WATER AND WASTEWATER
Year:2020 | Volume:31 | Issue:4|Papers Count:14

Nitrogen compounds such as ammonium and nitrate are among the most common pollutants in wastewater and water resources. Removal of these substances is essential for reducing their adverse environmental and health effects. One of the biological methods for eliminating nitrogen is the simultaneous nitrification and denitrification process (SND) which, due to simplicity and cost effectiveness has attracted much interest. The SND can be performed by using bacterial attachment growth. The COD/N ratio is one of the effective parameters on the SND process. It can influence the process performance by changing the biofilm mass and the bacterial population. For this reason, the purpose of this study was to investigate the effect of COD/N ratio on simultaneous nitrification and denitrification in aerobic moving-bed sequencing batch reactor (MBSBR). For this purpose, an aerobic MBSBR reactor was operated in two phases. The selected values for COD/N in phases 1 and 2 were 10 and 20, respectively. According to the results, doubling of COD/N significantly increased the biofilm mass from 15 mg/media to 25 mg/media and increased the effluent COD from 22 mg/L to 192 mg/L as well, for phases 1 and 2, respectively. However, it had trivial effect on the concentration of suspended solids. The ammonium concentration in effluent of phase 2 was around 30 mg N/L which was about 33% more than that of phase 1 (10 mg N/L). This indicates a decrease in the rate of ammonium oxidation in phase 2 which most probably was attributed to increase of the population of heterotrophic bacteria and inhibition of the growth of autotrophs as a result of the higher abundance of organic matter in this phase compared with phase 1. In phase 2, in spite of increasing biofilm mass and part of the organic matter remaining until the end of the cycle (the factors that make the conditions more desirable for denitrification), denitrification decreased and from about 39% in phase 1 reached 12 % in this phase. The reason for this observation was the lack of proper nitrification and low concentration of nitrate in phase 2. Therefore, it can be said that by increasing COD/N ratio, the nitrate concentration, or in the other words the nitrification process, has become the controlling factor of the denitrification process. In general, in phase 1 (COD/N of 10) simultaneous nitrification and denitrification took place much better so that more than three-fold nitrogen removal efficiency was achieved compared with phase 2 (COD/N of 20).

Conventional technologies for degradation of phenolic compounds encounter several challenges such as large energy consumption and sludge production. Enzymes, natural catalysts displaying a superb selectivity, can be used for phenol removal. In the present work, tyrosinase immobilized on cellulosic support was used for degradation of phenol in batch and continuous operation modes in different conditions. In this regard, the effect of concentration, flow rate and pH on degradation yield were investigated. The results proved that higher oxidation rates were clearly achieved in continuous operation compared with batch experiments. The pH of 6 and 7 were suitable for phenol removal. In continuous mode, the complete phenol degradation was observed where the initial phenol concentration of 25 ppm was applied at residence times between 3. 1 and 6. 4 min. However, the greatest overall degradation yield of 71% was obtained with the initial concentration of 25 ppm by utilizing the flow rate of 18 ml/h. The degradation yield of 54% was found in recycling modes at initial phenol concentration of 25 ppm and a flow rate of 30 ml/h. Based on the results, degradation of phenol using tyrosinase can be considered as a valuable and green method.

In many industrial processes, the acetone solvent is mixed with water in various proportions, and it is not possible to separate these mixtures without consuming a great deal of cost and energy. Nowadays, scientists are looking at some methods to separate solvents more efficiently without consuming too much energy. Therefore, given the importance of different solvent separation processes and their reuse in industry, in this research, for the first-time molecular dynamics simulation of water-acetone mixture separation using armchair carbon nanotube was performed. To separate the water-acetone mixture, the (5, 5) and (6, 6) armchair carbon nanotube was used so that these nanotubes acted as a separator filter for the water-acetone mixture. For this, we used molecular dynamics simulation method. Also, the hydrostatic pressure, as an external force, was applied to the desired system to separate water and acetone from each other with selectively passing them through the nanotubes. The results showed that by changing the type of the nanotube, the process of separating this mixture showed a different behavior; so that, this mixture was completely separated using the (5, 5) carbon nanotube with small diameter, while in the presence of (6. 6) carbon nanotube with large diameter, the separation was not complete and both solvents passed through this type of nanotube in different proportions, which was not desirable. To better understand the results and their interpretation, some analyses including the permeated water or acetone molecules through nanotubes, the density profile, the potential of the mean force, retention time, and hydrogen bonds of the system were also extracted. According to the results of the present study, armchair carbon nanotubes with suitable diameter can be used for separation of some aqueous mixtures, including water-acetone mixture, which will enable us to obtain pure species of each solvent, allowing them to be reused and save costs.

