Abiotic Cathode Research Articles

Simultaneous organic wastewater treatment and bioelectricity production in a dual chamber microbial fuel cell with Scenedesmus obliquus biocathode

Algal biocathode MFCs (ABMs) are recently being heavily studied due to their advantage over abiotic cathode MFCs (ACMs) as dissolved oxygen (DO) generated by algal growth in the cathodic chamber is directly utilized in cathodic oxidant reduction. In this work growth of pure algae species Scenedesmus obliquus used in the cathode chamber has been studied under a photoperiod of 24 h illumination to supplement oxygen for continual MFC operation without any external supply of air or carbon dioxide and treatment of synthetic wastewater having chemical oxygen demand (COD) equivalent to medium strength domestic wastewater (5.35 g/L COD). Results of ABM showed the highest continuous current density generation of 23.93 mA/m2 and the highest continuous volumetric power density generation of 13.24 mW/m3 were around 120 h with COD removal efficiency of 92.52 % and coulombic efficiency (CE) of 41.88 %. Initial ohmic (Roh) and charge transfer (Rct) resistance values of ABM were found to be 8.3 Ω and Rct of 22.5 Ω which after 216 h of algal growth got reduced to 1 Ω and 15.1 Ω respectively. 16S microbiome profiling of the mixed microbial sludge inoculum used in the anodic chamber showed dominance of Xanthomonadaceae stenotrophomonas (9.7 %), Chitinophaga flexibacter (8.65 %), Sphingomonadaceae sphingomonas (6.82 %), Sphingobacterium multivorum (6.55 %), Dyadobacter fermentans (6.05 %), and Alcaligenaceae achromobacter (5.51 %). Elemental investigation of the bioanode’s and biocathode’s surface carried out using EDS analysis also shows that oxygen was generated in the cathodic chamber by pure Scenedesmus obliquus species.

In-situ n-doped 3D-printed abiotic cathodes for implantable biofuel cells

In-situ n-doped 3D-printed abiotic cathodes for implantable biofuel cells

Autotrophic degradation of sulfamethoxazole using sulfate-reducing biocathode in microbial photo-electrolysis system

Sulfamethoxazole is a representative of sulfonamide antibiotic pollutants. This study aims to investigate the degradation pathways of sulfamethoxazole and the response of microbial communities using the autotrophic biocathode in microbial photo-electrolysis systems (MPESs). Sulfamethoxazole with an initial concentration of 2 mg L−1 was degraded into small molecule propanol within 6 h with the biocathode. Elemental sulfur (S0) was detected in the cathode chamber, accounting for 57 % of the removed sulfate. The conversion from sulfate to S0 indicated that autotrophic microorganisms might adopt a novel pathway for sulfamethoxazole removal in the MPES. In the abiotic cathode, sulfamethoxazole degradation rate was 0.09 mg L−1 h−1 with the electrochemistry process. However, sulfamethoxazole was converted to products that still contain benzene rings, including p-aminothiophenol, 3-amino-5-methylisoxazole, and sulfonamide. The microbial community analysis indicated that the synergistic interaction of Desulfovibrio and Acetobacterium promoted the autotrophic degradation of sulfamethoxazole. The results suggested that autotrophic microorganisms may play an important role in the environmental transformation of sulfamethoxazole.

3D printed cathodes for implantable abiotic biofuel cells

3D printing has recently triggered huge attention in several fields such as construction, artificial tissue engineering, food fabrication, wearable electronics, and electrochemical energy storage.This work investigates the fabrication of a 3D-printed abiotic cathode for implantable glucose/oxygen biofuel cells. The ink formulation was optimized to get printable ink with high electro-catalytic activity. Electrode macro porosity was screened in order to identify the better compromise between electrode density and electrochemical performance. A maximum current density of 260 μA/cm2 was obtained with cylindrical electrodes with linear mesh infill and a volumic infill rate of 40%.A complete biofuel cell was assembled using a 3D-printed abiotic cathode and an enzymatic anode in the form of a compressed pellet showing maximum power and current densities of 80 μW/cm2 and 320 μA/cm2, respectively. Moreover, the hybrid biofuel cell was implanted in the intraabdominal region of a rat for three months and after cell explantation, the abiotic cathode displayed a 50% decrease in the current density while the enzymatic anode did not display any residual activity.The 3D printed electrode displayed a 2–3.6 fold increase in current density when compared to homolog 2D electrodes.

