Cathode Chamber Research Articles

Enhanced ammonia recovery from strong ammonia wastewater via a transmembrane electro-chemisorption system with authigenic acid and base

A transmembrane electro-chemisorption system with authigenic acid and base was developed to enhance ammonia recovery from strong ammonia wastewater. The authigenic base from water electrolysis at the cathode could raise the wastewater pH, which transformed ammonium into free ammonia. Simultaneously, the authigenic acid from water electrolysis at the anode could adsorb free ammonia via transmembrane chemisorption. The recovered product was pure (NH4)2SO4, and two valued byproducts (pure H2 and pure O2) were obtained at the same time. Increasing applied voltage could promote the ammonia recovery. Keeping catholyte circulating flow or some headspace proportion in the cathode chamber was beneficial to the ammonia recovery. It took longer time for high influent NH4+-N concentration to achieve the same recovery efficiency with low influent NH4+-N concentration. Within the same operation time, the former could recover more amount of ammonia. Besides avoiding the addition of acid and base, the energy consumption of this system for ammonia recovery was low to 8.47 kWh/kg NH4+-N. Accordingly, the developed system showed good prospects in recovering ammonia from strong ammonia wastewater.

Electrochemically-mediated treatment of sulfur dioxide and purification of carbon dioxide coupled with hydrogen production

Sulfur dioxide emissions should be and have been regulated due to adverse effects on the environment, and purification of carbon dioxide from low-concentration sources requires energy-intensive steps. Here, we propose incorporating a NaOH-based absorbent with high pH, in which the two gases are simultaneously absorbed, into an electrochemical system that contributes to: (1) mineralizing sulfur dioxide into sulfate; (2) purifying carbon dioxide; and (3) producing hydrogen. Our electrolysis involves primarily anodic sulfite oxidation, and the hydroxide-consuming (proton-generating) sulfite oxidation coupled with cathodic hydrogen evolution allows to generate CO2 with > 85 % purity from an acidifying anodic chamber, and hydrogen evolution from a cathodic chamber with Faradaic efficiency close to 100 %, all at lower energy cost than water electrolysis. This proof-of-concept study demonstrates the feasibility of our functional electrochemical system as a sustainable solution for air pollution control, carbon neutrality, and energy production.

BIOELECTRICITY OF COCOA POD WASTE AS A SUBSTRATE IN A DOUBLE CHAMBER MICROBIAL FUEL CELL

Currently, the utilization of cocoa pod has not been maximized, resulting in waste and foul odors that disturb the environment. However, cocoa pod contain a relatively high amount of cellulose compounds that serve as an energy source or nutrition for bacteria to carry out metabolic activities, thus holding the potential to be used as a substrate in microbial fuel cells (MFC). Based on this, the aim of this research is to investigate the bioelectricity generated by a MFC using cocoa pod husk as a substrate, including voltage, current, and power density, in order to determine the potential of cocoa pod husk waste as an electrical energy source. In this study, a double chamber MFC consists of an anode chamber with copper electrodes and a cathode chamber with zinc electrodes, separated by a salt bridge. The bacteria used were Saccharomyces cerevisiae, and the substrate was made from cocoa pod husk waste. Bioelectricity testing involved measuring the voltage, current, and power density produced by the MFC over several minutes. The measurement results for maximum voltage, maximum current generated, and maximum electrical power (at 6 days) from the reactor were as follows: 36.0 mV, 0.19 mA, and 456 mW/m2, respectively.

Novel bipolar membrane electrolyzer for CO2 reduction to CO in organic electrolyte with Cl2 and NaOH produced as byproducts

Electrochemical reduction of CO2 to valuable products, powered by renewable energy, provides a promising strategy for reducing our dependence on fossil fuels. But up to now, no technology has been implemented for large-scale industrial applications. Without massive utilization of CO2, many vital practical problems, such as reducing CO2 emissions, storing renewable energy, and alleviating environmental pollution, cannot be resolved through this route. Herein, we propose a novel electrolyzer for CO2 electro-reduction, which is separated into three chambers by a bipolar membrane and a cation exchange membrane. In the cathodic chamber, CO2 is reduced to CO in organic electrolytes. In the anodic chamber, Cl- is oxidized to Cl2 in NaCl aqueous solution. In the central chamber, NaOH is obtained. The generated CO and Cl2 can be used as feedstock to produce phosgene (CO+Cl2 =COCl2). Through this route, phosgene can be produced from CO2 and NaCl, with NaOH generated as a byproduct. By substantially increasing the product value, we can promote CO2 electro-reduction technology to industrial applications.

