Mixture Of Volatile Fatty Acids Research Articles

Production of polyhydroxyalkanoates by halotolerant bacteria with volatile fatty acids from food waste as carbon source.

In this study, a halotolerant strain was isolated from high salinity leachate and identified as Bacillus cereus NT-3. It can produce a high concentration of polyhydroxyalkanoates (PHAs) with no significant changes when NaCl concentration is up to 50 g/L. FTIR and NMR spectra of PHAs synthesized by Bacillus cereus NT-3 were similar to the standard or previous results. Effluent from acidogenic fermentation of food waste and pure volatile fatty acids (VFAs) mixture was used as carbon source to check the effect of non-VFAs compounds of the effluent on PHAs production. The maximum PHAs production was 0.42 g/L for effluent fermentation, whereas it was 0.34 g/L for pure VFAs fermentation, indicating that bacteria could use actual effluent in a better way. Furthermore, a mathematical model was established for describing kinetic behavior of bacteria using different carbon sources. These results provided a promising approach for PHAs biosynthesis with a low-cost carbon source.

Volatile fatty acid production from semi-synthetic milk processing wastewater under alkali pH: The pearls and pitfalls of microbial culture.

Volatile fatty acids (VFA) are one of the most promising sustainable and environmentally friendly bioproduct owing to their wide usage area and high market demand. For this reason, in this study, the evaluation of VFA production from pure and mixed bacterial cultures was aimed. Three different mixed cultures with C. aceticum, C. butyricum and P. acidipropionici as pure cultures were used for inoculation of milk processing wastewater fermentation under pH 10 for 15days. The mixed culture fermentation had the highest VFA production efficiency whereas the highest amount of acetic, butyric and propionic acid productions were obtained by C. aceticum, C. butyricum and P. acidipropionici, respectively. Also, the mixed cultures demonstrated faster pH regulation and acclimation than the pure cultures tested. Therefore, development of synthetic cultures may offer a useful approach to produce VFA mixtures with one-dominant acid type and with high production efficiency.

Volatile fatty acids production via mixed culture fermentation: Revealing the link between pH, inoculum type and bacterial composition

The aim of the study was to investigate the effects of operational parameters, inoculum type and bacterial community on mixed culture fermentation to produce one dominant acid type in the mixture of volatile fatty acids (VFA). The study was performed using three different inocula (large&small granular and slurry) with glucose under various initial pH. The VFA production efficiency reached to 0,97 (gCOD/gSCOD) by granular sludge. VFA composition was changed by initial pH: in neutral conditions, acetic acid; in acidic conditions, acetic and butyric acids, in alkali conditions butyric acid were dominated, respectively. The VFA production was positively affected by the high relative abundance of Firmicutes. On the contrary, a negative correlation was seen between VFA production and the relative abundance of Chloroflexi. The results revealed the physical sludge structure of inoculum was the key factor for production efficiency, whereas, pH was the most important parameter to affect VFA composition.

Magnetite nanoparticles enhance the bioelectrochemical treatment of municipal sewage by facilitating the syntrophic oxidation of volatile fatty acids

AbstractBACKGROUNDMicrobial electrochemical technologies (METs) represent a novel platform to harvest the energy trapped in municipal wastewater. At the anode of METs, electro‐active bacteria (EAB) anaerobically oxidize wastewater constituents using the electrode as the terminal electron acceptor and, by so doing, generate an electric current. To convert complex wastewater constituents into electricity, EAB must not only establish syntrophic relationships with other members of the microbial community, but also compete with methanogens for consumption of hydrogen and acetate. Here, we examined the addition of magnetite nanoparticles (NPs) (250 mg Fe L−1) as a novel strategy to manipulate such metabolic interactions and in turn maximize the efficiency of wastewater treatment and the yield of electric current generation.RESULTSBatch experiments carried out either in the presence of a mixture of volatile fatty acids or of a synthetic sewage demonstrated that magnetite addition accelerate the rate of electrogenic oxidation of specific compounds, particularly propionate (up to 120%), an intermediate which frequently accumulates during anaerobic treatment processes, while correspondingly enhancing electric current generation (up to 90%), and diminishing the rate of competing methane generation (up to 50%). Notably, the composition of the microbial community was not substantially affected by the presence of magnetite nanoparticles, possibly suggesting that these latter facilitated extracellular electron transfer mechanisms (among microbes and with the electrode), rather than enriching conditions for specific microorganisms.CONCLUSIONThe addition of magnetite NPs may represent a practical strategy to kick‐start a bioelectrochemical system designed for wastewater treatment and improve the effectiveness of electrogenic substrate oxidation processes. © 2019 Society of Chemical Industry

