Mixture Of Volatile Fatty Acids Research Articles

Recycling potential of Cupriavidus necator for life support in space: Production of SCPs from volatile fatty acid and urea mixture

The International Space Station currently requires four annual replenishments for food supply, a practice that won't be feasible for deep space missions due to the greater distances. Based on the design of closed ecological life support systems, two waste streams were identified: urea from the crew urine, volatile fatty acids (VFAs) from a first stage of anaerobic digestion of waste. The objective of this study was to assess the ability of bacterium Cupriavidus necator to produce single cell protein on urea and VFAs. Thus, the effect of carbon sources (glucose vs VFAs) and the dilution rate on the biomass composition was determined in continuous cultures. Complete transformation of the carbon source into protein-rich biomass was achieved up to 78 % cell dry weight (CDW). For both carbon sources, the protein content increased from 55.0 %CDW to 78 %CDW with a decrease in the dilution rate. Conversely, the nucleic acid and polyhydroxyalkanoate contents decreased with the dilution rate from 8.8 %CDW to 4.8 %CDW and 9.8 %CDW to 0.6 %CDW respectively. Working at a low dilution rate seems to be a good way to maximize protein content while minimizing unwanted nucleic acids and polyhydroxyalkanoates.

Clostridium carboxidivorans and Rhodosporidium toruloides as a platform for the valorization of carbon dioxide to microbial oils

There is growing scientific interest in oleaginous yeasts producing microbial oils as precursors of biofuels and potential substitutes for fossil fuels. Due to the high cost of substrates commonly metabolized by yeasts, volatile fatty acids (VFAs) are gaining interest as alternative cheap and sustainable carbon sources, which can be obtained from solid, liquid and gas pollutants. In this research, Rhodosporidium toruloides was proven to be able to accumulate microbial oils from VFAs obtained from the fermentation of syngas by Clostridium carboxidivorans. Using CO2 and CO as carbon sources from the syngas mixture and H2 as energy source, this acetogen produced, via the Wood-Ljungdahl pathway, a mixture of acetic, butyric and caproic acids. It was first revealed that R. toruloides exhibited minimal inhibition at concentrations below 12 g/L when exposed to a mixture of VFAs, which included acetic, butyric and even hexanoic acids. The yeast was then grown on the culture medium derived from the acetogenic fermentation of syngas. Between the two yeast strains tested of the same species, R. toruloides DSM 4444 reached a total VFAs consumption of 69.1 g/L, supplied by successive additions of acids to the reactor, yielding a maximum lipid content of 29.7% w/w cell. The lipid profile obtained in this case, in terms of abundance followed the order C18:1 > C16:0 ≥ C18:0 > C18:2>others; in which the dominant compound (C18:1), represented approximately 50% of the total. This research opens new possibilities in the cultivation of oleaginous yeasts for the production of biofuels and bioproducts from C1 gases.

Effect of Agro-Industrial by Products Derived from Volatile Fatty Acids on Ruminant Feed In Vitro Digestibility.

The growing demand for sustainable ruminant feed alternatives has motivated the application of bioconversion approaches for the valorization of agro-food byproducts (AFB) into feed additives and supplements. The present study thoroughly investigated substituting volatile fatty acids (VFAs) obtained from acidogenic fermentation (AF) of AFB as an energy source in ruminant feed. Rumen in vitro digestibility assays were conducted utilizing the gas production method, wherein the VFAs obtained from AF of apple pomace and potato protein liquor was substituted with partial silage and concentrate energy at levels of 10%, 20%, and 30%. The results indicate that substituting 20% of the concentrate's energy with VFA mixture significantly reduced methane production and had no adverse effect on the production and accumulation of VFAs in the simulated rumen media. Conversely, replacing 10% of the silage energy with VFAs led to a decrease in methane production and further enhanced the production of VFAs. Readily digestible VFAs in ruminant feed have the potential to enhance energy availability and sustainability in ruminant farming practices, aligning with the principles of circular economy and waste valorization.

