WATER AND WASTEWATER
Year:2018 | Volume:29 | Issue:3 |Papers Count:10

Various reliability indices have been defined by researchers for the water distribution networks. Due to the complexity and heterogeneous nature of distribution networks, results of indicies can vary substantially and municipalities have hard time to select the most practical indicies for their networks. This study was undertaken to develop a new method for identifying the best reliability index by considering various factors including the appropriate sensitivity to changes in network parameters, the appropriate shift in extreme conditions, the capability in covering critical condition, hydraulic condition, and water quality reliability. To accomplish the objective of the study, several water distribution networks were evaluated under multiple scenarios and the optimum reliability indices were verified with an example real water distribution network in Ahar. Controlling parameters included in scenario analysis for network reliability indices include: minimum, maximum and optimal pressure, residual chlorine in nodes, velocity in pipes, nodal pressure reliability, pipe velocity reliability, and nodal residual chlorine reliability. To evaluate the performance of defined index, a two-loop test (critical) were compared with the conventional single-lop test (normal). The performance assessment of indices obtained from this study showed that the index values ranged between 0. 11 and 1. 0, which indicate the normality and the appropriate sensitivity of the indices. Also, by increasing the residual chlorine of the reservoir, the network reliability index changed from 0. 54 to 0. 75 and then as the residual chlorine decreases in the distributon network the reliability index decreased back to 0. 54. This appropriate shift in reliability index while changing residual chlorine in the network, cearly shows the the effectiveness of new method in determining the reliability indicies under extreme conditions. Also, the new method did not respond to the failure of some network components, as were evident with insignificant change in the indices values under critical conditions. From the results of this study generally can be concluded that the newly defined relability indices is an efficient way for evaluating the performance of water distribution networks.

Due to the importance and widespread applications of oil products as well as their threats to surface water bodies in Iran, it is inevitable to apply suitable simulation models to develop management plans, actions, and appropriate scenarios. There are two modified versions of CEQUAL-W2 and both can be used for simulations of emergency pills of toxic waste in transpotation roadways. In this research, both modified versions were employed to simulate the fate of Methyl tert-butyl ether (MTBE) (a gasoline oxygenated addetive) during an emergency spill. As a case study, the application of both models was used to evaluate the MTBE emergy spill that occurred on March 2003 near Khalifeh Torkhan river. Several remediation techniques including artificial turbulent, mixing, and aeration were used during the simulation study. Results showed that the modified version of the model (CE-QUAL-W2) depicted a better temporal and spatial distribution of MTBE pollution in reservoir compared compared to the first version of the model. Multiple scenarios were simulated in this study under various meteorological, hydrological, and MTBE loading for Gheshlagh reservoir. The simulation results showed that lower air temperature and higher wind speed are among the factors that reduces the reservoir recovery time. In addition, , another parameter that found to decrease the recovery time of Gheshlagh reservoir is an increase in reservoir inflow and/or outflow rate.

Discharge of toxic metals such as cadmium (Cu), lead (Pb), and zinc (Zn) in the environment can impact the quality of air and water. High concentration of these toxic metals larger than the regulated concentration in the air and water can pose serious human health risks. The aim of this research was to investigate the removal of these heavy metals (Cd, Pb and Zn) from aqueous solutions by using a multi walled carbon nanotubes modified by chitosan as an absorbent agent. To perform the experimental study, nitrate salt of heavy metals solution prepared with distilled water was used. Factors examined for the removal efficiency of heavy metals in this study include pH, absorbent dose concentration, retention time, and the initial concentration of heavy metals. All analytical analyses were performed according to standard methods. Also, the infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) used for identification and modification of the absorbent. The results obtained from this study showed that an increase in pH, retention time and initial concentration of heavy metals, also increased the adsorption efficiency rate. The optimum heavy metals removal efficiency was about 75% and that occurred when pH =7, retention time =120 minutes and the initial concentration of heavy metals =20 mg/L. In addition, plot of Langmuir and Freundlich adsorption isotherms for heavy metals showed that the adsorption process mostly follows the Freundlich isotherm. The limited data obtained from this experimental sudy, it can be concluded that using carbon nanotubes modified with chitosan as an absorbant agent is an effective method for the removal of heavy metals (Cd, Pb, and Zn) from aqueous solutions.

