Volatile Fatty Acid Production Research Articles

Enhancement of anaerobic digestion by adding elemental sulfur.

In this study, a new approach to enhance methane (CH4) production from organic substrates in anaerobic digestion (AD) has been discovered. That is, the addition of elemental sulfur (S0) particles into the AD system promotes the synergistic growth of elemental sulfur disproportionation bacteria, acidogenic bacteria and methanogenic archaea, thus facilitating hydrolysis, acidogenesis and methanogenesis. The efficacy of this AD enhancement pathway was confirmed in AD experiments with glucose as a model organic substrate. The results demonstrated that CH4 production in the AD system increased considerably with S0 dosages ranging from 20 mg/L to 300 mg/L. Two gas production peaks appeared at dosages of 20 mg/L and 180 mg/L, where the total CH4 production increased by 2.1 times and 2.5 times, respectively compared with the control group. However, inhibitory effect was observed for S0 dosages above 300 mg/L. The chemical states of S, the microbial community and the abundance of key functional enzymes in the AD system were analyzed. The results showed that S0 addition increased the relative abundance of Dethiobacteraceae, Caldatribacterium, Anaerolineaceae, Methanobacterium and Methanosaeta and considerably increased the abundance of key functional enzymes, such as dehydrogenase, D-glucosidic glucosidase, pyruvate synthase and acetyl-CoA deacetylase. The enrichment of these microorganisms and functional enzymes was strongly positively correlated with the production of volatile fatty acids and CH4, demonstrating that S0 addition effectively enhances methanogenesis during AD.

Characterization of Novel Multifunctional Xylanase from Rumen Metagenome and Its Effects on In Vitro Microbial Fermentation of Wheat Straw

This study investigated the characterization of a novel multifunctional enzyme, RuXyn394, derived from the metagenome of beef cattle rumen, and its impact on the in vitro microbial fermentation of wheat straw. RuXyn394, a member of the glycosyl hydrolase 11 family, displayed optimal activity under diverse pH and temperature conditions: xylanase at pH 5.5 and 50 °C, acetyl esterase at pH 6.5 and 60 °C, exoglucanase at pH 7.0 and 50 °C, and endoglucanase at pH 6.0 and 50 °C. The enzyme’s xylanase, endoglucanase, and exoglucanase activities exhibited remarkable pH stability across the range of pH 3–8 and maintained a relatively stable performance at temperatures from 20 to 50 °C, 20 to 60 °C, and 20 to 70 °C, respectively. The xylanase function, with the highest kcat/Km ratio, was identified as the predominant activity of RuXyn394. The enzyme’s various functions responded uniquely to metal ions; notably, the addition of 5 mM K+ significantly boosted the activities of xylanase, exoglucanase, and endoglucanase by 55.5%, 53.5%, and 16.4%, respectively, without affecting its acetyl esterase activity. Over the course of three time points (30 min, 60 min, 120 min), the degradation products of wheat straw xylan, including xylopentaose, xylotetraose, xylotriose, xylobiose, xylose, and total xylooligosaccharides, constituted an average of 18.4%, 33.7%, 20.6%, 22.9%, 4.3%, and 95.7% of the total products, respectively. RuXyn394 effectively hydrolyzed wheat straw, resulting in augmented volatile fatty acid production and ammonia-N levels during in vitro microbial fermentation. These findings indicate the potential of RuXyn394 as a novel and highly efficient enzyme preparation, offering promising prospects for the valorization of wheat straw, an agricultural by-product, in ruminant diets.

