مجله آب و فاضلاب
پیاپی 80 (زمستان 1390)

The aim of this study was to optimize electrocoagulation process for removal of chromium (VI) using Taguchi method. An elecrtrocoagulation reactor with six parallel electrodes was used in this study. For this purpose, effects of 7 parameters such as electrode material, electric current, time of reactions, initial pH, initial voltage, initial chromium concentration and rpm of impeller (agitation intensity) in two different levels were studied. Model of "OA_32" of Taguchi experimental design method was used. Among the above-mentioned parameters, electric current and electrode material had highest effects and rpm of impeller had the lowest effect on the electrocoagulation performance. According to the obtained results, highest chromium removal (168.33 mg/L) observed in the following conditions: electric current=3A, time of reaction=20min, initial pH=4, initial voltage=6v, initial chromium concentration=400mg/L, rpm of impeller=0rpm and iron as electrode material.

In this study the use of nano structured γ-alumina as a new and convince adsorbent for removal of cadmium ions from aqueous solution was investigated. The equilibrium adsorption level was determined as a function of the solution pH, temperature, contact time, initial adsorbate concentration and adsorbent doses. Adsorption isotherms of Cd(II) on adsorbents were determined and correlated with common isotherm equations such as Langmuir, Freundlich and Tempkin models. The isotherm data fitted well to the Langmuir isotherm. The maximum adsorption capacity for Cd(II) on nano structured γ-alumina was 76.92 mg g-1. The adsorption kinetics was investigated and the best fit was achieved by a second-order equation. The thermodynamic parameters such as free energy (ΔG0), enthalpy (ΔH0) and entropy changes (ΔS0) for the adsorption of Cd(II) were computed to predict the nature of adsorption process.

The Phosphorous discharge into the surface water led to excessive growth of algae and eutrophication in lakes and rivers. Therefore the phosphorus removal is important due to negative effect on water resources. The aim of this study was to investigat the modification of clinoptilolite and application of modified clinoptilolite for phosphorous adsorption from aqueous solution and isotherms and kinetics modeling. Hexadecyl Trimethyl Ammonium bromide (HDTMA-Br), Hexadecyl trimethyl Ammonium Chloride (HDTMA-Cl), Sodium Decyl Sulphate (SDS) and Cetrimide-C were used for modification of clinoptilolite. Experiments were conducted using jar apparatus and batch system. The effect of pH, adsorbent doses, contact time, phosphate initial concentration and particle size were studied surveyed on phosphate adsorption by modified clinoptilolite. The most common isotherms and the kinetics adsorption equations were used for determination of adsorption rate and dynamic reaction. The results showed that maximum phosphate adsorption was obtained in the pH of 7 and contact time 90min. Also it was found with the increasing of phosphate initial concentration, phosphate removal efficiency decreased significantly. Langmuir No 2 showed a good correlation compared to other isotherms (R2=0.997). Maximum adsorption capacity was obtained in 20g/L adsorbent dose (22.73mg/g). Also Interaparticle diffusion kinetics well fits with experimental data (R2=0.999) with constant rate of 3.84mg/g min0.5. The result showed that modified clinoptilolite can be used successfully as low cost and effective absorbent for phosphate removal.

The wastewaters of textile industries are large in volume and have different qualities. Therefore, their treatment is complicated. The main purpose of this research is to study the performance of dolomite wastes from stone industries, which are usually discharged into environment without being utilized, as an adsorbent for removal of dyes from textile industries wastewater. For this purpose, and because of wide usage of Acidic, Disperse and Reactive dyes in textile industries, color solutions containing C.I.Acid Red 88, C.I.Disperse Red 151 and C.I.Reactive Red 29 were used. For optimizing of different factors which affect the amount of adsorption, four factors of initial dye concentration, initial pH, stirring speed and adsorbent dosage were observed. In order to decrease the number of experiments, for minimizing the time and expenses, Taguchi method is utilized. Dolomite was incinerated at 800°C to increase adsorption capacity. The experiments were performed in batch reactors. In optimum conditions, the maximum color removal efficiencies for Acid Red 88 (initial concentrationof 50 mg/L, initial pH of 6, stirring speed of 200 rpm, adsorbent dosage of 8g/L), for Disperse Red 151 (initial concentration of 100 mg/L, initial pH of 4, stirring speed of 200 rpm, adsorbent dosage of 8g/L) and for Reactive Red 29 (initial concentration of 50 mg/L, initial pH of 2, stirring speed of 200 rpm, adsorbent dosage of 6g/L) were more than %99, that shows a high level of color removal performance by this adsorbent. Freundlich isotherm is the best model describing the adsorption process by charred dolomite in equilibrium condition for color removal.

