The photocatalytic fuel cell (PFC) system was developed in order to study the effect of several operating parameters in degradation of Reactive Black 5 (RB5) and its electricity generation. Light irradiation, initial dye concentration, aeration, pH and cathode electrode are the operating parameters that might give contribution in the efficiency of PFC system. The degradation of RB5 depends on the presence of light irradiation and solar light gives better performance to degrade the azo dye. The azo dye with low initial concentration decolorizes faster compared to higher initial concentration and presence of aeration in PFC system would enhance its performance. Reactive Black 5 rapidly decreased at higher pH due to the higher amount of OH generated at higher pH and Pt-loaded carbon (Pt/C) was more suitable to be used as cathode in PFC system compared to Cu foil and Fe foil. The rapid decolorization of RB5 would increase their voltage output and in addition, it would also increase their Voc, Jsc and Pmax. The breakage of azo bond and aromatic rings was confirmed through UV-Vis spectrum and COD analysis.
The objective of this study is to determine the reduction efficiency of Chemical Oxygen Demand (COD) as well as the removal of color and Amaranth dye metabolites by the Aerobic-anaerobic Baffled Constructed Wetland Reactor (ABCW). The ABCW reactor was planted with common reed (Phragmite australis) where the hydraulic retention time (HRT) was set to 1 day and was fed with synthetic wastewater with the addition of Amaranth dye. Supplementary aeration was supplied in designated compartments of the ABCW reactor to control the aerobic and anaerobic zones. After Amaranth dye addition the COD reduction efficiency dropped from 98 to 91% while the color removal efficiency was 100%. Degradation of azo bond in Amaranth dye is shown by the UV-Vis spectrum analysis which demonstrates partial degradation of Amaranth dye metabolites. The performance of the baffled unit is due to the longer pathway as there is the up-flow and down-flow condition sequentially, thus allowing more contact of the wastewater with the rhizomes and micro-aerobic zones.
A unidirectional flow solar photocatalytic fuel cell (PFC) was successfully developed for the first time to offer alternative for electricity generation and simultaneous wastewater treatment. This study was focused on the synthesis of α-, δ- and β-MnO2 by wet chemical hydrothermal method for application as the cathodic catalyst in PFC. The crystallographic evolution was performed by varying the ratios of KMnO4 to MnSO4. The mechanism of the PFC with the MnO2/C as cathode was also discussed. Results showed that the catalytic activity of MnO2/C cathode was mainly predominated by their crystallographic structures which included Mn-O bond strength and tunnel size, following order of α- > δ- > β-MnO2/C. Interestingly, it was discovered that the specific surface areas (SBET) of different crystal phases did not give an impact on the PFC performance. However, the Pmax could be significantly influenced by the micropore surface area (Smicro) in the comparison among α-MnO2. Furthermore, the morphological transformation carried out by altering the hydrothermal duration demonstrated that the nanowire α-M3(24 h)/C with 1:1 ratio of KMnO4 and MnSO4 yielded excellent PFC performance with a Pmax of 2.8680 μW cm-2 and the lowest Rint of 700 Ω.
Photocatalytic fuel cell (PFC) was employed to provide renewable power sources to photoelectro-Fenton (PEF) process to fabricate a double-chambered hybrid system for the treatment of azo dye, Amaranth. The PFC-PEF hybrid system was interconnected by a circuit attached to the electrodes in PFC and PEF. Circuit connection is the principal channel for the electron transfer and mobility between PFC and PEF. Thus, different circuit connections were evaluated in the hybrid system for their influences on the Amaranth dye degradation. The PFC-PEF system under the complete circuit connection condition attained the highest decolourization efficiency of Amaranth (PFC: 98.85%; PEF: 95.69%), which indicated that the complete circuit connection was crucial for in-situ formation of reactive species in dye degradation. Besides, the pivotal role of ultraviolet (UV) light irradiation in the PFC-PEF system for both dye degradation and electricity generation was revealed through various UV light-illuminating conditions applied for PFC and PEF. A remarkable influence of UV light irradiation on the production of hydrogen peroxide and generation and regeneration of Fe2+ in PEF was demonstrated. This study provided a comprehensive mechanistic insight into the dye degradation and electricity generation by the PFC-PEF system.