Predicting the flux of various volatile fatty acids mixtures in a membrane distillation

This study aims to predict the initial flux of various volatile fatty acids (VFAs) mixtures in direct contact membrane distillation (DCMD), focusing on understanding the interaction between the acids and improving a previous model to better suit the VFAs mixtures. The DCMD experiments were conducted under conditions of feed temperatures of 40, 50, and 60 °C, pH conditions of 3, 4.8, and 6, and VFA concentrations within the feed of 1000–4000 mg/L. The experiments investigated the influence of acids in the VFAs mixture. It was verified whether the ionization fraction of VFAs, even in multi-acid solutions, is proportionate to the flux. The correction coefficient and the overall mass transfer coefficient were introduced to enhance the model that previously used an empirical equation. The correction coefficients were derived, reflecting the interaction between acids and the hydrophobic membrane in the VFAs mixtures. A random factor experiment was conducted to verify the accuracy of the prediction model. Additionally, the sum of each VFA transport can be estimated and expressed using a common water quality measure, chemical oxygen demand. The modeling work can provide further insights into the relationship among the flux, ionization, hydrophobicity, and interactions among acids.

Denitrification Capacity of Volatile Fatty Acids from Sludge Fermentation: Lab-Scale Testing and Full-Scale Assessment

This work provides insights into the possibility of integrating recovered volatile fatty acids (VFAs) into biological nitrogen removal processes. VFAs are the main products of the acidogenic fermentation of waste sludge and are an effective carbon source for denitrification in activated sludge processes. The assessment of denitrification rates and the utilisation hierarchy of different VFAs are relevant to evaluating the possibility of replacing external carbon sources with the fermented liquid, FL, from acidogenic fermentation. To this scope, single VFAs, FL collected from a full-scale waste sludge fermenter, and commercial hydroalcoholic solutions have been tested with manometric lab-scale tests. Regarding single acids, acetic acid showed the highest denitrification rates, up to 4 mg N-NO3 g VSS−1 h−1, while more complex acids usually showed a lower denitrification rate. The synthetic VFA mixture and FL showed a higher denitrification rate than the sole acetate (up to 134% of the acetate denitrification rate). Mass balances across the full-scale wastewater treatment plant demonstrated the positive role of FL dosage in enhancing the denitrification process in the activated sludge treatment, with an average nitrogen removal equal to 57% and 78% without and with FL dosage, respectively. Batch manometric tests proved to be an efficient and reliable tool to assess the quality of the carbon sources as well as the activity of denitrifying bacteria in activated sludge samples.

Evaluation of the additive effects of volatile fatty acids and moderate heat treatment for enhancing the inactivation of vegetative cells and spores of Clostridium perfringens by flow cytometry

ObjectivesClostridium perfringens is a well-known spore-forming bacterium that can resist the environment. A mixture of volatile fatty acids or thermal treatments can interact with these bacteria. The aim of this study was to evaluate the effects of different volatile fatty acid concentrations and moderate heat treatment on Clostridium perfringens sporulation. MethodsA pure culture of Clostridium perfringens type A in Duncan Strong medium was treated with a mixture of volatile fatty acids at several concentrations. A thermal treatment was also tested. To evaluate the effects, a double staining method was employed, and treatments on Clostridium perfringens were analysed by flow cytometry. ResultsModerate heat treatment destroyed vegetative forms but had no effect on sporulating forms. Volatile fatty acids combined with moderate heat treatment inhibited Clostridium perfringens sporulation. ConclusionsThe use of flow cytometry as an original method for evaluating the treatment of Clostridium perfringens is of interest because of its simplicity, short time to obtain results, and the level of information provided on the microbial population (impact on metabolism). A combination of mild treatments (moderate heat treatment + volatile fatty acids) to decrease the Clostridium perfringens concentration when these bacteria sporulate is a very promising finding for inhibiting Clostridium perfringens propagation.

Two-stage syngas fermentation into microbial oils and β-carotene with Clostridium carboxidivorans and engineered Yarrowia lipolytica

An engineered Yarrowia lipolytica strain was able to simultaneously accumulate microbial oils and β-carotene from both acetic and butyric acids produced from syngas fermentation by Clostridium carboxidivorans, through the Wood-Ljungdahl pathway, with CO and CO2 as carbon sources. It was first determined that Y. lipolytica showed no inhibition at concentrations < 16 g/L of a mixture of VFAs (Volatile Fatty Acids) containing acetic, butyric, and even hexanoic acids. The yeast was then grown in a bioreactor with a culture medium derived from acetogenic syngas (CO, CO2, H2) fermentation containing all three acids. Y. lipolytica consumed a total of 91 g/L VFAs, progressively supplied through eight successive additions of these acids to the reactor. A maximum lipid content of 36.18% g/g cell was achieved at 61 g/L VFAs consumed and with an airflow rate of 2.0 vvm. Besides, a total of 88.4 mg/g cell and 759 mg/L β-carotene content and concentration were achieved at about 80 g/L VFAs consumed and with a 2.0 vvm airflow rate. It was concluded that; a non-limiting air flow favors the metabolic pathway for β-carotene formation against lipid accumulation.

