Search

In colder regions, relatively low temperatures results in low microbial activity and low biogas production in anaerobic digestion. This study investigated if microbial electrosynthesis system (MES) can enhance biogas production from pig manure wastewater under sub-psychrophilic conditions (20 °C). Results showed that the applied voltage of MES (0.4 V and 0.8 V) significantly increased the biogas production and COD removal rate. Biogas production and COD removal rate increased most when the voltage reached 0.8 V (34.77 %, 26.67 %), and decreased when the voltage was 1.2 V. Low voltage (≤ 0.8 V) did not significantly alter the microbial structure, but higher voltage (1.2 V) resulted in a significant decrease in Clostridium and Methanosarcina. Coenzyme F420, NADH, as indicators for methanogenic efficiency, showed the highest fluorescence intensity at 0.8 V and decreased at 1.2 V. Results indicated that the improvement of gas production was mainly due to the improvement of key enzymes rather than the shift of microbial structure. The information provided will be useful to improve the efficiency of biogas production. [Display omitted] • The optimal voltage was explored in 5 L MES under sub-psychrophilic condition. • Optimized applied voltage on MES was 0.8 V. • Applied voltage at 1.2 V led to lower concentration of F420 and NADH. • Clostridium and Methonasarcina were significantly reduced at 1.2 V. [ABSTRACT FROM AUTHOR]

Anaerobic digestion has been defined as a competitive approach to facilitate the recycling of corn stalks. However, few studies have focused on the role of direct interspecies electron transfer (DIET) pathway in the acidification stage under the addition of different particle sizes of zero-valent iron (ZVI). In this study, three types of ZVI, namely iron filings, iron powder and nanoscale iron, were investigated, respectively, to enhance its high-value conversion. Variations in volatile fatty acids (VFAs) and methane (CH 4) production associated with the underlying mechanisms were emphatically determined. Results indicated that the addition of ZVI could increase the concentration of VFAs, with the most outstanding performance observed with the use of nanoscale iron. Importantly, the conversion of propionic acid to acetic acid was driven by adding ZVI with no between-group differences in acidizing phase. Conversely, the substrate was more fully utilized when supplied with iron powder compared with other groups in methanogenic phase, thereby displaying the maximum CH 4 yield with a value of 263.1 mL/(g total solids (TS)). However, adding nanoscale iron could signally shorten the digestion time (T 80), saving 7 days in comparison to the group of iron powder. [Display omitted] [ABSTRACT FROM AUTHOR]

The steel industry is one of the hard-to-abate sectors for decarbonization, and direct electrification is not possible or economically infeasible. This study investigates the application of the Water-Energy-Carbon nexus in the steel industry through a multi-generation plant, addressing the industry's demands for water, energy, and alternative fuel. The proposed multi-generation plant consists of parabolic trough solar collectors, an organic Rankine cycle, urban wastewater treatment, carbon capture, anaerobic digestion combined with heat and power, a proton exchange membrane electrolyzer, and a steelmaking plant. Thermodynamic and exergoeconomic analyses are conducted to investigate the system's efficiency and economic performance. A sensitivity analysis is conducted to identify the optimal links between nexus resources, followed by a multi-dimensional evaluation and multi-objective optimization. The results showed that under base conditions, the plant can annually produce 900 ktons of steel, 105 GWh of net power, 430.1 tons of water, and 517 tons of hydrogen, while preventing 34.7 ktons of CO 2 emissions. The exergy efficiency and unit exergy cost of the products are 46.1% and 57.8 $/GJ, respectively. Under optimized conditions, the plant achieves a maximum net annual power output of 160 GWh, an exergy efficiency of 46.9%, and a minimum unit exergy cost of 51.4 $/GJ. [Display omitted] • Multi-generation plant for energy, water, and fuel for steel industry. • System integrates solar, wastewater treatment, and carbon capture. • Thermodynamic and exergoeconomic analyses assess efficiency and costs. • Optimization achieves 46.9% exergy efficiency and 51.4 $/GJ unit exergy cost. • Plant annually produces 900 kt steel, 105 GWh power, 430.1 t water, 517 t hydrogen. [ABSTRACT FROM AUTHOR]

[Display omitted] • Machine learning model could predict methane yield of pretreated LW accurately. • Digestion time, pretreatment agent and pretreatment agent were crucial factors. • NaOH, KOH and AHP pretreatments were suitable for LW with low lignin content. • LW with high lignin content preferred AHP pretreatment. Chemical pretreatment is a common method to enhance the cumulative methane yield (CMY) of lignocellulosic waste (LW) but its effectiveness is subject to various factors, and accurate estimation of methane production of pretreated LW remains a challenge. Here, based on 254 LW samples, a machine learning (ML) model to predict the methane production performance of pretreated feedstock was constructed using two automated ML platforms (tree-based pipeline optimization tool and neural network intelligence). Furthermore, the interactive effects of pretreatment conditions, feedstock properties, and digestion conditions on methane production of pretreated LW were studied through model interpretability analysis. The optimal ML model performed well on the validation set, and the digestion time, pretreatment agent, and lignin content (LC) were found to be key factors affecting the methane production of pretreated LW. If the LC in the raw LW was lower than 15%, the maximum CMY might be achieved using the NaOH, KOH, and alkaline hydrogen peroxide (AHP) with concentrations of 3.8%, 4.4%, and 4.5%, respectively. On the other hand, if LC was higher than 15%, only high concentrations of AHP exceeding 4% could significantly increase methane production. This study provides valuable guidance for optimizing pretreatment process, comparing different chemical pretreatment approaches, and regulating the operation of large-scale biogas plants. [ABSTRACT FROM AUTHOR]

Dry anaerobic digestion (dry-AD) is an attractive process for solid wastes such as agri-food waste. However, some limitations mainly associated to lack of effective mixing, can hinder the methane production capacity of the systems. Bulking agent (BA) has been proposed as a solution to the compaction issues in systems without mechanical agitation, such as leaching bed reactors. However, effects of BA are still not clear, and, thus, the factors to consider for its dose has not been optimized yet. This work studies the effect of BA in dry-AD. Two substrates with different characteristics were proposed as models, bean peel as a lignocellulosic substrate and a mixture of food waste as a readily biodegradable substrate. Inert plastic rings were used as BA at different BA:S ratios. Assessed BA:S ratio did not affect the performance of methane production for the lignocellulosic waste, but it did significantly affect to the easily biodegradable substrate, showing up to a 28% of methane production increase. This result could be due to the presence of lignocellulosic compounds in the bean peel, behaving like a natural BA. In assays with an increased bed height, the compaction of the system was more severe, resulting in the rapid acidification of the processes. At these conditions, the positive effect of BA addition was more marked, allowing methane production and no acidification of the system. Thus, the addition of BA is a suitable strategy for improving methane production or stability in dry-AD systems without requiring the stirring of the systems. • Bulking agent (BA) addition is assessed as alternative to stirring in dry AD. • Positive effects by BA was due to an increase of the porosity in the digester bed. • Optimal BA:S ratio was strongly dependent on the characteristics of the substrate. • Low lignocellulosic content substrates were more favoured by BA addition. • BA addition was able to avoid acidification by enhancing the methanogenic activity. [ABSTRACT FROM AUTHOR]

