Medium Chain Carboxylic Acids Production Research Articles

Single- vs. two-stage fermentation of an organic fraction of municipal solid waste for an enhanced medium chain carboxylic acids production − The impact of different pH and temperature

Single-stage fermentation was characterized by low medium chain carboxylic acids concentrations and different mesophilic temperatures had little effect on the process performance, whereas thermophilic conditions and pH 5.5 led to lactate and ethanol accumulation. Two-stage fermentation enabled almost twofold increase in the caproate productivity, that reached 0.8 g/L-d (1.7 ± 0.1 gCOD/L-d) with a caproate concentration of 4.0 g/L (8.4 gCOD/L) at specificity of 37 % and led to a reduced release of carbon dioxide. Under pH 6.5 and temperature of 37°C the production of medium chain carboxylic acids required higher concentrations of ethanol. Number of reads annotated to fatty acid biosynthesis pathway exceeded the number of sequences assigned to the reverse β-oxidation pathway. Core microorganisms encoding these pathways belonged to Caproiciproducens, Caproicibacterium and Clostridium. This study provides a valuable insight for valorisation of organic fraction of municipal solid waste into carboxylates in a single- and two-stage systems.

Comprehensive comparative study on n-caproate production by Clostridium kluyveri: batch vs. continuous operation modes

Recently, there has been notable interest in researching and industrially producing medium-chain carboxylic acids (MCCAs) like n-caproate and n-caprylate via chain elongation process. This study presents a comprehensive assessment of the behavior and MCCA production profiles of Clostridium kluyveri in batch and continuous modes, at different ethanol:acetate molar ratios (1.5:1, 3.5:1 and 5.5:1). The highest n-caproate concentration, 12.9 ± 0.67 g/L (92.9 ± 1.39 % MCCA selectivity), was achieved in batch mode at a 3.5:1 ratio. Interestingly, higher ratios favored batch mode selectivity over continuous mode when this was equal or higher to 3.5:1. Steady state operation yielded the highest n-caproate (9.5 ± 0.13 g/L) and n-caprylate (0.35 ± 0.020 g/L) concentrations at the 3.5:1 ratio. Increased ethanol:acetate ratios led to a higher excessive ethanol oxidation (EEO) in both operational modes, potentially limiting n-caproate production and selectivity, especially at the 5.5:1 ratio. Overall, this study reports the efficient MCCA production of both batch and continuous modes by C. kluyveri.

Nano zero valent iron stimulated acetaldehyde oxidation, electron transfer, and RBO pathway for enhanced medium-chain carboxylic acids production

Nano zero-valent iron (NZVI) has been shown to effectively enhance the chain elongation (CE) process, addressing the issue of limited yield of medium-chain carboxylic acids (MCCA) from organic wastewater. However, the specific impact of NZVI on the metabolism of CE bacteria (CEB) is not well understood. In this study, it was aimed to investigate the mechanism by which an optimal concentration of NZVI influences CE metabolism, particularly in relation to ethanol oxidation, electron transfer, and MCCA synthesis. This was achieved through single-factor influence experiments and metagenomic analysis. The results showed that the addition of 1 g/gVSS NZVI achieved the highest MCCA yield (n-caproic acid + n-octanoic acid) at 2.02 g COD/L, which was 4.9 times higher than the control. This improvement in MCCA production induced by NZVI was attributed to several factors. Firstly, NZVI facilitated the oxidation of acetaldehyde, leading to its reduced accumulation in the system (from 18.4 % to 5.8 %), due to the optimized chemical environment created by NZVI corrosion, including near-neutral pH and a more reductive oxidation–reduction potential (ORP). Additionally, the inherent conductivity property of NZVI and the additional Fe ions released during corrosion improved the electron transfer efficiency between CEB. Lastly, both the composition of microbial communities and the abundance of unique enzyme genes confirmed the selective stimulation of NZVI on the reverse β-oxidation (RBO) pathway. These findings provide valuable insights into the role of NZVI in CEB metabolism and its potential application for enhancing MCCA production in CE bioreactors.

