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Copyright of Advances in New & Renewable Energy is the property of Editorial Office of Advances in New & Renewable Energy and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Thermophilic anaerobic digestion (TAD) represents a promising biotechnology for both methane energy production and waste stream treatment. However, numerous critical microorganisms and their metabolic characteristics involved in this process remain unidentified due to the limitations of culturable isolates. This study investigated the phylogenetic composition and potential metabolic traits of bacteria and methanogenic archaea in a TAD system using culture-independent metagenomics. Predominant microorganisms identified in the stable phase of TAD included hydrogenotrophic methanogens (Methanothermobacter and Methanosarcina) and hydrogen-producing bacteria (Coprothermobacter, Acetomicrobium, and Defluviitoga). Nine major metagenome-assembled genomes (MAGs) associated with the dominant genera were selected to infer their metabolic potentials. Genes related to thermal resistance were widely found in all nine major MAGs, such as the molecular chaperone genes, Clp protease gene, and RNA polymerase genes, which may contribute to their predominance under thermophilic condition. Thermophilic temperatures may increase the hydrogen partial pressure of Coprothermobacter, Acetomicrobium, and Defluviitoga, subsequently altering the primary methanogenesis pathway from acetoclastic pathway to hydrogenotrophic pathway in the TAD. Consequently, genes encoding the hydrogenotrophic methanogenesis pathway were the most abundant in the recovered archaeal MAGs. The potential interaction between hydrogen-producing bacteria and hydrogenotrophic methanogens may play critical roles in TAD processes. [ABSTRACT FROM AUTHOR]

Poultry slaughter effluents contain biodegradable organics, which include blood, feathers, viscera, soft tissues removed during trimming and cutting, bones, and soil. Slaughterhouse sludge usually contains many of these compounds and a high concentration of pathogenic microorganisms. In this study, the influence of thermal pretreatment on the conversion of mesophilic anaerobic digestion (MAD) to thermophilic anaerobic digestion (TAD) was evaluated, and micronutrient supplementation (Fe, Co, Ni, and Mo) to improve the production of biogas from poultry slaughter sludge. Six experimental stages were carried out, sludge sampling and characterization, application of thermal pretreatment, the adaptation of the mesophilic to thermophilic process, operation of TAD with increased organic loading rate (OLR), selection of micronutrient doses, and semicontinuous operation of TAD with micronutrients. The application of thermal pretreatment led to notable increases in the levels of carbohydrates, lipids, and soluble proteins, and a high inactivation of pathogens was obtained. The adaptation process from MAD to TAD required equidistant increments in temperature (+ Δ5 °C) and operation time (Δ15 days), resulting in a cumulative biogas production of 144.5 L. The TAD system effectively accommodated an OLR of 5 kgVS/(m3 d) without encountering inhibition. Moreover, the initial dose of micronutrients administered during the semicontinuous operation resulted in a 16% increase in biogas production compared to the control. Analysis of kinetic parameters using the modified Gompertz equation consistently yielded R2 values above 0.96 in all experimental stages. Overall, the findings highlight the positive impact of micronutrient supplementation and thermal pretreatment on biogas production within an enhanced TAD system. [ABSTRACT FROM AUTHOR]

Using a batch thermophilic anaerobic system established with 60 mL serum bottles, the mechanism on how microbial enrichments obtained from magnetite-amended paddy soil via repeated batch cultivation affected methane production from acetate was investigated. Magnetite-amended enrichments (MAEs) can improve the methane production rate rather than the methane yield. Compared with magnetite-unamended enrichments, the methane production rate in MAE was improved by 50%, concomitant with the pronounced electrochemical response, high electron transfer capacity, and fast acetate degradation. The promoting effects might be ascribed to direct interspecies electron transfer facilitated by magnetite, where magnetite might function as electron conduits to link the acetate oxidizers (Anaerolineaceae and Peptococcaceae) with methanogens (Methanosarcinaceae). The findings demonstrated the potential application of MAE for boosting methanogenic performance during thermophilic anaerobic digestion. HIGHLIGHTS Magnetite boosted the syntrophic conversion of acetate to methane during thermophilic anaerobic digestion.; Magnetite-amended enrichments exhibited pronounced electrochemical response and electron transfer capacity.; Magnetite might act as electron conduits to link acetate oxidizers and methanogens.; Magnetite might facilitate the establishment of direct interspecies electron transfer.; The addition of magnetite altered the bacterial community composition.;

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

Maize straw has been widely used for the production of energy through anaerobic digestion, but biogas production can be hindered by a lack of trace elemental nutrients. To address this issue, a lab-scale anaerobic plug flow reactor was continuously operated at 55 °C for 300 days, with a hydraulic retention time of 42 days and an organic loading rate of 2.1 g total solids/(L·day). Results from this study showed that between days 101 and 194, the methane yield slightly decreased from 0.26 ± 0.04 to 0.24 ± 0.03 L/g volatile solids (VS), but significant volatile fatty acid accumulation was observed by reaching up to 2759 ± 261 mg/L. After trace elements were added to the reactor, the methane yield increased to 0.30 ± 0.03 L/g VS, with 53% methane content. Around 62% of the total chemical oxygen demand and volatile solids were broken down into methane. Volatile fatty acid levels dropped and stabilized at around 210 ± 50 mg/L, indicating restored process stability. The addition of trace elements increased the abundance of Firmicutes and decreased Synergistetes in bacteria while simultaneously increasing the abundance of Methanosarcina in archaea. In conclusion, trace element supplementation was experimentally found to be necessary for stable thermophilic anaerobic digestion of maize straw. [ABSTRACT FROM AUTHOR]

Most waste sludge belongs to long sludge-retention-time (SRT) sludge in China, but its outlet is becoming a severe environmental problem nowadays. In this study, the characteristics of mesophilic and thermophilic anaerobic digestion of long SRT sludge was investigated under different total solid content (TSC) of 4%, 6%, and 8% in batch reactors. The results showed that the methane production potential (Po) and methane production rate (Rmax) of thermophilic anaerobic digestion (TAD) were increased by about 60% and 200% compared with that of the mesophilic anaerobic digestion (MAD) at 4% TSC. In TAD groups, the Po of 240.95 LCH4 kgVS-1added and Rmax of 22.17 LCH4 kgVS-1added day-1 were achieved in the reactor of 4% TSC while the inhibition concentration of propionate and free ammonia reached 1022 mg L-1 and 603 mg L-1 in the reactor of 8% TSC. Although the diversity of microbial communities were poor in TAD, Coprothermobacter was enriched in TAD, which could degrade protein efficiently. In addition, the dewaterability of digested sludge in TAD was poorer than that in MAD, and both got worse with the increased TSC. Therefore, it is appropriate for the long SRT sludge to anaerobic digestion under thermophilic condition and lower TSC. So, thermophilic anaerobic digestion with lower TSC might be an alternative approach for the treatment and resource utilization of long SRT sludge.

