مجله آب و فاضلاب
پیاپی 94 (بهمن و اسفند 1393)

Some water and wastewater pollutants cannot be eliminated by traditional treatment methods. This has encouraged workers to focus on high performance and environmentally friendly methods for their removal. The main objective of this study was to evaluate the performance of the modified mobile crystalline matter (MCM-41) including Ti-MCM-41، Fe-MCM-41، MCM-SiC3H6NH2، Mo- MCM-41، and unmodified MCM-41 in phenol removal from water. For the purposes of this study، MCM-41 was synthesized by hydrothermal methods. SEM، XRD، and FTIR analyses were used to determine phenol adsorption. Adsorption was measured in a batch reactor and the parameters affecting the adsorption process such as sorbent quantity، sorbent particle size، and pH were studied using the Statistix statistical software. The results showed that the unmodified MCM-14 has a great potential as a phenol adsorbent from water. The optimum amount of adsorbent for a phenol removal efficiency of about 95% was found to be 1 g of MCM-41 with a pore diameter of below 0. 018 mm in 50 ml of phenol and a pH range of 7-9.

SBA-15 nanoporous silica was prepared and functionalized with propylamine groups via post-synthesis grafting to develop efficient adsorbents of dyes in wastewater. The materials thus prepared were then characterized by XRD, N2 adsorption-desorption, and FTIR. Adsorption of a cationic dye, malachite green, on functionalized SBA-15 was investigated under various conditions of pH (5, 6, and 7), temperature (10, 20, and 30 °C), adsorbent dosage (0.1, 0.3, and 0.5 g/L), and dye concentration (50, 100, 150, 200, 250, 300 mg/L). Maximum equilibrium adsorption capacity to achieve maximum removal percentage (R%=100%) in optimum conditions (dye concentration=100 mg/L, pH=7, adsorbent dosage= 0.3 g/L) was estimated at 333 mg/g. The Taguchi method was used to optimize the adsorption performances of the materials, and then the isotherm, kinetic, and thermodynamic properties were analyzed under the optimum conditions. The results showed that the overall process was fast and its kinetics was well-fitted by pseudo-second-order kinetic model. The experimental data agreed well with Freundlich model. Therefore, the maximum amount of multilayer dye adsorbed was estimated as 500 mg/g. Based on the results obtained, this process may be regarded as an endothermic one with a negative ∆G, which shows the process is also spontaneous. Finally, the results indicate that the silica‐based nanoporous organic–inorganic hybrid material can be a promising sorbent for the removal of malachite green from aquatic solutions

Polymeric adsorbents are useful tools for removing heavy metals from aqueous solutions. Adsorption models are efficient tools for accurate prediction and evaluation of the practical adsorption process in real situation. In this study, the two isotherms of Langmuir and Dubinin-Radushkevich models were employed to investigate the absorption performance of chitosan, PVA, and chitosan/PVA blend (with a weight ratio of 1:1) in the removal of Mn (II) and Ni (II) from aqueous solutions. The PVA adsorbent was crosslinked by both chemical and radiation methods while the others were crosslinked only chemically due to Chitosan’s lack of resistance to radiation. The results showed that the Langmuir model fitted the experimental data better than the Dubinin-Radushkevich one for both metals. The maximum adsorption capacity (qmax) of the Langmuir model showed that the PVA/Chitosan adsorbent had the best adsorption compared to other adsorbents, with 52.63 mg/g for Ni and 30.30 mg/g for Mn (evidently more Ni was absorbed than Mn). Also, maximum adsorption by the chemically crosslinked PVA was 38.46 mg/g for Ni and 19.23 mg/g for Mn, which exhibits a higher level than adsorption by the radiation crosslinked PVA The results indicate that absorption capacity depends on the type of adsorbed metal, absorbent structure, and the crosslinking method employed.

