Journal
WATER RESEARCH
Volume 93, Issue -, Pages 163-171Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.watres.2016.02.018
Keywords
Lactate; n-Caproate; Carboxylate platform; Reactor microbiome; Acrylate pathway; Reverse beta-oxidation pathway
Funding
- NSF SusChEM Program [1336186]
- U.S. Army Research Laboratory
- U.S. Army Research Office [W911NF-12-1-0555]
- National Science Foundation (NSF) through the Graduate Research Fellowship Program (GRFP) [2014192568]
- Cornell University's graduate school
- Sloan Foundation
- Directorate For Engineering
- Div Of Chem, Bioeng, Env, & Transp Sys [1336186] Funding Source: National Science Foundation
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Conversion of lactate to n-caproate had been described for the type strain Megasphaera elsdenii in batch systems. Recently, investigators have also described production of n-caproate from endogenous or exogenous lactate with batch-fed reactor microbiome systems. However, no reports exist of lactate to n-caproate conversion within a continuously fed bioreactor. Since continuously fed systems are advantageous for biotechnology production platforms, our objective was to develop such a system. Here, we demonstrated continuous lactate to n-caproate conversion for more than 165 days. The volumetric n-caproate production rate (productivity) was improved when we decreased the operating pH from 5.5 to 5.0, and was again improved when we utilized in-line product recovery via pertraction (membrane based liquid liquid extraction). We observed a maximum n-caproate productivity of 6.9 g COD/L-d for a period of 17 days at an L-lactate loading rate of 9.1 g COD/L-d, representing the highest sustained lactate to n-caproate conversion rate ever reported. We had to manage two competing lactate conversion pathways: 1) the reverse beta-oxidation pathway to n-caproate; and 2) the acrylate pathway to propionate. We found that maintaining a low residual lactate concentration in the bioreactor broth was necessary to direct lactate conversion towards n-caproate instead of propionate. These findings provide a foundation for the development of new resource recovery processes to produce higher-value liquid products (e.g., n-caproate) from carbon-rich wastewaters containing lactate or lactate precursors (e.g., carbohydrates). (C) 2016 Elsevier Ltd. All rights reserved.
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