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Household food waste (HFW), which is rich in organic matter, is a good candidate for producing added-value bio-based chemicals, such as volatile fatty acids (VFAs), by acidogenic fermentation processes. However, the lack of design tools, such as appropriate kinetic models, hinders the implementation of this technology because the results of these processes are affected by operational factors. In this work, VFA production by the acidogenic fermentation of HFW under uncontrolled pH levels (4–5) was studied at thermophilic (55 °C) and mesophilic (35 °C) temperature conditions. Batch reactors were used to digest HFW, and VFA production and the individual acid distributions were measured at different fermentation times from 0 to 624 h. The results showed higher individual and total VFA production at 35 °C and 120 h of fermentation time as a consequence of the competition between the VFA production and decomposition reactions. Acetic and valeric acids were VFAs mainly produced as a result of a high content of proteins in the initial substrate, and a small amount of propionic and butyric acids were present. A simplified kinetic model was successfully developed to represent the complex process of VFA formation from the acidogenic fermentation of HFW. A simple mechanism for the production–decomposition of VFAs, corresponding to a zero-order reaction for the first 48 h and a single consecutive reaction from that time on, was proposed. For both mesophilic and thermophilic conditions, the suggested kinetic model was able to predict the individual and total concentrations of VFAs along the fermentation time. [ABSTRACT FROM AUTHOR]

Household food waste (HFW), which is rich in organic matter, is a good candidate for producing added-value bio-based chemicals, such as volatile fatty acids (VFAs), by acidogenic fermentation processes. However, the lack of design tools, such as appropriate kinetic models, hinders the implementation of this technology because the results of these processes are affected by operational factors. In this work, VFA production by the acidogenic fermentation of HFW under uncontrolled pH levels (4–5) was studied at thermophilic (55 °C) and mesophilic (35 °C) temperature conditions. Batch reactors were used to digest HFW, and VFA production and the individual acid distributions were measured at different fermentation times from 0 to 624 h. The results showed higher individual and total VFA production at 35 °C and 120 h of fermentation time as a consequence of the competition between the VFA production and decomposition reactions. Acetic and valeric acids were VFAs mainly produced as a result of a high content of proteins in the initial substrate, and a small amount of propionic and butyric acids were present. A simplified kinetic model was successfully developed to represent the complex process of VFA formation from the acidogenic fermentation of HFW. A simple mechanism for the production–decomposition of VFAs, corresponding to a zero-order reaction for the first 48 h and a single consecutive reaction from that time on, was proposed. For both mesophilic and thermophilic conditions, the suggested kinetic model was able to predict the individual and total concentrations of VFAs along the fermentation time.

Conversion of wastewater treatment plants into biorefineries is a sustainable alternative for obtaining valuable compounds, thus reducing pollutants and costs and protecting the environment and human health. Under specific operating conditions, microbial fermentative products of sewage sludge are volatile fatty acids (VFA) that can be precursors of polyhydroxyalkanoate thermoplastic polyesters. The role of various operating parameters in VFA production has yet to be elucidated. This study aimed to correlate the levels of VFA yields with prokaryotic microbiota structures of sewage sludge in two sets of batch fermentations with an initial pH of 8 and 10. The sewage sludge used to inoculate the batch fermentations was collected from a Sicilian WWTP located in Marineo (Italy) as a case study. Gas chromatography analysis revealed that initial pH 10 stimulated chemical oxygen demands (sCOD) and VFA yields (2020 mg COD/L) in comparison with initial pH 8. Characterization of the sewage sludge prokaryotic community structures—analyzed by next-generation sequencing of 16S rRNA gene amplicons—demonstrated that the improved yield of VFA paralleled the increased abundance of fermenting bacteria belonging to Proteobacteria, Bacteroidetes, Chloroflexi, and Firmicutes phyla and, conversely, the reduced abundance of VFA-degrading strains, such as archaeal methanogens. [ABSTRACT FROM AUTHOR]