Life cycle sustainability assessment of microbial oil from organic waste

Microbial oils (MOs) are lipids produced by oleaginous microorganisms, which constitute an alternative to vegetable and fossil-derived oils. They can be produced from organic waste by coupling acidogenic fermentation (AF) with oleaginous fermentation (OF). This study addresses a life cycle sustainability assessment (LCSA) of MO produced from the organic fraction of municipal solid waste. First, a system was modelled using simulation tools. This model combines AF for the production of volatile fatty acids from organic waste, OF for the production of lipid-rich yeasts, and MO extraction. LCSA results indicate the need for improvements in the disruption of yeasts and the overall efficiency of the system. Particularly, slightly acidified thermolysis turned out to involve excessively high steam requirements. An enhanced sustainability performance could be achieved by exploring alternative disruption methods or alternative sources of energy for the production of steam such as biogas from the valorisation of the sludges produced in the system.

Enhancement of volatile fatty acids to extremely high content in fermentation of food waste: Optimization of conditions, microbial functional genes, and mechanisms

The engineering application of volatile fatty acids (VFA) production from food waste (FW) can significantly enhance resource utilization. Enhancing VFA production is crucial for advancing this engineering application. This study presented a economically-feasible method to achieve high VFA production from FW: Conducting fermentation at pH 9 and 37 ℃ with addition of 20 % anaerobic sludge significantly increased the conversion of FW to VFAs (80.56 g COD/L, accounting for 87.37 % of the soluble chemical oxygen demand), while also increasing the content of NH4+-N (2658.15 mg/L). Macrotranscriptomic sequencing showed that Anaerosalibacter, Amphibacillus, Wansuia, Clostridiisalibacter, unclassified Tissierellia, Massilibacterium, unclassified Bacteroidales, and Tissierellia were the key active microorganisms for VFA production. The expression abundance of functional enzymes and genes related to VFA production pathways increased during the fermentation. This study significantly advanced the practical application of VFA production from FW, offering both theoretical insights and bacterial resources.

Improved volatile fatty acid production in anaerobic digestion via simultaneous temperature regulation and persulfate activation by biochar: Chemical and biological response mechanisms

Increasing volatile fatty acid (VFA) production via persulfate activation (i.e., chemical effect) in anaerobic digestion (AD) is an emerging resource utilization method. However, the reaction mechanisms responsible for improving VFA production in AD via simultaneous temperature regulation and persulfate activation by biochar remain unclear. In this study, three PB15 treatment systems of low temperature (15 °C), medium temperature (35 °C) and high temperature (55 °C) were set to explore the relationship between VFAs production and treatment temperature and the influence of temperature on the reaction mechanism. The results show that the improvement of hydrolysis and acidification efficiency of the system in the medium temperature system is the highest. The VFA yield and acid production rate in the treatment group at 35°C were 2.49 and 5.22 times higher than those in the control group, respectively. The chemical effect effectively initiated the anaerobic acid production process and maintained the dominant role of the biological effect. The activity of persulfate is too low at low temperature, and its decomposition is too fast at high temperature. Plenty of free radicals lead to enhanced oxidation of the system, which may kill the fermentation bacteria. The NCM model indicates that microbial stability is reduced in high temperature systems. The SEM model showed that temperature change mainly affected substrate degradation by hydrolytic bacteria and indirectly affected acid production by acid-producing bacteria. This study provides a new strategy for realizing pollutant recycling and increasing VFAs production in cold area.

Undernutrition disrupts jejunal and ileal microbiota and epithelial tissue homeostasis in a pregnant sheep model

