Anaerobic Digestion Of Organic Waste Research Articles

MOF-based materials facilitate efficient anaerobic digestion of organic wastes: integrating substrate bioavailability and microbial syntrophism

MOF-based materials facilitate efficient anaerobic digestion of organic wastes: integrating substrate bioavailability and microbial syntrophism

Design and optimization of a novel intestinal reactor to efficiently improve organic waste uniformity and solid content in high solid organic waste anaerobic digestion

High solid anaerobic digestion (HSAD) technology, a major treatment method for solid organic waste. Existing HSAD reactors comprise primarily vertical and horizontal reactors. Vertical reactors use high-pressure pneumatic stirring, which has high energy consumption and poor stirring performance. Horizontal reactors use long-uniaxial mechanical stirring, which occupies large land areas and has high strength requirements for stirring shaft material. In addition, during the operation of the two reactor types, the continuous liquefaction of the solid waste produces solid-liquid stratification, thus affecting mixing effects and decreasing the reactor volume rate. To solve the above problems, we designed a new simulated intestinal anaerobic digestion reactor with a natural solid-liquid separation system, short-axis mechanical stirring, and a stirring blade optimized through CFD. Use of the solid-liquid separation system increased the solid content in the reactor by 44%–55%. The operation results indicated that the homogenization of the solid waste with the optimal stirring blade was more than 50% greater than that of a conventional vertical reactor. The intestinal reactor solves the problems of poor uniformity and solid content decrease during anaerobic digestion in traditional HSAD, decreases the strength requirements for stirring shaft material, and has potential to increase urban waste treatment capacity.

Prediction of anaerobic digestion performance by quantum convolutional reconstruction gated recurrent neural network* *This work was supported by the Open Fund of Advanced Cryptography and System Security Key Laboratory of Sichuan Province (Grant No. SKLACSS202208), National Natural Science Foundation of China (No.61772295),and the Science and Technology Research Program of Chongqing Municipal Education Commission (Grant no.KJZD-M202000501).

Methane as a renewable energy source has become a hot topic in recent years. Methane is a bioenergy source produced during the anaerobic digestion of organic waste, and the anaerobic digestion process must be monitored and controlled to produce the required amount of methane in a stable manner. Mathematical modeling is used to simulate digester operation to predict the biogas production from anaerobic digestion, to avoid reactor loading or performance degradation, and to ensure efficient operation of the system. In this paper, a Quantum Convolutional Reconstruction Gated Recurrent Neural Network is proposed. The original data features are extracted by convolutional neural network to reduce the dimensionality and retain the information, the parameterized quantum circuit is integrated in the gating recurrent unit, and the quantum reset gate and quantum update gate are constructed. The information extracted by the Convolution Neural networks is input into the quantum gated recurrent neural network, and the quantum storage unit integrates the information into the hidden layer state, thus processing the hidden layer state information more efficiently. The experimental results show that the prediction accuracy of the A Quantum Convolution Reconstructed Gated Recurrent Neural Network is improved from 81.95 to 88.21%, and the MAE value is reduced from 54.53% to 37.38%.

Techno-economic assessment of biopolymer production from methane and volatile fatty acids: effect of the reactor size and biomass concentration on the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) selling price

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) is a biobased and biodegradable polymer that could efficiently replace fossil-based plastics. However, its widespread deployment is slowed down by the high production cost. In this work, the techno-economic assessment of the process for producing poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from low-cost substrates, such as methane and valeric acid derived from the anaerobic digestion of organic wastes, is proposed. Several strategies for cost abatement, such as the use of a mixed consortium and a line for reagent recycling during downstream, were adopted. Different scenarios in terms of production, from 100 to 100,000 t/y, were analysed, and, for each case, the effect of the reactor volume (small, medium and large size) on the selling price was assessed. In addition, the effect of biomass concentration was also considered. Results show that the selling price of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) is minimum for a production plant with 100,000 t/y capacity, accounting for 18.4 €/kg, and highly influenced by the biomass concentration since it can be reduced up to 8.6 €/kg by increasing the total suspended solids from 5 to 30 g/L, This adjustment aligns the breakeven point of PHBV with the reported average commercial price.