Amino acids as in-situ electron donors drive medium chain fatty acids production from sludge acidogenic fermentation liquid by electro-fermentation enhancement

The production of medium chain fatty acids (MCFAs) from waste biomass by chain elongation often requires the supplementation of exogenous chemical electron donor (ED), to support the chain elongator. This study explored the feasibility of producing MCFAs using amino acids in acidogenic fermentation liquid from protein-rich sludge hydrolysate, and proposed a two-stage electro-fermentation process to realize MCFAs production without exogenous chemical ED. Stage I aimed to convert organic substrates into short chain fatty acids (SCFAs) through anodic alkaline acidogenic fermentation. Stage II utilized residual amino acids as in-situ ED in acidogenic fermentation liquid to generate MCFAs in cathodic chamber under open circuit (OC) and 0.9 V conditions. Results indicated that acetate (6.9 g/L) and butyrate (4.5 g/L) were accumulated as the main products in stage I, and 2.7 g/L of amino acids remained in acidogenic fermentation liquid. In stage II, the remained amino acids were consumed as in-situ ED to drive the conversion of acetate and butyrate into caproate, and 1.1 g/L and 3.01 g/L caproate were respectively determined at OC and 0.9 V conditions. Microbial community and function prediction mechanisms revealed the presence of abundant chain elongator (Clostridium_sensu_stricto_12) and electroactive bacteria (Desulfovibrio) in cathodic biofilm, as well as the organic degrader (Pseudomonas) in plankton, these microbes synergistically converted SCFAs and amino acids into MCFAs. This study for the first time explored the feasibility of using amino acids as alternative chemical ED to drive chain elongation, and provides a novel technical solution foralleviating dependence on exogenous chemical ED in the production of MCFAs from waste biomass.

Performance comparison of a photosynthetic and mechanically aerated microbial fuel cell for wastewater treatment and bioenergy generation using different anolytes

The use of expensive catalyst or mechanical aeration to carry out reduction reaction at cathode of conventional microbial fuel cell makes it costly and less efficient. Photosynthetic microbial fuel cell (PMFC) provides an option to overcome these issues by using microalgae as a biocatalyst at cathode chamber. This study aimed at assessing the performance of photosynthetic microbial fuel cell (PMFC) and its comparison with mechanically aerated MFC (MAMFC). The performance of both the systems was evaluated for two different anolytes namely, domestic wastewater and sugar industry wastewater. The PMFCs were inoculated with biocatalyst of Scenedesmus sp. in cathode chamber. Results showed that photosynthetic aeration significantly improved the efficiency of PMFCs as compared to MAMFCs. Maximum working voltage of 316 and 515 mV was achieved by PMFC with domestic wastewater and sugar wastewater, respectively, which was 15 % and 20 % higher than corresponding voltage of MAMFCs. Polarization and power curves showed that higher power density and lower internal resistance was achieved in PMFCs as compared to MAMFCs with both anolytes. Effect of light/dark regime on PMFCs resulted in a rise and drop pattern of dissolve oxygen and voltage generation. During light cycle, the average voltage was 214 mV and 370 mV for PMFC with domestic wastewater and sugar wastewater, respectively, which was 55 % and 54 % higher than corresponding dark cycle. Overall, the findings of the study suggested that PMFC support better power generation as compared to MAMFC, besides nutrients removal and production of algal biomass.

Cellulose-fueled microbial fuel cells equipped with a bipolar membrane using hydrogen phosphate as the final electron acceptor.

A bipolar membrane microbial fuel cell (bMFC) is used to generate electricity using cellulose in phosphate buffer solution as fuel, and the mechanism of electricity generation is elucidated from five reference experiments. The bMFC was operated for 20 days using cellulose as fuel and Cellulomonas fimi. In the first reference experiment, no microorganism was used. In the second experiment, a cation-exchange membrane was used instead of a bipolar membrane. In the third experiment, the bipolar membrane was used in the opposite orientation as in the main experiment. In the fourth experiment, D2O was used instead of H2O in the cathode chamber. In the final experiment, the tris-maleate buffer was used instead of a phosphate buffer. Sufficient power generation did not occur in either reference experiment. The bMFC continuously generated electricity for 20days, and elucidated H+ and OH- react in bipolar membrane, where the counter cation of dihydrogen phosphate served as the final electron acceptor.