The treatment of single and binary azo dyes, as well as the effect of the circuit connection, aeration, and plant on the performance of UFCW-MFC, were explored in this study. The decolorization efficiency of Remazol Yellow FG (RY) (single dye: 98.2 %; binary dye: 92.3 %) was higher than Reactive Black 5 (RB5) (single: 92.3 %; binary: 86.7 %), which could be due to monoazo dye (RY) requiring fewer electrons to break the azo bond compared to the diazo dye (RB5). In contrast, the higher decolorization rate of RB5 in binary dye indicated the removal rate was affected by the electron-withdrawing groups in the dye structure. The closed circuit enhanced about 2% of color and 4% of COD removal. Aeration improved the COD removal by 6%, which could be contributed by the mineralization of intermediates. The toxicity of azo dyes was reduced by 11-26% and the degradation pathways were proposed. The dye removal by the plants was increased with a higher contact time. RB5 was more favorable to be uptook by the plant as RB5 holds a higher partial positive charge. 127.39 (RY), 125.82 (RB5), and 58.66 mW/m3 (binary) of maximum power density were generated. The lower power production in treating the binary dye could be due to more electrons being utilized for the degradation of higher dye concentration. Overall, the UFCW-MFC operated in a closed circuit, aerated, and planted conditions achieved the optimum performance in treating binary azo dyes containing wastewater (dye: 87-92%; COD: 91%) compared to the other conditions (dye: 83-92%; COD: 78-87%).
Cathode in photocatalytic fuel cell (PFC) plays a crucial role in degradation of organic contaminants. In this study, synthesized copper oxide (CuO) was loaded on carbon plate and used as photocathode in PFC for degradation of synthetic azo dye Reactive Black 5 (RB5) and real textile wastewater. Morphology and structural phase of the synthesized CuO were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Several operating parameters had been investigated such as light irradiation, initial dye concentration, and pH of azo dye solution within 6 h of irradiation time. The lowest initial concentration of RB5 (10 mg L-1) achieved 100% color removal compared to the highest initial concentration (40 mg L-1) which only achieved 77.1% color removal within 6 h of irradiation time. The influence of external resistance was significant in electricity generation but trivial in dye degradation efficiency. The external resistance of 6000 Ω yielded highest maximum power density, with Pmax of 0.2631 μW cm-2, followed by 1000 Ω (0.2196 μW cm-2) and 8000 Ω (0.1587 μW cm-2), respectively. The real textile wastewater with dilution ratio (DR) 1:6 yielded the highest energy conversion efficiency, η (3.62%), followed by DR 1:4 (3.19%) and DR 1:2 (1.96%), respectively.
The enhancement of up-flow constructed wetland-microbial fuel cell (UFCW-MFC) performance in energy retrieval from caffeine containing wastewater has been explored via various operating conditions (hydraulic retention time (HRT), multianode (MA), multicathode current collector (MC), external resistance). The anaerobic decaffeination and COD removal improved by 37 and 12% as the HRT extended from 1 to 5 d. The increment in contact time between the microbes and organic substrates promoted the degradation and contributed to higher power output (3.4-fold), CE (eightfold), and NER (14-16-fold). The MA and MC connections facilitated the electron transfer rate and the degradation rate of organic substrates in the multiple anodic zones, which enhanced the removal efficiency in the anaerobic compartment (Caffeine: 4.2%; COD: 7.4%) and led to higher electricity generation (Power: 4.7-fold) and energy recovery (CE: 1.4-fold; NER: 2.3-2.5-fold) compared to SA. The lower external resistance favored the growth of electrogens and induced higher electron flux, where the best treatment performance and electricity production was obtained when the external resistance approached the internal resistance. Overall, it was noteworthy that the optimum operating conditions were achieved with 5 d HRT, MA, and MC connection along with external resistance of 200 Ω, which significantly outperformed the initial conditions (1 d HRT, SA connection, and 1000 Ω) by 43.7 and 29.8% of caffeine and COD removal in the anaerobic compartment, respectively as well as 14-fold of power generation.
This study was to investigate the mineralization of wastewater containing methyl orange (MO) in integrated anaerobic-aerobic biofilm reactor with coconut fiber as bio-material. Different aeration periods (3h in phase 1 and 2; 3, 6 and 15 h in phase 3; 24 h in phase 4 and 5) in aerobic chamber were studied with different MO concentration 50, 100, 200, 200 and 300 mg/L as influent from phase 1-5. The color removals estimated from the standard curve of dye versus optical density at its maximum absorption wavelength were 97%, 96%, 97%, 97%, and 96% and COD removals were 75%, 72%, 63%, 81%, and 73% in phase 1-5, respectively. The MO decolorization and COD degradation followed first-order kinetic model and second-order kinetic model, respectively. GC-MS analysis indicated the symmetrical cleavage of azo bond and the reduction in aromatic peak ensured the partial mineralization of MO.