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study evaluated different strategies to increase gas–liquid mass transfer in a randomly packed gas stirred tank reactor (GSTR) continuously fed with second cheese whey (SCW), at thermophilic condition (55 °C), for the purpose of carrying out in situ biogas upgrading. Two different H2 addition rates (1.18 and 1.47 LH2 LR−1 d−1) and three different biogas recirculation rates (118, 176 and 235 L LR−1 d−1) were applied. The higher recirculation rate showed the best upgrading performance; H2 utilization efficiency averaged 88%, and the CH4 concentration in biogas increased from 49.3% during conventional anaerobic digestion to 75%, with a methane evolution rate of 0.37 LCH4 LR−1 d−1. The microbial community samples were collected at the end of each experimental phase, as well as one of the thermophilic sludge used as inoculum; metanogenomic analysis was performed using Illumina-based 16S sequencing. The whole microbial community composition was kept quite stable throughout the conventional anaerobic digestion (AD) and during the H2 addition experimental phases (UP1, UP2, UP3, UP4). On the contrary, the methanogens community was deeply modified by the addition of H2 to the GSTR. Methanogens of the Methanoculleus genus progressively increased in UP1 (47%) and UP2 (51%) until they became dominant in UP3 (94%) and UP4 (77%). At the same time, members of Methanotermobacter genus decreased to 19%, 23%, 3% and 10% in UP1, UP2, UP3 and UP4, respectively. In addition, members of the Methanosarcina genus decreased during the hydrogen addition phases. [ABSTRACT FROM AUTHOR]

Copyright of Advances in New & Renewable Energy is the property of Editorial Office of Advances in New & Renewable Energy and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This laboratory‐scale study attempted performance improvement and decolourization in the high‐solid thermophilic anaerobic digestion of thermally pretreated sewage sludge, as it tends to be disturbed by ammonia inhibition and colour generation. Sewage sludge was adjusted to 7%–8% total solids (TS), and pretreated at 150°C for 1 h. The digesters were operated at 55°C and 20 days hydraulic retention time. An addition of powdered activated carbon (approximately 2% of the feed TS) significantly contributed to the removal of propionate and reduced the colour in digested sludge by about 27%. Microbial analysis detected less abundance of bacterial Synergistia and archaeal Methanosarcina and implied more hydrogenotrophic methanogenesis with the activated carbon addition. Conditioning with ferric chloride for dewatering digested sludge mitigated the colour of dewatered liquor by about 67%. Therefore, these methods were demonstrated to be effective and partly overcome the above‐mentioned problems. [ABSTRACT FROM AUTHOR]

• AWOEx pretreated DSS tested at various temperatures, residence times and O 2 dosages. • Methane yield of DSS is improved by 98% using AWOEx and Anaerobic digestion. • Oxygen addition during pretreatment resulted in significant improvement in methane yield. • First-time demonstration of 84% organics conversion in sewage sludge using AWOEx pretreatment. Anaerobic digestion (AD) of sewage sludge shows low carbon conversion efficiency (CCE) due to the poor biodegradability of sewage sludge. The lack of digestibility is specifically linked to the waste-activated sludge (WAS) making up the majority of sewage sludge along with a smaller portion of primary sludge, depending on the wastewater treatment plant configuration. In this study, we examine the Advanced Wet Oxidation & Steam Explosion process (AWOEx) for improving the CCE of digested sewage sludge (DSS) by thermophilic AD. The effect of the pretreatment temperature in the range between 160 and 185 °C at a fixed residence time of 20 min with and without oxygen added at a dosage of 5 % of the organics present was tested. Methane yield improved by 97.92 % to 183.91 ± 4.93 mL/g vS over the untreated DSS (control), whose methane yield was 92.92 ± 9.07 mL/g vS We have demonstrated for the first time that 84 % of the organics in sewage sludge can successfully be transformed into biogas following AWOEx pretreatment, which can contribute significantly to the circular economy instead of greenhouse gas emissions from landfilling. [ABSTRACT FROM AUTHOR]

This research paper presents the thermophilic anaerobic digestion (TAD) of palm oil mill effluent (POME), which is an extension of a previously conducted mesophilic anaerobic digestion (MAD) study. An anaerobic suspended growth closed bioreactor was operated at various hydraulic retention times (HRT) between 24 and 8 days. The effect of operating temperature on the performance, microbial identification, and biokinetic coefficients was evaluated. Performance was quantified by the production of biogas and the chemical oxygen demand (COD) reduction efficiency. Biogas production in TAD (64.56 L/day) was higher than MAD (46.76 L/day). A higher COD reduction efficiency was also achieved in TAD (90.90%) compared to MAD (89.66%). Other than that, more species of methanogenic bacteria were also identified in TAD through 16S rDNA. Furthermore, the modified Monod model implemented in the biokinetic evaluation revealed that higher values of maximum substrate utilization rate (rx,max) and maximum specific biomass growth rate (μmax) contributed to the better performance in TAD. The high rx,max value explains the higher COD reduction efficiency obtained in TAD. The critical retention time ( θ C) in TAD is also higher than MAD, making it less prone to the washout of active microbes when operating near low retention times. Additionally, TAD also achieved higher methane yield ( Y CH 4 ) as opposed to MAD. The extension study concluded that the TAD of POME demonstrated improved performance in terms of biogas production and COD reduction when evaluated against the previously conducted MAD. [ABSTRACT FROM AUTHOR]

Thermophilic anaerobic digestion (AD) offers many benefits for food waste treatment but is seldom adopted in industrial plants due to instability issue, particularly under higher loading conditions. This study thus conducted a 160-day continuous operation of a pilot-scale thermophilic AD system on-site. Results from the experiments showed that the system could operate under relatively lower loading but failed when the loading reached up to 5.69 kg·COD/(m 3 ·d). Volatile fatty acids increased to 6000 mg/L at the corresponding hydraulic retention time of 15 days. Trace elements were then introduced, which restored higher process stability by reducing volatile fatty acids to 400 mg/L. The mass balance and materials decomposition resutls revealed the system's strong resilience. Methanoculleus (92.52 %) and Methanomassiliicoccus (6.55 %) were the dominant methanogens, a phenomenon rarely observed in similar thermophilic systems. This system may tolerate more stressful conditions, as the loading limits had not been reached with the addition of trace elements., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This study evaluated different strategies to increase gas–liquid mass transfer in a randomly packed gas stirred tank reactor (GSTR) continuously fed with second cheese whey (SCW), at thermophilic condition (55 °C), for the purpose of carrying out in situ biogas upgrading. Two different H2 addition rates (1.18 and 1.47 LH2 LR−1 d−1) and three different biogas recirculation rates (118, 176 and 235 L LR−1 d−1) were applied. The higher recirculation rate showed the best upgrading performance; H2 utilization efficiency averaged 88%, and the CH4 concentration in biogas increased from 49.3% during conventional anaerobic digestion to 75%, with a methane evolution rate of 0.37 LCH4 LR−1 d−1. The microbial community samples were collected at the end of each experimental phase, as well as one of the thermophilic sludge used as inoculum; metanogenomic analysis was performed using Illumina-based 16S sequencing. The whole microbial community composition was kept quite stable throughout the conventional anaerobic digestion (AD) and during the H2 addition experimental phases (UP1, UP2, UP3, UP4). On the contrary, the methanogens community was deeply modified by the addition of H2 to the GSTR. Methanogens of the Methanoculleus genus progressively increased in UP1 (47%) and UP2 (51%) until they became dominant in UP3 (94%) and UP4 (77%). At the same time, members of Methanotermobacter genus decreased to 19%, 23%, 3% and 10% in UP1, UP2, UP3 and UP4, respectively. In addition, members of the Methanosarcina genus decreased during the hydrogen addition phases.