Sewage sludge in cities of Yangzi River Belt, China, generally exhibits a lower organic content and higher silt contentdue to leakage of drainage system, which caused low bioenergy recovery and carbon emission benefits in conventional anaerobic digestion (CAD). Therefore, this paper is on a pilot scale, a bio-thermophilic pretreatment anaerobic digestion (BTPAD) for low organic sludge (volatile solids (VS) of 4%) was operated with a long-term continuous flow of 200 days. The VS degradation rate and CH 4 yield of BTPAD increased by 19.93% and 53.33%, respectively, compared to those of CAD. The analysis of organic compositions in sludge revealed that BTPAD mainly improved the hydrolysis of proteins in sludge. Further analysis of microbial community proportions by high-throughput sequencing revealed that the short-term bio-thermophilic pretreatment was enriched in Clostridiales, Coprothermobacter and Gelria , was capable of hydrolyzing acidified proteins, and provided more volatile fatty acid (VFA) for the subsequent reaction. Biome combined with fluorescence quantitative polymerase chain reaction (PCR) analysis showed that the number of bacteria with high methanogenic capacity in BTPAD was much higher than that in CAD during the medium temperature digestion stage, indicating that short-term bio-thermophilic pretreatment could provide better methanogenic conditions for BTPAD. Furthermore, the greenhouse gas emission footprint analysis showed that short-term bio-thermophilic pretreatment could reduce the carbon emission of sludge anaerobic digestion system by 19.18%. [Display omitted] [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is widely employed for sludge stabilization and waste reduction. However, the slow hydrolysis process hinders methane production and leads to prolonged sludge issues. In this study, an efficient and eco-friendly lysozyme pre-treatment method was utilized to address these challenges. By optimizing lysozyme dosage, hydrolysis and cell lysis were maximized. Furthermore, lysozyme combined with hydrothermal pretreatment enhanced overall efficiency. Results indicate that: (1) When lysozyme dosage reached 90 mg/g TS after 240 min of pretreatment, SCOD, soluble polysaccharides, and protein content reached their maxima at 855.00, 44.09, and 204.86 mg/L, respectively. This represented an increase of 85.87%, 365.58%, and 259.21% compared to the untreated sludge. Three-dimensional fluorescence spectroscopy revealed the highest fluorescence intensity in the IV region (soluble microbial product), promoting microbial metabolic activity. (2) Lysozyme combined with hydrothermal pretreatment significantly increased SCOD, soluble proteins, and polysaccharide release from sludge, reducing SCOD release time. Orthogonal experiments identified Group 3 as the most effective for SCOD and soluble polysaccharide release, while Group 9 released the most soluble proteins. The significance order of factors influencing SCOD, soluble proteins, and polysaccharide release is hydrothermal temperature > hydrothermal time > enzymatic digestion time.(3) The lysozyme-assisted hydrothermal pretreatment group exhibited the fastest release and the highest SCOD concentration of 8,135.00 mg/L during anaerobic digestion. Maximum SCOD consumption and cumulative gas production increased by 95.89% and 130.58%, respectively, compared to the control group, allowing gas production to conclude 3 days earlier. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Comparison of different physical and enzymatic OFMSW pre-treatments. • Study of the pre-treatment effects on both the AD products: biogas and digestate. • Evaluation of the most energetically sustainable AD configurations. • Analyses of digestate quality in terms of nutrient content for the application as fertilizer. • UPP2 and cavitation are the best enzymatic and physical pre-treatments, respectively. This study optimized the anaerobic digestion (AD) of separated collected organic fractions of municipal solid waste (OFMSW) to produce energy and digestate as biofertilizer. Due to OFMSW's partial recalcitrance to degradation, enzymatic (UPP2, MCPS, USC4, USE2, A. niger) and physical (mechanical blending, heating, hydrodynamic cavitation) pre-treatments were tested. Experimental and modeling approaches were used to compare AD performance regarding energy sustainability and digestate quality. Digestate was separated into solid and liquid fractions, and then chemically and physically characterized by investigating the nutrient release mechanisms. Principal Component Analysis was applied, equally weighing energy and digestate productions. Unlike previous studies focusing only on biogas, this study evaluated the effects of pre-treatments on both biogas and digestate production, viewing AD as a biorefinery process for urban waste valorization. Results showed that all pre-treatments were energetically sustainable, but enzymatic pre-treatments yielded digestates richer in nutrients (increase of 80% N, 200% P and 150% K as compared to OFMSW) and with greater organic matter degradation compared to physical pre-treatments. The liquid fraction of digestate from enzymatic pre-treatments had higher nutrient concentrations, while those from physical pre-treatments had more balanced nutrient content, making them more suitable for fertigation. [ABSTRACT FROM AUTHOR]

• Compared US efficiency in CH 4 yield enhancement toward three different sludges. • US accelerates sludge disintegration and CH 4 yield at high specific energy input. • US-pretreated sludge feeding enhances microbial diversity in an anaerobic digester. • US improves more CH 4 yield of A 2 O-sludge than A 2 O-MBR- and AO-AO- sludge. A large amount of sludge is inevitably produced during sewage treatment. Ultrasonication (US) as anaerobic digestion (AD) pretreatment was implemented on different sludges and its effects on batch and semi-continuous AD performance were investigated. US was effective in sludge SCOD increase, size decrease, and CH 4 production in the subsequent AD, and these effects were enhanced with an elevated specific energy input. As indicated by semi-continuous AD experiments, the mean daily CH 4 production of US-pretreated A2O-, A2O-MBR-, and AO-AO-sludge were 176.9, 119.8, and 141.7 NmL/g-VS added , which were 35.1%, 32.1% and 78.2% higher than methane production of their respective raw sludge. The US of A2O-sludge achieved preferable US effects and CH 4 production due to its high organic content and weak sludge structure stability. In response to US-pretreated sludge, a more diverse microbial community was observed in AD. The US-AD system showed negative net energy; however, it exhibited other positive effects, e.g., lower required sludge retention time and less residual total solids for disposal. US is a feasible option prior to AD to improve anaerobic bioconversion and CH 4 yield although further studies are necessary to advance it in practice. [Display omitted] [ABSTRACT FROM AUTHOR]

Chemical looping dry reforming of methane (CLDRM) using perovskites as a catalyst is considered a promising option for producing hydrogen from biogas. In this work, the life-cycle performance of a system compiling a CLDRM unit paired with a water gas shift unit, a pressure swing adsorption unit, and a combined cycle scheme to provide steam and electricity was assessed. The main data needed to reflect the behavior of the reforming reaction was obtained experimentally and implemented in an Aspen Plus® simulation. Inventory data was obtained through process simulation and used to assess the environmental performance of the process in terms of carbon footprint, acidification, freshwater eutrophication, ozone depletion, photochemical ozone formation, and depletion of minerals and metals. Overall, the environmental viability of the production of green hydrogen from biogas was found to be heavily dependent on the biogas leakage in anaerobic digestion plants. The CLDRM system was benchmarked against a conventional DRM implementation for the same feedstock. While the conventional DRM plant environmentally outperformed the perovskite-based CLDRM, the latter might present advantages from an implementation point of view. [Display omitted] • Scaled-up chemical looping dry reforming of biogas for hydrogen production was simulated. • The life-cycle performance of the configuration with a perovskite catalyst was assessed. • Environmental hotspots refer to biogas leakage, natural gas processes, and catalyst metals. • Environmental advantages of conventional dry reforming were linked to heat integration. • Green hydrogen qualification requires avoiding leakages from anaerobic digestion plants. [ABSTRACT FROM AUTHOR]

As a new technology, microbial electrolysis cell-assisted anaerobic digestion (MEC-AD) has been applied to the utilization of swine manure. Methane production and total energy efficiency are both important indicators in MEC-AD; thus, it is necessary to simultaneously optimize methane production and total energy efficiency. In this study, the Box–Behnken design (BBD) was used as the experimental design, the response surface methodology (RSM) and back propagation neural network (BP-NN) methods were used to construct multi-objective models, and the non-dominated sorting genetic algorithm II (NSGA II) was used for multi-objective optimization. The BP-NN model was superior to the RSM model in terms of goodness of fit. Additionally, the relative error between the predicted and experimental values of the Pareto front was determined to be <3%. The maximum methane production and total energy efficiency were 333.97 mL/g total solid and 61.38%, respectively. Therefore, multi-objective optimization of MEC-AD systems may be accomplished using BBD-(BP-NN)-NSGA II. • A novel approach for multi-objective optimization of MEC-AD systems is presented. • The multi-objective optimization framework, BBD-(BP-NN)-NSGA II, was established. • The methane production and total energy efficiency were optimized simultaneously. • The BP-NN model demonstrated superior prediction capabilities in MEC-AD systems. • Maximum methane production and energy efficiency were 333.97 mL/g TS and 61.38%. [ABSTRACT FROM AUTHOR]

• Variability of food processor waste and derived hydrolysate quantified. • Addressing this variability is key for single-organism high-value bioproduct synthesis. • Hydrolysate assessed via bioproduct synthesis in yeast, bacteria, and archaea. • Importance of carbon and nitrogen levels, and specific substrates demonstrated. • Industrial-scale valorization strategies for variable food waste discussed in-depth. Unavoidable food wastes could be an important feedstock for industrial biotechnology, while their valorization could provide added value for the food processor. However, despite their abundance and low costs, the heterogeneous/mixed nature of these food wastes produced by food processors and consumers leads to a high degree of variability in carbon and nitrogen content, as well as specific substrates, in food waste hydrolysate. This has limited their use for bioproduct synthesis. These wastes are often instead used in anaerobic digestion and mixed microbial culture, creating a significant knowledge gap in their use for higher value biochemical production via pure and single microbial culture. To directly investigate this knowledge gap, various waste streams produced by a single food processor were enzymatically hydrolyzed and characterized, and the degree of variability with regard to substrates, carbon, and nitrogen was quantified. The impact of hydrolysate variability on the viability and performance of polyhydroxyalkanoates biopolymers production using bacteria (Cupriavidus necator) and archaea (Haloferax mediterranei) as well as sophorolipids biosurfactants production with the yeast (Starmerella bombicola) was then elucidated at laboratory-scale. After which, strategies implemented during this experimental proof-of-concept study, and beyond, for improved industrial-scale valorization which addresses the high variability of food waste hydrolysate were discussed in-depth, including media standardization and high non-selective microbial organisms growth-associated product synthesis. The insights provided would be beneficial for future endeavors aiming to utilize food wastes as feedstocks for industrial biotechnology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanobubble water was first used to improve the CE efficiency of cow manure AD. • NBW enhanced the electron transfer efficiency of the cow manure AD system. • NBW enhanced cow manure degradation. • NBW enhanced carbohydrate metabolism and ABC transporters for MCCAs synthesis. • NBW enhanced fatty acid recycling pathway of chain elongation. Nanobubble water promotes the degradation of difficult-to-degrade organic matter, improves the activity of electron transfer systems during anaerobic digestion, and optimizes the composition of anaerobic microbial communities. Therefore, this study proposes the use of nanobubble water to improve the yield of medium chain carboxylic acids produced from cow manure by chain elongation. The experiment was divided into two stages: the first stage involved the acidification of cow manure to produce volatile acidic fatty acids as electron acceptors, and the second phase involved the addition of lactic acid as an electron donor for the chain elongation. Three experimental groups were established, and air, H 2 , and N 2 nanobubble water were added in the second stage. Equal amounts of deionized water were added in the control group. The results showed that nanobubble water supplemented with air significantly increased the caproic acid concentration to 15.10 g/L, which was 55.03 % greater than that of the control group. The relative abundances of Bacillus and Caproiciproducens , which are involved in chain elongation, and Syntrophomonas , which is involved in electron transfer, increased. The unique ability of air nanobubble water supplemented to break down the cellulose matrix resulted in further decomposition of the recalcitrant material in cow manure. This effect subsequently increased the number of microorganisms associated with lignocellulose degradation, increasing carbohydrate metabolism and ATP-binding cassette transporter protein activity and enhancing fatty acid cycling pathways during chain elongation. Ultimately, this approach enabled the efficient production of medium chain carboxylic acids. [ABSTRACT FROM AUTHOR]