Conversion of wastewater treatment plants into biorefineries is a sustainable alternative for obtaining valuable compounds, thus reducing pollutants and costs and protecting the environment and human health. Under specific operating conditions, microbial fermentative products of sewage sludge are volatile fatty acids (VFA) that can be precursors of polyhydroxyalkanoate thermoplastic polyesters. The role of various operating parameters in VFA production has yet to be elucidated. This study aimed to correlate the levels of VFA yields with prokaryotic microbiota structures of sewage sludge in two sets of batch fermentations with an initial pH of 8 and 10. The sewage sludge used to inoculate the batch fermentations was collected from a Sicilian WWTP located in Marineo (Italy) as a case study. Gas chromatography analysis revealed that initial pH 10 stimulated chemical oxygen demands (sCOD) and VFA yields (2020 mg COD/L) in comparison with initial pH 8. Characterization of the sewage sludge prokaryotic community structures—analyzed by next-generation sequencing of 16S rRNA gene amplicons—demonstrated that the improved yield of VFA paralleled the increased abundance of fermenting bacteria belonging to Proteobacteria, Bacteroidetes, Chloroflexi, and Firmicutes phyla and, conversely, the reduced abundance of VFA-degrading strains, such as archaeal methanogens.

Baker's Yeast Industry (BYI) effluent was one of the strongest wastewaster type that contains high amount of organic matter, salinity, nitrogen and sulphate. These characteristics were unfavorable for the application of wastewater treatment. For this reason, a recovery-oriented approach was applied for the appropriate conditions to increase the Volatile Fatty Acid (VFA) production potential of BYI. In this concept, hydrolysis anaerobic Membrane Bioreactor was used to produce VFAs. The hydrolysis reactor was operated between 2.5 and 13.4 days in Hydraulic Retention Time, at a thermophilic temperature (55 °C) and at pH of 4.5–8 for 858 days. The highest biomass concentration was 26 g L−1 in the reactor, and mainly acetate, propionate and butrate production was observed. The highest acetate production was seen at pH 7 with an average concentration of 25,930 mg L−1. The highest total VFA production yield was 0.98 g VFA–COD g−1 COD. It was concluded that carrying out hydrolysis and acidification reactions at neutral pH was better as long as methane production could be avoided. In addition, a VFA-rich stream with free suspended solids could be obtained with the 0.05 µ pore diameter submerged membrane. Population dynamics remained quite stable and rich in biomass consortia throughout the study. It was suggested that a high commercial value could be obtained, especially by recovering acetate from the hydrolysis reactor's outlet stream. [ABSTRACT FROM AUTHOR]

Two studies were conducted to investigate the effect of live yeast (LY) on the in vitro fermentation characteristics of wheat, barley, corn, soybean meal (SBM), canola meal, and distillers dried grains with solubles (DDGS). In Study 1, LY yeast was added directly to in vitro fermentations inoculated with feces from lactating sows, whereas as in study 2, feces collected from lactating sows fed LY as a daily supplement was used. Selected feedstuffs were digested and the residue added to separate replicated (n = 3) fermentation reactions. Study 1 was conducted in two blocks, whereas study 2 was conducted using feces collected after a period of 3 (Exp. 1) or 4 wk (Exp. 2) of LY supplementation. Accumulated gas produced over 72 h was modeled for each substrate and the kinetics parameters compared between LY and control groups. The molar ratio of the volatile fatty acids (VFAs) produced in vitro were also compared at 12 and 72 h of incubation. In study 1, in vitro addition of yeast increased (P < 0.001) the rate of gas production (R max). However, a yeast × substrate effect (P < 0.05) observed for total gas accumulated (A), time to half asymptote (B), and time required to reach maximum rate of fermentation (T max) suggested that yeast-mediated increases in extent and rate of fermentation varied by substrate. Greater total gas production was observed only for corn and SBM, associated with greater B and T max. Supplementation with LY appeared to increase A and R max although with variation between experiments and substrates. In Exp. 1, LY decreased (P < 0.05) B and T max. However, a yeast × substrate effect (P < 0.05) was observed for only A (for wheat, barley, corn, and corn DDGS) and R max (wheat, barley, corn, and wheat DDGS). In Exp. 2, LY increased (P < 0.0001) A and decreased B. However, an interaction (P < 0.05) with substrates was observed for R max (except SBM) and T max. With exception of the DDGS samples, LY supplementation increased (P < 0.05) VFA production at 12 and 72 h of incubation. Yeast increased (P < 0.05) the molar ratios of acetic acid and branch-chain fatty acids at 12 h of incubation; however, this response was more variable by substrate at 72 h. In conclusion, LY supplementation increased the rate and extent of in vitro fermentation of a variety of substrates prepared from common feedstuffs. Greater effects were observed when LY was fed to sows than added directly in vitro, suggesting effects on fermentation were not mediated directly. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effects of 11 active compounds of essential oils (ACEO) on rumen fermentation characteristics and methane production. Two trials were conducted. In trial 1, ACEO (eugenol, carvacrol, citral, limonene, 1,4-cineole, p-cymene, linalool, bornyl acetate, α-pinene, and β-pinene) at a dose of 1,000 μL/L were incubated for 24 h in diluted rumen fluid with a 70:30 forage:concentrate substrate (16.2% crude protein; 36.6% neutral detergent fiber). Three fistulated Holstein cows were used as donors of rumen fluid. The reduction in methane production was observed with nine ACEO (up to 86% reduction) compared with the control (p

