Methanogenic Process Research Articles

The biological mechanism of a lower carbon/nitrogen ratio increases methane emissions during vegetable waste composting

The initial carbon/nitrogen (C/N) ratio is one of the most important factors impacting composting processes, such as methane (CH4) emissions. However, the effects of the C/N ratio on CH4 emissions and the associated biological mechanisms during vegetable waste composting are largely unknown. In this study, a lab-scale experiment was conducted to investigate the effects of different C/N ratios on CH4 emissions and the mechanisms associated with methane-metabolizing microorganisms (methanogens and methanotrophs) during capsicum straw composting. The initial C/N ratios were set to 18, 30 and 50 to simulate the low (L), medium (M) and high (H) C/N ratios, respectively. The results showed that CH4 emissions were mainly concentrated in the thermophilic phase and that the cumulative CH4 emissions were significantly greater in the L treatment than in the M and H treatments by 10.8 and 15.4 times, respectively. During the methanogenic process, the relative abundance of the dominant genus Methanoculleus (47.59 % ∼ 76.92 %) was higher than in the L treatment than in the M and H treatments at the thermophilic and maturation stages, and the Chao1 index and the mcrA gene abundance followed the order of L > M > H at each composting stage. During the methanotrophic process, the dominant genus unclassified_d_bacteria (51.3 % ∼ 91.87 %), Chao1 index, pmoA gene abundance and CO2 emissions were in the order of L > M > H at each composting stage. This pattern suggests that a lower C/N ratio simultaneously enhanced CH4 production and oxidation. A structural equation model further revealed that the methanogenic community, which was driven directly by the relative contents of hemicellulose and cellulose in the substrates, as indicated by the C/N ratio, made greater contributions to CH4 emissions than did the methanotrophic community. In conclusion, a lower C/N ratio increased CH4 emissions mainly by regulating the population and composition of methanogen community.

Application of organic silicon quaternary ammonium salt (QSA) to reduce carbon footprint of sewers: Long-term inhibition on sulfidogenesis and methanogenesis

Sulfidogenic and methanogenic processes are undesirable in sewer management, yet the derived problems regarding organic losses are often neglected. Traditional chemical dosing methods aimed at sulfide and methane control commonly involve similar mechanisms of oxidation and/or precipitation. Moreover, previous focuses were centered on elevating control efficacy rather than investigating interactions between dosed chemicals and biofilms. In this work, organic silicon quaternary ammonium salt (QSA) of 75 mg-N/L was firstly applied in laboratory pressurized sewer reactors. After three dosing events, it took 20 days for sulfidogenic activities to recover to 50 % without further elevations. Meantime, methanogenic activities were stable ca. 11 % without significant inclinations to recover. Notably, consumption rate of chemical oxygen demand (COD) was suppressed to 50 % at most, and no microbial resistance to QSA but better control efficacy was observed. Characterizations of physicochemistry, microbial community and metabolism were conducted to elucidate mechanisms. Results showed that QSA was attached on sewer biofilms via electrostatic attraction to exert enduring control efficacy. Biofilms tended to become more hydrophobic and compact after QSA exposure. Microbial analyses indicated that relative abundances of microbes regarding hydrolysis, acidogenesis and methanogenesis were sharply decreased together with down-regulation of pivotal enzymatic activities. Additionally, denitrification batch tests initially suggested that the biodegradability of effluent was significantly enhanced, which ensured the safety of QSA dosing into sewers. Overall, results of this work were expected to lay a theoretical foundation on employing QSA to wastewater management.

