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•Graphene nanomaterials (pGr, GO, RGO, FLG and MLG) have a different fate in WWTPs.•pGr, FLG and MLG settle down more easily than RGO in the primary clarifier.•GO hinders the ...anaerobic denitrification, but improves the anaerobic NH4+ oxidation.•Various minerals can adsorb GFNs and improve the pretreatment/primary sedimentation.•GO and RGO favoured the formation of disinfection by-products (trihalomethanes).
The release of graphene and its derivatives in soil, air and water seems an inevitable consequence of the massive future use of these carbonaceous allotropes. From an environmental engineering point of view, it should be noted that part of the aqueous streams containing these nanomaterials will end up in wastewater treatment plants, and there will be interactions between the nanomaterials, the other pollutants in the sewage and the microorganisms of the secondary treatment, which could affect the effectiveness of the depuration process. The present work reviews the available literature on the behaviour of these nanoallotropes in wastewater treatment plants (a literature which is almost exclusively focused on graphene oxide and reduced graphene oxide), and also includes research dealing with simpler systems: i) graphene in purified water, ii) graphene in purified water with salt, and iii) graphene in purified water with organic matter and salt. It is probable that the fate of most of the graphene-family nanomaterials will be the primary/secondary sludge, and that a small portion (mainly in the form of graphene oxide) will pass to the tertiary treatment. Besides, graphene oxide has a negative effect on the biological treatment.
Sewage sludge is considered a costly waste, whose benefit has received a lot of attention for decades. In this sense, a variety of promising technologies, such as thermal hydrolysis and wet ...oxidation, are currently employed. Thermal hydrolysis is used as a pretreatment step ahead of anaerobic digestion processes and wet oxidation is intended for the solubilization and partial oxidation of the sludge. Such processes could be utilized for solubilizing polysaccharides, lipids, fragments of them and phosphorus (thermal hydrolysis) or for generating carboxylic acids (wet oxidation). This article compiles the available information on the production of valuable chemicals by these techniques and comments on their main features. Temperature, reaction duration times and sludge characteristics influence the experimental results significantly, but only the first two variables have been thoroughly studied. For thermal hydrolysis, a rise of temperature led to an increase in the solubilized biomolecules, but also to a greater decomposition of proteins and undesirable reactions of carbohydrates with themselves or with proteins. At constant temperature, the amounts of substances that can be recovered tend to become time independent after several minutes. Diluted and activated sludges seem to be more readily hydrolyzable than the thickened and primary ones. For wet oxidation, the dependence of the production of carboxylic acids with temperature and time is not simple: their concentration can increase, decrease or go through a maximum. At high temperatures, acetic acid is the main carboxylic acid obtained. Concentrated, fermented and secondary sludge seem to be more suitable for yielding higher amounts of acid than diluted, undigested and primary ones.
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•Thermal hydrolysis solubilizes proteins, carbohydrates, lipids and phosphorus•Wet oxidation mainly produces soluble volatile fatty acids.•Temperature, reaction time and type of sludge determined the obtained products.•There is a lack of product characterization and absence of economic evaluations.
Experimental self-diffusivities of gases, vapors, and liquids obtained by means of tracer techniques and nuclear magnetic resonance are reviewed. The considered substances range from noble gases and ...simple diatomics (nitrogen, oxygen, carbon monoxide, etc.) to complex organic molecules, such as phenolphthalein dimethyl ether and 2-(α-methylbenzylamino)-5-nitropyridine, although polymers have not been included. Some comments on the applicability of neutron scattering to the determination of self-diffusion coefficients are also made. All the experimental results of the investigated systems are given as Supporting Information, whereas the references, temperatures, and pressures of these data and the main features of the measurement methods are compiled and classified.
Humic and fulvic acids constitute humic substances, a complex mixture of many different acids containing carboxyl and phenolate groups, which are not only the principal soil fertility factors but ...also the main pollutants present in landfill leachates or natural organic matter in water. Due to their low bacterial biodegradability, fungal biodegradation processes are key for their removal. The present study compiles and comments all the available literature on decomposition of aqueous humic substances by fungi or by their extracellular enzymes alone, focusing on the influence of the reaction conditions. The biodegradation extent mainly depends on the characteristics and concentration of the humic compounds, the type of microorganisms selected, the inoculation mode, the C and N sources, the presence of certain chemicals in the medium, the availability of oxygen, the temperature, and the pH.
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•Review of fungal treatment of real wastewaters with humic substances.•Effects of type of leachate, fungus, immobilization, medium, temperature and pH.•Fungal biodegradation is a ...complex function of the experimental conditions.•Bioadsorption and biodegradation should be measured separately.•Fungal processes provide higher purification and lower fouling than bacterial ones.
