WATER AND WASTEWATER
Year:2019 | Volume:30 | Issue:2 |Papers Count:12

In drinking water treatments, for coagulation and sedimentation of suspended particles, several coagulants are used such as Alum, PAC and ferric chloride. In spite of their positive effect on turbidity removal, these chemicals cause some problems like corrosion and harmful by-products which result in bad effects on human and environmental health. Therefore, finding and using better and more effective materials without such adverse effects is a necessity. The aim of this research was to study the effect of chemically synthetized sodium ferrate (S. F. ) in liquid state for the turbidity removal from Zayandehrud River in two conditions: normal turbidity (less than 100 NTU) and high turbidity (more than 900NTU). This research was performed in four states of 30×60, 40×60, 60×60, and 30×40; in each state, one of the water independent variables effective on water turbidity was changed. These four states were S. F. dosing rate, gentile mixing speed, rapid mixing time and pH. For the experiment design, analysis and optimization of independent variables effective on turbidity removal were used. In addition, the surface response method (RSM-D-Optimal) plus Design Expertv10 optimization software were used for this study. Finally, in this research, according to the standard methods, the residual total Fe (due to sodium ferrate) was checked in the research in order to ensure that its value was in the allowable range for drinking water. The results showed optimum conditions as: pH of 8. 5 and gentle mixing oscillating speed of 60rpm for 7min, 50rpm for 7min and 40rpm for 6min, (instead of 40rpm constant speed for 20min) and rapid mixing time of 30s with 120rpm (instead of 60s, which was conventional in Esfahan water treatment plant). In addition, the results showed that by using only 1. 54mg/L of S. F. in the above-mentioned optimum condition, the water turbidity removal efficiencies were 95. 17% and 99. 07% for normal and high turbidity states, respectively. A comparison was made in this research between using S. F. and poly aluminum chloride (PAC) for both normal and high turbidity. The results showed the better effect of S. F. than PAC. The results also showed that the residual total Fe was in the allowable range before and after the filter (because of the reactivity of ferrate with Fe). From the results of this research, it can be concluded that using S. F. has a positive effect, technically and economically, on water turbidity removal (better effect than conventional chemicals) in both normal and high turbidity. Moreover, the results showed that residual total Fe remains in the allowable range.

Nowadays, increasing population and reduced fresh water resources has led to the need for introducing seawater as a new water source, and sweetening it using new techniques including nanoparticles is being considered. Mineral clays, such as cationic exchangeable bentonite clays can exchange their own cations, including calcium and magnesium, with sodium ions of sea water. In this research, Kalkate's bentonite clay was used for seawater sweetening testing and the flame photometer device was used to measure the process of reducing sodium ions from seawater. The results showed using 5. 5 gr bentonite with 200 rpm mixing velocity, at a contact time of 15 minutes in 20 ml sea water is the optimal condition for mixing bentonite and seawater. On the other hand, in order to reduce the chloride ions from seawater, MgAl-CO3 layered double hydroxides nanoparticles were synthesized and used in water quality laboratory of the University of Zanjan. The results of this experiment also showed using 1. 25 gr LDH with 200 rpm mixing velocity at a contact time of 10 minutes in 5 ml seawater is the optimal mixing condition.

Wastewater Treatment Plants that are constructed in the coastal regions need more attention since the flood occurrence may cause excessive loads on the infrastructures. These excessive loads may result in the system’ s failure and innumerable damages on the infrastructure. In this study, in order to reduce WWTPs’ flood vulnerability, an index called Resiliency was developed to quantify system’ s characteristics. Later, two main approaches were considered to enhance the infrastructure performance: the “ Resource allocation” and the “ Cooperative behavior” method. The former method was applied employing those factors which were improvable with the investment of funds and financial allocations. They were utilized to make the system more robust. In addition, implementing some new agents with potential impacts on funding were described in order to have a more realistic vision. As for the latter method, the cooperative behavior approach, the cooperation was utilized to demonstrate joint operation among WWTPs and the way they interact. For this purpose, WWTPs’ placement was analyzed to check if they could operate jointly. Thereafter, effectiveness of these two approaches was compared in order to make the best decision regarding different cases. The results showed that in three collaborations among Bowery Bay, Tallman Island, Newtown Creek, and Red Hook WWTPs, cooperation has had a significant effect on the resiliency index.