Peracetic acid enhanced anaerobic co-digestion of excess sludge and food waste: performance and mechanism

ABSTRACT Anaerobic co-digestion of excess sludge (ES) and food waste (FW) has been proven to be a clean and efficient strategy for the resource recovery of organic waste. However, the methane production from the anaerobic co-digestion of ES and FW is not optimal. This study reports a new strategy of using peracetic acid (PAA) pretreatment to enhance the anaerobic co-digestion of ES and FW and reveals the underlying mechanisms. The results confirm that PAA can effectively promote the production of methane from the anaerobic co-digestion of ES and FW, with the maximum methane yield reaching 416 mL/g volatile suspended solids at a PAA content of 9% (w/w). Mechanistic analysis indicates that PAA efficiently facilitates the solubilization of organic matter, promoting the release of soluble proteins and polysaccharides, and accelerating the metabolic conversion of volatile fatty acids (VFAs) to prevent excessive acidification. The maximum output of VFA in the PAA group was 1,511–1,974 mg/L, which was lower than that in the control group. Batch experimental analysis revealed that PAA promoted the hydrolysis and acidification processes, but inhibited the methanogenic process. The PAA pretreatment technique provides a theoretical basis for the efficient treatment of organic matter in urban areas.

Mechanism of biochar in alleviating the inhibition of anaerobic digestion under ciprofloxacin press

The antibiotic ciprofloxacin (CIP), detected in various aqueous environments, has broad-spectrum antimicrobial properties that can severely affect methanogenic performance in anaerobic systems. In this study, a novel strategy to alleviate the inhibition of AD performance under CIP press with the direct addition of biochar (BC) prepared from corn stover was proposed and the corresponding alleviation mechanism was investigated. When the dosage of BC was 5 and 20 g/L, the cumulative methane production in AD could reach 317.9 and 303.0 mL/g COD, and the CIP degradation efficiencies reached 94.1 % and 96.6 %, significantly higher than those of 123.0 mL/g COD and 81.2 % in the Control system. BC avoided excessive reactive oxygen species in anaerobic systems and induced severe oxidative stress response, while protecting the cell membrane and cell wall of microorganisms. Microorganisms could consume and utilize more organic extracellular polymeric substances for their growth and metabolism. When BC was involved in AD, fewer toxic intermediates were generated during CIP biodegradation, reducing acute and chronic toxicity in anaerobic systems. Microbial diversity suggested that BC could enrich functional microorganisms involved in direct interspecies electron transfer like Methanosaeta, norank_f_Bacteroidetes_vadinHA17, JGI-0000079-D21 and Syntrophomonas, thus facilitating the methanogenic process and CIP degradation. Genetic analyses showed that BC could effectively upregulate functional genes related to the conversion of butyrate-to-acetate and acetyl-to-methane under CIP stress, while functional gene abundance associated with CIP degradation enhanced partially, about encoding translocases, oxidoreductases, lyases, and ligases. Therefore, BC can be added to AD under CIP press to address its inhibited methanogenic performance.

Silver nanoparticles incorporated with superior silica nanoparticles-based rice straw to maximize biogas production from anaerobic digestion of landfill leachate

Treating hazardous landfill leachate poses significant environmental challenges due to its complex nature. In this study, we propose a novel approach for enhancing the anaerobic digestion of landfill leachate using silver nanoparticles (Ag NPs) conjugated with eco-friendly green silica nanoparticles (Si NPs). The synthesized Si NPs and Ag@Si NPs were characterized using various analytical techniques, including transmission electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. The anaerobic digestion performance of Si NPs and Ag@Si NPs was tested by treating landfill leachate samples with 50 mg/L of each NP. The results demonstrated an enhancement in the biogas production rate compared to the control phase without the nanocomposite, as the biogas production increased by 14% and 37% using Si NPs and Ag@Si NPs. Ag@Si NPs effectively promoted the degradation of organic pollutants in the leachate, regarding chemical oxygen demand (COD) and volatile solids (VS) by 58% and 65%. Furthermore, microbial analysis revealed that Ag@Si NPs enhanced the activity of microbial species responsible for the methanogenic process. Overall, incorporating AgNPs conjugated with eco-friendly green Si NPs represents a sustainable and efficient approach for enhancing the anaerobic digestion of landfill leachate.

