WATER AND WASTEWATER
Year:2015 | Volume:26 | Issue:1 (95)|Papers Count:16

Magnetic nanoparticles modified by olive leaf ash were used in this study for the removal of heavy metal ions from aqueous solutions. The equilibrium adsorption level was determined as a function of solution pH, temperature, contact time, initial adsorbate concentration, and adsorbent dosage. Adsorption isotherms of heavy metal ions on adsorbents were determined and correlated with common isotherm equations such as Langmuir, Freundlich, and Tempkin models. The apparent characters and physical chemistry performance of the magnetic nanoparticles modified by olive leaf ash were investigated by scanning electron microscopy (SEM), transmition electron microscopy (TEM), and FT-IR. Results showed that the Langmuir isotherm model was fitted well with adsorption data. Kinetic studies were also carried out using various kinetic models such as Pseudo-first order, Pseudo-second order, Elovich and Intra particle diffusion model. The Pseudo-second order kinetic model was fitted very well with the experimental data. Based on thermodynamic studies, this process was found to be both endothermic and spontaneous and the enthalpy and entropy were found to be negative.

The presence of persistent organic pollutants and toxics (e.g., pesticides) in ground, surface, and drinking water resources combined with the inability of conventional treatment methods to remove these pollutants have led to the development of advanced oxidation processes. Nowadays, nanophotocatalyst processes are considered as clean and environmentally-friendly treatment methods that can be extensively used for removing contaminants. The objective of the present study was to determine the efficiency of the ultraviolet and zinc oxide (UV/ZnO) process in the removal of diazinon pesticide from aqueous solutions. For the purposes of this study, samples were adjusted in a batch reactor at five different detention times. The pH levels used were 3, 7, and 9. Irradiation was performed using a 125 W medium-pressure mercury lamp. The diazinon concentrations of the samples were 100 and 500 mg/L and the concentrations of zinc oxide nanoparticles were 50, 100, and 150 mg/L. The highest degradation efficiency was observed at pH 7 (mean = 80.92±30.3), while the lowest was observed for pH 3 (mean 67.11±24.49). Results showed that the optimal concentration of nanoparticles (6-12 nm) was 100 mg L-1.

In this study, graphene oxide was used as a nanostructured adsorbent with properties supposedly better than other common adsorbents to remove 4-chlorophenol from aqueous solutions. For this purpose, graphene oxide was initially synthesized using the Hummer's method and x-ray diffraction and scanning electron microscopy were employed to identify its morphology and structure. The variables involved in the absorption process (including 4-chlorophenol initial concentration, adsorbent dosage, and pH) were investigated based on the one-factor-at-a-time method. Eventually, the data were confirmed against the Langmuir and Freundlich isotherms. It was found that the adsorption process reached equilibrium in 20 minutes. A dosage of 0.4 g/L graphene oxide at pH=8 brought about 90% removal of 10 mg/L 4-chlorophenol within 5 minutes. The adsorption isotherm was described well by the Langmuir isotherm model and the values for R2 and RL were recorded as 0.99 for and 0.34, respectively. Being a low cost and highly efficient process, the adsorption process using graphene oxide adsorbent may be recommended for the reduction and elimination of pollutants in the environment, especially those in aqueous solutions.

Hexavalent chromium is a pollutant found in surface and underground waters that causes serious environmental hazards. Chromium enters water as a result of industrial activities such as electroplating, dyeing, leather tanning, and metal manufacturing. The objective of the present laboratory-experimental study was to remove chromate from industrial effluents using silicon nanoparticles. The experiments were performed with both simulated synthetic wastewater and true wastewater. Various parameters such as pH, contact time, and different concentrations of Cr (VI) and SiO2 were examined. The data obtained were analyzed using the Excel and SPSS Ver. 16. It was found that Cr (VI) removal increased with decreasing pH and increasing contact time. The highest Cr (VI) removal was achieved at pH=3 and a contact time of 120 minutes. It was also observed that removal observed to obey the Langmuir isotherm and pseudo second-order kinetic models, respectively. The findings indicate that silicon nanoparticles are capable of removeing Cr (VI) from industrial effluents. Given the Cr (VI) removal efficiency of 93.6% achieved under optimum conditions and the removal efficiency of 88.6% achieved in real samples, the method may be recommended as a highly efficient one for removing Cr (VI) from industrial wastewaters.