In-situ microbial protein production by using nitrogen extracted from multifunctional bio-electrochemical system

Upgrading of waste nitrogen sources is considered as an important approach to promote sustainable development. In this study, a multifunctional bio-electrochemical system with three chambers was established, innovatively achieving 2.02 g/L in-situ microbial protein (MP) production via hydrogen-oxidizing bacteria (HOB) in the protein chamber (middle chamber), along with over 2.9 L CO2/(L·d) consumption rate. Also, 69% chemical oxygen demand was degraded by electrogenic bacteria in the anode chamber, resulting in the 394.67 J/L electricity generation. Focusing on the NH4+-N migration in the system, the current intensity contributed 4%–9% in the anode and protein chamber, whereas, the negative effect of −6.69% on contribution was shown in the cathode chamber. On the view of kinetics, NH4+-N migration in anode and cathode chambers was fitted well with Levenberg-Marquardt equation (R2 > 0.92), along with the well-matched results of HOB growth in the protein chamber based on Gompertz model (R2 > 0.99). Further evaluating MPs produced by HOB, 0.45 g/L essential amino acids was detected, showing the better amino acid profile than fish and soybean. Multifunctional bio-electrochemical system revealed the economic potential of producing 6.69 €/m3 wastewater according to a simplified economic evaluation.

The importance of the electron acceptor: Comparison between flooded and tidal bioelectrochemical systems for wastewater treatment and nutrients enriched solution production

In this study, a new bioelectrochemical system (BES) with an alternative setup of microbial fuel cell (MFC) is proposed: an additional cathodic collecting chamber is added to the air-exposed cathode to allow the recovery of the cations migrating from the anodic chamber. Up to 60 % of inorganic nutrients and 85 % of COD were removed from wastewater (WW). In the cathodic chamber, recovered nutrients partitioned differently depending on their solubility: P, Mg and Ca were predominantly found in precipitates as insoluble salts, while Na and K in the cathodic solution. N was recovered from the cathodic chamber as ammonia (NH3) (22 %) and as precipitate while deposited on the cathode as salts (15 %). Flooded versus tidal operation modes were further compared to achieve the best oxygen (strong electron acceptors) supply in the anodic chamber to increase biological COD degradation and nutrients migration towards the cathodic chamber.

Potential use of pepper waste and microalgae Spirulina sp. for bioelectricity generation

The research aimed to generate bioelectricity using pepper waste and the microalgae Spirulina sp by a double-chamber microbial fuel cell (dcMFC). A dcMFC was constructed with Cu and Zn electrodes, where organic waste and microalgae were placed in the anodic and cathodic chambers, respectively. Also, electrochemical parameters were measured for 35 days. Finally, possible electrogenic microorganisms were isolated and identified. It was possible to generate maximum values of current (6.04414 ± 0.2145 mA) and voltage (0.77328 ± 0.213 V). The maximum conductivity value was 134.1636 ± 7.121 mS/cm, while the internal resistance value was 83.784 ±7.147Ω. The values of power and current density reached were 584.45 ± 19.14 mW/cm 2 and 5.983 A/cm 2, respectively. The optimal operating pH was 4.59 ± 0.14. From the microbial growth on the anode, the yeast Yarrowia phangngaensis (1) and Pseudomonas stutzeri (2) were identified, which may be involved in the transfer of electrons to the electrode. In conclusion, it was possible to generate clean energy in a laboratory-scale dcMFC when pepper waste and Spirulina sp. were used. These results are promising because organic waste can generate sustainable and environmentally friendly energy.