Biosorption is a novel technology that uses dead and inactive biomass for removal of heavy metals from aqueous solution. Some parameters such as temperature, contact time, solution pH, initial metal concentration, biosorbent dose and also agitating speed of solution and biosorbent mixing can affect the amount of metal sorption by biosorbent. The aim of this study was to investigate the effects of different treatments of temperatures (25, 35, 45 and 55oC) on biosorption of metals mixture in order to determine optimal temperature for more metals removal from aqueous solution. This study uses dead and pretreated biomass of Aspergillus niger with 0.5N NaOH for removal of Zn(II), Co(II) and Cd(II). In all temperature treatments and in the case of all of heavy metals, maximum amount of metal sorption and concentration decrease was occurred in first 5 minutes and achieved to equilibrium after 20 minute. The percent of metals sorption show growth trend with temperature increase. Between 4 experimental treatments, 55oC treatment was shown maximum sorption and 25oC was shown minimum sorption amount. The percent of Cr(II) sorption was increase from 28.5% in 25oC to 44.7% in 55oC. Also, this increase was from 40% to 58% for Cd(II) and from 37.7% to 65.6% for Zn(II). About 60% of increase in sorption by A. niger was due to increase in temperature. Therefore the amount of metals sorption can be increase, only with temperature increase and without any biomass addition.

Phenolic compounds have become a cause for of worldwide concern due to their persistence, toxicity and health risks. Hence, removal of these pollutants from aqueous effluents is an important practical problem. Ultrasonic technology may be used for water and wastewater treatment as an advanced oxidation process. Application of this technology, leads to the decomposition of many organic compounds during cavitation process. The degradation of 4-chlorophenol in aqueous solution under sonolysis at 45 kHz coupled with fFenton process was is investigated. The oxidation rate was influenced by many factors, such as the pH value, the amount of hydrogen peroxide, catalyst (FeSO4) and initial p-chlorophenol concentration. The experimental results showed that the decomposition of p-chlorophenol was affected by the various reaction conditions. The optimum conditions obtained for the best degradation rate were pH=3, H2O2 concentration of 0.05 mol/L and 0.025 mmol/L for catalyst, respectively. Also it was observed that the degradation of p-chlorophenol depended on its initial concentration.

The main aim of this work was to investigate Bacillus sp. strain MGL-75 as biosorbent, for the fixation of Cesium ions in batch reactor. Pollution of the environment by toxic metals is a major environmental problem. Biosorption kinetics and isotherms have been performed at pH= 7. The equilibrium time was about 5 min and the adsorption equilibrium data were well followed by the Langmuir`s equation. The maximum capacity has been extrapolated to 48 mg/g. The release of Cs ions, from Bacillus sp bye desorption agents such as EDTA, HNO3, KCl, CaCl2, CH3COOH, KCL, was studied. The effects of culture age of Bacillus and pH values on Cs ions uptake were studied. The effect of Na-Azid as an inhibitor and uncoupling agents such as 2, 4 Dinitrophenol and autoclave on cesium ions uptake also were examined. Results indicated that the Bacillus sp. strain MGL-75 can be an excellent candidate to remove Cesium ions from aqueous solution.

