Adsorption characteristics of surfactants and phenol on modified zeolites from their aqueous solutions

The role of surfactants in wastewater treatment: Impact, removal and future techniques: A critical review

Wastewater treatment has an important responsibility to react to changing consumer and industrial produced wastes that pose environmental challenges. Surfactants are one of these emerging contaminants. They are of interest because of their increasingly ubiquitous domestic and industrial use and the difficulty their presence causes traditional treatment. In response to this developing area, this critical review considers research from a variety of technical backgrounds to provide an up to date overview of the impact of surfactants on the environment, health and their removal. This found major concerns about surfactants on the environment and on health being corroborated in the past five years. Current research into removal focuses on existing biological and chemical wastewater treatment optimisation. Despite improvements being found to traditional biological methods using chemical pre-treatments there is a clear lack of consensus regarding the ideal strategy. Drawbacks and potential solutions for a range of these technologies, including Fenton reaction and aerobic degradation, are discussed. In this field the authors recommend an improved diversity in surfactants used for the research and addressing of significant knowledge gaps. Novel methods, such as Carbon Nanotube (CNT) use are also discussed. These methods, while showing promising results, will require continual research effort to resolve present issues such as variable performance and environmental concerns. Larger scale work is also needed to validate the initial work done. Potential uses of surfactants to optimise wastewater treatment, such as Surfactant Modified Zeolites (SMZs), are also discussed. This review finds that surfactant removal from wastewater is a promising and challenging field that warrants further investigation.

Hand-powered centrifugal microfluidic platform inspired by the spinning top for sample-to-answer diagnostics of nucleic acids

Point-of-care (POC), sample-to-answer and electricity-free nucleic acid diagnostic tools are vital for health care and disease control in resource-limited settings where centralized medical facilities or even electric power may remain unreliable. Inspired by one of the oldest recognizable toys, the spinning top, here we report a fully hand-powered centrifugal microfluidic platform for the diagnostics of pathogenic bacteria. Assay procedures such as zeolite-based purification of nucleic acids, loop-mediated isothermal amplification (LAMP) and visual detection of fluorescence signals are integrated into a single microfluidic disc. A simple pull-out operation of the top rack of the customized centrifuge initiates high-speed rotation of the disc, resulting in efficient actuation and mixing of preloaded sample/reagent fluids. This microfluidic platform enables the simultaneous detection of six kinds of pathogenic bacteria within a small disc in an electricity-free manner, showing great promise in sample-to-answer nucleic acid detection in remote settings.

Novel phenol capturer derived from the as-synthesized MCM-41

Novel phenol-capturer was prepared by modifying the as-synthesized mesoporous silica MCM-41 with tetraethylenepentamine (TEPA), not only saving the energy and time for removal of template, but also opening the way to utilize the micelles for adsorption. Once the organic modifier was distributed in the template micelle of MCM-41 to form a web within the mesoporous channel, the composite could adsorb more phenols in gas stream than activated carbon for the first time. With an unwanted high adsorption capacity, this mesoporous silica-amine composite represented potential application for trapping phenols, especially in tobacco smoke to protect environment.

Rapid decolourization and mineralization of the azo dye C.I. Acid Red 14 by heterogeneous Fenton reaction

The decolourization and mineralization of a solution of an azo dye using a catalyst based on Fe(II) supported on Y Zeolite (Fe(II)-Y Zeolite) and adding hydrogen peroxide (heterogeneous Fenton process) have been studied. The catalyst was prepared by ion exchange, starting from a commercial ultra-stable Y Zeolite. All experiments were performed on a laboratory scale set-up. The effects of different parameters such as initial concentration of the dye, initial pH of the solution of the dye, H(2)O(2) concentration, temperature and ratio of amount of catalyst by amount of solution on the decolourization efficiency of the process were investigated. A percentage of colour removal of 99.3±0.2% and a mineralization degree of 84±5% of the solution of the dye were achieved in only 6 min of contact time between the catalyst and the solution, under the following conditions: initial concentration of the dye of 50 ppm, pH 5.96, 8.7 mM of H(2)O(2), T of 80°C and catalyst concentration of 15 g/L. Moreover, the catalyst Fe(II)-Y Zeolite can be easily filtered from the solution, does not leach any iron into the solution (avoiding any secondary contamination due to the metal) and its effectivity can be reproduced after consecutive experiments.

