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

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.

Temperature-Phased Conversion of Acid Whey Waste Into Medium-Chain Carboxylic Acids via Lactic Acid: No External e-Donor

“…26 One exception was with wine lees, which is settled wine (with yeast cells) that is left over in the fermentation tank, and which already contains ethanol up to 14%. 27 Even though hints existed that lactic acid instead of ethanol could be utilized during chain elongation to n-caproic acid with complex feedstocks and microbiomes, [28][29][30] feeding solely lactic acid to produce n-caproic acid at production rates of up to 160 mmol L À1 day À1 proved that it was indeed possible. 10,11 Not many real waste streams exist with sufficiently high substrate fractions of lactic acid to primarily produce MCCAs.…”

Metatranscriptomic and thermodynamic insights into medium-chain fatty acid production using an anaerobic microbiome

“…In a system producing MCFA using thin stillage produced from corn ethanol, Lactobacillus were enriched alongside Megasphaera , a known MCFA-producing Firmicute (10). In a reactor converting wastes from wine production to MCFA, Lactobacillus and Clostridia related to Ruminococcus were enriched (9). In each case, a community containing carbohydrate fermenting organisms and potential MCFA producing organisms emerged.…”

“…Previous applications of the carboxylate platform have focused on converting organics from undistilled corn beer (5, 6), food (7, 8), winery residue (9), thin stillage from corn ethanol production (10), and lignocellulose-derived materials (11–13) to MCFA, and as we have shown for lignocellulosic biofuel production (4), one can anticipate economic benefits of converting organic residues from these industries into MCFA.…”

Enrichment and characterisation of ethanol chain elongating communities from natural and engineered environments

“…Most ethanol-chain elongation studies have been conducted at circumneutral pH, and result in Clostridium-dominated communities, often specifically enriched in C. kluyveri [24][25][26] . Only two studies have investigated the community structure at lower pH, both in reactors inoculated from the same system producing caproic acid from diluted corn-to-ethanol beer, and equipped with in-situ product extraction 7,27 . In a first study, a reactor coupled to in situ product extraction was operated at pH 5.5 for 186 days, fed with synthetic ethanol and acetate mixtures.…”