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Anaerobic digestion is a promising technology for the treatment of food waste (FW) but it requires optimization to improve its performance. This study investigated whether combining the addition of biochar with lipase pretreatment could improve the anaerobic digestion of FW. The results showed that biochar stimulated the release of soluble substances, resulting in an increase in the methane yield of groups with added biochar by 16.24% to 19.36% in comparison with the group without biochar. Lipase pretreatment substantially shortened the fermentation time required to complete the anaerobic digestion, from 15 to 9 days. Lipase pretreatment further improved microbial abundance and promoted the enrichment of functional microbes in the anaerobic digestion of FW mediated by biochar. It also changed the methane production pathway from acetotrophic to hydrogenotrophic, thereby ensuring the stability of the anaerobic digestion system in the presence of a high ammonia nitrogen concentration. [ABSTRACT FROM AUTHOR]

To solve the bottleneck of low degradation rate and low biogas yield in anaerobic digestion of food waste, the addition of anionic surfactant sodium N-lauroylsarcosinate (SN) and nonionic surfactant primary alcohol ethoxylate (AEO) were proposed. The results showed that both surfactants could promote the methane production and facilitate the degradation of food waste. The highest methane yield per mass of volatile solid was obtained in 0.1 g/L AEO (497.14 mL) and 1 g/L SN (445.51 mL), which was improved by 92% and 72% compared with the control group. While with the increase of surfactant concentration, methane yield was decreased due to negative effect caused by the surfactant. This corresponded with the variation of pH, total volatile fatty acids (TVFAs), and soluble chemical oxygen demand (SCOD). The microbial community analysis showed that the relative abundance of methanobacterium increased while the relative abundance of methanosaeta decreased after the addition of surfactant. Meanwhile, the methane production pathway was shifted from codominance of hydrogenotrophic and aceticlastic methanogens to predominance by hydrogenotrophic methanogens in the groups with low concentration of AEO and SN. [ABSTRACT FROM AUTHOR]

Abstract The study investigates the potential of anaerobic co-digestion (AcoD) as a sustainable solution for managing putrescible organic waste generated by leather processing. Three experiments were conducted to assess the impact of various tannery wastes, pretreatment methods, and waste combinations on methane production. Experiment 1 demonstrated that co-digesting tannery wastewater primary sludge (TWPS) and fleshings significantly increased methane yield compared to digesting TWPS alone, though the addition of chromium- and vegetable-tanned leather wastes decreased yield. Experiment 2 explored TWPS pretreatment methods and found that ultrasonic pretreatment increased soluble chemical oxygen demand (SCOD) but did not significantly improve methane yield, suggesting that pretreatment may not be necessary. Experiment 3 revealed that increasing the proportion of fleshings to TWPS resulted in higher methane yield, ranging from 226.52 mL/gVS with 6% fleshings to 395.71 mL/gVS and 538.34 mL/gVS with 12% and 20% of fleshings, respectively. Additionally, this increase in fleshings also led to a reduction in digester volume. These findings highlight the importance of AcoD in addressing both environmental and economic challenges in the leather industry. Graphical Abstract

BACKGROUND: The addition of conductive materials or the application of external voltage is a promising novel methodology to enhance methane production in anaerobic digesters. However, there is limited knowledge about their individual or combined effects on the anaerobic digestion of dairy wastewater. The aim of this study was to examine the effects of granular activated carbon (GAC) or magnetite addition and external voltage application, both individually and in combination, for the anaerobic digestion of real, undiluted dairy wastewater. RESULTS: The results showed that the estimated maximum methane production rate increased significantly (P < 0.05) from 143 ± 8 mL gVSadded−1 day−1 in the control reactors to 163 ± 11 mL gVSadded−1 day−1 and 166 ± 11 mL gVSadded−1 day−1 in the reactors containing GAC, with or without the combination of external voltage, respectively. The addition of GAC, in both cases, resulted in higher consumption rate of acetate, indicating a promotion of the methanogenesis step. By contrast, the application of external voltage or the addition of magnetite had no significant effect on either methane production rate nor methane yield. Moreover, the analysis of the microbial community showed that the addition of GAC resulted in the enrichment of Desulfobacterota, Methanosarcina, Candidatus Methanofastidiosum and Methanolinea. CONCLUSION: Overall, GAC addition seems a promising strategy to increase methane production in anaerobic digesters treating dairy wastewater. © 2024 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Anaerobic digestion of waste activated sludge (WAS) was one of the directions of sludge treatment, but how to effectively improve the production of methane as a resource product of anaerobic digestion of sludge still needs further research. The study examined how the combination of potassium ferrate (PF) and thermal hydrolysis (TH) pretreatment affected methane production from sludge. The results demonstrated a positive synergistic effect on methane production with PF-TH pretreatment. Specifically, by employing a 0.05 g/g TSS (total suspended solids) PF in conjunction with TH at 80 °C for 30 min, the methane yield increased from 170.66 ± 0.92 to 232.73 ± 2.21 mL/g VSS (volatile suspended solids). The co-pretreatment of PF and TH has been substantiated by mechanism studies to effectively enhance the disintegration and biodegradability of sludge. Additionally, the variation of microbial community revealed an enrichment of active microorganisms associated with anaerobic digestion after treated with PF + TH, resulting in a total abundance increase from 11.87 to 20.45% in the PF + TH group. [ABSTRACT FROM AUTHOR]

This study proposes the was to evaluate the stability and methane production with organic load differents in an upflow anaerobic sludge blanket reactor (UASB) treating swine wastewater by methods of multivariate analysis. Four organic loads were used with average hydraulic holding times of one day. The methods of data analysis of linear regression, Pearson correlation, principal component analysis and hierarchical clustering analysis were used for understanding stability and methane production in the reactor. The highest concentrations of bicarbonate alkalinity of 683 mg L−1 CaCO3 and total volatile acids of 1418 mg L−1 HAc with maximum organic loading applied were obtained. The optimal stability conditions occurred at an intermediate and partial alkalinity ratio between 0.24 and 0.25 observed in initial phases with a chemical oxygen demand (COD) removal of 47–57%. Maximum methane production was 9.0 L CH4 d−1 observed with linear regression positive and occurred at the highest applied organic load, corresponding to the highest COD removal efficiency and increased microbial biomass. Positive and negative correlation between functional stability in anaerobic digestion showed regular activity between acids, alkalinity and organic matter removal. This fact was also proven by the analysis of principal components that showed three components responsible for explaining 83.2% of the data variability, and the alkalinity, organic matter influent and organic acids had the greatest effects on the stability of the UASB reactor. Hierarchical clusters detected the formation of five groupings with a similarity of 50.1%, indicating that temperature and pH were variables with unitary influences on data dimensionality. [ABSTRACT FROM AUTHOR]

The integrated system of anaerobic digestion and microbial electrolysis cells (AD-MEC) was a novel approach to enhance the degradation of food waste anaerobic digestate and recover methane. Through long-term operation, the start-up method, organic loading, and methane production mechanism of the digestate have been investigated. At an organic loading rate of 4000 mg/L, AD-MEC increased methane production by 3–4 times and soluble chemical oxygen demand (SCOD) removal by 20.3% compared with anaerobic digestion (AD). The abundance of bacteria Fastidiosipila and Geobacter, which participated in the acid degradation and direct electron transfer in the AD-MEC, increased dramatically compared to that in the AD. The dominant methanogenic archaea in the AD-MEC and AD were Methanobacterium (44.4–56.3%) and Methanocalculus (70.05%), respectively. Geobacter and Methanobacterium were dominant in the AD-MEC by direct electron transfer of organic matter into synthetic methane intermediates. AD-MEC showed a perfect SCOD removal efficiency of the digestate, while methane as clean energy was obtained. Therefore, AD-MEC was a promising technology for deep energy transformation from digestate. [ABSTRACT FROM AUTHOR]