Fabrication of modified electrode by reduced graphene oxide (rGO) and polyaniline (PANI) for enhancing azo dye decolorization in bio-electrochemical systems (BESs)

Bio-electrochemical systems (BESs) have attracted wide attention in the field of wastewater treatment owing to their fast electron transfer rate and high performance. Unfortunately, the low electro-chemical activity of carbonaceous materials commonly used in BESs remains a bottleneck for their practical applications. Especially, for refractory pollutants remediation, the efficiency is largely limited by the cathode property in term of (bio)-electrochemical reduction of highly oxidized functional groups. Herein, a reduced graphene oxide (rGO) and polyaniline (PANI) modified electrode was fabricated via two-step electro-deposition using carbon brush as raw material. Benefiting from the modified graphene sheets and PANI nanoparticles, the rGO/PANI electrode shows highly conductive network with the electro-active surface area increased by 12 times (0.013 mF cm−2) and the charge transfer resistance decreased by 92% (0.23Ω) comparing with the unmodified one. Most importantly, the rGO/PANI electrode used as abiotic cathode achieves highly efficient azo dye removal from wastewater. The highest decolorization efficiency reaches 96 ± 0.03% within 24 h and the maximum decolorization rate is as high as 20.9 ± 1.45 g h−1·m−3. The features of improved electro-chemical activity and enhanced pollutant removal efficiency provide a new insight toward development of high performance BESs via electrode modification for practical application.

High efficiency electrochemical separation of uranium(VI) from uranium-containing wastewater by microbial fuel cells with different cathodes

As an emerging versatile technology for separating uranium from uranium-containing wastewater (UCW), microbial fuel cell (MFC) offers a novel approach to UCW treatment. Its cathode is essential for the treatment of UCW. To thoroughly investigate the efficacy of MFC in treating UCW, investigations were conducted using MFCs with five materials (containing iron sheet (IP), stainless steel mesh (SSM), carbon cloth (CC), carbon brush (CB), and nickel foam (NF)) as cathodes. The results revealed that each MFC system performed differently in terms of carbon source degradation, uranium removal, and electricity production. In terms of carbon source degradation, CB-MFC showed the best performance. The best uranium removal method was NF-MFC, and the best electricity production method was carbon-based cathode MFC. Five MFC systems demonstrated stable performance and consistent difference over five cycles, with CC-MFC outperforming the others. Furthermore, SEM and XPS characterization of the cathode materials before and after the experiment revealed that a significant amount of U(IV) was generated during the uranium removal process, indicating that uranium ions were primarily removed by electrochemical reduction precipitation. This study confirmed that abiotic cathode MFC had a high UCW removal potential and served as a good guideline for obtaining the best cathode for MFC.

Flexible doctor blade-coated abiotic cathodes for implantable glucose/oxygen biofuel cells.

Implantable devices powered by batteries have been used for sixty years. In recent devices, lithium-based batteries are the most widely used power source. However, lithium batteries have many disadvantages in terms of safety, reliability, and longevity and require regular monitoring and substitution. Implantable glucose biofuel cells (BFCs) are increasingly seen as a potential future technology for replacing lithium-based batteries because they do not require surgical replacement after 8-10 years and have a theoretically unlimited lifetime thanks to the continued recovery of glucose and oxygen present in the human body. This paper shows the fabrication of flexible implantable abiotic cathodes, based on a nitrogen/iron-doped graphene catalyst, for glucose/oxygen biofuel cell application. An ink, based on nitrogen-iron doped graphene as the abiotic catalyst and chitosan as a binder, was prepared and coated on a flexible teflonated gas diffusion layer using doctor blade coating. The characterization of the biocathode shows an open potential circuit corresponding to the potential of the abiotic catalyst and a high oxygen reduction current density of up to 66 μA cm-2 under physiological conditions. Those cathodes remain stable for up to two years with a current density loss of only 25%. The flexible abiotic electrode cytotoxicity was evaluated by cell culture experiments showing living cells' high tolerance on the biocathode surface. This work demonstrates that this abiotic catalyst can be a promising alternative for the development of implantable glucose BFCs due to its stability and its cytocompatibility.

