Granular Graphite Research Articles

An electrochemical method for the regeneration of trivalent iron to increase the efficiency of in-situ leaching of uranium

Due to the increasing demand for electricity with the development of production and general infrastructure, increasing the production of uranium as an economically and environmentally efficient source of energy is an urgent problem. The purpose of this study is to develop an electrochemical method for the regeneration of iron (III) ions used as a uranium oxidizer in the process of in-situ leaching of uranium minerals with sulfuric acid solutions. Methods. The mechanism of reactions in the iron (II)-iron (III) redox system was studied by recording potentiodynamic polarization curves and conducting electrolysis of the oxidation of divalent iron ions under galvanostatic conditions. Results and discussion. Cathode-anodic and anodic-cathode cyclic polarization curves taken on platinum electrodes showed that the redox reactions of iron ions are reversible and these reactions occur at a slight overvoltage. The influence of the main electrochemical parameters (current density, concentrations of iron (II) ions and sulfuric acid) on the oxidation of divalent iron ions was studied for the first time using granular anode electrodes, the electrode spaces of which are separated by an anionite membrane. It has been found that the use of granular graphite electrodes in the oxidation divalent iron ions increases the current output by more than 2 times compared to a plate graphite electrode. Conclusion. According to the results of the study, it was noted that under optimal conditions, the current output of the oxidation of divalent iron ions exceeds 90%. Extensive research has shown that trivalent iron ions, widely used in the in-situ leaching process for uranium production, can be regenerated by electrochemical methods.

Ex-situ electrochemical characterisation of fixed-bed denitrification biocathodes: A promising strategy to improve bioelectrochemical denitrification

The worldwide issue of nitrate-contaminated groundwater requires practical solutions, and electro-bioremediation offers a promising and sustainable treatment. While it has shown potential benefits, there is room for improvement in treatment rates, which is crucial for its further and effective implementation. In this field, electrochemical characterisation is a valuable tool for providing the foundation for optimising bioelectrochemical reactors, but applying it in fixed-bed reactors is challenging due to its high intrinsic electrical resistance. To overcome these challenges, this study employed the easy and swift eClamp methodology to screen different process parameters and their influence on the performance of fixed-bed denitrifying biocathodes composed of granular graphite. Granules were extracted and studied ex-situ under controlled conditions while varying key operational parameters (such as pH, temperature, and nitrate concentration). In the studied biocathode, the extracellular electron transfer associated with denitrification was identified as the primary limiting step with a formal potential of −0.225 ± 0.007 V vs. Ag/AgCl sat. KCl at pH 7 and 25 °C. By varying the nitrate concentration, it was revealed that the biocathode exhibits a strong affinity for nitrate (KMapp of 0.7 ± 0.2 mg N–NO3− L−1). The maximum denitrification rate was observed at a pH of 6 and a temperature of 35 °C. Furthermore, the findings highlight a 2e−/1H+ transfer, which holds considerable implications for the energy metabolism of bioelectrochemical denitrifiers. These compiled results provide valuable insights into the understanding of denitrifying biocathodes and enable the improvement and prediction of their performance.

Development of nature-based sustainable passive technologies for treating and disinfecting municipal wastewater: Experiences from constructed wetlands and slow sand filter