In order to improve the efficiency of anaerobic digestion of long sludge retention time (SRT) sludge and seek a suitable disposal method for the massive plants harvested from constructed wetlands, we prepared Calamus-derived biochar (Calamus-BC) and added it to thermophilic anaerobic digestion (TAD) system of long SRT sludge. Moreover, the effect of Calamus-BC supplemental level (0, 5, 10, 15, 20 g/L) on TAD was explored through a series of batch experiments. Results showed that Calamus-BC addition can increase the conductivity and pH in TAD of long-SRT sludge obviously, thereby promoting methane production, reducing total VFAs accumulation and shortening the lag phases. When the Calamus-BC dosage was 15 g/L, the cumulative CH4 yield reached the highest 246.73 mL/g VS, which was 43.4% higher than the control group. Furthermore, it proved the modified Gompertz model was suitable for the actual evolution of CH4 production in TAD of long-SRT sludge. This study provided an alternative for efficient biomass stabilization and bioenergy recovery from long-SRT sludge and supplied a feasible resourceful approach for massive Calamus from constructed wetlands in water rehabilitation engineering. [ABSTRACT FROM AUTHOR]

Sewage sludge represents an important resource for reuse in the wastewater treatment field. Hence, thermophilic anaerobic digestion (TAD) could be an alternative technique to recover renewable resources from sludge. In the TAD biodegradation process, volatile fatty acids (VFAs) are the intermediate products of methanogenesis. However, the higher formation and accumulation of VFAs leads to microbial stress, resulting in acidification and failure of the digester. Therefore, several batch TADs have been investigated to evaluate the VFAs production from sludge and their impact on biogas generation and biodegradation efficiency. Three types of sewage sludges, e.g., primary sludge (PS), secondary sludge (SS), and mixed sludge (MS) were used as substrates to estimate the accumulation of VFAs and yield of methane gas. The system showed the maximum total VFAs accumulation from both PS and MS as 824.68 ± 0.5 mg/L and 236.67 ± 0.5 mg/L, respectively. The dominant VFA accumulation was identified as acetic acid, the main intermediate by-product of methane production. The produced biogas from PS and MS contained 66.75 ± 0.5% and 52.29 ± 0.5% methane, respectively. The high content of methane with PS-feeding digesters was due to the higher accumulation of VFAs (i.e., 824.68 ± 0.5 mg/L) in the TAD. The study also predicted the design parameters of TAD process by fitting the lab-scale experimental data with the well-known first-order kinetic and logistic models. Such predicted design parameters are significantly important before the large-scale application of the TAD process. [ABSTRACT FROM AUTHOR]

This paper presents a newly created mathematical model of thermophilic anaerobic digestion of wheat straw carried out in a 2 dm3 bioreactor for methane production. Two batch processes, with 30 mL/dm3 and 35 mL/dm3 organic load, are carried out—one set for parameter identification and one set for model verification. The identification of model parameter values is based on dynamical experiments. It is fulfilled using two different techniques: deterministic sequential quadratic programming algorithm and metaheuristic genetic algorithm. Verification of the developed mathematical models is conducted based on the different data sets of the process. Both models predict the set of the experimental data for all considered process variables well. Genetic algorithm visually fits the data with a higher degree of accuracy, as confirmed by the numerical results for the objective function value. [ABSTRACT FROM AUTHOR]

To enhance methane production and ensure system stability in the thermophilic anaerobic digestion (TAD) of food waste (FW), bioaugmentation is a straightforward and effective strategy. This study investigated the bioaugmentation effect of Clostridium thermopalmarium HK1 on the TAD of FW. The results showed that the cumulative methane production (CMP) and the average methane content after bioaugmentation increased by 23.67% and 22.69%, respectively. Moreover, the addition of C. thermopalmarium HK1 contributed to alleviating ammonia inhibition and promoting volatile fatty acids (VFAs) conversion, thus maintaining the system stability. The dominant hydrolytic bacteria and hydrogenotrophic methanogens were enriched in the early stage after bioaugmentation. The genus Clostridium was positively correlated with methane content. Metagenomic analysis further suggested that methane metabolism was strengthened, and the relative abundances of genes encoding the key functional enzymes associated with hydrogenotrophic and acetoclastic methanogenic pathways were enhanced. Therefore, bioaugmentation with C. thermopalmarium HK1 had great potential for improving the efficiency of the TAD of FW. [Display omitted] • Methane production with adding C. thermopalmarium HK1 increased by 23.67%. • C. thermopalmarium HK1 contributed to maintaining system stability. • Bioaugmentation enriched key hydrolytic bacteria and hydrogenotrophic methanogens. • C. thermopalmarium HK1 strengthened methane metabolism. • Bioaugmentation improved key enzymes associated with the methanogenesis pathway. [ABSTRACT FROM AUTHOR]

In this research, the actual food waste was used for anaerobic digestion (AD) under the condition of thermophilic (50±1)°C in a continuous stirred tank reactor (CSTR), starting with a hydraulic retention time (HRT) of 20 days, and operating with HRT of 15 days for a total of 80 days. The fermentation characteristics during startup and operation of the reactor, and the operational stability and metabolic activity of AD of food waste were studied. Results showed that under the condition of an HRT of 15 days and an organic load rate (OLR) of 7.3 kgCOD/(m³⋅d), the volumetric methane production rate was 2.2 L/(L·d), and the methane yield reached to 480 L/kgVS. The organic conversion rate was about 95%. Thermophilic methanogens had a strong ability to metabolize acetic acid and can withstand 10 000 mg/L of acetic acid at a suitable pH value. The degradation rate of the food waste under thermophilic temperature was fast, and it took about 10 days to reach 90% of the methane production, it was possible to withstand higher OLR under this condition. The pH value of the system was stable at 7.6 - 7.7; the total ammonia nitrogen (TAN) and free ammonia (FAN) were below the inhibition level. The results showed that thermophilic AD of food waste can achieve higher biogas production and organic matter removal rate, with good system stability and high conversion efficiency. The thermophilic AD of food waste has the possibility to be applied in engineering. [ABSTRACT FROM AUTHOR]

Neutralization with liquid digestate and CO2 was compared herein to adjust the pH of lime-treated corn stover. The effects on the thermophilic (55 °C) anaerobic digestion were also analyzed. Liquid digestate neutralization (LDN) caused a decrease in pH from 10.5 to 7.5 in 60 h and accumulation of acetic/isobutyric acids. The CO2 neutralization (CN) under solid-state conditions reduced the pH from 10.5 to 8.5 in 30 min, which is faster than that of LDN and did not affect the subsequent anaerobic digestion. Biomethane production rate indicates that LDN contributed to the performance of anaerobic digestion, but this was not sufficient to compensate for the loss of total biomethane yield, resulting in a negative net profit (i.e., revenue from increased energy production minus reagent cost). For CN under solid-state conditions, the biomethane production was highest in both liquid- and solid-state anaerobic digestion, and also obtained a net profit of 98.74–100.89 RMB/tonne dry biomass. Therefore, the solid-state condition CN is a more efficient and economic method for adjusting initial pH of lime-treated corn stover. [ABSTRACT FROM AUTHOR]