Optimisation of the Production of Bio-Based Basic Chemicals from Biogenic Secondary Waste Through Dispersion

Biogenic waste from waste treatment plants, also known as secondary waste, can be used to produce bio-based carboxylic acids. Conventionally, these are produced by chemically synthesis of petroleum-based raw materials or synthesis of natural oils (e.g. coconut or palm kernel oil). Using organic residues and waste materials in a cascade to produce bio-based products can contribute to the circular bioeconomy. In the biological treatment process for production of bio-based carboxylic acids, microorganisms that are already present in the secondary waste use ethanol to convert short-chain carboxylic acids (with one to three carbon atoms) into medium-chain carboxylic acids (with four to ten carbon atoms). During the treatment process, medium-chain carboxylic acids are separated from the secondary waste by using in-situ extraction (liquid-liquid extraction). In previous studies, bioreactors without a dispersing function were used on a laboratory scale. In order to optimise the production and extraction of the formed medium-chain carboxylic acids, the bioreactors should be upgraded with a device for dispersing the extraction solvent in the secondary waste. Dispersing can increase the surface area between the extraction solvent and the secondary waste and therefore also the ability to extract the medium-chain carboxylic acids. To evaluate the effects of dispersing on the production of bio-based carboxylic acids, the production and extraction rates of static bioreactors without dispersing are compared with those of dynamic bioreactors with dispersing on a laboratory scale. Leachate from a composting plant was used as secondary waste. According to the results of the current study, it can be confirmed that dispersion has a positive effect on the biological treatment process. In addition to the increased degradation of the nutrient ethanol, the production of medium-chain carboxylic acids in the secondary waste as well as the extracted medium-chain carboxylic acids could be increased by dispersing.

Influence of pH and temperature on the performance and microbial community during the production of medium-chain carboxylic acids using winery effluents as substrate.

Winery effluents containing high ethanol concentrations and diverse organic matter are ideal substrates for producing medium-chain carboxylic acids via fermentation and chain elongation. However, the process needs to be better understood. This study presents novel insights into the bioconversion mechanisms of medium-chain carboxylic acids by correlating fermentation and chain elongation kinetic profiles with the study of microbial communities at different pH (5 to 7) conditions and temperatures (30 to 40°C). It was found that high productivities of MCCA were obtained using a native culture and winery effluents as a natural substrate. Minor pH variations significantly affected the metabolic pathway of the microorganisms for MCCA production. The maximal productivities of hexanoic (715mg/L/d) and octanoic (350mg/L/d) acids were found at pH 6 and 35°C. Results evidence that the presence of Clostridium, Bacteroides, and Negativicutespromotes the high productions of MCCA. The formation of heptanoic acid was favor when Mogibacterium and Burkholderia were present.

Impact of Dispersing on the Production and Extraction of Bio-Based Basic Chemicals from Biogenic Secondary Waste

Abstract Biogenic waste from waste treatment plants, secondary waste, can be used to produce bio-based carboxylic acids, conventionally produced by chemical synthesis from petroleum-based feedstocks or by synthesis from natural oils. The cascading use of organic residues and wastes to produce bio-based products can contribute to the circular bioeconomy. In the process of biologically treating waste to produce bio-based carboxylic acids, microorganisms already present in the secondary waste use ethanol to convert short-chain into medium-chain carboxylic acids. The medium-chain carboxylic acids were separated from the secondary waste using in-situ extraction (liquid-liquid extraction). In previous studies, laboratory-scale bioreactors without a dispersing function were used. To optimise production and extraction of medium-chain carboxylic acids, the bioreactors were equipped with a device to disperse the extraction solvent in the secondary waste. By increasing the surface area between the phases, the ability to extract the medium-chain carboxylic acids was improved. The study aimed to evaluate the impact of this dispersing process. Production and extraction rates of static bioreactors without dispersing were compared to those of dynamic bioreactors with dispersing on a laboratory scale, using leachate from a composting plant as secondary waste. The results confirmed that dispersion has a positive effect on the process. Dispersing increased the reduction of the nutrient ethanol, the production of medium-chain carboxylic acids in the secondary waste and the extracted medium-chain carboxylic acids.