Among the photocatalysts, Titanium dioxide (TiO2) is mostly used for wastewater treatment. Nevertheless, large band gap, rapid recombination of electron– hole along with difficult separation process limits TiO2 applications in industrial scale. In this study, the photocatalytic activity and separation of TiO2 were improved by combined application of Fe3O4 and graphene oxide. X-ray powder diffraction (XRD), scanning electron microscopy (FESEM), and magnetization measurement (VSM) was utilized to characterize the sample and the photocatalytic degradation of methylene blue under visible light irradiation was evaluated by UV-vis spectrophotometer. The results indicate the successful preparation of purified TiO2/Fe3O4/GO nanocomposite by a two-step sol gel-hydrothermal method. The enhanced photocatalytic activity of nanocomposite is attributed to the simultaneous application of iron oxide and graphene oxide. The maximum photocatalytic decoloration (90%) is achieved within 80 min under lamp irradiation. The superparamagnetism of nanocomposites provided a convenient route for separation of the catalyst from the reaction mixture by an external magnet.

Vortex drop shaft (Vortex structure) is used in sewage and drainage systems to transfer fluid from surface conduit to deep underground tunnels. During the plunge, large volume of air is entrained into the water and then released of the drop shaft downstream. In the current research, an experimental model, made of Plexiglas segments, was set up to investigate hydraulic performance of vortex structure. Dimensional analysis results illustrated that ratio of sump depth to shaft diameter (Hs/D), ratio of drop total height to shaft diameter (L/D), and Froude number (Fr) were considered effective variables on relative air discharge (l=Qa/Q). The ability of the full factorial method (FFM), to describe this structure’ s hydraulic characteristics, was validated using experimental data. The results indicated that the relative air discharge changed from 0. 048 to 0. 278 and increased with an increase in Fr, L/D and Hs/D factors. With respect to the maximum velocity of air outflow from the structure of the air vent pipes (with the same diameter Da), located between the 4Da and 9Da from the axis of the vertical shaft, this range is recommended for installation of air vent pipes. Furthermore, a regressionbased-equation in the form of a quadratic polynomial as a function of Hs/D, L/D and Fr was proposed to estimate relative air discharge (l).

The combination of oxidation and flocculation has been used to alleviate the membrane fouling in MBR systems. As common and cheap additives, NaOCl and FeCl3 were employed to prolong the operation life of the membranes. To achieve the highest performance in terms of the SMPs and COD removal, the optimum dosages of FeCl3 and NaOCl additives were first evaluated. To do so, using the jar test, optimum dosages of 2 mg/L and 2 mg/L were respectively determined for the FeCl3 and NaOCl, leading to the highest possible SMPs and turbidity removals of 20. 1% and 91%. Using such optimal dosages, different scenarios were examined and the MBR experiments were then conducted in three stages designed to have no chemical addition (stage 1), FeCl3 (stage 2), and a combination of FeCl3 and NaOCl (stage 3) to assess the effect of the additives on membrane performance under continuous flow condition. The results revealed that, although at such dosages, the additives were not able to affect the nitrifying and heterotrophic bacteria, when simultaneously employed (stage 3), they were able to significantly lower the cake layer resistance and the operating time by 4. 3 and 2. 6 times when compared to the conventional MBR systems (stage 1) and the ones flocculated by FeCl3 (stage 2).

Textile and dyeing industries are important industries in every country. Reactive colors soluble in water due to high brightness, low energy consumption and simple application method are one of the most important groups of colors used in the textile industries. Wastewater containing colors such as R198 is hazardous to the ecosystem and health, so a way to remove color from the wastewater is needed. The photocatalytic process is one of the advanced oxidation processes, that has shown the capability for eliminating various toxic and degradable compounds. In this study, zinc oxide nanoparticles were obtained from the purified solution of the residue of Zinc melting factory in Bafgh. The nanoparticles obtained by various devices were studied and analyzed. The formation, purity and optical properties of Zinc Oxide nanoparticles were investigated by Fourier Transform Infrared Spectrometer (FTIR) test. Finally, in order to investigate the photocatalytic properties of the nanostructures, NB21 reactive color, which is one of the most applicable and important colors in the textile industry, and is harmful to the environment was removed. The three parameters of color concentration, pH and amount of nanoparticle on its dye under UV rays were studied. The results of X-Ray Diffraction pattern (XRD), represents the crystalline and hexagonal structure of the samples. According to the Transmitted Electron Microscope (TEM) images, the sample has clear spherical shapes and distinct hexagonal dimensions in the range of 40-120 nm. Under optimum conditions, with 15 ml of color solution with concentration 0. 1912 g/L, pH=5 and nanoparticle 0. 06 gram at time interval of 120 minutes with application of bleaching process under UV rays, 94% of the color was degraded.