Nutrition consistently affects microbe-host interactions in the gastrointestinal tract. This study aimed to unravel how undernutrition reshapes the microbial composition and the homeostasis of epithelium in the jejunum and ileum. Sixteen late-gestation Hu-sheep were randomly assigned to the control group (n = 8, 100% ad libitum feeding levels) or the undernutrition group (n = 8, which received 30% ad libitum feeding levels). After 15-d treatment, all ewes were slaughtered, and jejunal and ileal digesta and epithelium samples were collected for 16S rRNA gene sequencing and transcriptome sequencing, respectively. Results indicated that undernutrition decreased the jejunal and ileal tissue weights (P = 0.005 and P = 0.022) and the levels of volatile fatty acids (P = 0.019 and P = 0.007) and microbial protein levels (P = 0.019 and P = 0.031) in jejunal and ileal digesta. The relative abundance of acetate producing microbiota, including Clostridia UCG-014 norank, Ruminococcus, [Ruminococcus] gauvreauii, and Lachnospiraceae_Blautia, were significantly reduced (P < 0.05) in the jejunum and ileum. Undernutrition up-regulated (P < 0.05) the expression of genes involved in amino acid synthesis and fatty acid oxidation, but down-regulated (P < 0.05) the expression of genes associated with amino acid degradation, fatty acid synthesis, and extracellular structures in jejunal and ileal epithelium. In the jejunal epithelium, genes associated with extracellular matrix-receptor interactions, cell growth, and immune response were down-regulated (P < 0.05) upon undernutrition. Taken together, undernutrition changed the microbial community in the jejunum and ileum, which altered the fermentation mode and the production of volatile fatty acids and microbial protein. These affected the energy and protein system in the epithelium and reprogrammed substance metabolism and extracellular structures, which probably further influenced cell growth and immune response. These insights provide a foundation for completely clarifying the crosstalk between small intestinal microbiota and the host.

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.

Yeast culture enhances long-term fermentation of corn straw by ruminal microbes for volatile fatty acid production: Performance and mechanism

Ruminal microbes can efficiently ferment biomass waste to produce volatile fatty acids (VFAs). However, keeping long-term efficient VFA production efficiency has become a bottleneck. In this study, yeast culture (YC) was used to enhance the VFA production in long-term fermentation. Results showed that YC group improved the volatile solid removal and VFA concentration to 47.8% and 7.82 g/L, respectively, 18.6% and 16.1% higher than the control, mainly enhancing the acetic, propionic, and butyric acid production. YC addition reduced the bacterial diversity, changed the bacterial composition, and improved interactions among bacteria. The regulation mechanism of YC was to increase the abundance and activity of hydrolytic and acidogenic bacteria such as Prevotella and Treponema, improve bacterial interactions, and further promote expression of functional genes. Ultimately, a long-term efficient ruminal fermentation of corn straw into VFAs was achieved.

Thermophilic dark fermentation for hydrogen and volatile fatty acids production from breadcrumbs

Thermophilic dark fermentation for hydrogen and volatile fatty acids production from breadcrumbs

Microbial approach towards anode biofilm engineering enhances extracellular electron transfer for bioenergy production

Applying microbial electrolysis cells (MEC) is a biological approach to enhance the growth of high amounts of electroactive biofilm for extracellular electron transfer. The electroactive biofilm degrades the organics by oxidizing them at the anode and producing electrical energy. Addition of waste-activated sludge (WAS) with fat grease oil (FOG) produces an optimal reactor environment for microbial growth to enhance the exchange of electrons between cells via microbial electrolysis. The present work aimed to investigate the microbial approach to increase the extracellular electron transfer (EET) in microbial electrolysis cells. Results revealed that metabolites in electroactive microbes (EAM) grow viable cells that initiate high EET at anode sites. At optimum WAS with FOG addition, volatile fatty acid and current generation yield production was 2.94 ± 0.19 g/L and 17.91 ± 7.23 mA, accompanied by COD removal efficiency of 89.5 ± 14.4%, respectively. This study introduces a novel approach to anode biofilm engineering that significantly enhances extracellular electron transfer, offering a fresh perspective on bioenergy production. Our approach, which demonstrates that anodic biofilm enhances intercellular electron transfer, increases NADH-NAD ratio, and increases metabolite yield-fluxes, has the potential to revolutionize bio-electricity production. Results indicated that the electrolysis highlights MEC performance in power generation of 788 mV with 200 mL of anode volume of active viable cells by utilizing WAS with 11% FOG. The achievements of this study provide critical parameters for the anode biofilm engineering, demonstrating how growth cell volume, intercellular electron transfer, and increases in NADH-NAD ratio are evidence of an increase in the EET, compelling evidence for the resilience treatment and efficient current production. These findings are significant in advancing our understanding of bioenergy production.