There is an urgent need to develop low-cost technology for effective wastewater treatment and its further disinfection to the level that makes it economically useful. This work has designed and evaluated the various types of constructed wetlands (CWs) followed by a slow sand filter (SSF) for wastewater treatment and disinfection. The studied CWs were, CWs with gravels (CW-G), free water surface-CW (FWS-CWs), and CWs integrated microbial fuel cell (MFC) with granular graphite (CW-MFC-GG) planted with Canna indica plant species. These CWs were operated as secondary wastewater treatment technologies followed by SSF for disinfection purposes. The highest total coliform removal was observed in the combination of CW-MFC-GG-SSF which achieved a final concentration of 172 CFU/100 mL, whereas faecal coliform removal was 100 % with the combinations of CW-G-SSF and CW-MFC-GG-SSF, achieving 0 CFU/100 mL in the effluent. In contrast, FWS-SSF achieved the lowest total and faecal coliform removal attaining a final concentration of 542 CFU/100 mL and 240 CFU/100 mL, respectively. Furthermore, E. coli were detected as negative/absent in CW-G-SSF and CW-MFC-GG-SSF, while it was positive for FWS-SSF. In addition, the highest turbidity removal was achieved in CW-MFC-GG and SSF combination of 92.75 % from the municipal wastewater influent turbidity of 82.8 NTU. Furthermore, in terms of overall treatment performance of CW-G-SSF and CW-MFC-GG-SSF, these systems were able to treat 72.7 ± 5.5 % and 67.0 ± 2.4 % of COD and 92.3 % and 87.6 % of phosphate, respectively. Additionally, CW-MFC-GG also exhibited a power density of 85.71 mA/m3 and a current density of 25.71 mW/m3 with 700 Ω of internal resistance. Thus, CW-G and CW-MFC-GG followed by SSF could be a promising solution for enhanced disinfection and wastewater treatment.

Evaluation of a bioelectrochemical reductive/oxidative sequential process for chlorinated aliphatic hydrocarbons (CAHs) removal from a real contaminated groundwater

In the present study, the sequential reductive/oxidative bioelectrochemical process has been tested with real groundwater from a contaminated site in Northern Italy for chlorinated aliphatic hydrocarbons (CAHs) removal. The sequential system was developed by connecting in series two membrane-less microbial electrolysis cells (MECs) equipped with an internal graphite counter electrode. The first MEC aimed at the CAHs reductive dechlorination (RD) and was constituted of a granular graphite working electrode. In the second MEC, a mixed metal oxide working electrode stimulated the oxidative dechlorination of the low chlorinated RD's by-products through oxygen production. The sequential process allowed complete mineralization of the CAHs contained in the real groundwater. A complete reduction of the perchloroethylene into vinyl chloride (VC) was observed in the first MEC polarized at −450 mV vs SHE, while the resulting VC was oxidized with a 92 ± 2 % efficiency in the second MEC due to the HRT increment from 0.7 to 1.7 days. Biomarkers of the reductive (Dehalococcoides mccartyi 16S rRNA and reductive dehalogenase genes) and oxidative (etnE, etnC genes) dechlorination have been monitored in the two MECs along with the ecotoxicity tests. Overall, they provide information on the efficiency of the applied technology and allow to assess the potential adverse effects. According to the Tetrahymena pyriformis reproduction inhibition test and Panagrellus redivivus mortality tests, showed a significant ecotoxicity reduction with respect its initial inhibitory effect at the tested concentrations.

Ultra-fast and low-cost electroactive biochar production for electroactive-constructed wetland applications: A circular concept for plant biomass utilization

This study demonstrates two sustainable processes to produce electroactive biochars and their application in electroactive constructed wetlands (CWs) for providing a circular route for biomass utilization and technology up-gradation for wastewater treatment along with electricity generation. With the use of Canna indica biomass generated in CWs operation, the current study produced two different biochars that differ in their physico-(electro)chemical properties related to the preparation method used. This study used plasma based processing to produce ultrafast biochar (PB) within a few minutes resulting in more crystalline biochar with high electrical conductivity compared to the amorphous biochar material produced by using the drum kiln processed biochar (KB) method. These biochars were used in developing electroactive constructed wetlands coupled with microbial fuel cells (CW-MFC) and were operated in batch mode together with commercial granular graphite (GG) substrate-based CW-MFC as control. PB was developed from high-temperature plasma processing in 6.0 min, whereas KB was prepared in bulk amount from semi-controlled combustion process in kiln method and took 3–4 days before final biochar preparation. Electrical conductivity (EC) of the biochar and GG material were found to be in the order of PB > GG > KB, indicating PB as a highly conductive material that assisted in microbial electron transfer. Accordingly, the highest current and power densities of 628 mA m-3 and 126 mW m-3, respectively, were also achieved with PB. The COD removal of 72.42 ± 2.61 %,72.32 ± 2.98 % and 59.91 ± 3.21 % was found in CW-MFC-GG, CW-MFC-KB and CW-MFC-PB microcosms, respectively.