The need for freshwater is rising rapidly, and fresh water resources cannot meet all human needs. People's access to freshwater is now diminishing with the increasing population and expansion of cities. Accordingly, the desalination of sea water has become increasingly important and selection and development of more efficient and cost-effective desalting process is a necessity. The present study was designed to optimize the operating conditions to reduce the effect of external concentration polarization on the performance of direct osmotic process. Due to the number and variety of parameters affecting the amount of water flowing through direct membranes and also with the aim of reducing the number of experiments and costs, the Taguchi experimental design method was used. The structure of membranes was investigated using scanning electron microscopy (SEM). The best performance of direct membrane was observed in membrane No. 1 with test conditions, concentration of molar salt solution, pressure head of 2 psi and pH = 9. In this condition, the flow rate of the flow through the direct osmosis membrane was 36. 42 L/m2h. The highest flux of salt passing through direct membranes was 26. 11g/m2h in test conditions and with the concentration of molar salt solution, the pressure head of 2 psi and pH = 9. By optimizing the operation conditions, 55. 51 percent increase in the water flux was observed.

In this work, hematite (]-Fe2O3) nanoparticles with novel surface-modified were synthesized using iron (III) chloride hexahydrate (FeCl3. 6H2O) and oleic acid (C₁ ₈ H₃ ₄ O₂ ) as raw materials by hydrothermal method at 250 ° C. The structural analysis such as XRD, FT-IR, SEM, TEM and BET showed the distribution of the synthesized nanoadsorbent, so that more (>90%) nanorod structures (diameter of 30-60 and length of 400-700 nm) were among the less nanoscale crystals with 40-100 nm as thickness. The high specific surface area of the novel synthesized hematite nanoparticles (31. 29 m2. g-1) determined their high capability for the removal of lead ions (Pb2+) from aqueous solutions. The adsorption of lead ions onto the synthesized nano ]-Fe2O3 was investigated by pH, adsorbent weight, lead ions concentration, and contact time in batch experiments and initial condition of 25± 1 ° C, 120 rpm, so that the optimum conditions for lead ions adsorption were obtained. On this basis, the removal of lead ions increased with an increase in pH; the optimum solution value was about 6. 5 due to the bothersome hydroxide constructions in higher pH values. The analysis of equilibrium data showed that the Langmuir isotherm model is suitable for describing the lead ions adsorption by nano ]-Fe2O3. Furthermore, the maximum sorption capacity of Pb2+ was estimated to be 111 mg. g-1. The kinetic of lead ions adsorption onto the synthesized nano ]-Fe2O3 was best fitted by the pseudo-second order model known as Ho model. As adsorption optimum condition, the maximum uptake capacity of 49. 31 mg. g-1 was recorded along with the efficiency of 98. 62% for the removal of Pb2+ ions from aqueous solution (1 mg. g-1), using 20 mg. L-1 nano ]-Fe2O3 adsorbent at 4 hour contact time. From these results, it can be concluded that the synthesized ]-Fe2O3 surface-modified nanoparticles is a promising and effective adsorbent to remove lead ions as a heavy metal pollutant from aqueous solutions.

The combination of magnetic nanoparticles with other adsorbents not only does not affect their magnetic properties, but also leads to the formation of adsorbents that improve the refining process. The aim of this study was synthesis of magnetic activated carbon by Fe3O4 and investigation of its efficiency in adsorption of Lead from aqueous solutions. Magnetic adsorbent prepared by the method of sequestration and physical characteristics and structure of synthesized absorbent were determined by XRD and TEM. To remove the Lead from aqueous solutions, the Box-Behnken design (BBD) of response surface methodology (RSM) was employed for optimizing all parameters affecting the adsorption process. The studied parameters were pH (5-9), temperature (25-45 ⁰ C) and the amount of adsorbent (0. 5-2 g). 15 experimental runs were calculated by using BBD. The optimal condition for removal of Lead by synthesis of magnetic activated carbon by Fe3O4 nanoparticles was pH=7, 450 ⁰ C temperature and 2 g of adsorbent. Kinetic studies of the adsorption process specified the efficiency of the pseudo second-order kinetic model and showed the optimal time was 15 min, respectively. The maximum percentage of Lead removed after 90 min was 86. 87%. The adsorption isotherm was well-fitted to Longmire model. The study showed that magnetic activated carbon has a high potential for Lead removal. Therefore, it is believed that magnetized active carbon by keeping its physical and surface properties could be a suitable method to solve some related problems including separation and filtration.

