Microbial fuel cells (MFCs) represent one of the most attractive and eco-friendly technologies that convert chemical bond energy derived from organic matter into electrical power by microbial catabolic activity. This paper presents the use of a H-type MFC involving a novel NAR-2 bacterial consortium consisting of Citrobacter sp. A1, Enterobacter sp. L17 and Enterococcus sp. C1 to produce electricity whilst simultaneously decolourising acid red 27 (AR27) as a model dye, which is also known as amaranth. In this setup, the dye AR27 is mixed with modified P5 medium (2.5 g/L glucose and 5.0 g/L nutrient broth) in the anode compartment, whilst phosphate buffer solution (PBS) pH 7 serves as a catholyte in the cathode compartment. After several electrochemical analyses, the open circuit voltage (OCV) for 0.3 g/L AR27 with 24-h retention time at 30 °C was recorded as 0.950 V, whereas (93%) decolourisation was achieved in 220-min operation. The maximum power density was reached after 48 h of operation with an external load of 300 Ω. Scanning electron microscopy (SEM) analysis revealed the surface morphology of the anode and the bacterial adhesion onto the electrode surface. The results of this study indicate that the decolourisation of AR27 dye and electrical power generation was successfully achieved in a MFC operated by a bacterial consortium. The consortium of bacteria was able to utilise AR27 in a short retention time as an electron acceptor and to shuttle the electrons to the anode surface for bioelectricity generation.
Horizontal subsurface-flow (HSF) constructed wetland incorporating baffles was developed to facilitate upflow and downflow conditions so that the treatment of pollutants could be achieved under multiple aerobic, anoxic and anaerobic conditions sequentially in the same wetland bed. The performances of the baffled and conventional HSF constructed wetlands, planted and unplanted, in the removal of azo dye Acid Orange 7 (AO7) were compared at the hydraulic retention times (HRT) of 5, 3 and 2 days when treating domestic wastewater spiked with AO7 concentration of 300 mg/L. The planted baffled unit was found to achieve 100%, 83% and 69% AO7 removal against 73%, 46% and 30% for the conventional unit at HRT of 5, 3 and 2 days, respectively. Longer flow path provided by baffled wetland units allowed more contact of the wastewater with the rhizomes, microbes and micro-aerobic zones resulting in relatively higher oxidation reduction potential (ORP) and enhanced performance as kinetic studies revealed faster AO7 biodegradation rate under aerobic condition. In addition, complete mineralization of AO7 was achieved in planted baffled wetland unit due to the availability of a combination of aerobic, anoxic and anaerobic conditions.
Fish scale (FS) loaded TiO2 composites were investigated as photocatalysts in degradation of Methyl Orange under solar light irradiation. Composites were prepared through sol-gel method by varying mass ratio of TiO2/FS at 90:10, 70:30 and 50:50, respectively. The catalysts prepared in this study were characterized by using XRD, SEM, FT-IR and nitrogen sorption. The effects of solar irradiation, mass ratio of TiO2/FS composites, irradiation time and catalyst loadings were studied. Synergistic effect was found in TiO2/FS of 90:10 composite which performed higher photocatalytic degradation than synthesized TiO2 under solar light irradiation. However, further increasing fish scale content in the composites reduced the photocatalytic activity drastically. Under solar light irradiation, all the catalysts in this study exhibited photocatalytic activity, except TiO2/FS of 50:50 composite that only acted as a weak biosorbent without performing any photocatalytic property. Photocatalytic degradation increased with increasing catalyst loading and irradiation time but decreased with increased of initial dye concentration.
A renewable waste tea activated carbon (WTAC) was coalesced with chitosan to form composite adsorbent used for waste water treatment. Adsorptive capacities of crosslinked chitosan beads (CCB) and its composite (WTAC-CCB) for Methylene blue dye (MB) and Acid blue 29 (AB29) were evaluated through batch and fixed-bed studies. Langmuir, Freundlich and Temkin adsorption isotherms were tested for the adsorption process and the experimental data were best fitted by Langmuir model and least by Freundlich model; the suitability of fitness was adjudged by the Chi-square (χ(2)) and Marquadt's percent standard deviation error functions. Judging by the values of χ(2), pseudo-second-order reaction model best described the adsorption process than pseudo-first-order kinetic model for MB/AB29 on both adsorbents. After five cycles of adsorbents desorption test, more than 50% WTAC-CCB adsorption efficiency was retained while CCB had <20% adsorption efficiency. The results of this study revealed that WTAC-CCB composite is a promising adsorbent for treatment of anionic and cationic dyes in effluent wastewaters.
