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• 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]

[Display omitted] • Food delivery boxes are tested for aerobic disintegration and anaerobic degradation. • Boxes made of paper only or with coatings (including polylactic acid) are analysed. • Paper is highly suitable for biological treatments behaving similarly to food waste. • Aerobic disintegration of coated boxes is much slower than that of paper only boxes. • Undigested polylactic acid coating is found in anaerobic semi-continuous tests. This study evaluated the fate of food delivery boxes when subjected to biological treatments, reproducing at the lab-scale the conditions of full-scale plants. Four paper-based boxes were composted: two made of paper only, one coupled with polylactic acid (PLA), and one with a barrier coating. One paper only box and the box with PLA were also investigated for their anaerobic degradability with biochemical methane potential (BMP) and semi-continuous tests. During composting, the boxes were not recognisable inside the compost after four (paper only boxes), eight (box with PLA), and twelve (box with barrier coating) weeks. In BMP tests, the paper only box showed a degradability similar to that of food waste (92 %), while the box with PLA degraded only at 76 %. Furthermore, undigested pieces of PLA were found in semi-continuous tests. Accordingly, paper resulted suitable for biological treatments, while the presence of PLA or other barrier coatings can be critical. [ABSTRACT FROM AUTHOR]

Biohythane, the promising gaseous biofuel, can be produced by the recirculated two-phase anaerobic digestion (R-TPAD). The effect of hydraulic retention time (HRT) as 30, 20 and 10 days on biohythane production via R-TPAD (recirculation ratio = 0.4) was investigated with co-digestion of food waste and paper waste. The results showed that HRTs of 30 and 20 days maintained stable performance for R-TPAD but HRT of 10 days led to the final decrease in biogas production. The failure in the end was attributed to the wash-out of microbes. The removal efficiencies for COD and carbohydrates were decreased by short HRTs while for VS it remained relatively stable at about 75.7 ± 4.0%. All through the operation, acidogenic phase and methanogenic phase were separated stably and butyrate pathway was the dominant pathway for hydrogen fermentation in the first stage. The microbial community in the first stage reached the highest diversity when total HRT was 20 days, where the hydrogen production rate was the highest. The genera Lactobacillus and Caproiciproducens kept dominating the dark fermentation in the acidogenic phase, and Ruminococcus and Methanosarcina were decreasing in the methanogenic phase. The biohythane yields were 411 mL/g-VS fed , 332 mL/g-VS fed and 253 mL/g-VS fed , respectively, where the H 2 contents were 18.4%, 14.7% and 8.8%, respectively. [Display omitted] • The R-TPAD system (R = 0.4) was operated for biohythane production. • R-TPAD operated under HRTs of 30 and 20 maintained stable performance. • Organic removals and biohythane yields were lowered by short HRTs. • Different microbial communities were identified by co-occurrence network. • Biohythane yields affected by different parameters were discussed. [ABSTRACT FROM AUTHOR]

• Simulation model developed for an anaerobic digester in Aspen Plus. • Organic feeds like cow dung, banana stem, and waste paper pulps are used. • Parameters like PTT, HRT, and F/W ratios are optimized for BioHydrogen production. • Sequence of influencing parameter is: PTT > HRT > F/W. • Optimal BioHydrogen yield obtained is 24.59% (CD), 25.27% (BS), and 24.21% (WPP). A simulation model was developed for biohydrogen production from organic feeds such as cow dung (CD), banana stem (BS), and waste paper pulps (WPP). Data from the model was used to generate a design of experiment (DoE) that analysed the data and optimizes the input parameters for optimized biohydrogen yield. Three input parameters taken for optimization were pretreatment temperature (PTT), hydraulic retention time (HRT), and feed-to-water (F/W) ratio. Results showed the optimal sequence of influencing parameters is PTT > HRT > F/W ratio. The optimal value of PTT was 75 ℃ for all feeds. In contrast, the HRT and F/W ratios were 13.1 days and 0.5 ratio for CD, 16.6 days and 1.5 ratio for BS, and 11.7 days and 1.4 ratio for WPP. At the same time, the optimal biohydrogen yield was 24.59 % (CD), 25.27 % (BS), and 24.21 % (WPP). Therefore, the current simulation and optimization had convincing results in optimizing commercial plants' biohydrogen production. [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]