The investigation of phenol removal from aqueous solutions by zeolites as solid adsorbents

This work reports results on phenol adsorption from aqueous solutions on synthetic BEA (β) and MFI (ZSM-5) zeolites, studied by heat-flow microcalorimetry. For the sake of comparison, the adsorption was performed on activated carbon, a solid customarily used for removal of phenol from water. The obtained values of heats evolved during phenol adsorption indicate the heterogeneity of active sites present on the investigated systems for the adsorption of phenol. In addition, the amounts of adsorbed pollutant were determined and presented in the form of adsorption isotherms, which were interpreted using Langmuir, Freundlich, Dubinin-Astakov and Sips' equations. The latter was found to express high level of agreement with experimental data. The results obtained in this work reveal that the adsorption of phenol on zeolites depends on both Si/Al ratio and on the pore size. Hydrophobic zeolites that possess higher contents of Si show higher affinities for phenol adsorption. Among investigated zeolites, zeolite β possesses the highest capacity for adsorption of phenol. The possibility of regeneration of used adsorbents was investigated by thermal desorption technique. It has been shown that in the case of β zeolite the majority of adsorbed phenol is easily released in the low temperature region.

Modeling and optimization of heterogeneous photo-Fenton process with response surface methodology and artificial neural networks

In this study, estimation capacities of response surface methodology (RSM) and artificial neural network (ANN) in a heterogeneous photo-Fenton process were investigated. The zeolite Fe-ZSM5 was used as heterogeneous catalyst of the process for degradation of C.I. Acid Red 14 azo dye. The efficiency of the process was studied as a function of four independent variables, concentration of the catalyst, molar ratio of initial concentration of H2O2 to that of the dye (H value), initial concentration of the dye and initial pH of the solution. First, a central composite design (CCD) and response surface methodology were used to evaluate simple and combined effects of these parameters and to optimize process efficiency. Satisfactory prediction second-order regression was derived by RSM. Then, the independent parameters were fed as inputs to an artificial neural network while the output of the network was the degradation efficiency of the process. The multilayer feed-forward networks were trained by the sets of input-output patterns using a backpropagation algorithm. Comparable results were achieved for data fitting by using ANN and RSM. In both methods, the dye mineralization process was mainly influenced by pH and the initial concentration of the dye, whereas the other factors showed lower effects.

Removal of perfluorinated surfactants by sorption onto granular activated carbon, zeolite and sludge

Perfluorinated surfactants are emerging pollutants of increasing public health and environmental concern due to recent reports of their world-wide distribution, environmental persistence and bioaccumulation potential. Treatment methods for the removal of anionic perfluorochemical (PFC) surfactants from industrial effluents are needed to minimize the environmental release of these pollutants. Removal of PFC surfactants from aqueous solutions by sorption onto various types of granular activated carbon was investigated. Three anionic PFC surfactants, i.e., perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutane sulfonate (PFBS), were evaluated for the ability to adsorb onto activated carbon. Additionally, the sorptive capacity of zeolites and sludge for PFOS was compared to that of granular activated carbon. Adsorption isotherms were determined at constant ionic strength in a pH 7.2 phosphate buffer at 30 degrees C. Sorption of PFOS onto activated carbon was stronger than PFOA and PFBS, suggesting that the length of the fluorocarbon chain and the nature of the functional group influenced sorption of the anionic surfactants. Among all adsorbents evaluated in this study, activated carbon (Freundlich K(F) values=36.7-60.9) showed the highest affinity for PFOS at low aqueous equilibrium concentrations, followed by the hydrophobic, high-silica zeolite NaY (Si/Al 80, K(F)=31.8), and anaerobic sludge (K(F)=0.95-1.85). Activated carbon also displayed a superior sorptive capacity at high soluble concentrations of the surfactant (up to 80 mg l(-1)). These findings indicate that activated carbon adsorption is a promising treatment technique for the removal of PFOS from dilute aqueous streams.

Comparative study of UV/TiO2, UV/ZnO and photo-Fenton processes for the organic reactive dye degradation in aqueous solution

In this study advanced oxidation processes (AOPs), UV/TiO(2), UV/ZnO and photo-Fenton, were applied in order to degrade C.I. Reactive Red 45 (RR45) dye in aqueous solution. The effects of key operating parameters, such as initial pH, catalyst and hydrogen peroxide dosage as well as the effect of initial dye concentration on decolorization and mineralization extents were studied. Primary objective was to determine the optimal conditions for each of the processes. The influence of added zeolite on the process efficiency was also studied. UV/vis spectrophotometric and total organic carbon (TOC) measurements were performed for determination of decolorization and mineralization extents. It has been found that photo-Fenton process was the most efficient with 74.2% TOC removal and complete color removal achieved after a 1h treatment.

