Anode Chamber Research Articles

Enhancing PFC ability to dye removal and power generation simultaneously via conductive spheres in the anodic chamber

Discharging organic contaminants into the water bodies has become one of the critical problems for the environment. Also, these pollutants are a source of chemical energy. In this study, we introduced a novel photocatalytic fuel cell system with a new design of photoelectrode to treat pollution and produce energy simultaneously. The effect of conductive copper spheres as an electron acceptor to reduce the recombination rate of photogenerated electronsand holes was investigated to improve dye removal, power generation and increase system conductivity. The TiO2/Ti photoanode is designed in a basket for the first time to keep the spheres in the anodic chamber and improve electron transfer through the external circuit. During 5 h, the decolorization of 20 mg/L of methyl orange (MO) reached 86.78%. The short-circuit current, open-circuit voltage, and maximum power density of the PFC were 0.21 mA/cm2, 0.69 V, and 0.033 mW/cm2, respectively. Using conductive spheres improved the system's overall performance by 10%, 23%, and 24%, respectively, compared to when conductive spheres were not used.

Highly efficient removal of Cu-organic chelate complexes by flow-electrode capacitive deionization-self enhanced oxidation (FCDI-SEO): Dissociation, migration and degradation

It is generally difficult to remove copper (Cu) from industrial wastewaters through traditional processes because Cu can form stable complexes with organic chelating agent. Here, the flow-electrode capacitive deionization-self enhanced oxidation (FCDI-SEO) system was applied to achieve highly efficient removal of two typical Cu-organic complexes (ethylenediaminetetraacetic acid-Cu (EDTA-Cu) and citric acid-Cu (CA-Cu)), and the underlying mechanism was also investigated. At the initial concentration of 1 mmol L−1, Cu removal efficiency reached 99.3% and approximately 100.0% respectively in FCDI-SEO treated EDTA-Cu and CA-Cu containing wastewaters after 75 min. Stable EDTA-Cu mainly migrated into the anode chamber as chelated Cu, while CA-Cu was easily dissociated and migrated into the cathode chamber as free Cu2+. After entering the anode chamber, the degradation rate of EDTA and CA was respectively 66.1% and 60.2%. Compared with the isolated closed-cycle mode, the short-circuited closed-cycle mode showed insignificant difference in Cu removal efficiency but higher energy efficiency. With pH increasing from 3.5 to 5.5, Cu removal efficiency showed little difference between the EDTA-Cu and CA-Cu system. With the addition of 180 mg L−1 extra Na+, Cu removal efficiency was about 80% and 90% in the EDTA-Cu and CA-Cu system, respectively. After operation for five cycles and regeneration of electrode, FCDI-SEO could still achieve stable removal efficiency. This work provides a new pathway for the removal of aqueous Cu-organic complexes.

Efficient removal of sixteen priority polycyclic aromatic hydrocarbons from textile dyeing sludge using electrochemical Fe2+-activated peroxymonosulfate oxidation-A green pretreatment strategy for textile dyeing sludge toxicity reduction

It is urgent to remove polycyclic aromatic hydrocarbons (PAHs) from textile dyeing sludge (TDS) before its final deposal due to their recalcitrant nature and generation of toxic byproducts during TDS treatment. In this study, an electrochemical Fe2+-activated peroxymonosulfate (PMS) oxidation process for removing 16 priority PAHs from real TDS was firstly investigated. The results showed that the removal efficiency of the ∑16PAHs in TDS was positively correlated to the concentration of Fe2+ released from sacrificial iron anode and the concentration of electroregenerated Fe2+ in the cathode by the reduction of Fe3+ within the applied voltage range of 3–7 V, but a higher voltage of 10 V did not lead to further improvement in ∑16PAHs removal due to the radical scavenging reaction resulted from the excessive accumulation of Fe2+. 64.7% and 16.1% of the ∑16PAHs were removed in the anodic and cathodic chamber under the optimum reaction conditions of 400 mg/g PMS/VSS, pH 3 and applied voltage 7 V, respectively. low-ring PAHs were preferentially degraded compared to high-ring PAHs. The O⋅Hplayed a major role while SO4⋅—had a minor role in PAHs degradation in TDS. The intracellular PAHs released from cracked sludge cells were found to undergo further degradation under free radical attack.