The co-conversion of methane and mixtures of volatile fatty acids into poly(3-hydroxybutyrate-co-3-hydroxyvalerate) expands the potential of an integrated biorefinery

In this work, the potential of Methylocystis hirsuta to simultaneously use methane and volatile fatty acids mixtures for triggering PHBV accumulation was assessed for the first time batchwise. Biotic controls carried out with CH4 alone confirmed the inability of Methylocystis hirsuta to produce PHBV and achieved 71.2 ± 7 g m−3d−1 of PHB. Pure valeric acid and two synthetic mixtures simulating VFAs effluents from the anaerobic digestion of food waste at 35 °C (M1) and 55 °C (M2) were supplied to promote 3-HV inclusion. Results showed that pure valeric acid supported the highest polymer yields of 105.8 ± 9 g m−3d−1 (3-HB:3-HV=70:30). M1 mixtures led to a maximum of 103 ± 4 g m−3d−1 of PHBV (3-HB:3-HV=85:15), while M2 mixtures, which did not include valeric acid, showed no PHV synthesis. This suggested that the synthesis of PHBV from VFAs effluents depends on the composition of the mixtures, which can be tuned during the anaerobic digestion process.

Conceptual system for sustainable and next-generation wastewater resource recovery facilities

Shifting the concept of municipal wastewater treatment to recover resources is one of the key factors contributing to a sustainable society. A novel concept based on research is proposed to recover four main bio-based products from municipal wastewater while reaching the necessary regulatory standards. The main resource recovery units of the proposed system include upflow anaerobic sludge blanket reactor for the recovery of biogas (as product 1) from mainstream municipal wastewater after primary sedimentation. Sewage sludge is co-fermented with external organic waste such as food waste for volatile fatty acids (VFAs) production as precursors for other bio-based production. A portion of the VFA mixture (product 2) is used as carbon sources in the denitrification step of the nitrification/denitrification process as an alternative for nitrogen removal. The other alternative for nitrogen removal is the partial nitrification/anammx process. The VFA mixture is separated with nanofiltration/reverse osmosis membrane technology into low-carbon VFAs and high-carbon VFAs. Polyhydroxyalkanoate (as product 3) is produced from the low-carbon VFAs. Using membrane contactor-based processes and ion-exchange techniques, high-carbon VFAs are recovered as one-type VFA (pure VFA) and in ester forms (product 4). The nutrient-rich fermented and dewatered biosolid is applied as a fertilizer. The proposed units are seen as individual resource recovery systems as well as a concept of an integrated system. A qualitative environmental assessment of the proposed resource recovery units confirms the positive environmental impacts of the proposed system.

Thorough Investigation of the Effects of Cultivation Factors on Polyhydroalkanoates (PHAs) Production by Cupriavidus necator from Food Waste-Derived Volatile Fatty Acids

Volatile fatty acids (VFAs) have become promising candidates for replacing the conventional expensive carbon sources used to produce polyhydroxyalkanoates (PHAs). Considering the inhibitory effect of VFAs at high concentrations and the influence of VFA mixture composition on bacterial growth and PHA production, a thorough investigation of different cultivation parameters such as VFA concentrations and composition (synthetic and waste-derived VFAs) media, pH, aeration, C/N ratio, and type of nitrogen sources was conducted. Besides common VFAs of acetic, butyric and propionic acids, Cupriavidus necator showed good capability for assimilating longer-chained carboxylate compounds of valeric, isovaleric, isobutyric and caproic acids in feasible concentrations of 2.5–5 g/L. A combination of pH control at 7.0, C/N of 6, and aeration of 1 vvm was found to be the optimal condition for the bacterial growth, yielding a maximum PHA accumulation and PHA yield on biomass of 1.5 g/L and 56%, respectively, regardless of the nitrogen sources. The accumulated PHA was found to be poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with the percentage of hydroxybutyrate in the range 91–96%. Any limitation in the cultivation factors was found to enhance the PHA yield, the promotion of which was a consequence of the reduction in biomass production.

