In the present manuscript, the energy efficiency and economic feasibility of different digestion configurations were evaluated by considering a double turbocharged engine, Jenbacher type JGS ...320 GS-BL. Scenarios considered a single farm producing the biogas needed to run the engine (Scenario 1). The second scenario assumed a centralized system treating manure from the surrounding farms (Scenario 2). The third scenario considered partial decentralization with farms treating locally produced wastes, and biogas being transported and valorized in a centralized engine (Scenario 3). Centralized valorization showed the best results. However, this scheme is inappropriate due to the size of the farm needed to support this configuration. The transport of wastes to a centralized treatment unit showed similar efficiency values but the economic feasibility was adversely affected. The worst performance was found for the decentralized configuration with efficiency in the range of 39–43%, much lower values than those obtained from previous cases (58%) with null economic feasibility due to the high costs associated with the transport of biogas either by truck or through a piping system.
Display omitted
The coupling of biological and thermal technologies allows for the complete conversion of wastes into energy and biochar eliminating the problem of sludge disposal. The valorisation of fatty residues ...as co-substrate in a mesophilic digester of a wastewater treatment plant was studied considering an integrated approach of co-digestion and pyrolysis. Four digested samples obtained from co-digestion of sewage sludge and butcher’s fat waste were studied by thermogravimetric analysis. The activation energy corresponding to the sludge pyrolysis was calculated by a non-isothermal kinetic. Arrhenius activation energy was lower for the pyrolysis of a digested grease sample (92 kJ mol
−1
obtained by OFW and 86 kJ mol
−1
obtained by Vyazovkin) than for the pyrolysis of sewage sludge and its blends (164–190 kJ mol
−1
obtained by OFW and 162–190 kJ mol
−1
obtained by Vyazovkin). The analysis of the integrated approach of anaerobic co-digestion and pyrolysis of digestates demonstrated that the addition of 3% (w/v) of fat to the feeding sludge results in a 25% increase in the electricity obtained from biogas (if a combined heat and power unit is considered for biogas valorisation) and increasing the fat content to 15% allows for covering all thermal needs for drying of digestate and more than doubles (2.4 times) the electricity production when the scenario of digestion and pyrolysis is contemplated.
•Coupling a batch hydrogen producing stage in a conventional WWTP is feasible.•A 10 % addition of food waste (FW) (VS percentage) increases energy recovery by 16 %.•Modifications in digestion unit ...are unnecessary, but increasing waste addition implies higher reactor volumes.•A 50 % addition of FW produces 2.4-fold more energy, but the sludge volume increases by 24 %.
Wastewater treatment plants are essential in improving life quality by degrading organic matter, reducing contamination, and therefore greatly impacting human activities. The role of these critical treatment units can be further promoted by integrating new biological processes that currently are still under experimental scale. The co-digestion of sewage sludge and food waste has been proposed as an efficient way to increase plant treatment capacity and energy recovery. The assessment of hydrogen production along with food waste co-digestion is carried out in the present manuscript. Assessing several parameters is necessary to implement a new biological process in an operating plant, and quantifying its effects on the plant's overall performance is crucial. The implications associated with the extra equipment needed to handle additional waste material were evaluated. Results indicated that a conventional unit may treat a 10 % addition of food waste (expressed as VS) without experiencing severe modifications in process parameters, thus obtaining 16 % extra energy. However, the increase in food waste by over 10 % translates into substantial plant modifications requiring the installation of digesters with higher volumes and handling an additional amount of sludge. Another relevant factor is the lower energetic content of biogas when mixed with hydrogen. The increase in food waste until 50 % VS in the mixture reduced the biogas lower heating value to 15.5 MJ/m3. Future research will deal with an economic analysis of the approach and the effect on engine performance when dealing with a fuel mixture with different combustion properties.
Display omitted
Ammonia can be considered a relevant compound in the future energy sector, playing a significant role as an energy carrier, storage, or carbon-free fuel. However, the production of this molecule has ...a high energy demand, and the use of natural gas, which is not free of controversy due to the accidental leakage into the atmosphere produced during extraction and the fact that it is a nonrenewable source, contributes to increasing greenhouse gas emissions. Reducing the process’s energy demand and carbon footprint will be essential to making ammonia a clear alternative for a carbon-free economy. Given the vast research in ammonia production and handling, this gas seems to be the logical step forward in the evolution of the energy sector. However, the current uncertainty in the global market requires cautiousness in decision making. Several factors may impact economic growth and human welfare, thus needing a careful assessment before making any transcendental decisions that could affect worldwide energy prices and raw material availability.