Autochthonous organic matter input in reservoirs: Limited methane oxidation in sediments fails to suppress methane emission

The interception of rivers leads to the accumulation of substantial organic matter in reservoirs, exerting a significant influence on greenhouse gas emissions. The diverse imported organic matter, coupled with sedimentary heterogeneity and intricate microbial processes, gives rise to seasonal variations in methane emissions from reservoirs. In this study, sediment cores were supplemented with terrestrial or autochthonous carbon to emulate reservoir carbon input across different seasons, thereby investigating methane emission potential and associated microbial mechanisms within the sediment cores. Results demonstrated that autochthonous organic matter enhanced sediment organic content, thereby providing more substrates for the methanogenic process and fostering the proliferation of methanogens (with a relative abundance of 47.17 % to 60.66 %). Notably, the dominant genera of Methanosaeta, Methanosarcina, and Candidatus Methanomethylicus were boost on the surface layer of sediment. Concurrently, the introduction of autochthonous organic carbon spurred an increase in methane-oxidizing microbe, reaching up to 5.59 %, with Methylobacter and Candidatus Methanoperedens as the predominant species, which led to a downward migration of the functional microbial group in the sediment. Under the priming impact of autochthonous carbon, however, the methane oxidation probably doesn't consume the substantial methane produced in sediment. Consequently, the sediment functions as a hotspot for methane release into the overlying water, highlighting the necessity to include summer as critical periods for integrated assessments, particularly during algae bloom.

Artificial electron snorkels reduce CH4 emissions in paddy soil: Regulation of the electron transfer pathway and microbial community ecology

Climate science has focused on reducing emissions of atmospheric CH4 from paddy soils, as CH4 has stronger infrared absorption characteristics than CO2. Like cable bacteria, artificial electron snorkels (made of solid graphite rods) have been proposed in this study to provide potential remote electron acceptors for soil anaerobic metabolism to compete with methanogenic processes. A systematic investigation was conducted on the modulation of the CH4 emission dynamics by electron snorkels at different densities, as well as the associated metabolism of C/N/Fe in paddy soil. During 124 days of operation, the electron snorkels suppressed CH4 emissions by 7–31% over ten sampling periods, and the high-density setting exhibited stronger performance. The electron snorkels accelerated the early mineralization of soil organic matter, increasing the content of dissolved organic matter by 20–236%. These organics were utilized by microorganisms, where O2, NO3−, and Fe3+ acted as electron acceptors, enhancing soil alternative respiration and producing CO2. Metagenomic and 16S rRNA gene sequencing revealed that microbial abundance and diversity were increased by 4–71% in the soil bottom layer (7 cm–8 cm depth) driven by electron snorkels. Moreover, electron snorkels potentially prevented CH4 escape by either improving soil permeability or electrically stimulating the abundance of methanotrophs (e.g., Methylocystis). The ratio of methanogenic to methane-oxidizing gene abundances was reduced by 22–66% under the electron snorkels. Our results indicate that the applied electron snorkels have significant potential in enriching the soil microbial community involved in methane cycling to mitigate CH4 emissions from paddy fields.

Biogenic sulfur recovery from sulfate-laden antibiotic production wastewater using a single-chamber up-flow bioelectrochemical reactor