Bio-based production of medium-chain carboxylic acids from food waste and sludge without chemical addition: The pivotal role of mix ratio and pretreatment

Medium-chain carboxylates such as caproic acid, have a plethora of applications, ranging from food additives to bioplastics, and can be produced via microbial chain elongation (CE), a process that can be more sustainable than conventional production routes. During CE short fatty acids accept electrons from donors as lactate or ethanol elongating into medium-chain carboxylates with higher economic value and easier recoverability. Nowadays, waste activated sludge (WAS) and food waste (FW) are the most abundant waste steams generated in European cities impacting dramatically on environment, society, and economic sectors. A novel sustainable biotechnology is here proposed to produce marketable caproic acid from mixed WAS and FW with in-situ self-formed lactate without buffering agents addition. Different mix ratios between WAS and FW, and thermal pretreatment strategies were compared by fermentation batch tests. The production of lactate as electron donor (ED), together with acetate and butyrate, and hydrogen assured high production of caproate only in presence of thermal pretreated WAS, able to reduce the potential risk of lactate accumulation and drop in pH. The findings of this study demonstrate that the initial soluble carboydrate/protein ratio significantly affected the pH of the fermentation broth in the first hours of fermentation, and that only using FW and pretreated WAS mixed using a ratio of 60/40 in terms of volatile solids, CE pathway and lactate utilization as ED were promoted obtaining the highest percentage of caproate (about 21% of the total produced carboxylic acids; 2 gCOD/L).

Acidogenic fermentation of food waste to generate electron acceptors and donors towards medium-chain carboxylic acids production

This study investigated the optimum pH, temperature, and food-to-microorganisms (F/M) ratio for regulating the formation of electron acceptors and donors during acidogenic fermentation to facilitate medium-chain carboxylic acids (MCCAs) production from food waste. Mesophilic fermentation at pH 6 was optimal for producing mixed volatile fatty acids (719 ± 94 mg COD/g VS) as electron acceptors. Under mesophilic conditions, the F/M ratio (g VS/g VS) could be increased to 6 to generate 22 ± 2 g COD/L of electron acceptors alongside 2 ± 0 g COD/L of caproic acid. Thermophilic fermentation at pH 6 was the best condition for producing lactic acid as an electron donor. However, operating at F/M ratios above 3 g VS/g VS under thermophilic settings significantly reduced lactic acid yield. A preliminary techno-economic evaluation revealed that converting lactic acid and butyric acid generated during acidogenic fermentation to caproic acid was the most profitable food waste valorization scenario and could generate 442–468 €/t VS/y. The results presented in this study provide insights into how to tailor acidogenic fermentation reactions to desired intermediates and will help maximize MCCAs synthesis.

Efficient conversion of wine lees into medium-chain carboxylic acids by mixed culture using an in-line extraction system

This study evaluates a process to generate medium-chain carboxylic acids (MCCA) from wasted wine lees. The effect of pH, feeding mode, organic loading rate, and the in-line extraction of the acids on the MCCA production rate was evaluated. Both the electron donor (ethanol) and acceptor (acetate) were generated in situ from the waste. First, the reactor was operated as a sequencing batch reactor (SBR), and pH 5.5 and 5.2 were evaluated. The caproate productivity was ten times higher at pH 5.5 than at 5.2. An in-line extraction system was next implemented, and the operation as SBR and the continuous mode was studied. The continuous mode allowed an increase of the residual ethanol; however, the feeding with concentrated wine lees caused an acetate over-accumulation. Caprylate was produced and extracted over caproate (caprylate/caproate ratio of 1.2) by avoiding the bioreactor overload and keeping a low ethanol broth concentration. In conclusion, the maximal MCCA production rate (143.4 ± 14.8 mmol C/L-d) was obtained when the organic loading rate was gradually increased in the continuous operation; under such conditions, Eubacterium pyruvativorans predominated. The in-line extraction system allowed the production and recovery of MCCA.

