Patterns of carbon flow from glucose to methane in a thermophilic anaerobic bioreactor

Abstract

[U‐14C]Glucose, added carrier‐free to sludge from a thermophilic anaerobic bioreactor being fed a lignocellulose waste, was rapidly turned over with less than one‐third of the original radiolabel remaining as glucose after 5 s of incubation. The primary labeled products found were [14C]acetate and 14CO2, which were in a ratio near 2:1. Further incubation resulted in the disappearance of [14C]acetate and the appearance of an equivalent amount of label as 14CH4 and 14CO2. No significant production of [14C]propionate, butyrate, lactate, or ethanol was detected from [14C]glucose, even if these potential intermediates (unlabeled) were added to the sludge at a concentration of 1 mM to trap any label entering their pools. Addition of 0.8 atm (80 kPa) of H2 to the headspace over sludge resulted in some accumulation of [14C]lactate and a corresponding decrease in [14C]acetate produced from [14C]glucose. Production of [14C]propionate, butyrate and ethanol were still not significant in the presence of H2. Incubation of sludge for 1 h in the presence of hydrogen resulted in increases in the lactate and formate concentrations, but not those of propionate, butyrate, or ethanol. These results demonstrate that glucose was metabolized directly to acetate, CO2, and H2 by the microbial populations in the bioreactor with little carbon from glucose flowing through other intermediates, indicating a high degree of coupling between glucose fermentation and hydrogen uptake. The short‐term response of these microbial populations to elevated H2 partial pressures was to increase lactate production.

Factors Influenced Continuous Dark Fermentative Hydrogen-Producing Reactor

“…The results were in accordance with S.H. Zinder's [27] . In general, the biomass yield of thermophilic bacteria is lower and this can be attributed to bacteria demanding more maintenance energy at higher temperatures.…”