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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.


Related in: MedlinePlus

Substrate conversion efficiencies and product yields for different operating and performance conditions during Period 5 (Phase II) and Periods 6–9 (Phase III). Substrate conversion efficiencies and undissociated n-caprylic acid concentrations were plotted as a function of the total organic and ethanol loading rates (A). Total substrate conversion efficiencies and MCC yields were each plotted as a function of the residual concentration of undissociated n-caprylic acid in the bioreactor broth (B). A color gradient was used within the squares for the MCC yield 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 triangles for the non-ethanol substrate conversion efficiency and the total substrate conversion efficiency identifies the five different operating periods.
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Figure 3: Substrate conversion efficiencies and product yields for different operating and performance conditions during Period 5 (Phase II) and Periods 6–9 (Phase III). Substrate conversion efficiencies and undissociated n-caprylic acid concentrations were plotted as a function of the total organic and ethanol loading rates (A). Total substrate conversion efficiencies and MCC yields were each plotted as a function of the residual concentration of undissociated n-caprylic acid in the bioreactor broth (B). A color gradient was used within the squares for the MCC yield 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 triangles for the non-ethanol substrate conversion efficiency and the total substrate conversion efficiency identifies the five different operating periods.

Mentions: During the study by Grootscholten et al. (2013a) with garden and food waste and during Period 8 of our study with wine lees waste (Phase III), the MCC yields were low due to overloading conditions (OLRs of 72.6 and 51.8 g COD/L-d, respectively). We had increased the OLR from ∼6 to 52 g COD/L-d (Period 5 to Period 8), but this large increase of 780% only led to marginally improved MCC productivities (<70%) (Figure 2A; Supplementary Table S2). It also led to increased production of reduced gases in the biogas (up to 0.6 g COD/L-d), but this constituted less than 10% of the overall COD balance. The maximum hydrogen concentration in the biogas was 45% in Period 9 (Supplementary Table S2). Overloaded conditions with synthetic lactate (Kucek et al., 2016a) and ethanol (Kucek et al., 2016b) also increased the production of reduced gases. In the present study, product inhibition had restrained further increases in MCC productivities. When the OLR was increased, we observed increased concentrations of undissociated n-caprylic acid in the bioreactor broth (Figure 2B), which are known to inhibit microbial activity (Butkus et al., 2011). Importantly, average undissociated n-caprylic acid (C8) concentrations increased to 0.06–0.11 g COD/L (0.17–0.31 mM) during both the batch phase (Phase I) and in the phase of continuous substrate addition (Phase III) (Figure 2B; Supplementary Table S2). Here, the maximum undissociated n-caprylic acid (C8) concentration was 0.11 g COD/L (6% of its maximum solubility), which was only surpassed by our other published study (0.22 g COD/L) (Kucek et al., 2016b) wherein the undissociated n-caprylic acid concentration also led to product inhibition. Meanwhile, average undissociated n-caproic acid (C6) concentrations remained ∼10-fold lower than 2.7 g COD/L (10.5 mM) that had been observed to inhibit reactor microbiomes (Ge et al., 2015). In addition, the accumulated concentrations of ethanol during our study (∼10 g COD/L; ∼100 mM) were also lower than reported inhibitory concentrations for microbiomes and C. kluyveri (20–40 g COD/L; ∼200–400 mM) (Weimer and Stevenson, 2012; Angenent et al., 2016; Kucek et al., 2016b). Therefore, we postulate that these high levels of undissociated n-caprylic acid led to product inhibition, rather than inhibition from undissociated n-caproic acid or ethanol. Indeed, we found negative correlations between concentrations of undissociated n-caprylic acid in the broth and ethanol conversion efficiency (Figure 3A), overall substrate conversion (Figure 3B), and MCC yield (Figure 3B). To support chain elongation, in-line extraction can prevent undissociated MCCAs from accumulating to inhibitory levels in the bioreactor broth, which can otherwise hinder chain elongation pathways and thermodynamic feasibility.