Determination of Microbial Maintenance in Acetogenesis and Methanogenesis by Experimental and Modeling Techniques.

For biogas-producing continuous stirred tank reactors, an increase in dilution rate increases the methane production rate as long as substrate input can be converted fully. However, higher dilution rates necessitate higher specific microbial growth rates, which are assumed to have a strong impact on the apparent microbial biomass yield due to cellular maintenance. To test this, we operated two reactors at 37°C in parallel at dilution rates of 0.18 and 0.07 days-1 (hydraulic retention times of 5.5 and 14 days, doubling times of 3.9 and 9.9 days in steady state) with identical inoculum and a mixture of volatile fatty acids as sole carbon sources. We evaluated the performance of the Anaerobic Digestion Model No. 1 (ADM1), a thermodynamic black box approach (TBA), and dynamic flux balance analysis (dFBA), to describe the experimental observations. All models overestimated the impact of dilution rate on the apparent microbial biomass yield when using default parameter values. Based on our analysis, a maintenance coefficient value below 0.2 kJ per carbon mole of microbial biomass per hour should be used for the TBA, corresponding to 0.12 mmol ATP per gram dry weight per hour for dFBA, which strongly deviates from the value of 9.8 kJ Cmol h-1 that has been suggested to apply to all anaerobic microorganisms at 37°C. We hypothesized that a decrease in dilution rate might select taxa with minimized maintenance expenditure. However, no major differences in the dominating taxa between the reactors were observed based on amplicon sequencing of 16S rRNA genes and terminal restriction fragment length polymorphism analysis of mcrA genes. Surprisingly, Methanosaeta dominated over Methanosarcina even at a dilution rate of 0.18 days-1, which contradicts previous model expectations. Furthermore, only 23–49% of the bacterial reads could be assigned to known syntrophic fatty acid oxidizers, indicating that unknown members of this functional group remain to be discovered. In conclusion, microbial maintenance was found to be much lower for acetogenesis and methanogenesis than previously assumed, likely due to the exceptionally low growth rates in anaerobic digestion. This finding might also be relevant for other microbial systems operating at similarly low growth rates.

Inhibitory effect of ethanol on the experimental electrical charge and hydrogen production in microbial electrolysis cells (MECs)

Fermentation effluents are exploited in microbial electrolysis cells (MECs) for hydrogen production, but they may include ethanol and other compounds that are detrimental to MEC performance. Ethanol can disrupt microbial viability, and lactate makes MEC feeding more complex. The present work aimed to assess the effects of lactate and ethanol on hydrogen and electric current production in MECs to determine the corresponding inhibitory concentrations. A two-chamber MEC was inoculated with compost leachate and fed with lactate-ethanol mixtures at four ratios (total 2.5g COD L−1), and a volatile fatty acid mixture was used as a base substrate to achieve anolyte at a final concentration of 3.5g COD L−1. The MEC operated at 1.0V for 21days, and its performance was evaluated for COD removal, cathodic and energy efficiency. The inhibitory ethanol concentration was 0.8g COD L−1 (0.38gL−1), and lactate reduced the current density lag phase. The start of hydrogen production required 218±35C in the MEC system utilized. This work shows that ethanol content exerts an inhibitory effect on current and hydrogen production; moreover, a relationship between accumulated charge and accumulated hydrogen volume was found suitable to characterize the process.