This is a prime time to develop and implement the "waste to energy" projects across the globe to attain a sustainable environment. Anaerobic digestion (AD) has attracted the scientific community due to its simplicity and easiness to handle, and has the potential to utilize any kind of organic waste to produce a mixture of combustible gases, i.e., biogas and digested slurry, which has further applications in agriculture, solid biofuels, and purification. The process, in turn, reduces the local waste and helps in recycling in a manner that reduces greenhouse gas (GHG) emission, conserves the resources, and establishes a circular economy in the time of undetermined future for the production of energy and safe disposal of the waste. However, the conventional processes encounter with the low biogas yield and long retention time, which discourage the developers. To enhance biogas yield and quality, the momentum of research has increased towards implementation of advanced techniques for development of efficient processes. The present article summarizes the effect of different operational parameters on AD and impact of advanced techniques for enhanced biomethane/biogas. The article further covers the life cycle assessment (LCA) and techno-economic aspect (TCA) of the AD process. This will provide the comparison of different advanced techniques in terms of biomethane/biogas yield. [ABSTRACT FROM AUTHOR]

The study investigates the potential of anaerobic co-digestion (AcoD) as a sustainable solution for managing putrescible organic waste generated by leather processing. Three experiments were conducted to assess the impact of various tannery wastes, pretreatment methods, and waste combinations on methane production. Experiment 1 demonstrated that co-digesting tannery wastewater primary sludge (TWPS) and fleshings significantly increased methane yield compared to digesting TWPS alone, though the addition of chromium- and vegetable-tanned leather wastes decreased yield. Experiment 2 explored TWPS pretreatment methods and found that ultrasonic pretreatment increased soluble chemical oxygen demand (SCOD) but did not significantly improve methane yield, suggesting that pretreatment may not be necessary. Experiment 3 revealed that increasing the proportion of fleshings to TWPS resulted in higher methane yield, ranging from 226.52 mL/gVS with 6% fleshings to 395.71 mL/gVS and 538.34 mL/gVS with 12% and 20% of fleshings, respectively. Additionally, this increase in fleshings also led to a reduction in digester volume. These findings highlight the importance of AcoD in addressing both environmental and economic challenges in the leather industry. [ABSTRACT FROM AUTHOR]

Psychrophilic anaerobic digestion emerges as an appealing integrated solution for the management of agricultural waste, particularly for farmers in regions where the average temperature does not exceed 26 °C, as seen in coffee cultivation. Therefore, this study seeks to assess the biomethane potential of thermochemical-treated coffee husk through psychrophilic anaerobic digestion (C3-20 °C-w/pretreatment). To examine its viability, outcomes were compared with reactors operating at both mesophilic (C1-35 °C) and psychrophilic (C2-20 °C) conditions, albeit without the use of pretreated coffee husk. The C3-20 °C-w/pretreatment test demonstrated a 36.89% increase (150.47 NmL CH4/g VS; 161.04 NmL CH4/g COD), while the C1-35 °C test exhibited a 24.03% increase (124.99 NmL CH4/g VS; 133.77 NmL CH4/g COD), both in comparison to the C2-20 °C test (94.96 NmL CH4/g VS; 101.63 NmL CH4/g COD). Notably, the C3-20 °C-w/pretreatment trial yielded superior outcomes, accompanied by an associated energy output of 3199.25 GWh/year, sufficient to meet the annual energy demands of 494 residences. This marks an increase of 83 and 182 million residences compared to the mesophilic and psychrophilic AD of CH without pretreatment, respectively. [ABSTRACT FROM AUTHOR]

Microbial electrochemical systems (MESs) can enhance methane production in anaerobic digestion, but their performance is hindered by inadequate electron transfer between the cathode and microbes. Magnetite–zeolite (MZ)‐based catalysts accelerate electron exchange; however, the optimal loading of MZ is crucial for maximizing MES performance. In this study, different loadings of the MZ catalyst ranging from 0 to 2 mg cm−2 on the cathode were evaluated to obtain an optimum loading for maximizing methane recovery from MES. Electrochemical analyses demonstrated enhanced electrochemical reduction kinetics of the cathode with increased MZ loading from 0 to 2 mg cm−2. Among the tested loadings, the MES with 1 mg cm−2 MZ on the cathode exhibited the highest methane production rate at 548 mL L−1 d−1, surpassing other MES operations with 2 and 0.5 mg cm−2 (499 and 434 mL L−1 d−1, respectively). Additionally, the MES with 1 mg cm−2 MZ demonstrated the highest soluble chemical oxygen demand removal efficiency of 87% and total coulomb recovery of 1444.06C ± 42.60C, with the lowest amount of volatile fatty acids accumulation. Consequently, MZ is recommended as a superior catalyst for enhancing MES performance and suggested to utilize 1 mg cm−2 MZ loading on the cathode to maximize methane production. [ABSTRACT FROM AUTHOR]

Vinasse, a byproduct of ethanol production from sugarcane, is a rich organic matter and poses environmental challenges due to its high pollutant content. Effective biomethane production from vinasse can mitigate its environmental impact by converting organic matter into a useful energy source while reducing its pollutant load. The biomethane production by anaerobic digestion (AD) process of the vinasse byproduct was examined on a laboratory scale. In this regard, several loads from 0.5 to 7 g VS/L were investigated to assess AD performance and methane production. This study investigated how two separate factors, namely the load and hydraulic retention time (HRT), affect both cumulative methane production (CMP) and methane yield (YCH4). This investigation utilized a response surface methodology known as the central composite design (RSM-CCD). Statistical analysis of variance (ANOVA) was employed to evaluate the effectiveness of the model generated. Thus, the model's fit, YCH4 has a maximum R2 value of 0.9759. The results revealed an astounding level of agreement between the experimental data and the proposed model. The RSM results revealed maximum CMP and YCH4 values of 409.82 ml and 178.95 ml/g VS respectively, obtained for optimum load values of 2.17 g VS/L and HRT of 15 h. The results emphasize the environmental and economic significance of AD, providing a sustainable waste management solution that helps reduce greenhouse gas emissions and organic pollution. Additionally, it generates valuable biogas and biofertilizers, presenting economic opportunities through renewable energy production and resource recovery. This approach not only alleviates the environmental burden of vinasse but also enhances the economic viability of ethanol production by creating additional revenue streams.

The presented set of data brings results of the experimental production of biogas and methane from silages of alternative substrates consisting of maize and three leguminous species with a potential to make the production of biogas more friendly to the environment because the cultivation of legumes is generally considered to be more environment friendly than the cultivation of maize: white sweet clover (Melilotus albus Medik.), fodder vetch (Vicia villosa Roth.) and white lupin (Lupinus albus L.). Obtained data allow to compare the composition of experimental substrates and their important parameters (VS, DM, NDF, ADF, CF, starch, cellulose, hemicellulose, CP, lipids and ADL) as well as the yield of biogas, methane and methane in biogas from silage produced as a monosubstrate from the biomass of maize shreddings on the one side with silages produced from the mixture of biomass from maize and diverse legumes on the other side. This set of data can contribute to awareness about possibilities for reducing environmental risks connected with the cultivation of maize in growers of energy crops and operators of biogas plants. The reason is that a considerable number of farmers do not use new technologies of growing biomass for the production of biogas as they cannot quantify the potential impact on biogas yield and hence on the profitability of biogas plant operation. The measured values demonstrate that silages made from the mixed culture were reaching at least the same production of biogas and its quality as the monocultural maize silage.

