Separation Of Volatile Fatty Acids Research Articles

Anhydrous volatile fatty acid extraction through omniphobic membranes by hydrophobic deep eutectic solvents: Mechanistic understanding and future perspective

Volatile fatty acids (VFAs) derived from arrested anaerobic digestion (AD) can be recovered as a valuable commodity for value-added synthesis. However, separating VFAs from digestate with complex constituents and a high-water content is an energy-prohibitive process. This study developed an innovative technology to overcome this barrier by integrating deep eutectic solvents (DESs) with an omniphobic membrane into a membrane contactor for efficient extraction of anhydrous VFAs with low energy consumption. A kinetic model was developed to elucidate the mechanistic differences between this novel omniphobic membrane-enabled DES extraction and the previous hydrophobic membrane-enabled NaOH extraction. Experimental results and mechanistic modeling suggested that VFA extraction by the DES is a reversible adsorption process facilitating subsequent VFA separation via anhydrous distillation. High vapor pressure of shorter-chain VFAs and low Nernst distribution coefficients of longer-chain VFAs contributed to DES-driven extraction, which could enable continuous and in-situ recovery and conversion of VFAs from AD streams.

Separation of nutrients and acetate from sewage sludge fermentation liquid in flow-electrode capacitive deionization system: Competitive mechanisms of ions and influence of activated carbon

Effective separation of volatile fatty acids (VFAs), ammonia (NH4+-N) and reactive phosphorous (RP) generated from anaerobic fermentation liquid is critically important for efficient resource recovery. Flow-electrode capacitive deionization (FCDI) is proven to be capable of efficient removal of ions, environmentally friendly and cost-effective in operation. The performances of FCDI system in the separation of NH4+-N, RP, and acetate and mechanism of pHs and activated carbon on their performances were investigated. Results showed that a pH of 5.0 promoted the removal of NH4+-N (53.1 %) and RP (39.5 %), and 72.0 % of acetate was retained in the solution, which revealed that removal of NH4+-N and RP, and retention of acetate were evidently affected by speciation of ions. Furthermore, the recovery of NH4+-N and RP was undermined by the adsorption of ions on activated carbon. This study provides a novel insight of ion selective mechanism during the operation of the FCDI system.

Enhanced, continuous, liquid-liquid extraction and in-situ separation of volatile fatty acids from fermentation broth

In 2018 alone, the US landfilled 35.3 million tons of food waste, about 24% of the total landfilled mass. In addition to the negative impacts landfills have demonstrated on the environment and human health, some states have begun to outlaw or dissuade the disposal of food waste and sewage sludge into landfills altogether. An urgent need has thus been created for the development of digestion processes like anaerobic digestion (AD) and arrested methanogenesis (AM) to convert food waste into valuable chemical products. Unfortunately, the buildup of volatile fatty acids (VFAs) during these processes eventually halts the reaction, and energy efficient methodologies for VFA removal are critical for the operation of fermenters. Additionally, VFAs themselves can serve as valuable chemical precursors, and recently AD processes have been modified to increase VFA production during fermentation. However, even with significant research over the past three decades, the separation of VFAs from the fermenter broth has remained expensive. Moreover, the separation of these VFAs from the fermenter broth may cost up to 50% of the entire process budget, hindering the widespread commercial adoption of AD and AM. In this work, we present a novel liquid–liquid extraction process termed CLEANS (Continuous Liquid-liquid Extraction And iN-situ Separation) as a highly efficient method for continuously separating VFAs from a real fermentation broth solely under gravity. Our optimized process (using an aqueous broth feed pH of 2.5, tri-n-octylamine as an extractant, and a 10:1 ratio of aqueous broth to organic extractant), achieved a VFA distribution constant KD = 44.5 ± 7.9, a single-pass recovery = 81.3 ± 2.5%, and an extraction factor = 8.1 ± 0.3. These KD values are over an order of magnitude higher than what has been previously reported for comparable processes. A high aqueous-to-organic flowrate ratio, enabled for the first time by CLEANS, was found to be particularly crucial for achieving optimal extraction. Our separation process demonstrates excellent reproducibility and potential for scalability. The economic and environmental implications of this work are briefly discussed.

