Anaerobic Fermentation Research Articles

Insights into multivalent metal removal-assistant anaerobic fermentation of waste activated sludge: Impact factor identification and mechanism clarification of metal removal

The study investigated the impact factors of metal removal and their role in enhancing anaerobic fermentation of waste activated sludge (WAS), aiming to identify key mechanisms. By optimizing the sludge concentration, it found that a sludge suspension solid range of 10–30 g/L significantly improved the efficiency of anaerobic fermentation, and yielded SCOD of 93.8–177.1 mg/g volatile suspension solid after 8 h, respectively, which was 3.67–4.77 times higher than the control. Correspondingly, the production of short-chain fatty acids (SCFAs) was significantly enhanced. At the optimal sludge suspension solid of 10–30 g/L, the SCFAs were 1.28–1.51 times higher than that of the control. Furthermore, the study evaluated the performance of different metal removal reagents and discovered that microporous COOH reagent outperformed gel SO3H and macroporous SO3H reagent. The macroporous COOH reagent achieved 1.54 and 1.22 times higher SCOD values and significantly enhanced the production of SCFAs, demonstrating its superiority in metal removal and fermentation enhancement. Moreover, the research revealed that sludge concentration and metal removal agent types influenced the activities of key enzymes involved in anaerobic fermentation. Additionally, the macroporous COOH reagent showed the most efficient ability to remove metal ions, contributing to increased nutrient recovery in terms of nitrogen (NH4+-N) and total phosphorus (TP) release during the acidification process. In summary, the enhancing mechanism of metal removal-assistant anaerobic fermentation was discussed from the sludge floc concentration, the skeleton structure and the ion exchange group type. The identified mechanism significantly improves fermentation efficiency and facilitate the organic recovery, representing an innovative approach for wide application in WAS management and resource recovery.

A novel strategy for waste activated sludge treatment: Recovery of structural extracellular polymeric substances and fermentative production of volatile fatty acids

Structural extracellular polymeric substances (SEPS) as valuable biopolymers, can be extracted from waste activated sludge (WAS). However, the extraction yield is typically low, and detailed information on SEPS characterizations, as well as proper treatment of the sludge after SEPS extraction, remains limited. This study aimed to optimize the conditions of heating-Na2CO3 extraction process to increase the yield of SEPS extracted from WAS. Subsequently, SEPS were characterized, and, for the first time, insights into their protein composition were uncovered by using proteomics. A maximum SEPS yield of 209 mg/g volatile solid (VS) was obtained under optimal conditions: temperature of 90°C, heating time of 60 min, Na+ dosage of 8.0 mmol/g VS, and pH required to precipitation of 4.0, which was comparable to that from the aerobic granular sludge reported in literature. Proteomics analysis unveiled that the proteins in SEPS primarily originated from microorganisms involved in nitrogen fixation and organic matter degradation, including their intracellular and membrane-associated regions. These proteins exhibited various catalytic activities and played crucial roles in aggregation processes. Besides, the process of SEPS extraction significantly enhanced volatile fatty acid (VFA) production during the anaerobic fermentation of residual WAS after SEPS extraction. A maximum VFA yield of 420 ± 14 mg COD/g VSadded was observed in anaerobic fermentation of 10 d, which was 77.2 ± 0.1% higher than that from raw sludge. Mechanism analysis revealed that SEPS extraction not only improved WAS disintegration and solubilization but also reduced the relative activity of methanogens during anaerobic fermentation. Moreover, SEPS extraction shifted the microbial population during anaerobic fermentation in the direction towards hydrolysis and acidification such as Fermentimonas sp. and Soehngenia sp. This study proposed a novel strategy based on SEPS extraction and VFA production for sludge treatment, offering potential benefits for resource recovery and improved process efficiency.