The cadmium metal not only has detrimental effects on the nervous system, the kidneys, and the human fetus but is also lethal because of its carcinogenic effects. Biological absorption of cadmium has a number of advantages over conventional methods that include high removal efficiency for eliminating heavy metals from dilute solutions, availability and abundance of the required materials in nature, and reproducibility and reusability of the materials. In this study, the biosorption of cadmium (II) ions onto the dry biomass of two brown algae, Cystoseira indica and Fucus serratus, was investigated. Cystoseira indica was collected from the coastal areas of the Oman Sea and Fucus serratus was collected from the coastal area of the Atlantic Ocean. The algae were first dried, washed three times with tap water, and finally washed with distilled water without ions before they were isolated in pieces 0.5-1.5 mm in diameter. In all the experiments, distilled water was used to which known amounts of cadmium were added before the algae were introduced into the solution. The metal ion concentrations in the solution were measured using the atomic absorption spectrophotometer before and after the metal came into contact with the algae. The optimum pH for the adsorption of cadmium was found to be 3/0 ± 5/6 and 3/0 ± 5/5 for Cystoseira indica and Fucus serratus, respectively. The maximum metal uptakes by both algae were observed in acidic pH conditions. The time required for the biosorption of the metal to reach equilibrium was 360 minutes for Cystoseira indica and 300 minutes Fucus serratus. The adsorption capacities for Cystoseira indica and Fucus serratus using the Langmuir isotherm were determined as 44/58 and 54/95 mg /g, respectively. Moreover, the functional groups involved in cadmium uptake in both algae were identified. Finally, the results of this study showed that Fucus serratus algae had a higher capacity for adsorbing cadmium ions than did Cystoseira indica.

In this paper, river water quality management was implemented to minimize the costs of environmental protection and to meet the environmental water quality requirements. For this purpose, the social choice approach was adopted to consider the role of wastewater dischargers in the decision-making process and to increase the applicability of the proposed waste load allocation programs. Firstly, different wastewater treatment scenarios were identified for each water pollutant and treatment alternatives which are combinations of treatment scenarios were defined. For each treatment alternative, penalties due to violations of river water quality standards were then calculated using the qualitative simulation model (Qual2kw) and each discharger was assumed to prioritize the treatment alternatives based on the treatment costs and the fines defined for water quality standard violations. Finally, using different social choice methods, the most preferred treatment alternative was identified. In order to reduce costs and to encourage dischargers to participate in river water quality protection programs, the most preferred treatment alternative was exchanged among the dischargers as an initial discharge permit using the extended trading-ratio system (ETRS). The results of applying the proposed model to a case study, the Zarjub River located in north Iran, showed the model’s efficiency in developing river waste load allocation strategies.

This study was conducted to determine the origin and distribution of the lead, copper, zinc, nickel, chromium, and vanadium metals in the surface sediments of the southwestern coasts of the Caspian Sea. Surface sediment samples were collected from the three transects of Kapourchal, Bandar-Anzali, and Kiashahr at three different depths of 10, 20, and 50 m. Metal concentrations were determined by ICP-OES. The metals in these areas were identified to originate from such natural sources as rock weathering and soil erosion transported by rivers into the sea. The mean total concentrations of the metals along the three transects showed significant increases with increasing distance from the shore, which might be due to the transportation of sediments as a result of increasing slope along the sampling transects. The same trend was observed in the samples taken from the coastal areas along Bandar-Anzali, which was could be due to the wetlands in the region and the multitude of rivers flowing into this wetland which eventually carried the sediments into the sea. Results revealed that the total metal concentrations in the region were below the SQGs and NOAA standards. Finally, risk assessment code did not show any serious risks, but indicated only a low risk due to lead and copper levels.

Detention basins are one of the structural measures for floodwater control in urban environments. They are effective tools in flood mitigation, but some studies have shown that they may aggravate the condition if not properly sited. This study presents an innovative approach which directly incorporates hydrologic-hydraulic modeling results to the site selection procedure for flood control detention basins. Darakeh Catchment located in Tehran is selected as the case study. Hydrologic, physiographic, and economic parameters are considered as siting criteria. SWMM model is employed for simulating hydrologic-hydraulic processes and evaluating the current drainage network against low-frequent storms. Modeling results, including flooded junctions and the flow hydrographs, are used as input parameters to the spatial decision making framework. The framework employs Analytical Hierarchy Process (AHP) as the decision making structure and geographic information system (GIS) as the spatial analyst tool. The output is a raster map which shows each cell potential for the placement of the detention basin. The proposed approach aims to improve the siting procedure based on these measures and other BMPs in an urban environment.

