Complete Decolourization Research Articles

Production, characterisation and immobilization of laccase for an efficient aniline-based dye decolourization

Laccase was produced by cultivation of Trametes versicolor on non-expensive substrates, barley husk and eggshell, in solid-state conditions. An efficiency of crude laccase extract in free and immobilized form for the degradation of aniline-based dye was investigated in batch experiments. Up to 91 % of dye conversion was achieved using free crude enzyme, while the use of partially purified enzyme led to 60.9 % of conversion. Crude laccase was immobilized on calcium alginate beads and used in 10 cycles-repetitive batch experiments where complete decolourization was achieved. The results of this study suggest that a) barley husk and eggshell can be used for laccase production without the need to add additional carbon and nitrogen sources or mineral compounds; b) crude laccase entrapped in alginate beads can be applied in aniline-based dye decolourization in repetitive batch experiments.

Green synthesis and evaluation of n-type ZnO nanoparticles doped with plant extract for use as alternative antibacterials

Emergence of resistance to antibiotics in bacterial pathogens and prevalence of residual effects of drugs pose serious challenges to public health worldwide. Diminishing efficacy of antibiotics calls for an expedited development of alternative antimicrobials. In this regard, zinc oxide (ZnO) nanoparticles (NPs) signify a latent and versatile inorganic nanostructure that possesses enhanced antimicrobial effects. In the present study, green synthesis of n-type ZnO-NPs was undertaken, which was then doped with various concentrations of extracts from ginger and garlic roots. The synthesized product was applied in low and high dosage to evaluate its antimicrobial efficacy against pathogenic E. coli. The results were compared to those obtained from chemically synthesized ZnO. Characterization of NPs was performed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy (UV–Vis), field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HR-TEM), energy-dispersive X-ray spectroscopy (EDS) and photoluminescence (PL) emission. Strong absorption at 362 nm was observed for green synthesized NPs. HR-TEM exhibited interlayer spacing of 0.317, 0.312 and 0.308 nm, which is consistent with XRD results. Significant inhibition zones of 2.95–4.00 mm were observed for ZnO-NPs doped with ginger extract at an optimized concentration of 6 ml: 1. Similarly, garlic-doped NPs exhibited 1.85 and 2.75 mm inhibition zones at low and high dosage, respectively. The photodegradation study of synthesized products was undertaken using methylene blue (MB) dye under visible light source, where ZnO exhibited nearly complete decolourization of MB dye following a pseudo-first-order kinetics. The present study exemplifies an eco-friendly green nanomaterials synthesis technique using natural products (i.e., garlic and ginger), which can be expanded to include other green synthesized metal oxide NPs.

Biodegradation of reactive yellow dye using mixed cells immobilized in different biocarriers by sequential anaerobic/aerobic biotreatment: experimental and modelling study

ABSTRACT In this study, the application of immobilized mixed cells for decolourization, biodegradation, and detoxification of reactive yellow dye (RY15) in textile wastewater was investigated via a sequential anaerobic–aerobic process in bench-scale bioreactors and lab-scale bioreactors as well. The mixed cultures were immobilized using three different biocarriers which were sodium alginate (SA), starch (St), and Gelatin (Ge), by the cross-linking with polyvinyl alcohol (PVA). Results revealed that the immobilized cultures had a potential degrading efficiency in the anaerobic and aerobic environment, targeting the initial structure and the formed compounds, respectively. Complete decolourization (100%) of RY15 was observed with a significant chemical oxygen demand (COD) removal, which enhanced the subsequent aerobic phase. Results demonstrated that COD removals were 92% ± 6.8, 96% ± 3.5, and 100%, using PVA-SA, PVA-St, and PVA-Ge at RY15 initial concentrations of 10 mg/L, respectively. The experimental work was extended to investigate the dye biodegradation in real textile wastewater using mixed cells in immobilized in PVA-SA. The Overloading rate (OLR) and Hydraulic retention time (HRT) of the aerobic bioreactor are 24.5 mg/L h and 41.37 h, respectively. The experimental profiles of RY concentration, COD reduction along with biomass growth, were in good agreement with the model predicted profiles. The effectiveness factors were 0.96 and 0.99 for the anaerobic and aerobic phases, respectively.