[Display omitted] • The controllability of N and metal elements transformation was achieved. • Hydrothermal-pyrolysis offered DFW efficient utilization and control NO x emissions. • Hydrothermal pretreatment enhances biochar pore structure and surface area. • O-containing functional groups and doped metal Ca were enriched on the biochar. • Maximum P removal efficiency of wastewater by DFW biochar upped to 94%. Pyrolysis has emerged as a promising technology for valorizing digestate resulting from the anaerobic digestion of food waste. However, the high NO X emissions during pyrolysis limit its application. This study proposed a hydrothermal coupled pyrolysis process to control the element transfer in digestate during biochar production. The efficient reduction of NO X emissions and the improvement of biochar adsorbability were realized. The hydrothermal process reduced the nitrogen content in solid digestate by 49.10 %–81.79 %, thus reducing the NO X precursors in syngas and the N-containing substances in bio-oil. Additionally, the specific surface area and the total pore volume of biochar were enhanced from 25 m2/g to 60–73 m2/g and 0.06 cm3/g to 0.12–0.14 cm3/g, respectively. More defects, oxygen-containing functional groups, and doped Ca on the biochar resulted in a high phosphate removal efficiency of 94 %. The proposed technology provides an efficient and environmentally friendly way to utilize the digestate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Using statistics provided best anaerobic digestion conditions for cattle manure. • The most effective pretreatment was thermal treatment at 129.3℃ for 49.6 min. • Optimal mixing ratio of cattle manure, food waste, and pig manure was 30.5:42.5:27. • The ideal co-digestion condition substantially improves synergy effect and stability. This study investigated the optimal pretreatment condition and mixture ratio of cattle manure (CM) for its efficient anaerobic co-digestion (AcoD) with food waste (FW) and pig manure (PM). The pretreatment performances of thermal (TM), microwave (MW), and ultrasound (US) technologies and the AcoD performance were statistically and experimentally evaluated at various mixture ratios of CM, FW, and PM. The results revealed that the most effective pretreatment condition with the TM, MW, and US pretreatments was 129.3 °C for 49.6 min, 824.2 W for 7.3 min, and 418.0 W for 36.3 min, respectively. The best AcoD performance of optimally pretreated CM (PCM) was achieved when 30.5 % PCM was mixed with 42.5 % FW and 27.0 % PM. A long-term evaluation showed that the start-up rate for the anaerobic mono-digestion of PCM was 2.3 times faster than that of CM and the amount of methane produced was 4.7 times higher; process stability was thus preferentially maintained under a higher organic loading rate (OLR) (2.0 kg-VS/m3∙d). The start-up rate for the AcoD of PCM with FW and PM was 1.2 times higher than that of the AcoD of CM with FW and PM. Although the performance gap between the AcoD reactors after steady state was not significantly different, the PCM AcoD reactor provided a more stable operation under a higher OLR (5.0 kg-VS/m3∙d). This study demonstrates that the pretreatment and co-digestion of CM could significantly enhance the production of biogas and improve process stability. [ABSTRACT FROM AUTHOR]

• Different configurations were tested for producing biogas from roadside grass. • Dry digestion succeeded at pilot and large scale, but the latter can be improved. • Digested fibers performed better than undigested fibers for biomaterial production. • Anaerobic digestion might be stopped midway for improved fiber recovery. • Market potential of roadside grass for biomaterials production was significant. Roadside grass clippings hold potential as a sustainable source of bioenergy as they do not compete with crops for land use, and are only partially utilized for low-value applications. In this study, we proposed using roadside grass as a sole feedstock for anaerobic digestion (AD) in three different settings, and assessed the potential of producing biomaterials and fertilizers from grass-based digestate. Wet continuous digestion at pilot scale and dry batch digestion at pilot and large scales resulted in biogas yields up to 700 Nm3.t−1 DOM with a methane content of 49–55 %. Despite promising results, wet AD had operational problems such as clogging and poor mixing; once upscaled, the dry digestion initially also presented an operational problem with acidification, which was overcome by the second trial. Digested grass fibers from the pilot dry AD were processed into biomaterials and performed similarly or better than the undigested fibers, while around 20 % performance reduction was observed when compared to reference wood fibers. A mass balance indicated reduced fiber recovery when higher biogas production was obtained. The liquid fraction from the pilot dry AD was characterized for its nutrient content and used as a biofertilizer in another study. In contrast, the leachate collected from the large-scale dry AD had a low nitrogen content and high chloride content that could hinder its further use. Finally, a regional market analysis was conducted showing that the biocomposites produced with the available grass fibers could substitute at least half of the current European market based on our results. [ABSTRACT FROM AUTHOR]

Due to the increased demand for energy resources and the continuous increase in population, the use of RES from biomass and waste is becoming increasingly popular. The work analyzed existing approaches to solving global environmental and social problems through the use of landfill gas generated at municipal solid waste (SMW) landfills, as well as further reforming of biogas into biohydrogen. Waste monitoring was also carried out on the territory of LR and St. Petersburg. It was found that more than 12 million m3 of SMW of hazard classes 1–5 are formed annually in the region. It has been shown that the majority of waste is biodegradable organic matter (about 20%). To increase the biogas potential of SMW landfills during degassing and create additional economic benefits, a system for blowing and irrigation of landfill masses with the addition of a substrate from residual biomass of Chlorella microalgae was proposed. It is proposed to improve the scheme for sorting and using organic waste through selective collection and separation from the total mass of waste at the site of generation. A waste flow diagram has been developed taking into account the material balance of SMW in LR and St. Petersburg. Using this scheme will avoid contamination of other recycled SMW components. In addition, the work proposes a scheme for the further use of biomethane obtained at SMW landfills. Using reforming, it is proposed to purify the resulting gas to biohydrogen. The production of biohydrogen from biogas is cost-effective and can become an alternative to petroleum products. This technology could become a key element in the production of environmentally friendly fuels and the reduction of harmful emissions into the atmosphere. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cork dust was processed by deep eutectic solvent for biogas and value-added products. • Highest phenolic extraction (137.4 mg GAE g cork dust−1) was at 110 °C for 20 min. • Highest biogas yield (115.1 mL N gVS-1) was observed at 130 °C for 60 min. • Catechin, 4-hydroxybenzoic acid and gallic acid were identified as primary phenolics. In this study, phenolic compounds using deep eutectic solvents (DES) were extracted from cork dust, and the biogas production potential of DES-treated cork dust samples was determined. The DES treatment was carried out using choline chloride and formic acid (1:2 M ratio) at various temperatures (90, 110 and 130 °C) and treatment times (20, 40 and 60 min) at a solid-to-solvent ratio of 1:10 g mL−1. The highest total phenolic content (137 mg gallic acid equivalent (GAE) g−1 dry cork dust) was achieved at 110 °C/20 min. The extracts exhibited an antioxidant capacity of up to 56.3 ± 3.1 % 1,1-diphenyl-2-picrylhydazyl (DPPH) inhibition at a dilution rate of 100. DES treatment resulted in minimal sugar solubilization at low temperatures, while approximately 42 % of the xylan fraction in the biomass degraded under severe conditions (e.g., 130 °C/60 min). Catechin, 4-hydroxybenzoic acid and gallic acid were the major phenolics in DES extracts. The biogas yield of DES-treated cork dust increased with treatment severity. The highest biogas yield (115.1 mL N g VS -1) was observed at 130 °C/60 min, representing an increase of 125 % compared to the untreated sample. SEM images revealed that the surface structure of the samples became smoother after mild pretreatment and rougher after harsh pretreatment. Compositional and FTIR analyses indicated that a higher biogas formation potential was associated with increased cellulose content in the substrate, which could be attributed to hemicellulose solubilization in the hydrolysate. Overall, DES pretreatment effectively enhanced phenol extraction and anaerobic degradability. [ABSTRACT FROM AUTHOR]

The co-digestion of a peach biowaste and parboiled rice effluent mixed with a sludge digester was investigated using a lab-scale biodigester. The biomasses used in the system were characterized by physical-chemical and microbiological analyses. Variations in substrate/inoculum (S/I) ratio of 1:1, 1:2, and 3:2, with different percentages of peach bagasse of 0%, 5%, and 10% in the substrate combination (peach bagasse + effluent), were performed. The study found that co-digestion of peach bagasse and parboiled rice effluent with digester sludge resulted in higher biomethane production, with reactors II and IV showing the best combination of factors both with a proportion of 3:2 (S/I). Reactor IV showed the maximum production of 27.51 mL CH 4 with a substrate composition of 10% peach bagasse and 90% effluent. The physical-chemical properties of the co-digestion substrate were optimal for anaerobic digestion, and the microbial community adapted to enhance biodegradation. The maximum COD removal was found in reactor IV at 88.06%, followed by reactor V at 82.10%. In contrast, the 1:2 (S/I) ratio in reactor I showed the lowest methane production. Furthermore, the co-digestion process resulted in stable and efficient digestion, indicating it is a viable alternative for treating rice parboiling effluent and peach waste. • Alternative for treating rice parboiling effluent and peach waste. • Peach biowaste and parboiled rice effluent characterization. • Maximum production of 27.51 mL CH 4 using anaerobic codigestion process. [ABSTRACT FROM AUTHOR]