Runoff in urban areas causes road flooding. This issue has many problems in itself. Identifying areas prone to urban floods and flood-prone areas can greatly assist in planning of prevention and control of possible floods. In this study, using SWMM model, Shahrekord surface runoff collection network was simulated in 2, 5 and 10 year return periods. Model calibration was performed on 2 rainfall events on runoff depth parameter in several canal and random nodes. Sensitivity analysis was performed on the parameters affecting the total runoff of the catchment, and the equivalent width parameter was identified as the most sensitive parameter of the catchment. After calibration, validation was performed with optimum values in 2 other rainfall events. NSE, RMSE, and BIAS% coefficients were used to determine the modeling error in the calibration and validation steps in witch the values of the coefficient of NSE obtained more than 0. 8 in calibration and more than 0. 9 in validation. These results showed that the simulation has a good accuracy. Results of SWMM model showed that surface runoff collection network is not sufficient for passing surface runoff during different return periods and the sub catchments 20, 90, 25, 39 and 99 have the highest amount of runoff, respectively. The results of TOPSIS method also showed that the most critical sub catchments are 92, 20, 25, 39 and 90, respectively. Most of these sub catchments are located in the southern part of the city. Due to the high density of residential and commercial areas and the lack of enough green space, the percentage of impermeable areas has been developed and as a result, the production of runoff has been increased. Comparison of SWMM model and TOPSIS method results shows 80% compliance in the selection of critical sub catchments. Therefore, using multi-criteria decision making algorithms such as TOPSIS can increase the accuracy of SWMM model in selecting and prioritizing the critical sub catchments. As a result, using this approach improves the decision making process in critical times.

Methylene blue is the most common colored material that is used to stain cotton, wool and silk; it has a high global consumption, and is found in high-tech textile wastewater. In this study, the photocatalysis degradation reaction of methylene blue (MB) in polluted water was performed using a ZnFe2O4-ZnO-perlite nanocomposite in suspension condition under UV and visible LED illumination in a batch photoreactor. To prepare ZnFe2O4-ZnO-perlite nanocomposite, first, ZnFe2O4 nanospheres were synthesized by hydrothermal route, ZnO nanoparticles were prepared via sol-gel method in media containing perlite and ZnFe2O4. To detect prepared nanocomposite, scanning electron microscopy (SEM) images, Fourier-transform infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRD) pattern were used. Effects of operating factors on photocatalyst degradation such as catalyst amount, powers of UV and visible LED lamps, radiation duration and reaction temperature were investigated. The highest efficiency was obtained under optimal conditions (3 g/L photocatalyst amount, UV power and LED power of 20 watts, the radiation time of 120 minutes and temperature of 35 º C). The kinetic reaction was investigated in optimal conditions and the results showed that its kinetics was first order and the results were acceptable in these studies. Based on these results, a method for photocatalytic degradation was obtained using a ZnFe2O4-ZnO-perlite nanocomposite, which can be used to expand it into industrial form, for wastewater treatment in industry.

The production of industrial wastewater with a variety of compounds is one of the major environmental challenges of human societies, posing a great threat to the health of society. In this study, synthesis of Y-type nanozeolite and its efficiency in reducing the Ca2+ of Shiraz oil refinery effluent compared to acid treated natural zeolite was investigated. Synthensis of nanozeolites was performed by sol-gel method using sodium silicate and sodium aluminate solution. The synthesized samples were analyzed by X-ray diffraction analysis, scanning electron microscopy, and Brunauer-Emmett-Teller (BET) test. The X-ray diffraction results confirmed the crystalline structure of Y-type nanozeolites. The scanning electron microscopy images showed the formation of mesoporous particles. The specific porosity of the synthesized nanozeolite and also the total porosity were determined as 805. 4m2/g and 0. 4222 m3/g, respectively by BET analysis. Based on the nitrogen gas absorption / desorption isotherm, the presence of mesopores along the micro-pore in synthesized nanozeolite was confirmed. Kinetic studies showed the adsorption kinetics of both adsorbents are fit well with pseudo-second-order model, indicating that the interaction between the absorber surface and the adsorbent is the determining factor in adsorption process and diffusion of the Ca2+ ions to the inside of mesoporous zeolite canals is fast. The removal amount of Ca2+ from wastewater of oil-refinery for natural zeolite(50 g) and nano zeolite(5 g) in 1 L wastewater after equilibrium time was determined as 60% and 95%, respectively and pH=7 was determined as the optimum pH.