ABSTRACT: Similar to all dairy systems internationally, pasture-based dairy systems are under increasing pressure to reduce their greenhouse gas (GHG) emissions. Ireland and New Zealand are 2 countries operating predominantly pasture-based dairy production systems where enteric CH4 contributes 23% and 36% of total national emissions, respectively. Ireland currently has a national commitment to reduce 51% of total GHG emissions by 2030 and 25% from agriculture by 2030, as well as striving to achieve climate neutrality by 2050. New Zealand's national commitment is to reduce 10% of methane emissions by 2030 and between 24% and 47% reduction in methane emissions by 2050. To achieve these reductions, factors that affect enteric methane (CH4) production in a pasture-based system need to be investigated. The objective of this study was to assess the relationship between enteric CH4 and other animal traits (feed intake, metabolic liveweight, energy corrected milk yield, milk urea concentration, and body condition score [BCS]) in a grazing dairy system. Enteric CH4 emissions were measured on 45 late lactation (213.8 ± 29 d after calving) grazing Holstein-Friesian and Holstein-Friesian × Jersey crossbred cows (lactation number 3.01 ± 1.65, 538.64 ± 59.37 kg live weight, and 3.14 ± 0.26 BCS) using GreenFeed monitoring equipment for 10 wk. There was a training period for the cows to use the GreenFeed of 3 wk before the 10-wk study period. The average enteric CH4 produced in the study was 352 g ± 45.7 g per day with an animal to animal coefficient of variation of 13%. Dry matter intake averaged 16.6 kg ± 2.23 kg per day, while milk solids (fat plus protein) averaged 1.62 kg ± 0.29 kg per day. A multiple linear regression model indicated that each one unit increase in energy corrected milk yield, metabolic liveweight and milk urea concentration, resulted in an increase in enteric CH4 production per day by 3.9, 1.74, and 1.38 g, respectively. Although each one unit increase in BCS resulted in a decrease in 39.03 g CH4 produced per day. When combined, these factors explained 47% of the variation in CH4 production, indicating that there is a large proportion of variation not included in the model. The repeatability of the CH4 measurements was 0.66 indicating that cows are relatively consistently exhibiting the same level of CH4 throughout the study. Therefore, enteric CH4 production is suitable for phenotyping.

Psychrophilic anaerobic digestion emerges as an appealing integrated solution for the management of agricultural waste, particularly for farmers in regions where the average temperature does not exceed 26 °C, as seen in coffee cultivation. Therefore, this study seeks to assess the biomethane potential of thermochemical-treated coffee husk through psychrophilic anaerobic digestion (C3-20 °C-w/pretreatment). To examine its viability, outcomes were compared with reactors operating at both mesophilic (C1-35 °C) and psychrophilic (C2-20 °C) conditions, albeit without the use of pretreated coffee husk. The C3-20 °C-w/pretreatment test demonstrated a 36.89% increase (150.47 NmL CH4/g VS; 161.04 NmL CH4/g COD), while the C1-35 °C test exhibited a 24.03% increase (124.99 NmL CH4/g VS; 133.77 NmL CH4/g COD), both in comparison to the C2-20 °C test (94.96 NmL CH4/g VS; 101.63 NmL CH4/g COD). Notably, the C3-20 °C-w/pretreatment trial yielded superior outcomes, accompanied by an associated energy output of 3199.25 GWh/year, sufficient to meet the annual energy demands of 494 residences. This marks an increase of 83 and 182 million residences compared to the mesophilic and psychrophilic AD of CH without pretreatment, respectively.

[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]

Similar to all dairy systems internationally, pasture-based dairy systems are under increasing pressure to reduce their greenhouse gas (GHG) emissions. Ireland and New Zealand are 2 countries operating predominantly pasture-based dairy production systems where enteric CH 4 contributes 23% and 36% of total national emissions, respectively. Ireland currently has a national commitment to reduce 51% of total GHG emissions by 2030 and 25% from agriculture by 2030, as well as striving to achieve climate neutrality by 2050. New Zealand's national commitment is to reduce 10% of methane emissions by 2030 and between 24% and 47% reduction in methane emissions by 2050. To achieve these reductions, factors that affect enteric methane (CH 4) production in a pasture-based system need to be investigated. The objective of this study was to assess the relationship between enteric CH 4 and other animal traits (feed intake, metabolic liveweight, energy corrected milk yield, milk urea concentration, and body condition score [BCS]) in a grazing dairy system. Enteric CH 4 emissions were measured on 45 late lactation (213.8 ± 29 d after calving) grazing Holstein-Friesian and Holstein-Friesian × Jersey crossbred cows (lactation number 3.01 ± 1.65, 538.64 ± 59.37 kg live weight, and 3.14 ± 0.26 BCS) using GreenFeed monitoring equipment for 10 wk. There was a training period for the cows to use the GreenFeed of 3 wk before the 10-wk study period. The average enteric CH 4 produced in the study was 352 g ± 45.7 g per day with an animal to animal coefficient of variation of 13%. Dry matter intake averaged 16.6 kg ± 2.23 kg per day, while milk solids (fat plus protein) averaged 1.62 kg ± 0.29 kg per day. A multiple linear regression model indicated that each one unit increase in energy corrected milk yield, metabolic liveweight and milk urea concentration, resulted in an increase in enteric CH 4 production per day by 3.9, 1.74, and 1.38 g, respectively. Although each one unit increase in BCS resulted in a decrease in 39.03 g CH 4 produced per day. When combined, these factors explained 47% of the variation in CH 4 production, indicating that there is a large proportion of variation not included in the model. The repeatability of the CH 4 measurements was 0.66 indicating that cows are relatively consistently exhibiting the same level of CH 4 throughout the study. Therefore, enteric CH 4 production is suitable for phenotyping. [ABSTRACT FROM AUTHOR]

Due to low degradability of plastic materials, high usage, and low cost, microplastics (MPs) is becoming ubiquitous environmental pollutant. Wastewater treatment plants (WWTP) are one of main sources, where most of the MPs from wastewaters ends in waste sludge. Anaerobic digestion is one of most promised techniques of waste sludge management. The aim of this paper was to evaluate the impact of polyethylene terephthalate (PET) and polypropylene (PP) microplastics in the waste sludge with and without ozonation as possible pretreatment, on biogas and methane production with OxiTop® method. In the first set of experiments, PET inhibited (up to 6% at 0.1 g L−1) or promoted (up to 3% at 1 g L−1) methane production but increased cumulative biogas production (up to 38% at 0.5 g L−1). PP inhibited methane production (up to 5% at 0.5 g L−1) but its impact on biogas production was dependent upon concentration of MPs added. In the second set of experiments, pretreatment of non-contaminated waste sludge by ozonation (3.54 gozone h−1) inhibited methane yield. Longer time of ozonation of PP-contaminated waste sludge reduced inhibition of methane yield, while in the case of PET-contaminated waste sludge, it was increased. [ABSTRACT FROM AUTHOR]

The aim of the present research was to investigate the influence of the application of a novel cold-pressing system in olive oil manufacturing on the characteristics of olive pomace (OP) and on its valorization by anaerobic digestion (AD). Green olives and olives in veraison, both from the Picual variety, were used with the objective of assessing the effect of ripening level on the performance of the AD processes. The AD processes of these OPs were assessed in biochemical methane potential (BMP) tests. The maximum methane yield (327 ± 5 mL CH4/g VS) and biodegradability value (90.8%) were found for the OP derived from green olives without cold-pressing, which showed the highest soluble COD (113 g O2/L) and the lowest total phenolic concentration (9 g gallic acid/L). The first-order and Transference Function (TF) kinetic models were employed to evaluate the variation in methane production with time and to obtain the kinetic parameters of the anaerobic processes of the four OPs tested. The kinetic constant from the first-order model, k, did not show significant differences for the four OPs tested and ranged between 0.23 and 0.27 day−1. The TF revealed that the values for the maximum methane production rate (Rmax) were slightly higher for the OPs derived from green olives compared to those obtained from olives in veraison. For the green olives, the cold-pressing system caused a decrease in the value of Rmax from 87 ± 7 to 73 ± 6 mL CH4/(g VS·d). [ABSTRACT FROM AUTHOR]