The objective of this study was to examine the effects of adsorbability and number of sulfonate group on solar photocatalytic degradation of mono azo methyl orange (MO) and diazo Reactive Green 19 (RG19) in single and binary dye solutions. The adsorption capacity of MO and RG19 onto the TiO₂ was 16.9 and 26.8 mg/g, respectively, in single dye solution, and reduced to 5.0 and 23.1 mg/g, respectively, in the binary dye solution. The data obtained for photocatalytic degradation of MO and RG19 in single and binary dye solution were well fitted with the Langmuir-Hinshelwood kinetic model. The pseudo-first-order rate constants of diazo RG19 were significant higher than the mono azo MO either in single or binary dye solutions. The higher number of sulfonate group in RG19 contributed to better adsorption capacity onto the surface of TiO₂ than MO indicating greater photocatalytic degradation rate.
This study demonstrated a successful operation of up-flow constructed wetland-microbial fuel cell (UFCW-MFC) in wastewater treatment and energy recovery. The goals of this study were to investigate the effect of circuit connection, organic loading rates, and electrode spacing on the performance of wastewater treatment and bioelectricity generation. The average influent of COD, NO3(-) and NH4(+) were 624 mg/L, 142 mg/L, 40 mg/L, respectively and their removal efficiencies (1 day HRT) were 99%, 46%, and 96%, respectively. NO3(-) removal was relatively higher in the closed circuit system due to lower dissolved oxygen in the system. Despite larger electrode spacing, the voltage outputs from Anode 2 (A2) (30 cm) and Anode 3 (A3) (45 cm) were higher than from Anode 1 (A1) (15 cm) as a result of insufficient fuel supply to A1. The maximum power density and Coulombic efficiency were obtained at A2, which were 93 mW/m(3) and 1.42%, respectively.
The main aim of this study is to investigate the performance of organic oxidation and denitrification of the system under long-term operation. The MFC reactor was operated in continuous mode for 180 days. Nitrate was successfully demonstrated as terminal electron acceptor, where nitrate was reduced at the cathode using electron provided by acetate oxidation at the anode. The removal efficiencies of chemical oxygen demand (COD) and nitrate were higher in the closed circuit system than in open circuit system. Both COD and nitrate reduction improved with the increase of organic loading and subsequently contributed to higher power output. The maximum nitrate removal efficiency was 88 ± 4 % (influent of 141 ± 14 mg/L). The internal resistant was 50 Ω, which was found to be low for a double chambered MFC. The maximum power density was 669 mW/m(3) with current density of 3487 mA/m(3).
An innovative design of upflow constructed wetland-microbial fuel cell (UFCW-MFC) planted with cattail was used for simultaneous wastewater treatment and electricity generation. The electrodes material employed in the study was carbon felt. The main aim of this study is to assess the performance of the UFCW coupling with MFC in term of ability to treat wastewater and the capability to generate bioelectricity. The oxidation reduction potential (ORP) and dissolved oxygen (DO) profile showed that the anaerobic and aerobic regions were well developed in the lower and upper bed, respectively, of UFCW-MFC. Biodegradation of organic matter, nitrification and denitrification was investigated and the removal efficiencies of COD, NO3(-), NH4(+) were 100%, 40%, and 91%, respectively. The maximum power density of 6.12 mW m(-2) and coulombic efficiency of 8.6% were achieved at electrode spacing of anode 1 (A1) and cathode (15 cm).