Visible-light enhanced azo dye degradation and power generation in a microbial photoelectrochemical cell using AgBr/ZnO composite photocathode

In this study, a dual-chamber microbial photoelectrochemical cell (MPEC) composed of a bio anode and a photoresponse AgBr/ZnO-modified graphite as a photocathode was investigated. The cell efficacy in degrading reactive black 5 (RB5), a diazo dye, in the cathodic chamber and simultaneously, electricity generation was analyzed. The synthesized AgBr/ZnO photocatalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectra (UV-vis DRS), photoluminescence (PL), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). Under light irradiation, the MPEC equipped with AgBr/ZnO-modified photocathode yielded 61% RB5 dye degradation over 72 h which indicated a highly enhanced performance compared with the irradiated bare graphite (11.74%). Besides, the maximum power density produced was 53.8 mW m−2 under visible light illumination and 32.5 mW m−2 in dark conditions. The MPEC reported in this research seems to be a promising system for bioelectricity generation, wastewater treatment in the anodic chamber, and also, dye pollutant degradation in the cathodic chamber.

Redox-flow battery with four-channel architecture for continuous and efficient desalination over a wide salinity working range

In this study, redox-flow battery desalination (FBD) with a four-channel cell architecture was utilized for electrochemical desalination at different salinity levels. Herein, continuous desalination without a discharge step was achieved by simultaneous generation of desalted and brine streams in the diluted and concentrated chambers, while the ferri-/ferrocyanide redox couple was independently recirculated between the anode and cathode chambers. Notably, a relatively low constant voltage of 0.2 V successfully drove redox reactions for ion motion. The salt removal rate was enhanced by increasing the applied voltage but at the cost of higher energy consumption. Employing a higher concentration of ferri-/ferrocyanide (i.e., 100 mM) provided faster reaction kinetics and charge transfer in the FBD chambers. By treating NaCl solutions with concentrations in the range 3000–35,000 mg/L at 0.2 V, we demonstrated that the average salt removal rate increased from 14.7 to 96.2 μg/min-cm2. The molar energy consumption increased slightly from 18.5 to 20.6 kJ/mole, which was associated with a high charge efficiency >93.8%. This feature indicates the possible utility of FBD for desalting solutions with high salinity levels up to that of seawater. As demonstrated, FBD delivered >90% salt removal for real seawater desalination with an energy consumption of 3.34 kWh/m3.

Influence of Fe2+ and Fe3+ on the Performance and Microbial Community Composition of a MFC Inoculated with Sulfate-Reducing Sludge and Acetate as Electron Donor

A sulfidogenic sludge supplemented with acetate was evaluated in the anodic chamber of microbial fuel cells (MFCs) in the presence of sulfate (SO4-2)/Fe3+ and sulfate (SO4-2)/Fe2+ to investigate the MFC performance and the effect of the iron ions on the composition of the microbial community since sulfate and iron ions are frequently present in wastewater derived from several anthropogenic activities. The current densities were up to 0.025 mA/cm2 and 0.017 mA/cm2 for MFCs with Fe2+ and Fe3+, respectively. Accordingly, the redox activity was slightly higher in the presence of Fe2+ than Fe3+. In general, the metabolic activity of the MFC supplemented with Fe2+ was higher than the system with Fe3+ reaching a percentage of sulfate reduction (% SR), sulfide concentration (mg/L HS-), and removal of chemical oxygen demand (% COD removal) of 35.2 ± 0.75 , 450.3 ± 3.6 , and 50.05 ± 0.24 for % SR, HS-, and % COD, respectively, whereas in the MFC with Fe3+, the percentages were of 30.1 ± 1.076 , 220.6 ± 2.0 , and 11.78 ± 10.81 for % SR, HS-, and % COD, respectively. The microbial population determined in each system was also correlated to the metabolic activity. Rhodospirillales, Caulobacterales, and Burkholderiales were the most abundant orders of bacteria in the MFC with Fe3+, whereas with Fe2+, Rhodobacterales, Sphingomonadales, and Rhizobiales. Desulfohalobiaceae and Desulfovibrionaceae were identified in the presence of Fe2+. Unexpected interactions and combinations of microorganisms were observed in a relatively short culturing time, demonstrating the importance of characterizing the anode biofilm prior to shifts in iron ion concentrations on a long-term basis.