Paper-recycling wastewaters have high volume and high pollution and its treatment is the most difficult and complicated process because of their colored pollutants and certain rigid chemical structure. In this study, the efficiency of alum in coupled with polyaluminum chloride (PACl) coagulant on the treatment of paper recycling wastewater was investigated. The effects of initial pH, initial COD and coagulation concentration on sludge volume index (SVI), and turbidity and COD removal were studied. Set tested for coagulation process was 2-12 initial pH, 200-2000 mg/l of alum concentration, 50-1500 mg/l of PACl concentration and 250- 2250 mg/l initial COD. According to the data obtained from batch studies, maximum percentage removal of turbidity and COD 89.90% and 85.16% respectively. The SVI of 193 ml/gr was found in this study. This study showed that the alum and PACl coagulants have high ability to remove pollutants from wastewater factory.

In this study Tehran’s drinking water was evaluated for the presence of chlorinated hydrocarbons during spring and summer of 2009. Chlorinated hydrocarbons are an important class of environmental pollutants that cause adverse health effects on human’s kidney, liver and central nervous systems. In this study six water districts were selected for taking drinking water samples in the city of Tehran as well as one location outside the city limits. The samples were analyzed by GC/MS using EPA method 8260. The average concentrations of 1,1-dichloroethylene, 1,2 Dichloromethane, Tetra chloromethane, Trichloroethylene and tetra chloroethylene were determined during a 7 month period and the results were 0.04ppb, 0.52ppb, 0.01ppb, 0.24ppb, 0.03ppb respectively. The highest concentration of chlorinated hydrocarbon observed in Tehran’s drinking water was Trichloroethylene and the lowest concentration was Tetra chloromethane. Districts 5 and 6 showed the highest concentrations of chlorinated hydrocarbons in the city of Tehran.

In this study the results of the experiments conducted in surface discharge of negatively buoyant flows in stagnant and non-stratified body are presented. Geometrical behavior of flow have been studied by simulating of discharged in a dark room and digital possessing of the photos. To determine the mixing behavior of flow the data obtained from 20 conductivity probes located along the trajectory of flow were utilized. Flow concentration profiles, flow self similar trajectory, variation in flow width and changes in flow dilution are the flow characteristics that were studied here. Regarding flow self similar properties the non dimensional behavior of flow will show similar behavior for different conditions of discharge. To have a comparative scale the experimental results were compared with the behavior that formerly reported for submerge horizontal discharges of positively buoyant flows. The analysis of flow behavior in these two discharges showed that despite the fact the flow general behavior is similar, geometric and mixing characteristics of flow in surface discharges are different from the those observed in submerge discharges. In surface discharges flow protrudes more in comparison to submerge discharges. The changes of flow width and dilution were also different from the one reported for submerge discharges.

In lateral intakes a portion of stream flow which enters the intake is divided from the upstream of the intake and is called stream tube. Past researchers have proved that the amount of flow and sediment discharge entering the intake as well as design of submerged vane to control sediment depends on determination of stream tube dimensions. In this study experimental and numerical investigation of the flow patterns at a 90° open-channel diversion is presented. In the experimental tests three components of velocity data obtained for different flow conditions. Then numerical SSIIM 2 model was calibrated and verified using tests data. More flow conditions were run using SSIIM 2 model to get enough hydraulic data. From analysis of these data it was found that the dividing stream tube dimensions depends upon directly to the ratio of diversion flow discharge to the main flow discharge. The strength of a secondary circulation was found to vary with inverse value of the main channel Froude number. Relations for predicting the stream tube dimensions and the strength of secondary circulations have been presented in this paper.

The missing data in database must be reproduced primarily by appropriate interpolation techniques. Radial basis function (RBF) interpolators can play a significant role in data completion of precipitation mapping. Five RBF techniques were engaged to be employed in compensating the missing data in event-wised dataset of Upper Paramatta River Catchment in the western suburbs of Sydney, Australia. The related shape parameter, C, of RBFs was optimized for first event of database during a cross-validation process. The Normalized mean square error (NMSE), percent average estimation error (PAEE) and coefficient of determination (R2) were the statistics used as validation tools. Results showed that the multiquadric RBF technique with the least error, best suits compensation of the related database.

