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•The combination of AC and CaO2 achieved superior anaerobic digestion performance.•AC/CaO2 induced more ROS production and bolstered metabolic activity.•AC/CaO2 promoted the formation ...of bio-aggregates.•AC/CaO2 enabled improved mutualism between facultative bacteria and methanogens.•AC/CaO2 built a robust enzymatic defense system and unique damage repair strategy.
This study examined the combination of activated carbon and magnetite with calcium peroxide in enhancing the anaerobic digestion (AD) performance of food waste (FW). The individual mechanisms of these two approaches were also clarified. The results indicated that AC/CaO2 achieved the highest specific methane yield of 434.4 mL/g VS, followed by Fe3O4/CaO2 (416.9 mL/g VS). Both were significantly higher than other groups (control, AC, Fe3O4, and CaO2 were 330.1, 341.4, 342.8, and 373.2 mL/g VS, respectively). Additionally, compared to Fe3O4/CaO2, AC/CaO2 further increased reactive oxygen species (ROS), thereby enhancing the hydrolytic acidification process. Simultaneously, the higher ROS levels of Fe3O4/CaO2 and AC/CaO2 promoted the formation of microbial aggregates and established a more robust enzymatic defense system and unique damage repair strategy. The research comparatively analyzed the synergistic mechanism of iron-based and carbon-based conductive materials with CaO2, providing new perspectives for optimizing the AD of FW.
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•Supercapacitor material (AC-PANi) was prepared and applied to the AD process.•Incorporation of AC-PANi significantly increased the methane production.•AC-PANi relieved metabolic ...imbalance between acetate-producing and methanogenesis.•AC-PANi promoted DIET between acetate-producing bacteria and methanogens.
Strengthening the direct interspecies electron transfer (DIET) is an effective strategy to improve the performance of anaerobic digestion (AD) process. In this study, the polyaniline functionated activated carbon (AC-PANi) was prepared by chemical oxidative polymerization. This material possessed pseudo-capacitance properties as well as excellent charge transfer capability. The experimental results demonstrated that the incorporation of AC-PANi in AD process could efficiently increase the chemical oxygen demand (COD) removal (18.6 %) and daily methane production rate (35.3 %). The AC-PANi can also act as an extracellular acceptor to promote the synthesis of adenosine triphosphate (ATP) and secretion of extracellular enzymes as well as cytochrome C (Cyt-C). The content of coenzyme F420 on methanogens was also shown to be increased by 60.9 % with the addition of AC-PANi in AD reactor. Overall, this work provides an easy but feasible way to enhance AD performance by promoting DIET between acetate-producing bacteria and methanogens.
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•Exploring adaptation of anaerobic digestion via gradual pH increase.•pH 8 was identified as upper limit for stable anaerobic digestion operation.•Eubacterium and Anaerobacterium ...enhanced reactor stability under high pH.•Stress applied via alkaline conditions increased syntrophic bacteria’s abundance.
This paper examines the adaptive responses of microbial communities to gradual shifts in pH toward the mild alkaline range in anaerobic digestion (AD) systems. The results indicate that a pH of 8.0 serves as a critical upper limit for stable AD operation, beyond which microbial efficiency declines, underscoring the importance of microbial resilience against elevated pH stress. Specifically, hydrolysis genera, e.g. Eubacterium and Anaerobacterium, and syntrophic bacteria were crucial for reactor stability. Fibrobacter had also been shown to play a key role in the accumulation of propionate, thus leading to its dominance in the volatile fatty acid profile throughout the experimental phases. Overall, this investigation revealed the potential adaptability of microbial communities in AD systems to mild alkaline pH shifts, emphasizing the hydrolysis bacteria and syntrophic bacteria as key factors for maintaining metabolic function in elevated pH conditions.
The effect of nitrite (...) on the nitrous oxide (N2O) production rate of an enriched ammonia-oxidizing bacteria (AOB) culture was characterized over a concentration range of 0-1000 mg N/L. The AOB ...culture was enriched in a nitritation system fed with synthetic anaerobic digester liquor. The N2O production rate was highest at NO2- concentrations of less than 50 mg N/L. At dissolved oxygen (DO) concentration of 0.55 mg O2/L, further increases in ... concentration from 50 to 500 mg N/L resulted in a gradual decrease in N2O production rate, which maintained at its lowest level of 0.20 mg N2O-N/h/g VSS in the ... concentration range of 500-1000 mg N/L. The observed ...-induced decrease in N2O production was even more apparent at increased DO concentration. At DO concentrations of 1.30 and 2.30 mg O2/L, the lowest N2O production rate (0.25 mg ...N/h/g VSS) was attained at a lower ... concentration of 200-250 mg N/L. These observations suggest that N2O production by the culture is diminished by both high ... and high DO concentrations. Collectively, the findings show that exceedingly high ...- concentrations in nitritation systems could lead to decreased N2O production. Further studies are required to determine the extent to which the same response to ... is observed across different AOB cultures. (ProQuest: ... denotes formulae/symbols omitted.)