Biofilm and suspension-based cultivation of microalgae to treat anaerobic digestate food effluent (ADFE)

Anaerobic digestion of organic waste produces effluent (ADE) that requires further treatment. Biofilm-based microalgal cultivation is a favoured approach to ADE treatment. This study compared Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 in biofilm and suspension cultures to treat anaerobic digestate food effluent (ADFE). Chlorella sp. MUR 268 biofilm had significantly higher biomass (50.38 g m−2) than Scenedesmus sp. biofilm (9.39 g m−2). Conversely, Scenedesmus sp. yielded 1.5 times more biomass (1.2 g L−1) than Chlorella sp. in suspension. Chlorella sp. biofilm had 49.3 % higher areal productivity than suspension, while Scenedesmus sp. showed 87.3 % higher areal growth in suspension. Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 significantly removed nutrients in ADFE. In suspension, COD, ammoniacal nitrogen, and phosphate were reduced to 94.9, 5.2, and 5.98 mg L−1 for Chlorella sp. MUR 268, and 245, 2.89, and 3.22 mg L−1 for Scenedesmus sp. MUR 269, respectively. In biofilm, Chlorella sp. MUR 268 achieved reductions to 149.9, 1.16, and 3.57 mg L−1, while Scenedesmus sp. MUR 269 achieved 100.2, 6.9 and 2.07 mg L−1. Most of these values are below the recommended effluent discharge standard, highlighting the efficacy of this system in ADFE treatment. Biofilm cultures fixed 68–81 % of removed nitrogen in biomass, while in suspension, only 55–71 % ended in the biomass. Chlorella sp. MUR 268 biofilm fixed 88 % of removed phosphorus, while Scenedesmus sp. MUR 269 suspension fixed more phosphorus (55 %) than the biofilm counterpart (34 %). This biofilm design offers advantages like simplified, cost-effective operation, easy biomass recovery, and reduced water usage.

Metabolism of novel potential syntrophic acetate-oxidizing bacteria in thermophilic methanogenic chemostats.

Acetate is a major intermediate in the anaerobic digestion of organic waste to produce CH4. In methanogenic systems, acetate degradation is carried out by either acetoclastic methanogenesis or syntrophic degradation by acetate oxidizers and hydrogenotrophic methanogens. Due to challenges in the isolation of syntrophic acetate-oxidizing bacteria (SAOB), the diversity and metabolism of SAOB and the mechanisms of their interactions with methanogenic partners are not fully characterized. In this study, the in situ activity and metabolic characteristics of potential SAOB and their interactions with methanogens were elucidated through metagenomics and metatranscriptomics. In addition to the reported SAOB classified in the genera Tepidanaerobacter, Desulfotomaculum, and Thermodesulfovibrio, we identified a number of potential SAOB that are affiliated with Clostridia, Thermoanaerobacteraceae, Anaerolineae, and Gemmatimonadetes. The potential SAOB possessing the glycine-mediated acetate oxidation pathway dominates SAOB communities. Moreover, formate appeared to be the main product of the acetate degradation by the most active potential SAOB. We identified the methanogen partner of these potential SAOB in the acetate-fed chemostat as Methanosarcina thermophila. The dominated potential SAOB in each chemostat had similar metabolic characteristics, even though they were in different fatty-acid-fed chemostats. These novel syntrophic lineages are prevalent and may play critical roles in thermophilic methanogenic reactors. This study expands our understanding of the phylogenetic diversity and in situ biological functions of uncultured syntrophic acetate degraders and presents novel insights into how they interact with methanogens.IMPORTANCECombining reactor operation with omics provides insights into novel uncultured syntrophic acetate degraders and how they perform in thermophilic anaerobic digesters. This improves our understanding of syntrophic acetate degradation and contributes to the background knowledge necessary to better control and optimize anaerobic digestion processes.

