•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.
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.)
Anaerobic digestion (AD) could be considered as a mature technology and nowadays it can still play a pivot role because of the urgent need to provide renewable energy sources and efficiently manage ...the continuously growing amount of organic waste. Biochar (BC) is an extremely versatile material, which could be produced by carbonization of organic materials, including biomass and wastes, consistently with Circular Economy principles, and “tailor-made” for specific applications. The potential BC role as additive in the control of the many well-known critical issues of AD processes has been increasingly explored over the past few years. However, a clear and comprehensive understanding of the connections between BC and AD is still missing. This review paper analyses and discusses significant references (review articles, research papers and international databases and reports), mostly published in the last 10 years. This review is aimed at addressing three key issues related to the better understanding of the BC role in AD processes: 1. Investigation of the influence of BC properties on AD performances and of their ability to counteract its main challenges; 2. Assessment of the optimal BC production chain (i.e. feedstock-pyrolysis-activation) to achieve the desired features; 3. Evaluation of the economic and environmental advantages connected to BC use in AD processes, compared to conventional solutions applied to address AD challenges.
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•Biochar key properties were specific surface, pores and surface functional groups.•Lignocellulosic biomass, slow pyrolysis and physical activation made the best biochar.•Biochar addition exhibited economic and environmental advantages.•Biochar improved methane production (in average 25 %) and digestate quality.
Tofu-processing wastewater (TPW) is very abundant in Indonesia. This study aimed to examine the impact of Fe additions (0–600 mg-FeCl3/L) on biogas yield from TPW through anaerobic digestion (AD) ...without and with microbial electrolysis cells (MEC). The presence of MEC in AD increased biogas yield by 14.4–114.5 %. The optimum Fe addition either in AD or MEC-AD was 400 mg-FeCl3/L. Prediction accuracy was higher for the modified Gompertz model compared to first-order and modified Logistic models because it had a higher R2 (0.9942). The presence of MEC in AD increased ym, μ, and λ values. MEC-AD resulted in pollutant removal efficiencies 1.09 to 1.63 times higher than AD. Based on energy analysis, AD and MEC-AD resulted in surplus energy of 3582.1 and 5325.1 J, respectively. It means that the presence of MC in AD successfully increased the surplus energy by about 1.5 times.
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•Two-stage anaerobic digestion should be more productive than traditional process.•Energy recoveries (H2+CH4vs CH4) were compared through a new method.•Four different substrates at nine different ...experimental conditions were tested.•Two-stage recovered 8%–43% more energy than one-stage and never significantly less.•Deeper research should be addressed to prove the convenience of two-stage approach.
The supremacy of two-stage on traditional one-stage anaerobic digestion (AD), in terms of overall energy recovery (ER) from biomass has often been proved. However, the process conditions ensuring this result, as well as the reasons for higher efficiency, have always been unclear. In this work, a new standardized approach is proposed: optimization at lab-scale of both hydrogen and methane generation processes allowed comparing the maximum potential ER of both two-stage (as H2+CH4) and one-stage AD (as CH4). Relatively high bio-hydrogen yields were obtained testing four different organic substrates (ER of 1–1.6MJkg−1VS-added). Biomethane generation resulted in ER in the range of 9–19MJkg−1VS-added., similarly for two-stage and one-stage systems. The overall ER resulted in significantly higher (8%–43%) for the two-stage in the large majority of experimental conditions and never significantly lower. These preliminary results should drive further research to better understand the conditions that can drive the two-stage AD to higher performance.
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•Biogas plants digested highly different feedstock, such as olive pomace.•Operational parameters and microbiomes were monitored over 18-months in six reactors.•Novel microorganisms ...were proposed as key anaerobic digestion players.•Microbe-level stability trends and links with reactor operation were discovered.•Putative bacteria with causative and remedial activity were proposed.
Anaerobic digestion is responding to the growing demand for sustainability by exploring alternatives for methane production through renewable processes. The target is to implement stable production systems at industrial scale that can accommodate heterogeneous feedstocks with seasonal or intermittent availability. In this study, we investigated the microbiomes of six full-scale biogas plant digesters, operated under continuous production with distinct feedstock and varying operating parameters, by monitoring multiple time points over an 18-month period. This time-course experiment analyzed 114 Metagenome-Assembled Genomes alongside physico-chemical assessments to identify common and plant-specific indicators for operational management. Results identify a Limnochordia and a Dysgonomonadaceae bacteria, as well as Candidatus Methanoculleus thermohydrogenotrophicum, as widespread and potentially desirable components of the microbiota for resilient digestion of varying waste, including the peculiar olive pomace. The abundance of individual taxonomic groups and their reconstructed metabolic pathways aligned with the availability of their fermentation substrates, finding a prevalence of beta-oxidizing bacteria with lipid-rich olive pomace. Monitoring through perturbation events revealed possible causative and remediative microbiological factors, in particular Methanosarcina flavescens and Candidatus Syntrophosphaera thermopropionivorans could contribute to restoration of reactor performance. This work showcases relationships between digester operation and its microbiome, supporting microbial monitoring as a tool to increase biogas production efficiency.