Crystallization and Melting Behavior of UHMWPE Composites Filled by Different Carbon Materials

In order to understand the effect of different carbon materials on the crystallization and melting behavior of ultrahigh molecular weight polyethylene (UHMWPE), UHMWPE composites were prepared by different carbon materials through solution mixing in this paper. UHMWPE was oxidized to improve the interfacial interaction between UHMWPE and carbon materials. The UHMWPE composites and oxidized UHMWPE composites were prepared using granular graphite particle (GP), graphite nanoplatelets (GNP), and flaky graphene oxide (GO) as fillers. The effect of the type and the content of carbon materials and the oxidization of UHMWPE on crystallization and melting temperatures, crystallinity, and crystal form of UHMWPE and oxidized UHMWPE composites was investigated by differential scanning calorimetry, X-ray diffraction, scanning electron microscope, X-ray photoelectron spectrum, and Fourier transform infrared spectroscopy. The results indicated that there are coexistence of the heterogeneous nucleation and the hindering effect of crystal growth by carbon materials for UHMWPE crystallization. The different influence of carbon materials on the crystallization and melting behavior of UHMWPE was discussed by the heterogeneous nucleation of carbon materials and the restriction of the macromolecular chain motion of UHMWPE by carbon materials.

Removal of copper (II) ions from spent solutions by granular graphite electrodes

The most abundant heavy non-ferrous metals in industrial wastewater and spent solutions are lead, copper, zinc, nickel, however, it depends on the type of the industry. This work proposes the concepts of an electrochemical method of divalent copper removal from spent solutions with help of granular graphite electrodes. The study was conducted changing the meanings of the five major parameters including the current density (i), the concentration of copper (II) ions (C), the surface area of graphite electrodes (S), the concentration of sulfuric acid in the solution (M) and the electrolysis duration (τ) affecting Cu (II) ions removal percentage from solution. Experimental results show that the current density, surface area of the granular graphite electrodes and the time are the main factors that affect the removal percentage of Cu (II), while the changes in sulfuric acid concentration in solution have a minor effect. Highest copper removal value 97% and 54 % current efficiency was observed in conditions: i =150A/m2, τ = 1.5 h, [H2SO4] = 0.4 M, S = 150 cm2 which is considered as an optimal condition for copper removal process by granular graphite electrode.

Ammonium recovery from agro-industrial digestate using bioelectrochemical systems.

Growing food and biomass production at the global scale has determined a corresponding increase in the demand for and use of nutrients. In this study, the possibility of recovering nitrogen from agro-industrial digestate using bioelectrochemical systems was investigated: two microbial electrolysis cells (MECs) were fed with synthetic and real digestate (2.5 gNH4+-N L-1). Carbon felt and granular graphite were used as anodes in MEC-1 and MEC-2, respectively. As to synthetic wastewater, the optimal nitrogen load (NL) for MEC-1 and -2 was 1.25 and 0.75 gNH4+-N d-1, respectively. MEC-1 showed better performance in terms of NH4+-N removal efficiency (39 ± 2.5%) and recovery rate (up to 70 gNH4+-N m-2d-1), compared to MEC-2 (33 ± 4.7% and up to 30 gN m-2d-1, respectively). At the optimal hydraulic retention time, lower NH4+-N removal efficiencies and recovery rates were observed when real digestate was fed to MEC-1 (29 ± 6.6% and 60 ± 13 gNH4+-N m-2d-1, respectively) and MEC-2 (21 ± 7.9% and 10 ± 3.6 gNH4+-N m-2d-1, respectively), likely due to the higher complexity of the influent. The average energy requirements were 3.6-3.7 kWh kgNremoved-1, comparable with values previously reported in the literature and lower than conventional ammonia recovery processes. Results are promising and may reduce the need for costly and polluting processes for nitrogen synthesis.