The Chinese dome digester (CDD) is a cost-effective, self-mixed biodigester that is widely used in developing countries to treat biodegradable waste such as food waste. However, the scum formation owing to inadequate mixing remains a persistent issue in CDD operations. To address this issue, a newly designed two-way flow CDD (TWF-CDD) was proposed to improve mixing, prevent scum, and enhance methane yield. Computational fluid dynamics (CFD) simulations, scum-breaking tests, and semi-continuous anaerobic digestion (AD) experiments were employed to assess the performance of the TWF-CDD and compared it with the conventional CDD (C -CDD). In the CFD simulation, a 3D volume of fluid model was applied. The mixing conditions of the semi-continuous AD were 0 (control) and 8 times per day. The regions inside the digester with slurry velocity <0.02 m s−1 were considered dead zones. The C -CDD and TWF-CDD exhibited dead zone volumes of 46.7% and 25.3%, respectively. The scum-breaking test aligned with the CFD observations. Scum persisted even after 5 mixing cycles in C -CDD, whereas TWF-CDD required only 3 mixing cycles to completely break scum, indicating its superior mixing performance. In the AD experiments, mixing 8 times per day effectively prevented scum formation in TWF-CDD, whereas C -CDD still showed an average scum thickness of 14 mm. The average methane yield was 477 mL g-VS−1 and 648 mL g-VS−1, respectively for TWF-CDD and C -CDD. These results effectively demonstrated the efficacy of the TWF-CDD design in improving mixing, eradicating scum, and maximizing methane yield with almost no additional investment cost. • CFD simulations demonstrated reduced dead zones in a two-way flow dome digester. • Scum formation was prevented during anaerobic digestion of food waste. • The absence of scum ensured an active working volume and enhanced methane yield. • The two-way flow Chinese dome digester showcased excellent mixing and treatment performance. [ABSTRACT FROM AUTHOR]

The current investigation delved into the utilization of cattle and municipal sanitary inocula for anaerobic digestion of poultry wastes, addressing a crucial and pragmatic challenge in waste management. The emphasis on poultry waste is pertinent due to its well-documented impediments in anaerobic digestion, attributed to heightened levels of ammonia and volatile fatty acids (VFAs). The strategic selection of cattle and municipal sanitary inocula suggests an approach aimed at bolstering the anaerobic digestion process. In this study, we evaluated the use of cattle and municipal sanitary inocula for the anaerobic digestion of various poultry wastes, which is often challenged by high levels of ammonia and volatile fatty acids (VFAs). The substrates tested included belt waste (Poultry A), poultry litter plus feed residues (Poultry B), tray hatchery ©, and stillage. These substrates were processed in two continuous stirred tank reactors (CSTRs), R-1 (with antibiotic monensin) and R-2 (without monensin). Initially, both reactors operated with the same hydraulic retention time (HRT), using a substrate ratio of stillage: belt: tray hatchery (S:B:T) of 70:15:15. On the 41st day, the HRT was adjusted to 20 days, and the substrate ratio was changed to S:A:T 70:40:40. The specific methane yield for R-1 started at 10.768 L g−1 COD, but decreased to 2.65 L g−1 COD by the end of the experiment. For R-2, the specific methane yield varied between 0.45 L g−1 COD and 0.243 L g−1 COD. Microbial composition in the reactors changed over time. In R-1, bacteroides were consistently dominant, while firmicutes were less abundant compared to R-2. Proteobacteria were initially low in abundance, but spirochetes were found in both reactors throughout the experiment. The study concluded that Poultry B substrates, due to their rich nutrient and trace element composition, are suitable for biogas plants. Municipal sanitary inocula also showed promise due to their resilience in high ammonia concentrations. Further research into biofilm interactions is recommended to better understand microbial responses to high ammonia concentrations, which can lead to propionate production in anaerobic digestion (AD). [ABSTRACT FROM AUTHOR]

Traditionally, anaerobic digestion has been applied to mixed sludge, combining primary sludge (PS) with secondary sludge. However, recent research has unveiled the advantages of dedicated PS digestion due to its higher energy content. Anaerobic digestion (AD) of primary sewage sludge can offer a sustainable solution for managing sewage sludge while generating renewable energy. The present study provides a comprehensive examination of the current state of knowledge regarding the anaerobic digestion of PS. Co-digestion of PS with organic substrates, including food waste and agro-industrial residues, emerges as a promising approach to boost biogas production. Additionally, the utilization of additives such as glucose and clay minerals has shown potential in improving methane yield. Critical factors affecting AD, such as pretreatment methods, carbon-to-nitrogen (C/N) ratio, temperature, pH, volatile fatty acids (VFAs) levels, organic loading rates (OLR), inoculum-to-substrate ratio (ISR), and the role of additives, have been meticulously studied. Finally, this review consolidates existing knowledge to advance our understanding of primary sewage sludge anaerobic digestion, fostering more efficient and sustainable practices in sludge management and renewable energy generation. [ABSTRACT FROM AUTHOR]

Dairy cows are the highest daily and annual methane (CH4) producers among all cattle categories. So, the present study aimed to evaluate the effect of increasing supplementation levels of a low-quality forage on dry matter intake (DMI), DM digestibility (DMD), milk production, enteric CH4 emission, gross energy, and protein partitioning in Holstein cows. In total, eight cows (112 ± 38 days postpartum; mean ± s.d.) were randomly assigned to 4 treatments composed of 4 dietary neutral detergent fibre (NDF) inclusion levels (40.2% (control), 43.3%, 46.5%, and 50.5%) in a 4 × 4 repeated Latin square experimental design. The cows were fed corn + alfalfa silage and a concentrate (60:40 forage:concentrate ratio). To increase the contents of low-quality NDF, part of the silage was replaced with maize stover (MSTV). The CH4 production was measured in an open-circuit respiration chamber. The DMI increased significantly and linearly (p < 0.05) with increasing levels of MSTV. However, the CH4 yield decreased (p < 0.0001) as the NDF level increased (32.1, 28.1, 23.1, and 21.3 CH4 L/kg DMI, respectively). DMD decreased as NDF levels in the diet increased (p < 0.0001). The NDF digestibility (DNDF) explained the better (p < 0.0001) CH4 production response than DMD. It was concluded that low-quality forages can be used to regulate CH4 production in subtropical and tropical climate regions. [ABSTRACT FROM AUTHOR]

Dairy cows are the highest daily and annual methane (CH4) producers among all cattle categories. So, the present study aimed to evaluate the effect of increasing supplementation levels of a low-quality forage on dry matter intake (DMI), DM digestibility (DMD), milk production, enteric CH4 emission, gross energy, and protein partitioning in Holstein cows. In total, eight cows (112 ± 38 days postpartum; mean ± s.d.) were randomly assigned to 4 treatments composed of 4 dietary neutral detergent fibre (NDF) inclusion levels (40.2% (control), 43.3%, 46.5%, and 50.5%) in a 4 × 4 repeated Latin square experimental design. The cows were fed corn + alfalfa silage and a concentrate (60:40 forage:concentrate ratio). To increase the contents of low-quality NDF, part of the silage was replaced with maize stover (MSTV). The CH4 production was measured in an open-circuit respiration chamber. The DMI increased significantly and linearly (p < 0.05) with increasing levels of MSTV. However, the CH4 yield decreased (p < 0.0001) as the NDF level increased (32.1, 28.1, 23.1, and 21.3 CH4 L/kg DMI, respectively). DMD decreased as NDF levels in the diet increased (p < 0.0001). The NDF digestibility (DNDF) explained the better (p < 0.0001) CH4 production response than DMD. It was concluded that low-quality forages can be used to regulate CH4 production in subtropical and tropical climate regions.