Volatile fatty acids impacting phototrophic growth kinetics of purple bacteria: Paving the way for protein production on fermented wastewater

Nutrient losses in our food chain severely surpass our planetary boundaries. Resource recovery can contribute to mitigation, for instance through converting wastewater resources to microbial protein for animal feed. Wastewater typically holds a complex mixture of organics, posing a challenge to selectively produce heterotrophic biomass. Ensuring the product's quality could be achieved by anaerobic generation of volatile fatty acids (VFAs) followed by photoheterotrophic production of purple non-sulfur bacteria (PNSB) with infrared light. This study aimed to determine the most suitable PNSB culture for VFA conversion and map the effect of acetate, propionate, butyrate and a VFA mixture on growth and biomass yield. Six cultures were screened in batch: (i) Rhodopseudomonas palustris, (ii) Rhodobacter sphaeroides, (iii) Rhodospirillum rubrum, (iv) a 3-species synthetic community (i+ii+iii), (v) a community enriched on VFA holding Rb. capsulatus, and (vi) Rb. capsulatus (isolate ‘v’). The VFA mixture elevated growth rates with a factor 1.3–2.5 compared to individual VFA. Rb. capsulatus showed the highest growth rates: 1.8–2.2 d−1 (enriched) and 2.3–3.8 d−1 (isolated). In a photobioreactor (PBR) inoculated with the Rb. capsulatus enrichment, decreasing sludge retention time (SRT) yielded lower biomass concentrations, yet increased productivities, reaching 1.7 g dry weight (DW) L−1 d−1, the highest phototrophic rate reported thus far, and a growth rate of up to 5 d−1. PNSB represented 26–57% of the community and the diversity index was low (3–7), with a dominance of Rhodopseudomonas at long SRT and Rhodobacter at short SRT. The biomass yield for all cultures, in batch and reactor cultivation, approached 1 g CODBiomass g−1 CODRemoved. An economic estimation for a two-stage approach on brewery wastewater (load 2427 kg COD d−1) showed that 0.5 d SRT allowed for the lowest production cost (€ 10 kg−1 DW; equal shares for capex and opex). The findings strengthen the potential for a novel two-stage approach for resource recovery from industrial wastewater, enabling high-rate PNSB production.

Effects of barium on the pathways of anaerobic digestion

The sufficient presence of trace elements (TE) is essential for anaerobic digestion. Barium (Ba) is considered a non-essential trace element that can be collaterally added to digesters as part of low-cost trace element sources or because of its presence in some feedstocks, such as crude glycerol. In the present study, the impact of Ba supplementation (2–2000 mg/L) on each stage of the anaerobic digestion (AD) process was evaluated using pure substrates (i.e., cellulose, glucose, a mixture of volatile fatty acids, sodium acetate and hydrogen) as well as a complex substrate (i.e., dried green fodder). Hydrolytic activity was affected at dosages higher than 200 mg Ba/L, whereas cellulose degradation was completely inhibited at 2000 mg Ba/L. The negative effects of the addition of Ba to methane production were observed only in the hydrolytic activity, and no effects were detected at any barium dosage in the subsequent anaerobic steps. Because Ba does not have a reported role as a cofactor of enzymes, this response could have been due to a direct inhibitory effect, a variation in the bioavailability of other trace elements, or even the availability of CO2/SO4 through precipitation as Ba-carbonates and sulphates. The results showed that the addition of Ba modified the chemical equilibrium of the studied system by varying the soluble concentration of some TEs and therefore their bioavailability. The highest variation was detected in the soluble concentration of zinc, which increased as the amount of Ba increased. Although little research has shown that Ba has some utility in anaerobic processes, its addition must be carefully monitored to avoid an undesirable modification of the chemical equilibrium in the system.