Advances in understanding entire process of medium chain carboxylic acid production from organic wastes via chain elongation

Chain elongation is an environmentally friendly biological technology capable of converting organic wastes into medium chain carboxylic acids (MCCAs). This review aims to offer a comprehensive analysis of MCCA production from organic wastes via chain elongation. Seven kinds of organic wastes are introduced and classified as easily degradable and hardly degradable. Among them, food waste, fruit and vegetable waste are the most potential organic wastes for MCCA production. Combined pretreatment technologies should be encouraged for the pretreatment of hardly degradable organic wastes. Furthermore, the mechanisms during MCCA production are analyzed, and the key influencing factors are evaluated, which affect the MCCA production and chain elongation efficiency indirectly. Extracting MCCA simultaneously is the most important way to improve MCCA production efficiency, and technologies for sequentially extracting different kinds of MCCAs are recommended. Finally, some perspectives for future chain elongation researches are proposed to promote the large-scale application of chain elongation.

Preparation and Application of Carbon-Based Materials in the Production of Medium-Chain Carboxylic Acids by Anaerobic Digestion: A Review

The main purpose of this article is to explore the mechanism of action of carbon-based materials in the anaerobic digestion (AD) production of medium-chain carboxylic acids (MCCA). Currently, there are various methods to increase production, but there is no review on how carbon-based materials improve MCCA. This paper first introduced the chain elongation (CE) technology, focusing on the factors affecting the production of MCCA by AD, such as pH, temperature, the ratio of electron donor (ED) to an electron acceptor (EA), substrate type, and other related factors. This article introduces the preparation and characteristics of carbon-based materials, as well as the effect and mechanism of adding carbon-based materials to AD acid production. Finally, the shortcomings of the current research were pointed out, and future research directions were prospected, aiming to provide a reference for improving the efficiency of AD of MCCA using carbon-based materials.

Experimental evaluation of temperature, nutrients, and initial concentration on medium-chain carboxylic acids production from winery wastes.

In the wine industry, grape processing is accompanied by waste generation, such as grape stalks, winery wastewater, and grape pomace (GP). GP can be used to produce value-added compounds such as medium-chain carboxylic acids (MCCA). This work aimed to determine the operational conditions (temperature, addition of nutrients, and initial waste concentration) to improve MCCA production using waste GP from the winery industry as a substrate. The electron donor (ethanol) and electron acceptor (acetate) were directly generated from the GP and consecutively used to produce MCCA. The treatment with high concentration, temperature, and nutrient addition promotes caproic acid's maximal yield and concentration (0.11 ± 0.02 g MCCA/g TS). Nutrients' presence and temperature significantly affected electron acceptor production. The addition of nutrients and 30 °C leads to elevated acetate production. However, at 37 °C, butyrate and MCCA were mainly produced without adding nutrients, and high ethanol consumption was observed. A higher metabolic diversification was observed at 37 °C than at 30 °C. Temperature and nutrient availability significantly affected the metabolic pathway and the type of carboxylic acid produced.

Ferric oxide stimulates medium-chain carboxylic acids synthesis from waste activated sludge via ethanol-driven chain elongation: Mechanisms and implications

Nowadays, conductive iron-containing materials (i.e., Fe3O4 and zerovalent iron) have attracted greatly attention in improving medium-chain carboxylic acids (MCCA) from waste activated sludge (WAS). However, the feasibility and mechanism of semi-conductive iron oxide, i.e., ferric oxide (Fe2O3), in stimulating MCCA synthesis from WAS via ethanol-driven chain elongation (CE) has been unclear. Therefore, this work is aimed to fill up the knowledge gap. Results showed that the MCCA yield in the Fe2O3-supplemented fermenter attained at 9162 mg COD/L (i.e., 6268 mg COD/L caproate and 2895 mg COD/L caprylate), which was 2.4 times that of the control system. Kinetic analysis proved that Fe2O3 enhanced both the potential and rate of MCCA synthesis. Mechanism analysis indicated that Fe2O3 facilitated the individual steps for MCCA production, i.e., hydrolysis, acidification and CE. Further investigation disclosed that the dissimilatory iron reduction (DIR) induced by Fe2O3 corrosion and released ferrous ions improved enzymes activities of hydrolysis and acidification, while the promotion of CE was mainly ascribed to increased electron transfer efficiency by crystalline Fe2O3. Further, Fe2O3 promotes electron transfer through several mechanisms, including stimulating extracellular polymeric substance (EPS) excretion, increasing EPS electroactivity, and enhancing electron transport system activity. Microbial analysis revealed that Fe2O3 induced microflora structure shifting towards substrates transformation, iron reduction and MCCA generation, and up-regulated the key enzymes in CE pathways. This work provides an efficient strategy for MCCA generation and WAS management.