The Biogas Production and its Application in Energy-Efficient Water Sprinkling Systems for Irrigation

This paper explores the integration of biogas production with energy-efficient water sprinkling systems for irrigation. Biogas, produced through the anaerobic digestion of organic waste, offers a renewable and sustainable energy source. Utilizing biogas to power irrigation systems can enhance energy efficiency and reduce reliance on fossil fuels. This research investigates the process of biogas production, its potential energy yield, and its application in water sprinkling systems. Additionally, the paper examines the economic and environmental benefits of this integrated approach, providing a comprehensive analysis of its feasibility and impact on sustainable agriculture.

Evaluation of Open Circuit Voltages (OCV) of Microbial Fuel Cells from Cow and Pig Dungs

A microbial fuel cell (MFC) has many potential applications, including wastewater treatment, environmental monitoring and bioenergy production. The comparison of the open circuit voltages OCV values for three MFC set-ups using cow dung, pig dung and the combination of cow and pig dungs was carried out in this study. The MFC fabricated locally consist of two chambers – the anode, which is an anaerobic digestion of organic waste with an electrode on top of the digester lid while potassium permanganate was mixed with water in a chamber to form the cathode with an electrode on top of the lid. The two chambers were linked with a proton exchange membrane (PEM) made with agarose agar using PVC pipe. For 30 days, the OCV of the MFC set-ups were recorded. The OCV values for the three set-ups were compared. According to the results, the average OCV values for cow dung, pig dung, and a mixture of both are 1.014 V, 0.610 V and 0.430 V, respectively. This shows that cow dung produced the highest OCV values, followed by pig dung. The OCV values from the mixture of both had the lowest results.

Predicting Biogas Production by Anaerobic Digestion of Organic Wastes through Kinetic Modeling

Predicting Biogas Production by Anaerobic Digestion of Organic Wastes through Kinetic Modeling

Biomethane and Compost Production by Anaerobic Digestion of Organic Waste: Suggestions for Rural Communities in Southern Italy

The sharp increase in rural tourism brings, on the one side, economic and social benefits among rural communities but, on the other, contributes to environmental challenges, specifically waste generation and natural resource consumption. From the ecological perspective, several pathways have been developed from local and global communities, such as prevention, reuse, recycling and energy recovery. The present research, by considering the need to boost separate collection and valorize organic waste among rural communities, evaluates the performance of a combined anaerobic digestion and composting plant in Southern Italy. The purpose is to investigate the advantages and disadvantages of collecting organic waste in rural areas and recovering it into biomethane, digestate and compost. First, the research develops the material flow analysis of a real, accessible and available anaerobic digestion and composting plant in Southern Italy. Secondly, on the basis of the results obtained, the research calculates the biomethane, digestate and compost potential in Southern Italy, considering the amount of organic waste produced in 14 rural communities identified as the most beautiful villages in Italy. Last, the research compares the advantages and disadvantages of producing biomethane through anaerobic digestion or resorting to community composting in rural areas. It results that the biomethane and compost potential through anaerobic digestion is 423,854 kg and 954,896 kg, respectively, but significant financial investments must be allocated in order to allow the municipalities to enhance the logistics and the separate collection facilities. The research highlights possible strategies under the circular economy lens to boost sustainability in rural areas, focusing on biomethane and compost production and providing policy implications in light of the National Recovery and Resilience Plan (NRRP) and the Common Agricultural Policy (CAP).

Study of start-up of a continuous digester on a laboratory scale treating the sludge issued from wastewater treatment plant in Adrar city (south west of Algeria)

A continuous digester type was designed at the laboratory scale with an aim to studying and improving anaerobic digestion of organic wastes. The results obtained can be extrapolated at large scale pilot plant. To study the digester start-up we have chosen as a substrate the sludge issued from the wastewater treatment plant located in Adrar city (south west of Algeria). Different parameters have been considered such as pH, VFA, COD, and volume of biogas generated during the digestion process.

