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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.

HighlightsA pilot microbial electrolysis cell (MEC) was tested for H2O2 production.Passive air diffusion to a carbon electrode successfully produced H2O2.The highest H2O2 conversion was only 7.2%.Catholyte pH over 11 can mitigate H2O2 loss in MECs.

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Bio-capacitive coulombs were tested for determination of the 5-day biochemical oxygen demand (BOD 5 ) using a dual-chamber microbial electrochemical cell (MxC) operated at charging (open circuit) and discharging (close circuit) conditions. For acetate medium, the cumulative coulombs charged in a capacitive biofilm anode (open circuit) were well correlated with BOD concentrations (R 2 ~ 0.9). The maximum detectable BOD 5 concentration with the biocapacitance MxC was close to 250 mg/L, and the cumulative coulombs were saturated for above the maximum BOD 5 concentration (Monod pattern). The bio-capacitance MxC sensor consistently showed high linearity between the cumulative coulombs and BOD 5 concentrations for domestic wastewater influent (R 2 = 0.93-0.99), despite of 1min charging. High correlation between the coulombs and BOD 5 concentration was also obtained for wastewater effluent at 1 min charging, which indicates that the bio-capacitance MxC sensor can semi-continuously measure BOD 5 concentration in wastewater at every 2 min (1min charging and 1min discharging).