Assessment of novel rotating bipolar multiple disc electrode electrocoagulation-flotation and pulsed plasma corona discharge for the treatment of textile dyes.

The current study evaluates the performance of the designed novel electrolytic reactor with rotating bipolar multiple disc electrode (RBDE) in the electrocoagulation-flotation (EC-F) process and a pulsed plasma reactor for the removal of toxic textile dyes. Two different classes of dyes, Methyl Orange (MO), an azo group of dye, and Reactive Blue 19 (RB19), a reactive group of dye, were selected. Efficient removal of both the dyes at a faster rate was obtained with the designed RBDE reactor compared to the EC-F process with static electrodes. RB19 and MO were completely decolourized (100%) within 2 min of electrolysis time with rotating and 6 min with static (non-rotating) electrodes, respectively. Similarly, the maximum chemical oxygen demand removal of 86.4% and 93.2% was obtained for RB19 and MO, respectively, with the rotating electrode EC-F process. On the other hand, complete decolourization was obtained in 10 min and 12 min of pulsed corona discharge for MO (50 mg/L) and RB19 (50 mg/L), respectively. The comparison studies of RBDE and pulsed power plasma reactor (PPT) showed that MO removal was faster than RB19 removal in both RBDE EC-F and PPT processes. Relatively long treatment time was needed for RB19 compared to MO due to its complexity of structure and high solubility. RB19 and MO were completely degraded through pulsed corona discharge without any sludge production. The results show that the designed RBDE reactor performed much better than existing conventional electrocoagulation reactors. The RBDE reactor can be used as a pre-treatment unit for industrial wastewater, which can improve the treatment efficiency and reduces the energy consumption. Plasma technology showed complete degradation of pollutant without sludge production. The formation of a wide variety of reactive oxygen species during corona discharge helps in degrading the pollutants. Plasma technology can be used as a secondary treatment system along with the RBDE as pre-treatment process for complex industrial wastewaters. This will improve the quality of treated effluent and reduce the overall cost of treatment.

Performance evaluation of a novel electrolytic reactor with rotating and non rotating bipolar disc electrodes for synthetic textile wastewater treatment

Textile industry is one of the leading polluters of surface water due to the presence of various types of dyes and other hazardous pollutants. In this study, a novel rotating bipolar disc electrolytic (RBDE) reactor was designed for the treatment of textile wastewater and the performance was evaluated. The turbulence created in the system and enhanced mass transport (coagulants/ions) improved the overall performance of electrolytic cell during rotation. The effect of various parameters like current density, electrical conductivity, pH, rotation speed, and pollutant concentration on the performance of the RBDE reactor was examined in terms of COD, colour and TSS removal. Complete decolorization was obtained in 2 min and 6 min of electrolysis time in rotating and non-rotating mode of operation. COD removal was 4.8 times more in rotating electrode system (230.4 mg/L to 14.05 mg/L, 93.9% removal) compared to static mode of electrodes (230.4 mg/L to 67.9 mg/L, 70.6% removal), in 10 min of electrolysis time. Profilometry analysis confirmed that the rotation increased the electrode dissolution (8.1 μm in static and 62.3 μm in rotating electrodes) and also decreased the thickness of oxide film formation on cathode surface compared to static electrodes (0.55 μm on rotating and 6.48 μm on static electrodes). Moreover, RBDE reduced the energy consumption (1.4 kW h/kg dye) compared to static (2.1 kW h/kg) electrodes system for the complete decolourization of Rhodamine B (RB) dye.