In this study, the operational factors affecting the bioregeneration of AO7-loaded MAMS particles in batch system, namely redox condition, initial acclimated biomass concentration, shaking speed and type of acclimated biomass were investigated. The results revealed that with the use of mixed culture acclimated to AO7 under anoxic/aerobic conditions, enhancement of the bioregeneration efficiency of AO7-loaded MAMS and the total removal efficiency of COD could be achieved when the bio-decolorization and bio-mineralization stages were fully aerated with dissolved oxygen above 7 mg/L. Shorter duration of bioregeneration was achieved by using relatively higher initial biomass concentration and lower shaking speed, respectively, whereas variations of biomass concentration and shaking speed did not have a pronounced effect on the bioregeneration efficiency. The duration and efficiency of bioregeneration process were greatly affected by the chemical structures of mono-azo dyes to which the biomasses were acclimated.
Cross-linked chitosan/sepiolite composite was prepared from sepiolite clay and chitosan, and was cross-linked using epichlorohydrin. Among the various weight ratio percentage of chitosan and sepiolite clay composites, CS50SP50 was selected as the best adsorbent for both methylene blue (MB) and reactive orange 16 (RO 16). At an optimum adsorbent dosage of 0.2g/100mL, the effects of initial dye concentration (25-400mg/L) and pH (3-11) on MB and RO 16 adsorption onto CS50SP50 composite were studied. Monolayer adsorption capacities of CS50SP50 composite for MB and RO 16 were 40.986mg/g and 190.965mg/g, respectively at 30°C. Freundlich, Langmuir and Temkin isotherms applied on the adsorption data for both the dyes reveal that data fitted best for Freundlich model. For both the dyes pseudo-second-order kinetics were found to describe the adsorption process better than pseudo-first-order kinetics. The adsorption capacity of CS50SP50 composite for both the dyes was found better compared to previous studies thus making it potentially low-cost adsorbent for removal of both cationic and reactive dyes.
Photocatalytic fuel cell (PFC) is a potential wastewater treatment technology that can generate electricity from the conversion of chemical energy of organic pollutants. An immobilized ZnO/Zn fabricated by sonication and heat attachment method was applied as the photoanode and Pt/C plate was used as the cathode of the PFC in this study. Factors that affect the decolorization efficiency and electricity generation of the PFC such as different initial dye concentrations and pH were investigated. Results revealed that the degradation of Reactive Green 19 (RG19) was enhanced in a closed circuit PFC compared with that of a opened circuit PFC. Almost 100% decolorization could be achieved in 8 h when 250 mL of 30 mg L(-1) of RG19 was treated in a PFC without any supporting electrolyte. The highest short circuit current of 0.0427 mA cm(-2) and maximum power density of 0.0102 mW cm(-2) was obtained by PFC using 30 mg L(-1) of RG19. The correlation between dye degradation, conductivity and voltage output were also investigated and discussed.
Cross-linked beads of activated oil palm ash zeolite/chitosan (Z-AC/C) composite were prepared through the hydrothermal treatment of NaOH activated oil palm ash followed by beading with chitosan. The effects of initial dye concentration (50-400mg/L), temperature (30°C-50°C) and pH (3-13) on batch adsorption of methylene blue (MB) and acid blue 29 (AB29) were studied. Adsorption of both dyes was better described by Pseudo-second-order kinetics and Freundlich isotherm model. The maximum adsorption capacities of Z-AC/C were 151.51, 169.49, and 199.20mg/g for MB and 212.76, 238.09, and 270.27mg/g for AB29 at 30°C, 40°C, and 50°C, respectively.
In this study, the adsorption behavior of azo dye Acid Orange 7 (AO7) from aqueous solution onto macrocomposite (MC) was investigated under various experimental conditions. The adsorbent, MC, which consists of a mixture of zeolite and activated carbon, was found to be effective in removing AO7. The MC were characterized by scanning electron microscopy (SEM), energy dispersive X-ray, point of zero charge, and Brunauer-Emmett-Teller surface area analysis. A series of experiments were performed via batch adsorption technique to examine the effect of the process variables, namely, contact time, initial dye concentration, and solution pH. The dye equilibrium adsorption was investigated, and the equilibrium data were fitted to Langmuir, Freundlich, and Tempkin isotherm models. The Langmuir isotherm model fits the equilibrium data better than the Freundlich isotherm model. For the kinetic study, pseudo-first-order, pseudo-second-order, and intraparticle diffusion model were used to fit the experimental data. The adsorption kinetic was found to be well described by the pseudo-second-order model. Thermodynamic analysis indicated that the adsorption process is a spontaneous and endothermic process. The SEM, Fourier transform infrared spectroscopy, ultraviolet-visible spectral and high performance liquid chromatography analysis were carried out before and after the adsorption process. For the phytotoxicity test, treated AO7 was found to be less toxic. Thus, the study indicated that MC has good potential use as an adsorbent for the removal of azo dye from aqueous solution.