The current investigation delved into the utilization of cattle and municipal sanitary inocula for anaerobic digestion of poultry wastes, addressing a crucial and pragmatic challenge in waste management. The emphasis on poultry waste is pertinent due to its well-documented impediments in anaerobic digestion, attributed to heightened levels of ammonia and volatile fatty acids (VFAs). The strategic selection of cattle and municipal sanitary inocula suggests an approach aimed at bolstering the anaerobic digestion process. In this study, we evaluated the use of cattle and municipal sanitary inocula for the anaerobic digestion of various poultry wastes, which is often challenged by high levels of ammonia and volatile fatty acids (VFAs). The substrates tested included belt waste (Poultry A), poultry litter plus feed residues (Poultry B), tray hatchery ©, and stillage. These substrates were processed in two continuous stirred tank reactors (CSTRs), R-1 (with antibiotic monensin) and R-2 (without monensin). Initially, both reactors operated with the same hydraulic retention time (HRT), using a substrate ratio of stillage: belt: tray hatchery (S:B:T) of 70:15:15. On the 41st day, the HRT was adjusted to 20 days, and the substrate ratio was changed to S:A:T 70:40:40. The specific methane yield for R-1 started at 10.768 L g−1 COD, but decreased to 2.65 L g−1 COD by the end of the experiment. For R-2, the specific methane yield varied between 0.45 L g−1 COD and 0.243 L g−1 COD. Microbial composition in the reactors changed over time. In R-1, bacteroides were consistently dominant, while firmicutes were less abundant compared to R-2. Proteobacteria were initially low in abundance, but spirochetes were found in both reactors throughout the experiment. The study concluded that Poultry B substrates, due to their rich nutrient and trace element composition, are suitable for biogas plants. Municipal sanitary inocula also showed promise due to their resilience in high ammonia concentrations. Further research into biofilm interactions is recommended to better understand microbial responses to high ammonia concentrations, which can lead to propionate production in anaerobic digestion (AD).

Traditionally, anaerobic digestion has been applied to mixed sludge, combining primary sludge (PS) with secondary sludge. However, recent research has unveiled the advantages of dedicated PS digestion due to its higher energy content. Anaerobic digestion (AD) of primary sewage sludge can offer a sustainable solution for managing sewage sludge while generating renewable energy. The present study provides a comprehensive examination of the current state of knowledge regarding the anaerobic digestion of PS. Co-digestion of PS with organic substrates, including food waste and agro-industrial residues, emerges as a promising approach to boost biogas production. Additionally, the utilization of additives such as glucose and clay minerals has shown potential in improving methane yield. Critical factors affecting AD, such as pretreatment methods, carbon-to-nitrogen (C/N) ratio, temperature, pH, volatile fatty acids (VFAs) levels, organic loading rates (OLR), inoculum-to-substrate ratio (ISR), and the role of additives, have been meticulously studied. Finally, this review consolidates existing knowledge to advance our understanding of primary sewage sludge anaerobic digestion, fostering more efficient and sustainable practices in sludge management and renewable energy generation.

Optimization of anaerobic co-digestion of fruits and vegetable waste (FVW) with cow manure (CD) and poultry manure (PM) was studied by conducting biochemical methane potential (BMP) tests at different mixing ratios using central composite design (CCD). Findings of this study showed that methane yields of co-digestion tests were improved in comparison to mono-digestion of single substrates. The two optimal responses predicted by mixture design, 0.5 FVW:0.5 PM and 0.54 FVW:0.16 CM:0.3 PM, allowed the maximum methane yields. The analysis of BMP results using Gompertz model has proved that FVW:CM:PM mixing ratio of 0.54:0.16:0.3 yielded the best methane production. This optimal mixture ratio was used to set a laboratory scale digester under mesophilic condition. Results showed that co-digestion of FVW with CM and PM achieved biogas yield of 899 mL/g VS, which is higher than that registered during a control experiment of FVW mono-digestion (399 mL/g VS). Moreover, a high methane percentage was registered during the co-digestion. Accordingly, our finding revealed that co-digestion of FVW with animal manure feedstocks produced 125.3% more biogas yield than mono-digestion of FVW and generated a good quality of digestate. [ABSTRACT FROM AUTHOR]

Biogas production from organic waste is a sustainable means of meeting household energy needs as well as a good waste management technique. Notably, the key players in the transformation of organic wastes into useful form of energy are microbes (bacteria, fungi and archaea). The activities of these microorganisms are influenced by a number of factors which could be biotic or abiotic. Consequently, this impacts on the efficiency of the anaerobic digestion process as well as the biogas yield. Hence, an adequate monitoring and control of biotic and abiotic factors are needed for optimum performance of the microbes. This review study, therefore, focuses on the dynamics of microbes in an anaerobic digester and their in-depth metabolic activities, while highlighting the key factors militating against optimum microbial bioconversion of substrates into biogas. The current findings in the field of biogas production are duly analysed. Proper understanding of the variations in the microbial communities and the conditions that shape them will facilitate an advancement in the establishment of stable biogas production plants to meet the global household energy needs. [ABSTRACT FROM AUTHOR]

The operating temperature of anaerobic digesters should be adjusted to adapt to seasonal variations in environmental temperature and the composition of organic solid waste. This study investigated the effects of one-step abrupt temperature changes (from mesophilic to thermophilic temperature, M–T, and from thermophilic to mesophilic temperature, T–M) and the inoculation ratio on methane yield and microbial diversity during the anaerobic co-digestion of kitchen waste with dewatered sludge. The results showed that the cumulative methane yield (CMY) level resulting from thermophilic control and the M–T digesters was greater than that resulting from mesophilic control and the T–M digesters. The CMF of M–T digesters increased, whereas the CMY of T–M digesters gradually decreased with an increase in the inoculation ratio. The maximal CMY was 385.1 mL/g-VSSadded, which corresponded to an M–T digester with a 5% inoculation ratio. In the later stage of anaerobic digestion, the bacterial community of T–M was more diverse than that of M–T, but the archaeal community of M–T was more diverse than that of T–M. The one-step temperature change from thermophilic to mesophilic temperature was more stable than that from mesophilic to thermophilic temperature. [ABSTRACT FROM AUTHOR]

A study was undertaken to compare the rumen microbial community composition, methane yield, rumen fermentation, and CAZyme profiles between cattle and buffaloes. The primary aim of this study was to ascertain the impact of the host species on the above when diet and environmental factors are fixed. A total of 43 phyla, 200 orders, 458 families, and 1722 microbial genera were identified in the study. Bacteroidetes was the most prominent bacterial phylum and constituted >1/3rd of the ruminal microbiota; however, their abundances were comparable between cattle and buffaloes. Firmicutes were the second most abundant bacteria, found to be negatively correlated with the Bacteroidetes. The abundances of Firmicutes as well as the F/B ratio were not different between the two host species. In this study, archaea affiliated with the nine phyla were identified, with Euryarchaeota being the most prominent. Like bacterial phyla, the abundances of Euryarchaeota methanogens were also similar between the cattle and buffaloes. At the order level, Methanobacteriales dominated the archaea. Methanogens from the Methanosarcinales, Methanococcales, Methanomicrobiales, and Methanomassiliicoccales groups were also identified, but at a lower frequency. Methanobrevibacter was the most prevalent genus of methanogens, accounting for approximately three percent of the rumen metagenome. However, their distribution was not different between the two host species. CAZymes affiliated with five classes, namely CBM, CE, GH, GT, and PL, were identified in the metagenome, where the GH class was the most abundant and constituted ~70% of the total CAZymes. The protozoal numbers, including Entodiniomorphs and Holotrichs, were also comparable between the cattle and buffaloes. Results from the study did not reveal any significant difference in feed intake, nutrient digestibility, and rumen fermentation between cattle and buffaloes fed on the same diet. As methane yield due to the similar diet composition, feed ingredients, rumen fermentation, and microbiota composition did not vary, these results indicate that the microbiota community structure and methane emissions are under the direct influence of the diet and environment, and the host species may play only a minor role until the productivity does not vary. More studies are warranted to investigate the effect of different diets and environments on microbiota composition and methane yield. Further, the impact of variable productivity on both the cattle and buffaloes when the diet and environmental factors are fixed needs to be ascertained. [ABSTRACT FROM AUTHOR]