Addition of commercial lactic acid bacteria as starter cultures in anaerobic fermentations of Coffea arabica L., in cherry or raisin stages

The objective of this research was to verify the efficiency of adding commercial lactic acid bacteria (LAB) on anaerobic fermentation of (cherry and raisin) arabica Yellow Catuaí coffees, studying the microbiological succession and its influence in modulating sensorial characteristics on their beverages. The study took place in a rural property in Marília region, Sao Paulo State, Brasil, and was performed according to three different treatments: 1) FNC = spontaneous fermentation of cherry coffees; 2) FCBAL = cherry coffee fermentation using Sacco Lyofast SYAB1 BAL; 3) FPBAL = raisin coffee fermentation using Sacco Lyofast SYAB1 BAL. Fermentations occurred in individual (60 liters) high density polyethylene containers, properly sealed to guarantee anaerobic conditions. After a 48-hour fermentation, all the coffee fruits were washed, beans were depulped and dried on suspended terrace until a 12% humidity was observed. Physical, chemical, microbiological and sensory analysis were performed in samples collected from each fermented batch. Fermentation processes of raisin coffees occurred more slowly than fermentations using cherry coffees and resulted in a lesser consumption of soluble solids and in a slower acidification. Fermentation treatments FNC, FCBAL and FPBAL reached the necessary reduction of Enterobateriaceae and molds. The addition of BAL stimulated the growth of yeasts, which are responsible for the inclusion of the most desired flavor. The fermentations conducted in this experiment resulted in coffee beverages that reached notes of specialty coffees (> 80 points). Even though the raisin coffee achieved a lower note than cherry, the LAB inclusion raised it from 77 (non-fermented raisins) to 80 (FPBAL) points. In cherry fruits, FCBAL got 2 points on final comparation to non-fermented cherries. Thus, the inclusion of LAB presented itself beneficial to anaerobic fermentations of cherry or raisin coffees.

Elucidating the synergic mechanism of sodium pyrophosphate assisted enzymolysis on the waste activated sludge fermentation enhancement: Insights from organic conversion and metagenomic analysis

Lysozyme has been identified as a promising approach for enhancing waste activated sludge (WAS) anaerobic fermentation. However, the extracellular polymeric substance (EPS), functioning as a ‘protective shell’ for microbial cells, hindered the lysozyme transfer and subsequent interaction with cell wall, resulting in excessive dosage and limited efficiency in practical engineering applications. This study innovatively proposed a sodium pyrophosphate (SP) assisted lysozyme treatment, aiming to overcome such limitations and enhance the solubilization and hydrolysis efficiency. As a result, 3583.5 mg COD/L short-chain fatty acids (SCFAs) and 23.1 % acidification rate were achieved after 2-day anaerobic fermentation within SP-lysozyme treatment. Mechanism investigation revealed that SP facilitated EPS disruption by inducing a loosening of the protein structure, leading to the enhanced solubilization of organic matter within the EPS and microbial cells. Consequently, the release of substantial substrates contributed to the enrichment of functional microbes associated with hydrolysis and acidogenesis, accompanied by the augmentation of corresponding metabolic functions. Besides, the key functional genes analysis demonstrated the amino acid metabolism, glycolysis, pyruvate metabolism and SCFAs transport were facilitated and the methanogenesis was inhibited on the contrary with SP-lysozyme treatment, which was undoubtedly responsible for the superior SCFAs accumulation in anaerobic fermentation process. Considering the carbon resource recovery in SCFAs form, such novel SP-lysozyme treatment exhibited 325.1 CNY /ton SS (45.5 USD / ton SS) economic benefit and avoided 0.12 CO2/ton SS carbon emission, suggesting its promising application potential in future WAS management.

Enhancement of Activated Carbon on Anaerobic Fermentation of Heavy-Metal-Contaminated Plants: Insights into Microbial Responses

Enhancement of Activated Carbon on Anaerobic Fermentation of Heavy-Metal-Contaminated Plants: Insights into Microbial Responses

Anaerobic Fermentation and High-Value Bioproducts: A Brief Overview of Recent Progress and Current Challenges

The global community is in a perpetual search for alternative energy sources that can effectively supplant fossil fuels and contribute to environmental stewardship [...]