The anaerobic digestion performance correlates with the functional microbial community. Mesophilic and thermophilic digestions of vegetable waste were conducted, and dynamics of the microbial community were investigated. The mesophilic and thermophilic collapsed stages occurred at organic loading rates of 1.5 and 2.0 g VS/(L d) due to the accumulation of volatile fatty acids with final concentrations of 2276 and 6476 mg/L, respectively. A high concentration of volatile fatty acids caused the severe inhibition of methanogens, which finally led to the imbalance between acetogenesis and methanogenesis. The mesophilic digestion exhibited a higher microbial diversity and richness than the thermophilic digestion. Syntrophic acetate-oxidizing coupled with hydrogenotrophic methanogenesis was the dominant pathway in the thermophilic stable system, and acetoclastic methanogenesis in the mesophilic stable system. The dominant acidogens, syntrophus, and methanogens were unclassified_f__Anaerolineaceae (8.68%), Candidatus_Cloacamonas (19.70%), Methanosaeta (6.10%), and Methanosarcina (4.08%) in the mesophilic stable stage, and Anaerobaculum (12.59%), Syntrophaceticus (4.84%), Methanosarcina (30.58%), and Methanothermobacter (3.17%) in thermophilic stable stage. Spirochaetae and Thermotogae phyla were the characteristic microorganisms in the mesophilic and thermophilic collapsed stages, respectively. These findings provided valuable information for the deep understanding of the difference of the microbial community and methane-producing mechanism between mesophilic and thermophilic digestion of vegetable waste. [ABSTRACT FROM AUTHOR]

[Display omitted] • FPEI grafted on silica or magnetic-biochar improved organic acid degradation. • FPEI-grafted magnetic biochar (PMB) enhanced sCOD removal efficiency by 29.8%. • In-situ CO 2 conversion of PMB was closely linked to hydrogenotrophic methanogenesis. • FPEI-grafted magnetic biochar can play a similar role as carbonic anhydrase enzyme. Redundant CO 2 produced during wet anaerobic digestion (AD) needs proper in-situ minimization, in which the amino groups in polyethyleneimine (PEI) can react with CO 2 to form bicarbonate by diffusing into the liquid phase. Hence, the addition of PEI-grafted material may provide a novel way to in-situ supplement bicarbonate in the AD system, which could further improve the buffer capacity and promote syntrophic methanogenesis. In this study, different CO 2 adsorbents prepared by grafting PEI or epoxide-functionalized PEI (FPEI) on alkali-magnetic biochar were used to investigate the in-situ application feasibility. A series of weight loadings of the FPEI to alkali-magnetic biochar (10BFP = 1:10, 5BFP = 1:5, 2BFP = 1:2, and BFP = 1:1) were evaluated in batch AD tests. Fumed silica was also used as an unconducive solid support material for FPEI grafting. After adding 5BFP, the methane production significantly increased by 17.8 %, along with an increased CH 4 /CO 2 ratio from 181.7 % to 219.6 %. The bicarbonate generated by PEI/FPEI facilitated the degradation of volatile fatty acids by enhancing syntrophic reactions. The increased relative abundance of the genera Acetomicrobium , Thermovirga , and Methanosarcina indicates that FPEI improved the stability of the AD system. The 5BFP adsorbent could play a similar role as the carbonic anhydrase enzyme, with lower dosages favouring methane production. [ABSTRACT FROM AUTHOR]

[Display omitted] • Combined microbial inoculant improved methane production by 24.77%. • Bioaugmentation increased microbial diversity and evenness. • Combined microbial inoculant enriched key functional bacteria. • Combined microbial inoculant augmented the conversion of FW to methane. Microbial bioaugmentation is a promising strategy to increase methane production in thermophilic anaerobic digestion (TAD). In this study, Clostridium thermopalmarium HK1 and Caldibacillus thermoamylovorans QK5 were combined to form a combined microbial inoculant, and the influence of this synergistic bioaugmentation strategy on the TAD of food waste was explored in batch and semi-continuous experiments. The cumulative methane production reached 512.74 ± 8.12 NmL g−1 VS with the addition of the combined microbial inoculant, which was increased by 24.77 % ± 1.98 % compared to the control group, and the bioaugmentation effect was significantly better than that of the group inoculated with C. thermopalmarium HK1 (458.44 ± 4.80 NmL g−1 VS, 11.56 % ± 1.17 %) or C. thermoamylovorans QK5 (478.74 ± 5.73 NmL g−1 VS, 16.50 % ± 1.39 %) individually. The addition of the combined microbial inoculant particularly enriched carbohydrate-degrading bacteria and protein-degrading bacteria. In terms of metabolic functions, bioaugmentation with the combined microbial inoculant enhanced carbohydrate metabolism, amino acid metabolism, and methane metabolism, promoting the complete oxidation of organic matter into CO 2 via the tricarboxylic acid cycle (TCA cycle) and driving the conversion of CO 2 to methane. In particular, the synergistic effect of C. thermopalmarium HK1 and C. thermoamylovorans QK5 in the combined microbial inoculant resulted in notably increases in the bioaugmentation of carbohydrate and protein degradation, the TCA cycle, and hydrogenotrophic methanogenesis. [ABSTRACT FROM AUTHOR]

• Anaerobic biodegradation of commercial single-use bioplastics was studied. • PLA, PBS and PBAT were detected in the polymeric blends. • Appreciable material degradation occurred only under thermophilic conditions. • Products composition highly affected the biodegradation process. • Correlations among degradation parameters and products composition were derived. In this study commercial starch-based (Mater-Bi®) disposable bioplastic tableware items, which are among the most widely used commercial products available on the market, were selected for lab-scale anaerobic degradability tests. Since the knowledge of the biodegradation profile of bioplastic products is still incomplete, the study was aimed at investigating the maximum biodegradation potential of the materials under ideal anaerobic conditions, as well as the biodegradability degree as a function of treatment time. The experiments were carried out under mesophilic and thermophilic conditions at different food to microorganism ratios and test material sizes, and the specific biogas production and associated kinetics were evaluated. Biogas production was observed only under thermophilic conditions, with conversion yields in the range 602–898 mL/gTOC for the tested cups and 1207 ± 52.8 mL/gTOC for the knives. The degrees of biodegradation and disintegration were found to be strongly dependent on the product composition. Physical, chemical and morphological analyses were used to characterize the tested materials before and after the degradation and potential correlations among process parameters and bioplastic characteristics were derived. [ABSTRACT FROM AUTHOR]