[Display omitted] • OLR of 2.5 g COD/L⋅d optimizes the methane yield of FW mono and co-digestion. • Accumulation of low biodegradable GPW reduces the methane yield in ACoD with FW. • ACoD of FW and PW enhances bacteria diversity, hydrolysis, and methane yield. • ACoD of FW and PW (2.5 g COD/L⋅d) shows synergistic effects (10 %) over FW digestion. • GPW hydrochar fulfills the ISO 17225-8 standard for industrial use as a solid fuel. The feasibility of anaerobic co-digestion in semicontinuous mode of two major urban biowaste, food waste (FW) and garden and park waste (GPW) (75 % FW and 25 % GPW) as well as the co-digestion of FW with the process water originated from the hydrothermal carbonization of GPW (95 % FW and 5 % process water), both on a COD basis, has been assessed. The effect of varying organic loading rate (OLR) from 1.5 to 3.5 g COD/L·d on methane yield, gross energy recovery, and microbiome population was evaluated. For comparison, anaerobic digestion of FW was also conducted to determine the best strategy for sustainable biowaste management. This study showed an optimal OLR of 2.5 g COD/L·d. Acetic and propionic acid content increased as OLR raised for each condition studied, while methane yield decreased at the highest OLR tested indicating overloading of the system. The anaerobic co-digestion of FW and process water showed a 10 % increase on methane production compared to anaerobic digestion of FW (324 vs. 294 mL CH 4 STP/L·d). Moreover, it enhances the process due to a greater abundance and diversity of hydrolytic and acidogenic bacteria belonging to Bacterioidota, Firmicutes, and Chloroflexi phyla, as well as promotes the hydrogenotrophic pathway under higher propionic concentrations which is not usually favoured for methane production. The integration of hydrothermal carbonization of GPW with the anaerobic co-digestion of 95 % FW and 5 % of process water results in the highest potential energy recovery and could be a good strategy for sustainable management of urban biowaste. [ABSTRACT FROM AUTHOR]

• Biohythane from two-stage anaerobic digestion (TSAD) of food waste (FW) is reviewed. • Main principle and influence factors of the TSAD of FW are identified. • Main strategies for enhancing biohythane from TSAD of FW are summarized. • Future research directions for biohythane from TSAD of FW are proposed. The biotransformation of food waste (FW) to bioenergy has attracted considerable research attention as a means to address the energy crisis and waste disposal problems. To this end, a promising technique is two-stage anaerobic digestion (TSAD), in which the FW is transformed to biohythane, a gaseous mixture of biomethane and biohydrogen. This review summarises the main characteristics of FW and describes the basic principle of TSAD. Moreover, the factors influencing the TSAD performance are identified, and an overview of the research status; economic aspects; and strategies such as pre-treatment, co-digestion, and regulation of microbial consortia to increase the biohythane yield from TSAD is provided. Additionally, the challenges and future considerations associated with the treatment of FW by TSAD are highlighted. This paper can provide valuable reference for the improvement and widespread implementation of TSAD-based FW treatment. [Display omitted] [ABSTRACT FROM AUTHOR]

• Environmental impacts of AD, Py, ADCo-Py and ADCo-INC were compared. • High environmental burden from pretreatment was mitigated by co-processing. • The most significant environmental burdens in each system were AP, ETP and GWP. • Co-processing of AD with Py demonstrated the highest environmental benefit. • Poor waste source separation can be partially mitigated by co-processing systems. This research conducted an environmental life cycle assessment (LCA) to evaluate an anaerobic digestion-co-pyrolysis (ADCo-Py) system in which pyrolysis was added to traditional food waste (FW) anaerobic digestion (AD) systems to treat the solid fraction and impurities separated from FW. The solid fraction, including impurities such as wooden chopsticks, plastics, eggshells, and bones, is usually incinerated, while pyrolysis can be a viable alternative to optimize FW treatment. The environmental impact of ADCo-Py was compared with stand-alone AD, pyrolysis, and ADCo-INC (AD with incineration of separated solids). The results indicated that both ADCo-Py (−1.726 kg CO 2 -Eq/kg FW) and ADCo-INC (−1.535 kg CO 2 -Eq/kg FW) outperform stand-alone AD (−0.855 kg CO 2 -Eq/kg FW) and pyrolysis (−0.181 kg CO 2 -Eq/kg FW) in mitigating global warming potential (GWP). Additionally, pretreatments were found to have the most significant influence on GWP, ecotoxicity potential (ETP), and acidification potential (AP). The two-step pretreatment in ADCo-Py, including the separation of solids and drying, significantly improved the environmental sustainability of the system when compared with standalone pyrolysis. [ABSTRACT FROM AUTHOR]

• Applied voltage and calcium addition increased biogas yield and CO 2 sequestration. • Wollastonite and CaCl 2 exhibited different CO 2 sequestration performances. • Wollastonite showed a better CO 2 sequestration effect with 2.22% CO 2 in biogas. • The contribution of chemical and biological CO 2 sequestration was clarified. The combination of microbial electrolytic cells and anaerobic digestion (MEC-AD) became an efficient method to improve CO 2 capture for waste sludge treatment. By adding CaCl 2 and wollastonite, the CO 2 sequestration effect with mineral carbonation under 0 V and 0.8 V was studied. The results showed that applied voltage could increase dissolved chemical oxygen demand (SCOD) degradation efficiency and biogas yield effectively. In addition, wollastonite and CaCl 2 exhibited different CO 2 sequestration performances due to different Ca2+ release characteristics. Wollastonite appeared to have a better CO 2 sequestration effect and provided a wide margin of pH change, but CaCl 2 released Ca2+ directly and decreased the pH of the MEC-AD system. The results showed methane yield reached 137.31 and 163.50 mL/g SCOD degraded and CO 2 content of biogas is only 12.40 % and 2.22 % under 0.8 V with CaCl 2 and wollastonite addition, respectively. Finally, the contribution of chemical CO 2 sequestration by mineral carbonation and biological CO 2 sequestration by hydrogenotrophic methanogenesis was clarified with CaCl 2 addition. The chemical and biological CO 2 sequestration percentages were 46.79 % and 53.21 % under 0.8 V, respectively. With the increased applied voltage, the contribution of chemical CO 2 sequestration rose accordingly. The findings in this study are of great significance for further comprehending the mechanism of calcium addition on CO 2 sequestration in the MEC-AD system and providing guidance for the later engineering application. [ABSTRACT FROM AUTHOR]

[Display omitted] • Intra-seasonal fruit waste generation requires digesters with feeding flexibility. • Feeding frequency effect was tested in four semicontinuous reactors for over 350 d. • Process resilience to variations in feeding frequency shown in methane production. • Reactors failed at high organic loading rates due to insufficient alkalinity. • Feeding frequency did not change the main methanogenic and bacterial genera. On-site anaerobic digesters for small agricultural farms typically have feeding schedules that fluctuate according to farm operations. Shocks in feeding, particularly for putrescible waste can disrupt the stable operation of a digester. The effect of intermittent feeding on the anaerobic digestion of rejected raspberries was investigated in four 3L reactors operated in semicontinuous mode for 350 days at 38 °C with a hydraulic retention time of 25 days and an organic loading rate (OLR) of 1gVS/L/d. During the acclimatisation period (147 days) the organic loading was 5 feeds per week. The feeding regime of two reactors was then changed while maintaining the same OLR and HRT to one weekly feed event in one reactor and 3 equal feeds per week in another. The feeding regime did not significantly affect specific methane yield (369 ± 47 L/kgVS on average) despite very different weekly patterns in methane production. Volatile fatty acids (VFA) comprised >83 % of the organics in the effluent, while the rest included non-inhibitory concentrations of phenolic compounds (515–556 mg gallic acid/L). The microbial composition and relative abundance of predominant groups in all reactors were the archaeal genera Methanobacterium and Methanolinea and the bacterial phyla Bacteridota and Firmicutes. Increasing the OLR to 2gVS/L/d on day 238 resulted in failure of all reactors, attributed to the insufficient alkalinity to counterbalance the VFA produced, and the pH decrease below 6. Overall results suggests that optimal digestion of raspberry waste is maintained despite variations in feeding frequency, but acidification can occur with OLR changes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermal pretreatment of raw tuna viscera increased methane yield by 50 %. • Large accumulation of VFA and LCFA observed in non-thermally pretreated raw viscera. • Anaerobic co-digestion of cooked tuna and fat waste reached a methane yield of 87 %. • An optimal C/N ratio was obtained in co-digestion of cooked viscera and fat waste. Fish canning industries generate large amounts of solid waste during their processing operations, creating a significant environmental challenge. Nonetheless, this waste can be efficiently and sustainably treated through anaerobic digestion. In this study, the potential of biogas production from anaerobic digestion of thermally pretreated and co-digested solid tuna waste was investigated. The thermal pretreatment of raw fish viscera resulted in a 50 % increase in methane yield, with a production of 0.27 g COD-CH 4 /g COD added. However, this pretreatment did not lead to a significant increase in biogas production for cooked tuna viscera. When non-thermally pretreated raw viscera was tested, a large accumulation of volatile fatty acids and long chain fatty acids was observed, with levels reaching 21 and 6 g COD/L, respectively. On the other hand, anaerobic co-digestion of cooked tuna viscera with fat waste significantly enhanced methane production, achieving 0.87 g COD-CH 4 /g COD added. In contrast, co-digestion of cooked tuna viscera with dairy waste and sewage sludge resulted in notably lower yields of 0.36 and 0.46 g COD-CH 4 /g COD added, respectively. These results may be related to the C/N ratio, which was found to be within the optimal range for anaerobic digestion only in the tuna and fat waste co-digestion assay. [ABSTRACT FROM AUTHOR]