High current density with spatial distribution of Geobacter in anodic biofilm of the microbial electrolysis desalination and chemical-production cell with enlarged volumetric anode

The aim of this study was to establish the relationship between spatial distribution of Geobacter and electric intensity in the microbial electrolysis desalination and chemical-production cell (MEDCC) and to investigate the effect of enlarged volumetric anode on the performance of MEDCC. The MEDCC was constructed with nine carbon brush anodes (length × diameter = 11 cm × 3 cm) as enlarged volumetric anode, and operated by feeding with 1 g/L acetate as substrate and 35 g/L NaCl as artificial seawater under the applied voltages of 1.2–4.5 V. Spatial distribution of Geobacter in the anodic biofilm was determined according to the bacterial community analysis on 27 biofilm samples from the top, middle and bottom layers of anodes (i.e., with distance of 4.5, 10, and 15.5 cm to the cathode, respectively). Results showed that the enlarged volumetric anode significantly improved the performance of MEDCC. The maximum desalination rate and current density reached 338.5 ± 21.8 mg/L∙h and 55.7 ± 3.7 A/m2 in the MEDCC, respectively. The electric intensity values decreased with the distance from the anode to the cathode and formed an uneven distribution in the anode chamber. The samples in the top layer of anodes had the highest average 16S rRNA gene copy number of Geobacter of 1.55 × 107 copies/μL, which was 18 times higher than that in the bottom layer of anodes. A linear relation was established between the spatial distribution of Geobacter and electric intensity (R2 = 0.994–0.999). The electric intensity gradient created the uneven spatial distribution of Geobacter in the biofilms of volumetric anode. Results from this study could be useful to enrich Geobacter in the anodic biofilm thus to improve the performance of MEDCC.

Promoting CO2 Release from CO3 2−-Containing Solvents during Water Electrolysis for Direct Air Capture

The pH swings from water electrolysis are leveraged to condition OH−-based facile CO2 capture solvents using an electrochemical flow cell for direct air capture (DAC). Besides demonstrating the DAC using a membrane contactor, promoting CO2 release from a CO3 2− solution at the anode is specifically studied by adjusting the volumetric flow rate, anode chamber volume, residence time, and K2CO3 concentration. Through case-by-case comparisons coupled with modeled results, increasing current, reducing volumetric flow rate, and/or reducing CO3 2− concentration are the effective methods to promote CO2 release from a CO3 2−-containing solvent, whereas enlarging the anode chamber volume poses a minor effect. Moreover, the discrepancies between the experimental and modeled results may be caused by H+ crossover rather than K+ transport through the Nafion membrane during water electrolysis based upon the total alkalinity measurements for the K2CO3 solutions gleaned from the anode. It is believed that such results will provide guidance to design and operate an electrochemical flow cell for electrochemistry-assisted DAC and point source CO2 capture.