In IRAN, inconsideration to water as a key sustainable development is the water crisis. This problem is the biggest factor for being marginalize planning and long-term management of water. The sustainable development policies in water resources management of IRAN require consideration of the different aspects of management that each of them required the scientific integrated programs. Optimal operation from inter-basin surface and groundwater resources and transfer surplus water to adjacent basins is important from different aspects. The purpose of this study is to develop an efficient optimization model based on inter-basin water resources and restoration of outer-basin water resources. In the proposed model the different three objective function such as inter-basin water supply demand, reduce the amount of water output of the boundary of IRAN and increase water transfer to adjacent basins are considered. In this model, water allocation is done based on consumption and resources priorities and groundwater table level constrain. In this research, the non-dominate sorting genetic algorithm is used for solution developed model because the objectives function and decision variables are complex and nonlinear. The optimal allocation of each water resources and Water transfer to adjacent basin are can be determined by using of proposed model. Based on optimal value and planning horizon, optimal allocation policy presented. The result as shown that applying the optimal operation policy can be transfer considerable volume of water resources within the basin for restoration the outside basin. Based on policy, can be prevented the great flow of water from river border.

During recent few decades, due to the importance of the availability of water, and therefore the necesity of predicting run off resulted from rain fall there has been an increase in developing and implementation of new suitable method for prediction of run off using precipitation data. One of these approaches that have been developed in several areas of sciences including water related fields, is soft computing techniques such as artificial neural networks and fuzzy logic systems. This research was designed to evaluate the applicability of artificial neural network and adaptive neuro –fuzzy inference system to model rainfall-runoff process in Zayandeh_rood dam basin. It must be mentioned that, data have been analysed using Wingamma software, to select appropriate type and number of training input data before they can be used in the models. Then, it has been tried to evaluated applicability of artificial neural networks and neuro-fuzzy techniques to predict runoff generated from daily rainfall. Finally, the accuracy of the results produced by these methods has been compared using statistical criterion. Results taken from this research show that artificial neural networks and neuro-fuzzy technique presented different outputs in different conditions in terms of type and number of inputs variables, but both method have been able to produce acceptable results when suitable input variables and network structures are used.

In this article, the current water pricing system in urban regions, which is based on IBT-Con (Increasing Block Tariff – per Connection), is being analyzed. The existing system has a lot of problems due to its improper executive structure; For instance, results showed that, more-populated houses (with larger dimensions), in some cases, have utilized water about 220% more than houses with lower dimensions; and consequently have paid about 300% more water-fees in comparison with less-populated houses. This research reveals that, less-populated houses have utilized about 2.5 times more water per-capita, compared to more-populated houses. However, water charges (per service-line) were almost the same for both groups, and even less for less-populated houses. This study, in order to set a resolution for existing tariff system structure has proposed a tariff system based on IRT-Cap (Increasing Rate Tariff – per Capita). The proposed tariff system for low and high income households showed that not only all problems (resulting from existing IBT-Con system) are removed, but also for equal conditions of per-house water utilization, charges paid by high-income households (with a dimension of two) is about 35% more than the low-income ones (with a dimension of eight). That is, with replacement of the proposed tariff system instead of the existing one, social equity in household potable water sector will be satisfied

Different sources of ground water contamination lead to non-uniform distribution of contaminant concentration in the aquifer. If elimination or containment of pollution sources was not possible, the distribution of contaminant concentrations could be modified in order to eliminate peak concentrations using optimal water pumping discharge plan. In the present investigation Visual MODFLOW model was used to simulate the flow and transport in a hypothetic aquifer. Genetic Algorithm (GA) also was applied to optimize the location and pumping flow rate of wells in order to reduce contaminants peak concentrations in aquifer.