Microalgae screening for heterotrophic and mixotrophic growth on butyrate

Volatile fatty acids (VFAs) produced by fermentative bacteria can be used instead of high value carbohydrates like glucose to reduce the costs associated to mixotrophic microalgal cultivation. This process is however limited by a poor assimilation of butyrate and a low tolerance of microalgae to high VFA concentrations. In this study, 10 microalgae strains, isolated from local natural environments or selected from culture collections were screened for their ability to grow on either acetate or butyrate. The non-photosynthetic Chlorophyte Polytomella sp. was found to be the fastest growing strain on both VFAs, exhibiting a growth rate of 4.0 d−1 on acetate and 2.5 d−1 on butyrate. The tolerance of the different strains to concentrated VFA was further assessed using increasing acid concentrations (1.5–60 g·L−1 for acetate and 1–40 g·L−1 for butyrate). Polytomella sp. appeared as the most resistant, being able to grow up to 38 g·L−1 on acetic acid and to 18 g·L−1 on butyric acid with no inhibitory effect. Finally, biomass yield and productivity, as well as lipid and carbohydrate yields were assessed on a synthetic VFAs mixture (0.8 g·L−1 acetate and 1.2 g·L−1 butyrate) for the most promising strains. Polytomella sp. and Euglena gracilis exhibited the highest carbohydrate yield (respectively 0.65 and 0.58 g·g−1) while lipid yield was maximum for Chlorella sorokiniana (0.42 g·g−1). This work provides new insights in the trophic metabolism of microalgae of highly divergent lineages using VFAs as substrates.

Enhancing Microbial Lipids Synthesis for Biodiesel Production by Y. lipolytica W29 from Volatile Fatty Acids: Two-Stage Batch Strategies

Microbial lipids produced by Y. lipolytica have the potential to be used as feedstock for the biodiesel industry, but the high costs of pure substrates used for its production are limiting the potential of this application. Volatile fatty acids (VFAs), obtained in anaerobic fermentation of organic wastes, are inexpensive carbon sources for the cost-effective production of microbial lipids. In this work, two-stage batch cultures were tested as a strategy to improve lipids production by Y. lipolytica W29. The process consists of a first growth phase in glucose or glycerol, followed by a lipogenic phase in VFAs medium composed of a mixture of acetate, propionate, and butyrate. The addition of three pulses of 6 g·L−1 VFAs mixture, or a single pulse of 18 g·L−1 VFAs mixture, in the lipogenic phase boosted microbial lipids production (23–25%, w/w) and prevented lipids mobilization. Microbial lipids synthesized in such conditions are mainly composed of oleic acid (54%) with an unsaturated/saturated fraction above 78%. The main properties of biodiesel produced from Y. lipolytica W29 lipids are within the ranges of the EU biodiesel standard EN 14214.

Preferential photoassimilation of volatile fatty acids by purple non-sulfur bacteria: Experimental kinetics and dynamic modelling

Purple non-sulfur bacteria (PNSB) are known for their metabolic versatility and thrive as anoxygenic photoheterotrophs. In environmental engineering and resource recovery, cells would grow on mixtures of volatile fatty acids (VFA) generated by anaerobic fermentation of waste streams. In this study, we aim to better understand the behavior of Rhodospirillum rubrum, a model PNSB species, grown using multiple VFA as carbon sources. We highlighted that assimilation of individual VFA follows a sequential pattern. Based on observations in other PNSB, this seems to be specific to isocitrate lyase-lacking organisms. We hypothesized that the inhibition phenomenon could be due to the regulation of the metabolic fluxes in the substrate cycle between acetoacetyl-CoA and crotonyl-CoA. Developed macroscopic dynamic models showed a good predictive capability for substrate competition for every VFA mixture containing acetate, propionate, and/or butyrate. These novel insights provide valuable input for better design and operation of PNSB-based waste treatment solutions.

Accumulation of lipids by the oleaginous yeast Yarrowia lipolytica grown on carboxylic acids simulating syngas and carbon dioxide fermentation

Volatile fatty acids (VFAs) can be considered as low-cost carbon substrates for lipid accumulation by oleaginous yeasts. This study demonstrates that a common mixture of VFAs, typically obtained from the anaerobic fermentation of C1-gases by some acetogenic bacteria, can be used in a second aerobic fermentation with the yeast Yarrowia lipolytica to obtain lipids as precursors of biodiesel. In the batch experiments, the preference of Yarrowia lipolytica W29 for acetic acid over butyric and caproic acids was demonstrated, with the highest consumption rate reaching 0.664 g/L·h. In the bioreactor experiments, the amount initial biomass inoculated, as well as the initial acid concentration, were found to have a significant influence on the process. Though the lipid content was relatively low, it can be optimized and further improved. Oleic, linoleic and palmitic acids accounted for about 80 % of the fatty acids in the lipids, which makes them suitable for biodiesel.