Outline of microbial fuel cells technology and their significant developments, challenges, and prospects of oxygen reduction electrocatalysts

The microbial fuel cells (MFCs) which demonstrates simultaneous production of electricity and wastewater treatment have been considered as one of the potential and greener energy production technology among the available bioelectrochemical systems. The air-cathode MFCs have gained additional benefits due to using air and avoiding any chemical substances as catholyte in the cathode chamber. The sluggish oxygen reduction reaction (ORR) kinetics at the cathode is one of the main obstacles to achieve high microbial fuel cell (MFC) performances. Platinum (Pt) is one of the most widely used efficient ORR electrocatalysts due to its high efficient and more stable in acidic media. Because of the high cost and easily poisoned nature of Pt, several attempts, such as a combination of Pt with other materials, and using non-precious metals and non-metals based electrocatalysts has been demonstrated. However, the efficient practical application of the MFC technology is not yet achieved mainly due to the slow ORR. Therefore, the review which draws attention to develop and choosing the suitable cathode materials should be urgent for the practical applications of the MFCs. In this review article, we present an overview of the present MFC technology, then some significant advancements of ORR electrocatalysts such as precious metals-based catalysts (very briefly), non-precious metals-based, non-metals and carbon-based, and biocatalysts with some significant remarks on the corresponding results for the MFC applications. Lastly, we also discussed the challenges and prospects of ORR electrocatalysts for the practical application of MFCs.

Scaling up of MFC technology using cost effective electrodes for treatment of kitchen wastewater

The current study aims to scale up Microbial Fuel cell (MFC) system for power generation and treat kitchen wastewater using a low-cost material. One MFC with stainless steel mesh as both anode and cathode and another MFC with carbon veil as anode and stainless-steel mesh as cathode with a natural clay as membrane was selected for this study. Ten cells, each with an anodic chamber of volume 275 mL and cathodic chamber of volume 90 mL were externally connected to perform the treatment. COD removal and power generation of the cells were monitored and the performances of electrically combined cells in series, parallel, series–parallel and parallel-series combinations were also studied. MFC with carbon veil as anode generates an open circuit voltage (OCV) of 476 mV, power density of 0.397 W/m3 and current density of 0.26 A/m2 which is higher than the system with stainless steel as the anode. The comparative study of the various electrical combinations concludes that the parallel combination shows a maximum power density of 0.55 W/m3. This study reveals that the best electrode material and electrical connection for a scaled up MFC were carbon veil as anode and stainless-steel mesh as cathode and a natural clay-based membrane connected in parallel combination.

Investigating the effect of anode materials on the performance and microbial community in an integrated chamber-free microbial fuel cell

Conventionally, there are two basic configurations for microbial fuel cell (MFC), one with anode and cathode chambers, as known as dual-chamber MFC, one with only anode chamber and a air–cathode, called single-chamber MFC. However, electrode materials' complex configuration and high resistance limit their practical applications in power generation and wastewater purification. To this end, we constructed three MFCs using carbon felt, Ni/Ti, and Ag-Ni/Ti as anodes based on our previously constructed integrated chamber-free MFC (iMFC). After 21 days of operation, the Ag-Ni/Ti-MFC performed best in bioelectricity output and removal of target pollutants. The bioelectricity output parameters were an open-circuit voltage of 0.773 V, a maximum current density of 552.1429 mA/m2, and a power density of 426.8064 mW/m2. Furthermore, the MFC achieved removals of 67.90% for the chemical oxygen demand (COD), 55.20% for total nitrogen (TN), and 61.83% for ammonia nitrogen (NH3-N). Introducing silver nanoparticles to the transmembrane and outer membrane boosted the charge extraction efficiency in the MFCs. Moreover, 16S rDNA analysis indicated that typical electricity-producing bacteria, including Comamonas, Paraclostridium, and Asaccharospora, had a higher relative abundance in the Ag-Ni/Ti-MFC anode than in other anodes. Overall, the surface structure of different anode materials plays a critical role in bioelectricity generation and wastewater purification using iMFC by affecting the mass transfer of substrates and metabolites.