Role of biomethane to offset natural gas

The use of biomethane, produced through anaerobic digestion of organic waste, holds promise as an energy source for mitigating climate change. This study quantifies the technical potential of biomethane, considering neither socio-economic nor political constraints, and then compares it to worldwide natural gas use and imports. Furthermore, it calculates the potential emission reduction achieved by substituting natural gas with biomethane. We find that biomethane can offset 29% of natural gas use and two-thirds of natural gas net-imports worldwide. Considering the European energy crisis arising from the Russian-Ukrainian conflict, we analyze the potential for each European country to generate enough biomethane to decrease their reliance on imported Russian natural gas. Our estimates indicate that almost one-third of European countries, including the United Kingdom, France, Spain, Ireland, Slovenia, Romania, Greece, Sweden, and Portugal, have the potential to completely replace their natural gas imports from Russia by utilizing domestic biomethane production. Our study also evaluates how biomethane can reduce greenhouse gas emissions by substituting fossil natural gas, while considering methane leaks in both biomethane and natural gas supply chains and carbon emissions from fossil natural gas combustion. Our results indicate that replacing fossil natural gas with biomethane will decrease emissions from natural gas systems by 11%, equivalent to 1.1 Gt CO2-eq per year. These findings illustrate the potential of biomethane in reducing our dependence on fossil natural gas and mitigating its emissions.

Focus on Co-digestion of waste activated sludge and food waste via yeast pre-fermentation and biochar supplementation: The optimization and mechanism

Anaerobic digestion is a promising method to recover energy from waste, but the slow rate of fermentation hinders its application. Yeast pre-fermentation has been reported to enhance organic matter solubilization and ethanol production to promote syntrophic metabolism and methanogenesis. However, the pre-fermentation with yeast has not been optimized so far. In this study, the lab-scale experiment was conducted to optimize operational conditions, and a pilot-scale study was conducted to evaluate the combined strategy of yeast pre-fermentation and biochar supplementation. Results demonstrated that at a fermentation time of 6 h, temperature of 30 °C, and dry yeast dosage of 2‰, the highest ethanol production was achieved, which accounted for 6.2% of the total COD of pre-fermentation effluent of a mixture of waste-activated sludge and food waste. The methane yield of the pre-fermented waste averaged 161.3 mL/g VS/d, which was 18.7% higher than that of the control group without the yeast inoculation (135.8 mL/g VS/d). With supplementing biochar of 0.5 and 1 g/L, the average methane production was 27.8% and 36.4% higher than the control group, respectively. The volatile solid removal rate was over 10% higher than the control (58.2 ± 3.12%). Consistently, the electrochemical properties of sludge with biochar were significantly improved. A pilot-scale experiment further showed that the methane production with the yeast pre-fermentation and biochar supplementation reached 227 mL/g VS/d, 54.3% higher than that without yeast pre-fermentation and biochar. This study provided a feasible method to combine yeast pre-fermentation and biochar supplementation under optimal conditions, which effectively increased methane production during anaerobic digestion of organic waste.

The short-term response of soil microbial communities to digestate application depends on the characteristics of the digestate and soil type

Anaerobic digestion of organic waste is a key process to produce renewable energy and meet the growing demand for sustainable energy. The residues of anaerobic digestion – called digestates – can be used as soil amendments to improve crop yields. However, the effect of digestates on the soil biota, especially on microorganisms, needs to be better documented before a large scale use of digestates in agriculture. In addition, how the quality and composition of the digestate may affect soil microbial communities has not been properly addressed yet. We designed a microcosm experiment under controlled experimental conditions to compare effects (42 days) of four digestates produced from varying intakes (cattle manure and/or energy crop and/or food residues and/or slurry) on soil microbial communities; a control microcosm made of undigested cattle manure was also used. Each digestate was applied on three contrasting soils representing contrasted pedo-climatic conditions (especially soil type and climate). These three soils presented different prokaryotic and fungal communities structures. The effect of digestate inputs on the soil microbial biomass and diversity was assessed using molecular DNA-based tools (quantification of extracted soil DNA and high-throughput sequencing, respectively) in comparison to the untreated cattle manure control condition. Our results show that 42 days after digestate application, significant differences of soil microbial communities were observed according to the digestate characteristics; these differences were soil-dependent. Thus, in the silty clay loam soil, no effect of digestates was observed on soil microbial biomass or diversity (P > 0.05), as compared to the undigested cattle manure. In the two other soil types (loam and sandy loam), soil microbial biomass decreased (around −40 %, P < 0.001) when digestates having a low total organic carbon content (from 0.61 to 3.3 g.100 g−1) were applied. None of the digestates affected the soil prokaryotic diversity whatever the soil type (P > 0.05). Digestate application resulted in higher fungal diversity (around +35 %; P < 0.001) in soils with low C/N ratio (9.14 in average). The microbial community structure of coarse-textured soil appeared more impacted by organic inputs than fine-textured soils. To conclude, our results show that different soil types, harboring distinct microbial community structures, responded differently to different digestates application. This response was also digestate-dependent.