Volatile fatty acid (VFA) production, utilization of soluble organic compounds, and associated microbial consortia were investigated after different pretreatments (untreated, alkaline, and thermal-alkaline) using cyanobacterial biomass as a substrate. Compared to the untreated control, soluble carbohydrate concentrations were almost the same after alkaline and thermal-alkaline pretreatments, but soluble protein concentration was 1.58 times higher after alkaline pretreatment and 1.81 times higher after thermal-alkaline pretreatment. However, the highest degree of acidification was obtained after alkaline pretreatment (55.36 ± 3.00%). Microbial communities in the untreated control differed only slightly from those after thermal-alkaline pretreatment, but were clearly distinct from those after alkaline pretreatment. After alkaline pretreatment, protein-utilizing bacteria became relatively predominant. These results revealed the relationships between efficiency of VFA production and the shift in microbial community. [ABSTRACT FROM AUTHOR]

The objectives of this study were to investigate the difference in the mechanism of VFAs production combined with macrogenome technology under different forage-to-concentrate ratios and sampling times. Six ruminally cannulated Holstein cows were used in a randomized complete block design. The high forage (HF) and high concentrate (HC) diets contained 70 and 35% dietary forage, respectively. The results showed that pH was affected by sampling time, at 4 h after feeding had lower value. Excepted for acetate, the VFAs was increased with forage decreased. Propionate formation via the succinic pathway, in which succinate CoA synthetase (EC 6.2.1.5) and propionyl CoA carboxylase (EC 2.8.3.1) were key enzymes, and significantly higher in HC treatment than in HF treatment, Selenomonas, Ruminobacter, Prevotella, and Clostridium were the main microorganism that encodes these key enzymes. Butyrate formation via the succinic pathway, in which phosphate butyryltransferase (EC 2.3.1.19), butyrate kinase (EC 2.7.2.7) and pyruvate ferredoxin oxidoreductase (EC 1.2.7.1) are the important enzymes, Prevotella and Bacteroides played important role in encodes these key enzymes. This research gave a further explanation on the metabolic pathways of VFAs, and microorganisms involved in VFAs production under different F:C ration, which could further reveal integrative information of rumen function.