(Invited) Next Generation Electrified Membrane Technology for Simultaneous Wastewater Treatment and Production of Nitrogen Fertilizer

Recovery and repurposing of wastewater nitrogen such as nitrate (NO3 −) and nitrite (NO2 −) receive increasing attention as the current approaches of biological nitrogen removal or conversion into nitrogen gas (N2) renders high energy footprints. This study reported the first electrified membrane upcycling of NO3 − into NH3 that further converted into ammonia sulfate (NH4SO4), a liquid fertilizer readily for use. Paired electrolysis was used to couple simultaneous cathodic and anodic electrochemical half-reactions to enable nitrate reduction and eliminate the external acid/base consumption. Under a partial current density of 63.8±4.4 mA·cm−2 on a cathodic membrane made of a mixed-valence copper oxide and a polytetrafluoroethylene (PTFE) hydrophobic substrate, a recovery rate and energy consumption of 3100±91 g-(NH4)2SO4·m−2·d−1 and 21.8±3.8 kWh·kg−1-(NH4)2SO4 were achieved with the synthetic feed solution (150 mM NO3 −) flowing into the cathode chamber and the produced NH3 migrating across the cathodic membrane into a trap and anode chambers filled with the flowing 0.5 M Na2SO4 solution. 99.9% NO3 − was removed in the feed after 5 h operation with a NH3 recovery rate of 99.5%. This electrified membrane process was demonstrated to achieve comparable performances of synergistic nitrate decontamination and nutrient recovery using real nitrate wastewater with durable catalytic activity and stability. Specifically, the required electricity cost for converting 10 to 100 mM NO3 − to (NH4)2SO4 was $675 to $408 ton−1, respectively. The obtained (NH4)2SO4 may be sold as fertilizer at a price of 533 $·ton−1 (according to USDA) and further offset the cost of the NO3 − removal.According to the International Fertilizer Association, in 2018 the U.S. ranked second in nitrogen production, representing 11.6% of global production. However, it still requires the importation of nitrogen fertilizer, to fully meet the national demand. The US Environmental Protection Agency reports that in 2013, ~38 kg of nitrogen per acre per year was used for fertilization, and in 2016, 94 million acres of corn were planted in the US, representing ~40% of US fertilizer demand. Roughly, this equates to ~8.9 billion kg of nitrogen per year needed to meet total US fertilization demand. The nitrogen available in drinking water sources is roughly 65 million kg per year, and the nitrogen available in wastewater sources is roughly 2.4 billion kg per year. Thus, by fully recovering the nitrogen from wastewater 34.3% of the US nitrogen fertilizer requirement could be met. This could also further mitigate the increase in nitrogen fertilizer prices due to blocked nitrogen fertilizer imports and even free the US from nitrogen fertilizer imports. According to U.S. Department of Agriculture, the average U.S. farm price of sulfate of ammonium fertilizers is $533 per ton. Even leaving aside the revenue generated by the treatment of nitrogen-containing sewage, the market size of nitrogen fertilizer produced through sewage is as high as $12.8 billion.

Selective Separation between Ammonium and Potassium in a Membrane-Separated Magnesium-Based Electrochemical Process

Increasing trends in global food and water demands alongside growing environmental concerns press the need for developing new wastewater management strategies. Modern wastewater treatment facilities should provide nutrient recovery and recycling, localized production capabilities, and low energy consumption. Magnesium-based electrochemical wastewater treatment processes are one technology option with the potential to address these needs by providing opportunities for simultaneous recovery of valuable resources from waste streams. In this system, phosphate and ammonium coprecipitate with the magnesium released from the sacrificial anode, producing struvite, NH4MgPO4, as a fertilizer. This technology also eliminates the disadvantages of the commonly used chemical precipitation method of struvite recovery, including magnesium salt dosing, and adding base to the system for pH control, due to in situ magnesium corrosion and hydroxide production at the magnesium anode surface.In this presentation, we specifically focus on a membrane-separated electrochemical process with a solid magnesium electrode. A complex synthetic water matrix including key ions such as ammonium, potassium, and phosphorus with other background salts was made for the anodic chamber to simulate animal liquid manures. Sodium sulfate solution was used as the supporting electrolyte on the cathodic chamber. Two different cation exchange membranes (CEMs) were placed between the two compartments to separate the anolyte from the catholyte. All experiments were conducted under OCV (no external energy input), and ion concentrations in each chamber were tracked over time using ion chromatography to perform kinetic study. The produced precipitates from each experiment are collected and have been characterized by scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) to identify the morphology and purity of the produced solid precipitates. Furthermore, X-ray diffraction (XRD) and Fourier-transform infrared spectrometry (FT-IR) were used to exactly identify the nature of the precipitates. Experimental results indicate that magnesium electrode corrosion under OCV in the anolyte will decrease ammonium separation through the CEM to the catholyte compared to potassium.