The high-concentration sulfate (SO42−) in the antibiotic production wastewater hinders the anerobic methanogenic process and also proposes possible environmental risk. In this study, a novel single-chamber up-flow anaerobic bioelectrochemical reactor (UBER) was designed to realize simultaneous SO42− removal and elemental sulfur (S0) recovery. With the carbon felt, the cathode was installed underneath and the anode above to meet the different biological niches for sulfate reducing bacteria (SRB) and sulfur oxidizing bacteria (SOB). The bio-anode UBER (B-UBER) demonstrated a much higher average SO42− removal rate (SRR) of 113.2 ± 5.7 mg SO42−−S L−1 d−1 coupled with a S0 production rate (SPR) of 54.4 ± 5.8 mg S0-S L−1 d−1 at the optimal voltage of 0.8 V than that in the abio-anode UBER (control reactor) (SRR = 86.6 ± 13.4 mg SO42−−S L−1 d−1; SPR = 25.5 ± 9.7 mg S0-S L−1 d−1) under long-term operation. A large amount of biogenic S0 (about 72.2 mg g−1 VSS) was recovered in the B-UBER. The bio-anode, dominated by Thiovirga (SOB genus) and Acinetobacter (electrochemically active bacteria genus), exhibited a higher current density, lower overpotential, and lower internal resistance. C-type cytochromes mainly served as the crucial electron transfer mediator for both direct and indirect electron transfer, so that significantly increasing electron transfer capacity and biogenic S0 recovery. The reaction pathways of the sulfur transformation in the B-UBER were hypothesized that SRB utilized acetate as the main electron donor for SO42− reduction in the cathode zone and SOB transferred electrons to the anode or oxygen to produce biogenic S0 in the anode zone. This study proved a new pathway for biogenic S0 recovery and sulfate removal from sulfate-laden antibiotic production wastewater using a well-designed single-chamber bioelectrochemical reactor.

Enhancing the Startup Rate of Microbial Methanogenic Systems through the Synergy of β-lactam Antibiotics and Electrolytic Cells.

The slow startup and suboptimal efficiency of microbial carbon sequestration and methane-production systems have not been fully resolved despite their contribution to sustainable energy production and the reduction of greenhouse gas emissions. These systems often grapple with persistent hurdles, including interference from miscellaneous bacteria and the slow enrichment of methanogens. To address these issues, this paper examines the synergistic effect of coupling β-lactam antibiotics with an electrolytic cell on the methanogenic process. The results indicated that β-lactam antibiotics exhibited inhibitory effects on Campylobacteria and Alphaproteobacteria (two types of miscellaneous bacteria), reducing their relative abundance by 53.03% and 87.78%, respectively. Nevertheless, it also resulted in a decrease in hydrogenogens and hindered the CO2 reduction pathway. When coupled with an electrolytic cell, sufficient electrons were supplied for CO2 reduction to compensate for the hydrogen deficiency, effectively mitigating the side effects of antibiotics. Consequently, a substantial improvement in methane production was observed, reaching 0.57 mL·L-1·d-1, exemplifying a remarkable 6.3-fold increase over the control group. This discovery reinforces the efficiency of methanogen enrichment and enhances methane-production levels.

Material and microbial perspectives on understanding the role of biochar in mitigating ammonia inhibition during anaerobic digestion

With the increasing adoption of carbon-based strategies to enhance methanogenic processes, there is a growing concern regarding the correlation between biochar properties and its stimulating effects on anaerobic digestion (AD) under ammonia inhibition. This study delves into the relevant characteristics and potential mechanisms of biochar in the context of AD system under ammonia inhibition. The introduction of optimized biochar, distinguished by rich CO bond, abundant defect density, and high electronic capacity, resulted in a significant reduction in the lag period of anaerobic digestion system under 5.0 g/L ammonia stress, approximately by around 63 % compared to the control one. Biochar helps regulate the community structure, promotes the accumulation of acetate-consuming bacteria, in the AD system under ammonia inhibition. More examinations show that biochar promotes direct interspecies electron transfer in AD system under ammonia inhibition, as evidenced by diminished levels of bound electroactive extracellular polymeric substances, increased abundance of electroactive bacteria, and notably, the up-regulation of direct interspecies electron transfer associated genes, including the conductive pili and Cytochrome C genes, as revealed by meta-transcriptomic analysis. Additionally, gene expression related to proteins associated with ammonium detoxification were found to be up-regulated in systems supplemented with biochar. These findings provide essential evidence and insights for the selection and potential engineering of effective biochar to enhance AD performance under ammonia inhibition.