Sewage sludge represents an important resource for reuse in the wastewater treatment field. Hence, thermophilic anaerobic digestion (TAD) could be an alternative technique to recover renewable resources from sludge. In the TAD biodegradation process, volatile fatty acids (VFAs) are the intermediate products of methanogenesis. However, the higher formation and accumulation of VFAs leads to microbial stress, resulting in acidification and failure of the digester. Therefore, several batch TADs have been investigated to evaluate the VFAs production from sludge and their impact on biogas generation and biodegradation efficiency. Three types of sewage sludges, e.g., primary sludge (PS), secondary sludge (SS), and mixed sludge (MS) were used as substrates to estimate the accumulation of VFAs and yield of methane gas. The system showed the maximum total VFAs accumulation from both PS and MS as 824.68 ± 0.5 mg/L and 236.67 ± 0.5 mg/L, respectively. The dominant VFA accumulation was identified as acetic acid, the main intermediate by-product of methane production. The produced biogas from PS and MS contained 66.75 ± 0.5% and 52.29 ± 0.5% methane, respectively. The high content of methane with PS-feeding digesters was due to the higher accumulation of VFAs (i.e., 824.68 ± 0.5 mg/L) in the TAD. The study also predicted the design parameters of TAD process by fitting the lab-scale experimental data with the well-known first-order kinetic and logistic models. Such predicted design parameters are significantly important before the large-scale application of the TAD process.

High-solids thermophilic anaerobic digestion fed with sewage sludge of 7–8% and 9–10% total solids was investigated at the hydraulic retention time of 20 days in this lab-scale study. The anaerobic digester fed with 7–8% sewage sludge was successfully operated, resulting in volatile solids (VS) destruction of 57.8% and methane production of 0.327 L/gVS (at standard temperature and pressure). When fed with 9–10% sewage sludge, the control digester was upset after about 80 days of operation. Total ammonia nitrogen (TAN) of 2500 mgN/L or more caused inhibition to anaerobic microorganisms. Another digester combined with weekly batch ammonia stripping of digested sludge in a side-stream configuration (80 °C, 2 h, initial pH of 9 with NaOH and return ratio of 70%), was maintained at the average TAN of 1720 mgN/L, and was able to continue without ammonia inhibition. TAN was a better indicator on inhibition of ammonia than free ammonia nitrogen (FAN). Microbial analysis revealed poor microbial diversity of digested sludge, that is, Class Clostridia for Bacteria and Geneus Methanothermobacter and Methanosarcina for Archaea were predominated. In conclusion, high-solids thermophilic anaerobic digestion can accommodate the influent sewage sludge up to 10%, as far as TAN is properly controlled in digester. [ABSTRACT FROM AUTHOR]

Acetate is a major intermediate in the anaerobic digestion of organic waste to produce CH 4 . In methanogenic systems, acetate degradation is carried out by either acetoclastic methanogenesis or syntrophic degradation by acetate oxidizers and hydrogenotrophic methanogens. Due to challenges in the isolation of syntrophic acetate-oxidizing bacteria (SAOB), the diversity and metabolism of SAOB and the mechanisms of their interactions with methanogenic partners are not fully characterized. In this study, the in situ activity and metabolic characteristics of potential SAOB and their interactions with methanogens were elucidated through metagenomics and metatranscriptomics. In addition to the reported SAOB classified in the genera Tepidanaerobacter , Desulfotomaculum , and Thermodesulfovibrio , we identified a number of potential SAOB that are affiliated with Clostridia , Thermoanaerobacteraceae, Anaerolineae, and Gemmatimonadetes. The potential SAOB possessing the glycine-mediated acetate oxidation pathway dominates SAOB communities. Moreover, formate appeared to be the main product of the acetate degradation by the most active potential SAOB. We identified the methanogen partner of these potential SAOB in the acetate-fed chemostat as Methanosarcina thermophila . The dominated potential SAOB in each chemostat had similar metabolic characteristics, even though they were in different fatty-acid-fed chemostats. These novel syntrophic lineages are prevalent and may play critical roles in thermophilic methanogenic reactors. This study expands our understanding of the phylogenetic diversity and in situ biological functions of uncultured syntrophic acetate degraders and presents novel insights into how they interact with methanogens.IMPORTANCECombining reactor operation with omics provides insights into novel uncultured syntrophic acetate degraders and how they perform in thermophilic anaerobic digesters. This improves our understanding of syntrophic acetate degradation and contributes to the background knowledge necessary to better control and optimize anaerobic digestion processes., Competing Interests: The authors declare no conflict of interest.

Polyacrylamide (PAM) is generally employed in wastewater treatment processes such as sludge dewatering and therefore exists in the sludge. Furthermore, it degrades slowly and can deteriorate methane yield during anaerobic digestion (AD). The impact or fate of PAM in AD under thermophilic conditions is still unclear. This study mainly focuses on PAM degradation and enhanced methane production from PAM-added sludge during 15 days of thermophilic (55°C) AD compared to mesophilic (35°C) AD. Sludge and PAM dose from 10 to 50 g/kg TSS were used. The results showed that PAM degraded by 76% to 78% with acrylamide (AM) content of 0.2 to 3.3 mg/L in thermophilic AD. However, it degraded only 27% to 30% with AM content of 0.5 to 7.2 mg/L in mesophilic AD. The methane yield was almost 230 to 238.4 mL g VSS on the 8th day in thermophilic AD but was 115.2 to 128.6 mL/g VSS in mesophilic AD. Mechanism investigation revealed that thermophilic AD with continuous stirring not only enhanced PAM degradation but also boosted the organics release from the sludge with added PAM and gave higher methane yield than mesophilic AD. [ABSTRACT FROM AUTHOR]

The accumulation of volatile fatty acids during the anaerobic digestion of biodegradable substrate such as Source Sorted Organic Fraction of Municipal Solid Waste (SS-OFMSW) is associated with an inhibitory effect on methane producing biochemical pathways. While inconclusive at times, the usage of two-stage digesters has been argued as a potential solution for this issue. In this study single-stage versus two-stage thermophilic digesters, fed with SS-OFMSW, were examined during the startup phase while increasing the loading rate from 0.5 to ~ 2 g VS L−1 d−1. While both systems exhibited a stable performance, with neutral pH and low intermediate-to-partial alkalinity, the two-stage digester exhibited better effluent quality with 79 and 57% lower average total chemical oxygen demand (TCOD) and soluble COD (SCOD), respectively. Also, upon reaching steady-state conditions, the two-stage system showed a superior performance with an overall methane content of 54%, compared to an average of 45% in the single-stage system. [ABSTRACT FROM AUTHOR]

