Toktam Shahriari; Abdolreza karbassi; Maryam Shirazinejad
Abstract
Introduction: Industrial plating wastewater contains various types of detrimental heavy metals in high concentrations. One of this toxic metal is Nickel that its discharge into the surface waters and soil is considered as an environmental problem. Hence removing of this metal from wastewaters is crucial ...
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Introduction: Industrial plating wastewater contains various types of detrimental heavy metals in high concentrations. One of this toxic metal is Nickel that its discharge into the surface waters and soil is considered as an environmental problem. Hence removing of this metal from wastewaters is crucial and vital for protecting the environment and human health. Applying of nanotechnology in elimination of environmental contaminants is one of the methods which attracted a great deal of attention in recent years. In present research, nanographite was utilized as efficient adsorbent in order to remove Ni ions. Materials and methods: In order to investigate the adsorption process, nanographite with a purity of 99.9% and a specific surface area of 18-24 m2/g and a plate morphology was prepared from Pishgaman Iranian Nanomaterials Company and used as an adsorbent. Also, the wastewater used in the experiments was prepared from one of the plating workshops in Tehran, which contained 765 mg/L of nickel and a pH of about 1. The parameters of pH, time and amount of adsorbent were evaluated. In each experiment, one of the parameters was considered variable and the other two parameters were considered constant. The amount of nickel was determined before and after each test.Results and discussion: In this study, the parameters including pH, adsorption time and adsorbent dosage were investigated as effective factors on Ni adsorption process. In order to analyze the adsorption mechanism, the obtained results were examined by the Langmuir and Fruendlich isotherm models. In addition, pseudo-first-order and pseudo-second-order models were studied to investigate adsorption kinetics. According to the results, the Ni uptake by nanographite was enhanced significantly with increasing of the pH value from 5 to 7. Thus the pH of 7 was determined as optimum pH for Ni removal. Investigations also showed that increasing the time up to the first 80 minutes had a relatively good effect on nickel adsorption by the nanoparticle, and after that the adsorption almost reached equilibrium. Finally, it was observed that in a constant time, increasing the amount of adsorbent led to an increase in adsorption, and to achieve the maximum adsorption of nickel, the amount of 2g was chosen for the adsorbent. Based on the obtained results, 97.52% primary nickel was adsorbed by nanographite. Results also revealed that the data were best fitted to the Fruendlich models. After determining the amount of nickel adsorption at different times, the resulting data were analyzed by the kinetic model.Kinetic studies also indicated that the adsorption data were described well by pseudo-second-order model. Conclusion: Examining the results showed that pH plays an important role in the adsorption process and the adsorption rate increases with increasing time until the equilibrium time is reached. One of the effective factors is the amount of adsorbent, which has a direct effect on adsorption. Following the Freundlich isotherm in this research indicates that the adsorption sites in the adsorbent have different energies. Also, the pseudo-second-order model in adsorption kinetics refers to the process of chemical adsorption in addition to physical adsorption.
Toktam Shahriari; Abdolreza Karbasi; Milad Reihani
Abstract
Introduction: Oil refinery is one of the industrial centers and its wastewater has a lot of environmental pollutants which are a serious threat to the environment and water resources. In this study, an electrocoagulation reactor was used to remove and reduce the amount of Chemical Oxygen Demand (COD) ...