Enhanced volatile fatty acids production in thermal hydrolysis pretreatment with constant pH regulation: Effects evaluation and mechanism elucidation

Enhanced volatile fatty acids production in thermal hydrolysis pretreatment with constant pH regulation: Effects evaluation and mechanism elucidation

Targeted volatile fatty acid production based on lactate platform in mixed culture fermentation: Insights into carbon conversion and microbial metabolic traits

Targeted volatile fatty acid production based on lactate platform in mixed culture fermentation: Insights into carbon conversion and microbial metabolic traits

Optimization of Volatile Fatty Acids Production Through Anaerobic Digestion for the Valorisation of Chicken Manure

The short-chain, volatile nature of volatile fatty acids (VFAs) distinguishes them as organic molecules. They are essential in organic chemistry, environmental science, microbiology, and many other natural processes. Here are some key details regarding VFAs: they are organic acids that typically have a carbon backbone with functional groups called carboxyl's (COOH). The three most prevalent VFAs are butyric acid (C4), acetic acid (C2), and propionic acid (C3). VFAs are produced when organic matter, especially complex chemical compounds and carbohydrates, is fermented by microorganisms.

Improvement of Phosphorus Removal from Wastewater Through Fermentation of Low-Concentrated Wastewater Sludge and Increased Production of Volatile Fatty Acids

This article presents the results of a two-stage study: the first stage involved assessing the dependence of the increase or decrease in the concentration of volatile fatty acids (VFAs) on external factors and then assessing the relationship between the VFA concentration in the supernatant after fermentation and the processing characteristics (temperature, mixing mode, alkalinity, pH, nitrogen and phosphorus content). The greatest increase in VFAs (content up to 285 mg/L in the supernatant) was achieved at a temperature in the range of 28 to 38 °C with constant mixing of the sludge. Based on the results of the second stage, a conclusion was made on the efficiency of using a particular substrate depending on the concentration of phosphorus phosphates in the incoming wastewater. The study results showed that 7.54 mg/L of phosphorus can be removed with a given probability (for activated sludge, raw sludge and wastewater). It is recommended to compensate for the excess of this concentration by dosing the acetic acid solution at a rate of 3800 meq/L of VFA per 1 mg/L of phosphorus phosphates. The literature does not contain any results of parallel studies of the operation of a controlled bioreactor with artificial external feeding and acidified VFA. The results of the study can be applied in planning sludge acidification systems in the technological scheme of wastewater treatment and sludge processing.

Sustainable Abiotic-Biotic Dechlorination of Perchloroethene with Sulfidated Nanoscale Zero-Valent Iron as Electron Donor Source.

Combining organohalide-respiring bacteria with nanoscale zero-valent iron (nZVI) represents a promising approach for remediating chloroethene-contaminated aquifers. However, limited information is available regarding their synergistic dechlorinating ability for chloroethenes when nZVI is sulfidated (S-nZVI) under the organic electron donor-limited conditions typically found in deep aquifers. Herein, we developed a combined system utilizing a mixed culture containing Dehalococcoides (Dhc) and S-nZVI particles, which achieved sustainable dechlorination with repeated rounds of spiking with 110 μM perchloroethene (PCE). The relative abundance of Dhc considerably increased from 5.2 to 91.5% after five rounds of spiking with PCE, as evidenced by 16S rRNA gene amplicon sequencing. S-nZVI corrosion generated hydrogen as an electron donor for Dhc and other volatile fatty acid (VFA)-producing bacteria. Electron balance analysis indicated that 68.1% of electrons from Fe0 consumed in S-nZVI were involved in dechlorination, and 6.2, 1.1, and 3.2% were stored in formate, acetate, and other VFAs, respectively. The produced acetate possibly served as a carbon source for Dhc. Metagenomic analysis revealed that Desulfovibrio, Syntrophomonas, Clostridium, and Mesotoga were likely involved in VFA production. These findings provide valuable insights into the synergistic mechanisms of biotic and abiotic dechlorination, with important implications for sustainable remediation of electron donor-limited aquifers contaminated by chloroethenes.