Leachates have different concentrations of organic matter and levels of biodegradability, depending on the age of the landfill and they must be treated using appropriate techniques, such as fungal degradation, in order to protect the environment and water resources. Natural organic matter contains the same type of organic species as old and medium age leachates, but at lower concentrations. The present study compiles and assesses all the available literature on the biotreatment of these compounds, mainly humic acids, by fungi.
It was found that the efficiency of the fungal biodegradation of these wastewaters depends on the characteristics and concentration of the organic matter in the leachate, the microorganisms selected and whether they were immobilized or not, the nutrients present in the medium and their concentrations, the experimentation time, the temperature and the pH. The influence of the mode of inoculation has only been studied in natural organic matter, but similar effects are expected in the treatment of the leachates.
The interactions between these parameters are complex and the optimal conditions have to be determined by laboratory and pilot testing, employing multivariate statistical techniques and experimental design.
Binary diffusion coefficients of isobutylbenzene, sec-butylbenzene, and 3-methylbutylbenzene (isopentylbenzene) in carbon dioxide were measured at supercritical conditions: temperatures of (313, 323, ...and 333) K and in a pressure range of (15.0 to 35.0) MPa using the Taylor–Aris technique. The dependency on temperature, pressure, carbon dioxide density, and carbon dioxide viscosity was examined. The experimental results were compared with the predictions of 14 semiempirical equations derived from the Stokes–Einstein equation (six equations) and from the model of the rough-hard-sphere (eight equations). Despite of the low errors of some of them, none reproduced the trend in which the isomers diffused.
The binary diffusion coefficients of 2-ethyltoluene, 3-ethyltoluene, and 4-ethyltoluene in supercritical carbon dioxide were determined in a pressure range of (15.0 to 35.0) MPa at temperatures of ...(313, 323, and 333) K by means of the Taylor−Aris dispersion technique. The influence of pressure, temperature, density, and viscosity on the binary diffusion coefficients was examined, and some general trends were established. The experimental results were compared with the values estimated by several semiempirical equations based on the Stokes−Einstein formula and on the Rough−Hard−Sphere model.
Binary diffusion coefficients at infinite dilution in supercritical carbon dioxide, D A B, were measured for five n-alkylbenzenes (n-butylbenzene, n-pentylbenzene, 1-phenylhexane, 1-phenyloctane, and ...1-phenyldodecane) by means of the Taylor−Aris technique in a chromatographic apparatus from 313 to 333 K and from 15.0 to 35.0 MPa. The experimental results were correlated with temperature, pressure, solvent viscosity, and solvent density. In the case of temperature dependence, additional measurements were carried out for n-pentylbenzene from 308 to 398 K at 35.0 MPa. As the five solutes are similar molecules, the corresponding states principle of Teja was tested together with the results obtained from several predictive equations based on the Stokes−Einstein formula and on the rough-hard-sphere model.
Diffusion coefficients of four solutes at infinite dilution (benzyl acetate, 2-phenylethyl acetate, 3-phenylpropyl acetate, and dibenzyl ether) were measured in the system CO2 + ethanol from 313.16 ...to 333.16 K and pressures between 15 and 35 MPa over the full concentration range of the CO2 + ethanol mixture. The diffusional behavior in the mixed solvent was compared with the estimation of seven simple predictive equations, Le Blanc, Wilke−Chang, Holmes−Olander−Wilke, Tang−Himmelblau (two formulas), Perkins−Geankoplis, and Leffler−Cullinam, observing that the first two give errors between 17 and 30% and that deviations lower than 11% are only obtained with the expressions of Tang−Himmelblau. Nevertheless, as none of the studied equations considers the self-association of ethanol nor complex formation between solute and alcohol molecules, the model of Lusis−Ratcliff and Mohan−Srnivasan was extended to a ternary liquid−supercritical system with the diffusing component dilute, obtaining average absolute deviations lower than 4.6% for the diffusivities of the four solutes. Nevertheless, the extension of this model is correlative (it needs one adjustable parameter for each solute), not predictive.
The measurement of the experimental binary diffusion coefficients of 2,3-dimethylaniline, 2,6-dimethylaniline, 2-methylanisol, 4-methylanisol and 3-nitrotoluene in supercritical carbon dioxide is ...reported. Results were obtained using the Taylor-Aris dispersion technique. The diffusivity experimental data were correlated with temperature, pressure and carbon dioxide density and viscosity. Moreover, the experimental results were compared with the values estimated by several predictive equations.
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The measurement and correlation of the experimental binary diffusion coefficients of 2,3-dimethylaniline, 2,6-dimethylaniline, 2-methylanisole, 4-methylanisole and 3-nitrotoluene in supercritical carbon dioxide is reported. Results were obtained using the Taylor-Aris dispersion technique, at 313, 323, and 333
K, and in a pressure range from 15.0 to 35.0
MPa. The diffusivity experimental data were correlated with temperature, pressure and carbon dioxide density and viscosity. Moreover, the experimental results were compared with the values estimated by several semiempirical equations.
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