Acid crisis characterized by acid accumulation and/or low pH is a common reason for the failure of anaerobic digestion (AD), which is usually applied for wastewater and waste treatment. Acid-tolerant methanogens are rarely reported to be active in the artificial anaerobic digester. In this study, we observed that the thermophilic methanogenesis by a consortium in the form of flocs and not granules could still be recovered during long-term operation at acetate concentration of up to 104 mM and pH 5.5 by adjusting the pH gradually or directly to pH 5.5 or 5.0. The acclimation process involving the gradual decrease in pH could enhance the resistance of the consortium against extreme acidification. The stable isotopic signature analysis of biogas revealed that Methanosarcina, which produced methane through acetoclastic methanogenesis (AM) pathway, was the predominant methane producer when the pH was decreased gradually to 5.0. Meanwhile, the abundance of Coprothermobacter increased with a decrease in pH. Contrastingly, when directly subjected to an environment of pH 5.5 and 104 mM acetate (15.84-mM free acetic acid) after a 42-day lag phase, Methanothermobacter was the predominant methanogen. Methanothermobacter initiated methane production through the hydrogenotrophic pathway and formed syntrophic relationship/consortium with the potential acetate-oxidizing bacteria, Thermacetogenium and Coprothermobacter. Comparative metagenomic and metatranscriptomic analysis on this self-adapted and acid-tolerant consortium revealed that the genes, such as GroEL, DnaK, CheY, and flagellum-related genes (FlaA, FlgE, and FliC) from Anaerobaculum, Thermacetogenium, and Coprothermobacter were highly overexpressed in response to system acidification. Microbial self-adaptation patterns (community structure adjustment, methanogenesis pathway shift, and transcriptional regulation) of thermophilic methanogenic consortium to gradual and sudden acidification were evaluated by integrated stable isotopic signature and comparative meta-omic approaches. The study elucidated the acid-resistant mechanism of thermophilic methanogenic consortium and deepened our knowledge of the function, interaction, and microbial characteristics of Methanosarcina, Methanothermobacter, and Coprothermobacter under extreme acidic environment.

Neutralization with liquid digestate and CO2 was compared herein to adjust the pH of lime-treated corn stover. The effects on the thermophilic (55 °C) anaerobic digestion were also analyzed. Liquid digestate neutralization (LDN) caused a decrease in pH from 10.5 to 7.5 in 60 h and accumulation of acetic/isobutyric acids. The CO2 neutralization (CN) under solid-state conditions reduced the pH from 10.5 to 8.5 in 30 min, which is faster than that of LDN and did not affect the subsequent anaerobic digestion. Biomethane production rate indicates that LDN contributed to the performance of anaerobic digestion, but this was not sufficient to compensate for the loss of total biomethane yield, resulting in a negative net profit (i.e., revenue from increased energy production minus reagent cost). For CN under solid-state conditions, the biomethane production was highest in both liquid- and solid-state anaerobic digestion, and also obtained a net profit of 98.74–100.89 RMB/tonne dry biomass. Therefore, the solid-state condition CN is a more efficient and economic method for adjusting initial pH of lime-treated corn stover.

Thermophilic anaerobic digestion (TAD) is an efficient method for biogas production. In this study, the TAD of Arundo donax cv. Lvzhou No. 1 (ADL-1, a new kind of energy crop with high cold tolerance) at different growth stages was carried out, in order to investigate the relationship between microbial community structure and its function during the fermentation process. The results showed that the most optimal growth period of ADL-1 was 3 months, regarding the yield of biogas production. The TAD process lasted for 10 days with cumulative biogas and methane yields of 312.7 mL/g VS and 231 mL/g VS, respectively. The degradation rates of hemicellulose, cellulose, and lignin were 41.78%, 27.99%, and 14.46%, respectively. The high-throughput sequencing of 16S rRNA gene amplicons revealed that the most abundant bacterial phylum in TAD was Firmicutes with three dominant genera of Tepidiphilus, Sedimentibacter, and Gelria. Also, the main archaeal order was Methanomicrobiales, in which Methanoculleus and Methanosarcina were detected as dominant genera. Therefore, this article reveals the dynamic changes of structure and function of microbial communities during TAD of ADL-1, providing the theoretical basis for the development of energy crops with cold tolerance as potential biogas feedstock. [ABSTRACT FROM AUTHOR]

This study investigated the advantages of the anaerobic codigestion process of two urban organic waste: the organic fraction of municipal solid wastes and the waste activated sludge produced during biological wastewater treatment. In particular, a comparison between mono and double stage anaerobic digestion for biogas and biohythane (hydrogen and methane) production, respectively, was conducted at thermophilic conditions in a pilot scale rig with a hydraulic retention time of 20 days. Considering yields, the specific gas productions for the single stage process was 490 l biogas per kg TVS fed to the system while in the two stage process hydrogen and methane productions reached average values of 24 LH2 and 570 LCH4 per kg VS fed to the system, respectively. Obtained biohythane, after upgrading, is particularly valuable for the automotive sector contributing to improve the combustion engine performance and to reduce the contaminants emissions in the atmosphere. [ABSTRACT FROM AUTHOR]

Anaerobic digestion has received significant attention in recent years due to dual benefits of waste diversion from landfill and bioenergy recovery. Among various temperature regimes, digesters operated under thermophilic (50–70 °C) condition has potential to provide several advantages over mesophilic (30–45 °C) and psychrophilic (<20 °C) conditions, which include faster degradation of organics and higher energy recovery. However, the operation of thermophilic digesters requires closer monitoring and control due to an additional risk of ammonia inhibition and irreversible acidification through the accumulation of volatile fatty acids. Conventional strategies to alleviate instabilities in thermophilic anaerobic digestion process have been focused primarily on the development of robust microbiome and co-digestion of complementary substrates. On the other hand, emerging strategies include the integration of digesters with microbial electrochemical systems and amendment of conductive additives. This review provides a critical overview of these strategies and summarizes research gaps to guide researchers and practitioners in the future research. Image 1 • Process instabilities due to ammonia inhibition and acidification are reviewed. • Methods for improving process stability in thermophilic digesters are summarized. • Research gaps associated with the implementation of these methods are identified. [ABSTRACT FROM AUTHOR]

Acid crisis characterized by acid accumulation and/or low pH is a common reason for the failure of anaerobic digestion (AD), which is usually applied for wastewater and waste treatment. Acid-tolerant methanogens are rarely reported to be active in the artificial anaerobic digester. In this study, we observed that the thermophilic methanogenesis by a consortium in the form of flocs and not granules could still be recovered during long-term operation at acetate concentration of up to 104 mM and pH 5.5 by adjusting the pH gradually or directly to pH 5.5 or 5.0. The acclimation process involving the gradual decrease in pH could enhance the resistance of the consortium against extreme acidification. The stable isotopic signature analysis of biogas revealed that Methanosarcina , which produced methane through acetoclastic methanogenesis (AM) pathway, was the predominant methane producer when the pH was decreased gradually to 5.0. Meanwhile, the abundance of Coprothermobacter increased with a decrease in pH. Contrastingly, when directly subjected to an environment of pH 5.5 and 104 mM acetate (15.84-mM free acetic acid) after a 42-day lag phase, Methanothermobacter was the predominant methanogen. Methanothermobacter initiated methane production through the hydrogenotrophic pathway and formed syntrophic relationship/consortium with the potential acetate-oxidizing bacteria, Thermacetogenium and Coprothermobacter. Comparative metagenomic and metatranscriptomic analysis on this self-adapted and acid-tolerant consortium revealed that the genes, such as GroEL, DnaK, CheY, and flagellum-related genes (FlaA, FlgE, and FliC) from Anaerobaculum , Thermacetogenium , and Coprothermobacter were highly overexpressed in response to system acidification. Microbial self-adaptation patterns (community structure adjustment, methanogenesis pathway shift, and transcriptional regulation) of thermophilic methanogenic consortium to gradual and sudden acidification were evaluated by integrated stable isotopic signature and comparative meta-omic approaches. The study elucidated the acid-resistant mechanism of thermophilic methanogenic consortium and deepened our knowledge of the function, interaction, and microbial characteristics of Methanosarcina , Methanothermobacter , and Coprothermobacter under extreme acidic environment. [ABSTRACT FROM AUTHOR]