Prediction and optimization of medium-chain carboxylic acids production from food waste using machine learning models

Machine learning models were developed in this study to predict and optimize the medium-chain carbolic acids (MCCAs) production from food waste. All three selected prediction algorithms achieved decent performance (accuracy > 0.85, R2 > 0.707). Three optimization algorithms were applied for MCCA production optimization based on the prediction algorithms. The maximum MCCA production rate (0.68 g chemical oxygen demand per liter per day) was achieved by simulated annealing coupled with random forest under the optimal conditions of pH 8.3, temperature 50 °C, retention time 4 days, loading rate 15.8 g volatile solid per liter per day, and inoculum to food waste ratio 70:30 with semi-continuous mode. Further experiments validated (18 % error) that the MCCA production rate was 113 % higher than the highest production rate of current lab experiments and 60 % higher than the statistical optimization using response surface methodology. This study demonstrates the potential of using machine learning for MCCA production prediction and optimization.

Impacts of 2-bromoethanesulfonic sodium on methanogenesis: Methanogen metabolism and community structure

Production of medium-chain carboxylic acids (MCCAs) by chain elongation (CE) presents a competitive alternative to conventional products of methane in anaerobic digestion treating organic waste streams, considering energy recovery, economic, and environmental profits. However, the system stability and performance largely rely on the selective suppression of methanogens while stimulation of CE bacteria. Commercial inhibitors such as 2-bromoethanesulfonic sodium (BES) was shown to be effective, but controversial conclusions exist on its inhibition characteristics and the inhibition mechanism remains unclear. Therefore, this study systematically investigated the responses of methanogenesis in granular sludge to various BES levels, focusing on methane production, methanogenic pathway, dynamic populations, electron transport and energy metabolism. Results showed that compared with the control, 3.0 g/L BES was sufficient to induce a 72.9% reduced level on accumulative methane production by the end of 4 cycles (28 days), which was likely to be attributed to the significantly suppressed metabolic pathways and intracellular regulations. Specifically, BES suppressed the electron transport via unproper electron carriers and reduced electron amount as indicated by the decreased level of enzymes and genes involved such as coenzyme F420, CO dehydrogenase and NADH:ubiquinone reductase (H+-translocating). Moreover, BES regulated the intracellular energy metabolism, leading to the impeded ATP synthesis but enhanced ATP consumption as evidenced by the variations on the activity or abundance of acetate kinase, A1Ao-ATP synthase, nitrogenase and ATP citrate synthase. Additionally, BES enriched hydrogenotrophic methanogenesis over acetoclastic one as supported by variations on the archaeal community structures and regulations of differentially expressed genes involved. Moreover, BES also reduced the contents of both protein and carbohydrate in extracellular polymeric substances (EPS). This study is expected to enhance understanding of BES contribution to methanogenesis inhibition but MCCAs production in CE bioreactors.