Novel pilot scale photocatalytic treatment of textile & dyeing industry wastewater to achieve process water quality and enabling zero liquid discharge

This paper presents a novel end-to-end pilot scale photocatalytic treatment of real textile & dyeing industry effluent, which involved innovative approach in primary treatment, followed by Heterogenous Photocatalysis (HP) involving nano-TiO2/UV as secondary treatment and suitable filtration leading to treated water meeting process water quality enhancing water re-use efficiency. This enables Zero Liquid Discharge (ZLD); which is the need of the hour in tackling problems of point source pollution and Water Conservation in developing countries like India. Overall treatment led to complete degradation and mineralization of organic pollutants and dye stuff thereby achieving adequate treatment, complete decolourization and deodorization of the effluent and almost hundred times less quantities of sludge residues in comparison to those obtained in conventional treatment methods. The nature and elemental composition of sludge residues, as investigated using Energy Dispersive X-ray (EDX) elemental analysis, confirms complex organic dye components mineralized and nature being non-toxic. The complete treatment took place in 5 h without any kind of bioremediation method, which further highlights highly efficient and fast treatment coupled with small footprint. Overall cost of treatment is estimated to be around 1.55 USD/m3. Such an innovation in wastewater treatment is expected to bring a revolution in developing countries, which are grappled together with problems of rapid industrialization, urbanization, regulatory compliances and environmental challenges.

Activation of Peroxymonosulfate and Persulfate by Metal Loaded Mesoporous Catalysts for Orange G Dye Degradation

The main objective of this research was to study the catalytic activation of two different oxidants (potassium persulfate, PS and peroxymonosulfate, PMS) employing sulfate-based Advanced Oxidation Processes (AOPs). For this purpose, heterogeneous copper and cobalt catalysts were synthesized supported on MCM-41 mesoporous material. These catalysts were characterized by means of Atomic Absorption Spectroscopy (AA), X-ray diffraction (XRD), and Transmission Electron Microscopy (TEM). The metal charge of the catalysts ranged from 5% to 18%. The mesoporous arrangement was held after the metal loading and calcination, as shown by XRD patterns and TEM micrographs. The catalytic degradation of Orange G azo dye (Orange G: OG, disodium 7-hydroxy-8-[(E)-phenyldiazenyl]-1,3-naphthalenedisulfonate) was analysed, and the catalyst activities were determined in a batch reactor. The combination of PMS and higher metal-content Co-supported catalyst attained the best efficiency. In these conditions, the complete decolourization (100%) of the dye was achieved in the first minutes of reaction, while its mineralization reached after 4 h was 49%. Additionally, the catalytic activity of the Co/PMS system (a measure of the catalyst’s reusability) remained constant after three cycles of usage.

Reusable floating polymer nanocomposite photocatalyst for the efficient treatment of dye wastewaters under scaled‐up conditions in batch and recirculation modes

AbstractBACKGROUNDIn the last decade, research on floating photocatalysts has increased rapidly with polymer substrates being a popular choice. However, most of the published work is on very small volumes and there is very little work on scale‐up of such systems.RESULTSPolystyrene–titanium dioxide nanocomposite floating films were prepared using a facile solvent casting method and tested for the photocatalytic degradation of four different dyes under UV irradiation. The prepared film was characterised by Fourier‐transform infrared (FTIR), scanning electron microscopy (SEM), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectrometry (ICP‐OES) and profilometry. Scale‐up studies were done in batch mode under optimised conditions, and for the larger reactor volume, the effect of recirculation was studied. Complete decolourisation of the model dye (Remazol Turquoise Blue) was observed within 80 min in the scaled‐up batch process. In the recirculation mode, for a much larger volume of the dye solution, around 75% decolourisation in 6 h was observed. The reusability of the photocatalytic film was tested, and the results promise a minimum decolourisation efficiency of around 70%. Finally, total organic carbon (TOC) and liquid chromatography mass spectrometry (LC‐MS) analysis were used to assess the degradation of the dye. The maximum TOC reduction observed was around 25% possibly due to the complex nature of the dye used in this study. The intermediate products of degradation were identified, and a tentative mechanism is suggested.CONCLUSIONThis work demonstrates the recirculation aspects of the photocatalytic reactor under the scaled‐up conditions for a complex dye. The prepared film showed excellent stability with satisfactory wastewater decontamination under UV irradiation even after repeated use. © 2019 Society of Chemical Industry

Degradation of malachite green by a pulsed light/H2O2 process.