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Introduction: Oil refinery is one of the industrial centers and its wastewater has a lot of environmental pollutants which are a serious threat to the environment and water resources. In this study, an electrocoagulation reactor was used to remove and reduce the amount of Chemical Oxygen Demand (COD) in the wastewater from the API unit of the Shazand Oil Refinery in Arak, which is a gravity separator of water and oil. Material and methods: In order to simulate the electrocoagulation process in experimental conditions, a 15 × 14 × 13 cm Plexiglas pilot was designed, in which six 10 × 12 cm aluminum electrodes with a thickness of 2 mm were put as sacrificial electrodes during the process. The distance between the electrodes was 2 cm. The monopolar arrangement was selected for electrodes. At each stage of the experiment, after measuring the pH and COD of the initial wastewater, the volume of 2 L was poured out as an internal sample into the coagulation reactor; after the electrochemical process, the secondary pH and COD were measured to determine the effect of the electrocoagulation process. Results and discussion: In this research, the effect of time, pH, and voltage in the electro-flocculation process has been evaluated. The amount of COD, pH, and lead were measured 450 mg/L, 5.5 and 5.27 mg/L in initial wastewater, respectively. To avoid the overlapping effect of time, pH, and voltage during the process, the value of one of the parameters was changed and two other parameters were kept constant and the optimum value was determined. In order to minimize the errors during the testing process, each step has been repeated three times. After performing different stages of the test and collecting and analyzing the results, the optimum time of the test, optimum pH, and optimum voltage were considered as 90 min, 6 and 30 V, respectively. Consequently, the COD decreased from 450 to 193 mg/L and 99.05% of lead was removed. The results of the experiments showed that by increasing the duration of electrolysis, the removal rate also increases. The results of other research also showed that the flow density is directly related to the reaction time, and by increasing the time, more removal rate can be obtained. As the results demonstrate, the removal rate is directly related to the applied voltage, which is due to the more production of aluminum hydroxides in the wastewater, which plays the role of coagulant. In previous studies, the results also indicated an increase in the removal rate of pollutants by increasing the applied voltage. The pH also had an important effect on the results. At low pH values, cationic monomeric species such as Al3+ and Al(OH)2+ were obtained from the dissolution of the aluminum anode. On the other hand, with the excessive increase in the pH of the solution, such compounds as Al(OH)4- were formed, which caused disruption and sluggishness in the removal process. Conclusion: The results of this study showed that aluminum hydroxides as coagulants, which are produced by the electrochemical dissolution of the sacrificial electrodes, play a major role in the pollutant removal process. The higher their production rates, the more removal will occur. To do this, the optimal parameters for producing them should be optimally set. By increasing the electrolysis time, the amount of aluminum hydroxides also increases. Also, adjusting the pH of the solution at an appropriate range provides optimum conditions for the production and formation of gelatin aluminum hydroxide polymer.
Hassan Hoveidi; Gholamreza Nabi Bidhendi,; Hamid Reza Jafari,; Touraj Nasrabadi; Toktam Shahriari
Volume 5, Issue 2 , January 2008
Abstract
During recent years, surface water resources supplying Tehran's potable water – Karaj, Lar and Jajrood Rivers – are contaminated with different microorganisms due to population growth. Additionally, the amount of organic materials generating odor, taste and color in the surface water has ...
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During recent years, surface water resources supplying Tehran's potable water – Karaj, Lar and Jajrood Rivers – are contaminated with different microorganisms due to population growth. Additionally, the amount of organic materials generating odor, taste and color in the surface water has increased sharply. By considering the trihalomethane (THM) production potential of dissolved chlorine in reaction with innocuous humic substances, future use of chlorine as a disinfectant in Tehran's drinking water is clouded in uncertainty. Accordingly, the use of ozone as another alternative was taken in to consideration for disinfection of drinking water in this mega city. In order to evaluate advantages and disadvantages of water ozonation a pilot with a generating capacity of 4 gr ozone per hour was designed. This study was performed between April and September 2005 and Tehran Pars water treatment plant in the Northeast of Tehran was chosen for the case study. Bacteria removal was considered to be at highest level in all monthly samples. Different ozone contact times and dosages were tested in the deactivation of nematodes and the results showed the perfect removal in specified periods. Although the initial investment for construction and implementation of the required apparatuses is relatively high, since the raw material for ozone generation is air, the use of ozone is financially justifiable during the predicted time of operation. Moreover, the transfer and storage of ozone is much easier in comparison with chlorine which is currently in use. Unlike chlorine, the use of ozone as a disinfectant does not have the potential of THMs generation. On the other hand, ozone must be generated on site and is instable in water. Therefore, a continuous and precise monitoring and maintenance process must be taken in to consideration. Furthermore, due to high corrosive potential of ozone, special resistant materials must be used in the applied instruments.
