Effect of electrode types on simultaneous anaerobic sulfide and nitrate removal in microbial fuel cell

Insights into microbial community in microbial fuel cells simultaneously treating sulfide and nitrate under external resistance

The effect of electricity, induced by external resistance, on microbial community performance is investigated in Microbial Fuel Cells (MFCs) involved in simultaneous biotransformation of sulfide and nitrate. In the experiment, three MFCs were operated under different external resistances (100 Ω, 1000 Ω and 10,000 Ω), while one MFC was operated with open circuit as control. All MFCs demonstrate good capacity for simultaneous sulfide and nitrate biotransformation regardless of external resistance. MFCs present similar voltage profile; however, the output voltage has positive relationship with external resistance, and the MFC1 with lowest external resistance (100 Ω) generated highest power density. High-throughput sequencing confirms that taxonomic distribution of suspended sludge in anode chamber encompass phylum level to genus level, while the results of principal component analysis (PCA) suggest that microbial communities are varied with external resistance, which external resistance caused the change of electricity generation and substrate removal at the same, and then leads to the change of microbial communities. However, based on Pearson correlation analyses, no strong correlation is evident between community diversity indices (ACE index, Chao index, Shannon index and Simpson index) and the electricity (final voltage and current density). It is inferred that the performance of electricity did not significantly affect the diversity of microbial communities in MFCs biotransforming sulfide and nitrate simultaneously.

Effect of external resistance on substrate removal and electricity generation in microbial fuel cell treating sulfide and nitrate simultaneously

The effect of external resistance on substrate removal and electricity generation was explored in microbial fuel cells (MFCs) simultaneously treating sulfide and nitrate. The MFCs were operated under three different conditions keeping open-circuit MFC as control. In batch mode, all the MFCs showed good capacity of simultaneously removing sulfide and nitrate regardless of external resistance. The voltage profile could be divided into rapid descent zone, bulge zone, and stability zone, which represents typical polarization behavior. Taking open circuit as control, low external resistance promoted the production of sulfate and nitrogen gas, while a strong link between product production and external resistance was evident based on Pearson correlation analyses. In addition, low external resistance improved the amount of transferred electrons, while the peak electronic quantity was noticed when the external resistance was equivalent to internal resistance. Moreover, the mechanism of substrate removal and electricity generation was hypothesized for the MFCs simultaneously treating sulfide and nitrate which explained the results well.

Enhanced sulfide removal and bioelectricity generation in microbial fuel cells with anodes modified by vertically oriented nanosheets

Anode materials and structures are of critical importance for microbial fuel cells (MFCs) recovering energy from toxic substrates. Carbon-fiber-felt anodes modified by layers of vertically oriented TiO₂ and Fe₂O₃ nanosheets were applied in the present study. Enhanced sulfide removal efficiencies (both over 90%) were obtained after a 48-h operation, with maximum power densities improved by 1.53 and 1.36 folds compared with MFCs with raw carbon-fiber-felt anode. The modified anodes provided more active sites for microbial adhesion with increasing biomass densities. High-throughput 16S rRNA gene sequencing analysis also indicated the increase in microbial diversities. Bacteroidetes responsible for bioelectricity generation with Thiobacillus and Spirochaeta dominating sulfide removal were found in the MFCs with the modified anodes, with less anaerobic fermentative bacteria as Firmicutes appeared. This indicates that the proposed materials are competitive for applications of MFCs generating bioelectricity from toxic sulfide.

Factors Affecting the Effectiveness of Bioelectrochemical System Applications: Data Synthesis and Meta-Analysis

Microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) are promising bioelectrochemical systems (BESs) for simultaneous wastewater treatment and energy/resource recovery. Unlike conventional fuel cells that are based on stable chemical reactions, these BESs are sensitive to environmental and operating conditions, such as temperature, pH, external resistance, etc. Substrate type, electrode material, and reactor configuration are also important factors affecting power generation in MFCs and hydrogen production in MECs. In order to discuss the influence of these above factors on the performance of MFCs and MECs, this study analyzes published data via data synthesis and meta-analysis. The results revealed that domestic wastewater would be more suitable for treatment using MFCs or MECs, due to their lower toxicity for anode biofilms compared to swine wastewater and landfill leachate. The optimal temperature was 25–35 °C, optimal pH was 6–7, and optimal external resistance was 100–1000 Ω. Although systems using carbon cloth as the electrodes demonstrated better performance (due to carbon cloth’s large surface area for microbial growth), the high prices of this material and other existing carbonaceous materials make it inappropriate for practical applications. To scale up and commercialize MFCs and MECs in the future, enhanced system performance and stability are needed, and could be possibly achieved with improved system designs.

Effect of cathode electron acceptors on simultaneous anaerobic sulfide and nitrate removal in microbial fuel cell

The current investigation reports the effect of cathode electron acceptors on simultaneous sulfide and nitrate removal in two-chamber microbial fuel cells (MFCs). Potassium permanganate and potassium ferricyanide were common cathode electron acceptors and evaluated for substrate removal and electricity generation. The abiotic MFCs produced electricity through spontaneous electrochemical oxidation of sulfide. In comparison with abiotic MFC, the biotic MFC showed better ability for simultaneous nitrate and sulfide removal along with electricity generation. Keeping external resistance of 1,000 Ω, both MFCs showed good capacities for substrate removal where nitrogen and sulfate were the main end products. The steady voltage with potassium permanganate electrodes was nearly twice that of with potassium ferricyanide. Cyclic voltammetry curves confirmed that the potassium permanganate had higher catalytic activity than potassium ferricyanide. The potassium permanganate may be a suitable choice as cathode electron acceptor for enhanced electricity generation during simultaneous treatment of sulfide and nitrate in MFCs.

Anaerobic microbial fuel cell treating combined industrial wastewater: Correlation of electricity generation with pollutants

Microbial fuel cell (MFC) is a new technology that not only generates energy but treats wastewater as well. A dual chamber MFC was operated under laboratory conditions. Wastewater samples from vegetable oil industries, metal works, glass and marble industries, chemical industries and combined industrial effluents were collected and each was treated for 98h in MFC. The treatment efficiency for COD in MFC was in range of 85-90% at hydraulic retention time (HRT) of 96h and had significant impact on wastewater treatment as well. The maximum voltage of 890mV was generated when vegetable oil industries discharge was treated with columbic efficiency of 5184.7C. The minimum voltage was produced by Glass House wastewater which was 520mV. There was positive significant co-relation between COD concentration and generated voltage. Further research should be focused on the organic contents of wastewater and various ionic species affecting voltage generation in MFC.