Functional and molecular approaches for studying and controlling microbial communities in anaerobic digestion of organic waste: a review

Functional and molecular approaches for studying and controlling microbial communities in anaerobic digestion of organic waste: a review

Production of high-quality biogas using recycled trimetallic nanoparticles from electronic waste

A plethora of nanoparticles (NPs) significantly enhanced the biogas production from organic waste anaerobic digestion upon their optimized addition to the reactors. In this study, trimetallic Sn–Mn–Fe.NPs, recovered from waste-printed circuit boards, were used to enhance the quality and productivity of the anaerobic digestion (AD) of cow manure as an organic substrate. This study aims to make the biogas production process more efficient and economically sustainable, taking into account the environmentally friendly nature of the AD process. The obtained nanoparticles were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) techniques. Various concentrations (20, 50, and 100 mg/L) of the trimetallic Sn–Mn–Fe NPs were added to the biogas reactors, which were made of 1000-ml autoclave glass bottles to host the animal waste during the AD process. The pressure of the biogas produced was monitored daily for 45 days as retention time, and the volume of the produced biogas was calculated at a constant temperature (15 °C) and pressure (1.013 bar). Generally, NP-based reactors showed superiority in biogas production over blank reactors. Also, among the different concentrations, the best biogas-producing digester (RC2200) revealed the highest performance with a 113.6% enhancement in biogas production. In addition, it showed a significant increase of 231.2% in methane production.

Effect of composition of volatile fatty acids on yield of polyhydroxyalkanoates and mechanisms of bioconversion from activated sludge

Polyhydroxyalkanoates (PHA) is green biodegradable natural polymer. Here PHA production from volatile fatty acids (VFAs) was investigated in sequential batch reactors inoculated with activated sludge. Single or mixed VFAs ranging from acetate to valerate were evaluated, and the dominant VFA concentration was 2 times of that of the others in the tests. Results showed that mixed substrates achieved about 1.6 times higher yield of PHA production than single substrate. The butyrate-dominated substrates maximized PHA content at 72.08% of VSS, and the valerate-dominated substrates were followed with PHA content at 61.57%. Metabolic flux analysis showed the presence of valerate in the substrates caused a more robust PHA production. There was at least 20% of 3-hydroxyvalerate in the polymer. Hydrogenophaga and Comamonas were the main PHA producers. As VFAs could be produced in anaerobic digestion of organic wastes, the methods and data here could be referred for efficient green bioconversion of PHA.