Selective separation of volatile fatty acids and phosphorous recovery from fermented broth using flow-electrode capacitive deionization

Volatile fatty acids (VFA) extracted from fermented liquids are a viable carbon source to improve the removal of biological nutrients due to a carbon shortage of sewage influent in China. However, nutrients released from the fermented liquid increase the influent nutrients loading, resulting in a lower removal efficiency. In this study, a flow-electrode capacitive deionization (FCDI) system was developed to verify the feasibility of VFA separation and simultaneous ammonium and phosphate recovery from synthetic fermented broth. The results showed that 35.87 % of NH4+-N (cations) were removed from the influent under the optimal conditions (carbon = 5 wt%, current density (j) = 8.75 A/m2, hydraulic retention time (HRT) = 7.5 min, and pH 4.5). Meanwhile, only 9 % of acetate and 32.4 % of phosphorous (P) were migrated into anodic chamber. The difference removal efficiencies of anions caused by the different charging characteristics in electric field contributed the selective separation of acetate. The removed P was concentrated in the anode and converted into neutral H3PO4 by controlling the pH of the electrolyte below 2. This facilitated P enrichment in the anode compartment during discharge. The long-term operation results showed that 110.78 mg/L of P in the anode chamber and 92 % of acetate in the effluent were obtained with a lower power consumption of 1.89 kWh/kg P. These findings indicated that FCDI is a feasible approach for separating VFA and recovering P from fermented broth.

Current Status and Prospects of Valorizing Organic Waste via Arrested Anaerobic Digestion: Production and Separation of Volatile Fatty Acids

Volatile fatty acids (VFA) are intermediary degradation products during anaerobic digestion (AD) that are subsequently converted to methanogenic substrates, such as hydrogen (H2), carbon dioxide (CO2), and acetic acid (CH3COOH). The final step of AD is the conversion of these methanogenic substrates into biogas, a mixture of methane (CH4) and CO2. In arrested AD (AAD), the methanogenic step is suppressed to inhibit VFA conversion to biogas, making VFA the main product of AAD, with CO2 and H2. VFA recovered from the AAD fermentation can be further converted to sustainable biofuels and bioproducts. Although this concept is known, commercialization of the AAD concept has been hindered by low VFA titers and productivity and lack of cost-effective separation methods for recovering VFA. This article reviews the different techniques used to rewire AD to AAD and the current state of the art of VFA production with AAD, emphasizing recent developments made for increasing the production and separation of VFA from complex organic materials. Finally, this paper discusses VFA production by AAD could play a pivotal role in producing sustainable jet fuels from agricultural biomass and wet organic waste materials.

Selective separation of volatile fatty acids, nitrogen and phosphorus from anaerobic acidogenic fermentation via forward osmosis membrane process

Selective separation and recovery of volatile fatty acids (VFA) and other valuable resources promotes a sustainable wastewater treatment system, but its cost-effective separation approaches are poorly understood. This study investigated the feasibility of applying a forward osmosis (FO) dewatering process for the selective separation of VFA, ammonium and phosphate from anaerobic acidogenic fermentation. Limited VFA rejection of fermentation broth, i.e., less than 20 %, was observed under acidic conditions, while the rejection rate was significantly increased to ∼90 % at neutral pH. The transfer of ammonium across the membranes was remarkably impacted by the feed solution pH. Lower pH (∼4) values resulted in higher rejection rates of ammonium (∼96 %), and the rate gradually declined as pH increased. The rejection of phosphate, which remained higher than 98 %, was less sensitive to pH variations. The increase in water flux promoted the rejection of VFA, ammonium and phosphate, and the membrane orientation significantly impacted the transfer of nutrients in the FO process. The active layer facing the feed solution (AL-FS) mode exhibited higher rejection rates of VFA, ammonium and phosphate than the active layer facing the draw solution (AL-DS) mode, which was ascribed to the internal concentration polarization effect. Furthermore, approximately 80 % of water could be effectively reduced from a real acidogenic fermentation liquor during the FO process; ammonium and phosphate were 3.72-fold and 4.10-fold concentrated in feed solution, respectively, and VFA was selectively separated in draw solution. The work confirmed the feasibility of utilizing FO processes in separating and enriching VFA, ammonium and phosphate from anaerobic fermentation liquors, providing meaningful information on promoting FO-based processes in treating wastewater.