• CTS-Fe effectively promoted the methane production during AD of WAS. • CTS-Fe addition enriched the abundance of IRB during AD process. • CTS-Fe had great promotion for hydrolysis process via dissimilatory iron reduction. • CTS-Fe inhibited acetoclastic and hydrogenotrophic methanogenesis process. Anaerobic digestion (AD) of waste activated sludge (WAS) is usually limited by the low generation efficiency of methane. Fe(III)-loaded chitosan composite (CTS-Fe) have been reported to effectively enhanced the digestion of WAS, but its role in promoting anaerobic sludge digestion remains unclear. In present study, the effects of CTS-Fe on the hydrolysis and methanogenesis stages of WAS anaerobic digestion were investigated. The addition of CTS-Fe increased methane production potential by 8%–23% under the tested conditions with the addition of 5–20 g/L CTS-Fe. Besides, the results demonstrate that the addition of CTS-Fe could effectively promote the hydrolysis of WAS, evidenced by lower protein or polysaccharides concentration, higher soluble organic carbon in rector adding CTS-Fe, as well as the increased activity of extracellular hydrolase with higher CTS-Fe concentration. Meanwhile, the enrichment of Clostridia abundance (iron-reducing bacteria (IRBs)) was observed in CTS-Fe adding reactor (8.9%–13.8%), which was higher than that in the control reactor (7.9%). The observation further suggesting the acceleration of hydrolysis through dissimilatory iron reduction (DIR) process, thus providing abundant substrates for methanogenesis. However, the presence of CTS-Fe was inhibited the acetoclastic and hydrogenotrophic methanogenesis process, which could be ascribed to the Fe(III) act as electron acceptor coupled to methane for anaerobic oxidation. Furthermore, coenzyme F420 activity in the CTS-Fe added reactor was 34.9% lower than in the blank, also abundance of microorganisms involved in hydrogenotrophic methanogenesis was decreased. Results from this study could provide theoretical support for the practical applications of CTS-Fe. [Display omitted] [ABSTRACT FROM AUTHOR]

This study evaluated the biomethane and biohydrogen production capacity of an anaerobic sludge collected from a rice parboiling industry. Three main parameters were assess from an experimental batch with varying substrate-inoculum ratios (S/I): the final mass production, the maximum generation rate, and the reactors' biomethane and biohydrogen yield. From the analysis of the final production and the maximum generation rate, the best S/I ratios found for the methanogenic and hydrogenic reactors were, respectively, 1.4 and 3.8 gCOD/gVSS. These proportions produced 102.65 mgCH 4 /gVSS and 27.96 mgH 2 /gVSS, reaching the following maximum generation rates: 32.91 mgCOD CH 4 /gVSS.h and 12.63 mgCOD H 2 /gVSS.h. In contrast to the methanogenic microorganisms of the studied sludge, the acetogenics allow the use of higher organic loads in the systems. However, the lowest S/I ratio (0.1 gCOD/gVSS) resulted in both the best biomethane and biohydrogen production yield, around 2.33 mol CH 4 /mol glucose and 2.46 mol H 2 /mol glucose. Compared to the maximum theoretical yields, whereas the sludge produced biohydrogen more effectively under high S/I ratios, biomethane was generated more efficiently in low S/I ratios. Finally, the anaerobic sludge can be employed as a satisfactory inoculum in anaerobic digestion and dark fermentation processes designed for biomethane and biohydrogen production. • Specific Methanogenic and Hydrogenic Activity. • Production of 27.96 mgH 2 /gVSS. • Satisfactory inoculum in anaerobic digestion and dark fermentation processes. [ABSTRACT FROM AUTHOR]

This study explores the treatment of low-organic strength wastewater by integrating bio-electrochemical technology with low-temperature anaerobic digestion. Composite electrode plates acted as carriers, maintaining an operating temperature of 17 °C through gradual acclimation. Results indicate that the bio-electrochemical reactor (R1) with an applied voltage of 0.6 V and electrode carriers, and the reactor (R2) with electrode carriers but without applied voltage, achieved soluble chemical oxygen demand (SCOD) removal rates of 92.2 % and 91.2 %, respectively. These rates were approximately 1.3 times higher than those of the conventional reactor (R3). Furthermore, the average SCOD concentration in R1 effluent was 15.95 % lower than that in R2. The application of voltage notably enhanced wastewater treatment efficacy at 17 °C in R1. Abundant electroactive microorganisms capable of direct interspecies electron transfer (DIET) were observed in both R1 and R2, promoting an accelerated electron transfer rate. Additionally, the electrodes facilitated a coexisting system wherein methane production increased due to a combination of a methane-producing system driven by H 2 mediation and an electroactive methanogenic system. [Display omitted] • Electroactive microorganisms were identified within the bioelectrochemical system. • Electroactive microorganisms promote the DIET pathways for methane production. • Cold-tolerant fermenting bacteria Trichococcus enriched in the low-temperature environment. • The abundance of Trichococcus by composite electrode plates addition was increased up to 37.80 %. • Formation of H 2 -mediated electricity-driven methane production system. [ABSTRACT FROM AUTHOR]

• Starch- and petro-based bioplastics were anaerobically digested under H 2 /CO 2 or N 2. • Higher methane yield in H 2 /CO 2 than N 2 accomplishing successful biogas upgrading. • H 2 /CO 2 can enhance methane production with breakdown of starch-based bioplastic. To identify an economically viable waste management system for bioplastics, thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (PBAT) were anaerobically digested under hydrogen (H 2)/carbon dioxide (CO 2) and nitrogen (N 2) gas-purged conditions to compare methane (CH 4) production and biodegradation. Regardless of the type of bioplastics, CH 4 production was consistently higher with H 2 /CO 2 than with N 2. The highest amount of CH 4 was produced at 307.74 mL CH 4 /g volatile solids when TPS digested with H 2 /CO 2. A stepwise increased in CH 4 yield was observed, with a nominal initial increment followed by accelerated methanogenesis conversion as H 2 was depleted. This may be attributed to a substantial shift in the microbial structure from hydrogenotrophic methanogen (Methanobacteriales and Methanomicrobiales) to heterotrophs (Spirochaetia). In contrast, no significant change was observed with PBAT, regardless of the type of purged gas. TPS was broken down into numerous derivatives, including volatile fatty acids. TPS produced more byproducts with H 2 /CO 2 (i.e., 430) than with N 2 (i.e., 320). In contrast, differential scanning calorimetry analysis on PBAT revealed an increase in crystallinity from 10.20 % to 12.31 % and 11.36 % in the H 2 /CO 2 - and N 2 -purged conditions, respectively, after 65 days of testing. PBAT surface modifications were characterized via Fourier transform infrared spectroscopy and scanning electron microscopy. The results suggest that the addition of H 2 /CO 2 can enhance the CH 4 yield and increase the breakdown rate of TPS more than that of PBAT. This study provides novel insights into the CH 4 production potential of two bioplastics with different biodegradabilities in H 2 /CO 2 -mediated anaerobic digestion systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • The hydrolysis of agave bagasse by rumen microorganisms was studied. • Substrate concentration had an inhibitory effect on hydrolytic activity. • Low S 0 /X 0 ratios increased agave bagasse's efficiency and hydrolysis rate. • With an S 0 /X 0 ratio of 0.33 up to 6.1 kJ/g TS (155 mL CH 4 /g TS) was obtained. • The most abundant ruminal bacteria were Prevotella , Ruminococcus , and Fibrobacter. Agave bagasse, a lignocellulosic waste that results from the milling and juice extraction of Agave tequilana var azul pineapples, is a suitable substrate for the production of methane through anaerobic digestion. However, it is necessary to apply a pretreatment to convert the bagasse into energy. In this context, this paper proposes using ruminal microorganisms to hydrolyze agave bagasse. This study evaluated the effect of the initial agave bagasse to ruminal fluid (S 0 /X 0) ratio (0.33, 0.5, 1, and 2) on the hydrolysis efficiency. Subsequently, the supernatant was used for methane production. The hydrolysis efficiency increased as the S 0 /X 0 ratio decreased. A hydrolysis efficiency of 60 % was achieved using an S 0 /X 0 ratio of 0.33. The S 0 /X 0 ratio of 0.33 optimally improved the specific methane production and energy recovery (155 ± 2 mL CH 4 /g TS and 6.1 ± 0.1 kJ/g TS) compared to raw biomass. The most abundant hydrolytic bacteria were Prevotella , Ruminococcus and Fibrobacter , and Engyodontium was the most abundant proteolytic fungus. [ABSTRACT FROM AUTHOR]