Fe-exchanged zeolite as the effective heterogeneous Fenton-type catalyst for the organic pollutant minimization: UV irradiation assistance

The issue of investigations in this study was an application of heterogeneous Fenton-type catalyst, Fe-exchanged zeolite FeZSM5, for the minimization of phenol and overall organic content in the model wastewater. Applied treatment systems included variation of heterogeneous and homogeneous Fenton-type catalyst with and without the assistance of UV irradiation, FeZSM5/H2O2, Fe2+/H2O2/NH4ZSM5, Fe3+/H2O2/NH4ZSM5, UV/FeZSM5/H2O2, UV/Fe2+/H2O2/NH4ZSM5 and UV/Fe3+/H2O2/NH4ZSM5. Processes efficiency was evaluated on the basis of phenol removal, mineralization extent, H2O2 consumption and concentration of iron ions in the bulk after the treatment. By all applied systems, complete phenol removal was achieved in less than 30 min of treatment time. Systems including heterogeneous Fenton-type catalyst showed somewhat lower mineralization efficiency in comparison to the corresponding systems applying homogeneous Fenton-type catalysts and the addition of synthetic zeolite NH4ZSM5. Significantly lower concentration of iron ions in the bulk after the treatment could give these systems, particularly UV/FeZSM5/H2O2, a great advantage over the homogeneous Fenton-type systems.

Adsorption characteristics of bisphenol-A in aqueous solutions onto hydrophobic zeolite

The adsorption behavior of bisphenol-A, which is a hydrophobic organic compound and also listed as one of endocrine disrupting chemicals, from aqueous solution onto hydrophobic zeolite at 25 degrees C have been studied using a batch adsorption process in terms of a pseudo-second-order equation and three common isotherms (i.e., the Langmuir, Freundlich, and Redlich-Peterson). The pore properties of the Y-type zeolite have been determined using N2 adsorption-desorption isotherms, indicating that it is a supermicroporous adsorbent associated with a lower percentage of mesopores. Based on the kinetic model the effects of particle size, initial bisphenol-A concentration, initial solution pH, and adsorbent dosage on the adsorption rate constant and equilibrium capacity have been estimated, showing that the adsorption process could be simulated well by the simplified kinetic model. From the data on the equilibrium adsorption capacities obtained by fitting the pseudo-second-order model, the adsorption isotherm could be better described by the three-parameter Redlich-Peterson model than by the two-parameter models (i.e., the Langmuir and Freundlich).

Advanced oxidation processes in azo dye wastewater treatment

The chemical degradation of synthetic azo dyes color index (C.I.) Acid Orange 7, C.I. Direct Orange 39, and C.I. Mordant Yellow 10 has been studied by the following advanced oxidation processes: Fenton, Fenton-like, ozonation, peroxone without or with addition of solid particles, zeolites HY, and NH4ZSM5. Spectrophotometric (UV/visible light spectrum) and total organic carbon measurements were used for determination of process efficiency and reaction kinetics. The degradation rates are evaluated by determining their rate constants. The different hydroxyl radical generation processes were comparatively studied, and the most efficient experimental conditions for the degradation of organic azo dyes solutions were determined.

Decomposition of phenol by hybrid gas/liquid electrical discharge reactors with zeolite catalysts

Application of hybrid gas/liquid electrical discharge reactors and a liquid phase direct electrical discharge reactor for degradation of phenol in the presence and absence of zeolites have been investigated. Hybrid gas/liquid electrical discharges involve simultaneous high voltage electrical discharges in water and in the gas phase above the water surface leading to the additional OH radicals in the liquid phase and ozone formation in the gas phase with subsequent dissolution into the liquid. The role of applied zeolites, namely NH4ZSM5, FeZSM5 and HY, were also studied. Phenol degradation and production of primary phenol by-products, catechol and hydroquinone, during the treatment were monitored by HPLC measurements. The highest phenol removal results, 89.4-93.6%, were achieved by electrical discharge in combination with FeZSM5 in all three configurations of corona reactors. These results indicate that the Fenton reaction has significant influence on overall phenol removal efficiency in the electrical discharge/FeZSM5 system due to the additional OH radical formation from hydrogen peroxide generated by the water phase discharge.