Complete degradation of azo dye has always been a challenge due to the refractory nature of azo dye. An innovative hybrid system, constructed wetland-microbial fuel cell (CW-MFC) was developed for simultaneous azo dye remediation and energy recovery. This study investigated the effect of circuit connection and the influence of azo dye molecular structures on the degradation rate of azo dye and bioelectricity generation. The closed circuit system exhibited higher chemical oxygen demand (COD) removal and decolourisation efficiencies compared to the open circuit system. The wastewater treatment performances of different operating systems were ranked in the decreasing order of CW-MFC (R1 planted-closed circuit) > MFC (R2 plant-free-closed circuit) > CW (R1 planted-open circuit) > bioreactor (R2 plant-free-open circuit). The highest decolourisation rate was achieved by Acid Red 18 (AR18), 96%, followed by Acid Orange 7 (AO7), 67% and Congo Red (CR), 60%. The voltage outputs of the three azo dyes were ranked in the decreasing order of AR18 > AO7 > CR. The results disclosed that the decolourisation performance was significantly influenced by the azo dye structure and the moieties at the proximity of azo bond; the naphthol type azo dye with a lower number of azo bond and more electron-withdrawing groups could cause azo bond to be more electrophilic and more reductive for decolourisation. Moreover, the degradation pathway of AR18, AO7 and CR were elucidated based on the respective dye intermediate products identified through UV-Vis spectrophotometry, high-performance liquid chromatography (HPLC), and gas chromatograph-mass spectrometer (GC-MS) analyses. The CW-MFC system demonstrated high capability of decolouring azo dyes at the anaerobic anodic region and further mineralising dye intermediates at the aerobic cathodic region to less harmful or non-toxic products.
To enhance dye removal and energy recovery efficiencies in single-pair electrode photocatalytic fuel cell (PFC-AC), dual cathodes PFC (PFC-ACC) and dual photoanodes PFC (PFC-AAC) were established. Results revealed that PFC-AAC yielded the highest decolorization rate (1.44 h-1) due to the promotion of active species such as superoxide radical (•O2-) and hydroxyl radical (•OH) when the number of photoanode was doubled. The results from scavenging test and UV-Vis spectrophotometry disclosed that •OH was the primary active species in dye degradation of PFC. Additionally, PFC-AAC also exhibited the highest power output (17.99 μW) but the experimental power output was much lower than the theoretical power output (28.24 μW) due to the strong competition of electron donors of doubled photoanodes to electron acceptors at the single cathode and its high internal resistance. Besides, it was found that the increments of dye volume and initial dye concentration decreased the decolorization rate but increased the power output due to the higher amount of sacrificial agents presented in PFC. Based on the abovementioned findings and the respective dye intermediate products identified from gas chromatography-mass spectrometry (GC-MS), the possible degradation pathway of RR120 was scrutinized and proposed.
This study demonstrated the effectiveness of single chamber up-flow membrane-less microbial fuel cell (UFML-MFC) in wastewater treatment concurrently with bioelectricity generation. The objectives of this study were to examine the effect of influent substrate concentration (0.405 g/L, 0.810 g/L, 1.215 g/L, 1.620 g/L), anode distributions (11 cm, 17 cm, 23 cm ) and surface morphologies for biofilm formation on the performance of wastewater treatment and power generation. The optimum performance was obtained with substrate concentration of 0.810 g/L. The COD removal efficiency, output voltage, internal resistance, power density and current density obtained were 84.64%, 610 mV, 200 Ω, 162.59 mW/m2 and 468.74 mA/m2, respectively. The Coulombic Efficiency (CE), Normalized Energy Recovery (NERS and NERv) were 1.03%, 789.38 kWh/kg COD and 22.56 kWh/m3, respectively. The results also indicate that the output voltage and power generation obtained in a continuous up-flow MFC were higher with A3 (23 cm), which is of larger electrodes spacing followed by A2 (17 cm) and A1 (11 cm) caused by the enrichment of anaerobic microbial population at A1.
The sorption of Cu(II) and Cd(II) from synthetic solution by powdered activated carbon (PAC), biomass, rice husk (RH) and activated rice husk (ARH) were investigate under batch conditions. After activated by concentrated nitric acid for 15 hours at 60-65 degrees C, the adsorption capacity for RH was increased. The adsorbents arranged in the increasing order of adsorption capacities to the Langmuir Q degree parameter were biomass > PAC > ARH > RH. The addition of adsorbents in base mix solution had increased the specific oxygen uptake rate (SOUR) activated sludge microorganisms with and without the presence of metals. The increased of SOUR were due to the ability of PAC and RH in reducing the inhibitory effect of metals on microorganisms and provide a reaction site between activated sludge microorganisms and substrates.