• Adjusting OLR alone is not sufficient in designing and operating TH-AD process, NH 4 +-N and VFAs should be equally considered. • NH 4 +-N, VFAs and tCOD in feed sludge were the most influential factors for AD microbial community structure. • Higher diversity of microorganisms and methanogens that adapted to more diverse substrate transformation pathways could lead to superior performance. • Microbial community information could help the precise design and operation of full-scale TH-AD process. Anaerobic digestion (AD) with thermal hydrolysis (TH) pretreatment is a promising process for excess sludge treatment, while there lacks of the knowledge from full-scale process about the impact of sludge composition and characteristics on microbial community and performance. The sludge physiochemical indices, microbial community and performance data of four full-scale TH-AD plants were characterized, and their relationships was elucidated. The four plants were operated under almost similar total organic loading rate (OLR) but their methanogenesis performance differentiate into two groups, namely superior group (SupG) and the inferior group (InfG). In both groups, TH effectively solubilized particulate organic compounds, meanwhile raised the ammonia nitrogen (NH 4 +-N) and volatile fatty acid (VFA) concentration. Compared with the SupG, thermal hydrolyzed sludge of InfG had higher level of VFAs, NH 4 +-N and total chemical oxygen demand (tCOD), which showed higher inhibition effect on microbes, leading to a community with lower diversity, lower abundance of carbohydrate degrading functional guild, higher protein degrading one, and methanogens that adapted to limited substrates, and further declined the methane production rate. Thus, it was recommended that OLR alone was not sufficient for controlling the system in design and operation, the concentration of VFAs, NH 4 +-N and tCOD should be equally considered. Their higher concentration, together with the higher abundance of Defluviitoga and Proteiniphilum were recommended as indicators for inferior running condition. Our results proposed that microbial communities played a role of bridge between environmental factors and performance, provided implications for engineering ecology and operational regulation for full-scale sludge TH-AD process. [Display omitted] [ABSTRACT FROM AUTHOR]

Dissolved air flotation (DAF) waste, a byproduct with high lipid content separated from dairy wastewater, is disposed of by land spreading and causing environmental pollution. To develop a sustainable treatment for DAF waste, this study investigated the effects of food to inoculum (F/I) ratio and ultrasound pre-treatment on the anaerobic digestion of DAF waste. The biochemical methane potential (BMP) of tested DAF waste ranged from 436–566 mL CH 4 /g VS fed. Increasing the F/I ratio (>1.0) inhibited methane production due to long chain fatty acids (LCFA) accumulation, which high concentrations of oleate inhibited methanogenesis and delayed palmitate degradation. Ultrasound pre-treatment with 30 min pulse (10 s on/ 10 s off) and 15 min continuous operations increased soluble chemical oxygen demand in DAF waste by 82% and 52%, respectively. Moreover, continuous sonication removed 38% of LCFA due to the implosion of cavitation bubbles. The BMP of DAF waste increased by 36% after sonication with F/I ratio 3.0. However, the lag time of methane production was prolonged after sonication due to the fast release of LCFA to the bulk solution. By implementing ultrasound pre-treatment and optimizing the F/I ratio, the energy potential of DAF waste can be harnessed, leading to more sustainable practices in dairy production. [ABSTRACT FROM AUTHOR]

To address climate change, energy security, and waste management, new sustainable energy sources must be developed. This study uses Aspen Plus software to extract bio-H2 from food waste with the goal of efficiency and environmental sustainability. Anaerobic digestion, optimised to operate at 20–25 °C and keep ammonia at 3%, greatly boosted biogas production. The solvent [Emim][FAP], which is based on imidazolium, had excellent performance in purifying biogas. It achieved a high level of methane purity while consuming a minimal amount of energy, with a solvent flow rate of 13.415 m³ /h. Moreover, the utilization of higher temperatures (600–700 °C) during the bio-H 2 generation phase significantly enhanced both the amount and quality of hydrogen produced. Parametric and sensitivity assessments were methodically performed at every stage. This integrated method was practicable and environmentally friendly, according to the economic assessment. H 2 generation using steam reforming results in a TCC of 1.92 × 106 USD. The CO 2 separation step has higher costs (TCC of 2.15 ×107 USD) due to ionic liquid washing and CO 2 liquefaction. Compressor electricity consumption significantly impacts total operating cost (TOC), totaling 4.73 × 108 USD. showing its ability to reduce greenhouse gas emissions, optimize resource utilization, and promote energy sustainability. This study presents a sustainable energy solution that addresses climate and waste challenges. [Display omitted] [ABSTRACT FROM AUTHOR]

Anaerobic digestion technology has gained significant attention as an organic solid waste treatment method due to its favorable economic and environmental benefits. However, after digestion, the digestate still contains a significant amount of underutilized organic matter. Sustainable management and resource utilization of digestate plays a crucial role in achieving resource circularity and implementing a circular economy. Previous reviews have mainly focused on improving the operational efficiency and stability of anaerobic digestion, with limited exploration of sustainable management and resource utilization of digestate. To address this gap, this review provides a systematic summary of the sustainable management and resource utilization of digestate. First, the basic characteristics of digestate are outlined. Then, based on a visual analysis of literature on digestate management from the past decade, the review highlights the hotspots in sustainable management and circular utilization of digestate. Finally, it summarizes the relevant policies on digestate management in different regions and outlines the challenges in digestate treatment and disposal. The challenges in digestate management remain a significant issue that requires further exploration and solutions. This review aims to promote the standardization of digestate management, provide direction for further in-depth research on digestate, and contribute to the continued development of resource cycling of anaerobic fermentation products. [Display omitted] [ABSTRACT FROM AUTHOR]

Biohydrogen production is influenced by various parameters such as production formation rate, substrates degradation, and biomass utilization. Therefore, it is crucial to predict the kinetics of proper yield. This study was designed to perform a comprehensive kinetic analysis based on several linear or non-linear models. The experimental data analyzed was different co-culture ratios of microalgae and activated sludge with hexitols (glucose, sorbitol, mannitol) as carbon substrates. Results suggest that modified Gompertz model best predicts biohydrogen potential and acetate production in different co-cultures with high R2 values (>0.977 and > 0.982), respectively. A maximum of 9.8 % energy conversion efficiency is achieved in 10 g/L glucose supplemented co-culture, equivalent to traditional fuels. The linearized Luedeking–Piret model also indicates that biohydrogen production is influenced more by substrate degradation/utilization than microalgal biomass. These tools can be utilized to optimize the operational parameters and access the best fit of experimental data for enhanced yield. [Display omitted] • Excellent data fittings of parameters involved in algal activated sludge co-culture. • Biohydrogen and acetate yield can be best predicted by Modified Gompertz model. • Michaelis–Menten model best described kinetic of substrate degradation/utilization. • Relationship of products, substrate, and biomass predicted by Luedeking–Piret model. • Maximum energy conversion efficiency (9.8 %) was achieved in 1:1.5 co-culture ratio. [ABSTRACT FROM AUTHOR]

Biohythane production through anaerobic digestion of organic waste in a single reactor is a potentially more cost-effective process compared to the traditional two-stage scheme. In this work, the production and composition of biohythane obtained from complex organic waste in a semi-continuous thermophilic anaerobic bioreactor was studied with a gradual increase in hydraulic retention time (HRT) from 2 to 5 days and a corresponding decrease in the organic loading rate from 12.27 to 4.8 g VS/(L·d). At low HRT, a significant predominance of hydrogen content in biogas was observed. However, with an increase in HRT to 5 days, the volumetric and specific yield of methane increased. The modified Gompertz model and the first order model showed a high coefficient of determination (R2 = 0.97–1) for the calculated kinetic parameters of hydrogen and methane formation. At all values of HRT, the predominance of the hydrogen-producing genus Thermoanaerobacterium was observed in the microbial community. When HRT was increased to 5 days, representatives of methanogenic archaea of the genera Methanosarcina and Methanosaeta actively developed. The hydrogen and methane content in the final biogas mixture was approximately 37 % and 30 %, respectively. Potential research avenues for improving biohythane production in a single reactor have been considered. [ABSTRACT FROM AUTHOR]

[Display omitted] • AD-microalgae treatment resulted stable without biomass recirculation at HRT 20 d. • Biomass recover was 1.85 ± 0.02 g l−1 with lipid storage of 33.48 ± 7.54 %. • Lipids storage resulted in line with EN14214 for biodiesel production. • HRT 10 d optimization had stable biomass output and high ammonia removal. Wine production represents one of the most important agro-industrial sectors in Italy. Wine lees are the most significant waste in the winery industry and have high disposal and storage costs and few applications within the circular economy. In this study, anaerobic digestion and a microalgae coupled process was studied in order to treat wine lees and waste activated sludge produced within the same facility, with the aim of producing energy and valuable microalgae biomass that could be processed to recover biofuel or biostimulant. Chlorella vulgaris was cultivated on liquid digestate in a semi-continuous system without biomass recirculation. The best growth and phytoremediation performance were achieved applying a hydraulic retention time (HRT) of 20 days with a stable dry weight, lipid and protein storage of 1.85 ± 0.02 g l−1, 33.48 ± 7.54 % and 57.85 ± 10.14 % respectively. Lipid characterization highlighted the potential use in high quality biodiesel production, according to EN14214 (<12 % v/v linolenic acid). The microalgae reactor's liquid output showed high removal of ammonia (95.72 ± 2.10 %), but low organic soluble matter reduction. Further semi-continuous process optimization was carried out by increasing the time between digestate feeding and biomass recovery at HRT 10. These operative changes avoided biomass wash-out and provided a stable phytoremediation of the digestate with 84.58 ± 4.02 % ammonia removal, 33.01 ± 1.44 % sCOD removal, 38.06 ± 2.65 % of polyphenols removal. [ABSTRACT FROM AUTHOR]