A High-Performance Hybrid Biofuel Cell with a Honeycomb-Like Ti3 C2 Tx /MWCNT/AuNP Bioanode and a ZnCo2 @NCNT Cathode for Self-Powered Biosensing.

This work focusses on developing a hybrid enzyme biofuel cell-based self-powered biosensor with appreciable stability and durability using murine leukemia fusion gene fragments (tDNA) as a model analyte. The cell consists of a Ti3 C2 Tx /multiwalled carbon nanotube/gold nanoparticle/glucose oxidase bioanode and a Zn/Co-modified carbon nanotube cathode. The bioanode uniquely exhibits strong electron transfer ability and a high surface area for the loading of 1.14×10-9 molcm-2 glucose oxidase to catalyze glucose oxidation. Meanwhile, the abiotic cathode with a high oxygen reduction reaction activity negates the use of conventional bioenzymes as catalysts, which aids in extending the stability and durability of the sensing system. The biosensor offers a 0.1 fm-1nm linear range and a detection limit of 0.022fm tDNA. Additionally, the biosensor demonstrates a reproducibility of ≈4.85% and retains ≈87.42% of the initial maximal power density after a 4-week storage at 4°C, verifying a significantly improved long-term stability.

Sustainable and Reagentless Fenton Treatment of Complex Wastewater.

Conventional Fenton treatment is fundamentally impractical for large-scale applications, as the consumption of Fe(II), H2O2, and pH regulators and the accumulation of iron hydroxide sludge are very costly. This paper describes a new method for Fenton treatment of complex wastewater without additional dosing of Fe(II) and H2O2, without iron-sludge accumulation, and with less consumption of pH regulators, using a novel bioelectrode system. Our new system includes a novel three-chamber microbial electrolysis unit and Fenton reaction unit, where Fenton reagents are generated by biotic and abiotic cathodes, while the bioanode simultaneously degrades biodegradable organics from the wastewater. The system's self-alkalinity buffering also waives the need for pH regulators. Dissolved organic carbon and 22 specific recalcitrant organics were removed by 99% and between 78 and 100%, respectively. The bioelectrode system generated 13 ± 3 mg/L dissolved Fe(II) and 5 ± 0.4 mg/L H2O2 for the Fenton reaction unit. The closed iron cycle avoided iron loss and iron sludge accumulation during operation. The pH regulator dosage and operating costs were just 9.7 and 1.4%, respectively, of what is required by classic Fenton. The low operating cost and reduction in chemical usage make it an efficient, sustainable alternative to the conventional treatment processes currently used for complex wastewater.

Biocathode regulates enrofloxacin degradation by coupling with different co-metabolism conditions

In this study, biocathode system coupled with different co-metabolism conditions (NaAc, glucose and NaHCO3) were developed to degrade quinolones enrofloxacin (ENR) due to its poorly metabolization, easily accumulation and potential toxicity. Simultaneously, ENR reduction kinetic rate constant in NaAc-fed, glucose-fed and NaHCO3-fed biocathodes, and sole biocathode were increased by 343.62%, 320.46%, 189.19% and 130.88% when compared with that of abiotic cathode when the operational time and ENR concentration were set to 48 h and 25 mg/L. In addition, transformation pathways of ENR revealed pathway II were dominantly occurred in NaAc- and glucose-fed biocathode while pathway IV acting as key metabolic process were shown in NaHCO3-fed biocathode. Moreover, 16S rRNA high-throughput sequencing analysis indicated that biocathodic communities were sensitive to switch-over of carbon source, namely Delftia and Bosea as organohalide-respiring bacteria (OHRB) were abundant in NaAc- and glucose-fed biocathodes while Mesotoga and Syntrophorhabdus that responsible for benzoyl-CoA metabolic process were enriched in NaHCO3-fed biocathode. Overall, this study could unravel the underlying relationship between biocathode degradation pattern of ENR and different co-metabolism conditions, and further offer valuable scientific information on treating refractory quinolones antibiotics via green bioelectrochemical method.