In order to realize the rapid start-up of upflow anaerobic sludge blanket (UASB) reactor, the iron ion in different valence state was added to UASB. The results indicated that the start-up time of R3 (FeCl) was 48 h faster than that of R2 (zero-valent iron (ZVI)). It was because the FeCl could rapidly promote granulation of sludge as a flocculant. However, ZVI released Fe through corrosion slowly, and then the Fe increased start-up speed by enhancing enzyme activity and enriching methanogens. In addition, the ZVI and FeCl could promote hydrolysis acidification and strengthen the decomposition of long-chain fatty acids. The detection of iron ions showed that iron ions mainly existed in the sludge. Because the high concentration of Fe could inhibit anaerobic bacteria activity, excess Fe could be changed into iron hydroxide precipitation to hinder the mass transfer process of anaerobic bacteria under the alkaline condition. The FeCl was suitable to be added at the initial stage of UASB start-up, and the ZVI was more fitted to be used in the middle stage of reactor start-up to improve the redox ability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three digester configurations produced similar methane yield (269–283 L CH 4.kg-1VS). • 44% of the distillery's thermal demand can be satisfied with biogas. • Two-phase systems can produce 11.2 mg VFA. g-1ww of distillery by-products. • The potential value of the VFAs produced was 0.14 €. L-1 of whiskey. The valorisation of whiskey by-products was assessed and compared in three anaerobic digestion systems. The systems produced similar methane yields, which could satisfy up to 44% of the thermal energy demand at a distillery. Using methane generated from by-products would displace natural gas and reduce the distillery's carbon footprint. Two-phase systems had higher methane content (ca. 75 %vol) than the traditional system (54 %vol) and furthermore, unlocked opportunities for volatile fatty acid production. The potential value that could be generated from the extraction of butyric acid and caproic acid was approximately €6.76 million for a 50 million litre alcohol facility (0.14 € per litre of whiskey). All three anaerobic digestion systems showed the potential to valorise whiskey by-products and convert current linear distillery production processes into circular repurpose and reuse production processes. [ABSTRACT FROM AUTHOR]

The aim of the present experiment was to study changes in volatile fatty acid (VFA) production using an isotope dilution technique, and changes in VFA fractional absorption rate (kaVFA) using a buffer incubation technique (BIT) during the dry period and early lactation, as affected by the postpartum (pp) rate of increase of concentrate allowance. The current results are complementary to previously reported changes on rumen papillae morphology from the same experiment. From 50 d antepartum to 80 d pp, VFA production rate was measured 5 times and kaVFA was measured 10 times in 12 rumen-cannulated Holstein Friesian cows. Cows had free access to a mixed ration, consisting of grass and corn silage, soybean meal, and (dry period only) chopped straw. Treatment consisted of either a rapid (RAP; 1.0 kg of DM/d; n = 6) or gradual (GRAD; 0.25 kg of DM/d; n = 6) increase of concentrate allowance (up to 10.9 kg of DM/d), starting at 4 d pp, aimed at creating a contrast in rumen-fermentable organic matter intake. For the BIT, rumen contents were evacuated, the rumen washed, and a standardized buffer fluid introduced [120 mM VFA, 60% acetic (Ac), 25% propionic (Pr), and 15% butyric (Bu) acid; pH 5.9 and Co-EDTA as fluid passage marker]. For the isotope dilution technique, a pulse-dose of 13C-labeled Ac, Pr, and Bu and Co-EDTA as fluid passage marker was infused. The rate of total VFA production was similar between treatments and was 2 times higher during the lactation (114 mol/d) than the dry period (53 mol/d). Although papillae surface area at 16, 30, and 44 d pp was greater in RAP than GRAD, Bu and Ac production at these days did not differ between RAP and GRAD, whereas at 16 d pp RAP produced more Pr than GRAD. These results provide little support for the particular proliferative effects of Bu on papillae surface area. Similar to developments in papillae surface area in the dry period and early lactation, the kaVFA (per hour), measured using the BIT, decreased from 0.45 (Ac), 0.53 (Pr) and 0.56 (Bu) at 50 d antepartum to 0.28 (Ac), 0.34 (Pr) and 0.38 (Bu) at 3 d pp. Thereafter, kaVFA (/h) rapidly increased up to 0.67 (Ac), 0.79 (Pr), and 0.79 (Bu) at 80 d pp. Although papillae surface area was greater at 16, 30, and 44 d pp in RAP than GRAD, no differences in kaVFA between RAP and GRAD were observed during these days showing papillae surface area is not the limiting factor for ka VFA during early pp adaptation. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effects of 11 active compounds of essential oils (ACEO) on rumen fermentation characteristics and methane production. Two trials were conducted. In trial 1, ACEO (eugenol, carvacrol, citral, limonene, 1,4-cineole, p-cymene, linalool, bornyl acetate, a-pinene, and β-pinene) at a dose of 1,000 µL/L were incubated for 24 h in diluted rumen fluid with a 70:30 forage:concentrate substrate (16.2% crude protein; 36.6% neutral detergent fiber). Three fistulated Holstein cows were used as donors of rumen fluid. The reduction in methane production was observed with nine ACEO (up to 86% reduction) compared with the control (p<0.05). Among these, only limonene, 1,4-cineole, bornyl acetate, and a-pinene did not inhibit volatile fatty acid (VFA) production, and only bornyl acetate produced less methane per mol of VFA compared with the control (p<0.05). In a subsequent trial, the effects on rumen fermentation and methane production of two concentrations (500 and 2,000 µL/L) of bornyl acetate, the most promising ACEO from the first trial, were evaluated using the same in vitro incubation method that was used in the first trial. In trial 2, monensin was used as a positive control. Both doses of bornyl acetate decreased (p<0.05) methane production and did not inhibit VFA production. Positive effects of bornyl acetate on methane and VFA production were more pronounced than the effects of monensin. These results confirm the ability of bornyl acetate to decrease methane production, which may help to improve the efficiency of energy use in the rumen. [ABSTRACT FROM AUTHOR]