Effects of two different start-up methods were compared during conversion from mesophilic to thermophilic anaerobic digestion of sewage sludge. During the batch operation, a transient increase in both total bacterial concentration and relative abundance of thermophilic bacteria in R1 (a one-step increase method) resulted in 34% higher volatile solids (VS) removal efficiency by R1 compared to R2 (a step-wise increase method). Meanwhile, higher total archaeal concentration and increased relative abundance of thermophilic archaea in R2 were attributed to 65% higher methane production by R2 compared to R1. The same trends for VS removal and methane production were observed during the subsequent continuous mode, although the microbial composition of the two reactors became similar. These findings may prove helpful for determining the preferred start-up method for thermophilic anaerobic digestion: a one-step method can be proposed for higher VS removal efficiency, or a step-wise method can be selected for enhanced methane production. Unlabelled Image • Two start-up strategies were compared: one-step (R1) and step-wise (R2). • R1 showed enhanced VS reduction, while R2 produced more CH 4. • More VFAs were accumulated in R1 batch mode with higher BAR. • The relative abundance of thermophilic archaea increased in only R2 batch mode. • Firmicutes and Methanosarcina were most abundant in both systems. [ABSTRACT FROM AUTHOR]

Thermophilic anaerobic digestion (TAD) can provide superior process kinetics, higher methane yields, and more pathogen destruction than mesophilic anaerobic digestion (MAD). However, the broader application of TAD is still very limited, mainly due to process instabilities such as the accumulation of volatile fatty acids and ammonia inhibition in the digesters. An emerging technique to overcome the process disturbances in TAD and enhance the methane production rate is to add conductive materials (CMs) to the digester. Recent studies have revealed that CMs can promote direct interspecies electron transfer (DIET) among the microbial community, increasing the TAD performance. CMs exhibited a high potential for alleviating the accumulation of volatile fatty acids and inhibition caused by high ammonia levels. However, the types, properties, sources, and dosage of CMs can influence the process outcomes significantly, along with other process parameters such as the organic loading rates and the type of feedstocks. Therefore, it is imperative to critically review the recent research to understand the impacts of using different CMs in TAD. This review paper discusses the types and properties of CMs applied in TAD and the mechanisms of how they influence methanogenesis, digester start-up time, process disturbances, microbial community, and biogas desulfurization. The engineering challenges for industrial-scale applications and environmental risks were also discussed. Finally, critical research gaps have been identified to provide a framework for future research. [Display omitted] • Conductive materials enhance methane yield in thermophilic anaerobic digestion. • Conductive materials successfully offset process instabilities. • Types and properties of different conductive materials were reviewed. • Technical challenges and ecological risks of applying additives are highlighted. [ABSTRACT FROM AUTHOR]

This work examined the performance and microbial traits in a thermophilic anaerobic digestion (TAD) of waste activated sludge that was impacted by micron zero valent iron (mZVI). Results showed that methane production was promoted by 0.8, 11.9, and 12.0 times, respectively, when mZVI was at dosages of 25, 100, and 250 mg/g total solid (TS). Also, the consumption of volatile fatty acids was increased by mZVI at higher dosages (100 and 250 mg/g TS). Furthermore, 16S rRNA sequencing demonstrated that microbial community stabilized after day 18 regardless of the dosage of mZVI, and that different dosages of mZVI induced different shifts in the functional community of the archaea rather than the bacteria involved in TAD. As a result, mZVI at 100 mg/g TS could increase the relative abundance of archaeal genera Methanothermobacter the most, increasing by 22.8% at the end of TAD compared to CK. Besides, redundancy analysis revealed that the physicochemical properties explained 79.65% and 89.10% of the variations of bacterial and archaeal abundance, respectively. Also, the findings of the correlation analysis revealed that total dissolved iron, ferrous iron, pH, and ammonium nitrogen, may be the key divers of altering functional communities, particularly archaea. Moreover, mZVI at 100 and 250 mg/g TS boosted the metabolic pathways of environmental information processing (ABC transporters) in bacteria and carbon metabolism and methane metabolism for archaea, as well as relative abundances of enzymes and their activities involved in various methanogenic pathways. This study provides new perspectives on the application of mZVI in solid wastes treatments. • Dose effect of micron ZVI (mZVI) in sludge anaerobic digestion (55 °C) is revealed. • mZVI at 100 mg/g total solid performs better in increasing methane production. • mZVI, regardless of dosages, promotes the hydrogenotrophic Methanothermobacter. • mZVI boosts enzymes engaged in hydrotrophic and acetotrophic pathways. • Dissolved iron, Fe2+, pH, NH 4 +-N, and fatty acids shift the functional community. [ABSTRACT FROM AUTHOR]

Tobacco processing generates large amounts of waste, which can potentially serve as feedstock for the biogas production by anaerobic digestion (AD) technology. In this study, the thermophilic AD of flue-cured tobacco leaf waste with a high solid content was conducted, and the effects of biochar on biogas production at different organic loads were evaluated. The fermentation performance and microbial community with biochar addition (BAT) and without biochar addition (WBA) were thoroughly compared to explore the biochar-mediated enhancement mechanisms. Biochar addition enhanced methane production by 1.12–1.20 fold at the tested organic loads. Fermenting a low organic load (seed sludge/feedstock ratio: 2.0) in the BAT had the highest methane yield (120.4 mL/g-volatile total solids). Biochar addition significantly shortened the lag period of methane production and increased the methane production rate with an increasing organic load. The cellulolytic and fermentative bacterial genus Hydrogenispora , polysaccharide-degrading and syntrophic acetate-oxidizing bacterial genus norank_o_MBA03 , and hydrogenotrophic methanogens were crucial for thermophilic flue-cured tobacco leaf digestion. Biogas production was enhanced by Hydrogenispora and Methanoculleus enrichment. These results demonstrate effective methane production from flue-cured tobacco leaves via biochar-assisted thermophilic fermentation with a high solid content and provide a useful reference for tobacco waste treatment. [Display omitted] • CH 4 production from flue-cured tobacco leaves was improved by biochar addition. • Biochar enhanced CH 4 production by approximate 12.0–20.0 % at test organic loads. • Biochar shortened the lag time and increased maximum rate of CH 4 production. • Biochar enriched cellulolytic Hydrogenispora and hydrogenotrophic Methanoculleus. [ABSTRACT FROM AUTHOR]