A Novel and Green Method for Turning Food Waste into Environmentally-Friendly Organic Deicing Salts: Enhanced VFA Production through AnMBR

In order to improve the production efficiency of volatile fatty acids (VFAs) by anaerobic fermentation of food waste and reduce the cost for the production of organic deicing salt (ODS), ceramic microfiltration (MF) membrane separation was applied in the conventional food waste fermenter to build an anaerobic membrane bioreactor (AnMBR). Results showed that the maximum VFA concentration in AnMBR was up to 55.37 g/L. Due to the fact that the MF membrane could realize in situ separation of VFAs, the recovery of VFAs could reach 95.0%; 66.6% higher than that of traditional fermentation reactors. After the application of the MF membrane, more than 20.0% of soluble COD, 40.0% of proteins, and 50.0% of polysaccharides were retained and more than 90.0% of VFAs could be transferred in a timely fashion in the AnMBR system. In addition, the enrichment effect of the MF membrane enhanced enzymatic activities such as protease, α-Glucosidase and acetate kinase, and increased the abundance of some important bacteria for organic acid generation such as Amphibacter, Peptoniphilus and Halomonas, which made a significant contribution to the yield of VFAs. After concentration, evaporation and crystallization, the melting efficiency of obtained ODS can reach more than 90.0% in chloride salts, which was 112.0% of commercial calcium magnesium acetate (CMA). When compared to chloride salts and CMA, ODS was more environmentally-friendly as it can reduce the corrosion of carbon steel and concrete significantly. This study created a new way of converting food waste into a high-value organic deicing agent, realizing the resource utilization of solid waste and reducing the production cost of organic deicing agents.

Selective Separation of Volatile Fatty Acids, Nitrogen and Phosphorus from Anaerobic Acidogenic Fermentation Via Forward Osmosis Membrane Process

Selective Separation of Volatile Fatty Acids, Nitrogen and Phosphorus from Anaerobic Acidogenic Fermentation Via Forward Osmosis Membrane Process

Enhanced biological hydrogen production through the separation of volatile fatty acids and ammonia based on microbial bipolar electrodialysis during thermal dark fermentation

Biological hydrogen (H2) is a clean fuel which can be produced by dark fermentation of food waste (FW). Some inhibitors including volatile fatty acids (VFAs) and ammonia can influence on H2 production rate. In the present work, a bio-electrochemical system, Thermal Dark Fermentation - Microbial Bipolar Electrodialysis (TDF-MBED) process, was used to separate VFAs and ammonia during FW fermentation, and thereby enhancing H2 production. From the three configurations employed, that novel design which consisted of two Anion Exchange Membranes (AEM), one on the anode side and another on the cathode side of working chamber (WC) had better results. The cumulative H2 increased from 2879 to 3511 mL L−1 as well as H2 production yield increased from 51 to 63.15 mL mg−1 compared to control, while at the same time, 50 mL H2 was produced in the cathode chamber. The VFAs concentration raised up to 507 mg L−1 in the separation chamber after 24 h. Although the VFAs production in TDF-MBED increased up to 2314 mg L−1 compared to 714 mg L−1 in the control, pH value remained above 5.15 (0.65 higher) during 24 h. In the configuration that contains two AEM, alkalinity and ammonia remained higher than other configurations, which are favorable for H2 production. Moreover, when cation exchange membrane (CEM) was used, the ammonia separation became higher and its concentration in fermenter decreased sharply from 1372 to 952 mg L−1 during 10–24 h. The TDF-MBED is a promising bio-electrochemical and sustainable approach for enhancing simultaneous H2 and VFAs production during TDF of FW.

