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Paper-recycling mills are serious environmental threats due to their high water consumption and highly polluted wastewater. Particles are the most common issue of paper-recycling wastewater, and their removal is of particular interest for recycling. Rotating dissolved air flotation (RDAF) is a system for separating particles, and the mixing zone of this system, where particles collide with air bubbles, is the most important part. As a widely used system in various industries, RDAF has rarely been investigated in the literature in terms of its optimization and efficiency improvement. In general, RDAF processes are basically the same as those of conventional dissolved air flotation (DAF) systems; thus the results of RDAF can be applied to other DAF systems. In this work, the mixing zone of a full-scale RDAF for the paper-recycling mill wastewater treatment was investigated to predict particle-bubble collision efficiency, consisting of both particle-bubble transport and attachment, and the diameter of the formed particles in different turbulence conditions. ANSYS CFX R18.0, mathematical modeling, and experimental analysis were simultaneously conducted in this research. Based on experimental operation, four scenarios including flow rates and the discharge condition of effluent into the mixing zone were studied. Bubbles with sizes of 60, 80, and 100 µm, the turbulences were calculated. The obtained particle-bubble collision efficiencies indicated the diameter of output particles ranged from 50 to 300 µm. Also, the static light scattering test was performed to determine the particle sizes. The modeling and experimental results both showed that the collision efficiency was higher with the production of larger particles when valves #3 and #4 were opened in the mixing zone. [ABSTRACT FROM AUTHOR]

The aim of the present study was to evaluate the photocatalytic degradation of anthracene using Fe-doped TiO2 nanoparticles in the presence of UV. The structure and morphology of Fe-doped TiO2 nanoparticles were studied by X-ray diffraction, scanning electron microscopy, and energydispersive X-ray spectroscopy. The applied nanoparticles were synthesized by the sol--gel method. The effect of influential parameters on the degradation of anthracene, including pH, time, nanoparticles dosage, and the concentration of anthracene was studied. Using the UV/Fe-doped TiO2 system, the optimum experimental values were obtained to be as follows: pH = 7, contact time = 60 min, anthracene concentration = 5 mg/L, and nanoparticle dosage = 100 mg/L. Based on the results, it could be concluded that the photocatalytic degradation of anthracene using the UV/Fe-doped TiO2 provides suitable efficiency. In addition, it was found that the doped TiO2 could be considered as a proper catalyst in photocatalytic degradation processe [ABSTRACT FROM AUTHOR]

In this study, silica-coated magnetic nanoparticles (SCMNPs) were modified with ten generations of organic dendrimer containing methyl acrylate and melamine. At the final stage, benzophenone ligand bonded as an active surface actuator functional group on the sorbent product. This novel nanosorbent was used for naphthalene (NAP) removal. The synthesized nanosorbent was characterized by X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, vibrating sample magnetometry, Brunauer-Emmett-Teller, and scanning electron microscopy- energy-dispersive X-ray spectroscopy. The diameter range of the final sorbent was found 20-70 nm. The operational sorption parameters were optimized in a batch system. The best removal efficiency was obtained at pH = 7 during a 20 min process with the 0.4 g L-1 sorbent dosage in the presence of 20 mg L1 NAP at 25°C. Finally, NAP removal from the real samples (complex industrial waste and aqueous samples) was studied via gas chromatography-mass spectrometry with the 90%-100% NAP removal from the samples. The data were evaluated with various isotherm models and kinetic studies where the Langmuir isotherm exhibited a high compatibility (R2 = 0.9969) in the pseudo-second- order kinetic (R² = 0.9998) process. The present study revealed that the synthesized magnetic polymer has a high protentional for NAP removal from aqueous samples (>99%), because of the high sorption capacity (qm = 94.33 mg g-1), pH independence, rapid sorption process, and high recovery. [ABSTRACT FROM AUTHOR]

TiO2/Zeolite composite was synthesized through a sol-gel approach continuously. TiO2/Zeolite composite was exposed to laser irradiation until conversion to TiO2/Zeolite nanocomposite (T/Z) and T/Z was modified with m-phenylenediamine (N-T/Z). The resulting N-T/Z was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray, dynamic light scattering, and thermogravimetric analysis. The average range of particle size of the N-T/Z was about ~140 nm. The N-T/Z product was evaluated as a sorbent for removing 2,4-D from aqueous solutions. The adsorption operational parameters were investigated in a batch system. The complete removal of 2,4-D was investigated under optimum conditions in real samples by high-performance liquid chromatography. A 2,4-D removal efficiency of 72%-99% was obtained from the river, well, and agricultural drainage water samples. The pseudo-second-order kinetic model fitted the 2,4-D removal, and equilibrium data well followed the Langmuir model. The maximum adsorption capacity of the obtained sorbent was qmax = 4.914 mg g-1. The product had excellent stability for reprocessing in several runs without losing adsorptivity significantly. [ABSTRACT FROM AUTHOR]