Efficient conversion from food waste to composite carbon source through rapid fermentation and ceramic membrane filtration

Anaerobic fermentation of food waste (FW) produces a broth rich in small-molecule organic substances, which has the potential as a composite carbon source for denitrification in wastewater treatment. In this study, the idea was tested by optimizing the fermentation process at different hydraulic residence time (HRT), refining fermentation broth through ceramic membrane filtration, and comparing the performance of fermentation filtrate and other commercial carbon sources. A short HRT of 3 days was a suitable fermentation condition with 88% polysaccharide degradation. Acetic acid contributed 40% of soluble chemical oxygen demand in the fermentation broth, followed by ethanol, propanol, lactic acid, and propionic acid, and the five products accounted for 80%. Ceramic membrane filtration can recover more than 70% of dissolved organic matter and more than 60% of small molecular organic matter and simultaneously remove 99% of SS, 41% of total nitrogen, and 62% of total phosphorus. At the rapid degradation stage, the denitrification rates reached 6.68–10.39 mg NOx−-N/(g VSS·h), which was on par with commercial carbon sources. The short fermentation and the rapid membrane separation were integrated to create an efficient treatment system, which provided a feasible pathway to utilize FW combining wastewater treatment.

Hexanoic acid production from anaerobic fermentation of Chinese cabbage waste with exogenous lactic acid as electron donor

The lack of electron donors is one of the key factors hindering hexanoic acid production from anaerobic fermentation. In this study, three different types of lactic acids were supplemented as exogenous electron donors to the anaerobic fermentation system of Chinese cabbage waste (CCW). The yields of hexanoic acid in the reactors supplemented with CCW lactic acid pre-fermentation broth (PFB), lactic acid diluent (LAD) and chemical lactic acid (LA) were 6996.8 mg COD/L, 4534.8 mg COD/L and 6777.1 mg COD/L, respectively. Compared with the reactor supplemented with LA, the electron efficiency of hexanoic acid in reactor supplemented with PFB increased by 188 %. Supplementing PFB shifted the microbial communities towards a direction favorable to hydrolysis and chain elongation, thereby facilitating the synthesis of hexanoic acid.

Progress and Trends in Forage Cactus Silage Research: A Bibliometric Perspective

Opuntia spp. (forage cactus or spineless cactus) is a plant native to Mexico that is commonly used as alternative nutrient-rich fodder in semi-arid regions. Due to its resistance to drought, forage cactus has become an important least-cost ingredient for formulating balanced rations for ruminants during times of scarcity. In addition, ensiling, an anaerobic fermentation process, is also a strategy used to allow a supply of bulky food all year round, since it conserves forage and maintains its nutritional value. In this sense, using the Scopus database and the visualization tool VOSviewer, the present work proposes a bibliometric analysis of forage cactus silage to track and map the evolution and main issues in the research field, current trends, and future directions. The results revealed that the first publication was in 2013; and since 2020, the number of publications has been growing. Brazil was highlighted, by far, as the most relevant country on the topic, and the top institutions were from northeast Brazil, which has been working on co-authored articles. The current hot research topics are focusing on the mixed silage of forage cactus and other forages such as gliricidia, maniçoba, and sorghum biomass, as well as evaluating the fermentative performance and chemical characteristics for improving ruminal diets, especially for goats and sheep. This study provides important information for researchers to identify gaps and direct their studies to better use the whole potential of forage cactus as an alternative roughage source.

