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.
Anaerobic
technologies have been proposed as a promising solution
to enhance bioenergy recovery and to transform a wastewater treatment
plant (WWTP) from an energy consumer to an energy exporter. However,
20–60% of the methane produced remains dissolved in the anaerobically
treated effluent, which is a potent greenhouse gas and is easily stripped
out in the aeration tank. This study aims to develop a solution using
dissolved methane to support denitrification, thus simultaneously
enhancing nitrogen removal and achieving beneficial use of dissolved
methane. By coupling anaerobic ammonium oxidation (anammox) with nitrite/nitrate-dependent
anaerobic methane oxidation (n-DAMO), up to 85% of dissolved methane
and more than 99% of nitrogen were removed in parallel in a biofilm
system. Mass balance was conducted during both long-term operation
and short-term batch tests, which indicated that n-DAMO bacteria and
n-DAMO archaea indeed contributed jointly to the methane removal.
The 16S rRNA gene amplicon sequencing further showed the co-presence
of n-DAMO bacteria and n-DAMO archaea, while anammox bacteria were
detected with a low relative abundance. This proposed technology can
potentially be applied to reduce the carbon footprint and to save
the organic carbon consumption in WWTPs.
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