Graphene oxide-iron oxide (GO-Fe3O4) nanocomposites were synthesised by co-precipitating iron salts onto GO sheets in basic solution. The results showed that formation of two distinct structures was dependent upon the GO loading. The first structure corresponds to a low GO loading up to 10 wt%, associated with the beneficial intercalation of GO within Fe3O4 nanoparticles and resulting in higher surface area up to 409 m(2) g(-1). High GO loading beyond 10 wt% led to the aggregation of Fe3O4 nanoparticles and the undesirable stacking of GO sheets. The presence of strong interfacial interactions (Fe-O-C bonds) between both components at low GO loading lead to 20% higher degradation of Acid Orange 7 than the Fe3O4 nanoparticles in heterogeneous Fenton-like reaction. This behaviour was attributed to synergistic structural and functional effect of the combined GO and Fe3O4 nanoparticles.
In this work, quantum chemical analysis was used to predict the degradation potential of a recalcitrant dye, Acid blue 113, by hydrogen peroxide, ozone, hydroxyl radical and sulfate radical. Geometry optimization and frequency calculations were performed at 'Hartree Fock', 'Becke, 3-parameter, Lee-Yang-Parr' and 'Modified Perdew-Wang exchange combined with PW91 correlation' levels of study using 6-31G* and 6-31G** basis sets. The Fourier Transform-Raman spectra of Acid blue 113 were recorded and a complete analysis on vibrational assignment and fundamental modes of model compound was performed. Natural bond orbital analysis revealed that Acid blue 113 has a highly stable structure due to strong intermolecular and intra-molecular interactions. Mulliken charge distribution and molecular electrostatic potential map of the dye also showed a strong influence of functional groups on the neighboring atoms. Subsequently, the reactivity of the dye towards the oxidants was compared based on the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy values. The results showed that Acid blue 113 with a HOMO value -5.227 eV exhibits a nucleophilic characteristic, with a high propensity to be degraded by ozone and hydroxyl radical due to their lower HOMO-LUMO energy gaps of 4.99 and 4.22 eV respectively. On the other hand, sulfate radical and hydrogen peroxide exhibit higher HOMO-LUMO energy gaps of 7.92 eV and 8.10 eV respectively, indicating their lower reactivity towards Acid blue 113. We conclude that oxidation processes based on hydroxyl radical and ozone would offer a more viable option for the degradation of Acid blue 113. This study shows that quantum chemical analysis can assist in selecting appropriate advanced oxidation processes for the treatment of textile effluent.
A molybdenum reducing bacterium with the novel ability to decolorise the azo dye Metanil Yellow is reported. Optimal conditions for molybdenum reduction were pH 6.3 and at 34°C. Glucose was the best electron donor. Another requirement includes a narrow phosphate concentration between 2.5 and 7.5 mM. A time profile of Mo-blue production shows a lag period of approximately 12 hours, a maximum amount of Mo-blue produced at a molybdate concentration of 20 mM, and a peak production at 52 h of incubation. The heavy metals mercury, silver, copper and chromium inhibited reduction by 91.9, 82.7, 45.5 and 17.4%, respectively. A complete decolourisation of the dye Metanil Yellow at 100 and 150 mg/L occurred at day three and day six of incubations, respectively. Higher concentrations show partial degradation, with an approximately 20% decolourisation observed at 400 mg/L. The bacterium is partially identified based on biochemical analysis as Bacillus sp. strain Neni-10. The absorption spectrum of the Mo-blue suggested the compound is a reduced phosphomolybdate. The isolation of this bacterium, which shows heavy metal reduction and dye-decolorising ability, is sought after, particularly for bioremediation.