Pulsed light (PL) is a type of photonic technology characterized by intense short light pulses that enhance the speed of photochemical reactions, and which might be useful as light source in advanced oxidation processes. This work aimed to test PL as light source for the degradation of the dye malachite green (MG) by combining PL with H2O2. To this end, the effect of dye and H2O2 concentrations and pH on the degradation rate of MG was studied and a degradation pathway was proposed. Dye degradation followed a pseudo-first order kinetics; it increased with low initial dye concentration, high H2O2 concentration and low pH. Complete decolourization was achieved after 35 light pulses (75 J/cm2), with a degradation rate of 0.0710 cm2/J. The degradation was initiated by the attack of hydroxyl radicals to the central carbon of MG generating 4-(dimethylamino)benzophenone (DLBP) followed by the addition of hydroxyl radicals to the non-amino aromatic ring of DLBP and the demethylation of the amino group. Results indicate that PL technology has potential to be implemented to decrease the environmental impact of dyeing industries.

Highly stable binder free CNTs/rGO aerogel electrode for decolouration of methylene blue & palm oil mill effluent via electro-Fenton oxidation process.

In this study, single wall carbon nanotubes (CNTs)/reduced graphene oxides (rGO) aerogels were prepared by a one-pot hydrothermal process without using a binder. The produced CNTs/rGO aerogel was used as cathode in electro-Fenton system for the decolouration of methylene blue (MB) and palm oil mill effluent (POME). The addition of CNTs increased the surface area, pore volume and conductivity of the rGO aerogel, which further enhanced their performance as cathode towards the decolouration of MB and POME via electro-Fenton reaction. Complete decolouration of MB using rGO aerogel without CNTs could not be achieved. The effect of electro-Fenton reaction parameters conducted using the aerogel samples including, current, electrolyte concentrations and pH, were investigated accordingly. The CNTs/rGO aerogel electrode also showed high stability and reusability for up to six consecutive treatment cycles for MB. Besides, the CNTs/rGO aerogel also showed good performance in treating POME with 69.8%, 47.6% and 58.1% of reduction in true colour, total organic carbon (TOC) and chemical oxygen demand (COD), respectively, via 60 minutes electro-Fenton reaction. This study showed that CNTs/rGO aerogels with high porosity and stability can be prepared using simple procedure without adding binder. This fully carbon-based aerogel can serve as effective cathode for decolouration of organic dye and effluent.

Treatment of Methylene Blue and Methyl Orange Dyes in Wastewater by Grafted Titania Pillared Clay Membranes.

Background: Amphoteric membranes such as Titania Pillared Clay (TiPILC) membranes exhibit different charges at different pH ranges, subsequently show efficient separation for cationic and anionic organic pollutants in wastewater based on solution pH. The structural properties of such membranes determine their permeability and selectivity to a large extent. The present work is initiated to explore the possibility of enhancing the surface area of TiPILC membranes by grafting with 3-aminopropyltriethoxysilane.Method: Grafted TiPILC membranes were fabricated by colloidal sol- gel route followed by dip coating, drying and sintering the membranes at 300oC. X-ray diffraction (XRD) spectra of the pillared photocatalyst membranes show the presence of only anatase phase, which exhibits better photocatalytic activity. Fourier Transform Infrared (FT-IR) spectra reveal the formation of delaminated TiPILC material. The specific surface area of TiPILC membrane obtained at pH3.5 is 183m2/g.Results: Literature survey of 47 papers was carried out for the work. 10 papers were based on patents being dealt on degradation of organic dyes in wastewater by conventional methods, though reports of membrane technology are limited in literature. The rest 37 papers outlined the importance of widespread use of titania photocatalyst powder for degradation studies.Conclusion: The membrane material thus developed is efficient in complete decolouration of both Methylene Blue and Methyl Orange dyes on account of the high surface charge and high surface area in just one cycle of filtration.

