WATER AND WASTEWATER
Year:2008 | Volume:19 | Issue:3 (67)|Papers Count:11

This study was conducted to investighate the adsorption of Cadmium from aqueous solutions by using the powder of excess sludge (biosolid) from municipal wastewater, at 24 to 26oC, a pH value of 2 to 6, over a contact time of 5-420 minutes, and at 50 to 300 rpm stirring rate in a batch reactor on the laboratory scale. The pretreatment of biosolids consisted of dewatering, grinding, and grainsizing with sieves (mesh dimensions between 50 and 120). According to the results, the best conditions for biosolids to adsorb Cadmium was pH=4, 120 minutes of contact time, and a stirring rate of 200 rpm. Cadmium adsorption kinetics followed the pseudo second order model. Maximum equilibrium adsorption was observed after two hours. The adsorption isotherm was in accordance with the Langmuir model. Maximum Cadmium adsorption capacity of biosolids (qmax) was estimated at 0.38 m-mol/g of dry biosolid (41.5 mg/g) and the Langmuir constant (kd) was found to be 0.1044 m-mol/lit (11.37 mg/lit).

The concentration of heavy metals in soil is increasing mainly due to the use of fertilizers, pesticides, and urban and industrial wastewaters. Field application of wastewater may contaminate food chains and water resources if environmental standards are not duly observed. The objective of this research was to determine the mass balance and transport of Cd, Cr, Co in a sewage sludge amended calcareous soil.  Sewage sludge was applied at 50 t/ha to 4×4 plots in three replications. After 5 years from sludge application, soil samples were collected to a depth of 100 cm at 20 cm increments and analyzed for their total heavy metal concentration. We were not able to recover 100% of the metals added into the soil at a depth of 100 cm. Our results indicate that 14, 38, and 46 percent of Cd, Cr, and Co, respectively, had been lost over five years. The results also show that some of the metals may have moved to depths below 100 cm through preferential flow paths.

Increasing surface and groundwater pollution by ammonium and nitrate makes it necessary to find solutions with minimal environmental impacts. For this purpose, using abundant and high sorption potential soil minerals offers cost-effective and environmentally sound remediation techniques. In this study, Firoozkouh and Semnan zeolites were used for removal of nitrate and ammonium from laboratory solutions and groundwater (Batch method). Zeolite minerals were modified by using the organic surfactant hexadecyltrimethylammonium. A one to tenth ratio of absorbent to solution was used. Results showed that the Semnan natural zeolite and the Firoozkouh modified zeolite treatements, respectively, had the highest and the lowest ammonium sorption levels. The Firoozkouh modified zeolite had the highest nitrate sorption while Semnan natural zeolite had the lowest ammonium sorption. The highest sorption level for ammonium was found to be 0.96 meq g-1 for the Semnan natural zeolite treatment at a concentration of 10 meql-1 and pH=5.5 while the highest sorption for nitrate was found to be 0.8 meq g-1 for the Firoozkouh modified zeolite. Isotherms of nitrate and ammonium sorption levels by natural and modified zeolites showed to match with those of the linear and Fraundlich models.

This paper studies the effect of different molarities of sodium bicarbonate on enhanced absorption capacity of rice husk to remove cadmium in low concentrations. Maximum absorption efficiency was achieved at a pH of 6 and absorption equilibrium time was 1.5 hours. Results of chemical experiments and photography by electronic microscope from improved rice husk revealed a good relationship to exist between number and average diameter of absorber pores, on the one hand, and absorption efficiency, on the other. Meanwhile maximum absorption efficiency of rice husk in cadmium removal was 99.1 percent which shows improvement due to 0.3 molar sodium bicarbonate. In this study, kinetic absorption models were also studied. Both Lagergrn (1898) and Ho et al. (1996) models satisfactorily described data with a confidence level of 95 percent; however, the latter model was found superior in this respect. Comparison of the coefficients calculated here with those reported in other models showed a faster cadmium absorption rate by improved rice husk due to 0.3 molar sodium bicarbonate.