CRISPRi-mediated metabolic switch enables concurrent aerobic and synthetic anaerobic fermentations in engineered consortium

Replacing petrochemicals with compounds from bio-based manufacturing processes remains an important part of the global effort to move towards a sustainable future. However, achieving economic viability requires both optimized cell factories and innovative processes. Here, we address this challenge by developing a fermentation platform, which enables two concurrent fermentations in one bioreactor. We first construct a xylitol producing Escherichia coli strain in which CRISPRi-mediated gene silencing is used to switch the metabolism from aerobic to anaerobic, even when the bacteria are under oxic conditions. The switch also decouples growth from production, which further increases the yield. The strain produces acetate as a byproduct, which is subsequently metabolized under oxic conditions by a secondary E. coli strain. Through constraint-based metabolic modelling this strain is designed to co-valorize glucose and the excreted acetate to a secondary product. This unique syntrophic consortium concept facilitates the implementation of “two fermentations in one go”, where the concurrent fermentation displays similar titers and productivities as compared to two separate single strain fermentations.

Effect of salinity on anaerobic fermentation gas production behaviors of the thermal pretreated fruit waste

Effect of salinity on anaerobic fermentation gas production behaviors of the thermal pretreated fruit waste

Comprehensive evaluation of Flammulina velutipes residues polysaccharide based on in vitro digestion and human fecal fermentation

Flammulina velutipes residues (FVR) are the waste culture medium derived from the collection of Flammulina velutipes fruiting bodies, with an annual output that remains largely unexplored. The characteristics of digestion and fermentation of Flammulina velutipes residues polysaccharide (FVRP) are still relatively unknown. This study investigated the structure of the gut microbiota through 16 s rDNA gene sequencing and analyzed changes in short-chain fatty acid (SCFA) content via targeted metabolome analysis. The aim was to explore the prebiotic activity of FVRP based on a simulated digestion model combined with an in vitro anaerobic fermentation model. The results demonstrated that FVRP did not exhibit significant changes during in vitro digestion and fermentation but did enhance antioxidant activity. Furthermore, FVRP was found to rapidly reduce the pH value and increase SCFA production in the fermentation broth from lactic acid bacteria and human feces. Notably, FVRP altered the gut microbiota structure, significantly increasing the relative abundance of Firmicutes and Bacteroidota. Thus, FVRP could be considered a promising prebiotic food and feed additive that promotes the generation of short-chain fatty acids by modulating gut microbiota.

Lysozyme coupling protease pretreatment to relieve the humic acid inhibition on excess sludge anaerobic fermentation

The asynchronous dosed protease and lysozyme combination pretreatment was proved to be effective in enhancing the anaerobic fermentation of waste activated sludge (WAS). However, humic acid (HA) in the sludge could interact with hydrolase and restrain the hydrolysis efficiency, thus inhibiting short-chain fatty acids (SCFAs) production. This study investigated the effectiveness and mechanism of enzymatic pretreatment against HA. Results showed that the enzyme cocktail method increased the extracellular bioavailable contents by 34 %, which raised SCFAs production by 89.69 % (1269.65 mg COD /L). The balanced ratio of hydrolysis and fermentation communities suggested that the small molecular organics generated by the hydrolysis community could be sufficiently utilized by fermentation communities. The metabolism of amino acids and glucose was facilitated, and the activities of key enzymes were enhanced. These results clarified the effect of asynchronous enzyme cocktail pretreatment against HA inhibition and contributed to SCFAs production, which offered fresh perspectives on carbon recovery.

Effect of D-limonene on volatile fatty acids production from anaerobic fermentation of waste activated sludge under pH regulation: performance and mechanisms

D-limonene extracted from citrus peels possesses an inhibitory effect on methanogenic archaea. This study is aimed to bridge the research gap on the influence of D-limonene on volatile fatty acids (VFA) production from waste activated sludge (WAS) and to address the low VFA yield in standalone anaerobic fermentation of WAS. When the initial pH was not controlled, 1.00 g/g TSS D-limonene resulted in a VFA accumulation of 1175.45 ± 101.36 mg/L (174.45 ± 8.13 mgCOD/gVS). When the initial pH was controlled at 10 and the D-limonene concentration was 0.50 g/g TSS, the VFA accumulation reached 2707.44 ± 183.65 mg/L (445.51 ± 17.10 mgCOD/gVS). The pH-regulated D-limonene treatment enhanced solubilization and acidification, slightly inhibited hydrolysis, and significantly suppressed methanogenesis. D-limonene under alkaline conditions can increase the relative abundance of Clostridium_sensu_stricto, significantly enhancing acidification. Moreover, it markedly inhibited methanogenesis by particularly reducing the relative abundance of Methanothrix that was responsible for acetate consumption, thus favoring the accumulation of VFA. The research reveals the potential mechanism of pH regulation and D-limonene on anaerobic fermentation acid production, providing a theoretical basis for improving the acid production performance of the anaerobic fermentation of WAS.