Electrochemical Method of Lead (II) Ions Removal from Wastewater Using Granular Graphite Electrodes

The article presents an electrochemical method of wastewater treatment from Pb (II) ions through granular graphite electrodes. The cathode was made of graphite particles and the anode was made of rod graphite. Fea-tures of wastewater treatment from heavy metals by using developed surface granular graphite electrodes were revealed. Electrochemical research was carried out in a flow mode in a two-chamber electrolyzer. Effect of different electrochemical parameters (current density, electrolyte flow rate, initial concentration of lead (II) ions in solution, size of graphite granules, and concentration of additional cations in solution) to the reduction process of Pb (II) on lump graphite was studied. Results revealed that the removal value of Pb (II) hit a peak at 150A/m2 current density and gradually decreased at a higher value. The efficiency of electrolysis in the flow mode was demonstrated. It was found that the initial concentration of lead ions in the electrode process was insignificant, while the concentration of additional cations had a significant effect. Using very small par-ticles of granular graphite electrodes caused an agglomeration. At an optimal condition, (i=150 A/m2; V=150 ml/h; [Pb2+] = 200 mg/l; s= 0.05 cm3) treatment value of wastewater from Pb (II) ions reached 97.6±0.3 %.

Evaluating the application ability of membrane-less microbial fuel cells in shrimp farming wastewater recirculation

Microbial fuel cell (MFC) was considerable as a promising saline wastewater treatment which using microorganism to convert organic compounds to electrical energy. Most of wastewater generated from aquaculture farming contained highly saline effluents. In addition, the maintenance of good water quality was essential for optimum growth and survival of shrimp. This study aimed to evaluate the ability of Membrane-less Microbial Fuel Cells (MFCs) to treat wastewater for recirculation of shrimp culture wastewater, and improvement in the growth performance of Penaeus vannamei (White Leg Shrimp). Six MFCs models were built with locally available materials such as: polyvinyl chloride (PVC), anaerobic sludge, carbon cloth anode and cathode electrodes, granular graphite, glass wool and glass bead. This study compared two different treatments including: control (cultivation with no MFCs models) and MFCs models (application models with shrimp culture), run in continuous mode at room temperature (250C – 30oC). Each treatment was run in triplicate with shrimp at size PL30-PL45, average initial weight of 0.91 +/- 0 (g) and average initial length of 3.03 +/- 0.6 (cm). Experiments were set up using the 120 L tanks (working volume of 90 L), input with seawater at 20 ppt salinity, temperatures range of 22◦C to 26◦C, pH range of 7.5 to 9.4, and dissolve oxygen range of 5.5 to 7.2. The density of shrimp was 5 post larvae (PL) per liter. Research results achieved the removal of chemical oxygen demand, ammonia, nitrite and nitrate were up to 58.83%, 76.1%, 56.33% and 70.90%, respectively. The survival rate of shrimp was maintained, and growth rate was enhanced significantly compared with control treatment. The obtained results in this study presented that MFCs has ability to treat pre-circulation of shrimp culture wastewater and improved in the growth performance of Penaeus vannamei (White Leg Shrimp).