•Different methanogenic communities in mesophilic and thermophilic reactors.•High VFA levels do not cause major changes in archaeal communities.•Real-time PCR indicated greater diversity than ...ANAEROCHIP microarray.
A study was conducted to determine whether differences in the levels of volatile fatty acids (VFAs) in anaerobic digester plants could result in variations in the indigenous methanogenic communities. Two digesters (one operated under mesophilic conditions, the other under thermophilic conditions) were monitored, and sampled at points where VFA levels were high, as well as when VFA levels were low. Physical and chemical parameters were measured, and the methanogenic diversity was screened using the phylogenetic microarray ANAEROCHIP. In addition, real-time PCR was used to quantify the presence of the different methanogenic genera in the sludge samples. Array results indicated that the archaeal communities in the different reactors were stable, and that changes in the VFA levels of the anaerobic digesters did not greatly alter the dominating methanogenic organisms. In contrast, the two digesters were found to harbour different dominating methanogenic communities, which appeared to remain stable over time. Real-time PCR results were inline with those of microarray analysis indicating only minimal changes in methanogen numbers during periods of high VFAs, however, revealed a greater diversity in methanogens than found with the array.
The fate of diverse antibiotic resistance genes (ARGs) in anaerobic digestion (AD) system under different temperature remains largely unknow. This study employed the shotgun metagenomic sequencing ...and 16S rRNA amplicon sequencing approaches and investigated the shifts of composition and abundance of more than 1360 ARGs, as well as microbial community, in a temperature-raising AD system (from 35 °C to 55 °C) treating municipal sewage sludge. Results suggested that the six ARGs, inlcuding macB, tetA(58), bcrA, evgS, mtrA, and oleC, were predominated in digested sludge. More than 407ARG subtypes (30%) could be largely reduced under high temperature condition. Thermophilic AD (55 °C) provided a better removal for tetracycline, macrolide, penam, fluoroquinolone, acridine dye, and peptide resistance genes when compared to mesophilic AD (35 °C). The removal rates of these genes reached 29.7%–32.3%. In addition, at the end of thermophilic digestion process, the relative abundance of Firmicutes increased (from 18.22% to 74.89%), while Proteobacteria and Chloroflexi both decreased, from 36.39% to 6.80% and 20.29%–2.64%. This study further proposed the underlying mechanisms of effective elimination of ARGs under high temperature by: (1) the reduction of genes encoding antibiotic efflux pump, (2) the promotion of sludge biomass degradation rate, (3) the loss of microbial community diversity in AD systems, and (4) the inactivation of multidrug-resistant bacteria. The significance of current study is in characterizing the fate of ARGs across AD process, which allows to correlate diverse genetic properties with digesters’ operational condition. Results provided an insight into the manipulation of AD technology (e.g. temperature) to efficiently remove ARGs from municipal sewage sludge.
•Fate of ARGs in a temperature-raising anaerobic digester was investigated.•More than 1360 ARG subtypes were identified by metagenomics approach.•Effective reduction of ARGs under thermophilic condition was confirmed.•Underlying mechanisms of ARGs removal were proposed.
The use of biochar (pyrolysed biomass) in anaerobic digesters can improve the efficiency of methane production at a low cost. However, the biochar dosage and the ability to re-use biochar affects the ...viability of this process improvement. This study shows the effects of high dosages of both pristine and re-used wood-pellet biochar on the performance of high-solids anaerobic digesters processing chicken litter. Performance was assessed on a basis of methane yield per gram of volatile solids and the volumetric efficiency. The 90-day methane yield increased by 39% with a pristine biochar dosage of 1 gTS−char/gTS−feed but unchanged under pristine biochar at lower dosages and re-used biochar at all three dosages. The use of pristine biochar at the highest dosage increased propionate degradation compared with other treatments. In addition, the highest dosage of pristine biochar causes the largest reduction in lag time compared with the control, a reduction of 35%. Lowering the biochar dosage affects the concentration of methanogens on the biochar. Methanosaetaceae and hydrogenotrophic methanogens had greater concentrations on the biochar at dosages of 0.25 and 0.5 gTS−char/gTS−feed. The addition of both pristine and re-used biochar at all three dosages investigated allows for shorter retention times and a greater number of batches to be processed per annum compared with digesters without biochar.
•High dosage of wood-pellet biochar increases methane yield and VFA degradation.•Addition of re-used biochar improved performance compared with control digesters.•Biochar addition increases potential annual throughput of batch digesters.•Lower dosages increases concentration of methanogens on biochar.
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