Accurate modeling of runoff in watersheds requires calibration and uncertainty analysis of effective flow parameters and identifying of their statistical characteristics based on inter-parameter relationships and model inputs. In this research, the transport and diffusion of pollution (nutrients) in the river were simulated through the two-dimensional finite-volume method using the shallow water equations. To numerically solve these equations, the governing equations were converted into linear equations. Uncertainty and sensitivity of the prepared pollution model were analyzed to achieve better results in estimating pollution concentrations in rivers within a reliable range. In this study, the likelihood weight (LW) method was used for each parameter in which the ratio of sensitivity and probability density function for the sets of good and bad parameters are computed. To this end, 6,000 iterations of the uncertainty domain for 3 calibration parameters of the pollution transport and dispersion model were carried out using a modification of the general likelihood uncertainty estimation (GLUE) method prepared by the authors. The three considered parameters were n (manning coefficient), Sx, and Sy (riverbed slope parameters in x and y directions) since they were more prone to measurement errors compared to the other hydraulic parameters. In the next step, the eutrophication issue and transport and diffusion of the nutrients (TDN model) in the estuaries of the Peer-Bazar River and Anzali Wetland were analyzed. A total of 1,500 simulations were considered as efficient simulations by applying the acceptable threshold values to the sum of squared errors indicator for all the simulations. The corresponded set of parameters was considered as good set parameters and the others as bad set parameters. By extracting the diagrams of the posterior probability distribution for the parameters included in the efficient simulations, parameter n with an optimal value of 0.2502 was recognized as the sensitive and influential parameter of the model. Sx and Sy with the optimal values of 0.0169 and 0.0776 were recognized as the less sensitive parameters due to their larger level of uncertainty. Assuming a confidence interval of 95% for the upper and lower bounds of uncertainty, p- and d-factors were, respectively, obtained as 0.78 and 0.73, indicating the high level of observational concentrations for the considered confidence interval. It can be concluded that the GLUE approach has been successfully applied to the TDN model. Also, the comparison of sensitivity analysis of parameters based on the LW methods and variation coefficient of parameters indicated that LW is an efficient method for sensitivity analysis of model parameters. [ABSTRACT FROM AUTHOR]

The oil-based compounds are widely used in modern human life, and the accidental release or leakage of these compounds is led to water and soil pollution and creates many problems for the environment. The purpose of this study was to determine the efficiency of photo-catalytic degradation of pyrene using Fe-doped TiO2 in the presence of UV. This experimental study was carried out at laboratory scale in a 2 L pilot reactor. The nanoparticle was synthesized by the sol-gel method. Pyrene degradation was investigated under different conditions of pH, reaction time, nanoparticle concentration and pollutant concentration. For the statistical analysis, SPSS V.16 software and oneway analysis of variance were used. The results showed that the optimum values of studied variables were as follows: pH = 9, contact time = 45 min, initial concentration of pyrene = 25 mg/L and nanoparticle dosage = 150 mg/L. It was also observed that the highest pyrene degradation efficiency was 98.66%. The obtained results suggested that the photo-catalytic process using the doped nanoparticle revealed the excessive potential to remove and to mineralize the oil-based pollutants, and it can be considered an effective alternative for this purpose. [ABSTRACT FROM AUTHOR]

Condensation has a considerable effect on the performance of air gap membrane distillation (AGMD) process. In this study, a novel module arrangement was successfully introduced with the aim of improving the condensation phenomena and consequently enhancing the efficiency. In this newly designed AGMD arrangement, the common flat coolant plate was replaced with several horizontal copper tubes that has been named tubular condenser. Coolant fluid was streamed inside the tubes and condensation occurred outside the tubes. To measure the performance of this new module, two types of polytetrafluoroethylen (PTFE) commercial flat sheet membranes supported by polypropylene (PP) non woven layer with different pore sizes were employed. To measure water permeation flux, laboratory prepared brackish water was introduced into the system at different temperatures, which were 40, 50, 60, 70 and 80°C. The average flux produced by the system at 80°C for a flat plate condenser with an equivalent air gap was 11.7 kg/(m²·h); it increased up to 19.45 kg/(m²·h) using a simple tubular condenser. To improve more, tubular condenser was developed using zigzag copper ribbons, enhancing the water permeation flux to 30.08 kg/(m²·h). To realize the performance of developed tubular module, the effect of membrane pore size and air gap width as well as ribbons arrangement were studied. [ABSTRACT FROM AUTHOR]