Salinity Inhibition in Thermophilic Anaerobic Digestion of Organic Waste

Anaerobic digestion, despite its preferable use as a treatment for high organic matter polluted waste streams, is susceptible to inhibitors, salt included. Therefore, two different experiments were conducted to observe the responses of bacterial and archaeal communities to hypersaline environments. In the first experiment, salt was added gradually, while in the second experiment, salt was added rapidly (so-called salt shocks were performed). The results of the gradual addition of salt showed a recovery of methane production after the salt concentration decreased. The NaCl concentration of 28.2 g/L seems to be the limit between stable operation and occurrence inhibition. The specific biogas production varied between 0.490 and 0.562 m3/kgtCOD during the stepwise salt addition, depending on the salt concentration, while the maximal achieved COD removal was 79.8%. The results of the rapid salt addition showed good recovery of the bacterial community, while a reduction of salt-sensitive species was observed in the archaeal community. The trend of specific biogas production during rapid salt addition was stable with an average value of 0.590 m3/kgtCOD, and it was observed that higher concentrations of up to 39.4 g/L of NaCl were tolerated. The maximum COD removal achieved during rapid salt addition was 83.1%. In conclusion, certain bacterial and archaeal communities were well-adapted to the hypersaline environment and remained active during the anaerobic digestion of substrates with high salt concentration.

Crop diversification and digestate application effect on the productivity and efficiency of irrigated winter crop systems

Irrigated winter crops can reduce input demands when compared with irrigated summer cropping systems in the Mediterranean area. The sustainability of these systems can be further improved resorting to diverse rotations, but also to fertilisation with digestate, a by-product from anaerobic digestion of organic waste. Post-treatments such as drying and acidifying can improve the fertiliser value of this product. In this study, we compare wheat performance in a three-year full cereal rotation or in a diverse rotation, with pea and canola. Besides, untreated and dried acidified digestates are tested as fertilisers for all crops, comparing to mineral fertilisation at a rate of 140 kg N ha−1 and a control with no fertilisation. To assess productivity and efficiency of the different systems, grain yield and N concentration, N uptake efficiency (NUpE) and water use efficiency (WUE) were determined, along with soil nitrate dynamics and total N at the end of the experiment. Results showed an average wheat yield increase of 1.79 t ha−1 by the last year of the diverse crop rotation rather than the cereal rotation (p < 0.001). Although there was no yield increase in the previous year, wheat after pea showed higher grain N concentration (p < 0.001). However, the NUpE of wheat remained steady due to a higher soil N availability after pea, which suggests that fertilisation can be adjusted. Although wheat WUE increased due to canola and pea precedents (p < 0.001), the cereal rotations should be more adapted to systems with low water availability. Nonetheless, both rotations required about 30% of irrigated water than the typical irrigated summer crops of the Ebro valley region. Fertiliser effect on yields was variable according to the tested crop mainly due to differences in N demand along each growing cycle. Overall, dried acidified digestate application resulted in similar soil nitrate levels than the mineral fertiliser. The diverse rotation raised soil nitrates content compared to the cereal rotation at sowing and harvesting times (p = 0.002 and p < 0.001, respectively). Higher soil nitrate levels were found when associating these two practices, while nitrate levels after mineral fertilisation showed to be less dependent on the implemented rotation. The diverse rotation also raised soil total N at the end of the experiment (p = 0.023). Similarly, the dried acidified digestate application resulted in higher soil total N than mineral fertilisation (p = 0.011). These findings show how these management practices should allow for a chemical fertilisation reduction in irrigated winter crop systems.

Hexanoic acid improves the production of lipid and oleic acid in Yarrowia lipolytica: The benefit of integrating biorefinery with organic waste management

Microbial oil serves as a sustainable feedstock for producing biodiesel and bio-jet fuels in biorefineries. Sustainable and economical microbial oil production requires the combination of the biorefinery concept and organic waste management. Here, volatile fatty acids (VFAs), by-products of anaerobic digestion of organic waste, have been incorporated as co-substrates in lignocellulosic microbial oil production by an oleaginous yeast of Yarrowia lipolytica. The supplementation of VFAs (acetic, butyric, and hexanoic acids) increased microbial oil production of Y. lipolytica by up to 47%. Specifically, the oleic acid content in microbial oil increased from 41% to 64% with hexanoic acid supplementation, resulting in a 1.5-fold increase in oleic acid titer. Transcriptome analysis showed that hexanoic acid altered fatty acid metabolism (through β- and ω-oxidation) and global transcriptional regulation during microbial oil production. These findings suggest that hexanoic acid is a useful supplement that improves the industrial yield of microbial oil and selectively increases oleic acid content.