Scaled-up multi-anode shared cathode microbial fuel cell for simultaneous treatment of multiple real wastewaters and power generation

Microbial fuel cell (MFC) is lauded for its capacity to valorize organic substrates in wastes, providing a solution to environmental pollution and energy crisis. While different types of organic substrates affect removal efficiency and current output, most MFCs are designed to only be able to utilize one type of wastewater. However, many real wastewater treatment sites generate more than one type of wastewater which hinders the installation of most MFCs. This study aimed to investigate the performance of the novel-designed multi-anode shared cathode MFC (MASC-MFC) compared with a standard single anode/cathode MFC (SAC-MFC) and the simultaneous treatment of different types of real wastewaters (sewage, slaughterhouse, and hospital) in one MFC unit. The MASC-MFC (9025 mW/m2 at 23.332 mA/m2) produced 1.7 times and 1.6 times higher in power density and current density and 2.2 times lower in internal resistance than the standard single anode/cathode MFC (SAC-MFC). A maximum COD removal efficiency of 62.7% was achieved with synthetic wastewater. Feeding the MASC-MFC with multiple real wastewaters decreased maximum power density 3.5 (2599 mW/m2) times and increased internal resistance 2.7 times. Stable current generation 1.575 mA was achieved over 300 h despite the different and complex wastewater physio-chemical compositions. The MASC-MFC achieved over 40% and approximately 30% coulombic efficiency independently in all the anode chambers irrespective of the type of real wastewater used, demonstrating the MASC-MFC's capacity to treat different real wastewaters with the added benefit of electricity production.

Reagent-free electrokinetic remediation coupled with anode oxidation for the treatment of phenanthrene polluted soil

Electrokinetic in-situ chemical oxidation (EK-ISCO) has attracted much attention during remediation of organic contaminated soil. Oxidants in EK-ISCO brings high cost and negative effects on soil physicochemical properties. In this study, a novel approach of combined electrokinetic treatment and anode oxidation was investigated to remediate phenanthrene polluted soils without adding oxidants. The fabricated Ti4O7 acted as anode, and could generate •OH at the rate of 9.31 × 10−7 mol h−1 at current 5.10 mA cm−2 through direct H2O electrolysis. Electro-osmotic flow (EOF) was used to transport phenanthrene to anode for the subsequent degradation. Sandy soil, fluvo-aquic soil and red soil were selected as typical soil samples, because pH and buffer capacity were two important factors affecting the direction of EOF. Strategies were developed to regulate the direction of EOF, including adding CEM membrane, maintaining soil pH at 3.5–4.0 and mixing solution from anode and cathode chambers. After treatment, more than 81.9% of phenanthrene was removed without adding any oxidants, and the remediated soil had low toxicity for Lolium perenne growth based on 3-d cultivation results. The results indicated that EK-AO had the advantage of less energy consumption and superior environmental friendliness than traditional EK-ISCO.

Coke-oven wastewater treatment in a dual-chamber microbial fuel cell with thiocyanate-degrading biofilm enriched at the air cathode

Abstract Coke-oven wastewater is usually treated with the activated sludge process, which requires large amounts of electrical energy for aeration and sludge disposal. A more sustainable treatment is strongly required. Recently, microbial fuel cells (MFCs) are focused as a technology for the production of electricity from wastewaters with simultaneous removal of organic matter. However, no MFC has been reported that can remove phenol, thiosulfate and thiocyanate simultaneously without aeration. Phenol can generally be removed well, whereas thiocyanate is relatively difficult to degrade. In this study, a dual-chamber MFC (D-MFC) was designed and equipped with a thiocyanate-degrading biofilm enriched on an air cathode. The D-MFC degraded phenol and thiosulfate in the anode chamber at the rate of 104 and 331 mg/L/day, respectively and subsequently degraded thiocyanate in the cathode chamber at the rate of 250 mg/L/day. The D-MFC showed high thiocyanate degradation rate. This suggests that pre-enrichment could accelerate thiocyanate degradation in MFC. In addition, thiocyanate degradation was not inhibited by phenol as thiocyanate was removed in the cathode chamber after phenol was removed in the anode chamber. This study demonstrated the feasibility of treating coke-oven wastewater by a D-MFC with a thiocyanate-degrading biofilm enriched at the air cathode.