Mercury is one of the heavy metals that is toxic to humans, animals and the environment. The contribution of mercury in the water resources are from various sources including the discharge from industry and municipal wastewater. Hence, removal of mercury from water resources, especially for human consumption, is extreamely important. The removal of mercury is usually accomplished through adsoption and one method is through use of carbon nanotubes as the absorbent. The available commercial nanotubes are often synthesized by chemical vapor deposition which is done easily in an industrial scale. The aim of this research was to find an optimum condition to remove mercury from water by using a multi walled carbon nanotubes modified with Tris (2-aminoethyl) amine. To accomplish the main objective of the study, multi walled carbon nanotubes were machined in laboratory with chemical vapor deposition and later modified with Tris (2-aminoethyl) amine. These multi walled nanotubes then used to absorb mercury ions in water and the amount of absorption measured by induced coupled plasma (ICP). The nanoparticles in this study were analyzed by FT-IR, Raman, TG-DTA, SEM, and EA. To evaluate the optimum adsorption for the removal of mercury, several influencing factors such as pH fluctuations, concentration of the initial mercury in solution, absorbent weight, and contact time were investigated. The results obtained from this study conformed mercury adsorption to Langmuir and Freundlich Isotherms. The removal of mercury ions drastically increased with the increase in pH. The optimum adsorption capacity was 115 mg/g and the highest absorption yield was 95± 1. In summary, based on the limited results obtained from this study, it is fair to conclude that the MW-CNT modified with Tris (2-aminoethyl) amine is a useful method for the removal of mercury from water.

Surfactants are considered as chemical combinations with many environmental impacts such as eutrophication, foam generation, and oxygen reduction. This experimental study is conducted to evaluate the removal of Sodium dodecyl benzene sulfonate (SDBS) using unipolar electro-flotation and electro coagulation system. The experimental set up was installed as a cubic shape with effective volume of 735 ml and stainless steel monopolar electrodes arranged in a horizontal fashion. Parameters evaluated individualy for the overall system optimization include: distance between electrodes (0. 5-1. 5 cm), surfactants initial concentration (50-1000 mg/L), pH (3-11), current density (0. 5– 1. 5 A), and electric conductivity (950-3500 S/cmμ ). Results obtained during the 1 hr operation time showed that the optimum surfactant and COD removal efficiency were about 94 and 90 percent, respectively. This optimum removal eficciencies were accomplished under the following condition: pH=8, distance between electrodes =1 cm, initial surfactant concentration = 750 mg/L, current density = 1 A, and EC = 1440 μ S/cm. In addition, the energy consumption and anode dissolution were 45. 03 kWh/kg and 1. 04 kg Fe/kg for SDBS removal, respectively. In conclusion, the results obtained in this study support the application of electro-flotation and electro coagulation as an appoperiate system for the removal of surfactants such as detergent.

Recently, water crisis has been a global threat for most countries, particulately for midelist countries. In this regard industrial wastewaters treatment is a vital to prevent unfavorable environmental consequences. Advanced oxidation processes are the preferred treatment process for the removal of resisitant organic pollutants without producing secondary wastes. In this research study, the removal of RG19 from aqueous solution was studied by O3/UV processes. A recirculation system equipped with an UV lamp and ozonation tank was applied for the degradation of model di-azo dye from textile industry. The RG19 concentration was measured using a spectrophotometer at 625 nm. Comparison of RG 19 removal by O3 and O3/UV showed that, under same operational condition, the combined process had more decolorization efficiency (DE%). Moreover, the experimental results revealed that the DE% increased by increasing the ozone amount and decreasing the concentration of RG19. The efficiency of degradation process was performed at the basic (alkali) condition due to the production of extra hydroxyl radicals. The pseudo-first order kinetic was observed for the dye decolorization. The consumption of electrical energy decreased per order using the O3/UV process at the desired basic pH; indicating adequate synergistic effect of the photolysis and ozonation. In addition, central composite design (CCD) approach was applied for prediction of the DE% at pH= 10 for independent variables including the RG19 concentration range (379. 6-1220. 4 mg/L), ozone mas flow rate range (2. 5-7. 2 g/h), and process duration time range (4. 8-55. 2 min). After investigating the effect of the operational parameters on the decolorization efficiency, a nonlinear CCD model was developed for prediction of DE%. The optimum operational conditions for the complete dye degradation at pH=10 was experimentally verified when: [RG19] concentration was of 524 mg/L, ozone mass flow rate was 7 g/h, and process time was 54 min. The EEO declined at the optimized pH for the coupled process owing to the synergistic effect of ozonation and UV.