Sudden changes in the boundary conditions of water transmission systems, such as sudden opening and closing of valves or abrupt on and off switching of pumps and turbines cause a transient flow called ‘water hammer’. In this study, comparisons were made between the effective parameters including pipeline material, on the one hand, and the equipment and tools available for reducing the effects of water hammer, on the other. For this purpose, a practical example of a water transmission line from a pumping station located near Shahid Shirdom Residential District to the upstream reservoir in Tehran was used for modeling by the Bentley Hammer XMV: 8 software. The results obtained for the different parameters and options were compared and it was revealed that, regarding the pipe material, GRP pipes reduced pressure by 49.1 Kpa compared to the Asbestos cement pipes and by 50.3 Kpa compared to the iron pipes. Comparison of the results for the protective systems indicated that the surge tank outperformed the other alternatives in controlling pressure such that maximum pressure was reduced by 3.9 bar when using surge tanks compared to the flywheel and by 5 bar compared to the check valve. Finally, it was found that the concurrent use of the surge tank and the flywheel would be the most ideal method for controlling the water hammer effects.

Conventional methods for solving the problem of site location for booster chlorination stations have assumed the use of linear superposition principle for first-order kinetics of chlorine decay in water distribution systems in order to speed up the process of evolutionary algorithms. However, examination of this assumption in this paper shows that it causes a non-trivial error, especially when the order of chlorine decay rate is more than one. This paper presents a novel meta-model for solving the multi-objective optimization problem of optimal locations for booster chlorination stations for the nonlinear order of chlorine decay rate. In the proposed model, the meta-model is the water quality simulation model quantified by the principle of linear superposition for nonlinear kinetics of chlorine decay. To do so, residual chlorine concentration is calculated from the injection unit chlorine concentration at each node in the network as offline outside the optimisation loop. Then, within the optimization loop, the residual chlorine concentration in the network obtained for the optimal solutions is calculated as the combined chlorine injected from different locations and at different concentrations based on the linear superposition meta-model of the previous part. Objective functions of the optimisation solutions are quickly evaluated by this meta-model. In order to mitigate the significant error due to the estimation of this meta-model, the fitness of the best solutions are again evaluated using the real water quality simulation model (nonlinear chlorine decay rate) and replaced with the evaluations previously approximated by the meta-model. The results show the desirable accuracy of the proposed model and the high speed in the run time of the hybrid optimisation model.

The increasing demand for water in developed regions has led to numerous water supply challenges. Given their sensitivity and strategic importance as zones of cargo and passenger transfer, international airports are no exception to this general rule. The potential dangers to ground subsidence on the runway as a result of excessive groundwater withdrawal warrant plans aimed at developing models for optimal groundwater withdrawal as a measure of sustainable use of aquifers. In this study, consumption and withdrawal data are used and future development plans of the Imam Khomeini International Airport are considered to develop a model for groundwater use within the region based on multi-objective programming. Considering the objectives of maximizing water supply and minimizing costs of water transmission to demand zones, the model was used to develop an optimal water allocation system for the region containing monthly groundwater withdrawal policies and graphical distribution plans. The results show that the operation instructions thus developed for each well need to be carefully executed in order to ensure its safe exploitation. Strict adherence to the instructions is expected to enhance water supply reliability and to reduce the associated costs. This approach can be tailored and scaled up for future planning horizons and is also replicable in other areas by developing the relevant objective functions and constraints.

Startup is one of the most important stages in the operation of a wastewater treatment plant (WWTP). In this paper, a novel method is presented for the startup of Arak Activated Sludge WWTP, which is shown to contain more advantages than other common methods. In this method, a portion of the inflow is initially allowed to enter gradually into an aeration basin prior to seeding. Under these conditions, less seeding is required due to the low flow of the influent and the low volume of the aeration basin. Once MLSS in the basin reaches the desired level, the rest of the system comes into operation and the sludge developed in the system is used for further seeding. In the case of the WWPT in Arak, it took about 2 months for the total MLSS to be developed and wasting the sludge to start because of the cold weather conditions in the region. The wasted sludge was controlled by the F/M ratio at a constant sludge age. During the start-up, the MLSS increase exhibited a linear trend and the low loading allowed for the variation in influent contaminants to be controlled. The effluent contaminants were below the standard levels recommended by the Environment Protection Organization. BOD5 and COD removals increased from 40% and 60% to 90% and TSS removal increased from 70% to 96%. Lower loading levels, better process control, and lower sludge processing costs are the benefits of this system