In this study, hybrid nano adsorbent supported carbon dots was prepared and used for removing Cr(VI) from aqueous solution. Carbon dots were synthesized from sugarcane molasses under microwave irradiation. Hybrid nano adsorbent was prepared by impregnating carbon dot with H3 PO4 in a ratio of 2:1 and introducing 0.01 M FeCl3 into the slurry. The carbon dot hybrid was activated via a conventional thermal method under N2 flow. The physico-chemical properties of the synthesized material were investigated using X–ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption/desorption, and field emission scanning electron microscopy (FESEM). Chromium adsorption was studied in a synthesized aqueous solution using hybrid Fe–carbon dots as the adsorbent under various adsorption conditions like solution pH, adsorbent dosage, various initial chromium concentrations, and contact time. Adsorption isotherms were conducted and it was indicated that the adsorption equilibrium data was well fitted for both the Langmuir (R² > 0.99) and Freundlich (R² > 0.97) models. The maximum adsorption capacity of Cr(VI) onto Fe–CDs was obtained at 81.97 mg g–1. Adsorption kinetics for Cr(VI) was followed. The pseudo-second-order model indicated very well that the rate-controlling step in the adsorption is mainly chemisorption. The saturated hybrid nano adsorbent could be easily regenerated using dilute 1 N NaOH and 1 N HCl aqueous solutions and high desorption efficiency (up to 74%) of Cr(VI) was achieved for various initial chromium concentrations after 5 adsorption-desorption cycles. The obtained results proved that the hybrid Fe–CDs is a low–cost and effective adsorbent for Cr(VI) ions removal. [ABSTRACT FROM AUTHOR]

The Peer-Bazar river delivers pollutants in the water bodies of Anzali International Wetland especially during flood events. Here, the two-dimensional (2D) finite volume hydrodynamic models for the prediction of nutrients are developed. The model is based on the mass balance equation including advection and diffusion transport and chemical and biological transformation considering the impact of inflowing river and climate change. The model is formulated to simulate nutrients such as Amonia-Nitrogen (NH3-N), Nitrate (NO3-N) or overall Total Nitrogen (TN), Phosphorus (PO43-) or TP, Dissolved Oxygen (DO) and Total Dissolved Solids (TDS) and prediction of spatial and temporal distributions of concentration of each parameter in the Peer-bazar estuaries leading to the Anzali International Wetland. Ten points of the Peer-bazar River were studied during an 18-month period from June 2014 to December 2015. The simulation and numerical analysis of water quality parameters were conducted in a 2-dimensional approach using the geometric and topographic data and imposing boundary conditions. This research used the software developed by the author, FLOW-3D mathematical model, and HEC-RAS for simulation and qualitative evaluation of the river. Results revealed that the mean concentration of phosphorous, nitrogen and TDS exceeded the permissible limits reported by the European Directive 80/778/EEC and OECD and USEPA standards. Therefore, water of the region is subject to the advanced eutrophic conditions. Simulation predictions showed that the variation in TDS and nutrients contents will increase in the next coming years and the region will reach to the stable conditions. Using regression, a relationship between EC and TDS was obtained in the next step. Comparing the results obtained by the simulator and the values measured in laboratory indicated the suitable performance of reference values. [ABSTRACT FROM AUTHOR]

Biological water treatment using granular activated carbon (GAC) and anthracite improves water quality by reducing total organic carbon (TOC), colour, nitrogen content and turbidity. This study investigated the operation of aerobic biofilm on two pilot biofilters designed to remove turbidity, TOC, NO-3 and NH+ 4 in water. The results show that the GAC-sand pilot filter at a low hydraulic loading rate (HLR) increased the empty bed contact time and recorded the highest production of heterotrophic bacteria and biofilm, which increased the efficiency of treatment. Breakthrough occurred in the GAC-sand pilot filter at 72 h and low HLR, but occurred sooner for medium and high HLRs at 48 and 24 h, respectively. The run-time for the anthracite-sand pilot filter at high, medium and low HLRs was 70, 46 and 22 h, respectively. The microorganisms Pseudomonas, Bacillus and Citrobacter were identified in the GAC-sand filter. [ABSTRACT FROM AUTHOR]

In the present work, ultrafiltration membranes were prepared using emulsion polyvinyl chloride (EPVC) with the addition of various concentrations of polyethylene glycol (PEG) to investigate the morphological structure and separation properties. The effects of polymer concentration, coagulation bath temperature (CBT), and PEG (6 kDa) concentrations—a pore former hydrophilic additive—were studied. Through the phase inversion, the membranes—which were induced by immersion precipitation in a water coagulation bath—were fabricated through dissolving EPVC in N-methyl-pyrrolidinone, a polymer solvent. Morphological features of the membranes were characterized through scanning electron microscopy, pore size and porosity, and contact angle measurements. Water and bovine serum albumin (BSA) were used in order to study the separation and permeation performance of the fabricated membranes at 3 bar, which is operating pressure. The results which were obtained from contact angle test indicated an increment in the membranes hydrophilicity with an increase in PEG concentrations, and then it decreased again. Increasing the CBT led to macrovoid formation in the membrane structure and the appreciation of both membrane permeability and BSA rejection. The addition of PEG resulted in a more porous structure and a higher water flux for those membranes, which were prepared with 13 wt.% EPVC; while, for those which were fabricated with 15 wt.% polymer, an opposite trend was observed. [ABSTRACT FROM AUTHOR]