The synergistic effect of carbon materials on properties of copper-based friction materials

PurposeThis study aims to investigate the effect of combined use of granular graphite and petroleum coke on the properties of copper-based friction materials and the friction and wear mechanisms.Design/methodology/approachCopper-based friction materials with different proportions of petroleum coke and granular graphite were prepared by using powder metallurgy. The friction surfaces were analyzed.FindingsChanging the ratio of petroleum coke/granular graphite affects the formation of oxides and sulfides on the surface of the materials. Increasing the petroleum coke promotes the production of metal sulfide and sulfate in the friction materials and reduces coefficient of friction (COF) and wear. Increasing petroleum coke also increases the amount of carbonic oxide (CO) released during the braking process and promotes the reduction process of iron oxide on the friction surface.Originality/valueThe synergistic effect of carbon materials on copper-based friction materials was studied in terms of the tribological chemical reaction. This research provides useful information for the selection of carbon materials in friction materials.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2020-0075/

Effects of Different Biological Carriers in Microbial Fuel Cells.

In this study, to investigate their effects on battery power generation performance and wastewater treatment capacity, coal semicoke granular-activated carbon, granular graphite, and walnut shell-activated carbon were added to the anode compartment of a microbial fuel cell. As revealed from the experimental results, adding activated carbon and graphite can significantly decrease the startup time of microbial fuel cells as well as provide the shortest startup time of coal semicoke-activated carbon fluidized bed microbial fuel cells (MGAC-MFCs). The activated carbon particle diameter did not increase from 0.275 to 0.55 mm, and the voltage changed the chemical oxygen demand (COD) degradation efficiency. However, the 0.275 mm activated carbon exhibited a maximum open-circuit voltage of 935 mV as well as a COD degradation efficiency of 95%, and the operation cycle was shortened. After running a cycle, the COD removals of different systems were 85, 93, and 89%, and the maximum value was obtained by the MGAC-MFC system. After the activated carbon and graphite particles were added, the electrical performance and production capacity of the sewage treatment microbial fuel cells were significantly enhanced.

Hydrodynamics of up-flow hybrid anaerobic digestion reactors with built-in bioelectrochemical system

Understanding the electrode configuration is vital for the successful application of bioelectrochemical system (BES) in recalcitrant wastewater treatment. Especially in those traditional anaerobic processes that integrate with BES to construct effective hybrid bioreactors. Hybrid bioreactors employed granular graphite as electrode material achieved 86.62 ± 1.83% decolorization efficiency of azo dye acid orange 7 (AO7) at influent AO7 loading rate of 800 g/(m3∙d) and it was about 6% higher than that with carbon fiber brush electrodes. Such electrodes were positioned above the anaerobic sludge layer and higher efficiency (8%) than the reactors with electrodes placed beneath the sludge layer was observed. Tracer experiments and modeling of residence time distribution indicated that the fluid pattern in hybrid bioreactors was modified to plug flow pattern and had a better consummate mixing ability compared to the conventional anaerobic reactor. Simulation using computational fluid dynamics technique showcased favorable mass transfer near electrode modules. The hydrodynamics of simulation and experimental results were connected by simplifying electrode module as a porous media model. This study thus proved that hybrid bioreactors can effectively enhance wastewater treatment comprehensively through the analysis of decolorization performance and hydrodynamics.

Effect of graphite type on the contact plateaus and friction properties of copper-based friction material for high-speed railway train

Copper-based friction materials containing the same graphite concentrations but varied proportion of granular graphite to flake graphite were prepared by powder metallurgy for high-speed railway trains. The friction coefficient and specific wear rate were tested on pin on disc machine. The results showed that the addition of appropriate granular graphite can improve the magnitude and stability of friction coefficient and help to form the secondary plateaus on friction surface. However, excessive addition of granular graphite led to a significant decrease in friction coefficient. The flake graphite had better lubricity but promoted the occurrence of delamination due to its weak strength. Statistical analysis revealed that the specific wear rate was negatively linear correlated with the graphite coverage area on the friction surface. In addition, there was a critical plateau coverage on friction surface, above which the specific wear rate can be effectively reduced. Comprehensive evaluation of the magnitude and stability of the friction coefficient as well as wear rate, the ratio of 5 wt% granular graphite to 5 wt% flake graphite is the most suitable for high performance copper-based friction material.