Synthetic dyes used in the textile and paper industries pose a major threat to the environment. In the present research work, the adsorption efficiency of the natural adsorbent Strychnos potatorum Linn (Fam: Loganiaceae) seeds were examined against the reactive orange-M2R dye from aqueous solution by varying the process conditions such as contact time, pH, adsorbent dosage, and initial dye concentration on adsorption of anionic azo dye. This study compares different types of artificial neural networks which are feedforward artificial neural network (FANN) and nonlinear autoregressive exogenous (NARX) model to predict the efficiency of a cost-effective natural adsorbent Strychnos potatorum Linn seeds on removing reactive orange-M2R dye from aqueous solution. Twelve training algorithms of neural network were compared, and the prediction on the adsorption performance of anionic azo dye from aqueous solution using Strychnos potatonum Linn seeds was evaluated by using the root mean squared error (RMSE), mean absolute error (MAE), coefficient of determination (R2), and accuracy. For FANN model, Levenberg-Marquardt (LM) backpropagation with 19 hidden neurons was selected as the optimum FANN model, with R2 of 0.994 and accuracy of 87.20%, 98.21%, and 66.60% for training, testing, and validation datasets, respectively. For NARX model, LM with 8 hidden neurons was selected as the most suitable training algorithm, with R2 value of more than 0.99 and accuracy of 88.00%, 90.91%, and 75.00% for training, testing, and validation datasets, respectively. NARX model accurately predicted the adsorption of anionic azo dye from aqueous solution using Strychnos potatonum Linn seeds with better performance than FANN model.
Mixed microbial culture used in this study was developed from sludge that was taken from local textile wastewater treatment tank. Acclimatization process was performed before starting the biodegradation experiment to obtain a microbial culture with high degradation properties. Kinetic studies by the mixed microbial culture were determined quantitatively for the model pollutant, Reactive Black 5 (RB 5). By using Michaelis-Menten model, the constants were found to be 11.15 mg l-1 h -1 and 29.18 mg l-1 for Vm and Km respectively. The values of kinetic constants for Monod model were found to be 33.11 mg l-1 cell h-1 for the maximum specific microbial growth rate, µm and 86.62 mg l-1 for Monod constant, Ks. The effects of process parameters such as pH, inoculum size and initial dye concentration on the biodegradation of azo dye, RB 5 were systematically investigated. Maximum removal efficiencies observed in this study were 75% for pH 6, 100% for 15% inoculum concentration and 75% for 20 ppm of initial dye concentration.
In the present study, locally isolated Rhodococcus strains were attempted as biological tools for methyl red removal, a mutagenic azo dye posing threat to the environment if left untreated. Rhodococcus strain UCC 0016 demonstrated superior methyl red-decolourizing activity of 100% after 24 h at static condition in comparison to Rhodococcus strain UCC 0008 which recorded 65% decolourization after 72 h. Optimization of physicochemical parameters at 30°C, pH 7 and supplementing glucose as the carbon source resulted in improved methyl red-decolourizing activity at static condition and reduced the time taken to achieve complete decolourization by 80%. Higher concentration of methyl red (5 g/L) was able to be decolourized completely within 10 h by adopting the technology of immobilization. The encapsulated cells of Rhodococcus strain UCC 0016 demonstrated higher substrate affinity (Km = 0.6995 g/L) and an accelerated rate of disappearance of methyl red (Vmax = 0.3203 g/L/h) compared to the free cells. Furthermore, the gellan gum beads could be reused up to nine batches without substantial loss in the catalytic activity indicating the economic importance of this protocol. Analysis of methyl red degradation products revealed no germination inhibition on Triticum aestivum and Vigna radiata demonstrating complete toxicity removal of the parent dye after biological treatment. The occurrence of new and altered peaks (UV-Vis and FTIR) further supported the notion that the removal of methyl red by Rhodococcus strain UCC 0016 was indeed through biodegradation. Therefore, this strain has a huge potential as a candidate for efficient bioremediation of wastewater containing methyl red.
In this study two deep eutectic solvents (DESs) were prepared using ethylene glycol (EG) and two different ammonium-based salts. The potential of these DESs as novel agents for CNTs functionalization was examined by performing a comprehensive characterization study to identify the changes developing after the functionalization process. The impact of DESs was obvious by increasing the surface area of CNTs to reach 197.8 (m2/g), and by adding new functional groups to CNTs surface without causing any damage to the unique structure of CNTs. Moreover, CNTs functionalized with DESs were applied as new adsorbents for the removal of methyl orange (MO) from water. The adsorption conditions were optimized using RSM-CCD experimental design. The kinetics and the equilibrium adsorption data were analyzed using different kinetic and isotherm models. According to the regression results, adsorption kinetics data were well described by pseudo-second order model, whereas adsorption isotherm data were best represented by Langmuir isotherm model. The highest recorded maximum adsorption capacity (qmax) value was found to be 310.2 mg/g.