Immobilized cells of Rhodococcus strain UCC 0004 as source of green biocatalyst for decolourization and biodegradation of methyl orange

Abstract The bulk presence of methyl orange is contributed by anthropogenic sources which poses substantial threat to health and the environment. Locally isolated Rhodococcus strains were used as alternatives to develop greener and cost effective methyl orange removal technology. Rhodococcus strain UCC 0004 in particular demonstrated complete removal of 0.5 g/L methyl orange after 2 days of incubation and this strain exhibited 513% higher methyl orange removal efficiency under static mode in comparison to agitated mode. Adopting the technology of immobilization enabled the decolourization of higher concentration of methyl orange which resulted in 66% greater methyl orange removal activity as opposed to the non-immobilized cells. Optimization of immobilization parameters at 0.4% (w/v) alginate concentration, 0.3 M CaCl2, 3 mm bead diameter and 50 beads led to improved methyl orange-decolourizing activity and reduced the time taken to achieve complete decolourization by 67%. The immobilized beads could be reused up to nine batches without significant loss of methyl orange-decolourizing ability which is advantageous economically. The immobilized cells demonstrated higher substrate affinity (Km = 0.3771 g/L) and accelerated rate of disappearance of methyl orange (Vmax = 0.05903 g/L/h) compared to free cells. No germination inhibition was observed on Triticum aestivum and Vigna radiata indicating complete removal of dye toxicity. The decolourization of methyl orange occurred through biodegradation as supported by complete disappearance of the major peak from UV–vis spectrum. Therefore, this strain has a huge potential to be developed as biological tool for efficient removal of wastewater containing methyl orange.

Energy intensified integrated advanced oxidation technology for the treatment of recalcitrant industrial wastewater

This work aimed at providing additional information and knowledge on the possibility to overcome the limitation of conventional advanced oxidation processes (AOPs) through hybridization. In the present work, a number of photochemical and non-photochemical AOPs such as direct photolysis (UV), photolysis of hydrogen peroxide using UV light (UV/H2O2), UV assisted coagulation (UV Fe2+ coagulation), Fenton process, Fe2+ coagulation and photo-Fenton process were compared to determine their feasibility to treat real textile wastewater. The Batik industry, which is a textile cottage industry in Malaysia has reported problems related to safe environmental disposal of its pollutants, mainly dyestuff. The comparison was made in terms of Chemical oxygen demand (COD), Total organic carbon (TOC) and colour removal together with electricity consumption. Among the processes evaluated, the highest COD removal was achieved for photo -Fenton oxidation (91.2%), followed by Fenton oxidation (81.4%), UV/H2O2 (68.0%), UV- Fe2+ coagulation (55.0%), Fe2+ coagulation (43.0%) and UV photolysis (10.0%). At the optimal operating conditions (room temperature, undiluted contaminants), the photo-Fenton hybrid process achieved complete decolourization and higher removal of COD (91.2%) and TOC (78.5%) with minimum electrical energy per order of 0.02 kWhr/m3 compared to other AOPs. About 13% reduction in the total chemical cost and 10% increase in the degradation were observed by combining the Fenton process with UV radiation compared to the conventional Fenton process. The GC/MS analysis revealed that the photo-Fenton process successfully removed 87% of organic compounds. The sludge characterization studies by Particle Size Distribution proved that the Fenton-generated sludge achieved quality suitable for disposal. Photo-Fenton is the cheapest option with highest removal (91%) as its required only $0.0016 to degrade 1 g of COD compared to Fenton which cost $0.0021. Therefore, this study concluded that the photo-Fenton process was an economically viable and appropriate treatment method for enhancing biodegradability of recalcitrant contaminants.

Degradation of rhodamine B with manganese dioxide nanorods.