[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]

[Display omitted] • EET enhancement strategies in AD for treating refractory wastewaters are reviewed. • Applications of refractory wastewaters treatment by enhanced EET are discussed. • Prospects of enhanced treating refractory wastewaters based on EET are proposed. In anaerobic digestion (AD) system for the treatment of refractory wastewater, extracellular electron transfer (EET) by microorganisms is critical in influencing pollutant degradation and wastewater resourcing. However, when removing pollutants from refractory wastewater using AD technology, hydrolysis by extracellular enzymes is limited by EET efficiency, which often difficult to achieve their efficient degradation. Meanwhile, the anaerobic bacterial community was impacted by the toxicity of pollutants, which also affected the interspecies electron transfer, which seriously affected the effluent water quality and methane production. Therefore, intensifying the EET efficiency of the anaerobic system has become the key to break through the bottleneck of refractory wastewater treatment and resource utilization technology. In this paper, the EET mechanisms in the AD system for treating refractory wastewaters are summarized and a systematic review of EET intensification strategies for AD systems for treating refractory wastewaters, including EET from microorganisms to pollutants and electroactive bacteria to methanogens, is presented. In addition, this paper discusses in detail the application of EET based on enhanced treatment of refractory wastewaters containing pollutants with electron-absorbing groups (azo dyes, halogenated compounds, nitroaromatic compounds) and heavy metal oxides, and it also looks forward to the research direction and application prospect of regulating EET. This paper will provide a reference for treating and resourcing refractory wastewaters by AD technology. [ABSTRACT FROM AUTHOR]

• Developed a novel toolbox, CHAD, able to combine AD models with Lagrangian CFD. • CHAD is validated against benchmark ADM1 implementation and OpenFOAM. • Benefits of incorporating CFD results to ADM is highlighted in case studies. Conventional anaerobic digestion models used in wastewater treatment plants suffer from inaccuracies due to the limited consideration given to hydrodynamics within the digester tank. A solution to this is to combine computational fluid dynamics simulations with anaerobic models. This paper introduces a novel methodology in the form of a software toolbox that implements the standard anaerobic digestion model no.1 in C++ and can interface with particle-based Lagrangian simulations. This method provides significantly more insights into the biochemical conversion process by accounting for the impact of the hydrodynamics on the biochemical reactions. The paper presents the background of the method along with a conceptual and numerical verification. It also presents a case study of a 3D lab scale digester comparing the results from the solver with the standard anaerobic digestion model. This integrated approach can be used by operators and designers for optimisations and also for predictive modelling. [Display omitted] [ABSTRACT FROM AUTHOR]

Various carbonaceous structures, such as graphite- and biochar-derived materials, have been recently developed to enhance biogas production by 1.3%–1130 % during anaerobic digestion (AD). There are several reviews discussing the promotion of direct interspecies electron transfer, but they lack a critical discussion of the various mechanisms that CMs can induce upon addition to AD systems. This paper specifically explores how the characterization of CMs (electrical conductivity, surface functional groups, specific surface area, surface charge, and hydrophobicity) affects the major mechanisms of action involved, i.e., interspecies electron transfer, buffering capacity, adsorption, and colonization, to fill the knowledge gap in this field. The feedstocks used and methods developed for synthesizing CMs and the applicability of various modification techniques to enhance the properties of CMs for such applications have been critically addressed. This review closes with a review of current challenges in the application of CMs and provides recommendations for future research. In conclusion, this review helps academic researchers and industrial professionals select suitable feedstocks and employ appropriate synthesis methods and modification strategies to prepare the most efficient CMs for AD enhancement. The figure was generated with BioRender. [Display omitted] • Enhance biogas yield achieved via DIET, colonization, adsorption and pH regulation. • Conductive materials enhance syntrophic microbe interactions via electron transfer. • Porous materials facilitate microbial colonization, boosting bioconversion. • Adsorptive materials like graphene oxide reduce the bioavailability of inhibitors. • Alkaline-modified biochar effectively mitigates acidification during digestion. [ABSTRACT FROM AUTHOR]