Continuous synthesis of graphite with tunable interlayer distance

A study was carried out to produce graphite with controlled interlayer distance synthesized from methane using hydrogen as modifying agent. The synthesis was carried out in radio frequency (r.f.) thermal plasma where the methane-to‑hydrogen ratio varied systematically over a wide range. The synthesized materials were investigated in terms of structure, morphology and the interlayer distance. It is found that there is a critical fraction of hydrogen, around half of that of methane flow rate, up to which it is possible to control the interlayer distance as well as the number of layers making up the platelet in the synthesized material. The number of layers which were around 25 in the granular graphite obtained with methane only was modified into a flaky graphite of 10 μm in size with as few as 12 layers yielding a surface area of 300 m2/g. The result combined with data from literature show that it is possible to adjust the interlayer distance in graphite from Lc = 0.334 to 0.369 nm even up to 0.416 nm. The significance of this was discussed within the context of the use of graphite as anode in rechargeable batteries.

Influence of reactor’s hydrodynamics on the performance of microbial fuel cells

Microbial fuel cells (MFCs) were the first bioelectrochemical systems to have been intensively studied and applied. In this study, two double-chamber MFCs (MFC1 and MFC2), identically designed and built as completely-mixed systems, were run for 69 days using dairy wastewater as anode substrate. To characterize the hydrodynamic behavior of the MFCs, a comprehensive specific study was performed, to identify any reactors’ dead spaces, and the hydrodynamic model closer to their real performance. Both anodic chambers showed to behave as completely stirred tank reactors (CSTRs) without perceivable dead spaces, while cathodic chambers showed a radically different hydrodynamic behavior. While MFC1’s cathode system performed as two CSTR reactors in series, with 9–13% dead space, MFC2′s cathode system was best described by a single CSTR model with dead space varied in the wider range 11–30%. Electric production and organic matter removal were also monitored, and correlated to the MFCs’ hydrodynamics, showing the latter’s influence on the entire process. Interesting considerations can be drawn from this study on MFC constructive methods: the absence of hydrodynamics’ invariance in MFCs equipped with granular graphite electrodes suggests the unfeasibility of their scaling up.

Optimizing the performance of organics and nutrient removal in constructed wetland–microbial fuel cell systems

No studies have reported the operation optimization of constructed wetland–microbial fuel cell (CW–MFC) systems in terms of pollutant removal under the influence of multiple factors. Multifactor orthogonal experiment (L25(55)) was designed in this study to investigate the influence of multiple factors on the CW–MFC performance and determine the optimal operating conditions for the organics and nutrient removal. The tested factors include volume ratio of granular graphite in the substrates (A), dissolved oxygen (DO) concentration in the cathode zone (B), hydraulic retention time (HRT) (C), effluent reflux ratio (D), and external resistance (E). The results showed that the sequence and degree of the influence of the tested factors were C** > B** > E** > D* > A for chemical oxygen demand (CODCr) removal, C** > B** > D* > E > A for ammonia nitrogen (NH3-N) removal, C** > D** > B** > E* > A* for total nitrogen (TN) removal, and C** > D* > B > A > E for total phosphorus (TP) removal (* denotes significant influence (0.01 < p < 0.05) and ** denotes extremely significant influence (p ≤ 0.01)). HRT was found to be the most influential factor for pollutant removal in CW–MFCs with a contribution of over 50% for CODCr, NH3-N and TP removal, and over 45% for TN removal. The optimal operating conditions for CODCr, NH3-N, TN and TP removal in CW–MFCs were quite different from each other. Comprehensively considering the treatment efficiency of pollutant, treatment capacity of wastewater, and energy consumption from artificial aeration, the selected comprehensive optimal operating conditions for CW–MFCs were A = 20%, B = 1.5 mg/L, C = 1.5 days, D = 50%, and E ≤ 250 Ω. Moreover, incorporating the MFC significantly enhanced the organics and nitrogen removal in CWs by 8.72–11.04% CODCr and 9.78–12.04% TN.