Pervaporative Separation of Mixed Volatile Fatty Acids: A Study Towards Integrated VFA Production and Separation

Volatile fatty acids (VFAs) are heavily synthesized from fossil-based processes regardless of the scarcity of non-renewable resources. Anaerobic fermentation of organic wastes can be an alternative way to produce VFAs, however the recovery of VFAs from fermentation broths is the bottleneck of the resource recovery. In this study, membrane contactor based pervaporation system was used to recover VFAs through polytetrafluoroethylene (PTFE), tridodecylamine (TDDA) filled PTFE, and composite silicone rubber/PTFE membranes. Synthetic VFA mixtures were used as feed solutions representing fermentation broths composed of acetic, propionic, butyric, valeric, and caproic acids. Effect of temperature on recovery of VFAs through PTFE and TDDA filled PTFE liquid membrane was investigated at 21 °C, 35 °C, and 55 °C. In addition, effect of increased membrane thickness on VFA recovery efficiency of composite membranes was assessed at 35 °C. The results of the study revealed that TDDA filled PTFE liquid membrane resulted in significantly higher VFA flux, separation factor, permeance, and selectivity compared to that of PTFE membrane, which was presumably due to strong ion-pair formation between TDDA and carboxylic acids. The highest permeance of VFAs were observed at 35 °C through TDDA filled PTFE liquid membrane. Membrane thickness significantly influenced the VFA separation efficiency in composite membranes. The highest membrane selectivity of VFAs was observed in a composite membrane with 190.2 ± 4.8 µm thickness. The results of the study are significant in terms of the development of integrated fermentation and membrane-based VFA separation applications, which will hopefully decrease the reliance on fossil-fuels for VFA production.

Dynamics and the interaction effects of trace elements and volatile fatty acids concentrations on methanization processes during thermophilic anaerobic digestion

Volatile fatty acids (VFA) and trace elements (TEs) influence methane production and VFA metabolism in positive and negative ways during methanization. There is insufficient knowledge on why the interactions could go either way and this has generated unpleasant consequences for biogas operators. To fill the knowledge gap, statistically designed thermophilic batch experiments were conducted with VFA mixture as substrate to investigate the dynamics and interaction effects of TEs including Nickel (Ni), Cobalt (Co), Selenium (Se) and Molybdenum (Mo) on the methanization processes of CH4 production and VFA degradation rate. Response surface model and desirability functions were used to determine TEs and VFA interaction effects and the dynamics of the optimum TEs configurations for CH4 production and VFA degradation rate at different VFA concentrations. The results showed that TEs supplementation influenced YCH4 production by -14% to 11%: whereas the positive interaction effects of VFA and TEs were by Co*Mo, VFA*Se and VFA*Mo; the interaction effects of Se*Mo and VFA*Co were negative. -15% to 45% increase in YVFA-DR was obtained with TEs supplementation: Ni*Co interaction produced the positive influences; and Co*Se produced negative effects. The optimum TEs configuration for CH4 production and VFA degradation rate varied with changes in VFA concentrations.Keywords: Thermophilic methanization, trace elements, VFA metabolism, methane production, trace elements synergism, trace elements interaction

Electro-biocatalytic conversion of carbon dioxide to alcohols using gas diffusion electrode

Impact of gas diffusion electrodes (GDEs) was evaluated in enhancing the CO2 bio-availability for its transformation to C4-organics, especially to alcohols using selective mixed culture. Observed current density was more stable (9–11 A/m2) than submerged experiments reported and significantly varied with pH and respective CO2 solubility. Uncontrolled operating pH (starting with 8.0) showed its impact on shifting/triggering alternate metabolic pathways to increase the carbon length (butyric acid) as well as producing more reduced end products, i.e. alcohols. During the experiments, CO2 was transformed initially to a mixture of volatile fatty acids dominated with formic and acetic acids, and upon their accumulation, ethanol and butanol production was triggered. Overall, 21 g/l of alcohols and 13 g/l of organic acids were accumulated in 90 days with a coulombic efficiency (CE) of 49%. Ethanol and butanol occupied respectively about 45% and 16% of total products, indicating larger potential of this technology.