4-chlorophenol (4-CP) is one of the seriously toxic chlorophenol compounds found in the effluent wastewater generated by oil refineries, pharmaceutical factories, and paper and leather producers which is introduced into surface and ground water resources. This research aimed to study the feasibility of nZVI nanoparticles in activation of H2O2 and persulfate under UVALED irradiation based on Taguchi experimental design for 4-CP removal. This experimental study was conducted using a lab-scale batch reactor equipped with 18 ultraviolet light emitting diodes lamps with a wavelength of 390 nm. The effects of operating parameters such as pH of solution, contact time, dosage of nZVI, dosages of H2O2 and persulfate and different initial 4-CP concentration were evaluted by defined factor of 4*4 using Taghuchi L-16 orthogonal array. Based on the results of the Taguchi method, the optimum conditions for removal of 4-CP in nZVI activated persulfate process included the initial 4-CP concentration of 25 mg/L, pH=3, reaction time of 60 min, nZVI and persulafte respective dosages of 2 and 2 mM. The highest removal efficiency and S/N values for this process were 51. 83% and 34. 29%, respectively. Also, optimum conditions for removal of 4-CP in nZVI activated H2O2 process were the initial 4-CP concentration of 25mg/L, pH=3, reaction time of 30 min, nZVI and H2O2 dosages of 0. 75 and 1 mM. In this condition, the highest removal efficiency and S/N values were 81. 76% and 38. 25%, respectively. In both processes in this case, under acidic conditions, an increase in the active catalyst (Fe2+) activated more and more oxidants (radical hydroxide and radical sulfate) in both reactants, resulting in better efficiency of processes in these conditions. UVALED/ H2O2/nZVI process could serve as a new and feasible approach for the degradation of 4-CP as well as other organic contaminants containing wastewater due to high efficiency, low contact time and need of the lowest oxidants agents. UVA-LED/H2O2/nZVI process could serve as a new and feasible approach for the degradation of 4-CP as well as other organic contaminants contained in wastewater due to high efficiency, low contact time and need of the lowest oxidants agents.

The presence of chromium in drinking water and the entry of industrial wastewater into groundwater resources endangers human health and the environment. This study was done to investigate the effect of leonardite to remove Cr+6, Cr+3 from aqueous environments. The optimal values of factors were determined by the surface response model and the central composite design. Adsorption data were fitted with the pseudofirst order and pseudo-second order kinetic models. In addition, the effects of interfering cations and anions on chromium adsorption were determined. The results showed that the contact time, amount of leonardite and pH significantly affect chromium sorption. Chromium kinetic data were well fitted (R2=0. 995) to the pseudo second order equation. The capacity (qe) and adsorption coefficient (Kads) parameters for Cr3+ were higher than Cr6+. As a large amount of Cr3+ was adsorbed by leonardite in a short time. Fe3+ and SO4 2-as interfering ions reduced the removal of Cr3+ and Cr6+ by leonardite respectively. It is concluded that leonardite, as a biodegradable adsorbent, is suitable for removal of chromium from contaminated waters.

Lead is one of the most dangerous and toxic elements that is considered a serious threat to human and the environment. One of the effective technologies for removing this metal from wastewater is the use of adsorption with natural adsorbents. The main objective of this study was to investigate the chitin Nano-fiber as natural absorption for removal of lead metal from aqueous solutions in a discontinuous system. X-ray diffraction (XRD), infrared spectrometer (FT-IR) and transient electron microscopy (TEM) were used to identify the physical, chemical and structural characteristics of chitin Nano-fiber. In the discontinuous system, pH (4-9), absorption dose (0. 1-1 g), contact time(15-120 min), lead initial concentration (10-50 mg/L) and temperature (15-40 ° C) were studied. The results were analyzed by one-way ANOVA and Duncan's tests for significant evaluation of changes in parameters. The highest percentage of removal of lead (98. 95%. ) was obtained at 25 ° C, pH 5, 60 min contact time, absorbent dose of 0. 3 g and lead concentration of 10 mg/L. The results of this study showed that chitin Nano-fiber is considered as an optimal absorber for removal of lead from aqueous solutions by removing more than 98% of lead from aqueous solutions.

In the current situation, water resources are facing quantitative and qualitative issues which leave us with no other choice except to change our perspective towards consumption management. Separating drinking water from sanitary water is one of the components of the consumption quality management. This study was carried out based on SWOT analysis and AHP. At first, strengths, weaknesses, opportunities and threats of the separation of drinking water from sanitation water was obtained by survey of experts’ opinions. Priorities among SWOT factors and inconsistency rate of matrices were obtained by pairwise comparison matrices. In SWOT analysis the internal factor evaluation matrix (IFE), the external factors evaluation (EFE) and the internal and external factors (IE) were used. IFE and EFE matrices showed the final score of internal and external factors as 2. 51 and 1. 78, respectively. This indicated that the condition in Yazd is favorable in terms of internal factors while it is not positive in terms of using opportunities or staying away from threats. According to the internal and external factors, strategies are considered as drinking water distribution network (pipeline for drinking water) (SO), Governmental centralized drinking water distribution network (ST), private sector centralized drinking water distribution network (WO) and private sector mobile distribution systems of drinking water (WT). IE matrix showed that the Water and Sewage Company should choose the ST strategy (centralized drinking water distribution network) to avoid the threats and as a solution to water scarcity in a 5-to 10-year horizon.