Waste Conversion into n -Caprylate and n -Caproate: Resource Recovery from Wine Lees Using Anaerobic Reactor Microbiomes and In-line Extraction
Substrate conversion efficiencies and product yields for different operating and performance conditions during Period 5 (Phase II) and Periods 6–9 (Phase III). Substrate conversion efficiencies and undissociated n-caprylic acid concentrations were plotted as a function of the total organic and ethanol loading rates (A). Total substrate conversion efficiencies and MCC yields were each plotted as a function of the residual concentration of undissociated n-caprylic acid in the bioreactor broth (B). A color gradient was used within the squares for the MCC yield 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 triangles for the non-ethanol substrate conversion efficiency and the total substrate conversion efficiency identifies the five different operating periods.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
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Figure 3: Substrate conversion efficiencies and product yields for different operating and performance conditions during Period 5 (Phase II) and Periods 6–9 (Phase III). Substrate conversion efficiencies and undissociated n-caprylic acid concentrations were plotted as a function of the total organic and ethanol loading rates (A). Total substrate conversion efficiencies and MCC yields were each plotted as a function of the residual concentration of undissociated n-caprylic acid in the bioreactor broth (B). A color gradient was used within the squares for the MCC yield 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 triangles for the non-ethanol substrate conversion efficiency and the total substrate conversion efficiency identifies the five different operating periods.
Mentions: During the study by Grootscholten et al. (2013a) with garden and food waste and during Period 8 of our study with wine lees waste (Phase III), the MCC yields were low due to overloading conditions (OLRs of 72.6 and 51.8 g COD/L-d, respectively). We had increased the OLR from ∼6 to 52 g COD/L-d (Period 5 to Period 8), but this large increase of 780% only led to marginally improved MCC productivities (<70%) (Figure 2A; Supplementary Table S2). It also led to increased production of reduced gases in the biogas (up to 0.6 g COD/L-d), but this constituted less than 10% of the overall COD balance. The maximum hydrogen concentration in the biogas was 45% in Period 9 (Supplementary Table S2). Overloaded conditions with synthetic lactate (Kucek et al., 2016a) and ethanol (Kucek et al., 2016b) also increased the production of reduced gases. In the present study, product inhibition had restrained further increases in MCC productivities. When the OLR was increased, we observed increased concentrations of undissociated n-caprylic acid in the bioreactor broth (Figure 2B), which are known to inhibit microbial activity (Butkus et al., 2011). Importantly, average undissociated n-caprylic acid (C8) concentrations increased to 0.06–0.11 g COD/L (0.17–0.31 mM) during both the batch phase (Phase I) and in the phase of continuous substrate addition (Phase III) (Figure 2B; Supplementary Table S2). Here, the maximum undissociated n-caprylic acid (C8) concentration was 0.11 g COD/L (6% of its maximum solubility), which was only surpassed by our other published study (0.22 g COD/L) (Kucek et al., 2016b) wherein the undissociated n-caprylic acid concentration also led to product inhibition. Meanwhile, average undissociated n-caproic acid (C6) concentrations remained ∼10-fold lower than 2.7 g COD/L (10.5 mM) that had been observed to inhibit reactor microbiomes (Ge et al., 2015). In addition, the accumulated concentrations of ethanol during our study (∼10 g COD/L; ∼100 mM) were also lower than reported inhibitory concentrations for microbiomes and C. kluyveri (20–40 g COD/L; ∼200–400 mM) (Weimer and Stevenson, 2012; Angenent et al., 2016; Kucek et al., 2016b). Therefore, we postulate that these high levels of undissociated n-caprylic acid led to product inhibition, rather than inhibition from undissociated n-caproic acid or ethanol. Indeed, we found negative correlations between concentrations of undissociated n-caprylic acid in the broth and ethanol conversion efficiency (Figure 3A), overall substrate conversion (Figure 3B), and MCC yield (Figure 3B). To support chain elongation, in-line extraction can prevent undissociated MCCAs from accumulating to inhibitory levels in the bioreactor broth, which can otherwise hinder chain elongation pathways and thermodynamic feasibility.

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