Synergistic and antagonistic influences of trace elements on volatile fatty acids degradation and methane production during the methanization of a mixture of volatile fatty acids

Anaerobic digestion (AD33Anaerobic digestion.) for methane production is also known as methanization. Trace elements (TEs44Trace elements including nickel, cobalt, selenium and molybdenum.) as supplements are essential for enzyme activities and may improve methanization, but could also be toxic. Volatile fatty acids (VFA55Volatile fatty acids.) are formed during the AD of substrates and become inhibitory if accumulated. The level of ambiguity regarding optimum combination and concentration (configuration) of TEs for the improvement of VFA degradation and methane production during methanization is high. Therefore, mesophilic batch AD experiments with TEs supplementation were carried out in 1L reactors. A mixture of VFA (butyric, propionic and acetic acids) that was prepared in different concentrations (28-, 116-, and 213 mmol/L VFA) was used as substrate. The VFA degradation rate and methane production were the main responses that were investigated and analysed using multivariate analyses. The major aim of the work was to model interaction effects of the most important TEs in AD − Ni, Co, Se and Mo, and of VFA. Also, the adaptation time of the methanization process to the TEs was investigated. In the result, TEs supplementation caused variable effects on VFA degradation rate (from −10% to +139%); and methane production (from −33% to +55%). Regarding TEs interactions, for VFA degradation rate, the significant synergistic interactions included VFA*Se, Ni*Mo, VFA*Mo and Ni*Se; and the antagonistic interaction was Co*Mo. Similarly, for methane production, the significant synergistic interaction included Ni*Co and the antagonistic interaction was VFA*Ni.

Synthetic Copulin Does Not Affect Men\u2019s Sexual Behavior

Chemical communication plays an important role in the social interactions and mating behavior of diverse animal taxa; yet its role in humans remains equivocal. Using a randomized, placebo-controlled experiment involving 243 male participants, we test whether exposure to synthetic copulin – a mixture of volatile fatty acids secreted vaginally in primates, increases 1) men’s sexual motivation using an incentivized behavioral task, 2) self-reported willingness to take sexual risks, 3) preference for short-term mating, 4) perceptions of female attractiveness and 5) self-reported mate value. Because chemical receptors are found throughout the body and human chemosensory pathways have yet to be definitively identified, we also manipulate the location of copulin exposure (i.e. olfactory epithelium versus epidermal keratinocytes in the genital region). Finally, we examine whether prior sexual experience mediate any behavioral effects. Unlike previous reports, we fail to find any effects of copulin exposure on measures of men’s sexual behavior.

Oleaginous yeast Yarrowia lipolytica culture with synthetic and food waste-derived volatile fatty acids for lipid production

BackgroundThe sustainability of microbial lipids production from traditional carbon sources, such as glucose or glycerol, is problematic given the high price of raw materials. Considerable efforts have been directed to minimize the cost and find new alternative carbon sources. Volatile fatty acids (VFAs) are especially attractive raw materials, because they can be produced from a variety of organic wastes fermentation. Therefore, the use of volatile fatty acids as carbon sources seems to be a feasible strategy for cost-effective microbial lipid production.ResultsLipid accumulation in Y. lipolytica using synthetic and food waste-derived VFAs as substrates was systematically compared and evaluated in batch cultures. The highest lipid content obtained with acetic, butyric, and propionic acids reached 31.62 ± 0.91, 28.36 ± 0.74, and 28.91 ± 0.66%, respectively. High concentrations of VFA inhibited cell growth in the following order: butyric acid > propionic acid > acetic acid. Within a 30-day experimental period, Y. lipolytica could adapt up to 20 g/L acetic acid, whereas the corresponding concentration of propionic acid and butyric acid were 10 and 5 g/L, respectively. Cultures on a VFA mixture showed that the utilization of different types of VFA by Y. lipolytica was not synchronized but rather performed in a step-wise manner. Although yeast fermentation is an exothermic process, and the addition of VFA will directly affect the pH of the system by increasing environmental acidity, cultures at a cultivation temperature of 38 °C and uncontrolled pH demonstrated that Y. lipolytica had high tolerance in the high temperature and acidic environment when a low concentration (2.5 g/L) of either synthetic or food waste-derived VFA was used. However, batch cultures fed with food fermentate yielded lower lipid content (18.23 ± 1.12%) and lipid productivity (0.12 ± 0.02 g/L/day). The lipid composition obtained with synthetic and food waste-derived VFA was similar to commercial biodiesel feedstock.ConclusionsThis work demonstrated the feasibility of utilizing synthetic and food waste-derived VFA for lipid production by Y. lipolytica. The good adaptability of Y. lipolytica to the high temperature and acidic environment further illustrated its considerable potential for practical application.