Cooperative denitrification in biocathodes under low carbon to nitrogen ratio conditions coupled with simultaneous degradation of ibuprofen in photoanodes

A two-chamber microbial photoelectrochemical cell (MPEC) with a denitrification biocathode and an α-Fe2O3/P3HT photoanode was established aimed to enhance nitrate removal from wastewater of low carbon sources and achieve simultaneous ibuprofen degradation. The results demonstrated that the average removal of NO3–-N in the biocathode reached 96.56 ± 0.72% when the COD/NO3–-N was 0.75, and the relative contributions of heterotrophic and autotrophic denitrification were 21.47% and 78.53%, respectively. When there was no organic source in the influent, the maximum removal of NO3–-N was less than 45%. High-throughput sequencing revealed that both heterotrophic bacteria, such as Bacillus, and autotrophic bacteria (e.g., Thermomonas and Hydrogenophaga) dominated in the cooperative denitrification biocathode. Moreover, the functional gene analysis showed that the abundance of genes related to denitrification was highest in the cooperative denitrification biocathode. In addition, the photocatalytic degradation efficiency of ibuprofen in the anode chamber attained 67.95% ± 0.97%.

Accumulation of Inert Impurities in a Polymer Electrolyte Fuel Cell System with Anode Recirculation and Periodic Purge: A Simple Analytical Model

Anode recirculation with periodic purge is commonly used in polymer electrolyte fuel cell systems to control the accumulation of nitrogen, water, and other impurities that are present in the fuel or diffuse through the membrane from the cathode compartment. In this work, we develop a simple, generalized analytical model that simulates the time dependence of the accumulation of inert impurities in the anode compartment of such a system. It is shown that, when there is transport out of the anode chamber, the inert species is expected to accumulate exponentially until equilibrium is reached when the rate of inert entering the anode in the fuel supply and/or via crossover from the cathode is balanced by the rate of leakage and/or crossover to the cathode. The model is validated using recently published experimental data for the accumulation of N2, CH4, and CO2 in a recirculated system. The results show that nitrogen accumulation needs to be taken into account to properly adjust system parameters such as purge rate, purge volume, and recirculation rate. The use of this generalized analytical model is intended to aid the selection of these system parameters to optimize performance in the presence of inerts.

Microbial fuel cell coupled Fenton oxidation for the cathodic degradation of emerging contaminants from wastewater: Applications and challenges.

Urbanization and industrialization have resulted in the escalation of the occurrence of emerging contaminants (EC) in the wastewater and ultimately to the receiving water bodies due to their bio-refractory nature. The presence of ECs in the water bodies adversely affects all three domains of life, viz. bacteria, archaea and eukaryotes, and eventually the ecosystem. Fenton oxidation is one of the most suitable method that is capable of degrading a variety of ECs by employing a strong oxidizing agent in the form of •OH. The coupling of Fenton oxidation with microbial fuel cell (MFC) offers benefits, such as low-cost, minimal requirement of external energy, and in-situ generation of oxidizing agents. The resulting system, termed as bio-electro-Fenton MFC (BEF-MFC), is capable of degrading the ECs in the cathodic chamber, while harvesting bioelectricity and simultaneously removing oxidizable organic matter from wastewater in the anodic chamber. This review discusses the applications of BEF-MFC for the treatment of dyes, pharmaceuticals, pesticides, and real complex wastewaters. Additionally, the effect of operating conditions on the performance of BEF-MFC are elaborated and emphasis is also given on possible future direction of research that can be adopted in BEF-MFC in the purview of up-scaling.

Improving the Performance of Baker’s Yeast-powered MFCs by Adding Dehydrogenase Enzymes to Oxidize Yeast-produced Ethanol

This study focuses on theoretically and experimentally enhancing the performance of a baker’s yeast-powered microbial fuel cell (MFC) by hybridizing the MFC and EFC (enzymatic fuel cells) technologies. To improve the power density of the MFC, commercially available alcohol and aldehyde dehydrogenase enzymes (ADHE) have been added to the anode chamber to oxidize ethanol, which is produced by Baker’s yeast (BKY) during the metabolic process, to acetic acid. This oxidation process contributes more power output for the MFC. BKY biofilm was formed in porous 3D activated carbon paper to make the anode. The combination of using the biofilm anode and ADHE for electricity generation by the MFC enabled about 19% improvement in the maximum power density if compared with the MFC without using ADHE. Also, aerobic and anaerobic culture conditions were investigated. The result showed that under the anaerobic culture condition, the MFC generated about 22% higher maximum power density than that of the aerobic condition. These results imply that the addition of ADHE can take full advantage of BKY-produced ethanol to boost overall BKY-powered MFC performance.