Microbial Lipid Production from High Concentration of Volatile Fatty Acids via Trichosporon cutaneum for Biodiesel Preparation.

Direct bioconversion of high concentration of volatile fatty acids (VFAs) into microbial lipid is challenging due to the aggravated cytotoxicity of VFAs at high loadings. Herein, a robust oleaginous yeast Trichosporon cutaneum was screened for lipogenesis from high concentration of VFAs using a regular batch culture. Biomass and lipid content of 8.9g/L and 49.1%, respectively, were attained from 50g/L acetic acid with 90.9% of which assimilated within 10days. The blend of VFAs (50g/L), with mass ratio of acetic, propionic, and butyric acids of 6:3:1, was found superior to acetic acid for lipogenesis. Biomass and lipid titer increased by 16.9% and 18.2%, respectively, with the three VFAs completely consumed within 8days. Butyric acid was assimilated simultaneously with acetic acid at the beginning of the culture. Heptadecanoic acid (C17:0) and heptadecenoic acid (C17:1) were produced when propionic acid co-existed with acetic and butyric acids. The estimation of biodiesel properties indicated that lipid prepared from VFA blend showed superiority to acetic acid for high-quality biodiesel production. This study strongly supported that T. cutaneum permitted high concentration of VFA mixture for lipid production.

Reverse osmosis and nanofiltration opportunities to concentrate multicomponent mixtures of volatile fatty acids

The application of reverse osmosis (RO) and nanofiltration (NF) to concentrate and/or fractionate volatile fatty acids (VFAs, occurring in acidogenic effluents) was systematically assessed for the first time using three commercial spiral wound modules. A bench scale plant was used to test the polyamide membrane cartridges, namely: AG1812-34D, DK1812-34D and NFS-3B-1812F. The effects of main operational parameters (pH, temperature, applied pressure) were firstly studied in total recirculation mode, using different total and relative VFA compositions. Thereafter, batch concentration tests were carried out (at constant applied pressure, ca. 30 bar) to fully characterize the RO and NF modules. AG1812-34D performed as an RO module and it allowed concentrating target solutions almost 3 times without relevant VFA losses (<4%) in the permeate side. All tested parameters were observed to affect concentration performances. However, typical pH levels occurring in acidogenic effluents allowed to achieve fully satisfactory VFA rejections. DK1812-34D and NFS-3B-1812F performed as NF modules and could represent suitable solutions for VFA fractionation. Separation factors significantly increased by pH rise; in particular, high acetic and propionic acid separation factors over butyric acid were achieved at pH 9, with DK1812-34D module.

Establishing Mixotrophic Growth of Cupriavidus necator H16 on CO2 and Volatile Fatty Acids

The facultative chemolithoautotroph Cupriavidus necator H16 is able to grow aerobically either with organic substrates or H2 and CO2 s and it can accumulate large amounts of (up to 90%) poly (3-hydroxybutyrate), a polyhydroxyalkanoate (PHA) biopolymer. The ability of this organism to co-utilize volatile fatty acids (VFAs) and CO2 as sources of carbon under mixotrophic growth conditions was investigated and PHA production was monitored. PHA accumulation was assessed under aerobic conditions, with either individual VFAs or in mixtures, under three different conditions—with CO2 as additional carbon source, without CO2 and with CO2 and H2 as additional sources of carbon and energy. VFAs utilisation rates were slower in the presence of CO2. PHA production was significantly higher when cultures were grown mixotrophically and with H2 as an additional energy source compared to heterotrophic or mixotrophic growth conditions, without H2. Furthermore, a two-step VFA feeding regime was found to be the most effective method for PHA accumulation. It was used for PHA production mixotrophically using CO2, H2 and VFA mixture derived from an anaerobic digestor (AD). The data obtained demonstrated that process parameters need to be carefully monitored to avoid VFA toxicity and low product accumulation.