Application of propionate-producing bacterial consortium in ruminal methanogenesis inhibited environment with bromoethanesulfonate as a methanogen direct inhibitor.

Methane production in ruminants is primarily due to the conversion of metabolic hydrogen (H2), produced during anaerobic microbial fermentation, into methane by ruminal methanogens. While this process plays a crucial role in efficiently disposes of H2, it also contributes to environmental pollution and eliminating methane production in the rumen has proven to be challenging. This study investigates the use of probiotics, specifically propionate-producing bacteria, to redirect accumulated H2 in a methane-mitigated environment. For this objective, we supplemented experimental groups with Lactiplantibacillus plantarum and Megasphaera elsdenii for the reinforced acrylate pathway (RA) and Selenomonas ruminantium and Acidipropionibacterium thoenii for the reinforced succinate pathway (RS), as well as a consortium of all four strains (CB), with the total microbial concentration at 1.0 × 1010 cells/mL. To create a methane-mitigated environment, 2-bromoethanesulfonate (BES) was added to all experimental groups at a dose of 15 mg/0.5 g of feed. BES reduced methane production by 85% in vitro, and the addition of propionate-producing bacteria with BES further decreased methane emission by up to 94% compared with the control (CON) group. Although BES did not affect the alpha diversity of the ruminal bacteriome, it reduced total volatile fatty acid production and altered beta diversity of ruminal bacteriota, indicating microbial metabolic adaptations to H2 accumulation. Despite using different bacterial strains targeting divergent metabolic pathways (RA and RS), a decrease in the dominance of the [Eubacterium] ruminantium group suggesting that both approaches may have a similar modulatory effect. An increase in the relative abundance of Succiniclasticum in the CB group suggests that propionate metabolism is enhanced by the addition of a propionate-producing bacterial consortium. These findings recommend using a consortium of propionate-producing bacteria to manage H2 accumulation by altering the rumen bacteriome, thus mitigating the negative effects of methane reduction strategies.

Caproiciproducens converts lactic acid into caproic acid during Chinese strong-flavor Baijiu brewing

Strong-flavor Baijiu, a type of Chinese liquor, is produced through anaerobic solid-state fermentation in a sealed mud pit. Ethyl caproate, the characteristic flavor compound of strong-flavor Baijiu, is influenced by caproic acid-producing bacteria in the pit mud. To better understand the formation of caproic acid, this study investigated the microbial composition and physicochemical parameters of pit mud from different layers (top, middle, and bottom) in Hubei and Sichuan provinces, China. The results revealed that Caproiciproducens plays a key role in caproic acid production by using lactic acid as a substrate, with its abundance increasing with the depth of the pit mud. A strain Caproiciproducens sp. R1, isolated from the pit mud, was shown to produce caproic acid from lactic acid within an initial pH range of 5.5–9.0 and lactic acid concentrations of 1 %–5 % (m/v). In addition, inoculation of strain R1 into Huangshui (a lactic acid-rich liquid from Baijiu production) resulted in 40.72 mM caproic acid production. This study demonstrates that Caproiciproducens plays a crucial role in caproic acid production from lactic acid during the fermentation process of strong-flavor Baijiu.

