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Waste Conversion into n -Caprylate and n -Caproate: Resource Recovery from Wine Lees Using Anaerobic Reactor Microbiomes and In-line Extraction

View Article: PubMed Central - PubMed

ABSTRACT

To convert wastes into sustainable liquid fuels and chemicals, new resource recovery technologies are required. Chain elongation is a carboxylate-platform bioprocess that converts short-chain carboxylates (SCCs) (e.g., acetate [C2] and n-butyrate [C4]) into medium-chain carboxylates (MCCs) (e.g., n-caprylate [C8] and n-caproate [C6]) with hydrogen gas as a side product. Ethanol or another electron donor (e.g., lactate, carbohydrate) is required. Competitive MCC productivities, yields (product vs. substrate fed), and specificities (product vs. all products) were only achieved previously from an organic waste material when exogenous ethanol had been added. Here, we converted a real organic waste, which inherently contains ethanol, into MCCs with n-caprylate as the target product. We used wine lees, which consisted primarily of settled yeast cells and ethanol from wine fermentation, and produced MCCs with a reactor microbiome. We operated the bioreactor at a pH of 5.2 and with continuous in-line extraction and achieved a MCC productivity of 3.9 g COD/L-d at an organic loading rate of 5.8 g COD/L-d, resulting in a promising MCC yield of 67% and specificities of 36% for each n-caprylate and n-caproate (72% for both). Compared to all other studies that used complex organic substrates, we achieved the highest n-caprylate-to-ncaproate product ratio of 1.0 (COD basis), because we used increased broth-recycle rates through the forward membrane contactor, which improved in-line extraction rates. Increased recycle rates also allowed us to achieve the highest reported MCC production flux per membrane surface area thus far (20.1 g COD/m2-d). Through microbial community analyses, we determined that an operational taxonomic unit (OTU) for Bacteroides spp. was dominant and was positively correlated with increased MCC productivities. Our data also suggested that the microbiome may have been shaped for improved MCC production by the high broth-recycle rates. Comparable abiotic studies suggest that further increases in the broth-recycle rates could improve the overall mass transfer coefficient and its corresponding MCC production flux by almost 30 times beyond the maximum that we achieved. With improved in-line extraction, the chain-elongation biotechnology production platform offers new opportunities for resource recovery and sustainable production of liquid fuels and chemicals.

No MeSH data available.


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Production performance parameters for different recycle rates in the forward membrane module during Periods 2–5. The MCC productivity, undissociated MCCA extraction rate, MCC production flux, and undissociated MCCA extraction flux were plotted as a function of the recycle rate. The broth-recycle (flow) rate (bottom axis) and broth-recycle superficial velocity (top axis) are alternative ways to represent the same recycle rate. The square for the production rate represents the productivity (left axis) and production flux (right axis), while plus for the MCCA extraction rate represents the extraction rate (left axis) and extraction flux (right axis). A color gradient was used within the squares for the production rate to show the n-caprylate-to-n-caproate product ratio (green-to-purple, respectively), with blue representing a more equal mixture of these two products. A white font within the squares for the MCC production rate identifies the four different operating periods. Productivity uncertainty is represented by 95% confidence intervals.
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Figure 5: Production performance parameters for different recycle rates in the forward membrane module during Periods 2–5. The MCC productivity, undissociated MCCA extraction rate, MCC production flux, and undissociated MCCA extraction flux were plotted as a function of the recycle rate. The broth-recycle (flow) rate (bottom axis) and broth-recycle superficial velocity (top axis) are alternative ways to represent the same recycle rate. The square for the production rate represents the productivity (left axis) and production flux (right axis), while plus for the MCCA extraction rate represents the extraction rate (left axis) and extraction flux (right axis). A color gradient was used within the squares for the production rate to show the n-caprylate-to-n-caproate product ratio (green-to-purple, respectively), with blue representing a more equal mixture of these two products. A white font within the squares for the MCC production rate identifies the four different operating periods. Productivity uncertainty is represented by 95% confidence intervals.

Mentions: By increasing the broth-recycle rate for our bioreactor, we improved the undissociated MCCA extraction rates (MMCCA) and fluxes by an order of magnitude (Figure 5). The maximum recycle superficial velocity (u) that we applied was 207 m/d (k = 50 mm/d) (Figures 4 and 5). From several previous abiotic membrane-based extraction experiments, much higher superficial velocities were used, which led to improved overall mass transfer coefficients (Baudot et al., 2001; Schlosser et al., 2005) (Supplementary Figure S1). A maximum superficial velocity of 6,000 m/d (6.9 × 10-2 m/s) was employed in a previous study, which resulted in a mass transfer coefficient of ∼4,500 mm/d (Baudot et al., 2001). Our hollow-fiber membrane contactors are designed to accommodate shell-side superficial velocities of at least 10,000 m/d. Since the present study utilized a much lower superficial velocity (below 207 m/d), new experiments should be conducted to ascertain the maximum extraction fluxes at these drastically increased superficial velocities. If the correlation between the overall mass transfer coefficient and the superficial velocity remains linear (Figure 4), we anticipate that an overall mass transfer coefficient of more than 1,400 mm/d could be achieved at a superficial velocity of 6,000 m/d (Supplementary Figure S1). The resulting overall mass transfer coefficient would be almost 30 times larger than what we achieved in Period 4, which should lead to proportional increases in the corresponding MCCA extraction rates.