Increasing 2 -Bio- (H2 and CH4) production from food waste by combining two-stage anaerobic digestion and electrodialysis for continuous volatile fatty acids removal

A novel approach of using two stage anaerobic digestion coupled with electrodialysis technology has been investigated. This approach was used to improving bio hydrogen and methane yields from food waste while simultaneously producing a green chemical feedstock. The first digester was used for hydrogen production and the second digester was used for methane production. The first digester was combined with continuous separation of volatile fatty acids using electrodialysis. The concentrations of carbohydrates, proteins and fats in the prepared food waste were 22.7%, 5.7% and 5.2% respectively. Continuous removal of volatile fatty acids during fermentation in the hydrogen digester not only increased hydrogen yields but also increased the production rate of volatile fatty acids. As a result of continuous VFA separation, hydrogen yields increased from 17.3mL H2/g VS fermenter to 33.68mL H2/g VS fermenter. Methane yields also increased from 28.94mL CH4/g VS fermenter to 43.94mL CH4/g VS fermenter. This represents a total increase in bio-energy yields of 77.1%. COD reduced by 73% after using two stage anaerobic digestion, however, this reduction increased to 86.7% after using electrodialysis technology for separation of volatile fatty acids. Electrodialysis technology coupled with anaerobic digestion improved substrate utilization, increased bioenergy yields and looks to be promising for treating complex wastes such as food waste.

Life cycle assessment of volatile fatty acids production from protein- and carbohydrate-rich organic wastes

Volatile fatty acids (VFAs) are platform molecules with numerous applications. They can be obtained by adjusting the operational conditions of anaerobic digestion to avoid methanogenesis while focusing on fermentative stages. There are gaps in the knowledge of how, from a life-cycle perspective, the fermentative process performs in VFAs production from waste, including environmental consequences of substituting common commodities in the current market. Mass and energy balances of VFAs production from protein-rich microalgal and carbohydrate-rich agro-industrial wastes were used herein as a key source of inventory data for life cycle assessment. Two waste treatment options were considered: (i) VFAs production (anaerobic fermentation) plus anaerobic digestion of the resulting waste after VFAs separation, and (ii) anaerobic digestion of the original waste for bioenergy. Several scenarios were formulated to evaluate their life-cycle performance. VFAs production generally shows a better environmental behaviour than conventional anaerobic digestion, principally due to the substitution of conventional chemicals.

Separation of Volatile Fatty Acids from Model Anaerobic Effluents Using Various Membrane Technologies.

Effluents of anaerobic processes still contain valuable components, among which volatile fatty acids (VFAs) can be regarded and should be recovered and/or used further in applications such as microbial electrochemical technology to generate energy/energy carriers. To accomplish the separation of VFAs from waste liquors, various membrane-based solutions applying different transport mechanisms and traits are available, including pressure-driven nanofiltration (NF) and reverse osmosis (RO) which are capable to clarify, fractionate and concentrate salts and organics. Besides, emerging techniques using a membrane such as forward osmosis (FO) and supported liquid membrane (SILM) technology can be taken into consideration for VFA separation. In this work, we evaluate these four various downstream methods (NF, RO, FO and SILM) to determine the best one, comparatively, for enriching VFAs from pH-varied model solutions composed of acetic, butyric and propionic acids in different concentrations. The assessment of the separation experiments was supported by statistical examination to draw more solid conclusions. Accordingly, it turned out that all methods can separate VFAs from the model solution. The highest average retention was achieved by RO (84% at the applied transmembrane pressure of 6 bar), while NF provided the highest permeance (6.5 L/m2hbar) and a high selectivity between different VFAs.

Selective Separation of Acetic and Hexanoic Acids across Polymer Inclusion Membrane with Ionic Liquids as Carrier.

This paper first reports on the selective separation of volatile fatty acids (VFAs) (acetic and hexanoic acids) using polymer inclusion membranes (PIMs) containing quaternary ammonium and phosphonium ionic liquids (ILs) as the carrier. The affecting parameters such as IL content, VFA concentration, and the initial pH of the feed solution as well as the type and concentration of the stripping solution were investigated. PIMs performed a much higher selective separation performance toward hexanoic acid. The optimal PIM composed of 60 wt% quaternary ammonium IL with the permeability coefficients for acetic and hexanoic acid of 0.72 and 4.38 µm s−1, respectively, was determined. The purity of hexanoic acid obtained in the stripping solution increased with an increase in the VFA concentration of the feed solution and decreasing HCl concentration of the stripping solution. The use of Na2CO3 as the stripping solution and the involvement of the electrodialysis process could dramatically enhance the transport efficiency of both VFAs, but the separation efficiency decreased sharply. Furthermore, a coordinating mechanism containing hydrogen bonding and ion exchange for VFA transport was demonstrated. The highest purity of hexanoic acid (89.3%) in the stripping solution demonstrated that this PIM technology has good prospects for the separation and recovery of VFAs from aqueous solutions.