Amphibitic stoneflies (Plecoptera) are integrators of ecosystem processes in alluvial aquifers of gravel‐bed river floodplains

AbstractOver 50 years ago nymphs of the Plecoptera species, Paraperla frontalis Banks, 1906 (Plecoptera: Chloroperlidae), were shown to exist in a shallow floodplain aquifer of the Tobacco River, a gravel‐bed river in western Montana and later they were documented throughout the main stems of the Flathead River system. Nymphs are almost never found in surface waters, until they emerge on the river shorelines. As teneral adults, they mate and subsequently deposit fertilized eggs into the river. This novel life cycle is termed “amphibitic.” Over the years we and others have found P. wilsoni Ricker, 1965 (Plecoptera: Chloroperlidae), Kathroperla perdita Banks, 1920 (Plecoptera: Kathroperlidae), and five species of Isocapnia Banks, 1938 (Plecoptera: Capniidae), including long‐winged and brachypterous adults and wingless dwarfs (male and female), occupying amphibitic niches in the alluvial aquifers of rivers in Washington, Idaho, Colorado, Alaska and British Columbia. These stoneflies are remarkably tolerant of hypoxia which allows them to exist as abundant consumers in aquifer food webs subsidized by ancient methane. Indeed, stonefly tissues contain carbon that is up to 7000 years old, underscoring the existence of a strong interaction involving the uptake of labile carbon derived from methanogenic and methanotrophic process in aquifers. Details of life cycles, trophic relationships, distribution and abundance have been documented by a suite of studies on the Nyack Floodplain of the Middle Flathead River, Montana. In this paper we review the ecophysiology and ecology of these unique stoneflies in the context of their functional role in gravel‐bed river ecosystems.This article is categorized under: Water and Life > Nature of Freshwater Ecosystems Water and Life > Conservation, Management, and Awareness

Impact analysis of hydraulic residence time and dissolved oxygen on performance efficiency and microbial community in N, N-dimethylformamide wastewater treated by an AnSBR-ASBR

Suitable operating parameters are one of the key factors to efficient and stable biological wastewater treatment of N, N-dimethylformamide (DMF) wastewater. In this study, an improved AnSBR-ASBR reactor (anaerobic sequencing batch reactor, AnSBR, and aerobic SBR, ASBR, run in series) was used to investigated the effects of operating conditions such as hydraulic residence time (HRT), AnSBR stirring speed and ASBR dissolved oxygen (DO) for DMF wastewater treatment. When HRT decreased from 24 h to 12 h, the average removal rates of COD by the AnSBR were 34.59% and 39.54%, respectively. Meanwhile, the removal rate of NH4+-N by ASBR decreased from 88.38% to 62.81%. The DMF removal rate reached the best at 18 h and the expression of dehydrogenase was the highest in the AnSBR. The abundance of Megasphaera, the dominant sugar-degrading bacteria in the AnSBR, continued to decline due to the decrease of HRT. The relative abundance of Methanobacterium gradually increased to 80.2% with the decrease of HRT and that hydrotrophic methanogenesis dominated the methanogenic process. The HRT decrease promoted butyrate and pyruvate metabolism in anaerobic sludge, but the proportion of glycolysis and methane metabolism decreased. The AnSBR-ASBR reactor had the best operation performance when HRT was 18 h, AnSBR speed was 220 r/min, and ASBR DO content was 3–4 mg/L. This study provided an effective reference for the reasonable selection of operating parameters in the treatment of DMF-containing wastewater by the AnSBR-ASBR.