Effective municipal solid waste management (MSWM) posed a significant challenge for numerous developing nations, including Algeria. The imperative to convert household waste into value-added products for both environmental and economic benefits was crucial. However, limited knowledge and resources often hindered the exploitation of waste for energy generation. In Algeria, as in many African countries, landfilling remained the predominant method for disposing of household waste. This paper presented findings from a study conducted in Tlemcen Province, Algeria, shedding light on the severe environmental and health consequences resulting from mismanaged waste in the region. The investigation revealed that all waste sites in Algeria were not harnessed for energy production. A detailed analysis was conducted on a specific site, Jabal Al-Hadid, uncovering a waste composition of 62 % organic, 33 % recyclable, and 5 % non-recyclable materials. Anaerobic digestion was estimated to have produced approximately 84.23 × 106 m3/year of methane, with a potential electricity generation of about 192.37 GWh/year at this site. Highlighting the untapped potential, the utilization of landfill sites for energy production in Algeria could have reduced national electricity consumption in the construction sector by approximately 11.3 %. Despite the focus on a specific province, these findings had broader implications for addressing waste management challenges on a national scale. • Municipal Mismanagement Stalls Algeria's Zero Waste Goal. • Landfills in all Algerian cities can generate approximately 9485 GWh/year. • Algeria's waste-to-energy potential can cut 11.3 % of construction sector energy use. • Altering sites landfill into economic hubs offers novel waste management solution. [ABSTRACT FROM AUTHOR]

In recent decades, biogas production from anaerobic digestion of organic fractions of municipal solid waste and agricultural residues has emerged as a promising strategy for waste management and renewable energy generation. However, due to the complexity and heterogeneity of these feedstocks, an appropriate pre-treatment is required before anaerobic digestion to maximise biodegradability and enhance biogas production. This is especially true for lignocellulosic biomass, where maximum biogas potential is often difficult to reach due to the presence of a lignin barrier, which is not easily biodegradable. Pre-treatment technologies may significantly increase biogas production, up to 360 %, from organic fractions of municipal solid waste and agricultural residues. This paper first provides an overview of the pre-treatment technologies, including mechanical, chemical, biological, thermal, plasma, and combined treatments for a wide variety of feedstocks for biogas production from anaerobic digestion. These studies indicate that the selection of a pre-treatment technology mainly depends on the waste substrate characteristics, the desired end results, and resource availability. Furthermore, most studies emphasise the significance of balancing the benefits and drawbacks of pre-treatment technologies for sustainable waste-to-energy practices. Then, the article evaluates the scalability, technical feasibility, economic viability, industrial applicability and environmental sustainability of appropriate pre-treatment methods. This review will be a valuable resource for researchers, policymakers, and practitioners working in the field of waste-to-energy conversion through anaerobic digestion. • Pre-treatment enhances biodegradability and biogas production from lignocellulosic feedstock. • Variability of lignocellulosic feed necessitates novel and effective pre-treatment methods. • Effectiveness, cost, scalability, and sustainability dictate industrial applicability. • Up to 360 % improvement in AD biogas yields was reported with pre-treatment. • Choosing a suitable pretreatment requires a comprehensive context-specific approach. [ABSTRACT FROM AUTHOR]

[Display omitted] • Exploring adaptation of anaerobic digestion via gradual pH increase. • pH 8 was identified as upper limit for stable anaerobic digestion operation. • Eubacterium and Anaerobacterium enhanced reactor stability under high pH. • Stress applied via alkaline conditions increased syntrophic bacteria's abundance. This paper examines the adaptive responses of microbial communities to gradual shifts in pH toward the mild alkaline range in anaerobic digestion (AD) systems. The results indicate that a pH of 8.0 serves as a critical upper limit for stable AD operation, beyond which microbial efficiency declines, underscoring the importance of microbial resilience against elevated pH stress. Specifically, hydrolysis genera, e.g. Eubacterium and Anaerobacterium , and syntrophic bacteria were crucial for reactor stability. Fibrobacter had also been shown to play a key role in the accumulation of propionate, thus leading to its dominance in the volatile fatty acid profile throughout the experimental phases. Overall, this investigation revealed the potential adaptability of microbial communities in AD systems to mild alkaline pH shifts, emphasizing the hydrolysis bacteria and syntrophic bacteria as key factors for maintaining metabolic function in elevated pH conditions. [ABSTRACT FROM AUTHOR]