• The PBAT/PLA coated paper shows high methane yield under AD condition. • Plastic film residues remain after the digestion of PBAT/PLA coated paper. • The decrease of hydrophobicity for PBAT/PLA bags is due to the formation of PLA monomers. • The bacterial community shows difference between PBAT/PLA coated paper and bags. • Methanoculleus is enriched on the plastic surface under mesophilic AD. Poly (lactic acid) (PLA) and Poly(butylene adipate-co-terephthalate) (PBAT) are two of biodegradable plastics with the highest production capacities in 2021. Bioplastic waste management can be easily integrated with organic waste management, especially when bioplastics are used as food packaging material, since they are potentially biodegradable. The aim of this study was to assess the biodegradability of biodegradable polymer-coated paper (BPCP) and bioplastic bags made from PBAT/PLA blend during mesophilic and thermophilic anaerobic digestion (AD) and to reveal the changes in the physicochemical properties of the bioplastics. BPCP obtained 155 NmL-CH 4 /g VS and 307.3 NmL-CH 4 /g VS under mesophilic and thermophilic conditions, respectively, but left bioplastic film residues. The bioplastic bags did not exhibit significant biodegradation during the AD processes. 1H NMR results indicated that the ratio of PLA to PBAT decreased significantly after AD of the BPCP film and that PLA monomers were formed from the bioplastic bags, leading to a decrease in the hydrophobicity on the surfaces of the materials. Methanoculleus was found to be enriched on the bioplastic surface after mesophilic AD. From the perspective of coupling bioplastic waste management with the food waste management, the incorporation of BPCP into the AD reactor not only enhances system stability and methane production to a greater extent than biodegradable plastic bags but also raises concerns regarding the residual biofilm when utilizing the digestate for direct land applications. [ABSTRACT FROM AUTHOR]

Agricultural waste, called biomass, is of great interest as a renewable energy source. The purpose of this work was to determine the optimal recirculation rate (RR) values of the solid digestate when applying a new approach to the intensification of anaerobic conversion, providing a high quality biogas yield. This approach includes solid digestate recirculation and pre-processing a mixture of raw waste and solid digestate in a vortex layer apparatus. For this, the operation of an experimental biogas plant without recirculation and with recirculation was considered, starting from very low RR values, from 0.034 to 1, to ensure a high methane production rate (MPR) and methane yield (MY). From the point of view of MPR and MY, the recirculation ratios of 0.034 and 0.071 look the most attractive, however, with a recirculation ratio of 0.5, the content of hydrogen sulfide de-creased to 14 ppm with a simultaneous increase in MPR by 12 % compared to the control. [ABSTRACT FROM AUTHOR]

Water hyacinth (Eichhornia crassipes) was anaerobically digested with waste sludge in a batch system at varying total solid (TS) contents (3.3–8.3%) and temperatures (35–55 °C). Then, the high organic content of digested biomass was utilized for hydrothermal liquefaction/gasification in the batch reactor system at different temperatures (200–600 °C) to yield biofuels and biochemicals. Hydrothermal liquefaction/gasification was performed in sub- and super-critical water (above 374 °C and 221 bar) conditions. Prevailing products are some biochemical compounds (carboxylic acids, furfurals, aldehyde/ketones, phenols etc.) at lower temperatures (200–300 °C) while biohythane (total of hydrogen and methane) gaseous fuel are produced at higher temperatures (400–600 °C). The highest carbon gasification efficiency (73 g C in product/g C in feed) was obtained at 600 °C with the sample that has a high anaerobic digestion efficiency (digested at 6.3 TS% at 35 °C). The highest carbon liquefaction efficiency (37.2 g C in product/g C in feed) was obtained at 200 °C with the sample which has a low anaerobic digestion yield (digested at 8.3 TS% at 35 °C). [Display omitted] • Biorefinery concept as hybrid application of biological and thermal processes. • Biochemicals and biofuels can be produced from water hyacinth by hybrid processes. • Biohythane content of gas product reached to 66 %mole at 600 °C. • Liquid product yields: carboxylic acids > furfurals > aldehydes and ketones > phenols. [ABSTRACT FROM AUTHOR]

Novel, environmentally friendly, and clean energy sources have been developed in response to increased global energy demand and the associated effects of global warming produced by greenhouse gas emissions from fossil fuels. As a result, the development of renewable and clean energy depends largely on hydrogen as a key component. Even, nanomaterial procured from waste for Hydrogen synthesis can be processed through several biochemical/thermochemical procedures. Variables comprising feedstock characteristics, operation needs and technology availability were examined to support technology choice and system features. Such amendments proceed with costly synthesis and operation strategies, low operating efficiencies, insufficient management along with logistics, as well as lack of operation policies. Perhaps, nanotechnology is now crucial in the creation of nanomaterials for the production of hydrogen as a pertinent origin through renewable energy causatives. Nanomaterials have received a great deal of interest in recent years owing to their unusual mechanical, electrical, electronic, optical, and magnetic properties on their surfaces. These features had a predominant impact on the evolution of production and storage techniques, as well as the difficulties experienced in bringing the product to market. This article provides an overview of the nanomaterials that contributed to hydrogen synthesis, storage, and usage. This article will cover a wide range of issues, including Nanomaterials for Photocatalytic (PC) reactions, anaerobic digestion, hydrothermal gasification, microbial fuel cells, lifespan evaluation, and future research studies. • A comprehensive analysis of the techniques and procedures used to produce hydrogen. • A systematic exploration of the many different kinds of nanomaterials that are utilized in the creation of hydrogen. • Utilization includes photo-catalysis, anaerobic digestion, hydrothermal gasification, and microbial fuel cells. • Recent achievements, problems and possibilities are explored in depth. [ABSTRACT FROM AUTHOR]

The performance of different applied voltages on the biomethanation of lignite is investigated in microbial electrolytic cells coupled with anaerobic digestion (MEC-AD). The cumulative methane production is only 35.1 mL/g lignite in the control reactor. However, the cumulative methane production is increased to 44.3 mL/g lignite in the MEC-AD reactor at the applied voltage of 1 V, and followed by 62.6 mL/g lignite (2 V), 102.8 mL/g lignite (4 V), and 123.8 mL/g lignite (8 V). The 3D fluorescence spectra further clarified that the applied voltage favored the hydrolysis of macromolecular organic matter such as humic acid in lignite. The microbial community abundance in the bulk solution shows that some specific microorganisms such as electroactive bacteria (Chloroflexi) and hydrogenotrophic methanogenic archaea (Methanobacterium) were well enriched in the MEC-AD reactors. These results indicate that MEC-AD facilitates direct interspecies electron transfer (DIET) between electroactive bacteria and archaea, and significantly increases methane production. However, the economic analysis concludes that the methane production at the applied voltage of 8 V could not compensate for the cost incurred by electricity. The MEC-AD reactor with an applied voltage of 4 V showed excellent biomethanation characteristics of lignite, which provides a basis for the resource utilization of lignite. • MEC-AD system promotes the production and biodegradation of humic acid from lignite. • Hydrogenotrophic methanogenic archaea in MEC-AD are well enriched in bulk solution. • MEC-AD system significantly enhance the DIET for methane production from lignite. • The applied voltage of 4V performs better lignite biomethanation and economic benefit. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is the mainstream method for energy conversion of food waste, but dewatering and resource utilization of its digestate is the downstream technical obstacle. In this study, an energy and resource utilization scheme via the integrated process of anaerobic digestion and hydrothermal carbonization of food waste is proposed, among which the hydrothermal carbonization not only is used to remove water from digestate in a non-phase change manner with low energy consumption but also convert digestate into hydrochar. Moreover, the scheme has the least environmental impact compared to the anaerobic digestion and composting treatment by life cycle assessment. In particular, it has a lower impact potential (−141.46 kg CO 2 eq) than anaerobic digestion (−38.87 kg CO 2 eq) for the global warming category, indicating that the addition of hydrothermal carbonization can bring better environmental benefits. This study provides a reference for the development of disposal technology for food waste. • An energy and resource utilization scheme of food waste is proposed. • Hydrothermal carbonization converts the digestate into hydrochar. • The treatment scheme has a lower global warming potential (−141.46 kg CO 2 eq). • Shortening transportation distance can reduce the environmental burden. [ABSTRACT FROM AUTHOR]