Coupling between 2, 2′, 4, 4′-tetrabromodiphenyl ether (BDE-47) debromination and methanogenesis in anaerobic soil microcosms

Polybrominated diphenyl ethers (PBDEs) are persistent pollutants that may undergo microbial-mediated debromination in anoxic environments, where diverse anaerobic microbes such as methanogenic archaea co-exist. However, current understanding of the relations between PBDE pollution and methanogenic process is far from complete. To address this knowledge gap, a series of anaerobic soil microcosms were established. BDE-47 (2, 2′, 4, 4′-tetrabromodiphenyl ether) was selected as a model pollutant, and electron donors were supplied to stimulate the activity of anaerobes. Debromination and methane production were monitored during the 12 weeks incubation, while obligate organohalide-respiring bacteria (OHRBs), methanogenic, and the total bacterial communities were examined at week 7 and 12. The results demonstrated slow debromination of BDE-47 in all microcosms, with considerable growth of Dehalococcoides and Dehalogenimonas over the incubation observed in most BDE-47 spiked treatments. In addition, the accumulation of intermediate metabolites positively correlated with the abundance of Dehalogenimonas at week 7, suggesting potential role of these OHRBs in debromination. Methanosarcinaceae were identified as the primary methanogenic archaea, and their abundance were correlated with the production of debrominated metabolites at week 7. Furthermore, it was observed for the first time that BDE-47 considerably enhanced methane production and increased the abundance of mcrA genes, highlighting the potential effects of PBDE pollution on climate change. This might be related to the inhibition of reductive N- and S-transforming microbes, as revealed by the quantitative microbial element cycling (QMEC) analysis. Overall, our findings shed light on the intricate interactions between PBDE and methanogenic processes, and contribute to a better understanding of the environmental fate and ecological implication of PBDE under anaerobic settings.

Effects and mechanisms of nZVI on CO2 and CH4 emissions in uncontaminated and pentachlorophenol-contaminated soils

With the increasing application of nanoscale zero-valent iron (nZVI) for in situ soil remediation, its effects on soil functionality and ecosystem need to be thoroughly evaluated. Herein, we investigated the effects of nZVI on CO2 and CH4 emissions from uncontaminated and pentachlorophenol (PCP)-contaminated soils and the underlying microbial mechanisms by designing a 68-day anaerobic soil culture experiment; thereafter, the effects of above aged nZVI on soil CO2 and CH4 emissions in the following 20 days were further studied. In the uncontaminated soil, 1–10 g/kg nZVI treatments reduced soil CO2 emission by 17.4–82.6% and increased soil CH4 emission by 10.8%–119.7%, but these effects disappeared after the nZVI was aged. The emissions of soil CO2 and CH4 were significantly inhibited by the PCP contamination (100 mg/kg) mainly due to the toxicity to related soil microorganisms. The applications of 1–10 g/kg nZVI significantly reduced CO2 emissions from the PCP-contaminated soil by 24.0–86.7%, while 10 g/kg nZVI markedly increased soil CH4 emission by 1875.4% and restored the methanogenic activity to the control level after the nZVI was aged. The 10 g/kg nZVI treatment enriched hydrogenotrophic methanogen (Methanobacterium) and organics-degrading bacteria by releasing H2, increasing soil pH, and decreasing soil Eh; the abundance of genes encoding key enzymes (Mcr, Mtr, Hdr, Mta, and Mtb) in all methanogenic pathways significantly increased after the nZVI treatment, indicating that nZVI could have a broad promoting effects on soil methanogenic processes. The findings demonstrate that the addition of nZVI for in situ remediation of organochlorines-contaminated soils will affect soil greenhouse gas emissions and provide basic data for safe nZVI applications.