Separation of volatile fatty acids from biogas plant hydrolysates

In this study the separation of volatile fatty acids (VFAs) from biogas plant hydrolysates and from each other was investigated. This creates the possibility to make the biogas process more profitable by selling these marketable volatile fatty acids (e.g. butyric acid, caproic acid, valeric acid) as isolates or as highly concentrated mixtures.Four kinds of screw-pressed liquid hydrolysates were used: sugar beet, grass cut and grass-corn hydrolysate from a bench-scale unit as well as a corn-triticale hydrolysate from a real biogas plant. The separation and the concentration of the VFAs were carried out by nanofiltration (NF) and reverse osmosis (RO). It was possible to separate acetic acid from the other acids in the permeate but only in low concentrations (0.25%). All VFAs were enriched in the retentate anyway. With the membrane SWC4 (RO) a total mass concentration enrichment of about factor 19 could be reached (from 7 g/l to 134.6 g/l).A further approach for concentration and separation of the investigated VFAs was their extraction with organic solvents (diethyl ether (DEE), methyl-isobutyl-ketone (MIBK)), followed by a consecutive distillation of the solvent. In this manner it was possible to extract the rather nonpolar butyric acid, valeric acid and caproic acid nearly completely, while the polar, shorter-chain VFAs remained in the aqueous phase. After distillation of the organic solvent, a highly concentrated mixture of butyric acid, valeric acid and caproic acid could be obtained (cVFA;DEE = 805 g/l).As the liquid hydrolysate still contained suspended particles, which possibly could clog the NF and RO membranes and disturb the extraction, tests were carried out to remove these particles by microfiltration (MF) and ultrafiltration (UF). UF membranes with separation limits from 10 kDa to 50 kDa proved to be the best.An assessment of the probably most valuable acid product was carried out against market prices for the individual acids and against calculated possible extractable yields for a hydrolysate of a 250 kW biogas plant.

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.

Electrodialytic separation of volatile fatty acids from hydrogen fermented food wastes

In this study, we investigated the electrodialysis (ED) process for the economic and efficient recovery of volatile fatty acids (VFAs) from the hydrogen fermentation broth of food wastes. Among tested operational variables, the volumetric ratio of the feed to the concentrate (VF:VC) was found to be the most critical for the fast and economic recovery of VFAs. Meanwhile, the increase in the applied voltage did not result any significant impact in the enhancement of VFA recovery due to the intrinsic resistance of anionic exchange membrane against to VFAs. The maximum VFAs purity of 96.2% was successfully achieved at the operational condition of VF:VC of 1:2 and 8 V with energy consumption of 0.395 kWh/kg-VFAs.

Recovery of mixed volatile fatty acids from anaerobically fermented organic wastes by vapor permeation membrane contactors

Volatile fatty acids (VFAs) are attractive compounds in renewable based bio-refinery industries and can be produced through anaerobic digestion of organic wastes. Nevertheless, the recovery of VFAs from anaerobically digested organic wastes is the bottleneck of the resource recovery. In this study, VFA recovery from synthetic VFA solutions and fermented organic wastes via air-filled and tertiary amine extractant-filled PTFE membranes through vapor pressure membrane contactors (VPMC) was investigated. Acetic acid was recovered with greater than 45% efficiency in all the fermented wastes. Recovery of propionic, butyric, valeric, and caproic acids through trioctylamine-filled PTFE membrane was greater than 86% and 95% from landfill leachate and fermentation broth of anaerobically digested organic waste, respectively. This study reveals that VFA separation can be effectively achieved via economic and environmental friendly VPMC system and the process is implementable as it can be coupled to a fermentation process to prevent inhibition and to recover VFAs.