A rechargeable microbial electrochemical sensor for water biotoxicity monitoring

Microbial electrochemical sensor has been regarded as a promising technology for water biotoxicity monitoring, while its practical application is partially restricted by the requirement of organic substrate or power supply in real time. In the present study, rechargeable microbial electrochemical sensors were constructed, with the ex-situ preparation of bioanode and the in-situ preparation of biocathode. Acetate, formate, and hydrogen were identified as the charge carriers, and a Coulombic efficiency of 38% ± 18% and an energy efficiency of 2.2% ± 0.7% were obtained. The increase of charge current could decrease the energy efficiency as well as maximum acetate accumulation, while increase the H2 component. The increase of discharge resistor could enhance the energy efficiency, while had little impact on the Coulombic efficiency. Good reusability of rechargeable biosensors was observed with an injection of formaldehyde from 0% to 0.05%, but the sensors could not be fully recovered after the injection of 0.1% formaldehyde. The exposure of formaldehyde could affect the relative abundance of Acetobacterium, Acetoanaerobium, and Geobacter. When an abiotic cathode was used, the formate and hydrogen produced during the charging process were converted into acetate as an intermediate product during the discharging process. This study demonstrates the potential of the rechargeable microbial electrochemical system as a novel sensor for water biotoxicity monitoring.

Advancing Microbial Electrolysis Technology via Impedance Spectroscopy and Multi-Variate Analysis

In this study, EIS data collected from three electrode half-cell configurations was used to qualitatively identify and quantitatively determine the responses of ohmic, kinetic, and mass transfer impedances to buffer concentration, flow rate, and applied potential in an MEC consisting of a bioanode and an abiotic nickel-mesh cathode separated by a microporous membrane. EIS measurements were collected during startup and growth (including an abiotic run) at closed circuit and open circuit conditions to accurately match portions of the EIS spectra with the corresponding physical processes and to quantify kinetic changes as the biofilm matured. Once the MEC reached a target current density of 10 A/m2, a multifactorial experimental design formulated as a Taguchi array was executed to assess the impact of flow rate, buffer concentration, and applied voltage on EIS and performance response variables. Multivariate analysis was conducted to ascertain the relative importance of the independent variables and identify any correlations between process conditions and system response. The liquid flow through the anode was found to be strongly correlated with the impedance parameters and the MEC performance, while applied voltage influenced them to a lesser degree. The results are important from an industrial application perspective and provide insights into parameters important for process optimization.

Sequential anaerobic-aerobic treatment of rice mill wastewater and simultaneous power generation in microbial fuel cell

Microbial fuel cells (MFCs) have attracted widespread interest due to their capability to generate power while treating wastewater. In the present investigation, rice mill wastewater (RMW) was treated in a dual-chamber MFC with a biological cathode (MFCB), in which anaerobic treatment was provided in the anode compartment, and aerobic treatment was enployed in the cathode compartment. The performance was compared with an identical MFC with an abiotic cathode (MFCA). During continuous operation, the hydraulic retention time (HRT) of the anode compartments of both MFCs was kept at 12 h. The maximum volumetric power density obtained in MFCB (379.53 mW/m3) was lower than MFCA (791.72 mW/m3). Similarly, the maximum open-circuit voltage (OCV) and operating voltages were 0.519 V and 0.170 V for MFCB, while for the MFCA, they were 0.774 V and 0.251 V, respectively. The internal resistance of MFCA was 372.34 Ω while the MFCB showed a higher internal resistance of 533.89 Ω. The linear sweep voltammetry and cyclic voltammetry also demonstrated high electrochemical activity in MFCA compared to MFCB. However, MFCB has shown a higher chemical oxygen demand (COD) removal efficiency (96.8%) than MFCA (88.4%) under steady-state conditions. Both anaerobic and aerobic degradation of organic substrates significantly reduced the COD of RMW. Furthermore, the absence of an expensive catalyst in the cathode substantially reduces the cost of the system. The electrical performance of the system can be enhanced by employing novel cathode material with surface modification.