A proof-of-concept graphite anode with a lithium dendrite suppressing polymer coating

Dendritic Li deposition on graphite anodes of Li-ion batteries (LIBs) not only deteriorates the anode performance but also causes safety concerns. We demonstrate here a proof-of-concept graphite anode containing a polymer coating that effectively mitigates Li dendrite formation under harsh lithiation conditions. It is shown that Li dendrites with dimensions ranging from a few tens nanometers to microns occur readily on granular graphite electrodes either under 20% over-lithiation at 0.2C or fast lithiation up to 10C rate. In contrast, the graphite anode with a conformal thin coating of high-polarity β-phase polyvinylidene difluoride (PVDF) on graphite particles exhibits dendrite-free Li plating under either condition. Moreover, the PVDF coated graphite anode exhibits substantially improved cycling stability with high Coulombic efficiencies under the Li-plating conditions. The rise of charge-transfer resistance due to over-lithiation is reduced. The proof of concept for adopting a dendrite-suppressing polymer coating on graphite anodes offers a new strategy for improving battery safety and renders more options for cell design in enhancing energy and power performances for the state-of-the-art LIBs.

Enhanced methane recovery and exoelectrogen-methanogen evolution from low-strength wastewater in an up-flow biofilm reactor with conductive granular graphite fillers

Methane production from low-strength wastewater (LSWW) is generally difficult because of the low metabolism rate of methanogens. Here, an up-flow biofilm reactor equipped with conductive granular graphite (GG) as fillers was developed to enhance direct interspecies electron transfer (DIET) between syntrophic electroactive bacteria and methanogens to stimulate methanogenesis process. Compared to quartz sand fillers, using conductive fillers significantly enhanced methane production and accelerated the start-up stage of biofilm reactor. At HRT of 6 h, the average methane production rate and methane yield of reactor with GG were 0.106 m3/(m3·d) and 74.5 L/kg COD, which increased by 34.3 times and 22.4 times respectively compared with the reactor with common quartz sand fillers. The microbial community analysis revealed that methanogens structure was significantly altered and the archaea that are involved in DIET (such as Methanobacterium) were enriched in GG filler. The beneficial effects of conductive fillers on methane production implied a practical strategy for efficient methane recovery from LSWW.

Denitrification in a low carbon environment of a constructed wetland incorporating a microbial electrolysis cell

The main aim of this study was to explore the possibility of denitrification under low carbon conditions in a microbial electrolysis cell (MEC) integrated into a constructed wetland (CW). To our knowledge, this is the first systematic study of the incorporation of an MEC into a CW for enhancing denitrification. CWs are an efficient and low-cost technology for wastewater treatment facing problems in denitrification under low carbon conditions. Two CW-microcosms were fabricated: one included an MEC arrangement with granular graphite electrodes attached to a power source and the other with a microcosm fabricated with normal stone gravel as a control. These microcosms were fed with synthetic wastewater containing 50 mg/l of nitrate-nitrogen (NO3-N) with different ratios of organic carbon. Carbon to nitrogen ratio (C: N) were kept to 2:1, 1:1 and 0.5:1. The maximum concentration of organic carbon was 100 mg/l, subsequently decreased to 50 mg/l to 25 mg/l. The highest percentage removal achieved from CW-MEC in C: N ratios of 2:1 were 69.3% on 0.583 mA applied current, whereas the control microcosm’s removal efficiency on the same C:N was 66.2%. The outcomes of this study show that the NO3-N removal was always higher in the MEC integrated CW compared to the normal CW. The study concludes that the higher denitrification is possible by incorporation of an MEC into a constructed wetland under low carbon condition. This approach can provide a new direction for denitrification enhancement in a CW.