• The highest concentration and yield of VFAs were achieved with pH 7.0. • Butyric acid and acetic acid was the dominant product under acidic and alkaline pH, respectively. • When the NADH level achieves a relatively low state, VFA production is improved. • Alkaline and neutral pH had higher hydrolysis efficiency than acidic pH. In this study, potato peel waste was used as feedstock to produce volatile fatty acids (VFAs) by anaerobic digestion. The effects of different pH levels (pH 5.0, pH 7.0, pH 11.0, and uncontrolled pH) on VFA concentration and composition, intermediate products, and metabolic state were evaluated. The results showed that the highest total VFA production was achieved with pH 7.0 (41.9 g COD/L and 632.2 mg COD/g VS fed), followed by that with uncontrolled pH. Butyric acid was the dominant product under acidic pH, whereas acetic acid dominated under alkaline pH. The type of acidogenic fermentation at pH 7.0 was the mixed-acid type. The change in NADH level in the mixed-acid type of fermentation consisted of small fluctuations, enhancing the stability and efficiency of fermentation. The enzymatic activities of acetate kinase and butyrate kinase were slightly inhibited at pH 5.0 and 11.0, resulting in relatively low VFAs production. [ABSTRACT FROM AUTHOR]

The valorisation of protein-rich residual streams by anaerobic mixed-culture fermentation (MCF) has been barely studied in contrast to carbohydrate-rich wastes. The aim of this work was, therefore, to investigate how protein composition, i.e. the amino acid (AA) profile, affects the individual consumption of amino acids and, consequently, the outcome of the process. Mixed-culture fermentations were performed with two model proteins (casein and gelatin) using continuous and batch reactors at neutral pH values and 25 °C. The acidification was incomplete for both proteins, with casein achieving a higher value than gelatin. Albeit dominated by acetic acid, product spectra were different as well, with n-butyric acid as the second major product for casein and propionic acid for gelatin. The preferential consumption of amino acids was demonstrated, which interestingly depends on protein composition. The previously accepted stoichiometry accurately describes iso and n-butyric acid production, but it fails for propionic, iso and n-valeric acid generation. Overall, this study offers a better understanding of protein fermentation mechanisms, which will help to improve degradation models and to design fermentation processes, based on optimal substrate selection. Image 1 • Protein fermentation generally results in incomplete acidification. • Balanced amino acid redox roles do not guarantee higher acidification degrees. • The preferential consumption of amino acids was demonstrated. • Protein composition affects acidification, selectivity and preferential consumption. • The accepted stoichiometry is not sufficient to describe protein conversion to VFA. [ABSTRACT FROM AUTHOR]

