Nowadays, the importance of ensuring the effluent standards of wastewater treatment plants is obvious. It is necessary to pay attention to the selection of the biological wastewater treatment process by considering different and diverse criteria. Because, the incorrect choice of the process increases costs and does not achieve the desired result. In this research, the technique of analytical hierarchy process and its combination with Taguchi method was used. By weighting and prioritizing the criteria and options by two groups of experts, including the scientific group and the executive group, the weight of each criterion and option was calculated. In the present study, options (in two cases including 7 conventional options and 7 advanced options), criteria (4 items) and comprehensive and complete sub-criteria (13 items) for selecting biological wastewater treatment processes in rural areas under various conditions have been considered. Finally, it was concluded that in both perspectives, the sub-criteria of providing disposal criteria and standards and the ability to reuse wastewater and climatic conditions were placed in the first and second priority. These sub-criteria received weights of 0.113 and 0.108 from the scientific point of view and 0.122 and 0.106 from the executive point of view. Also, the present study showed that the model of combining AHP and Taguchi method is a successful model for determining the method of biological wastewater treatment for various conditions. Finally, according to the results of this study, the prioritization of biological wastewater treatment options for wastewater treatment in Ahar village was done as a case study and the output results showed that the first priority of all experts is the artificial wetland method and MBBR, from a scientific point of view, Extended Aeration and ABR-Wetland, and in the executive point of view, artificial wetland and A2O methods were prioritized (conventional and advanced methods, respectively).
Chlorine is used as the most common disinfectant to prevent microbial growth in water networks. The concentration of chlorine in distribution systems or water conveyance lines is reduced due to two different types of bulk and wall decay. In this study EPANET software is applied to numerically simulate chlorine decay in the Isfahan water supply line from the Baba Sheikhali water treatment plant to Naein. Two methods are applied for simulation and the results are compared to the measurement. In the first method, chlorine simulation was performed taking into account the whole Isfahan water conveyance line as one section (integrated) and determining a bulk decay and wall decay coefficient for the entire conveyance line. In the second method, the line was divided into two sections (bisection) and decay coefficients of chlorine for each section was separately considered. To determine the bulk reaction rate, the bottle tests were performed at 6o and 18o Celsius corresponding to winter and summer. The results indicated that separating the line to two and applying independent coefficients and decay parameters to each part improves the results and the RMSE values are reduced from 0.09 to 0.03 in summer and from 0.064 to 0.025 in winter. Therefore, dividing the line in two or more sections substantially improves the accuracy of the simulation of chlorine decay.
Dehnavi, A., Tavakoli aminian, S., Rouhbakhsh meyari, M.
آب و فاضلاب (10245936)(6)pp. 71-79
Hydrocyclones are used for removing suspended solids such as silt and sand from water. In this study, all the factors involved in the performance of hydrocyclones were initially identified and listed before they were optimized using the Taguchi experiment design method. It was the objective of the present study to optimize the efficiency of hydrocyclones in removing sand from water. For this purpose, 18 hydrocyclones were designed and constructed to test all the variables affecting their performance including hydrocyclone inlet, overflow, apex, and body diameters as well as cylindrical, total, and vortex finder heights. Minimum (20 mg/l) and maximum (100 mg/l) concentrations of total suspended solids (sand) in the samples from the water wells in Mashhad city along with the observed particle distribution were used in the optimization. Statistical analysis of the results showed that the ratio of the inlet and overflow diameters to that of the hydrocyclone was 0.225 and that the ratio of the apex diameter to that of the hydrocyclone was 0.15. Also, the ratios of the cylindrical and vortex finder heights to the total height of the hydrocyclone were 0.12 and 0.08, respectively. Under optimum conditions, sand removal efficiency varied from 95.9% to 98.4% in different experiments. This is while a value of 97.2±1.1% was obtained as the result of three tests in the hydrocyclone optimized in this experiment. Comparison of the mass removal efficiencies predicted by the Taguchi method and the values measured in the optimal hydrocyclone tests showed that both sets of data were very close and substantially high. Moreover, it was found that the geometric elements obtained in this study were generally in the range of minimum and maximum ratios proposed for hydrocyclones used in mining. These ratios may, therefore, be recommended for use in the construction of real-scale hydrocyclones for sand removal from water.
This study investigates the amount of suspended solid particles in three drinking water wells, conducted several times per day in the city of Mashhad. The results have also been used for the review and optimization of tested hydro-cyclones. For this purpose, 18 different hydro-cyclones, based on the experimental design process of the Taguchi method, were designed and the affecting factors were investigated. These factors include inlet diameter, overflow diameter, apex diameter, body diameter of the hydro-cyclone, the cylindrical height, and the total height of the hydro-cyclone. For the optimization process, the maximum concentration observed within all samples from the Mashhad wells, equating to 100 mg per liter was used. The results of the laboratory study, for two repeats, showed that in optimum conditions, the mass removal efficiency of the suspended solids was up to 97.2 ± 1.1 percent. In these circumstances, the ratio of inlet and overflow diameter size to the hydro-cyclone diameter size was similar and equivalent to 0.225, and the apex diameter size ratio to the hydro-cyclone diameter size was 0.15. Also, the ratio of cylindrical and overflow height to the total height of the hydro-cyclone were 0.12 and 0.08 respectively.
Badalians gholikandi g., , Dehghanifard e., , Noorisepehr m., , Torabian a., , Moalej s., , Dehnavi, A., Yari a.r., , Asgari a.r.,
Iranian Journal Of Public Health (22516085)41(4)pp. 87-93
Background: Water filtration units have been faced problems in water turbidity removal related to their media, which is determined by qualitative indices. Moreover, Current qualitative indices such as turbidity and escaping particle number could not precisely determine the efficiency of the media in water filtration, so defining new indices is essential. In this study, the efficiency of Anthracite-Silica and LECA-Silica media in turbidity removal were compared in different operating condition by using modified qualitative indices. Methods: The pilot consisted of a filter column (one meter depth) which consisted of a layer of LECA (450 mm depth) and a layer of Silica sand (350 mm depth. Turbidities of 10, 20, and 30 NTU, coagulant concentrations of 4, 8, and 12 ppm and filtration rates of 10, 15, and 20 m/h were considered as variables. Results: The LECA-Silica media is suitable media for water filtration. Averages of turbidity removal efficiencies in different condition for the LECA-Silica media were 85.8±5.37 percent in stable phase and 69.75±3.37 percent in whole operation phase, while the efficiency of total system were 98.31±0.63 and 94.49±2.97 percent, respectively. Conclusion: The LECA layer efficiency in turbidity removal was independent from filtration rates and due to its low head loss; LECA can be used as a proper medium for treatment plants. Results also showed that the particle index (PI) was a suitable index as a substitute for turbidity and EPN indices.
