The bioconversion of methane to liquid chemicals has attracted much attention. However, the production rate reported to date has been far lower than what is required for economical viability. This is partly due to the low solubility of methane, the low mass transfer rate, and low microbial activities. This study demonstrates a production rate of close to 10 g of short-chain fatty acids (SCFAs) per liter per day with a mixed-culture biofilm growing in a membrane biofilm reactor (MBfR). Hollow fiber membranes were used both to deliver a high flux of methane and to provide a surface on which slow-growing microorganisms could form biofilms with intensified activities. The rate achieved is nearly 2 orders of magnitude higher than the highest SCFA production rate reported to date and is close to the rates required for practical applications (∼12−120 g L −1 day −1 ). The consortium in the biofilm was dominated by methanogens Methanosarcina and Methanobacterium and acid-producing bacteria Sporolactobacillus and Propionispora, suggesting likely roles of these organisms in the bioconversion of methane into SCFAs. This work shows a methane-based MBfR represents a promising technology for achieving high-rate production of chemicals from methane.
The
mainstream anaerobic ammonium oxidation (anammox) process provides
strong support to the on-going paradigm shift from energy-negative
to energy-neutral in wastewater treatment plants. However, the low
temperature (e.g., below 15 °C) represents one of the major challenges
for mainstream anammox in practice. In this study, a stable nitrogen
removal rate (0.13 kg m–3 day–1), together with a high-level effluent quality (<5.0 mg N L–1), was achieved in a lab-scale upflow membrane biofilm
reactor (MBfR) by coupling anammox with nitrite/nitrate-dependent
anaerobic methane oxidation (n-DAMO) microorganisms, at a temperature
as low as 10 °C. With the temperature being progressively decreased
from 25 to 10 °C, the total nitrogen removal efficiency was maintained
in the range of 90–94% at a constant hydraulic retention time
of 9 h. The impact of temperature on the biofilm system coupling anammox
and n-DAMO reactions increased at a lower temperature range with higher
Arrhenius coefficients. Additionally, 16S rRNA gene sequencing results
showed that anammox bacteria, n-DAMO bacteria, and n-DAMO archaea
jointly dominated the biofilm, and their respective abundances remained
relatively stable when the temperature was decreased. The major reason
for this temperature-tolerated performance is the overcapacity developed,
which is indicated by biofilm thickness measurements and mathematical
modeling. The stable performance obtained in this study shows promise
for the n-DAMO application in domestic wastewater.
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