Contribution of Liquid/Gas Mass-Transfer Limitations to Dissolved Methane Oversaturation in Anaerobic Treatment of Dilute Wastewater

Abstract

The mechanisms controlling the accumulation of dissolved methane in anaerobic membrane bioreactors (AnMBRs) treating a synthetic dilute wastewater (a glucose medium) were assessed experimentally and theoretically. The AnMBR was maintained at a temperature of 24-26 °C as the organic loading rate increased from 0.39 to 1.1 kg COD/m(3)-d. The measured concentration of dissolved methane was consistently 2.2- to 2.5-fold larger than the concentration of dissolved methane at thermodynamic equilibrium with the measured CH4 partial pressure, and the fraction of dissolved methane was as high as 76% of the total methane produced. The low gas production rate in the AnMBR significantly slowed the mass transport of dissolved methane to the gas phase. Although the production rate of total methane increased linearly with the COD loading rate, the concentration of dissolved methane only slightly increased with an increasing organic loading rate, because the mass-transfer rate increased by almost 5-fold as the COD loading increased from 0.39 to 1.1 kg COD/m(3)-d. Thus, slow mass transport kinetics exacerbated the situation in which dissolved methane accounted for a substantial fraction of the total methane generated from the AnMBR.

Anaerobic membrane bioreactors for wastewater treatment: Challenges and opportunities

“…Which parameters mainly influence oversaturation of aqueous methane in liquid? Yeo et al (2015) developed an equation for dissolved methane concentration at a steady-state bioreactor.…”

“…The first issue is accumulation of dissolved methane in AnMBR permeates. Literature reported dissolved methane concentration ranges from 16 to 35.1 mg/L (Kim et al, 2011; Yeo et al, 2015; Yoo et al, 2012), indicating methane loss up to 63% in AnMBR systems. Methane loss as aqueous methane decreases economic return from reuse of methane gas, which indicates that the economic benefit in AnMBRs could be small; consequently energy neutrality could not be achieved.…”

Resource recovery from wastewater by anaerobic membrane bioreactors: Opportunities and challenges

“…During AnMBR treatment, the CH4 yield increases linearly with the organic loading rate (Yeo et al, 2015). Under an optimized condition, AnMBR can convert up to 98% of the influent COD into biogas, which is equivalent to seven times of the energy…”

Azo dye decolorization in an up-flow bioelectrochemical reactor with domestic wastewater as a cost-effective yet highly efficient electron donor source

“…The rate of CH 4 production in R DW was 0.29 ± 0.06 mmol l À1 influent (equal to 2.32 mmol electrons l À1 influent), which was much lower than that in R Glu (0.50 ± 0.07 mmol l À1 influent or 4.00 mmol electrons l À1 influent) and R Ac (1.26 ± 0.02 mmol l À1 influent or 10.08 mmol electrons l À1 influent). The dissolved CH 4 (Table 2) were estimated according to the Henry's law based on the CH 4 volume fraction in gas phases (Sander, 2015;Yeo et al, 2015) (details can be found in SI). In addition to methanogenesis, electrons can be also used to supporting bacteria growth.…”

“…COD consumptions and reductant usage ratios (RURs) of domestic wastewater, NaAc and glucose feeding BESs at different loading rates. (Sander, 2015;Yeo et al, 2015).…”