Modelling the cathodic reduction of 2,4-dichlorophenol in a microbial fuel cell

This work presents a simplified mathematical model able to predict the performance of a microbial fuel cell (MFC) for the cathodic dechlorination of 2,4-dichlorophenol (2,4-DCP) operating at different cathode pH values (7.0 and 5.0). Experimental data from previous work were utilized for the fitting of the model. The MFC modelled consisted of two chambers (bioanode and abiotic cathode), wherein the catholyte contained 300 mg L−1 of 2,4-DCP and the anolyte 1000 mg L−1 of sodium acetate. The model considered two mixed microbial populations in the anode compartment using sodium acetate as the carbon source for growth and maintenance: electrogenic and non-electrogenic biomass. 2,4-DCP, its intermediates of the reductive process (2-chlorophenol, 2-CP and 4-chlorophenol, 4-CP) and protons were considered in the model as electron acceptors in the electrogenic mechanism. The global process rate was assumed to be controlled by the biological mechanisms and modelled using multiplicative Monod-type equations. The formulation of a set of differential equations allowed to describe the simultaneous evolution of every component: concentration of sodium acetate in the anodic compartment; and concentration of 2,4-DCP, 2-CP, 4-CP, phenol and chloride in the cathode chamber. Current production and coulombic efficiencies were also estimated from the fitting. It was observed that most of the organic substrate was used by non-electrogenic mechanism. The influence of the Monod parameters was more important than the influence of the biomass yield coefficients. Finally, the model was employed to simulate different scenarios under distinct experimental conditions.

Bioelectrocatalytic Reduction of Tellurium Oxyanions toward Their Cathodic Recovery: Concentration Dependence and Anodic Electrogenic Activity

Regulation on the usage of trace toxic metals and their depletion necessitates their detoxification/recovery. Tellurium scarcity in the environmental matrix and its multitude applications depicts its worth for recovery from toxic ionic forms. Bioelectrochemical systems (BESs) facilitate metal detoxification/recovery. In this study, a novel double-chambered BES coupled with a biotic anode and abiotic cathode was operated using varied concentrations of toxic tellurite oxyanions (Te4+) as a terminal cathodic electron acceptor (CEA), facilitating bioelectroreduction of Te4+ to elemental tellurium (Te0) (cathode) and wastewater treatment (anode). Results depicted a Te0 element recovery of 45.3% with a tellurite removal of 54.7% in the abiotic cathode with a simultaneous substrate degradation of 67% in the biotic anode. The cathodic Te0 recovery with increased CEA-dependent electrotrophy has proportionally influenced the anodic microbial enzymatic activity. Bioelectrochemical characterization showed an increased anodic electrogenic performance relative to the increased CEA concentrations, achieving a comparatively higher power density of 0.044 W/m2 in the Te-C condition. Recovered Te0 samples were analytically characterized for structural/compositional functionalities and speciation variations to confirm the presence of Te0 element and its crystalline nature at the cathode. The study provided the application feasibility of BESs in favoring Te detoxification/recovery at the abiotic cathode, while regulating the anodic microbial electron/enzymatic/metabolic flux.

Bioelectricity generation using long-term operated biocathode: RFLP based microbial diversity analysis

In the present work, power generation and substrate removal efficiencies of long-term operated microbial fuel cells, containing abiotic cathodes and biocathodes, were evaluated for 220 days. Among the two microbial fuel cell (MFC) types, the one containing biocathode showed higher power density (54 mW/m2), current density (122 mA/m2) coulombic efficiency (33%), and substrate removal efficiency (94%) than the abiotic cathode containing MFC. Voltammetric analysis also witnessed higher and sustainable electron discharge for the MFC with biocathode, when compared with the abiotic cathode MFC. Over the tested period, both MFC have shown a cell voltage drop, after 150 and 165, days, for the MFC with biocathode and abiotic cathodes, respectively. Polymerase chain reaction (PCR) based restriction fragment length polymorphism (RFLP) analysis identified 281 clones. Bacteria belonging to Acinetobacter, Acidovorax, Pseudomonas and Burkholderia were observed in the abiotic cathode MFC. Bacteria belonging to Geobacter, Cupriavidus and Acidobacteria were observed in the biocathode MFC. Almost similar types of archaea (Methanosarcinales, Methanolinea, Nitrososphaera and Methanomicrobiales) were observed in both MFCs.