Acclimation Strategy Using Complex Volatile Fatty Acid Mixtures Increases the Microbial Fuel Cell (MFC) Potential

AbstractThe start‐up of microbial fuel cells (MFCs) requires biofilm development onto electrodes and acclimation of the microbial community to specific substrates. This process is time‐consuming and shows low effectivity when complex substrates are utilized. The varying proportions and complex mixtures of volatile fatty acids (VFAs) in bioprocess effluents makes it difficult to predict the power output of VFA‐based MFCs when this technology is coupled to a previous bioprocess. In this work, the effect of the degree of reduction of single VFAs on MFC potential was investigated, and a novel acclimation procedure involving the feeding of gradually more complex VFA mixtures is proposed. The power output obtained with butyric acid (6.1 ± 2 mW m−2) was higher than that obtained with propionic acid (5.0 ± 1 mW m−2), as expected based on their degree of reduction. The MFC potential generated by an acetic acid‐fed MFC reached 60 mV, but an acetic‐butyric acid mixture reduced the cell potential by one order of magnitude. The subsequent addition of propionic acid to the acetic‐butyric mixture increased the MFC potential from 1.9 ± 0.1 mV to 35 ± 10 mV in sequential feeding cycles. Consequently, the feeding sequence of acetic, acetic‐butyric, and acetic‐butyric‐propionic acids is proposed as an efficient strategy for the acclimation of MFCs to complex substrates.

Effect of Operational Parameters in the Continuous Anaerobic Fermentation of Cheese Whey on Titers, Yields, Productivities, and Microbial Community Structures

Volatile fatty acids (VFAs) were produced using cheese whey as feedstock. A mixed culture packed bed bioreactor was set up to digest anaerobically, under an acidogenic condition, a water solution of a cheese whey powder. Batch tests pointed out that the whole VFAs production process occurred via two sequential phases: (a) conversion of lactose into lactic acid and (b) conversion of lactic acid into a mixture of VFAs. Furthermore, the same tests showed that the ceramic material Vukopor S10 can be used as an effective support for cell immobilization in anaerobic fermentation processes. The effect of the hydraulic retention time (HRT) and organic loading rate (OLR) were then studied in a benchtop bioreactor operated continuously. By a HRT of 6 days, ORL of 4.2 g/L/d, and pH 5.8–6, 16 g·L–1 of total VFAs were produced, with a yield higher than 75% (CmolVFAs·Cmollactose–1). Characterization with Illumina-based sequencing suggested that high VFAs productivities were obtained when microbial community structures ...

Effect of volatile fatty acids in anaerobic conditions on viability of helminth ova (Ascaris suum) in sanitization of municipal sludge

ABSTRACTThe present work aimed at evaluating the effect of four different mixtures of diverse volatile fatty acids (VFAs) on the viability of helminth ova (Ascaris suum), under mesophilic (35°C) anaerobic conditions and at different incubation times, in order to reproduce the process of two-phase anaerobic digestion. The mixtures of VFAs contained acetic, propionic, butyric, valeric, and isovaleric acids, used at concentrations normally found in acidogenic anaerobic digesters. The four treatments all showed a reduction in Ascaris suum ova viability, among which Treatment III (4.2 g-acetic acid L−1 + 2.2 g-propionic acid L−1 + 0.6 g-valeric acid L−1 + 0.6 g-isovaleric acid L−1) resulted the most efficient. We found that the full effect of VFAs on the viability loss of Ascaris suum ova in mesophilic conditions requires a minimum incubation time of 3 days. The highest efficiency in the loss of viability was observed with Treatment III and 4-day incubation. Interestingly, the proportion of acetic acid was three times as much in this treatment than in the other ones and resulted in an effect in a minimum time of 3 days. The mesophilic condition, however, was not sufficient to induce a complete loss of viability.