The discharge of phenol and chlorinated compounds, fatty acids, tannin, lignin, and their by-products into receptive waters poses serious hazards for the aquatic life. In this study, the efficiency of a tow-step process of activated sludge-trickling filter (AS/TF) in the removal of inert chemical materials that defy conventional treatment processes was investigated. For this purpose, an integrated activated sludge process (industrial scale) was used sequentially with a trickling filter (pilot scale). Inside a tank with an effective volume of 6.87 m3 was installed 5.78 m3 of polypropylene 2HX media with a specific area of 240 m2/m3. The hydraulic loading rate (HLR) of the trickling filter during the startup period (90 days) was 3.6 m3/h which was raised to 3.6-6 m3/h in the operation period (120 days), with the best effluent quality achieved at HLR=5.4 m3/h. For the purposes of the experiments in this study, four reactors, each 1256 cm3 in volume, were fed the WWTP effluent and concurrently a glucose substrate containing a COD content equal to that fed to the four reactors was fed into two identical reactors; all the reactors were subsequently run for 480 h in aerobic conditions. Nutrients, pH, and DO (as environmental control indicators) as well as soluble and total COD were measured twice daily. The effluent values of soluble inert materials (SI), total soluble COD (STO), degradable suspended materials (XSO), degradable COD (CSO), refractory suspended materials (XI), and degradable soluble materials (SSO) for AS were calculated as 40, 227, 94, 281, 251, and 187, respectively, while the same parameters for the AS/TF were 20, 227, 104, 311, 241, and 207 mg/l, respectively. The results showed that the activated sludge process when combined with the trickling filter has a twofold capability, compared to when used alone, in removing inert COD. It was also shown that treatment levels in conventional WWTPs can be improved by integrating conventional treatment processes.

Phenol is a highly toxic aromatic compound discharged into the environment through industrial effluents. The natural biological treatment process has been widely used as one of the most feasible, eco-friendly, and cost-effective options for the treatment of pollutants such as phenol. The objective of the present experimental-analytical study was to evaluate the performance of the facultative stabilization pond in removing phenol and other organic compounds from oil refinery effluents. For the purposes of this study, a pilot-scale anaerobic stabilization pond 1.2×0.6×0.55 m in size was constructed of fiberglass sheets 6 mm in thickness. The experiment was run with a hydraulic retention time of 10 days and a hydraulic loading rate of 43.5 l/d. The organic loading rate for the facultative pond was 150 kg/h.day. Samples were taken after pond operation and seeding when the pond reached its biological stability. Depending on phenol removal levels in the anaerobic stabilization pond, initial phenol concentrations at the inlet to the facultative pond were assumed to be 0-28, 30-80, 90-130, and 150-200 under warm conditions and 100-140, and 200b-260 mg/l in cool conditions. For each sample, the parameters NH3, PO4, and Phenol were measured using the Varian spectrophotometer (model UV-120-02) at the wavelengths of 425, 690, 500 nm, respectively. TCOD, SCOD, TBOD, SBOD, pH, and ORP were also measured according to the standard methods of water and wastewater. The results showed that phenol removal efficiency of the facultative pond was 71.8% for warm temperatures and 14.66% for cool temperatures. It was also found that temperature and phenol concentration significantly affected the performance of the pond. Moreover, its performance was observed to enhance with reducing phenol concentration and increasing temperature (p<0.001). Maximum phenol removal efficiency of the system was recorded at 71.8% for warm temperatures and a low phenol concentration of 0–28 mg/l while its minimum of 14.66% was recorded at a high phenol concentration of 200-260 mg/l under cold weather conditions. Based on the results obtained, it may be concluded that the pilot-scale facultative pond has a high performance in removing organic compounds with different concentrations of phenol under warm weather conditions.

Environmental and health hazards are regarded among the problems associated with the disposal of raw or undertreated wastewaters containing reactive dyes discharged into the environment, and especially into receiving waters. Conventional treatment methods lack the desirable efficiency in removing these compounds. For this type of wastewater, researchers, therefore, recommend methods, collectively called "advanced oxidation processes" such as the Fenton process, that are capable of removing toxic and non-biodegradable compounds. This experimental-intervention study was carried out on the laboratory scale to investigate the Rodamine B and COD removal efficiency of the Fenton oxidation process. The effects of such parameters as H2O2, Fe2+, and reaction time were investigated using a 1-L batch reactor. The results revealed that the process achieved a decolorization efficiency of 58% and a COD removal of 48% after 60 min of reaction time when the initial concentrations of Rodamine B, COD, Fe2+, and H2O2 in the influent were 100 mg/L, 270 mg/L, 40 mg/L, and 200 mg/L, respectively, at a constant pH level of 3.