Effects of ozone on activated sludge: performance of anaerobic digestion and structure of the microbial community

Abstract The treatment and disposal of activated sludge are currently challenging tasks in the world. As a common biological engineering technology, biological fermentation exists with disadvantages such as low efficiency and complex process. Ozone pretreatments are commonly applied to improve this problem due to their high efficiency and low cost. In this study, the significant function of ozone in anaerobic fermentation gas production was verified with excess sludge. Compared with other untreated sludge, ozone pretreatment can effectively degrade activated sludge. After ozone treatment and mixing with primary sludge, the methane production of excess sludge increased by 49.30 and 50.78%, and the methanogenic activity increased by 69.99 and 73.83%, respectively. The results indicated that the mixing of primary sludge with excess sludge possessed synergistic effects, which contributed to the anaerobic fermentation of excess sludge. The results of microbial community structure exhibited that methanogenic processes mainly involve hydrogenogens, acidogens and methanogens. The relative abundance of both bacteria and microorganisms changed significantly in the early stage of hydraulic retention time, which coincided exactly with the gas production stage. This study provided a feasible pretreatment strategy to improve sludge biodegradability and revealed the role of microorganisms during anaerobic digestion.

Biodigestion of easily-acidifying cheese whey in a sequential fermentative-methanogenic process: Strategies for boosting energy production and minimizing alkalinization costs

The biodigestion of cheese whey towards enhanced bioenergy production still challenges researchers, considering incipient biohydrogen (bioH2) production during fermentation and the great dependence on an efficient (usually high-cost) alkalinization strategy to achieve high and stable methane production. Using a sequential fermentative-methanogenic process in fixed-film reactors, this study assessed strategies to boost bioH2 production (pH control at ca. 5.5 + prevention of biomass accumulation) and achieve a low-cost stable methanogenic process (replacing NaHCO3 dosing by effluent recirculation and further eliminating any alkalinization approaches). Maintaining fermentation pH values between 5.0 and 5.5 favored bioH2 and butyrate production, but the enhanced establishment of homoacetogenesis (accounting for 70–100 % of the acetate produced) associated with the selective removal of hydrogen-producing bacteria in biomass discharges resulted in a marked unstable hydrogenogenic activity. Processing fermented cheese whey without applying any alkalinization strategy in methanogenesis was further demonstrated to be technically feasible at an OLR of 5.0 kg COD m−3 d−1. COD removal (70–75 %) and the methane yield (150–170 NmL CH4 g−1COD) were equivalent regardless of the alkalinization (NaHCO3 dosing or effluent recirculation) or non-alkalinization approach. However, the alkalinization-derived production cost of methane was reduced from 1.55 USD Nm−3CH4 to zero when fully removing NaHCO3.

Phaffia rhodozyma biorefinery: A sustainable pathway to obtain natural pigments and production of methane biogas as renewable fuel

As the world strives to create a more sustainable and healthier lives, natural pigments are coming to the fore in an attempt to minimize the use of synthetics counterparts and shift the focus towards microbial sources. In this in mind, the yeast Phaffia rhodozyma was used in this study, in a biorefinery context, as biomass feedstock for the intracellular astaxanthin production and reuse of biomass to produce biogas (cf., methane). A sustainable extraction procedure using bio-based solvents was established to directly recover astaxanthin-rich extract from P. rhodozyma dry biomass. The molecular influence of the solutes and solvents involved in the solid–liquid extraction procedures was investigated. Envisioning the full sustainability of the process, and to estimate if the biosolvents used to the process is astaxanthin-friendly, the evaluation of antioxidant activity was confirmed by determining the antioxidant activity using Electron Paramagnetic Resonance (EPR) and toxicological (mutagenicity and ecotoxicity) properties of astaxanthin-rich extract, and the recyclability of solvent was efficiently accomplished. Furthermore, to demonstrate the circularity of the process, the remaining biomass (waste biomass) obtained after astaxanthin-rich extract recovery was effectively used in methanogenic process to produce biogas. The anaerobic digestion used to evaluate methane production from the waste biomass demonstrated the potential to generate 86.88 kWh/year, 225,774.95 kcal/year and 10,287.53 kg/year of electricity, heat recovery and savings on waste management in an P. rhodozyma plant/biorefinery, respectively.

