobic digestion systems that should be removed to reduce engine-generator set maintenance costs. This study was conducted to provide a more complete understanding of two H₂S scrubbers in terms of efficiency, operational and maintenance parameters, capital and operational costs, and the effect of scrubber management on sustained H₂S reduction potential. For this work, biogas H₂S, CO₂, O₂, and CH₄ concentrations were quantified for two existing H₂S scrubbing systems (iron-oxide scrubber, and biological oxidation using air injection) located on two rural dairy farms. In the micro-aerated digester, the variability in biogas H₂S concentration (average: 1938 ± 65 ppm) correlated with the O₂ concentration (average: 0.030 ± 0.004%). For the iron-oxide scrubber, there was no significant difference in the H₂S concentrations in the pre-scrubbed (450 ± 42 ppm) and post-scrubbed (430 ± 41 ppm) biogas due to the use of scrap iron and steel wool instead of proprietary iron oxide-based adsorbents often used for biogas desulfurization. Even though the capital and operating costs for the two scrubbing systems were low (<$1500/year), the lack of dedicated operators led to inefficient performance for the two scrubbing systems. Full article

Upgrading consists of a range of purification processes aimed at increasing the methane content of biogas to reach specifications similar to natural gas. In this perspective, an environmental assessment, based on the Life Cycle Assessment (LCA) method, of different upgrading technologies is helpful to identify the environmental characteristics of biomethane and the critical steps for improvement. The aim of this work is to conduct an LCA of biomethane production from waste feedstock, using the SimaPro software. The study focuses on the comparison of several upgrading technologies (namely, membrane separation, cryogenic separation, pressure swing adsorption, chemical scrubbing, high pressure water scrubbing) and the on-site cogeneration of electricity and heat, including the environmental benefits deriving from the substitution of fossil-based products. The results show a better environmental performance of the cogeneration option in most of the impact categories. The Fossil resource scarcity is the impact category which is mainly benefited by the avoided production of natural gas, with savings of about 0.5 kg oil eq/m³ of biogas for all the investigated technologies, with an average improvement of about 76% compared to conventional cogeneration. The results show that the membrane upgrading technology is slightly more environmentally convenient than the other upgrading technologies. Full article

Two-stage pressurized anaerobic digestion is a promising technology. This technology integrates in one process biogas production with upgrading and pressure boosting for grid injection. To investigate whether the efficiency of this novel system could be further increased, a water scrubbing system was integrated into the methanogensis step. Therefore, six leach-bed reactors were used for hydrolysis/acidification and a 30-L pressurized anaerobic filter operated at 9 bar was adopted for acetogenesis/methanogenesis. The fermentation liquid of the pressurized anaerobic filter was circulated periodically via a flash tank, operating at atmospheric pressure. Due to the pressure drop, part of dissolved carbon dioxide was released from the liquid phase into the flash tank. The depressurized fermentation liquid was then recycled to the pressurized reactor. Three different flow rates (0 L·day⁻¹, 20 L·day⁻¹ and 40 L·day⁻¹) were tested with three repetitions. As the daily recycled flashed liquid flow was increased from 0 to 40 L, six times as much as the daily feeding, the methane content in the biogas increased from 75 molar percent (mol%) to 87 mol%. The pH value of the substrate in the methane reactor rose simultaneously from 6.5 to 6.7. The experimental data were verified by calculation. Full article