Simulating anaerobic digestion (AD) using a machine learning (ML) is important for guiding methane production in practice. But the performance of the ML is affected by operational conditions and microbial types and quantities, which lead to low accuracy of the traditional model. In this study, a combined ML algorithm SMOTER-GA-RF was constructed by expanding the number of genomic data, introducing oversampling technique (SMOTER) and genetic algorithm (GA) to increase prediction accuracy, which the test set R2 increased 36.22%. The normalized root mean square error and percent bias of the validation set (D2) were 8.92% (<10%) and 4.13% (<15%), indicating the accuracy of prediction. Simultaneously, the predictive accuracy of the validation sets (V1–V5) in the presence of Gaussian white noise remained high, confirming the robustness of the SMOTER-GA-RF. Furthermore, similar ML models were collected and compared, and it was found that SMOTER-GA-RF constructed in this paper had best effect. Finally, important factors affecting the AD performance of straw were analyzed using SHAP. The hydraulic retention time was controlled at approximately 40 d, volatile fatty acid should be controlled within 1000 mg/L, and the relative abundances of the important archaea Methanoculleus , Methanobacterium and Methanosarcina in the second stage of AD were controlled at 5–10%, <18%, and <5%. [Display omitted] • GA determined the hyper-parameters of the RF to increase the prediction performance. • SMOTER generated new samples strengthened the learning capacity of extreme data. • SMOTER-GA-RF model had good predictive ability and robustness in monitoring and controlling the AD process. • SHAP quantified the range of important features promoting the AD of straw lignocellulose. [ABSTRACT FROM AUTHOR]

In light of the substantial global production of biomass waste, effective waste management and energy recovery solutions are of paramount importance. Hydrothermal liquefaction (HTL) and anaerobic digestion (AD) have emerged as innovative techniques for converting biomass waste into valuable resources. Their integration creates a synergistic framework that mitigates inherent limitations, leading to improved efficiency, enhanced product quality, and the comprehensive utilization of biomass. This review paper investigates the integration of HTL and AD, highlighting its significance and potential benefits as well as the optimal sequencing (HTL followed by AD and AD followed by HTL). The review encompasses experimental procedures, factors influencing both sequencing options, energy recovery characterizations, final product outcomes, as well as toxicological assessments and discussions on reduction. Additionally, it delves into the transition towards a circular bioeconomy and discusses the challenges and opportunities intrinsic to these processes. The findings presented in this review offer valuable insights to shape future research in this evolving field. [Display omitted] • The integration of AD and HTL offers a complementary approach to waste treatment. • Our review examines both sequencing approaches: HTL followed by AD, and vice versa. • Key parameters and pretreatments were assessed to enhance overall energy recovery. • Integrating AD and HTL aligns with the circular bioeconomy for waste valorization. • Innovative methods for toxicity reduction in the HTL-AD systems were reviewed. [ABSTRACT FROM AUTHOR]

Energy scarcity and environmental pollution from biogenic residues and wastes are major challenges in the 21st century, which can be converted to useful renewable energy and reduce environmental threats. In Bangladesh, a tremendous amount of biogenic residues is generated which remains largely underutilized. Mono-digestion, which is a common practice in Bangladesh for biogenic residue processing, resulted in low biogas yield. However, Bangladesh has a vast source of biogenic residues which can be utilized through anaerobic co-digestion to increase biogas production. In this paper, a desk study and comprehensive review has been conducted in finding potentiality of biogenic residues in biogas production from available biogenic residues in Bangladesh. Research studies on co-digestion of biogenic residues were reviewed critically, and their practices and benefits on energy production and impact on the environment were stipulated in this study. The study shows that co-digestion of biogenic residues in appropriate ratio increases the biogas production, improves digested quality and reduces GHG emissions. [Display omitted] • Biogas production potential from agricultural and livestock sectors were analyzed. • State of art co-digestion options of animal dung as main feedstock was reviewed. • Co-digestion of crop residues and animal dung lessened environmental burden. • Digestate can be used as bio fertilizer or converted into other forms of fuels. [ABSTRACT FROM AUTHOR]

