Impact of antimicrobial silver nanoparticles on anode respiring bacteria in a microbial electrolysis cell

This study assessed the impact of antimicrobial AgNPs (50 mg L^-1, 30-50 nm) on the electrocatalytic activity of a mixed-culture anode biofilm enriched with Geobacter species. The current densities and electrochemical kinetics were maintained after exposure to AgNPs in consecutive fed-batch cycles, despite significant changes in morphological structures and bacterial communities. Bacterial community analysis showed a substantial increase in the Geobacter population in response to AgNPs exposure, indicating their higher tolerance to AgNPs. In contrast, the population of other anode respiring bacteria (ARB) belongs to Acinetobacter, Dysgonomonas, and Cloacibacillus genera appeared to be very sensitive to AgNPs toxicity as their relative abundance significantly decreased. Microscopic imaging showed that AgNPs were accumulated within anode biofilm matrix without penetration inside the cells. Moreover, the anode biofilm became denser because of enhanced extracellular polymeric substances (EPSs) production by ARB after exposure of AgNPs, implying that EPS could protect ARB against AgNPs toxicity.

Characterization of the Electric Current Generation Potential of the Pseudomonas aeruginosa Using Glucose, Fructose, and Sucrose in Double Chamber Microbial Fuel Cell

Background: Different concentrations of the simple carbon substrates i.e. glucose, fructose, and sucrose were tested to enhance the performance of the mediator-less double chamber microbial fuel cell (MFC). Objectives: The power generation potential of the different electron donors was studied using a mesophilic Fe (III) reducer and non-fermentative bacteria Pseudomonas aeruginosa-isolated from municipal wastewater. Materials and Methods: A double chamber MFC was operated with three different electron donors including glucose, sucrose, and fructose. Substrate utilization pattern was determined through chemical oxygen demand (COD) removal rate and voltage generation. In addition, electrochemical, physicochemical, and microscopic analysis of the anodic biofilm was conducted. Results:P. aeruginosa was proven to effectively utilize hexose and pentose sugars through anode respiration. Higher power density was generated from glucose (136 ± 87 mWm²) lead by fructose (3.6 ± 1.6 mWm²) and sucrose (8.606 ± mWm²). Furthermore, a direct relation was demonstrated between current generation rate and COD removal efficiency. COD removal rates were, 88.5% ± 4.3%, 67.5% ± 2.6%, and 54.2% ± 1.9% with the three respective sugars in MFC. Scanning electron microscopy (SEM) demonstrated that the bacterial attachment was considerably abundant in glucose fed MFC than in the fructose and sucrose operated MFC. Conclusion: This study has revealed that electron donor type in the anodic compartment controls the growth of anodic biofilm or anode-respiring bacteria (ARB).

Microbial characterization of anode-respiring bacteria within biofilms developed from cultures previously enriched in dissimilatory metal-reducing bacteria

This work evaluated the use of a culture enriched in DMRB as a strategy to enrich ARB on anodes. DMRB were enriched with Fe(III) as final electron acceptor and then transferred to a potentiostatically-controlled system with an anode as sole final electron acceptor. Three successive iron-enrichment cultures were carried out. The first step of enrichment revealed a successful selection of the high current-producing ARB Geoalkalibacter subterraneus. After few successive enrichment steps, the microbial community analysis in electroactive biofilms showed a significant divergence with an impact on the biofilm electroactivity. Enrichment of ARB in electroactive biofilms through the pre-selection of DMRB should therefore be carefully considered.

Fermentation pre-treatment of landfill leachate for enhanced electron recovery in a microbial electrolysis cell

Pre-fermentation of poorly biodegradable landfill leachate (BOD5/COD ratio of 0.32) was evaluated for enhanced current density (j), Coulombic efficiency (CE), Coulombic recovery (CR), and removal of organics (BOD5 and COD) in a microbial electrolysis cell (MEC). During fermentation, the complex organic matter in the leachate was transformed to simple volatile fatty acids, particularly succinate and acetate in batch tests, but mostly acetate in semi-continuous fermentation. Carbohydrate had the highest degree of fermentation, followed by protein and lipids. j, CE, CR, and BOD5 removal were much greater for an MEC fed with fermented leachate (23 A/m(3) or 16 mA/m(2), 68%, 17.3%, and 83%, respectively) compared to raw leachate (2.5 A/m(3) or 1.7 mA/m(2), 56%, 2.1%, and 5.6%, respectively). All differences support the value of pre-fermentation before an MEC for stabilization of BOD5 and enhanced electron recovery as current when treating a recalcitrant wastewater like landfill leachate.