Granular media including rapid gravity sand filters are used in water and wastewater treatments. When sand filters are clogged due to deposits of particles and particul-bound pollutants, it will lead to head loss and under this situation it is necessary to perform filter backwashing. Prediction of sand filter head loss is the major focus of this study. To meet the primary ojective of this study, a single-layer rapid gravity filter with sandy media was tested with inflow water containing different concentrations of lead (Pb). The amount of deposited sediments and the resulting head loss were simulated in the filter media by combination of Karman-Cozeny, Rose and Gregory equations under different discharges. The maximum time to reach the various amounts of head loss was obtained when the inflow lead concentration was lowest (25 ppm) and the surface filter leading was the highest (6. 22 m3/m2/hr). The highest lead removal efficiency (92%) was obtained when the input lead concentration was 25 ppm and filter surface loading was 3. 11m3/m2/hr. Comparing the specific head loss under different operating condition it has been shown that the time difference is less under lower head losses of 5 and 7 centimeters. In addition, the slopes of filtration discharge under similar operating condition showed to be steeper verifying a higher filtration performance when the concentration of input lead and filter surface loading was lower.

User-friendly and low-cost wastewater treatment plants are good options for treating wastewater of small communities. The effluent of these treatment plants can be improved by various methods including using a horizontal rouphing filter (HRF). In this paper, HRF performance was evaluat by passing the Parkandabad wastewater treatment plant effluent through pilot scale constructed HRF. The HRF was constudted with fourcompartments of different sand sizes and was operated under three filtration rates of 0. 5, 1 and 1. 5 m3/m2. h. The results obtained from this study showed that the HFR performed the best at filtration rate of 0. 5m/h when the removal efficiency for BOD5 and COD was 61 and 63 %, respectively. Optimum removal efficieny of BOD5 and COD up to 65% could be achieved with an extended filtration run length. However, longer duration of filter operation after 4 months, reduced the filter performance for BOD5 and COD removal efficiency to 56. 8 and 61. 5%, respectivel. In conclusion, by using 4-compartment HRFs, compared with the conventional 3-compartment filtration, it may be possible to produce effluent quality for BOD5 and COD that is permissible for agricultural irrigation purposes.

Nowadays at the same time with population growth in urban areas, healthy potable water supply has become a challenge especially in arid and semi-aris countries who intend to fulfil a sustainable development. Due to the increasing importance of water treatment and its key role throughout the world, improvement of water treatment plants is becoming more visible. In this research, the criteria and effective factors influencing the quantitative performance evaluation of three treatment plants were investigated using AHP approach. The three treatment plants used in this study were selected from three provences in Iran including Hamedan, Ilam and Kermanshah. The model performance were quantitatively evaluated by using the physical, chemical, and biological characteristics of effluent data. Model performance evaluation revealed that E. Coli; turbidity; ammonia, nitrate and nitrite is most important microbilogical, physical, and chemical water quality parameters when assessing the performance of effluent quality of treatment plants. Based on the the evaluated results, the performance of treatment plants in Kermanshah was better than the other two treatment plants. It will also be equaliy important to indicate that if any of the treatment plants met the effluent standards set by the Iranian authorities.

Requirements of the Issue Sixteen of the Iranian National Building Code demand the protection of the drinking water network inside residential buildings over 4 stories or with more than 10 units. These buildings should aslo be supplied by a storage tank with sufficient amout of water supplying for 12 hours of consumption. Without proper regulations, the implementation of this newly building code may create problems including degradation of on-site water quality. To address this problem partially, this research has been undertaken to evaluate the effect of: incorrect operation on water meter failures, extra repairs may be needed in the distribution network, and the quality of drinking water in storage tanks installed in high-rise buildings. To carryout the objective of this study, regular field inspection of pump and reservoir system was performed, during each in each field observation water samples were collected, and all water samples were analyzed according to the methods specified in the 2005 edition of the “ Standard Methods for the Examination of Water and Wastewater” . In addition to the analytical data collected from this study, the existing water quality data from Tehran water and wastewater company were also utilized. All together, routine qualitative tests were performed on 50 on-site reservoir tanks in residential high rise buldings. The results of sampls’ water quality showed that: (i) about 10% of the samples had higher level of heterotrophic bacteria with standard deviation of 56%, (ii) 8% of the samples had concerned level of total Coliforms contamination. In addition, the turbidities of higher than1 NTU in some tanks were observed that may be an indicative of an additional water water quality problems. Aside from water quality problem, direct pumping was made by 4. 82% of the users in which this activity significantly contributed to an increased energy costs, water meter failures, and water pressure drops. From the preliminary findings of this study, it has been concluded that there is a potential risk for microbial contamination in drinking water storage tanks and there is also potentials for pump and meter failures and as a results additional requirements for regular maintenance. Because the accurance of these problems are inevidable, it is recommended to development a proper regulatory guidance and enforcement by Tehran’ s water and wastewater company in order to protect Public Health safety.