[Display omitted] • Meta-analysis provided the first insights into the anaerobic digestion of wood waste. • Pretreatment increased methane yield from wood waste more than other organic wastes. • A combination of pretreatment techniques could be more effective than a single method. • Random forest was the most precise model for predicting methane yield from wood waste. • Feature analysis showed that digestion time and particle size were the key variables. Anaerobic digestion is widely employed to process various organic wastes while generating renewable energy and nutrient-rich digestate. However, lignocellulosic wastes, especially wood waste, suffer from the recalcitrance associated with high lignin content, thereby adversely impacting on biogas production. It remains unclear whether wood waste is suitable as a feedstock for anaerobic digestion and to what extent pretreatment techniques could affect its biochemical methane potential. In this paper, 769 datasets on methane production from wood waste were collected for meta -analysis. The results showed an average 146 % increase in methane production for other organic wastes compared to wood waste when pretreatment techniques were not applied, but this gap could be mitigated to 99 % when pretreatment techniques were considered, indicating that pretreatment techniques could be more effective for wood waste. A further analysis of different pretreatment techniques showed that pretreatment significantly increased the methane production of wood waste by 113 % and that a combination of pretreatment techniques was more effective than a single method. Finally, three machine learning algorithms were applied to explore the relationship between methane production and selected variables. The results showed that the random forest method yielded better predictive performance for methane production (R2 = 0.9643) than artificial neural networks and support vector regression. Feature importance analysis found that particle size had a higher influence than temperature or feedstock composition. Overall, this study gives insight into the potential of utilizing wood waste as a feedstock for anaerobic digestion and the importance of employing suitable pretreatment methods. This work also reveals correlations between methane production and critical variables, which could serve as a guide for optimizing operational adjustments during anaerobic digestion. [ABSTRACT FROM AUTHOR]

This paper presents a novel method to incorporate the seasonal variations in gas demand and technical considerations of gas networks into the assessment of environmental sustainability and economic viability of biomethane production and injection into the grid. A consequential life-cycle assessment (LCA) is conducted to determine the environmental impacts of offsetting diesel in heavy goods vehicles (HGVs) and natural gas for residential heating. This is combined with an economic analysis to determine the total cost of carbon abatement. The results find that biomethane use in HGVs or for residential heating shows a significant reduction in emission in the selected impact categories of global warming potential (GWP), fine particulate matter formation (PM), and terrestrial acidification (AP). However, the freshwater eutrophication (EP) impact shows a slight increase when used to offset residential heating. A sensitivity analysis of the methane emissions leakage from the anaerobic digester and upgrader, finds that when the cumulative methane emissions leakage exceeds 5.5%, the production of bioCNG can be more greenhouse gas (GHG) intensive than fossil diesel on a well-to-tank basis. The results of the TCA highlight the importance of considering the technical constraints imposed by gas networks on the grid capacity to accept biomethane when considering the techno-econo-environmental impact of a biomethane plant size and location, with a range of 73 €/tCO 2 –177€/tCO 2 depending on the scenario. The authors conclude that while biomethane has significant potential as a sustainable alternative to reduce the consumption of fossil diesel for transport and natural gas for heating, consideration must be given to technical constraints of the gas network to maximise emission mitigation at minimal cost. [Display omitted] • Incorporates the seasonality of gas demand in an environmental assessment of biomethane. • The cumulative methane emissions leakage has a significant impact on the GHG intensity. • BioCNG offers greater emissions reduction compared to biomethane for residential heating. • The grid capacity to accept biomethane strongly influences the TCA. [ABSTRACT FROM AUTHOR]