Abstract The feasibility of thermophilic anaerobic digestion (AD) for the attenuation of antibiotic resistance genes (ARGs) in biomass wastes under high antibiotic concentrations remains unclear. In this study, a thermophilic completely stirred digester (55 °C) was fed with municipal excess sludge spiked with increasing concentrations of oxytetracycline (OTC) (0–1000 mg/L) over a period of 280 days. Results showed that thermophilic AD could maintain stable methane production (338.40 ± 26.26 mL/d/gVS) even at an OTC dose of 1000 mg/L with the sludge phase OTC concentration reaching around 24,000 mg/kg. More important, the abundance of resistome detected by high-throughput quantitative PCR in the substrate was reduced (p < 0.01) by 55.54%–86.27% by thermophilic AD over the whole period. Partial canonical correspondence and network analyses showed that the reduction of ARGs was achieved mainly through two ways: eliminating the original hosts of ARGs in the substrate (from 41.74% ± 2.60% in the substrate to 12.08% ± 1.02% in digested sludge), and blocking the horizontal proliferation of ARGs in the digested sludge by reducing the abundance of mobile genetic elements and restricting their horizontal exchange within a small number of thermophilic genera. This study showed that thermophilic AD is feasible for the attenuation of ARGs in biomass even containing high level of OTC. Graphical abstract Image 1 Highlights • Thermophilic AD could maintain stable methane production under high OTC stress. • Resistome in the substrate was reduced by thermophilic AD under high OTC stress. • Original hosts of ARGs in the substrate were eliminated by thermophilic AD. • HGT of ARGs in thermophilic digested sludge was blocked even under high OTC stress. [ABSTRACT FROM AUTHOR]

Abstract Palm oil mill effluent is a highly polluting and corrosive liquid waste generated from crude palm oil processing. Its varying characteristics depending on the crop season and loading rate of the milling process complicate the handling of anaerobic digestion of palm oil mill effluent. To ease monitoring and aid decision making to handle operation anomalies, this study adopts Adaptive Neuro-Fuzzy Inference System with hybrid learning algorithm and subtractive clustering to predict the output from a thermophilic high-rate anaerobic digester treating palm oil mill effluent. Influent pH, chemical oxygen demand, organic loading rate and historical data of effluent pH, chemical oxygen demand and total suspended solids were utilized to build the model for output prediction of treated effluent (pH, chemical oxygen demand and total suspended solids). Trained models were validated with experimental data. The models were able to predict the effluent pH, chemical oxygen demand and total suspended solids satisfactorily with average error of less than 8.32% and standard deviation of less than 7.65% with closely followed pattern between the actual values and simulated results. The viability of adaptive neuro-fuzzy inference system in modelling palm oil mill effluent using thermophilic high-rate anaerobic digester is further demonstrated by coefficient of determination, R2 of 0.82, Root Mean Square Error of 0.0377, Index of Agreement of 0.95 and d-factor of 0.0496. Graphical abstract Image 1 Highlights • POME is treated under thermophilic anaerobic digestion using UASB-HCPB reactor. • Three models were developed predicting effluent pH, COD and TSS for modelling of POME treatment shows good prediction trend with errors less than 10%. • The best model which predicts M3 has a R2 of 0.82; RMSE = 0.0377; IA = 0.95; d-factor = 0.0496 • Advanced corrective and preventive measures can be taken earlier to maintain digester stability with the model. [ABSTRACT FROM AUTHOR]

• Swine manure anaerobic digestion (AD) at 55 °C raised 47.9% methane than at 35 °C. • More oxytetracycline (OTC) led to less methane from mesophilic and thermophilic ADs. • Adding 400 mg/L OTC reduced energy conversion efficiencies of ADs by 21.4–48.4%. • More than 63.0% and 72.5% OTC were removed via mesophilic and thermophilic ADs. • Methanolinea was bearable to high content OTC in mesophilic and thermophilic ADs. Anaerobic digestion (AD) technology is a valuable method for producing biogas fuels and treating livestock wastes such as swine manures concurrently. However, the effect of emerging antibiotics on the AD process is still undiscovered. In this study, the influence of oxytetracycline (OTC) on the AD process was investigated under mesophilic (35 ± 0.5 °C) and thermophilic (55 ± 0.5 °C) conditions, respectively. The presence of OTC significantly inhibited the production of methane in AD process, where the methane yields decreased by 58.6% and 73.3% in mesophilic and thermophilic ADs when the initial concentration of OTC was 400 mg/L, respectively. Besides, OTC can be markedly degraded by the AD process with a removal efficiency higher than 90% when the OTC initial concentration is lower than 10 mg/L. Furthermore, a higher concentration OTC led to a lower biomethane yield, energy conversion efficiency, and contaminant removal during both mesophilic and thermophilic ADs. With adding of 400 mg/L OTC, Clostridium sensu stricto 1 (32.9%) and Anaerolinea (29.3%) are dominant to biodegrade organic matter during mesophilic and thermophilic AD systems. Correspondingly, Methanosaeta was functional in producing biomethane in both mesophilic (60.8%) and thermophilic (56.4%) AD systems. Additionally, Methanolinea was bearable to high concentrations of OTC during mesophilic and thermophilic AD processes. [ABSTRACT FROM AUTHOR]

Microbial activity determining the speed of the changes occurring during the process of anaerobic digestion depends on the environmental conditions of the process. The factor intensifying the process of methane fermentation is an increase of temperature. The conducting of the methane fermentation in thermophilic conditions affect the rate of the reactions taking place during the phase of hydrolysis, thus contributing to increase the concentration of volatile fatty acids generated from the sludge, resulting in increasing the production of biogas. It should be noted, however, that thermophilic bacteria have a high sensitivity to temperature changes already the order of ± 0.5 ° C/d at their optimum growth in the range of 52-55 °C. Therefore, for the process would run optimally smoothly unnecessary to ensure stable environmental conditions leading to maximum reduction of organic substances. The basic test substrate, characterized by a high content of organic and nitrogen compounds, is excess sludge. To determine the effect of generating the volatile fatty acids during the thermophilic fermentation the sludge was submitted 8-daily anaerobic stabilization. The following designations of physico-chemical characteristics were made: dry matter, pH, alkalinity, volatile fatty acids, the chemical oxygen demand. In the following days of the process operation with regard to fermentation carried out under mesophilic conditions the increase of volatile fatty acids generation was observed, which also correlated with the increase of the chemical oxygen demand. In the 8th day of thermophilic conditions the concentration of volatile fatty acids was 1749 mgCH3COOH/dm3, while the chemical oxygen demand 3,279 mgO2/dm3 and the alkalinity row of 3800 mgCaCO3/dm3.

Residual solid and liquid streams from the one-pot CRUDE (Conversion of Raw and Untreated Disposal into Ethanol) process were treated with two separate biochemical routes for renewable energy transformation. The solid residual stream was subjected to thermophilic anaerobic digestion (TAD), which produced 95 ± 7 L methane kg −1 volatile solid with an overall energy efficiency of 12.9 ± 1.7%. A methanotroph, Methyloferula sp., was deployed for oxidation of mixed TAD biogas into methanol. The residual liquid stream from CRUDE process was used in a Microbial Fuel Cell (MFC) to produce electricity. Material balance calculations confirmed the integration of biochemical routes (i.e. CRUDE, TAD, and MFC) for developing a sustainable approach of energy regeneration. The current work demonstrates the utilization of different residual streams originated after food waste processing to release minimal organic load to the environment. [ABSTRACT FROM AUTHOR]