Degradation of azo dyes by using advanced oxidation processes (AOPs) was conducted. In this approach, different AOPs, which are Fenton process and titanium dioxide (TiO2) catalyst, were examined and compared for the degradation of an azo dye (i.e., Congo red dye). The sample was tested under UV light and the experiment was conducted for 90 min with 15 min interval. The degradation rate of dye was determined using UV-Vis spectrophotometry. The effect of several parameters on the degradation process such as the concentration of metal ions (Fe2+, Cu2+, and Mn2+) as the catalyst in Fenton process, the concentration of hydrogen peroxide (H2O2), the mass of TiO2, and pH value of the dye solution were investigated. The initial Congo red concentration used for both techniques was 5 ppm. The results showed that the percentage degradation followed the sequence of H2O2/Fe2+/UV, H2O2/Cu2+/UV, H2O2/Mn2+/UV, and TiO2/UV. The best operating conditions for H2O2/Fe2+/UV were pH 3, 0.2 M concentration of H2O2, and 0.02 M concentration of metal ion in 15 min, which achieved 99.92% degradation of dye. The Fourier transform infrared (FTIR) spectrum showed the absence of azo bond (N=N) peak after degradation process, which indicates the successful cleavage of azo bond in the chemical structure of Congo red.
The crab carapace is a waste which cannot be decomposed. This waste was used to
remove the Reactive Orange 16 (RO16) and Basic Blue 3 (BB3) from aqueous solution
at different operational parameters such as pH, mass load, the concentrations of dye and
the temperature. The crab collected was modified to obtain quaternized crab (QC) using
(3-chloro-2-hydroxypropyl) trimethylammonium chloride solution (C6H15Cl2NO, 65% w/w
in water). The pH of the dyes solution was varied from pH 4 to 10. The highest adsorption
percentage was achieved at pH 7 for both dyes. Increasing the QC mass for the adsorption
process had granted an increase of dyes removal percentage. The highest adsorption
percentage was achieved at 91.00% for RO16 and 29.40% for BB3 dyes with 7.5 g/L QC
used. However, the adsorption capacity of QC decreased with higher QC mass because the
dye molecules occupied on the surface and prevented other molecules to diffuse into the
QC. At higher concentration beyond 20 mg/L and 10 mg/L of RO16 and BB3, respectively,
the maximum adsorption was achieved at 2.5362 mg/g and 0.6812 mg/g. The adsorption of
both dyes by QC was best fitted using Langmuir isotherm model, explaining the adsorption
mainly occurred as a single layer on the surface of QC. Comparison to the results obtained
from the kinetic models, the adsorption was
chemisorption in nature. According to the
thermodynamic studies, the adsorption of
RO16 was an exothermic, while BB3 was
an endorthermic process.
In this work, poly(MBAAm-co-SBMA) zwitterionic polymer nanoparticles were synthesized in one-step via distillation-precipitation polymerization (DPP) and were characterized. [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) as monomer and N, N'-methylene bis(acrylamide) (MBAAm) as cross-linker are used for the synthesis of nanoparticles. As far as our knowledge, this is the first such report on the synthesis of poly(MBAAm-co-SBMA) nanoparticles via DPP. The newly synthesized nanoparticles were further employed for the surface modification of polysulfone (PSF) hollow fiber membranes for dye removal. The modified hollow fiber membrane exhibited the improved permeability (56 L/ m2 h bar) and dye removal (>98% of Reactive Black 5 and >80.7% of Reactive orange 16) with the high permeation of salts. Therefore, the as-prepared membrane can have potential application in textile and industrial wastewater treatment.
Monoazo and diazo dyes [New coccine (NC), Acid orange 7 (AO7), Reactive red 120 (RR120) and Reactive green 19 (RG19)] were employed as electron acceptors in the abiotic cathode of microbial fuel cell. The electrons and protons generated from microbial organic oxidation at the anode which were utilized for electrochemical azo dye reduction at the cathodic chamber was successfully demonstrated. When NC was employed as the electron acceptor, the chemical oxygen demand (COD) removal and dye decolourisation efficiencies obtained at the anodic and cathodic chamber were 73±3% and 95.1±1.1%, respectively. This study demonstrated that the decolourisation rates of monoazo dyes were ∼50% higher than diazo dyes. The maximum power density in relation to NC decolourisation was 20.64mW/m2, corresponding to current density of 120.24mA/m2. The decolourisation rate and power output of different azo dyes were in the order of NC>AO7>RR120>RG19. The findings revealed that the structure of dye influenced the decolourisation and power performance of MFC. Azo dye with electron-withdrawing group at para substituent to azo bond would draw electrons from azo bond; hence the azo dye became more electrophilic and more favourable for dye reduction.