Hydrogen peroxide production in a pilot-scale microbial electrolysis cell

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.btre.2018.e00276 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/A pilot-scale dual-chamber microbial electrolysis cell (MEC) equipped with a carbon gas-diffusion cathode was evaluated for H2O2 production using acetate medium as the electron donor. To assess the effect of cathodic pH on H2O2 yield, the MEC was tested with an anion exchange membrane (AEM) and a cation exchange membrane (CEM), respectively. The maximum current density reached 0.94–0.96 A/m2 in the MEC at applied voltage of 0.35–1.9 V, regardless of membranes. The highest H2O2 conversion efficiency was only 7.2 ± 0.09% for the CEM-MEC. This low conversion would be due to further H2O2 reduction to H2O on the cathode or H2O2 decomposition in bulk liquid. This low H2O2 conversion indicates that large-scale MECs are not ideal for production of concentrated H2O2 but could be useful for a sustainable in-situ oxidation process in wastewater treatment.Ontario Early Researcher Awar

Upflow anaerobic-microaerobic fixed biofilm reactor integrating methanogenesis with partial nitrification

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.cej.2018.05.013 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/An anaerobic-microaerobic fixed biofilm (AMFB) reactor, that integrates methanogenesis with partial nitrification within a single unit was investigated to achieve carbon removal simultaneously with ammonium oxidation in dilute wastewater. Membrane aeration was used for a controlled and efficient oxygen supply for partial nitrification and to prevent oxygen related inhibition of methanogens in the AMFB reactor. Removal of chemical oxygen demand (COD) and ammonium oxidation was first tested on synthetic wastewater, followed by domestic wastewater. The COD removal efficiency ranged between 92 and 99% on synthetic wastewater at hydraulic retention time (HRT) of 8–24 h. Nearly complete removal of biochemical oxygen demand (BOD5) was obtained for domestic wastewater. Influent COD was mainly removed by fermentation and methanogenesis, resulting in high methane yields of up to 0.33 LCH4 gCOD−1anaerobic. Ammonium oxidation efficiency of 69–86% was obtained. Microbial community analysis showed proliferation of fermenters and methanogens exclusively in the anaerobic section of the reactor, while aerobic heterotrophs and nitrifiers were mainly identified in the membrane aerated section. This study first proves that the single-stage AMFB reactor can treat municipal wastewater economically to meet the wastewater standards, although further research for improving water quality (e.g., denitrification) would be required.Natural Sciences and Engineering Research Council of Canada, Discovery Gran

Semi-continuous measurement of oxygen demand in wastewater using biofilm-capacitance

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.biteb.2018.08.009 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/Bio-capacitive coulombs were tested for determination of the 5-day biochemical oxygen demand (BOD5) 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 (R2 ~ 0.9). The maximum detectable BOD5 concentration with the bio-capacitance MxC was close to 250 mg/L, and the cumulative coulombs were saturated for above the maximum BOD5 concentration (Monod pattern). The bio-capacitance MxC sensor consistently showed high linearity between the cumulative coulombs and BOD5 concentrations for domestic wastewater influent (R2 = 0.93–0.99), despite of 1 min charging. High correlation between the coulombs and BOD5 concentration was also obtained for wastewater effluent at 1 min charging, which indicates that the bio-capacitance MxC sensor can semi-continuously measure BOD5 concentration in wastewater at every 2 min (1 min charging and 1 min discharging).Natural Sciences and Engineering Research Council of Canada Collaborative Research and Development (CRD) Gran

Evaluation of limiting factors for current density in microbial electrochemical cells (MXCs) treating domestic wastewater

This study quantitatively assessed three limiting factors for current density in a microbial electrochemical cell (MXC) treating domestic wastewater: (1) buffer concentration, (2) biodegradability, and (3) particulates. Buffer concentration was not significant for current density in the MXC fed with filtered domestic wastewater (180 mg COD/L). Current density reduced by 67% in the MXC fed with filtered sewage having similar COD concentration to acetate medium, which indicates poor biodegradability of soluble organics in the wastewater. Particulate matters seriously decreased current density down to 76%, probably due to the accumulation of particulates on biofilm anode. Our study quantitatively showed that buffer concentration does not limit current density much, but biodegradability of soluble organics and fermentation rate of particulate matters in domestic wastewater mainly control current density in MXCs

Examination of Extracellular Polymer (EPS) Extraction Methods for Anaerobic Membrane Bioreactor (AnMBR) Biomass

Membrane bioreactor fouling is a complex process, which is typically driven by extracellular polymeric substances (EPS), a complex mixture of polysaccharides, proteins, lipids, humic substances, and other intercellular polymers. While much is known about fouling in aerobic membrane reactors, far less is known about fouling in anaerobic membrane bioreactors (AnMBR). Much of this knowledge, including EPS extraction methods, has been extrapolated from aerobic processes and is commonly assumed to be comparable. Therefore, several extraction methods commonly used for aerobic EPS quantification, including ultrasonication, ethylenediaminetetraacetic acid (EDTA), and formaldehyde plus sodium hydroxide (CH2O+NaOH), were evaluated to determine the most suitable extraction method for EPS of anaerobic microorganisms in an AnMBR. To maximize EPS yields, each extraction was performed four times. Experimental results showed that the EDTA method was best for EPS quantification, based on chemical oxygen demand (COD), dissolved organic carbon (DOC), and protein yields: 1.43 mg COD/mg volatile suspended solids (VSS), 0.14 mg DOC/mg VSS, and 0.11 mg proteins/mg VSS. In comparison, the CH2O+NaOH method maximized the extraction of carbohydrates (0.12 mg carbohydrates/mg VSS). However, multiple extraction cycles with EDTA and ultrasonication exhibited lower extracellular adenosine triphosphate (ATP) concentrations compared to CH2O+NaOH extractions, indicating lower levels of released intracellular substances. Successive EPS extractions over four cycles are better able to quantify EPS from anaerobic microorganisms, since a single extraction may not accurately reflect the true levels of EPS contents in AnMBRs, and possibly in other anaerobic processes.Other UBCAlumniReviewedFacult

Spatial distribution of biofilm conductivity in a Geobacter enriched anodic biofilm

This study assessed the spatial distribution of biofilm conductivity (Kbio) across a multi-centimetre long anodic biofilm grown on an eight-electrode anode array at different growth conditions. A strong correlation was found between the spatial distribution of Kbio and the anodic biofilm thickness (Lf). The Kbio for different electrode pairs ranged between 0.6 and 0.7 mS/cm for Lf of 17–22 µm and increased to 1.15–1.64 mS/cm upon Lf growth to 38–53 µm. This increase in Kbio was accompanied by increase in current density from 1.15 ± 0.12 A/m2 to 2.1 ± 0.02 A/m2. Low half saturation potential was consistently found for electrode pairs having high values of Kbio and Lf. Microbial community revealed the dominance of Geobacter (>85%) on all electrode pairs. Acetate concentration significantly influenced the spatial distribution of Kbio. Long-term acetate starvation (3 days) resulted in up to 83% drop in Kbio along with decrease in current density to marginal values (<0.3 A/m2). However, the Kbio and current density rapidly recovered on restoring the acetate feed

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

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/m³-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/m³-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