Agricultural residues have been identified as potential substrates for anaerobic digestion, which indicates them as alternative energy sources. But enzymatic hydrolysis of these residues has been observed as the rate-limiting step due to their recalcitrant characteristics. Therefore, pretreatment before anaerobic digestion is required to reduce the retention time and increase the methane yield. This study investigates the influence of thermal, alkali, acid, nanoparticle additive, and combined pretreatments on the methane yield of groundnut shells. The effect of pretreatment methods on the structural arrangement was investigated with scanning electron microscopy, X-ray diffraction, and Fourier transform infrared, and methane yield was investigated after anaerobic digestion at mesophilic temperature. The morphological analysis shows that all the treatment methods alter the microstructural arrangement of groundnut shells at varying degrees, except the particle size reduction, which does not significantly influence them. Cumulative methane yields of 222.92, 214.00, 171.02, 140.99, and 261.36 ml CH4/g VSadded were recorded for thermal, alkali, acid, nanoparticle additive, and combined pretreatment methods, which represents 112.77, 70.03, 40.18, and 159.85% improvement compared to the untreated substrate (100.58 ml CH4/g VSadded). Combined pretreatment was found to release the highest cumulative yield, and thermal pretreatment produced the least retention period. Therefore, combined and thermal pretreatments could be a bright means to deconstruct the recalcitrant characteristics of lignocellulose feedstocks arrangement to reduce the retention period and improve the methane yield. These methods can be experimented with further at the industrial scale to establish economic viability. [ABSTRACT FROM AUTHOR]

This research was carried out with the aim to evaluate the anaerobic digestion (AD) of llama and dromedary dungs (both untreated and trampled) in batch mode at mesophilic temperature (35 °C). The biochemical methane potential (BMP) tests with an inoculum to substrate ratio of 2:1 (as volatile solids (VS)) were carried out. The methane yield from trampled llama dung (333.0 mL CH4 g−1 VSadded) was considerably higher than for raw llama, raw and trampled dromedary dungs (185.9, 228.4, 222.9 mL CH4 g−1 VSadded, respectively). Therefore, trampled llama dung was found to be the best substrate for methane production due to its high content of volatile solids as well as its high nitrogen content (2.1%) and more appropriate C/N ratio (23.6) for AD. The experimental data was found to be in accordance with both first-order kinetic and transference function mathematical models, when evaluating the experimental methane production against time. By applying the first-order kinetic model, the hydrolysis rate constants, kh, were found to be 19% and 11% higher for trampled dungs in comparison with the raw dung of dromedary and llama, respectively. In addition, the maximum methane production rate (Rm) derived from the transference function model for trampled llama dung (22.0 mL CH4 g−1 VS d−1) was 83.3%, 24.4% and 22.9% higher than those obtained for raw llama manure and for raw and trampled dromedary dungs, respectively. [ABSTRACT FROM AUTHOR]

Introduction Anaerobic digestion (AD) can be used to produce a more environmentally friendly form of energy from municipal solid waste (MSW) and to clean up urban environments. The application of this technology to MSW produced in Kinshasa city (KC) is highly desirable to alleviate the waste management problem it currently faces and to combat indoor air pollution caused using biomass energy, which causes over 1.1 million deaths in Africa every year. However, the successful implementation of AD technology in Kinshasa City (KC) will depend on the level of anaerobic biodegradability (AB) of its MSW. Purpose This work aimed to assess the AB of household organic waste (HOW) produced in large quantities in the KC, namely: leaves and stems of Manihot utilissima (MU), leaves of Mangifera indica (MI), leaves of Persea americana (PA), stems of Amaranthus viridis (AV), stems of Ipomoea batatas (IP) and peels of Musa paradisiaca (MP). Methods AB tests were carried out under mesophilic conditions in 750 mL bottles. These bottles were filled with a mixture consisting of 6.7 g, 13.3 g, or 50.0 g DW/L of these waste products (substrates); inoculum, at a substrate/inoculum ratio of 4:1 and water, at a substrate/water ratio of 1:4. After 70 days of AD, the methane yield (BMP) of each substrate was then calculated. Results The highest BMP (0.09534 ± 0.00024 m3 CH4/kg.VS) was recorded for stems of AV at a concentration of 13.3 g DW/L, while leaves of PA at a concentration of 50.0 g DW/L gave the lowest BMP (0.00860 ± 0.00023 m3 CH4/kg.VS). Stems of AV stems and leaves of MU, and peels of MP showed good AB, compared with stems of IB and leaves of MI and PA. Co-digestion of these wastes is desirable to further improve their AB and enable the implementation of household-scale AD technology in KC. Conclusion The results obtained confirm that this waste could be recycled by AD to produce a clean form of energy for cooking and to clean up the KC.

The effect of olive pomace hydrochar (OPHC) on food waste (FW) anaerobic digestion (AD) was investigated experimentally at five concentrations (5.85, 10, 20, 30, and 34.11 g/L). The selective concentrations are based on an experimental approach that was utilized to study the effect of adding 10-30 g/L OPHC to the AD of FW. The highest experimental methane yield (YCH4) and biodegradability are obtained for 10 and 20 g/L of OPHC, with 33 and 82 % improvement, respectively. Response surface methodology (RSM) was used to assess the impact of independent factors, including hydraulic retention time (HRT) and olive pomace hydrochar (OPHC) added, on YCH4. The R2 of 0.9073 and 0.9485 are obtained for YCH4 using face-centered and circumscribed designs, respectively, due to the model's accuracy. The optimal YCH4 was 428.81 ml/g VS with an OPHC added of 20 g/L and an HRT of 20 days.