Effect of volatile fatty acids mixtures on the simultaneous photofermentative production of hydrogen and polyhydroxybutyrate.

Purple non-sulfur bacteria generate hydrogen and polyhydroxybutyrate (PHB) as a mechanism for disposing of reducing equivalents generated during substrate consumption. However, both pathways compete for the reducing equivalents released from bacteria growing under certain substrates, thus the formation of hydrogen or PHB is detrimental to the formation of each other. The effect of mixtures of acetic, propionic and butyric acids on the formation of H2 and PHB was evaluated using Box-Behnken design. A bacterial community mainly constituted by Rhodopseudomonas palustris was used as inoculum. It was observed that the three volatile fatty acids had a significant effect on the specific PHB production. However, only the propionic acid had a significant effect on the specific H2 production activity and the highest value was observed when acetate was the main component in the mixture. The maximum values forthespecific PHB and hydrogen production rates were 16.4mg-PHB/g-TSS/day and 391mL-H2/g-TSS/day, respectively.

Hydrolytic-Acidogenic Fermentation of Organic Solid Waste for Volatile Fatty Acids Production at Different Solids Concentrations and Alkalinity Addition

Intermediate products from anaerobic fermentation, such as volatile fatty acids (VFA), are the preferred carbon sources for the production of added-value products, namely polyhydroxyalkanoates (PHA) or bioenergy. Organic fraction of municipal solid waste (OFMSW) can be valorized through the application of a hydrolytic-acidogenic stage, thus reducing its pollutant content and at the same time that it is obtaining high-value products (VFA). In this work, the anaerobic fermentation of OFMSW into VFA (production and profile) and the influence of both total solids (TS) content in the reactor and alkalinity addition were studied. The increase on TS content led to a decrease on the acidification degree whereas the increase on the alkalinity addition led to a higher degree of acidification. Hence, the highest degree of acidification (77.59 %) was obtained at the lowest TS content (5 %) and at the highest alkalinity addition (50 g CaCO3 L−1). However, depending on the ultimate use of the produced VFA, the acidified residue presenting the highest VFA content (98.96 %) with higher propionic acid concentration, which is a more suitable VFA mixture for the production of high-quality PHA, was obtained at an intermediate TS content (8 %). From the response surfaces obtained, it was observed that all response variables (VFA production, degree of acidification, and effluent quality) presented a higher dependency on TS content than on initial alkalinity addition.

PHA production from the organic fraction of municipal solid waste (OFMSW): Overcoming the inhibitory matrix

Leachate from the source separated organic fraction of municipal solid waste (OFMSW) was evaluated as a substrate for polyhydroxyalkanoates (PHA) production. Initially, the enrichment step was conducted directly on leachate in a feast-famine regime. Maximization of the cellular PHA content of the enriched biomass yielded to low PHA content (29 wt%), suggesting that the selection for PHA-producers was unsuccessful. When the substrate for the enrichment was switched to a synthetic volatile fatty acid (VFA) mixture -resembling the VFA carbon composition of the leachate-the PHA-producers gained the competitive advantage and dominated. Subsequent accumulation with leachate in nutrient excess conditions resulted in a maximum PHA content of 78 wt%. Based on the experimental results, enriching a PHA-producing community in a “clean” VFA stream, and then accumulating PHA from a stream that does not allow for enrichment but does enable a high cellular PHA content, such as OFMSW leachate, makes the overall process much more economically attractive. The estimated overall process yield can be increased four-fold, in comparison to direct use of the complex matrix for both enrichment and accumulation.