Wastewater treatment systems employing simultaneous adsorption and biodegradation processes have proven to be effective in treating toxic pollutants present in industrial wastewater. The objective of this study is to evaluate the effect of Cu(II) and the efficacy of the powdered activated carbon (PAC) and activated rice husk (ARH) in reducing the toxic effect of Cu(II) on the activated sludge microorganisms. The ARH was prepared by treatment with concentrated nitric acid for 15 h at 60-65 degrees C. The sequencing batch reactor (SBR) systems were operated with FILL, REACT, SETTLE, DRAW and IDLE modes in the ratio of 0.5:3.5:1:0.75:0.25 for a cycle time of 6 h. The Cu(II) and COD removal efficiency were 90 and 85%, respectively, in the SBR system containing 10 mg/l Cu(II) with the addition of 143 mg/l PAC or 1.0 g PAC per cycle. In the case of 715 mg/l ARH or 5.0 g ARH per cycle addition, the Cu(II) and COD removal efficiency were 85 and 92%, respectively. ARH can be used as an alternate adsorbent to PAC in the simultaneous adsorption and biodegradation wastewater treatment process for the removal of Cu(II). The specific oxygen uptake rate (SOUR) and kinetic studies show that the addition of PAC and ARH reduce the toxic effect of Cu(II) on the activated sludge microorganisms.
The application of simultaneous adsorption and biodegradation processes in the same reactor is known to be effective in the removal of both biodegradable and non-biodegradable contaminants in various kinds of wastewater. The objective of this study is to evaluate the efficacy of the two processes under sequencing batch reactor (SBR) operation in treating copper and cadmium-containing synthetic wastewater with powdered activated carbon (PAC) as the adsorbent. The SBR systems were operated with FILL, REACT, SETTLE, DRAW and IDLE periods in the ratio of 0.5: 3.5: 1.0: 0.75 :0.25 for a cycle time of 6 h. In the presence of 10 mg/L Cu(II) and 30 mg/L Cd(II), respectively, the average COD removal efficiencies were above 85% with the PAC dosage in the influent solution at 143 mg/L compared to around 60% without PAC addition. Copper(II) was found to exert a more pronounced inhibitory effect on the bioactivity of the microorganisms compared to Cd(II). It was observed that the combined presence of Cu(II) and Cd(II) did not exert synergistic effects on the microorganisms. Kinetic study conducted for the REACT period showed that the addition of PAC had minimized the inhibitory effect of the heavy metals on the bioactivity of microorganisms.
A novel sustainable hybrid system of photocatalytic fuel cell (PFC) and Fenton process is an alternative wastewater treatment technology for energy-saving and efficient treatment of organic pollutants. The electrons generated from PFC photoanode are used to produce H2O2 in the Fenton reactor and react with the in situ generation of Fe2+ from sacrificial iron for hydroxyl radical formation. In this study, the effect of different initial Amaranth dye concentrations on degradation and electricity generation were investigated. ZnO/Zn photoanode was prepared by anodizing method and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Results revealed that the maximum power density (9.53 mW/m2) and current density (0.0178 mA/m2) were achieved at 10 mg/L of Amaranth. The correlation between dye degradation, voltage output, and kinetic photocatalytic degradation were also investigated and discussed.
The hybrid system of photocatalytic fuel cell - peroxi-coagulation (PFC-PC) is a sustainable and green technology to degrade organic pollutants and generate electricity simultaneously. In this study, three different types of photocatalysts: TiO2, ZnO and α-Fe2O3 were immobilized respectively on carbon cloth (CC), and applied as photoanodes in the photocatalytic fuel cell of this hybrid system. Photocatalytic fuel cell was employed to drive a peroxi-coagulation process by generating the external voltage accompanying with degrading organic pollutants under UV light irradiation. The degradation efficiency of Amaranth dye and power output in the hybrid system of PFC-PC were evaluated by applying different photoanode materials fabricated in this study. In addition, the effect of light on the photocurrent of three different photoanode materials was investigated. In the absence of light, the reduction of photocurrent percentage was found to be 69.7%, 17.3% and 93.2% in TiO2/CC, ZnO/CC and α-Fe2O3/CC photoanodes, respectively. A maximum power density (1.17 mWcm-2) and degradation of dye (93.8%) at PFC reactor were achieved by using ZnO/CC as photoanode. However, the different photoanode materials at PFC showed insignificant difference in dye degradation trend in the PC reactor. Meanwhile, the degradation trend of Amaranth at PFC reactor was influenced by the recombination rate, electron mobility and band gap energy of photocatalyst among different photoanode materials.