A study to compare the rumen microbial community composition, functional potential of the microbiota, methane (CH4) yield, and rumen fermentation was conducted in adult male cattle and buffaloes fed on the same diet. A total of 41 phyla, 169 orders, 374 families, and 1,376 microbial genera were identified in the study. Bacteroidetes and Firmicutes were the two most dominant bacterial phyla in both cattle and buffaloes. However, there was no difference in the abundance of Bacteroidetes and Firmicutes in the rumen metagenome of cattle and buffaloes. Based on the abundance, the Proteobacteria was the 3rd largest phylum in the metagenome, constituting 18--20% in both host species. Euryarchaeota was the most abundant phylum of the methanogens, whereas Methanobacteriales and Methanobrevibacter were the most abundant orders and genera in both species. The methanogen abundances were not different between the two host species. Like the metagenome, the difference between the compositional and functional abundances (metagenome vs. metatranscriptome) of the Bacteroidetes and Firmicutes was not significant, whereas the proteobacteria were functionally less active than their metagenomic composition. Contrary to the metagenome, the Euryarchaeota was the 3rd most functional phylum in the rumen and constituted -15% of the metatranscriptome. Methanobacteriales were the most functional methanogens, accounting for more than 2/3rd of the total archaeal functionality. These results indicated that the methanogens from Euryarchaeota were functionally more active as compared to their compositional abundance. The CH4 yield (g/kg DMI), CH4 emission (g/kg DDM), dry matter (DM) intake, and rumen fermentation did not vary between the two host species. Overall, the study established a substantial difference between the compositional abundances and metabolic functionality of the rumen microbiota; however, feeding cattle and buffaloes on the same diet resulted in similar microbiota composition, metabolic functionality, and CH4 yield. Further studies are warranted to investigate the effect of different diets and environments on the composition and metabolic functionality of the rumen microbiota. [ABSTRACT FROM AUTHOR]

Hydrogen and methane, as chemical raw materials with broad application prospects in the future market, can be produced by the two-phase anaerobic co-digestion of rice straw and sludge. The study was carried out using a medium-temperature batch experiment with rice straw, a rural crop residue from Sichuan, and residual sludge from a sewage treatment station. The effect of the mixing ratio of rice straw and rural sludge on hydrogen and methane production from anaerobic digestion was investigated with a view to alleviating the energy crisis and efficient resource utilization. The experimental results showed that hydrogen production was most favorable when rice straw/sludge = 5:1, with a cumulative hydrogen yield as high as 38.59 ± 1.12 mL/g VSadded, while methane production was most favorable when 3:1, with a cumulative methane yield as high as 578.21 ± 29.19 mL/g VSadded. By calculating the energy yield, it was determined that 3:1 is more favorable for the two-phase anaerobic digestion capacity of rice straw and sludge, which is as high as 20.88 ± 1.07 kJ/g VSadded, and its conversion of hydrogen and methane is 0.75% and 78.19%, respectively. The hydrogen production pathway was dominated by the butyric acid type, whose hydrogen production phase pH (5.84 ± 0.13) was slightly higher than the optimal pH for hydrogen-producing bacteria, while the methanogenic phase could meet the optimal pH for methanogenic bacteria (6.93 ± 0.17). [ABSTRACT FROM AUTHOR]

• Biochar-amended soils as intermediate covers mitigates acid accumulation. • Biochar-amended soils as intermediate and final covers increases CH 4 yield by 25%. • Biochar-amended soils as intermediate covers enhances decomposition of MSWs. • Biochar-amended soils as landfill covers reduces ammonia accumulation. The effects of biochar-amended soils as landfill covers have been extensively studied in terms of liquid and gas permeability. However, the influences of biochar-amended soils on the performance of municipal solid wastes (MSWs) in bioreactor landfills have not been well understood. This paper investigates the potential application of biochar-amended soils as final and intermediate covers in landfills. The MSWs with biochar-amended soils as final and intermediate covers were recirculated with mature leachate in laboratory-scale bioreactors. The pH, chemical oxygen demand, ammonia and volatile fatty acids (VFAs) concentrations of leachates, mass reduction rates, settlement, methane, and total gas generations of MSWs were investigated. The results indicate that biochar-amended soils as intermediate landfill covers can provide pH-buffer capacity, increase the pH of leachate and decrease the accumulation of VFAs in the early stage of decomposition. The concentration of ammonia in the leachate with biochar-amended soils as intermediate cover is lower than that with natural soils. The application of biochar-amended soils as intermediate and/or final covers increases the biocompression ratios and settlement of MSWs. The application of biochar-amended soils as final cover slightly decreases the methane generation potential (L 0). Biochar-amended soils as intermediate covers increase L 0 by 10%, and biochar-amended soils as both intermediate and final covers enhance L 0 by 25%. The increase in the ammonia removal, settlement, and methane yield indicates the viability of biochar-amended soils as intermediate landfill covers. Further studies can focus on the long-term behaviour of MSWs with soil covers with different biochar amendment rates and particle sizes. [ABSTRACT FROM AUTHOR]

While palm oil mill effluent (POME) from different sources will have varying characteristics due to the different process flows in mills, efficient monitoring and performance evaluation of anaerobic digesters in POME treatment are crucial to ensure stable biogas production with minimal operational problems. Therefore, this study aims to evaluate and compare the performances of in‐ground lagoon anaerobic digesters under mesophilic conditions in four different biogas plants (BGPs A, B, C and D) located in Malaysia with respect to total chemical oxygen demand (COD) removal and total biogas produced. Results show that all BGPs are still functioning well with satisfactory methane yields (.135–.364 Nm3 CH4/kgCOD removed) and COD removal efficiencies (67%–85%). ANOVA analysis shows that organic loading rate (OLR), temperature (T) and recirculation ratio (RR) have significant effects on the COD removal and biogas production of all four plants. BGP B has the highest amount of biogas produced (4.12 × 105 Nm3/month) and COD removal rate amongst other BGPs due to its most stable and lowest T (<40°C), high RR, and consistent and high COD load. Conversely, BGP D has the lowest COD removal and biogas production, which are mainly contributed by a high COD inlet (92 000 mg/L) and a high T in the anaerobic digester (48.7°C). Despite having a similar design of an anaerobic digester, this comparative study reveals that different BGPs will have different optimum operating conditions and limitations, depending not only on the operating conditions of the BGP (OLR, T and RR) but also on the raw POME quality stemming from the palm oil milling process. A future study would be focused on the optimisation of four BGPs for maximum biogas removal. [ABSTRACT FROM AUTHOR]

Methane production by microbial fermentation of municipal waste is a challenge for better yield processes. This work describes the characterization of a hydrogenotrophic methanogen microbial community used in a bioaugmentation procedure to improve the methane yield in a thermophilic anaerobic process, digesting the organic fraction of municipal solid waste. The performance of the bioaugmentation was assessed in terms of methane production and changes in the microbial community structure. The results showed that bioaugmentation slightly improved the cumulative methane yield (+ 4%) in comparison to the control, and its use led to an acceleration of the methanogenesis stage. We observed associated significant changes in the relative abundance of taxa and their interactions, using high throughput DNA sequencing of V3-16S rRNA gene libraries, where the abundance of the archaeal hydrogenotrophic genus Methanoculleus (class Methanomicrobia, phylum Euryarchaeota) and the bacterial order MBA08 (class Clostridia, phylum Firmicutes) were dominant. The relevant predicted metabolic pathways agreed with substrate degradation and the anaerobic methanogenic process. The purpose of the study was to evaluate the effect of the addition of hydrogenotrophic methanogens in the generation of methane, while treating organic waste through anaerobic digestion. [ABSTRACT FROM AUTHOR]

The digestion of community solid waste has great development prospects and economic benefits in the context of waste segregation. However, a large amount of biogas slurry is produced in the anaerobic digestion process and needs to be treated. In this study, the digestion performance and optimal recirculation batch in the digestion of community solid waste were investigated when multiple batches of recirculated slurry were mixed with inoculated sludge in the optimal ratio (a sludge volume percentage of 50%) as the inoculum. The results showed that the biogas yield and methane yield per unit load increased gradually with the number of recirculation batches and reached their maximum values in the seventh batch, which were 80.63% (1382.2 mL/g volatile solids) and 51.0% (812.4 mL/g volatile solids) more than the respective initial values. After four cycles of cultivation, the accumulation of volatile fatty acids (VFAs) was significantly alleviated, and the total VFA concentration in the seventh batch was reduced by 49.7% in comparison with the initial value. The digestion process produced methane mainly via hydrogenotrophic methanogenesis and syntrophic acetic acid-oxidizing methanogenesis. The genera Methanobacterium and Methanomassiliicoccus were closely associated with the biogas production performance. These results are helpful to increase the utilization rate of biogas slurry, improve the performance of multiple-batch digestion of community solid waste, and provide relevant biological evidence. [ABSTRACT FROM AUTHOR]