Bioprocessing of volatile fatty acids by oleaginous freshwater microalgae and their potential for biofuel and protein production

To address the issue of high organic carbon costs in heterotrophic cultivation of microalgae, we evaluated the hypotheses by employing microalgae as a biorefinery for proteins and advanced biofuels after cultivation on volatile fatty acids (VFAs) instead of pure glucose. To prevent the inhibitory effect of VFAs on lipid synthesis, strains capable of tolerating high levels of VFAs were selected. Growth and lipid synthesis by two freshwater microalgae, Auxenochlorella protothecoides and Chlorella sorokiniana, was optimized at different VFA concentrations. Maximum biomass and lipid content in A. protothecoides (10.66 g/L, 33.93%) and C. sorokiniana (7.98 g/L, 39.80%) were obtained by replacing glucose with 30 g/L acetate at C/N 60. The generated lipids were compliant with existing standards for biodiesel. Moreover, when grown on acetate, both microalgae contained the complete range of essential and non-essential amino acids. Finally, single-source commercial VFAs were replaced with VFAs mixture after acidogenic fermentation of waste lignocellulosic biomass from brewers’ spent grain. The mixture allowed successful mixotrophic and heterotrophic cultivation of both microalgae, demonstrating feasibility of this low-cost carbon source in fuel-grade biodiesel production.

Regulating light, oxygen and volatile fatty acids to boost the productivity of purple bacteria biomass, protein and co-enzyme Q10

Purple non‑sulfur bacteria (PNSB) possess significant potential for bioresource recovery from wastewater. Effective operational tools are needed to boost productivity and direct the PNSB biomass towards abundant value-added substances (e.g., protein and co-enzyme Q10, CoQ10). This study aimed to investigate the impact of light, oxygen and volatile fatty acids (VFAs) on PNSB growth (i.e., Rhodobacter sphaeroides) and productivity of protein and CoQ10. Overall, the biomass yields and specific growth rates of PNSB were in the ranges of 0.57–1.08 g biomass g−1 CODremoved and 0.48–0.71 d−1, respectively. VFAs did not influence the biomass yield, yet acetate and VFA mixtures enhanced the specific growth rate with a factor of 1.2–1.5 compared to propionate and butyrate. The most PNSB biomass (1.08 g biomass g−1 CODremoved and 0.71 d−1) and the highest biomass quality (protein content of 609 mg g−1 dry cell weight (DCW) and CoQ10 content of 13.21 mg g−1 DCW) were obtained in the presence of VFA mixtures under natural light and microaerobic (low light alternated with darkness; dissolved oxygen (DO) between 0.5 and 1 mg L−1) conditions (vs. light anaerobic and dark aerobic cultivations). Further investigation on VFAs dynamics revealed that acetate was most rapidly consumed by PNSB in the individual VFA feeding (specific uptake rate of 0.76 g COD g−1 DCW d−1), while acetate as a co-substrate in the mixed VFAs feeding might accelerate the consumption of propionate and butyrate through providing additional cell metabolism precursor. Enzymes activities of succinate dehydrogenase and fructose-1,6-bisphosphatase as well as the concentration of photo pigments confirmed that light, oxygen and VFAs regulated the key enzymes in the energy metabolism and biomass synthesis to boost PNSB growth. These results provide a promising prospect for utilization of fermented waste stream for the harvest of PNSB biomass, protein and CoQ10.

Influence of the total concentration and the profile of volatile fatty acids on polyhydroxyalkanoates (PHA) production by mixed microbial cultures

Polyhydroxyalkanoates (PHAs) production from lignocellulosic biomass using mixed microbial cultures (MMC) is a potential cheap alternative for reducing the use of petroleum-based plastics. In this study, an MMC adapted to acidogenic effluent from dark fermentation (DF) of exhausted sugar beet cossettes (ESBC) has been tested in order to determine its capability to produce PHAs from nine different synthetic mixtures of volatile fatty acids (VFAs). The tests consisted of mixtures of acetic, propionic, butyric, and valeric acids in the range of 1.5–9.0 g/L of total acidity and with three different valeric:butyric ratios (10:1, 1:1, and 1:10). Experimental results have shown a consistent preference of the MMC for the butyric and valeric acids as carbon source instead other shorter acids (propionic or acetic) in terms of PHA production yield (estimated in dry cell weight basis), with a maximum value of 23% w/w. Additionally, valeric-rich mixtures have demonstrated to carry out a fast degradation process but with poor final PHA production compared with high butyric mixtures. Finally, high initial butyric and valeric concentrations (1.1 g/L and 4.1 g/L) have demonstrated to be counterproductive to PHA production.