• Self-developed vertical continuous push-flow dry anaerobic digestion reactor. • At an OLR of 3 g VS L-1 d-1, the operational performance of the system at this stage was the best in the whole set of experiments. • Methanoculleus and Methanobacterium play a key role in maintaining methanogenesis. • Functional genes were identified to reconstruct the methane metabolic pathway. In this study, the vertical continuous push-flow dry anaerobic digestion (AD) reactor was developed independently. Typical agricultural organic waste straw and cow dung were used as raw materials in this paper to carry out long-term continuous mixed dry AD experiments on a controlled laboratory scale. The experimental results showed that the system was in low-stress operation at an organic load rate (OLR) of 3 g VS L-1 d-1, the VS methane production rate was located at 225 ∼ 272 mL CH 4 g VS-1, and the volumetric methane production rate was located at 0.95 ± 0.08 L (L·d)-1, and the combination of the volumetric methane production rate, VS methane production rate, methane content of the gas, and the VS removal rate showed that the system's operational performance in this stage was in the best condition in the whole set of experiments. When the OLR reached 25 g VS L-1 d-1, the content of VFAs all began to climb rapidly above 8000 mg/L, with the content of acetic acid increasing most significantly due to the fact that the activity of acetic acid-type methanogenic bacteria was the first to be inhibited. Eventually, because of the kinetic differences between the hydrolytic acidifying bacteria and the methanogenic archaea, the final acidification destabilisation of the anaerobic digestion reactor occurred and the system was irreversibly destabilised. The system performance at this stage was in the best condition in the whole set of experiments. The study of microbial community succession and metabolic mechanisms showed that Methanoculleus and Methanobacterium play a key role in sustaining methane production, and the increased abundance and dominance of hydrogen methanogens implies that methane is produced via the hydrogen methanogenic pathway under high organic loading conditions. [ABSTRACT FROM AUTHOR]

The impact of ammonia on anaerobic digestion performance and microbial dynamics has been extensively studied, but the concurrent effect of anions brought by ammonium salt should not be neglected. This paper studied this effect using metabolomics and a time-course statistical framework. Metabolomics provides novel perspectives to study microbial processes and facilitates a more profound understanding at the metabolic level. The advanced statistical framework enables deciphering the complexity of large metabolomics data sets. More specifically, a series of lab-scale batch reactors were set up with different ammonia sources added. Samples of nine time points over the degradation were analyzed with liquid chromatography-mass spectrometry. A filtering procedure was applied to select the promising metabolomic peaks from 1262 peaks, followed by modeling their intensities across time. The metabolomic peaks with similar time profiles were clustered, evidencing the correlation of different biological processes. Differential analysis was performed to seek the differences in metabolite dynamics caused by different anions. Finally, tandem mass spectrometry and metabolite annotation provided further information on the molecular structure and possible metabolic pathways. For example, the consumption of 5-aminovaleric acid, a short-chain fatty acid obtained from l -lysine degradation, was slowed down by phosphates. Overall, by investigating the effect of anions on anaerobic digestion, our study demonstrated the effectiveness of metabolomics in providing detailed information in a set of samples from different experimental conditions. With the statistical framework, the approach enables capturing subtle differences in metabolite dynamics between samples while accounting for the differences caused by time variations. [Display omitted] • Ammonium salt anions affected microbial metabolite dynamics in anaerobic digestion. • 19 clusters of metabolites sharing similar time-course trajectories were identified. • Differential analyses selected 48 metabolites typically affected by anions and time. • 28 metabolites were annotated by MS-DIAL software with confident dot product scores. • Phosphates slowed down the consumption of 5-aminovaleric acid. [ABSTRACT FROM AUTHOR]

[Display omitted] • Food waste can be a promising bioethanol source. • First conversion of food waste to bioethanol using amylolytic yeast. • The higher food waste starch content was, the higher were the ethanol levels. • Co-fermentation of food waste and rice waste boosted bioethanol production. Organic fraction of municipal solid waste (OFMSW) has the potential to sustain large-scale biofuel production. So far, OFMSW is mainly converted into biogas by anaerobic digestion (AD), and limited research is available on its use to produce bioethanol. This paper reports, for the first time, the conversion of starch-rich OFMSW to bioethanol by using a novel yeast co-secreting both glucoamylase and alpha-amylase enzymes. As such, OFMSW can be converted to bioethanol without adding costly enzymes following a consolidated bioprocessing (CBP) approach. The OFMSW, sampled at an industrial AD plant, was processed to bioethanol with an outstanding yield, approaching 100 % of the theoretical maximum. Moreover, the co-conversion of OFSMW with starch-rice waste, namely discolored rice (DR) available in large quantities close to the AD plant, was performed to test the feasibility of valorizing different waste substrates simultaneously. The ethanol levels reached 60 g/L, indicating that both the developed process and yeast strain have important features towards ethanol production from organic waste streams. [ABSTRACT FROM AUTHOR]