Electrocoagulation is an electrochemical method for the treatment of water and wastewater. The present cross sectional study was designed to investigate the removal efficiency of total coliform and heterotrophic bacteria from surface water using the process. For this purpose, water samples were taken from the drinking water intake at Suleiman-Shahsonghur Dam. The electrocoagulation process was carried out in a Plexiglas reactor in the batch mode with Al and Fe used electrodes. The experiment design was carried out using the Design Expert Software (Stat-Ease Inc., Ver. 6.0.6). After each run, the values of metals dissolved due to anode electrode dissolution were measured using the Inductively Coupled Plasma (ICP) and the results were analyzed using the RSM model. Results revealed maximum removal efficiencies of 100% and 89.1% for total coliform and heterotrophic bacteria using the Al electrode, respectively. Also, maximum removal efficiencies using the Fe electrode for the same pollutants were 100% and 76.1%. The measurements clearly indicate that the quantities of Al and Fe released in water were higher than the recommended values. While the electrocoagulation process showed to be effective in removing microbial agents from surface waters, the high concentrations of dissolved metals due to the dissolution of the anode electrode seem to remain a health problem that requires optimal conditions to be determined for acheiving standard concentrations of the dissolved metals.

The effluent from Zarshouran gold mineral processing plant contains high quantities of arsenic, antimony, mercury, and bismuth. These metals and metalloids are soluble in water and very toxic when they enter the environment. Their solubility in water causes the polluted area to extend beyond their point of origin. In this article, different methods of antimony removal from water and wastewater were reviewed and the zero-valent iron nanoparticles coated on Bentonite were selected as an effective and low cost material for removing antimony from wastewater. For the purposes of this study, zero-valent iron nanoparticles of 40-100 nanometers in size were synthesized by dropwise addition of sodium borohydride solution to an Iron (III) aqueous solution at ambient temperature and mixed with nitrogen gas. To avoid particle agglomeration and to enhance the product’s environmentally safe application, the nanoparticles were coated on Bentonite and characterized by SEM/EDAX and BET. The experiments were carried out by intense mixing of the adsorbent with 10ml of real/synthtic wastewater samples in 20ml bottles. The effects of pH, contact time, temperature, and adsorbent dosage on antimony removal efficiency were investigated under intense mixing using a magnetic mixer. Finally, the effluents were filtered upon completion of the experiments and used for atomic adsorption analysis. The results of the experiments showed that the adsorption isotherms of the synthesized nanoparticles obeyed the Langmuir and Freundlich models. The experiments carried out on real samples showed that antimony adsorption capacity for B-nZVI was 2.6 mg/g of the adsorbent and that the highest antimony removal efficiency was 99.56%.

The aim of this study was to evaluate the growth of Vetiveria zizanioides under hydroponic conditions and its efficiency in removing nitrogen and phosphorus compounds from wastewaters. For this purpose, a pilot plant was constructed with a net volume of 60 liters which was intermittently fed for three months with the effluent from a domestic wastewater treatment plant. It was found that Vetiver exhibited a significant capability for living in polluted waters under hydroponic condition as evidenced by the growth of its leaves to 130 cm. Moreover, the average values of total nitrogen, total phosphorus, and biochemical oxidation demand (BOD) removal efficiencies over four days of retention time were 91%, 97%, and 75%, respectively. If used as a tertiary treatment unit, the plant needs a minimum retention time of two days to allow adequate time for the removal of such vital compounds as Ammonia and Phosphate by 95%, which is the typical standard limit for wastewater reuse or free discharge. Finally, it was observed that the total values of nitrogen and phosphorus absorbed in the leaves were 17 and 2.3 (mg/gr dry weight) while the same elements absorbed in the roots were measured as 13 and 1.8 (mg/gr dry weight), respectively.

The design and upgrade of sludge treatment systems generally depend on the decision made regarding the appropriate system from among the options available. The selection process has become increasingly important and complex due to recent technological developments that have led to increased diversity in the available options which offer a wide variety of capabilities. The multi-criteria decision making method is one of the techniques recently developed which takes into account all the criteria involved in the decision making process. The Ghods Town WWTP in the west of Tehran located in the vicinity of residential areas has given rise to claims by citizens due to the odors emitted by the sludge sand drying bed, which justifies the replacement of the present sludge dewatering system. For this purpose, the multi-criteria decision making method based on the fuzzy synthetic evaluation method was used to identify the optimal sludge dewatering system appropriate for the WWTP under consideration. Furthermore, weighting of the subjective (social, environmental, and administrative) criteria was accomplished using the analytical hierarchy process and the objective (i.e., economic) criteria were weighted using the entropy concept. In this method, the triangular fuzzy membership function was also used to take into account the uncertainty associated with each of the decision making parameters. Based on the results obtained, the belt filter press dewatering system and the filter press were identified as the preferred solutions.

