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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.


Pertraction correlation between the overall mass transfer coefficient and broth-recycle superficial velocity through the forward membrane module during Periods 2–5. The overall mass transfer coefficient (k) was plotted as function of the broth-recycle superficial velocity (u) for a lumped extraction of n-caprylic and n-caproic acid. These undissociated MCCAs were corrected by using g COD. The resulting k could be used in the undissociated MCCA extraction rate equation.
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Figure 4: Pertraction correlation between the overall mass transfer coefficient and broth-recycle superficial velocity through the forward membrane module during Periods 2–5. The overall mass transfer coefficient (k) was plotted as function of the broth-recycle superficial velocity (u) for a lumped extraction of n-caprylic and n-caproic acid. These undissociated MCCAs were corrected by using g COD. The resulting k could be used in the undissociated MCCA extraction rate equation.

Mentions: During Phase II (Periods 2–5; before we overloaded the reactor), we varied the broth-recycle rate through the forward membrane contactor (Atransfer = 1.4 m2, Across = 1.56 × 10-3 m2) within this biotic study to evaluate its impact on the undissociated MCCA extraction rates. Because we simultaneously extracted a mixture of undissociated MCCAs, we based the extraction rates, concentrations, and overall mass transfer coefficients on the lumped MCCA products of n-caprylic acid and n-caproic acid in g COD. We knew from previous work that increasing the recycle rates for the hydrophobic solvent or the alkaline extraction solution through the membrane contactors did not improve the undissociated MCCA extraction rates. By varying the broth-recycle rates, we confirmed a fundamental relationship that governs undissociated MCCA extraction rates: the broth-recycle superficial velocity (u) through the forward membrane contactor was directly proportional to the overall mass transfer coefficient (k) (Figure 4). The recycle superficial velocity (u) is the speed at which bioreactor broth flows past the membrane surface, and it is known that higher speeds increase turbulence and decrease resistance to MCCA transfer across the membrane (i.e., turbulence enhances extraction) (Wickramasinghe et al., 1992). Therefore, for an equivalent membrane surface area (Atransfer) and undissociated MCCA concentration gradient (ΔCMCCA) (Figure 4), this relationship suggests that higher broth-recycle rates would improve undissociated MCCA extraction rates. Previously, an abiotic n-caproic acid extraction study employed a larger forward membrane contactor (Atransfer = 8.1 m2 and Across = 6.09 × 10-3 m2) and also established a linear correlation between the superficial velocity and the overall mass transfer coefficient (Kucek et al., 2016b). We observed a similar correlation for the lumped n-caprylic acid and n-caproic acid overall mass transfer coefficient under biotic conditions when compared to only n-caproic acid extraction under abiotic conditions (all carboxylic acids were corrected for reduced equivalents [g COD]) (Supplementary Figure S1). This indicates that the recycle superficial velocity (u) is directly proportional to the overall mass transfer coefficient (k) for Membrana Liqui-Cel X50 membrane contactors, regardless of their size.


Waste Conversion into n -Caprylate and n -Caproate: Resource Recovery from Wine Lees Using Anaerobic Reactor Microbiomes and In-line Extraction
Pertraction correlation between the overall mass transfer coefficient and broth-recycle superficial velocity through the forward membrane module during Periods 2–5. The overall mass transfer coefficient (k) was plotted as function of the broth-recycle superficial velocity (u) for a lumped extraction of n-caprylic and n-caproic acid. These undissociated MCCAs were corrected by using g COD. The resulting k could be used in the undissociated MCCA extraction rate equation.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 4: Pertraction correlation between the overall mass transfer coefficient and broth-recycle superficial velocity through the forward membrane module during Periods 2–5. The overall mass transfer coefficient (k) was plotted as function of the broth-recycle superficial velocity (u) for a lumped extraction of n-caprylic and n-caproic acid. These undissociated MCCAs were corrected by using g COD. The resulting k could be used in the undissociated MCCA extraction rate equation.
Mentions: During Phase II (Periods 2–5; before we overloaded the reactor), we varied the broth-recycle rate through the forward membrane contactor (Atransfer = 1.4 m2, Across = 1.56 × 10-3 m2) within this biotic study to evaluate its impact on the undissociated MCCA extraction rates. Because we simultaneously extracted a mixture of undissociated MCCAs, we based the extraction rates, concentrations, and overall mass transfer coefficients on the lumped MCCA products of n-caprylic acid and n-caproic acid in g COD. We knew from previous work that increasing the recycle rates for the hydrophobic solvent or the alkaline extraction solution through the membrane contactors did not improve the undissociated MCCA extraction rates. By varying the broth-recycle rates, we confirmed a fundamental relationship that governs undissociated MCCA extraction rates: the broth-recycle superficial velocity (u) through the forward membrane contactor was directly proportional to the overall mass transfer coefficient (k) (Figure 4). The recycle superficial velocity (u) is the speed at which bioreactor broth flows past the membrane surface, and it is known that higher speeds increase turbulence and decrease resistance to MCCA transfer across the membrane (i.e., turbulence enhances extraction) (Wickramasinghe et al., 1992). Therefore, for an equivalent membrane surface area (Atransfer) and undissociated MCCA concentration gradient (ΔCMCCA) (Figure 4), this relationship suggests that higher broth-recycle rates would improve undissociated MCCA extraction rates. Previously, an abiotic n-caproic acid extraction study employed a larger forward membrane contactor (Atransfer = 8.1 m2 and Across = 6.09 × 10-3 m2) and also established a linear correlation between the superficial velocity and the overall mass transfer coefficient (Kucek et al., 2016b). We observed a similar correlation for the lumped n-caprylic acid and n-caproic acid overall mass transfer coefficient under biotic conditions when compared to only n-caproic acid extraction under abiotic conditions (all carboxylic acids were corrected for reduced equivalents [g COD]) (Supplementary Figure S1). This indicates that the recycle superficial velocity (u) is directly proportional to the overall mass transfer coefficient (k) for Membrana Liqui-Cel X50 membrane contactors, regardless of their size.

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.