Waste Conversion into n -Caprylate and n -Caproate: Resource Recovery from Wine Lees Using Anaerobic Reactor Microbiomes and In-line Extraction
Production performance parameters for different recycle rates in the forward membrane module during Periods 2–5. The MCC productivity, undissociated MCCA extraction rate, MCC production flux, and undissociated MCCA extraction flux were plotted as a function of the recycle rate. The broth-recycle (flow) rate (bottom axis) and broth-recycle superficial velocity (top axis) are alternative ways to represent the same recycle rate. The square for the production rate represents the productivity (left axis) and production flux (right axis), while plus for the MCCA extraction rate represents the extraction rate (left axis) and extraction flux (right axis). A color gradient was used within the squares for the production rate to show the n-caprylate-to-n-caproate product ratio (green-to-purple, respectively), with blue representing a more equal mixture of these two products. A white font within the squares for the MCC production rate identifies the four different operating periods. Productivity uncertainty is represented by 95% confidence intervals.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121217&req=5

Figure 5: Production performance parameters for different recycle rates in the forward membrane module during Periods 2–5. The MCC productivity, undissociated MCCA extraction rate, MCC production flux, and undissociated MCCA extraction flux were plotted as a function of the recycle rate. The broth-recycle (flow) rate (bottom axis) and broth-recycle superficial velocity (top axis) are alternative ways to represent the same recycle rate. The square for the production rate represents the productivity (left axis) and production flux (right axis), while plus for the MCCA extraction rate represents the extraction rate (left axis) and extraction flux (right axis). A color gradient was used within the squares for the production rate to show the n-caprylate-to-n-caproate product ratio (green-to-purple, respectively), with blue representing a more equal mixture of these two products. A white font within the squares for the MCC production rate identifies the four different operating periods. Productivity uncertainty is represented by 95% confidence intervals.
Mentions: By increasing the broth-recycle rate for our bioreactor, we improved the undissociated MCCA extraction rates (MMCCA) and fluxes by an order of magnitude (Figure 5). The maximum recycle superficial velocity (u) that we applied was 207 m/d (k = 50 mm/d) (Figures 4 and 5). From several previous abiotic membrane-based extraction experiments, much higher superficial velocities were used, which led to improved overall mass transfer coefficients (Baudot et al., 2001; Schlosser et al., 2005) (Supplementary Figure S1). A maximum superficial velocity of 6,000 m/d (6.9 × 10-2 m/s) was employed in a previous study, which resulted in a mass transfer coefficient of ∼4,500 mm/d (Baudot et al., 2001). Our hollow-fiber membrane contactors are designed to accommodate shell-side superficial velocities of at least 10,000 m/d. Since the present study utilized a much lower superficial velocity (below 207 m/d), new experiments should be conducted to ascertain the maximum extraction fluxes at these drastically increased superficial velocities. If the correlation between the overall mass transfer coefficient and the superficial velocity remains linear (Figure 4), we anticipate that an overall mass transfer coefficient of more than 1,400 mm/d could be achieved at a superficial velocity of 6,000 m/d (Supplementary Figure S1). The resulting overall mass transfer coefficient would be almost 30 times larger than what we achieved in Period 4, which should lead to proportional increases in the corresponding MCCA extraction rates.

View Article: PubMed Central - PubMed

ABSTRACT

To convert wastes into sustainable liquid fuels and chemicals, new resource recovery technologies are required. Chain elongation is a carboxylate-platform bioprocess that converts short-chain carboxylates (SCCs) (e.g., acetate [C2] and n-butyrate [C4]) into medium-chain carboxylates (MCCs) (e.g., n-caprylate [C8] and n-caproate [C6]) with hydrogen gas as a side product. Ethanol or another electron donor (e.g., lactate, carbohydrate) is required. Competitive MCC productivities, yields (product vs. substrate fed), and specificities (product vs. all products) were only achieved previously from an organic waste material when exogenous ethanol had been added. Here, we converted a real organic waste, which inherently contains ethanol, into MCCs with n-caprylate as the target product. We used wine lees, which consisted primarily of settled yeast cells and ethanol from wine fermentation, and produced MCCs with a reactor microbiome. We operated the bioreactor at a pH of 5.2 and with continuous in-line extraction and achieved a MCC productivity of 3.9 g COD/L-d at an organic loading rate of 5.8 g COD/L-d, resulting in a promising MCC yield of 67% and specificities of 36% for each n-caprylate and n-caproate (72% for both). Compared to all other studies that used complex organic substrates, we achieved the highest n-caprylate-to-ncaproate product ratio of 1.0 (COD basis), because we used increased broth-recycle rates through the forward membrane contactor, which improved in-line extraction rates. Increased recycle rates also allowed us to achieve the highest reported MCC production flux per membrane surface area thus far (20.1 g COD/m2-d). Through microbial community analyses, we determined that an operational taxonomic unit (OTU) for Bacteroides spp. was dominant and was positively correlated with increased MCC productivities. Our data also suggested that the microbiome may have been shaped for improved MCC production by the high broth-recycle rates. Comparable abiotic studies suggest that further increases in the broth-recycle rates could improve the overall mass transfer coefficient and its corresponding MCC production flux by almost 30 times beyond the maximum that we achieved. With improved in-line extraction, the chain-elongation biotechnology production platform offers new opportunities for resource recovery and sustainable production of liquid fuels and chemicals.

No MeSH data available.


Related in: MedlinePlus