The sludge biogranulation technology, including the two aerobic and anaerobic processes, is an important development in the field of wastewater treatment. Much is know about the process and operation of the anaerobic granulation thanks to the rather large number of studies carried out. Aerobic granulation, however, has been only recently investigated and a limited number of studies have been dedicated to such aspects of the process as the organic source, hydrodynamic shear stress, cycle, settling time, reactor configuration, solid retention time, oxygen concentration, metallic concentration, and pH. This article tries to provide a brief review of these studies and the results obtained in an attempt to identify the most important study so far conducted. Using the results, a comparison will also be made between the anaerobic and aerobic granulation processes to gain a better understanding of both.

Maharloo Lake is one of the most important water ecosystems in Iran, which is nowadays exposed to multiple risks and threats due to poor water management, salt extraction, and heavy metal pollution. In this study, the concentrations of such heavy metals as chromium, copper, zinc, arsenic, cadmium, and lead in both water and salt samples collected from areas in the north and south of the lake were determined by atomic absorption (AA-670G) after the samples had been digested. Results showed that metal concentrations in the salt samples taken from both the northern and southern areas had identical mean values in the order of Cr> Cu> As> Cd> Pb. An almost similar pattern was detected in metal concentrations in water samples taken from the same areas but with a slight difference in the way they were ordered (Cr> Cu> As> Pb> Cd). It was found that both water and salt samples collected from the northern areas had higher metal concentrations, except for that of Pb which was slightly lower. Comparison of the mean values of metal concentrations in the Salt Lake and those of Sirjan, Lar, and Firoozabad salt mines revealed that copper, cadmium, and lead had their highest concentrations in the Salt Lake while arsenic and chromium recorded their highest values in samples taken from Lar and Firoozabad salt mines, respectively. Based on these findings, it may be concluded that the increased metal concentrations observed in samples from both northern and southern areas of the lake are due to the sewage and effluents from urban, industrial, and hospital sources in Shiraz disposed into the lake as well as such other human activities as farming in the areas around the lake, especially in the northern stretches. These observations call for preventive measures to avoid further water quality degradation in the area.

Water demand management policies and water pricing tools have important effects on optimal water allocation. An important water pricing policy is determining suitable water tariffs for urban water uses. In this regard, the emphasis laid by the targeted subsidy law on water pricing based on supply cost will have a great impact on the price of water and on water resources management. Based on these considerations, the present study was designed and conducted in 2010-2011 to identify proper water prices for Golestan Province under the targeted subsidy law. For this purpose, the economic value of water as veiwed by urban users was estimated using the contingent valuation method. In a second stage, the average cost approach was employed to determine the cost of water production from surface and ground water resources from the viewpoint of suppliers. Finally, the present water tariffs, the economic value of water, and the average cost of water production obtained in the previous sategs were compared to evaluate various scenarios of water pricing under the targeted subsidy law. Based on our findings, a stepwise water pricing system that strikes a balance between the economic value of water and water production cost is recommended for implementation in order achieve simultaneous improvements in both water demand and supply management.

In recent years, the optimal design of pipeline systems has become increasingly important in the water industry. In this study, the two methods of genetic algorithm and mathematical optimization were employed for the optimal design of pipeline systems with the objective of avoiding the water hammer effect caused by valve closure. The problem of optimal design of a pipeline system is a constrained one which should be converted to an unconstrained optimization problem using an external penalty function approach in the mathematical programming method. The quality of the optimal solution greatly depends on the value of the penalty factor that is calculated by the iterative method during the optimization procedure such that the computational effort is simultaneously minimized. The results obtained were used to compare the GA and mathematical optimization methods employed to determine their efficiency and capabilities for the problem under consideration. It was found that the mathematical optimization method exhibited a slightly better performance compared to the GA method.

The supply of water with a desirable quality and at required quantities by water distribution networks (WDNs) requires exorbitant costs over their effective life. Optimized network design is, therefore, not only a basic and most decisive step toward reducing costs but will also serve a means for considering other quantitative and qualitative criteria in the design process. In this study, a gravitational network with two reservoirs was investigated to determine the effects of the quantitative parameter of resilience index and the qualitative parameter of free chlorine residual on network design costs. The quantitative parameter used gurantees network efficiency at critical demand times through creating extra capacity while the qualitative one is meant to ensure adequate concentrations are maintained throughout the network. For this purpose, a Genetic Algorithm (GA) was written in the Matlab code and incorporated into the EPANET Toolkit to perform thorough WDN hydraulic and water quality analyses. Results showed that the proposed method was capable of creating a logical and consistent relationship between quantitative and qualitative parameters, on the one hand, and design objectives, on the other, although the WDN costs are only slightly increased. It was concluded that the method could be exploited as a new basis for selecting the final WDN optimal design.