Effects of Formaldehyde-Treated Feed on Rumen Metabolism and Blood Biochemistry in Lambs: A Review

This review evaluates the impact of formaldehyde treatment on feed for lambs, focusing on its effects on rumen metabolism and blood biochemical indicators. Formaldehyde is commonly used as a feed additive to improve nutritional efficiency and preserve feed quality. This review synthesizes data from various studies to assess how formaldehyde-treated feed influences rumen fermentation parameters, including volatile fatty acid (VFA) production, rumen pH, and microbial activity. Additionally, the review examines the effects of formaldehyde treatment on key blood biochemical markers such as glucose, urea nitrogen, and liver enzymes. Studies indicate that formaldehyde treatment can enhance the stability and digestibility of feed, potentially improving nutrient utilization and overall animal performance. The preservation of protein and reduction in feed spoilage are highlighted as significant benefits, contributing to more consistent rumen function and metabolic efficiency. However, the impact on rumen microbial populations and VFA profiles shows mixed results, with some studies reporting improved microbial efficiency and others noting minimal changes. The review also discusses potential adverse effects, including alterations in blood biochemical parameters. While formaldehyde treatment generally maintains or improves key indicators like blood glucose and protein levels, excessive use may lead to concerns such as elevated urea nitrogen levels and potential liver enzyme disruptions, the review concludes that formaldehyde-treated feed can be a valuable tool in optimizing feed efficiency and lamb health, provided it is used judiciously. Future research is recommended to further elucidate the long-term effects on rumen microbiota and metabolic processes, ensuring balanced benefits without compromising animal welfare.

The effects of headspace volume reactor on the microbial community structure during fermentation processes for volatile fatty acid production.

The transition from traditional wastewater treatment plants to biorefineries represents an environmentally and economically sustainable approach to extracting valuable compounds from waste. Sewage sludge produced from wastewater treatment is incinerated or disposed of in specific landfills. Repurposing this waste material to recover valuable resources could help lower disposal costs and reduce environmental impact by producing other beneficial polymers. Microorganisms present in the sewage sludge can ferment organic pollutants, producing volatile fatty acids (VFA), precursors for biopolymers that could be used as an alternative to petroleum-derived plastics. To boost VFA production during sewage sludge fermentation, it is necessary to understand the operating microbial community and its metabolic capacities in anaerobic conditions. This study presents the influence of the headspace volume on the microbial community and the VFA production to define the best operational parameters in a 225 L pilot plant fermenter. The wasted sewage sludge was withdrawn from an oxic-settling-anaerobic plant that collected wastewater from the canteen and dormitory of the UNIPA Campus (Palermo University, Italy) and incubated using a 40% and a 60% headspace volume. The microbial community was analysed before and after the fermentation process through metataxonomic analysis, and VFA yields were determined by gas chromatography analysis. Our results showed that the 40% headspace volume induced a tenfold higher VFA production than the 60% headspace volume, modulating the microbial community's efforts to establish a VFA-producing factory. Notably, at 40% headspace, the relative abundance of bacteria, like Proteobacteria, Firmicutes, Actinobacteria, and Chloroflexi, significantly increased, as well as the relative abundance of Bacteroidetes and Verrucomicrobia decreased during the fermentation process. This result is consistent with the selection of efficient VFA-producing bacteria that lead to increased VFA yields that are not obtained at 60% headspace. Thus, reducing headspace is a promising strategy that can be implemented, even in full-scale plants, to optimise the wastewater reuse process and maximise VFA production to produce bioplastics, like polyhydroxyalkanoate, for the transition from linear wastewater treatment plants to circular biorefineries.

