SPEAKER: Ala'a Ragab
TITLE: Electrode-assisted methanogenesis in a microbial electrolysis cell: Examining the effect of set potential on the microbial activity and functional response
Electrode-assisted methanogenesis in microbial electrolysis cells (MECs) involves the reduction of CO2 to methane by methanogens at the biocathode. While studies have demonstrated the effect of set potential on reactor performance, little is known regarding the functional response of methanogenic biofilms in MECs. The objective of this study was to understand the functional dynamics of a methanogenic community in a MEC as a function of set cathode potential using metagenomics and metatranscriptomics. We hypothesize that differences in hydrogen evolution and electron availability due to different set potentials will affect the gene expression of methanogenic biofilms and, consequently, current and product formation. Methanogenic biocathodes were enriched for three months in duplicate single-chamber MECs, then transferred to two dual-chambered MECs for the set cathode potential experiments with 20% CO2 in the headspace and no additional carbon sources. The MECs were operated for 48 hours at each set cathode potential (-1.0 V, -0.8 V and -0.6 V vs Ag/AgCl) with samples taken before and after each change. Current densities were about 0.3 – 0.4 mA/cm2 at -1.0 V, and close to 0 mA/cm2 at less negative potentials in both reactors. However, the current density increased in one of the reactors to about 0.3 mA/cm2 after operating for 15 hours at -0.6 V, with a corresponding increase in methane and hydrogen production. Metagenomic analyses revealed that the enriched biocathodes were dominated by three Methanobacterium sp., with relative abundances that varied with set potential. Metatranscriptomic analyses are currently underway to quantify the dynamic responses of key genes associated with electron uptake, hydrogen production/utilization and carbon dioxide fixation.
Ala’a Ragab is a Ph.D. student in the Water Desalination and Reuse Center (WDRC), working under the supervision of Professor Pascal Saikaly. Her research interest is focused on electrode-assisted methanogenesis and understanding the microbial processes at the biocathode to improve methane yields.
SPEAKER: Dario Rangel Shaw
TITLE: Electro-anammox: electrochemically active anammox bacteria
To date, nitrogen removal by anaerobic ammonium oxidation (anammox) is the most cost-effective process for the treatment of ammonium in wastewater. The application of anammox process appears to be a pre-requisite for achieving energy neutral/positive wastewater treatment. In anammox process, ammonium is converted to nitrogen gas using nitrite as the electron acceptor. The supply of electron acceptor (i.e. nitrite) required by anammox bacteria is obtained from the interaction with different types of microorganisms such as ammonia oxidizing archaea/bacteria, denitrifiers, anaerobic methane oxidizing archaea and commamox bacteria. In three-electrode electrochemical systems, electrochemically active bacteria use the anode as the electron acceptor by applying a potential. A recent review showed that there is no specific ecological niche for electrochemically active microorganisms (Koch and Harnisch, 2016). Thus, this study was motivated by the question: are anammox bacteria electrochemically active? To address this question, we tested eight different potentials in a three-electrode electrochemical system inoculated with highly enriched (>99%) anammox culture. The reactor was operated for more than two months without the presence of any electron acceptor other than the electrode. Biotic and abiotic controls, inhibition of nitrifiers and metagenomics analysis revealed that anammox bacteria were responsible for the oxidation of ammonium and current generation without any production of nitrite or nitrate. To our knowledge, this is the first report showing the ability of anammox bacteria to use a solid-state electron acceptor and behave as an electrochemically active microorganism. Also, this study showed that there is no need for partial nitrification and/or the requirement of nitrite for anammox process. The implication of this study is that it opens the possibility of simultaneous removal of organics and nitrogen at the anode of bioelectrochemical systems.
Dario Rangel Shaw is a Ph.D. student at the Water Desalination and Reuse Center. He had his bachelor and master degree in Microbiology and Molecular Biology from Los Andes University in Colombia. He joined KAUST under the supervision of Professor Pascal Saikaly. His research is focus on the integration of anaerobic ammonium oxidation (Anammox) into domestical wastewater treatment.