Abstract

When a mixed-culture microbial electrolysis cell (MEC) is fed with a fermentable substrate, such as glucose, a significant fraction of the substrate’s electrons ends up as methane (CH4) through hydrogenotrophic methanogenesis, an outcome that is undesired. Here, we show that free ammonia-nitrogen (FAN, which is NH3) altered the glucose fermentation pathways in batch MECs, minimizing the production of H2, the “fuel” for hydrogenotrophic methanogens. Consequently, the Coulombic efficiency (CE) increased: 57% for 0.02 g of FAN/L of fed-MEC, compared to 76% for 0.18 g of FAN/L of fed-MECs and 62% for 0.37 g of FAN/L of fed-MECs. Increasing the FAN concentration was associated with the accumulation of higher organic acids (e.g., lactate, iso-butyrate, and propionate), which was accompanied by increasing relative abundances of phylotypes that are most closely related to anode respiration (Geobacteraceae), lactic-acid production (Lactobacillales), and syntrophic acetate oxidation (Clostridiaceae). Thus, the microbial community established syntrophic relationships among glucose fermenters, acetogens, and anode-respiring bacteria (ARB). The archaeal population of the MEC fed 0.02 g FAN/L was dominated by Methanobacterium, but 0.18 and 0.37 g FAN/L led to Methanobrevibacter becoming the most abundant species. Our results provide insight into a way to decrease CH4 production and increase CE using FAN to control the fermentation step, instead of inhibiting methanogens using expensive or toxic chemical inhibitors, such as 2-bromoethanesulfonic acid.

Original languageEnglish (US)
Pages (from-to)13461-13470
Number of pages10
JournalEnvironmental Science and Technology
Volume51
Issue number22
DOIs
StatePublished - Jan 1 2017

Fingerprint

Regenerative fuel cells
Ammonia
Fermentation
Methanogens
fermentation
electrokinesis
glucose
ammonia
Glucose
Lactic Acid
Anodes
Fermenters
substrate
Butyrates
Poisons
acid
Organic acids
Methane
Propionates
methanogenesis

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

Cite this

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title = "Changes in glucose fermentation pathways as a response to the free ammonia concentration in microbial electrolysis cells",
abstract = "When a mixed-culture microbial electrolysis cell (MEC) is fed with a fermentable substrate, such as glucose, a significant fraction of the substrate’s electrons ends up as methane (CH4) through hydrogenotrophic methanogenesis, an outcome that is undesired. Here, we show that free ammonia-nitrogen (FAN, which is NH3) altered the glucose fermentation pathways in batch MECs, minimizing the production of H2, the “fuel” for hydrogenotrophic methanogens. Consequently, the Coulombic efficiency (CE) increased: 57{\%} for 0.02 g of FAN/L of fed-MEC, compared to 76{\%} for 0.18 g of FAN/L of fed-MECs and 62{\%} for 0.37 g of FAN/L of fed-MECs. Increasing the FAN concentration was associated with the accumulation of higher organic acids (e.g., lactate, iso-butyrate, and propionate), which was accompanied by increasing relative abundances of phylotypes that are most closely related to anode respiration (Geobacteraceae), lactic-acid production (Lactobacillales), and syntrophic acetate oxidation (Clostridiaceae). Thus, the microbial community established syntrophic relationships among glucose fermenters, acetogens, and anode-respiring bacteria (ARB). The archaeal population of the MEC fed 0.02 g FAN/L was dominated by Methanobacterium, but 0.18 and 0.37 g FAN/L led to Methanobrevibacter becoming the most abundant species. Our results provide insight into a way to decrease CH4 production and increase CE using FAN to control the fermentation step, instead of inhibiting methanogens using expensive or toxic chemical inhibitors, such as 2-bromoethanesulfonic acid.",
author = "Mohamed Mahmoud and Cesar Torres and Bruce Rittmann",
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T1 - Changes in glucose fermentation pathways as a response to the free ammonia concentration in microbial electrolysis cells

AU - Mahmoud, Mohamed

AU - Torres, Cesar

AU - Rittmann, Bruce

PY - 2017/1/1

Y1 - 2017/1/1

N2 - When a mixed-culture microbial electrolysis cell (MEC) is fed with a fermentable substrate, such as glucose, a significant fraction of the substrate’s electrons ends up as methane (CH4) through hydrogenotrophic methanogenesis, an outcome that is undesired. Here, we show that free ammonia-nitrogen (FAN, which is NH3) altered the glucose fermentation pathways in batch MECs, minimizing the production of H2, the “fuel” for hydrogenotrophic methanogens. Consequently, the Coulombic efficiency (CE) increased: 57% for 0.02 g of FAN/L of fed-MEC, compared to 76% for 0.18 g of FAN/L of fed-MECs and 62% for 0.37 g of FAN/L of fed-MECs. Increasing the FAN concentration was associated with the accumulation of higher organic acids (e.g., lactate, iso-butyrate, and propionate), which was accompanied by increasing relative abundances of phylotypes that are most closely related to anode respiration (Geobacteraceae), lactic-acid production (Lactobacillales), and syntrophic acetate oxidation (Clostridiaceae). Thus, the microbial community established syntrophic relationships among glucose fermenters, acetogens, and anode-respiring bacteria (ARB). The archaeal population of the MEC fed 0.02 g FAN/L was dominated by Methanobacterium, but 0.18 and 0.37 g FAN/L led to Methanobrevibacter becoming the most abundant species. Our results provide insight into a way to decrease CH4 production and increase CE using FAN to control the fermentation step, instead of inhibiting methanogens using expensive or toxic chemical inhibitors, such as 2-bromoethanesulfonic acid.

AB - When a mixed-culture microbial electrolysis cell (MEC) is fed with a fermentable substrate, such as glucose, a significant fraction of the substrate’s electrons ends up as methane (CH4) through hydrogenotrophic methanogenesis, an outcome that is undesired. Here, we show that free ammonia-nitrogen (FAN, which is NH3) altered the glucose fermentation pathways in batch MECs, minimizing the production of H2, the “fuel” for hydrogenotrophic methanogens. Consequently, the Coulombic efficiency (CE) increased: 57% for 0.02 g of FAN/L of fed-MEC, compared to 76% for 0.18 g of FAN/L of fed-MECs and 62% for 0.37 g of FAN/L of fed-MECs. Increasing the FAN concentration was associated with the accumulation of higher organic acids (e.g., lactate, iso-butyrate, and propionate), which was accompanied by increasing relative abundances of phylotypes that are most closely related to anode respiration (Geobacteraceae), lactic-acid production (Lactobacillales), and syntrophic acetate oxidation (Clostridiaceae). Thus, the microbial community established syntrophic relationships among glucose fermenters, acetogens, and anode-respiring bacteria (ARB). The archaeal population of the MEC fed 0.02 g FAN/L was dominated by Methanobacterium, but 0.18 and 0.37 g FAN/L led to Methanobrevibacter becoming the most abundant species. Our results provide insight into a way to decrease CH4 production and increase CE using FAN to control the fermentation step, instead of inhibiting methanogens using expensive or toxic chemical inhibitors, such as 2-bromoethanesulfonic acid.

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