Development of Membranes for Alkaline Water Electrolysis

Alkaline water electrolysis is one of the important methods for generating high purity hydrogen. Alkaline electrolysis, because of the possibility of using relatively inexpensive electrode materials, is more economical than hydrolysis in acidic medium; the medium is also less corrosive. The challenges in water electrolysis in general are to reduce the cost, energy consumption and maintenance, hence increase the efficiency of the overall process. An important consideration in the above is the separator between the two electrode compartments, which has to be such that it minimizes (or eliminates) the possibility of mixing of gases evolved at the two electrodes, while not adding much to the overall voltage drop in the electrolyzer. The objective of this study is to develop a membrane separator with low ohmic resistance and hydrogen permeability, essential for the alkaline electrolysis operation. A thorough analysis of the membrane’s resistance is done based on a study of how synthesis parameters, and (through them) the structure, determine the physical and electrochemical properties and influence the electrolysis. Three categories of separators have been reported for alkaline water electrolysis: porous separators, anion exchange membranes and ion-solvating membranes. Anion exchange membranes have a functionalized polymeric base with cationic groups linked to the polymer backbone, for anion conduction across the membrane separator. An ion-solvating membrane is a dense polymeric material containing a polymer backbone with affinity to aqueous KOH (the normally used electrolyte) to achieve ionic conductivity. Porous separators are diaphragms which physically separate the anodic and cathodic chambers, although allowing some ion conduction by virtue of their ability to sorb the electrolyte. Our focus in this study is on the last type of separators. We report here our studies on a porous composite Zirfon membrane separator made up of polysulfone polymer and zirconium dioxide, with 80wt% loading of zirconium dioxide and a nylon mesh support. The membranes were made in-house and had an average thickness and ohmic area-resistance of 320μm and 4.5Ω-cm2 (measured in 0.5M NaOH via Electrochemical Impedance Spectroscopy), respectively. A lab-scale electrolyzer cell was installed with the composite Zirfon membrane and commercial Zirfon membrane and was tested for alkaline electrolysis; a quantitative relationship between the cell voltage, current and impedance results is established and analyzed by calculating the expected ohmic losses, Tafel kinetics and purity of hydrogen gas evolved. The electrolyzer achieved a cell voltage of 2.4V with the in-house membrane and 2V with the commercial membrane at a current density of 0.06Acm-2 in 0.5M NaOH solution with Nickel foam as electrodes. The Tafel slopes obtained for both hydrogen and oxygen evolution reactions for Nickel foam electrodes with commercial Zirfon and in-house composite Zirfon separator was 200 mV/dec and 220 mV/dec, respectively. The results obtained for the in-house membrane are benchmarked against the commercial Zirfon membrane. Figure 1

Harnessing plant microbial fuel cells for resource recovery and methane emission reduction in paddy cultivation

The primary objective of this study is to improve the eco-sustainability of the flooded rice-based system by integrating a tubular configuration of a plant microbial fuel cell (plant-MFC) with a terracotta membrane. The emphasis was placed on enhancing resource recovery and mitigating greenhouse gas emissions from rice cultivation. The study utilizes the 'Improved White Ponni' variety of medium duration Paddy (Oryza sativa L.) as the model plant. Additionally, biochar derived from Typha angustifolia L. was incorporated in the paddy growing matrix as a dual-purpose element, serving both as a soil amendment and as an integral part of the plant-MFC anode. The plant-MFCs with additional floating cathodes coupled with biochar amended paddy microcosm (PMFC-BC) exhibited the highest power density (46.8 mW/m2) with reduced methane emissions compared to the other types of plant-MFCs studied. A total of 1.27 L of catholyte was collected from PMFC-BC for the 15-week study period. The energy-dispersive X-ray analysis of the catholyte sediments showed the presence of various elements including N, Na, C, Mg, K, Cl, P, Ca, Si, Fe, O, Ti, etc., indicating the migration of soil nutrients across the terracotta membrane and chemical precipitation in the cathode chamber of plant-MFC. In the active tillering phase of the paddy, the methane emission flux from PMFC-BC was 57 % less when compared to the paddy microcosm without any MFC integration. It is believed that the integration of this type of plant-MFCs which can generate direct electricity, recover catholyte with nutrients, and reduce methane emissions from the paddy growing matrix will make rice cultivation truly sustainable and carbon negative.