Simple Summary: The rumen is well known as a natural bioreactor for highly efficient degradation of fibers, and rumen microbes play an important role on fiber degradation. Carbohydrates are fermented by a variety of bacteria in the rumen and transformed into volatile fatty acids (VFAs) by the corresponding enzymes. However, the content of forage in the diet affects the metabolism of cellulose degradation and VFA production. Therefore, we combine metabolism and metagenomics to explore the effects of High forage/concentrate diets and sampling time on enzymes and microorganisms involved in the metabolism of fiber and VFA in cow rumen. This study showed that propionate formation via the succinic pathway, in which succinate CoA synthetase (EC 6.2.1.5) and propionyl CoA carboxylase (EC 2.8.3.1) were key enzymes. Butyrate formation via the succinic pathway, in which phosphate butyryltransferase (EC 2.3.1.19), butyrate kinase (EC 2.7.2.7) and pyruvate ferredoxin oxidoreductase (EC 1.2.7.1) are the important enzymes. The microorganisms are mainly affected by diet and sampling time. The objectives of this study were to investigate the difference in the mechanism of VFAs production combined with macrogenome technology under different forage-to-concentrate ratios and sampling times. Six ruminally cannulated Holstein cows were used in a randomized complete block design. The high forage (HF) and high concentrate (HC) diets contained 70 and 35% dietary forage, respectively. The results showed that pH was affected by sampling time, at 4 h after feeding had lower value. Excepted for acetate, the VFAs was increased with forage decreased. Propionate formation via the succinic pathway, in which succinate CoA synthetase (EC 6.2.1.5) and propionyl CoA carboxylase (EC 2.8.3.1) were key enzymes, and significantly higher in HC treatment than in HF treatment, Selenomonas, Ruminobacter, Prevotella, and Clostridium were the main microorganism that encodes these key enzymes. Butyrate formation via the succinic pathway, in which phosphate butyryltransferase (EC 2.3.1.19), butyrate kinase (EC 2.7.2.7) and pyruvate ferredoxin oxidoreductase (EC 1.2.7.1) are the important enzymes, Prevotella and Bacteroides played important role in encodes these key enzymes. This research gave a further explanation on the metabolic pathways of VFAs, and microorganisms involved in VFAs production under different F:C ration, which could further reveal integrative information of rumen function. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the effect of time of rumen fluid collection relative to feeding on volatile fatty acid (VFA) production for in vitro rumen fermentation. Three ruminally cannulated Holstein heifers were used as rumen fluid donors. Feed was removed from heifers 12 h prior to feeding, rumen fluid was collected from each heifer before feeding (0 h), and at 2, 4, and 6 h after feeding, repeated on three separate incubation days. Buffered rumen fluid (100 mL) was incubated in 250-mL bottles containing 1.4 g of dried TMR, in duplicate for each heifer at each collection time. All bottles were incubated for 24 h at 39°C and constant agitation (60 rpm), and capped with monitors to capture temperature and pressure every 15 min (RF1, Ankom Technology, Macedon, NY). At the end of incubation, final pH and a sample of rumen fluid were collected for VFA and ammonia nitrogen. Data were analyzed using PROC GLIMMIX of SAS, with donor as the experimental unit and day as the random blocking factor; significance is defined as P ≤ 0.05. Time of rumen fluid collection significantly affected acetate (mmol/liter; P = 0.0004), propionate (mmol/liter; P = 0.02), isobutyrate (mmol/liter; P < 0.0001), valerate (mmol/liter; P = 0.004), isovalerate (mmol/liter; P < 0.00001), and total VFA concentrations (mmol/liter; P = 0.004). All VFA relative proportions were altered due to time of rumen fluid collection ( P < 0.02). VFA production was highest when rumen fluid was collected 4-h post-feeding. There was little to no effect on pH. Our findings suggest that VFA production is maximized when rumen fluid is collected between 2 and 4 h after feeding., (© The Author(s) 2018. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)