Y(III) Ion Migration in AlF3–(Li,Na)F–Y2O3 Molten Salt

In this study, three slots containing an anode chamber, a cathode chamber, and a middle pole chamber were designed by applying the Hittorf method, and a two-way coupling model of the flow field and electric field was established using the COMSOL system. The electric field distribution in the constructed model was simulated, and the model reliability, boundary conditions, and related parameters were verified. A three-chamber tank was utilized to investigate the migration numbers change rule and migration mechanism of Y(III) ions in the AlF3–(Li,Na)F system. The migration number of Y(III) ions in the AlF3–(Li,Na)F–Y2O3 molten salt linearly increased from 0.70 to 0.80 with an increase in temperature from 900 to 1000 °C. When the (Li,Na)F/AlF3 molar ratio was between 2.0 and 2.5, the migration number of Y(III) ions was relatively constant, and its average value was approximately 0.75. Meanwhile, at (Li,Na)F/AlF3 molar ratios higher than 2.5, the migration number of Y(III) ions linearly decreased from 0.75 to 0.45. Finally, in the current density range of 1.0–2.0 A/cm2, the migration number of Y(III) ions increased almost linearly from 0.65 to 0.85.

Electrical generation and methane emission from an anoxic riverine sediment slurry treated by a two-chamber microbial fuel cell.

A two-chamber slurry microbial fuel cell (SMFC) was constructed using black-odorous river sediments as substrate for the anode. We tested addition of potassium ferricyanide (K3[Fe(CN)6]) or sodium chloride (NaCl) to the cathode chamber (0, 50, 100, 150, and 200mM) and aeration of the cathode chamber (0, 2, 4, 6, and 8h per day) to assess their response on electrical generation, internal resistance, and methane emission over a 600-h period. When the aeration time in the cathode chamber was 6h and K3[Fe(CN)6] or NaCl concentrations were 200mM, the highest power densities were 6.00, 6.45, and 6.64 mW·m-2, respectively. With increasing K3[Fe(CN)6] or NaCl concentration in the cathode chamber, methane emission progressively decreased (mean ± SD: 181.6 ± 10.9 → 75.5 ± 9.8mg/m3·h and 428.0 ± 28.5 → 157.0 ± 35.7mg/m3·h), respectively, but was higher than the reference having no cathode/anode electrodes (~ 30mg/m3·h). Cathode aeration (0 → 8h/day) demonstrated a reduction in methane emission from the anode chamber for only the 6-h treatment (mean: 349.6 ± 37.4 versus 299.4 ± 34.7mg/m3·h for 6h/day treatment); methane emission from the reference was much lower (85.3 ± 26.1mg/m3·h). Our results demonstrate that adding an electron acceptor (K3[Fe(CN)6]), electrolyte solution (NaCl), and aeration to the cathode chamber can appreciably improve electrical generation efficiency from the MFC. Notably, electrical generation stimulates methane emission, but methane emission decreases at higher power densities.