Production of medium-chain carboxylic acids using sewage sludge pretreated by combined Fenton and persulfate oxidation

Medium chain carboxylates (MCCs) production from sewage sludge (SS) is an economically and environmentally feasible technology for recovering value-added chemicals from SS. To improve MCCs production from SS, Fe (II)-mediated advanced oxidation processes (AOPs) including Fenton oxidation (FO), persulfate oxidation (PO), and combined Fenton-persulfate oxidation (CFP) were adopted to examine their effect on fermentation. Highest total MCCs concentration of 3445.85 mg COD/L was achieved in CFP treated group, followed by PO treated group (2678.78 mg COD/L), control group (2367.72 mg COD/L) and FO treated group (2294.14 mg COD/L). MCCs produced in all groups were dominated by caproate, and all three AOPs treatment promoted longer-chain MCCs (i.e. heptylate and caprylate) production. Microbial analysis showed that genus Romboutsia, Paraclostridium, Clostridium_sensu_stricto_1, norank_f_Anaerolineaceae and Acetobacterium that were positively correlated with MCCs production were significantly enriched in CFP treated group, which contributed to the highest MCCs production in CFP treated group. The functional enzymes analysis showed that both PO and CFO treatment promoted MCCs production by strengthening the fatty acid biosynthesis pathway during the chain elongation (CE) process.

Produce individual medium chain carboxylic acids (MCCA) from swine manure: Performance evaluation and economic analysis

Environmental issues caused by untreated animal manure require the development of resource recovery from waste through a circular economy approach. Producing medium chain carboxylic acids (MCCA) with higher value than biogas from manure has become promising. The objective of this study was to develop an effective individual MCCA produce process utilizing manure. In this study, animal manure was firstly anaerobic fermentation into short chain fatty acids (SCFA), then acidified manure and ethanol were fed into the chain elongation reactor with gradually increasing the organic loading rate (OLR) from 7.0 to 18.5 gCOD/L/d, and the mixed MCCA was separated individually via a fractional distillation process. The SCFA fermentation occurred mainly at the first 10 days, and the optimum concentrations of SCFA for treatments at 2 %VS, 4 %VS and 6 %VS were 6.58, 10.40 and 14.10 g/L, respectively. For the chain elongation reactor, the maximum concentrations of n-caproate and n-caprylate were 10.25 and 0.63 g/L, respectively, which were comparable with that obtained from other complex wastes. Over 90% MCCA can be recovered from the fermentation broth via the optimized extractant of methyl tert-butyl ether (MTBE) and the fractional distillation system. Preliminary economic analysis shows that this MCCA production process presented a higher economic benefit (9.25 $/m3 manure) than traditional biogas production (2.65 $/m3 manure), making MCCA production from swine manure economically competitive. This work provides a new route for manure resource recovery besides the biogas process.

Lactate and Ethanol Chain Elongation in the Presence of Lactose: Insight into Product Selectivity and Microbiome Composition

Organic waste streams rich in carbohydrates are costly to treat; however, they can be valorized to commodity chemicals such as medium-chain carboxylic acids (MCCAs), for example, caproic acid. Simple carbohydrates are easily fermentable, providing different intermediates for competing bacterial groups, which may lead to product diversification. For that reason, it is essential to understand the impact of sugar fermentation on chain elongation (CE) in the presence of key electron donors to control the biochemical pathways for MCCAs production. The research provides an insight into the impact of co-fermentation of lactose with lactate and ethanol as electron donors on CE and process selectivity in open culture fermentation. Co-fermentation of lactose with ethanol led mostly to acetogenesis and development of the Clostridium genus, while co-fermentation of lactose with solely lactate or with both electron donors activated the propionate production and diversified the process outcome to mix short- and medium-chain carboxylates. The highest caproate production efficiency and selectivity were achieved (53 and 65%, respectively) when lactose in the presence of lactate were used; CE improved with a higher initial lactose load. Interestingly, the microbiome was highly enriched in members of the Bacillaceae family, which was not reported before.

Production of Medium-Chain Carboxylic Acids by Co-Fermentation of Antibiotic Fermentation Residue with Fallen Ginkgo Leaves

Production of Medium-Chain Carboxylic Acids by Co-Fermentation of Antibiotic Fermentation Residue with Fallen Ginkgo Leaves

Prediction and Optimization of Medium-Chain Carboxylic Acids Production from Food Waste Using Machine Learning Models

Prediction and Optimization of Medium-Chain Carboxylic Acids Production from Food Waste Using Machine Learning Models