Anaerobic digestion is one of the technologies that will play a key role in the decarbonization of the economy, due to its capacity to treat organic waste, recover nutrients and simultaneously ...produce biogas as a renewable biofuel. This feature also makes this technology a relevant partner for approaching a circular economic model. However, the low biogas yield of traditional substrates such as sewage sludge and livestock waste along with high installation costs limit its profitability. Further expansion of this technology encounters several barriers, making it necessary to seek improvements to attain a favorable financial balance. The use of co-substrates benefits the overall digestion performance thanks to the balancing of nutrients, the enhanced conversion of organic matter and stabilization, leading to an increase in biogas production and process economics. This article reviews the main co-substrates used in anaerobic digestion, highlighting their characteristics in terms of methane production, kinetic models commonly used and the synergistic effects described in the literature. The main process parameters and their influence on digestion performance are presented, as well as the current lines of research dedicated to improving biogas yields, focusing on the addition of hydrogen, bioaugmentation, supplementation with carbon compounds and nanoparticles, the introduction of bioelectrodes and adsorbents. These techniques allow a significant increase in waste degradation and reduce inhibitory conditions, thus favoring process outcomes. Future research should focus on global process efficiency, making particular emphasis on the extrapolation of laboratory achievements into large-scale applications, by analyzing logistical issues, global energy demand and economic feasibility.
Display omitted
•Biochar had a positive influence on digestion of sludge and orange peels waste.•Eubacterial populations were more sensitive than archaeal to biochar addition.•Biochar provides higher ...surface area favoured adhesion and growth of microorganisms.•For batch systems biochar leads to a decrease in lag phase and an increase in gas yields.•Under semicontinuous regimen an enhancement of methane yield was observed.
In this study, the effects on process performance and changes in microbial populations with the addition of biochar to the anaerobic digestion of sludge and orange peels were evaluated. Biochar had a positive influence in batch digestions, leading to a decrease in the lag phase and an increase in methane yields; this was even more evident for citrus peel wastes, which reached an increase of approximately 33% when 10 g L−1 of biochar was added and 56% when 30 g L−1 was added. Particle size analysis performed for the experiments shows greater surface area available in biochar systems for biomass immobilization.
Analysis of the microbial communities by means of 16S rRNA gene pyrosequencing shows that the biochar addition favoured the electro-active microorganisms consortia creating a synthrophic metabolism between eubacterial and archaeal populations, which resulted in an improvement of the anaerobic digestion performance.
The codigestion of the mixture under a semicontinuous regimen showed an improvement in methane yields of approximately 60% and at hydraulic retention times of 30–20 days (reaching methane production values above 500 L CH4 kg VS−1 at an OLR of 1.49 kg VS m−3 d−1). The enhancement observe in biochar supplemented fermentations may be explained by the adsorption of inhibitors and the relatively high surface area favoured the adhesion and growth of microorganisms.
The effect of char addition on the digestion of animal by-products was evaluated as a way for enhancing the performance of the process. Two different types of carbonaceous materials were tested as ...carbon conductive elements to improve biological treatment. One was derived from a torrefaction process intended for increasing the energy density of lignocellulosic biomass, and the other was obtained from a hydrothermal carbonisation process. In this research, batch digestion systems of animal waste samples were evaluated at a volatile solid (VS) ratio of 1:1 inoculum–substrate (where the content of the substrate in the system was 1.69 ± 0.2 g). The system reported a baseline methane yield of 380 L CH
4
kg VS
-1
which increased on average to 470 L CH
4
kg VS
-1
following to the addition of char. The presence of char allowed a faster degradation of the lipid and protein material, reducing inhibitory interactions. The use of Fourier transformed infrared spectroscopy was applied for elucidating the predetermination of the degradation process and bring an insight into the greater degradation potential attained when carbon materials are used for enhancing microbial performance.
The fermentation of syngas is an attractive technology that can be integrated with gasification of lignocellulosic biomass. The coupling of these two technologies allows for treating a great variety ...of raw materials. Lignin usually hinders microbial fermentations; thus, the thermal decomposition of the whole material into small molecules allows for the production of fuels and other types of molecules using syngas as substrate, a process performed at mild conditions. Syngas contains mainly hydrogen, carbon monoxide, and carbon dioxide in varying proportions. These gases have a low volumetric energy density, resulting in a more interesting conversion into higher energy density molecules. Syngas can be transformed by microorganisms, thus avoiding the use of expensive catalysts, which may be subject to poisoning. However, the fermentation is not free of suffering from inhibitory problems. The presence of trace components in syngas may cause a decrease in fermentation yields or cause a complete cessation of bacteria growth. The presence of tar and hydrogen cyanide are just examples of this fermentation’s challenges. Syngas cleaning impairs significant restrictions in technology deployment. The technology may seem promising, but it is still far from large-scale application due to several aspects that still need to find a practical solution.
The societal demand for biomethane production by anaerobic digestion of waste and biomass is rapidly growing to build a circular economy, yet actual efficiency is limited. Biochar addition has been ...technically shown to enhance methane yields in general, but economics are unknown so far. Here, we evaluated the profitability of adding biochar into orange peel waste using the method of the discounted cash flow. We also studied biochar prices and incentives for biomethane production. Results indicate that adding biochar decreases 17 times the overall economy of the process. This decline is explained by high current prices of biochar. To reach profitability, subsidies should be higher than 20 Eur per MWh of biomethane.
PDF