Microalgae-assisted fixed-film activated sludge MFC for landfill leachate treatment and energy recovery

The sustainability and innovation of a novel leachate treatment technology is a matter of vital significance. Bio-electrochemical-driven wastewater and leachate treatment methods, particularly MFC, and their improvements have attracted scientists’ attention recently. This study developed a new MFC system, which consisted of an anodic chamber, a cathode chamber with fixed biofilm carriers and a low-cost sheet of carbon felt between them as a membrane-like separator. The study was conducted to evaluate the capacity of MFC coupled with integrated fixed-film activated sludge (IFAS), to enhance the efficiency of the treatment and the amount of energy produced. Three MFC systems with different cathode processes were compared, namely, conventional activated sludge (MFC-AS), MFC-IFAS, and microalgae coupled MFC-IFAS (MFC-IFAS/MA). The experimental results revealed that MFC-IFAS/MA produced higher power density and nitrogen removal than the other two systems. The average removals of COD, NH4+-N, and total nitrogen (TN) were, 69.9%, 84.2% and 60.5% for MFC-AS, 84.3%, 79.2% and 71.6% for MFC-IFAS; and 82.0%, 90.3% and 88.6% for MFC-IFAS/MA. MFC-IFAS/MA demonstrated its superior electrochemical behaviors and nitrogen removal and this behavior was referring to the dual effect of fixed-biofilm and microalgae assimilation. This study investigated for the first time the symbiosis between microalgae and IFAS in an MFC reactor, which may open a new prospect for MFC application.

Simultaneous recovery of nutrients and power generation from source-separated urine based on bioelectrical coupling with the hydrophobic gas permeable tube system

Source-separated urine has been regarded as a precious treasure on account of its rich nitrogen content and is suitable for fertilizer production. In this study, a novel bioelectrical coupling with hydrophobic gas permeable tube system (BGTS) was developed to treat urine, for removing organic matter, and recover nitrogen as value-added products in the form of nitrogen fertilizer. In the presence of the electric field, the hydrolysis process of urea in the anode chamber was accelerated, and the NH4+ driven by electric field force and concentration difference reached the cathode through the cation exchange membrane. The cathode made use of oxygen and electrons to produce alkali in situ to promote the conversion of NH4+ to NH3, which was straightforwardly absorbed in hydrophobic gas permeable tube circulating sulfuric acid solution, so as to promote the rapid migration of nitrogen and build an efficient dynamic recovery of nitrogen. After a 48-h cycle, the BGTS achieved a 95.28 ± 0.60% COD removal ratio, 91.60 ± 0.29% nitrogen recovery efficiency, and 3.48 kg m−3 ammonium sulfate fertilizer. Economic analysis indicated a profit of 5.75 $ associated with the utilization of the BGTS system for nitrogen fertilizer recovery from source separation in urine. Consequently, this study manifested that the BGTS system can recover nitrogen from human urine in a high-recovery and cost-effective way, and is of great significance in the sustainable recovery of nitrogen resources.

Enhanced sulfur recovery and sulfate reduction using single-chamber bioelectrochemical system

The aim of this study was to investigate the feasibility of sulfate removal and elemental sulfur (S0) recovery in the single-chamber bioelectrochemical system (S-BES). The performance of S-BES was compared with that of dual-chamber bioelectrochemical system (D-BES). The S-BES was constructed with graphite felt as the anode and graphite brush as the cathode. The D-BES was constructed with proton exchange membrane as the separator between anode and cathode chambers. With an applied voltage of 1.0 V and 1 g/L acetate as the substrate, the S-BES and D-BES were tested by feeding with 480 mg/L SO42− in the phosphate buffer. Results showed that the maximum current density of 37.6 ± 4.5 mA/m3 was reached in the S-BES, which was higher than that in the D-BES (i.e., 22.2 ± 2.6 mA/m3). The SO42− removal was much higher in the S-BES than in the D-BES (99.5% vs. 57.2%). In the effluent and the electrodes of S-BES, S0 was identified with Raman and X- Ray diffraction analyses. The S0 recovery on the anode was 13.7 times of that on the cathode of S-BES, indicating that S0 was mainly produced on the anode. The measured total S0 recovery reached 67.5% in the S-BES. High relative abundance of Desulfurella (47.1%) and Geobacter (26.1%) dominated the community in the anode biofilm of S-BES. The excellent performance of S-BES may be attributed to the neutral pH in the solution and the synergistic reaction between the anode and cathode. Results from this study should be useful to enhance the S-BES applications in treating wastewater containing sulfate.