Photoelectrocatalytic degradation of wastewater and simultaneous synthesis of NH3 on Fe-CNTs-supported octahedral Cu2O composite nanocatalysts

Fe-core carbon nanotubes (Fe-CNTs) were produced by vapor deposition using coal as a carbon source. Then, octahedral copper oxide nanoparticles (Cu2ONO) (prepared by solvent reduction method) were loaded on Fe-CNTs by hydrothermal method to prepare the composite catalyst Cu2ONO/Fe-CNTs. While characterizing (TEM, XRD, FTIR, XPS, N2-TPD, BET, etc.) the material structure, the performance of Cu2ONO/Fe-CNTs in photoelectrocatalytic (PEC) degradation of cotton pulp black liquor (CPBL an organic wastewater with high CODCr) and simultaneous synthesis of NH3 was studied. The PEC reaction was carried out in an H-type reactor. CPBL was oxidized at the anode to produce H+, CO2, H2O and other small molecules, where H+ passes through a proton exchange membrane and is reduced with N2 to produce NH3 at the cathode. After 4 h of reaction, the CODCr removal rate of CPBL in the anode chamber reached 95.42%, and the yield of NH3 in the cathode chamber reached 9.06 mmol L−1 cm−2. The dual purpose of synthesizing NH3 while degrading wastewater was achieved.

Simultaneous removal of sulfide and bicarbonate from synthetic wastewater using an algae-assisted microbial fuel cell

ABSTRACT The anaerobic digestion (AD) process is one of the most practiced technologies for the remediation of organic waste and maximization of energy recovery in terms of biogas or biomethane. The presence of other gaseous components in biogas, e.g. CO2 and H2S, often makes its direct application in engines and electricity production unsuitable. This work aimed to develop and utilize an algae-assisted microbial fuel cell (AMFC) for the purification of biogas by removing both CO2 and H2S and simultaneous bioelectricity generation. In addition to biogas clean-up, elemental sulfur recovery and CO2 utilization for algae cultivation add value to the proposed AMFC process. Experiments were performed with both sulfide and bicarbonate in their dissolved form, in the respective anodic and cathodic chambers of the AMFC. The sulfide concentration was varied from 100 to 800 mg/l and the AMFC exhibited a sulfide removal efficiency exceeding 97% at all concentrations tested. The process efficiency dropped, however, at sulfide concentrations above 300 mg/l in terms of both sulfide removal and power output. The AMFC performed best at 400 mg/l sulfide by exhibiting a power density of 24.99 mW/m3 and sulfide removal efficiency of 98.87%. The system exhibited columbic efficiency (CE %) in the range of 7.85–80%. The total alkalinity representing CO2, carbonate and bicarbonate levels in the algae-based system was reduced by 49.54%. The electrical energy recovered from the AMFC was 0.1 kWh/m3 and the total energy recovery, which is the sum of the electrical and algal lipid energy, amounted to 7.25 kWh/m3.

Amorphous Ni-Mo-B-O Bifunctional Electrocatalyst for Simultaneous Production of Hydrogen and Value-added Chemicals.

Hydrogen evolution reaction (HER) coupled with biomass conversion is a sustainable route to produce clean energy H2 and value-added chemicals simultaneously. Herein, an amorphous Ni-Mo-B-O bifunctional electrocatalyst was synthesized through a facile electrodeposition method and employed as a cathode for HER to produce H2 and as an anode for the conversion of hydroxymethylfurfural (HMF) to furandicarboxylic acid (FDCA). Besides leading to the formation of amorphous structures, the introduction of Mo and B can increase the electron density and optimize the electronic structure of the electrocatalyst, thus substantially increasing the catalytic activity of the catalyst. After continuous reaction at a constant potential of 0.58 V vs. Hg/HgO for 8 hours, the conversion of HMF reached 98.86 %, and the selectivity of the target product FDCA was as high as 92.97 %. Finally, a two-electrolyzer system was constructed using the amorphous Ni-Mo-B-O as both cathode and anode to achieve simultaneous H2 production in the cathode chamber and FDCA production in the anode chamber at a low voltage. This work presents a promising strategy for the design and synthesis of high-performance non-noble metal electrocatalysts for efficient and cost-effective H2 production.