This is an investigation on oxidative degradation of rhodamine B (RhB) by manganese dioxide (MnO2) nanorods synthesized by redox co-precipitation method. Field emission scanning electron microscopy of MnO2 nanorods at an electron voltage of 10 kV revealed a rod-like morphology for the synthesized nanoparticles. Fourier transform infrared spectra exhibited characteristic peaks of MnO2. Surface area of MnO2 nanorods was 277 m2/g. Effect of various parameters like initial concentration and pH of RhB solution, time of contact between MnO2 nanorods and RhB, dosage of MnO2, and stirring speed on decolouration of RhB was evaluated in batch experiments. Rapid decolouration in the initial period of the reaction was observed due to the adsorption of RhB molecules onto the surface of MnO2 nanorods followed by oxidative degradation. Percentage decolouration decreased with increase in initial concentration and increased with increase in dosage, speed of stirring the mixture and with increase in pH up to pH 7. Near complete decolouration was achieved at a dose of 0.5 g/L of MnO2 nanorods from 20 mg/L RhB solution within 3 min. Observations fitted best to the pseudo second order kinetic model. This study could pave the way for development of cost-effective, nontoxic nanostructures for treatment of wastewaters containing RhB.

Development of calcined catalytic membrane for potential photodegradation of Congo red in aqueous solution

A novel approach to fabricate calcined catalytic membrane was developed through electrospinning of Co/TiO2–PVA solution on a polyethersulphone (PES) membrane sheet. The aim of this study was to develop and characterize a Co/TiO2–PVA nanofibre PES catalytic membrane and evaluate its potential application in the photocatalytic degradation of dye from an aqueous solution. Three materials namely Co/TiO2, calcined catalytic nanofibres and calcined catalytic membrane were prepared and characterized with SEM-EDS, FTIR, XPS, XRD, TGA, and UV–vis DRS. XPS and EDS spectra revealed successful incorporation of cobalt in our developed materials. SEM cross-section image of calcined catalytic membrane depicted three layers which could be attributed to bottom layer (PES membrane), PVA nanofibres (middle layer) and top layer (Co/TiO2). UV–vis DRS spectra of samples showed absorbance in the visible range (400 to 800 nm) indicating that these three materials can be used as photocatalysts. Tauc plots revealed low energy band gap 1.86 eV for calcined catalytic membrane. Of the three catalytic materials evaluated, the calcined catalytic membrane was observed to have the highest photocatalytic activity. The preliminary data revealed complete (100%) decolourisation of dye within 150 min when the calcined catalytic membrane was used. Electron holes and hydroxyl radicals played the main role in the degradation process. LCMS results evinced the photodegradation of CR by revealing mass spectra of intermediate molecules. These findings provide valuable insight into the possibility that the calcined catalytic membrane developed during this study could be considered for further catalytic applications, especially in wastewater treatment.

Decolourization and biodegradation of azo dye methyl red by Rhodococcus strain UCC 0016

ABSTRACTIn 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.

Rapid microwave – Hydrothermal synthesis of CeO2 nanoparticles for simultaneous adsorption/photodegradation of organic dyes under visible light

Cerium oxide nanoparticles, synthesized by microwave mediated hydrothermal method, was characterized by using XRD, FT-IR, SEM, TEM, XPS, DR/UV–vis, and BET analyzer and applied for simultaneous adsorption/ photocatalytic decolourisation of two commonly used organic dyes namely Alizarin red S (ARS) and Eriochrome black-T (EBT). Powder XRD pattern coupled with SEM/TEM revealed the formation of single cubic phase spherical CeO2 nanoparticles with average particle size of ∼15 nm. The sample showed moderate specific surface area (47.73 m2 g−1) and relatively lower band gap (2.78 eV) than bulk CeO2. XPS study confirmed the existence of both Ce4+ and Ce3+ in the prepared sample. Batch adsorption studies without light irradiation showed significant adsorption of both the dyes on CeO2 nanoparticles with monolayer adsorption capacity (Qo) values 44.1 and 57.8 mg g−1 for ARS and EBT, respectively. Under visible light irradiation, the overall decolourisation (adsorption/photo-degradation) of both the dyes increased substantially and the optimum amount of CeO2 required for complete decolourisation of ARS (100 mg L−1) was 0.80 g L−1 while relatively lesser dose of catalyst (0.60 g L−1) was required for the same concentration of EBT. Suitable mechanisms were proposed for the decolourisation of dyes under visible light based on GC–MS/LC–MS data of the degraded products/intermediates.

Photocatalytic Degradation of Textile Reactive Dyes-A Comparative Study Using Nano Silver Decorated Titania-Silica Composite Photocatalysts.