Novel insights into fouling mechanisms in anaerobic acidification membrane bioreactor: The leading role of pH value

Anaerobic acidification membrane bioreactors (AAMBRs) have recently emerged as effective systems for recovering volatile fatty acids (VFAs) from municipal wastewater. However, membrane fouling remains a critical challenge, with its underlying mechanisms not yet fully understood. Given its importance in inhibiting methanogenic bacteria and stabilizing VFAs production, this study explores the direct and indirect effects of pH on membrane fouling mechanisms in AAMBRs. The results demonstrated that compared to pH 7, the fouling potential of anaerobic sludge was significantly higher at pH levels of 5 and 10 owing to a decrease of sludge floc size and an increase of soluble microbial products (SMP) especially proteins. Analytical techniques such as confocal laser scanning microscopy (CLSM), fourier transform infrared spectroscopy (FTIR), and fluorescence excitation-emission matrix (F-EEM) analyses revealed a substantial increase in organic foulants particularly proteins on the membrane surface at pH levels of 5 and 10. Circular dichroism (CD) spectroscopy further indicated a significant change in protein secondary structure, specifically an increase in α-helix content under extreme pH conditions. Furthermore, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory indicated that elevated protein concentrations enhance the adhesion of sludge and SMP to membrane surfaces. Insights from the Flory-Huggins theory demonstrated that variations in protein structure significantly contribute to increased filtration resistance within the gel layer. Both experimental data and theoretical models underscore the dual role of pH in optimizing VFAs production and managing membrane fouling, offering insights for enhancing AAMBR performance and mitigating fouling issues.

Effect of aeration pretreatment on anaerobic digestion of swine manure

ABSTRACT To investigate the effects of aeration pretreatment on the anaerobic digestion (AD) of swine manure, five pretreatment groups were established with dissolved oxygen (DO) in each group set to 0.0, 0.4, 0.8, 1.4, and 2.0 mg/L, respectively. The results demonstrated that compared to the non-aeration group, methane production increased to varying degrees with different aeration pretreatments (AP), with a maximum increase of 27.98% (DO = 2.0 mg/L). AP reduced the hydrogen sulfide (H2S) content of biogas. The H2S concentration in the DO = 2.0 mg/L was only 0.209%, and this represented an increased H2S removal rate of 49.27% compared to that of the DO = 0.0 mg/L (0.412%). Simultaneously, AP increases the hydrolysis rate. When the DO concentration reached 2.0 mg/L, the hydrolysis rate reached its maximum. An increase in the hydrolysis rate further enhanced the removal rate of organic matter. The organic matter removal rate was highest (36.96%) at DO = 2.0 mg/L. AP effectively prolonged the methane generation time and shortened the lag time of methane generation. AP creates a brief micro aerobic environment, accelerates substrate hydrolysis, and promotes the production and consumption of total volatile fatty acids, particularly acetic acid. Additionally, AP promoted the symbiotic relationship between Caldicoprobacter (20.93%–34.96%) and Metanosaeta (14.73%–18.45%).

Enhanced performance and economic feasibility of sewage sludge digestion using a two-stage anaerobic digestion with a dynamic membrane and alkaline-thermal pretreatment

This study suggests a high-rate sewage sludge anaerobic digestion (AD) process. An alkaline-thermal pretreatment and a dynamic membrane (DM) were used to enhance AD efficiency and economic feasibility in a two-stage system. The effect of pretreatment on volatile fatty acid (VFA) production in the acidogenic phase was investigated at various hydraulic retention times (HRT). After optimizing the acidogenic phase condition (HRT of 3 days), single- and two-stage AD processes with DM modules were operated simultaneously to compare performance. The highest methane production rates of 0.69 L/L/d for single-stage AD and 1.10 L/L/d for two-stage AD were observed at a total HRT of 12 days. Phase separation enhanced the growth of acetoclastic methanogens. A techno-economic analysis showed that the two-stage AD system would achieve a positive net present value within 2 years. This study demonstrated the feasibility of high-rate AD systems for sewage sludge using DM, alkaline-thermal pretreatment, and phase separation.