Contamination of a water distribution network (WDN) is one of the most dangerous events which may occur in accidental or deliberate conditions. The contamination spreads across the network based on the water flow and, as a result, has negative consequences on public health. In this regard, one of the most effective strategies is to install quality sensors. These sensors could reduce the damage due to detecting the contamination and applying appropriate policies. In this study, an optimization approach for quality sensor placement is presented. In this model, based on spatial and temporal uncertainty of input contaminant, a new parameter called maximum possible damage is introduced. Using EPANET as a hydraulic and quality simulator, the damage matrices are calculated for all possible values of temporal and spatial input contamination. In the following, these matrices are used in an optimization model in order to calculate the maximum possible damage. The genetic algorithm is implemented here to solve the problem. The presented method is investigated on a case study network, and results show that this method could find the optimal sensor placement and reduce the damage caused by contamination. As an example, it can be seen that installing one or two sensors could reduce the contaminated water damage by 56% and 78%, respectively.

The trapped air in the water conveyance systems may cause the obstruction of flow, corrosion and adverse effect on the performance of valves and pumps. This study is part of the Abbas Abad Dam Drinking Water Transmission Line using Ansys Fluent Software, The behavior of air entrapped during the filling and discharging process and the effect of its existence on pressure changes were studied. Entrapped air was simulated at 0. 5, 2, 3 m lengths and inlet pressures of 1. 2456, 1. 7456 and 2. 2456 atmospheres for a 35-meter-long metal pipe with a discharge valve embedded in its outlet end. The effects of pressure-time changes were investigated in two ways: a) pressure changes in the pipe and drain valve and b) pressure changes inside the entrapped air. The results showed that the pressure changes in both cases were due to the large fluctuations in confined air and that the fluctuations continued until the drain valve was fully opened and the longer the confined air length was, the greater the amplitude and length of the created fluctuations. Modeling with similar boundary conditions without the presence of air indicates no pressure fluctuations. The results of the verification confirm the research results. Besides the Palau et al, 2019 results, calculation of relative error, RMSE and NRMSE were used in order to validate the numerical model results.

Linear alkylbenzenes is one of the most important surfactants in the industry. Due to their source specificity, degradation resistance and long-term survival in marine sediments, these compounds are unique molecular markers for studying organic matter input derivatives and their effects on aquatic environments. Due to the presence of multiple sources of these compounds in the study areas, this study was conducted to determine the linear alkyl benzene concentrations in the 5 rivers of Nekaroud, Tajan, Talaroud, Babolroud and Sorkhroud that lead to the Caspian Sea. In this study, 15 river samples were collected from the bottom of rivers (near estuaries) from 0-5 cm depth by Grab van veen device. After preparation, the extracted samples were injected into a gas chromatography-mass spectrometer (GC-MS). Finally, the concentration of linear alkyl benzene compounds in surface sediments of 5 rivers leading to the Caspian Sea was determined. The average concentration of linear alkylbenzene compounds in rivers was determined in the range of 56730/28-91288/58 ng/g dry weight. Based on the results, stations in the densely populated and urban areas showed higher concentrations of these compounds. There was also a positive correlation between these compounds and total organic carbon (TOC) (p< 0. 05). Therefore, the concentration changes of these compounds are a function of the TOC concentration changes in the sediments. The ratio of internal to external isomers (I/E) in the studied rivers ranged from 0. 25 to 0. 44. High concentrations of alkyl benzene with a low I/E ratio showed that the streams of Mazandaran province were heavily influenced by human activities. According to cluster analysis, Nekaroud and Tajan rivers have lower concentration than other rivers and are more desirable for release of fish than other rivers.

Detection of tampering in water meters as part of unauthorized usage is a key step in development of service delivery and increasing water resource productivity, and requires special attention. Data used to identify unauthorized water usage, due to tampering in water meters, include 671 subscribers with a history of meter tampering during the years 2017-2019 and a random sample of 3120 subscribers with no tampering record (clean) among Qom’ s residential water users. Data analysis was conducted using subscriber’ s water consumption and invoice payment history as well as supervised data mining techniques such as decision tree, support vector machine, neural network, logistic regression, K-nearest neighbor and unsupervised clustering method. The comparison of different data mining techniques between two groups of tampered and non-tampered water meters showed that among the supervised methods, the accuracy of the models is close to each other and there is a 1– 3% difference between them. On the other hand, given the percentage of correct responses among the methods, logistic regression, as the best data mining model, with correct detection of 85% of tampered and 91% of non-tampered cases as well as 89% overall accuracy on the testing data, can be used for identification of tampered meters. The study used clustering as an unsupervised technique. The subscribers were grouped into six clusters. Cluster 3 (n=160 subscribers) showed distinct behavior from the other clusters. About 86% of subscriptions in cluster 3 are tampered cases. Moreover, 18% of the tampered cases detected by logistic regression are in this cluster. Data mining techniques for identification of water meter tampering were presented in this study. Findings of the study indicated that both supervised (including response variable) and unsupervised methods (no response variable) such as clustering can be used for the identification of unauthorized water consumption In this study, logistic regression, due to its high accuracy, was selected as the most appropriate model for detection of tampered meters.