Sargassum muticum (SM) is an invasive macroalgal species seasonally occurring in large quantities. While generally suitable for anaerobic digestion, recent studies resulted in low specific methane yields (SMYs), presumably due to salt, polyphenol, and high fiber contents of this marine biomass. In this study, the specific biogas yield (SBY) and SMY of SM alone as well as in co-digestion with wheat straw (WS) were investigated in batch tests at process temperatures of 44 ± 1.4 °C with a retention time of approx. 40 d. The pretreatment variants of SM were examined with regard to desalination and disintegration to potentially improve digestibility and to enhance the overall performance in anaerobic digestion. A sole mechanical treatment (pressing) and a thermo-mechanical treatment (heating and pressing) were tested. Batch assays showed that pressing increased the SMY by 15.1% whereas heating and pressing decreased the SMY by 15.7% compared to the untreated variant (87.64 ± 8.72 mL/gVS). Both anaerobic digestion experiments generally showed that co-digestion with WS can be recommended for SM, but the observed SBY and SMY were still similar to those of other studies in which SM was not pretreated. The mechanical pretreatment of SM, however, offers the potential to enhance the SMY in the anaerobic digestion of SM with WS, but further research is necessary to identify the optimum upgrading approaches since the overall SMY of SM is relatively low compared to other substrates that are commonly used in anaerobic digestion. In addition to anaerobic digestion, SM as an already available biomass could also be of interest for further utilization approaches such as fiber production. [ABSTRACT FROM AUTHOR]

A study to compare the rumen microbial community composition, functional potential of the microbiota, methane (CH4) yield, and rumen fermentation was conducted in adult male cattle and buffaloes fed on the same diet. A total of 41 phyla, 169 orders, 374 families, and 1,376 microbial genera were identified in the study. Bacteroidetes and Firmicutes were the two most dominant bacterial phyla in both cattle and buffaloes. However, there was no difference in the abundance of Bacteroidetes and Firmicutes in the rumen metagenome of cattle and buffaloes. Based on the abundance, the Proteobacteria was the 3rd largest phylum in the metagenome, constituting 18–20% in both host species. Euryarchaeota was the most abundant phylum of the methanogens, whereas Methanobacteriales and Methanobrevibacter were the most abundant orders and genera in both species. The methanogen abundances were not different between the two host species. Like the metagenome, the difference between the compositional and functional abundances (metagenome vs. metatranscriptome) of the Bacteroidetes and Firmicutes was not significant, whereas the proteobacteria were functionally less active than their metagenomic composition. Contrary to the metagenome, the Euryarchaeota was the 3rd most functional phylum in the rumen and constituted ~15% of the metatranscriptome. Methanobacteriales were the most functional methanogens, accounting for more than 2/3rd of the total archaeal functionality. These results indicated that the methanogens from Euryarchaeota were functionally more active as compared to their compositional abundance. The CH4 yield (g/kg DMI), CH4 emission (g/kg DDM), dry matter (DM) intake, and rumen fermentation did not vary between the two host species. Overall, the study established a substantial difference between the compositional abundances and metabolic functionality of the rumen microbiota; however, feeding cattle and buffaloes on the same diet resulted in similar microbiota composition, metabolic functionality, and CH4 yield. Further studies are warranted to investigate the effect of different diets and environments on the composition and metabolic functionality of the rumen microbiota.

Sewage sludge is regarded by wastewater treatment plants as problematic, from a financial and managerial point of view. Thus, a variety of disposal routes are used, but the most popular is methane fermentation. The proportion of macromolecular compounds in sewage sludges varies, and substrates treated in methane fermentation provide different amounts of biogas with various quality and quantity. Depending on the equipment and financial capabilities for methane fermentation, different methods of sewage sludge pretreatment are available. This review presents the challenges associated with the recalcitrant structure of sewage sludge and the presence of process inhibitors. We also examined the diverse methods of sewage sludge pretreatment that increase methane yield. Moreover, in the field of biological sewage sludge treatment, three future study propositions are proposed: improved pretreatment of sewage sludge using biological methods, assess the changes in microbial consortia caused with pretreatment methods, and verification of microbial impact on biomass degradation. [ABSTRACT FROM AUTHOR]

The aim of the study was to assess the effect of silage additive containing heterofermentative lactic acid bacteria (LAB) strain of Lactobacillus buchneri species on ensiling quality, as well as methane yield and the kinetics of biogas production from ensiled perennial energy grasses: Miscanthus × giganteus (miscanthus), Spartina pectinata (cordgrass), Panicum virgatum (switchgrass) and Andropogon gerardii (big bluestem). The listed plants are not commonly used for biogas production, their susceptibility to ensiling is also little known, hence the need to investigate their suitability for these processes. Effective methods for increasing the biogas yield from biomass are still demand, hence the research on the use of LAB for this purpose. After harvesting the grasses were cut and ensiled in barrels with and without (controls) the usage of commercial silage inoculant containing Lactobacillus buchneri LN40177. After 90 days of ensiling obtained silages were analysed in order to compare their chemical composition: organic acids content, the loss of dry matter, the differences in particular fibres composition. The silages were then subjected to methane fermentation using OxiTop® sensors and exposed to air in order to check their aerobic stability. The silages prepared with LAB additive had higher concentration of acetic acid than the control silages prepared without LAB addition, which contributed to increased aerobic stability but had no effect on the methane yield of miscanthus, switchgrass and big bluestem. Using the microbial inoculant during ensiling had beneficial effect in terms of reducing the duration of biogas production process from obtained silages: lag phase was shortened, daily biogas production rate was increased and 90% of biogas was produced in a shorter period of time compared to the control silages from investigated grasses. The modified Gompertz model well reflected the kinetics of biogas production process.

Abstract The objective of the present study was an optimization of operating parameters and the performance of the methanogenesis reactor in phased anaerobic digestion (AD) of slaughterhouse wastewater at 37.5°C. Accordingly, the feedstock of the methanogenic reactor was effluent from the hydrolytic-acidogenic reactor operating at HRT of 3-days and OLR of 1789 mg/L. The methanogenesis phase was also investigated at different hydraulic retention time (HRT) values ranging from 12 to 3 days at 3-day intervals, and organic loading rates (OLR) of 149, 199, 298, and 596 mg of COD/L. The methanogenesis reactor effluent concentrations of TN, TP, PO4 − 3, SO4 − 2, and S2 − 2 were ranging between 424–464, 83–117, 63–86, 130–197, and 0.98–1.02 mg/L, respectively. The removal efficiencies of TN and TP were vary from 10–17% to 17–21%, respectively. The average biogas production was 125 ± 16, 150 ± 10, 185 ± 4, and 154 ± 17 mL at HRT of 12, 9, 6, and 3 days, respectively. Methane quality (%) and yield (mg/L of COD) were 55–67% and 0.02–0.03, respectively. Furthermore, the average stability indicator parameter values of (total volatile fatty acid (TVFA) = 520 ± 19 mg/L, total alkalinity (TotA) = 1424 ± 10 mg/L, TVFA:TotA. Ratio = 0.36, salinity = 1172 mg/L, pH = 6.92) and performance indicator parameters removal efficiency (RE) for (chemical oxygen demand (COD) = 81%, volatile solid (VS) RE = 95%, biogas production = 185 ± 4 mL, methane yield = 0.03 per mg COD consumed) were achieved at HRT of 6 days and OLR of 298 mg of COD/L. Low removal efficiencies of TP and TN at all HRT/OLR were observed for the methanogenic reactor signifying further treatment system. Graphical Abstract