Recovery of Volatile Fatty Acids from Fermented Wastewater by Adsorption.

Separation of volatile fatty acids (VFAs) from fermented wastewater is challenging, due to low VFA concentrations in mineral-rich streams. As a result, separation capacity and selectivity with traditional solvents and adsorbents are both compromised. In this study, using a complex artificial model solution mimicking real fermented wastewaters, it is shown that a simple and robust adsorption-based separation technique can retain a remarkable capacity and selectivity for VFAs. Four types of polystyrene-divinylbenzene-based resins (primary, secondary, and tertiary amine-functionalized, and nonfunctionalized) were examined as the adsorbents. The presence of chloride, sulfate, and phosphate salts resulted in coadsorption of their acidic forms HCl, H2SO4, and H3PO4 on amine-functionalized adsorbents, and severely reduced the VFA capacity. With the nonfunctionalized adsorbent, almost no mineral acid coadsorption was observed. This together with a high total VFA capacity of up to 76 g/kg in equilibrium with the model solution containing a total VFA concentration of 1 wt % resulted in a very high selectivity for the VFAs. Nitrogen-stripping with various temperature profiles was applied to regenerate the adsorbent, and study the potential for fractionation of the VFAs during regeneration. Butyric acid (HBu) was obtained in mole fractions of up to 0.8 using a stepwise increase in the stripping temperature from 25 °C via 120 to 200 °C. During four successive adsorption–regeneration cycles, no reduction in the adsorption capacity was observed.

Recovery of volatile fatty acids (VFA) from complex waste effluents using membranes

Waste effluents from anaerobic digesters of agricultural waste were treated with a range of membranes, including microfiltration and nanofiltration (NF), to concentrate volatile fatty acids (VFA). Microfiltration was applied successfully to produce sterile, particle-free solutions with a VFA concentration of 21.08 mM of acetic acid and 15.81 mM of butyric acid. These were further treated using a variety of NF membranes: NF270 (Dow Chemicals, USA), HL, DL, DK (Osmonics, USA) and LF10 (Nitto Denko, Japan), achieving retention ratios of up to 75%, and giving retentates of up to 53.94 mM of acetate and 28.38 mM of butyrate. DK and NF270 membranes were identified as the best candidates for VFA separation and concentration from these multicomponent effluents, both in terms of retention and permeate flux. When the effluents are adjusted to alkali conditions, the highest productivity, retention and flux were achieved at pH 7. At higher pH there was a significant reduction in flux.

Online δ13C analysis of volatile fatty acids in sediment/porewater systems by liquid chromatography-isotope ratio mass spectrometry

Volatile fatty acids (VFAs) are central intermediates of anaerobic metabolism and present in aquatic environments such as marine sediments. Conceptually, the isotopic composition of volatile fatty acids is presumed to be sensitive to the specific biogeochemical processes involved in their production and consumption. However, due to generally low environmental concentrations, our knowledge on isotopic variability of VFAs is limited. We report the development and application of a new protocol for compound-specific carbon isotopic analysis of VFAs in marine porewaters and other aqueous liquids. This new protocol involves reversed-phase separation of volatile fatty acids with an aqueous mobile phase by high performance liquid chromatography (HPLC) combined with chemical oxidation of the effluents by the FinniganTM LC IsoLink interface (Krummen et al. 2004) and subsequent online transfer of the resulting CO2 into an isotope ratio mass spectrometer. We obtained reproducible and accurate results for pure Na-acetate dissolved in artificial seawater at concentrations as low as 2 µM, whereas minimum concentrations in marine porewaters were 10 µM. Our technique extends the previously accessible concentration range and the fully automated online operation allows for systematic analysis of large sample sets. These technical improvements make carbon isotopic analysis of selected VFAs a realistic perspective for many sedimentary environments. Our initial survey of acetate in porewaters and fluids obtained from incubations of marine sediments has revealed an unexpectedly large range of isotopic compositions from −5‰ to −85‰ and provides strong support for process-specific information encoded in the isotopic compositions of VFAs.