Photocatalytic degradation of commercial textile azo dyes such as Reactive Red 120 (RR 120), Acid Orange 20 (AO 20), Reactive Orange 16 (RO 16) and Congo Red (CR) was studied under UV light and visible light irradiations of wave length 365 nm and 420 nm respectively over bare and modified titania catalysts such as TiO2, 1% Ag/TiO2, 30% TiO2/SiO2 and 1% Ag/30% TiO2/SiO2. On comparison of the catalytic activity of all the synthesized catalysts under UV and Visible irradiations, it was found that the composite catalysts showed higher photocatalytic activity than bare TiO2. Among the catalysts 1% Ag/30% TiO2/SiO2 composite catalyst was the best catalyst for the decolourization of the chosen dyes. Results obtained showed that the time taken for the complete decolourization of dyes was found to be significantly different for different dyes under both UV and visible light irradiations. Among the four dyes, AO 20 decolourised completely (100%) in 2 hrs, whereas Congo Red (CR) decolourised to the least extent (35%) over 1% Ag/30% TiO2/SiO2 under UV light irradiation. Experiments carried out under dark condition in the presence of catalyst revealed very high adsorption of CR (≈60%) over titania catalysts and hence this could be reason for suppressed catalytic activity of 1% Ag/30% TiO2/SiO2. Various optimization studies such as effects of substrate concentration, weight of catalyst and substrate pH were carried out. TOC analysis revealed a very high mineralization of all the dyes.

Screening of catalytic activity of natural iron-bearing materials towards the Catalytic Wet Peroxide Oxidation of Orange II

Natural materials were evaluated in the Catalytic Wet Peroxide Oxidation of a commonly used azo-compound, Orange II. Volcanic ash, black sand, pumice and Montanit300® were selected for evaluation. The materials were thoroughly characterized by several techniques (XRD, SEM/EDX, BET surface area and pore size distribution, TPD, Mössbauer spectroscopy, etc.). Peroxidation experiments were performed varying reaction temperatures (50–80 °C), catalyst loads and pH value (3–8). Complete decolouration was reached in most experiments; however, mineralization levels, peroxide consumptions and stabilities differed between materials. The activity of Fe leached during the reaction was evaluated and a combination of heterogeneous and homogeneous mechanism cannot be discarded. Thus, the materials may behave as Fe dispensers. Long-term stability experiments were also performed. While Montanit300® showed a decreased performance (20% activity reduction in 16 h) due to a higher leaching (20% Fe loss), ash and pumice performances remained almost steady at pH = 3 (Fe loss: 3% ash and 1.3% pumice).Mineralization levels obtained were outstanding (40–70%) and comparable to performances showed by more sophisticated catalysts. The use of these natural materials will optimize the Fenton process economics, since they are unexpensive, abundant and require only minimal modifications.

Integrated system of multiple batches to evaluate the continuous performance of microbial cells in decolourization processes

Azo dye degradation in wastewater treatment is a subject which has garnered the attention of many research studies. In this study, an innovative approach, namely, an integrated system of five batches (ISFB), was developed to investigate the capability of Saccharomyces cerevisiae ATCC 9763 for continuous degradation of methyl red as a representative azo dye. Toward this end, an expanded immobilized microbial bed (EIMB) reactor was established with a bed of encapsulated yeast cells in sodium alginate. EIMB reactor was run in two modes, single batch and ISFB. Moreover, durability of the microbial cells was evaluated by repeating the continuous decolourization eight sequential times in EIMB at ISFB mode with the same cells. ISFB set-up can simulate a continuous process while avoiding the complexity of utilizing continuous reactors. Spectrophotometry results show that 6 ± 0.17 h was required for complete decolourization in EIMB reactor at single batch mode which estimates a decolourization rate (RDec) of 8.9 ± 0.3 g h−1in this set-up. Subsequently, decolourization rate incrementally increased ≃2.8 times while ISFB mode was applied to the EIMB system and this rate was approximately maintained during eight consecutive runs. The changes in morphology and bioavailability of the immobilized S. cerevisiae were monitored through scanning electron microscopy.