With the development of the world economy and society, the living standards of residents have been improved, along with a large amount of food waste and carbon dioxide (CO2) emissions. In the face of ...global warming and energy shortages, food waste can be used as high-value bio-energy raw materials which is also an effective way to reduce CO2 emissions. Therefore, this paper proposes a novel anaerobic digestion and CO2 emissions efficiency analysis based on a Slacks-Based Measure integrating Data Envelopment Analysis (SBM-DEA) model to evaluate and optimize the process structure of anaerobic treatment of food waste. The total feed volume and the discharge volume of liquid digestate are taken as inputs, and the total methane (CH4) production volume is taken as the desirable output and CO2 emissions are regarded as the undesirable output to build the biogas production and CO2 emissions evaluation model during the anaerobic digestion process. Finally, the proposed method is used in the actual anaerobic digestion process. The results show that the overall efficiency values in January, April, May, and June in 2020 are higher than those in other months. At the same time, due to the optimal allocation of slack variables of inputs and undesirable outputs, the efficiency values of other inefficient anaerobic digestion days can be improved.
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•Novel anaerobic digestion and CO2 emissions efficiency analysis method is proposed.•Inefficient and efficient anaerobic digestion days of food waste treatment can be effectively distinguished.•CO2 emissions and CH4 production optimization of food waste treatment are obtained.•Production efficiency of inefficient production configuration can be improved.
Anaerobic digestion (AD) for biogas production is affected by many factors that includes organic loading rate (OLR). This OLR appears to be closely linked to various other factors and understanding ...these linkages would therefore allow the sole use of OLR for process performance monitoring, control, as well as reactor design. This review's objective is to collate the various AD factor specific studies, then relate these factors' role in OLR fluctuations. By further analyzing the influence of OLR on the AD performance, it would then be possible, once all the other factors have been determined and fixed, to manage an AD plant by monitoring and controlling OLR only. Decisions on reactor design, process kinetics, biogas yield and process stability can then be made much more quickly and with minimal troubleshooting steps.
In light of the substantial global production of biomass waste, effective waste management and energy recovery solutions are of paramount importance. Hydrothermal liquefaction (HTL) and anaerobic ...digestion (AD) have emerged as innovative techniques for converting biomass waste into valuable resources. Their integration creates a synergistic framework that mitigates inherent limitations, leading to improved efficiency, enhanced product quality, and the comprehensive utilization of biomass. This review paper investigates the integration of HTL and AD, highlighting its significance and potential benefits as well as the optimal sequencing (HTL followed by AD and AD followed by HTL). The review encompasses experimental procedures, factors influencing both sequencing options, energy recovery characterizations, final product outcomes, as well as toxicological assessments and discussions on reduction. Additionally, it delves into the transition towards a circular bioeconomy and discusses the challenges and opportunities intrinsic to these processes. The findings presented in this review offer valuable insights to shape future research in this evolving field.
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•The integration of AD and HTL offers a complementary approach to waste treatment.•Our review examines both sequencing approaches: HTL followed by AD, and vice versa.•Key parameters and pretreatments were assessed to enhance overall energy recovery.•Integrating AD and HTL aligns with the circular bioeconomy for waste valorization.•Innovative methods for toxicity reduction in the HTL-AD systems were reviewed.
•Hydrochar alleviated the ammonia inhibition on anaerobic digestion.•Hydrochar promoted the methane production rate by 220% at 8 g/L ammonia.•The enriched Methanosarcina upregulated hydrogenotrophic ...& aceticlastic pathways.•The enriched Methanosaeta was involved in direct interspecies electron transfer.•The Wood-Ljungdahl pathway was upregulated for the enriched Clostridium.