Monitoring of a microbial community during bioaugmentation with hydrogenotrophic methanogens to improve methane yield of an anaerobic digestion process

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

Performance and stability enhancement of methanogenic granular sludge process: Feed pre-acidification and magnetite-embedded granule formation

Recently, inducing the formation of conductive magnetite-embedded granules (MEGs) by self-embedding submicron magnetite particles into anaerobic granules has been demonstrated to be effective in enhancing methanation and improving sludge stability in upflow anaerobic sludge blanket (UASB) reactors. However, MEGs still suffer structural and functional destabilization at high organic loading rates (OLRs) due to the excessive secretion of extracellular polymeric substances (EPS), resulting in a significant washout of active microbes. This is particularly true when treating carbohydrate-rich wastewater that is prone to producing excessive EPS. In order to address this issue, this study explored the potential of combining MEG-UASB process with feed pre-acidification as a means of improving the methanogenic treatment performance and stability of whey, a carbohydrate-rich dairy effluent. Two UASB reactors, one with MEGs and one without, were operated to treat pre-acidified whey at increasing OLRs of 2–11 g chemical oxygen demand/L·d. Feed pre-acidification was effective in preventing granule destabilization and maintaining stable UASB performance with or without MEGs. Meanwhile, the reactor with MEGs (JM) showed significantly better performance and stability than the one without MEGs (JC), especially at high OLRs, which was likely because MEGs improved sludge retention and promoted electro-syntrophic methanogenic activity. Accordingly, JM sludge exhibited greater electron transfer capability and a more pronounced enrichment of electroactive microbes than JC sludge. External voltage application (0.6 V) did not relieve but rather aggravated the process upset under overloading conditions for both reactors. The overall results suggest that the MEG-UASB process coupled with pre-acidification holds promise for efficient and stable treatment of carbohydrate-rich wastewater.

Variations in Methanogenic and Methanotrophic Communities Resulted in Different Methane Emissions from Paddy Soil Applied with Two Types of Manure

Organic manure application is crucial for the maintenance and improvement of soil fertility. However, it inevitably results in increased paddy CH4 emissions, restricting the use of organic manure in the rice fields. In the present study, two kinds of manures, rapidly composted manure (RCM) and non-composted manure (NCM), were investigated through a 19-week greenhouse experiment, during which the dynamics of CH4 emission, soil parameters (DOC, acetate, NH4+, NO3−, and SO42−), and communities of methanogens and methanotrophs were simultaneously measured. The results showed that NCM significantly enhanced CH4 emission, while RCM decreased CH4 emission by 65.03%; there was no significant difference with the manure-free treatment. In order to well understand the methanogenic process, the seasonal CH4 flux was divided into two periods, namely Stage 1 (before drainage) and Stage 2 (after drainage), on the basis of CH4 emission intensity. The different CH4 production abilities among the three treatments could contribute to the varied CH4 emissions at Stage 1. The much higher soil DOC concentrations were observed in the manure-amended soils (NCM- and RCM-treatments), which could correspondingly lead to the relative higher CH4 emissions compared to the control during Stage 1. Furthermore, the increased methanogenic abundance and the shifted methanogenic archaeal community characterized by the functionally stimulated growth of Methanosarcina genus were observed in the NCM-treated soils, which could consequently result in a higher CH4 emission from the NCM treatment relative to the RCM treatment. As for Stage 2, apart from the significant decrease in soil DOC, the increased contents of soil NO3− and SO42−, especially with the RCM-treated soils, were also detected following the drainage, which might retard CH4 production. The lower CH4 emission at Stage 2 could also be attributed to the vigorous aerobic CH4 oxidations, especially in the RCM-treated soils. As a support, the amount of methanotrophs revealed an increasing trend during the late rice growth period, as did the predominance of the methylotrophy of Methylophilaceae species, which showed robust co-occurrence with methanotrophs, inferring interspecies cooperation in methane oxidation.