Novel Insights into the Long-Term Thiosulfate Pretreatment for Enhanced Short-Chain Fatty Acids Production from Sludge Anaerobic Fermentation: Organics Transformation, Electron Transfer, and Microbial Cooperation

Novel Insights into the Long-Term Thiosulfate Pretreatment for Enhanced Short-Chain Fatty Acids Production from Sludge Anaerobic Fermentation: Organics Transformation, Electron Transfer, and Microbial Cooperation

New insight into Clostridium butyricum-ferroferric oxide hybrid system in exogenous carbon dioxide-assisted anaerobic fermentation for acetate and butyrate production

Mixotrophic cultivation, utilizing both gas and organic substances, is commonly employed to minimize the carbon loss during anaerobic fermentation of bulk chemicals. Herein, a novel Clostridium butyricum-ferroferric oxide (Fe3O4) hybrid system, enhanced by exogenous carbon dioxide (CO2), was proposed to improve carbon recovery and optimize metabolite production. The results demonstrated that exogenous CO2 improved metabolite selectivity towards acetate/butyrate, while also accelerating CO2 fixation. Compared to pure Clostridium butyricum, the hybrid system significantly increased carbon conversion to primary metabolites, boosting butyrate and acetate production by 18.7 % and 18.4 %, respectively. Enzyme activity assays revealed that Fe3O4 and exogenous CO2 acted synergistically, enhancing the activities of key enzymes involved in CO2 assimilation. Additionally, Fe3O4 facilitated intra- and extracellular electron transfer, further improving the fermentation process. This study offers new insights into the combined effects of exogenous CO2 and Fe3O4 on anaerobic fermentation, providing an efficient strategy for carbon recovery and selective acetate/butyrate production.

Game changer for anaerobic fermentation of paper mulberry: Sucrose-loaded biochar enhancing microbial communities and lactic acid fermentation

This study investigated biochar effects, either alone or combined with sucrose, on fermentation quality, microbial communities, and in vitro rumen digestion of anaerobic fermented paper mulberry. The biochar alkaline functional groups bind to lactic acid, reducing acid inhibition and promoting Lactiplantibacillus proliferation. Owing to the low sugar content of paper mulberry, lactic acid bacteria in the biochar group primarily underwent heterofermentation, resulting in the lowest lactic and highest acetic acid contents. Treated with sucrose-loaded biochar, the increased substrate supported homofermentation, leading to the highest lactic and lowest acetic acid contents, with a 15.0 % increase in lactic acid and a 22.2 % decrease in ammoniacal nitrogen compared with the control after 75 days. In vitro rumen tests showed that the biochar-sucrose group had the highest dry matter degradation rate (45.9 %) and a 24.2 % reduction in methane emissions. Concludingly, sucrose-loaded biochar is recommended as effective for lactic acid production under anaerobic conditions.

Insides into molecular structural elucidation on the pesticidal and herbicidal potency of AD biogas slurry

Biogas slurry is the residue liquid after anaerobic fermentation of biomass. The bio-slurry has the potential to promote plant growth and control pests. This study explores the pesticidal potency of anaerobic digestate focusing on structural elucidation through gas chromatography–mass spectrometry analysis. Samples were collected from three anaerobic digesters processing cow dung, mixed substrates, and pig waste. Physicochemical parameters such as pH, electrical conductivity, total dissolved solids, and nitrogen content were measured. The slurries exhibited slightly basic pH values (7.5–7.8) and electrical conductivity (13.8–21.9 mS/m). GC–MS analysis revealed diverse phytochemical compounds in the bio-slurries, such as gramine, 2,2-dimethoxybutane, and 4-methyl-3-penten-2-one, with potential pesticidal properties. Gramine exhibited insecticidal, herbicidal, and algaecidal effects, while 2,2-dimethoxyethane demonstrated fungicidal and herbicidal properties. Gramine was identified and possesses its potential as a natural biopesticide. The identified compounds offer promising alternatives to synthetic pesticides, emphasizing the potential of biogas slurry as a sustainable biopesticide resource.