Anaerobic digestion (AD) is known to be inhibited by high concentration of ammonia. The present study proposed and demonstrated the utilization of hydrochar, which is produced by hydrothermal liquefaction of biomass, to alleviate ammonia inhibition. Three different concentrations (0.5, 4 and 8 g/L) of ammonia were tested with acetate as substrate. It was found that hydrochar significantly reduced the lag phase and promoted the methane production rates. The methane production rate was increased by around 10% at both 0.5 and 4 g/L ammonia, while it was increased by as high as 220% at 8 g/L ammonia with the addition of hydrochar. Although hydrochar adsorbed certain amounts of organics and ammonia, the adsorption did not have apparent positive effect on methane production rate. 16S rDNA analysis revealed that hydrochar increased the α-diversity at higher ammonia concentration, and enriched different microbes at each ammonia concentration. Considering the significant increase of methane production rate at 8 g/L ammonia, proteomic analysis was also conducted. Although 16S rDNA analysis showed hydrochar resulted in the enrichment of Clostridium, Methanobacterium and Methanosarcina, slightly different results were obtained by proteomic analysis, which showed hydrochar enriched Clostridium, Methanosarcina and Methanosaeta. The growth of Methanosarcina was inhibited at 8 g/L ammonia, while hydrochar facilitated its growth. The proteins of Methanosarcina involved in both hydrogenotrophic (HM) and aceticlastic methanogenesis (AM) pathways were upregulated by hydrochar. The proteins involved in HM pathway of strictly aceticlastic methanogen Methanosaeta was found to be up-regulated with hydrochar, and it indicated Methanosaeta was involved in direct interspecies electron transfer (DIET), which might be related with the enhanced methane production rate. In addition, Wood–Ljungdahl (WL) pathway of Clostridium was also found to be upregulated with hydrochar. Clostridium might be the bacteria that provide H+ and e- to Methanosaeta for DIET considering its enrichment with hydrochar.
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•Anaerobic digestion could be promising approach for LDPE waste plastic mitigation.•Biological pretreatmentenhancedbiogas(162.9%) and methane (196.2%) production.•AD-1 digester showed ...the highest cumulative methane production (154.9 NmL/g VS).•The maximum methane energy and βece were observed in AD-1, AD-2 and AD-6 digesters.
Waste plastic (WP) and lignocellulosic biomass (LCB) are both refractory polymers that can provide feedstocks for the production of fuels. Anaerobic digestion (AD) is a widely recognized technology utilized in waste management and renewable energy production. It involves the utilization of microorganisms to decompose organic matter into methane (CH4). Nevertheless, mono-digestion, which refers to AD utilizing a single feedstock, encounters difficulties related to the properties of the feedstock. Therefore, the utilization of co-digestion with multiple feedstocks provides the potential to overcome these limitations. This study might be the first to examine the impact of co-digestion of low-density polyethylene (LDPE) with rice straw (RS) for biogas and CH4 production. The cumulative CH4 production for AD-1, AD-2, AD-3, AD-4, AD-5, and AD-6 was 154.9, 177.4, 52.0, 81.2, 98.43, and 135.15 NmL/g VS. The methane energy yields varied between 2.29 and 7.64 MJ/m3, while their respective βece values spanned from 17.6 to 58.8 %. Volatile solid removal was enhanced for the treated RS-LDPE mixture, as demonstrated in AD-6, in comparison to the untreated substrate in the AD-2 digester. There is a notable disparity in the composition of bacterial communities within the bioreactors that were constructed prior to and subsequent to the AD process. The proliferating Firmicutes, Bacteroidetes, and Protobacteria were crucial to the AD of RS and LDPE. The three predominant methanogenic genera present in the constructed digesters and inoculum were Methanobacterium, Methanolinea, and Methanosarcina, each with a distinct abundance level. The findings open up the possibility of better understanding the effect of co-digestion of WP and LCB on enhancing CH4 production, which is critical for developing strategies for bioremediation and waste valorization simultaneously with biofuel production.
•Comprehensive exergy analysis of an OFMSW-fed anaerobic digestion plant was done.•The overall exergetic efficiency of the plant was found to be 72.8%.•Electric power contributed to 15.4% of the ...overall exergy efficiency of the plant.•Liquid and solid biofertilizers accounted for 84.6% of the efficiency of the system.
This study was devoted to comprehensively investigating the exergetic performance of a gas-engine equipped anaerobic digestion plant producing electric power as well as biofertilizer from organic fraction of municipal solid waste (OFMSW). The main aim of the current survey was to reveal the reasons and sources of thermodynamic losses occurring in the plant based on real operational data. The required data for the analysis were collected from a local OFMSW anaerobic digestion plant located in Tehran, Iran. After writing energy and exergy balances for all components of the plant, their exergetic performance parameters were measured individually. An attempt was also undertaken to quantify the contributions of the products to the overall exergetic efficiency of the plant. The exergetic value of the net electric power was determined at 1596.0kW, while the chemical exergetic content of the biofertilizer was found to be 8758.3kW. The overall exergetic efficiency of the plant was determined at 72.8%. The contributions of the electric power and the biofertilizer to the overall exergetic efficiency of the plant were found to be 15.4% and 84.6%, respectively. Generally, the exergetic analysis presented herein could provide important guidelines and methodological blueprints for futureinvestigations in order to develop thermodynamically-efficient and environmentally-benign waste-to-energy plants.