[Display omitted] • Maximal VFAs and hydrogen yields reached 0.66 g/g-VS and 109 mL/g-VS, respectively. • SCG-derived VFAs offer a potential feedstock for microbial protein production. • Candida maltosa KKU-ARY2, a newly isolated yeast, accumulated protein of 43%. • Recycled solid residue after VFAs separation showed a promising methane production. Recovering nutrients from waste for biological processes aligns with sustainability principles. This study aimed to convert spent coffee grounds (SCG) into valuable products, including fermentable sugars, volatile fatty acids (VFAs), yeast-based single-cell protein and biofuels. Alkaline pretreatment was conducted before enzymatic hydrolysis, in which the pretreated SCG was hydrolyzed with varying enzyme loadings (20–60 filter paper units (FPU)/g-solid) and solid loadings (3–15 % w/v). The hydrolyzed slurry was utilized for VFAs and hydrogen production, yielding high values of 0.66 g/g-volatile solids (VS) and 109 mL/g-VS, respectively, using an enzyme loading of 50 FPU/g-solid and a solid loading of 3 % (w/v). The derived VFAs were used to cultivate a newly isolated yeast, Candida maltosa KKU-ARY2, resulting in an accumulated protein content of 43.7 % and a biomass concentration of 4.6 g/L. This study highlights the conversion of SCG into essential components, emphasizing the benefits of waste utilization through cascade bioprocesses. [ABSTRACT FROM AUTHOR]

[Display omitted] • The machine learning model for methane yield prediction was constructed. • Lignin content, organic loading and nitrogen content were vital predictive features. • The interaction of digestion time, cellulose and lignin contents was uncovered. • An online platform for methane yield prediction was created for public access. The biochemical methane potential test is a standard method to determine the biodegradability of lignocellulosic wastes (LWs) during anaerobic digestion (AD) with disadvantages of long experiment duration and high operating expense. This paper developed a machine learning model to predict the cumulative methane yield (CMY) using the data of 157 LWs regarding physicochemical characteristics, digestion condition and methane yield, with the coefficient of determination equal to 0.869. Model interpretability analyses underscored lignin content, organic loading, and nitrogen content as pivotal attributes for CMY prediction. For the feedstocks with a cellulose content exceeding about 50%, the CMY in the early AD stage would be relatively lower than those with low cellulose content, but prolonging digestion time could promote methane production. Besides, lignin content in feedstock surpassing 15% would significantly inhibit methane production. This work contributes to valuable guidance for feedstock selection and operation optimization for AD plants. [ABSTRACT FROM AUTHOR]

This paper presents a first-principles model for the recovery of dissolved gases from liquids using a sidestream hollow-fiber membrane module. The model avoids the use of new empirical coefficients, thus providing a parametric understanding of the process behavior for future design and optimization of membrane modules. This type of first-principles model could be particularly useful when gas recovery is beneficial to biological or chemical reactions of interest, such as the acetogenesis reactions in two-stage anaerobic digesters. The steady-state behavior of the model was validated against both new experimental data for the recovery of H 2 , CH 4 and H 2 –CH 4 mixtures from pure water, as well as existing published data. The modeled gas recovery predictions agreed with experimental data to an absolute average error of 13%, and an average R 2 value of 0.98. Parametric analysis of mixed-gas recovery suggests possible key transition points in the composition of the recovered gases. For example, at 40 °C, increasing trans-membrane pressure while keeping hydraulic residence time (HRT) under 0.5 s will result in an increase in the ratio of H 2 to CH 4 recovered. Otherwise, increasing trans-membrane pressure will instead decrease the ratio of H 2 to CH 4 recovered. The model has potential to be extended to transient analysis, but has yet to be validated with transient experimental data. This model was successfully implemented in both Python and MATLAB, and provides valuable insights for future net-energy optimization for anaerobic digestion systems with in-situ gas recovery. [Display omitted] • Hollow-fiber gas extraction model accurate to within 15% of experimental data. • Successfully modeled O 2 , N 2 , H 2 , and CH 4 extraction from water. • Lumen-side model only requires knowledge of fluid, gas, and membrane properties. • Model can be used to predict kinetic effects of changing liquid residence time. • Model can be extended to include transient effects. [ABSTRACT FROM AUTHOR]