Biohythane (a mixture of hydrogen and methane) may play a significant role in a future decarbonised energy system. The production of biohythane can be achieved by sequential dark hydrogen fermentation and anaerobic digestion. However, the technology readiness level of biohythane can be limited by many process constraints negatively affecting its commercial feasibility. Here, a pilot experiment on fermentative hythane production from cassava stillage residue (CSR) incorporating dilute acid pretreatment and enzymolysis was undertaken. The production of hydrogen and methane was 72.0 ± 10.7 and 295.4 ± 28.5 mL/g volatile solid, respectively. Different scenarios for techno-economic analysis were developed in terms of the dried/wet form of CSR and total solids content during fermentation. Results suggested that hythane from CSR was not economically feasible with a high production cost (1.39–2.33 €/m3). There was a trade-off relationship between the increase in methane yield through pretreatment and the associated cost. • Pilot-scale biohythane production from cassava stillage residue was studied. • Four scenarios for techno-economic analysis of hythane production were developed. • The production cost was not economically viable varying between 1.39 and 2.33 €/m3. • Profit was affected by total solid content, pretreatment and hydrogen production. [ABSTRACT FROM AUTHOR]

5-hydroxymethylfurfural (5-HMF) is typically found in hydrolysate produced by thermal pretreatment and wastewater streams, and its presence can significantly inhibit anaerobic digestion (AD) performance. This study comprehensively investigates the impact of adding 1–5 g/L granular activated carbon (GAC) on the AD of 0.5–4 g/L 5-HMF. The innovation of this study is to clarify the mechanism of direct interspecies electron transfer (DIET) in the AD system with 5-HMF as the sole source. Compared to the control group, adding 5 g/L GAC shows the most significant promotion effect, which increases the electron transfer activity of the sludge by 27.0%–75.0% and enhances the methane production peak rate by 27.5%–68.1%. GAC supplementation can rapidly reduce the concentration of 5-HMF by adsorption and alleviate its inhibition of microorganisms. SEM and microbial community analyses show that GAC enriches electroactive microbes and can promote AD by establishing the DIET pathway. [Display omitted] • First study to investigate the DIET potential in anaerobic digestion of 5-HMF. • GAC supplementation evidently intensified 5-HMF degradation and methane production. • The maximum methane yield by GAC addition was increased up to 36.7%. • Electron transfer activities of microbes increased by 27.0%–75.0% by GAC addition. • DIET connection was possibly established between exoelectrogens and methanogens. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is an efficient way to process organic waste to produce biogas. At the same time, one of the stages of anaerobic digestion so called dark fermentation (DF), which makes it possible to obtain biohydrogen. To increase the bioavailability and efficiency of mass transfer between feedstock particles and hydrolytics and, as a result, increase the DF efficiency, it is advisable to pretreat organic waste by various methods. One of the most promising and energy efficient methods of preparing the feedstock for anaerobic fermentation, including DF, is its processing in the vortex layer apparatus (VLA). However, not all aspects of VLA application in anaerobic digestion feedstock pretreatment systems have been fully considered: in order to introduce the VLA into the organic waste DF system, it is necessary to determine, among other things, the energy characteristics of VLA under various modes of its operation, and the data obtained must be used in the development of the energy balance of the anaerobic processing system. Thus, the purpose of this work is to experimentally determine the thermal effects of pretreatment of DF feedstocks in VLA under various modes of its operation using the response surface methodology. To achieve this goal, an experimental setup was developed and created, which made it possible to conduct an experiment based on the central composite design (CCD) using Design-Expert software. The resulting models and their response surfaces have a determination coefficient of more than 0.99, which indicates their adequacy. The coefficient of conversion of electricity into heat on the VLA coil is on mean at the level of 0.54 ± 0.11, and the coefficient of useful use of heat VLA for heating the feedstock is 0.42 ± 0.06, which indicates a high potential for using waste heat. Thus, the obtained models of thermal effects of pretreatment of DF feedstocks in the VLA can be used to determine both the heat directly introduced into the feedstock during pretreatment and the heat removed by the heat exchanger to maintain the VLA operating mode. In this case, the heat removed by the heat exchanger can be used as a source of low-grade heat. [ABSTRACT FROM AUTHOR]

Accurate prediction of biogas yield is crucial for optimizing waste-to-energy conversion systems in anaerobic co-digestion processes. In this study, a double input and single output (DISO) fuzzy mamdani model (FMM) was developed for the prediction of biogas yield in a pilot scale of 105-L mesophilic anaerobic sludge bio-digester. The input variables considered are the combination of cow dung and pig waste and the retention time (RT), while the output variable is the experimental biogas yield. Triangular Fuzzy Membership Functions (TFMF) were utilized to define the input and output datasets, and rules were derived from de-fuzzification. Comparative analysis between the FMM's predicted results and experimental values showcased its effectiveness in forecasting biogas yield during the anaerobic co-digestion of the hybrid wastes. Significantly, the FMM consistently produced results with low error values for the sample dataset, underscoring its accuracy even under stochastic conditions. This study emphasizes the FMM's ability to generate predictions with minimal deviations, offering superior results. As a prospect for future research, the implementation of hybrid algorithms may further enhance biogas yield prediction accuracy within waste-to-energy systems. [ABSTRACT FROM AUTHOR]

Biogas, a renewable energy source produced by the anaerobic digestion of organic matter, can reduce greenhouse gas emissions. The purification and hydrogen conversion of biogas enhance its versatility as an energy carrier and reduce dependency on fossil fuels. This sustainable process fosters a cleaner future. In this study, simulation models were used to optimize the process conditions and assess the technical feasibility of the biogas-to-hydrogen production. In addition to the anaerobic digestion process, simulation models were also developed for biogas purification via water scrubbing and hydrogen production via steam methane reforming (SMR) using Aspen Plus simulation software. Simulation results demonstrated that the maximum methane yield of 520 mL/gVS was achieved at an organic loading rate of 20 g/L, while the minimum yield of 230 mL/gVS was observed below 10 g/L. Optimal anaerobic digestion temperature for maximum gas yield (548 mL/gVS) was found to be 30 °C, with a decrease in biogas production above 40 °C. In the water scrubbing model, maximum CO 2 absorption occurred at 15 bar pressure, whereas reducing the pressure to 5 bar significantly lowered the absorption rate. The SMR model yielded the highest hydrogen production rate of 10.15 kg/h using purified methane (99%) as feed, but the methane content was affected by the biogas composition. [Display omitted] • Biogas production, purification, and hydrogen production model developed. • Biogas potential of biomasses predicted from ultimate and proximate values. • The model was validated with experiments, theory, and simulations models. [ABSTRACT FROM AUTHOR]

The Leach Bed Reactor (LBR) application is a promising alternative for the anaerobic digestion of solid waste and wastewater. In this study, the LBR was continuously operated for 160 days in four different phases, for co-fermentation of solid and liquid waste from the citrus agroindustry, at 37 °C, evaluating the effect of hydraulic retention time (HRT) and organic loading rate (OLR). The maximum volumetric hydrogen production (VHPR) was observed at an HRT of 12h (958.3 mLH 2.L-1.d-1); however, the highest hydrogen yield (HY) was identified at an HRT of 24h (104.9 mLH 2.g-1CHO). Based on the metabolic characteristics of microorganisms identified in higher relative abundance, by 16S rRNA sequencing, such as Lactobacillus, Caproicoproducens, Bifidobacterium, Olsenella, and Solobacterium, an occurrence of chain elongation pathways in the production of butyric and caproic acids was inferred, with hydrogen production resulting from the lactic acid oxidation. The maximum electricity production potential of 16.3 kWh.m-3 liquor was estimated. [Display omitted] • The leach bed reactor was applied to the dark fermentation of citrus waste. • The highest H 2 yield was obtained in a hydraulic retention time (HRT) of 24h. • The highest volumetric H 2 production rate was verified in HRT of 12h. • Lactobacillus was predominant in the fixed bed and leachate tank at HRT of 12h. • Caproiciproducens were identified with high relative abundance in HRT of 36h. [ABSTRACT FROM AUTHOR]

[Display omitted] • At OLR of 24.7 gVS/L, CH 4 yields of AD reactor at 45 °C was 536.23 mLCH 4 /gVS. • Fe0 and Fe 3 O 4 played a co-enhancing role in increasing CH 4 yield in AD at 45 °C. • Methanobacterium sp and Syntrophaceticus schinkii were key species in AD at 45 °C. • SAO-HM was main pathway to eliminate acidification and methanogenesis in AD at 45 °C. Deoiling of food waste (FW) after hydrothermal pretreatment occurs at high temperatures, and more energy is required for substrate cooling before the anaerobic digestion (AD) process. AD at the transition temperature (for example 45 °C) is good for energy saving and carbon emission reducing when treating deoiling FW. However, the metabolic activity of methanogens must increase at the transition temperatures. This study proposes the use of zero-valent iron (Fe0) and magnetite (Fe 3 O 4) to boost CH 4 yield from deoiling FW. The results showed a co-enhancing effect on CH 4 yield upgradation when using Fe0 and Fe 3 O 4 simultaneously, and the highest CH 4 yield reached 536.23 mLCH 4 /gVS, which was 67.5 % higher than that of Fe0 alone (320.14 mLCH 4 /gVS). In addition, a high organic loading was favorable for increasing the CH 4 yield from deoiling FW. Microbial diversity analysis suggested that the dominant methanogenic pathway at 45 °C was hydrogenotrophic methanogenesis. Herein, a potential metabolic pathway analysis revealed that the co-enhancing effects of Fe0 and Fe 3 O 4 enhanced syntrophic methanogenesis and possibly boosted electron transfer efficiency. [ABSTRACT FROM AUTHOR]