Copper removal and microbial community analysis in a single medium sediment microbial fuel cell

In this study, we developed a single-medium, membraneless microbial fuel cell (SM-MFC) to examine the migration and types of Cu(II) migration in sediment and the difference in the microorganism community under various cathode conditions. To prevent O2 from competing with Cu(II) for electrons in the cathode and limiting the Cu(II) migration efficiency, we buried the cathode in sediment to facilitate Cu(II) migration. Modified stainless steel was used as a biocathode to increase electron migration in the MFC and enhance the electromigration of Cu(II). In the initial phase, voltages were applied to the MFC for microorganism acclimation, and the results revealed that the average voltage of the MFC reached 67.2 mV, which was 9.29 times higher than that of the MFC without voltage application. When the Cu(II) in the sediment is 172 mg/kg, after 100 days of operation, the MFC with a 10-cm electrode spacing exhibited the highest Cu(II) removal efficiency (57%) and voltage output (57.7 mV). The voltage output of the SM-MFC with a biocathode was 1.72 times higher than that of the cell with an abiotic cathode. The migrated Cu(II) formed Cu2O and CuO at the cathode. The dominant bacteria phyla discovered at the cathode of the SM-MFC (i.e., Proteobacteria, Firmicutes, and Actinobacteria) could degrade organic matter, generate electricity, and tolerate Cu(II).

In Situ Electrochemical Characterization of a Microbial Fuel Cell Biocathode Running on Wastewater

The electrochemical features of microbial fuel cells’ biocathodes, running on wastewater, were evaluated by cyclic voltammetry. Ex situ and in situ electrochemical assays were performed and the redox processes associated with the presence of microorganisms and/or biofilms were attained. Different controls using sterile media (abiotic cathode microbial fuel cell) and membranes covering the electrodes were performed to evaluate the source of the electrochemistry response (surface biofilms vs. biotic electrolyte). The bacteria presence, in particular when biofilms are allowed to develop, was related with the enhanced active redox processes associated with an improved catalytic activity, namely for oxygen reduction, when compared with the results attained for an abiotic microbial fuel cell cathode. The microbial main composition was also attained and is in agreement with other reported studies. The current study aims contributing to the establishment of the advantages of using biocathodes rather than abiotic, whose conditions are frequently harder to control and to contribute to a better understanding of the bioelectrochemical processes occurring on the biotic chambers and the electrode surfaces.

Cobalt/nitrogen doped porous carbon as catalysts for efficient oxygen reduction reaction: Towards hybrid enzymatic biofuel cells

Electrochemical oxygen reduction reaction (ORR) represents a crucial cathodic process of different fuel cells. The development of highly active and stable noble metal-free ORR electrocatalysts remains as one of major challenges. Herein, we report cobalt/nitrogen co-doped porous carbon materials (Co-N-C) originated from well-designed bimetal-organic frameworks (Zn100-xCox-ZIF) as efficient ORR electrocatalysts in both pH-neutral and alkaline solutions. The compositional and structural features, and the corresponding ORR activity can be tailored by tuning the Zn/Co ratio in the precursor. Remarkable features of large surface-area and suitable graphitization degree and well-dispersed Co-N-C moieties, enable a high catalytic efficiency. The optimized electrocatalyst registers considerable ORR performance with a high half-wave potential of 0.65 V vs RHE and a saturated current density of 5.30 mA cm−2 close to the value of the commercial Pt/C in 0.1 M pH 7.0 PBS, along with considerable operational stability and tolerance to glucose. A preliminary one-compartment hybrid glucose/O2 enzymatic biofuel cell, consisting of the Co-N-C-10 abiotic cathode and a glucose oxidizing bioanode, is constructed and tested. Furthermore, Co-N-C presents reasonable ORR electrocatalytic activity and operational stability in alkaline condition.

Bio-electrocatalytic dechlorination of 2,4-dichlorophenol. Effect of pH and operational configuration

Bioelectrochemical systems (BESs) are regarded as effective green technologies for wastewater treatment, with low associated energy costs. This work studies the influence of the cathode pH and operational mode, as microbial fuel cell (MFC) or microbial electrolysis cell (MEC), on the electrocatalytic hydrodechlorination (ECH) of 2,4-dichlorophenol (2,4-DCP) in an abiotic cathode. When operating as MFC, the results showed that more acid cathode pH enhances the ECH reactions. Practically a total dechlorination was obtained after 72 h at cathode pH=5, whereas only an 88% dechlorination was obtained at pH=7. Also, ECH was further enhanced by operating under MEC mode, where the cathode was poised towards more negative potentials and higher current densities were achieved. The MEC presented a faster kinetics, reaching an 81% of dechlorination after 24 h of operation in batch mode and the full dechlorination after 48 hours. Additionally, when operating as MEC, the phenol obtained after the dechlorination reaction was further hydrogenated to cyclohexanone under these mild operating conditions, which would drastically reduce the toxicity of the effluent.