Longitudinal dispersion coefficient in rivers and natural streams is usually estimated by simple inaccurate empirical relations because of the complexity of the phenomenon. In this study, the adaptive neuro-fuzzy inference system (ANFIS) is used to develop a new flexible tool for predicting the longitudinal dispersion coefficient. The system has the ability to understand and realize the phenomenon without the need for mathematical governing equations. The training and testing of this new model are accomplished using a set of available published filed data. Several statistical and graphical criteria are used to check the accuracy of the model. The dispersion coefficient values predicted by the ANFIS model compares satisfactorily with the measured data. The predicted values are also compared with those predicted by existing empirical equations reported in the literature to find that the ANFIS model with R2=0.99 and RMSE=15.18 in training stage and R2=0.91 and RMSE=187.8 in testing stage is superior in predicting the dispersion coefficient to the most accurate empirical equation with R2=0.48 and RMSE=295.7. The proposed methodology is a new approach to estimating dispersion coefficient in streams and can be combined with mathematical models of pollutant transfer or real-time updating of these models.

Sedimentation in reservoirs not only reduces the storage capacity but also decreases the useful life of the reservoirs. It also creates problems in operation of bottom outlets and increases, the reservoir surface area and the evaporation loss. To alleviate these problems, it is necessary to investigate the sediment deposit distribution in an attempt to make predictions of that the process possible. Management measure are also required to control reservoir sedimentation. Mathematical models are used today to evaluate reservoir sedimentation rates and to predict the reservoir useful life. These models are based on the analysis of equations governing sediment transportation, distribution, deposition, and scouring. In this study, the hydrographical measured data obtained from Alavian Dam in Maragheh are first used to calibrate the mathematical model. Then, the Volume-Area-Height variation graphs and the manner of sedimentation along longitudinal and transversal sections are plotted, compared, and evaluated for the pre-sedimentation, post-sedimentation stages and the mathematical model results for a period of 50 years. The results obtained from this study shows that after 50 years of reservoir operation, the sediment deposit volume in the reservoir amounts to about 15 MCM, which accounts for 25 percent of the reservoir active capacity.

Fluid transportation systems are among the high energy consumers in different industries such as water distribution systems. It is, therefore, important to study their optimized performance as regards their energy consumption. The fluid behavior in these systems under different operational conditions is actually dynamic, or time-dependent; the study of these systems by a dynamic model, hence, allows system performance to be evaluated more accurately. In this paper, a dynamic model is presented for a fluid transportation system consisting of a pumping station, a pipeline, and a reservoir tank. Sample calculations of energy consumption for a pumping station are presented. The results obtained from this study can be used for formulating recommendations on energy consumption estimation of pumping stations based on their operational conditions and control method used.

Among the alternative techniques available for flood control, infiltration of rainwater is one of the most important methods to control stormwater effects. Conceptual river infiltration models are very useful for application to control urban flood water, especially in the case of infiltration basins. Contrary to mathematical models, these models are very simple, and unlike empirical models, their parameters are very easy to calculate. Four selected models (Dupuit-Forchheimer, Ernst, Miles and Morel-Seytoux) were employed for simulation of the infiltration process in infiltration basins. The study showed that the hydrograph computed by these models were closely similar to the real hydrograph. The three models (Dupuit-Forchheimer, Ernst, and Miles) showed far lower sensitivity to their parameters than the Morel-Seytoux one.

Pipes are the most important components of wastewater collection systems accounting for considerable costs in constructing such systems. In view of this and regarding the growing trend in design and execution of wastewater collection and transmission lines in recent years, various types of pipes have been introduced into the market. Selection of appropriate pipes and their qualitative and quantitative control, therefore, call for due consideration given their high cost share in collection systems. In this paper, efforts are made to consider various types of pipes used in (urban and rural) wastewater collection networks in an attempt to signal the significance of qualitative and quantitative control of different dual wall polyethylene pipes used as sewers. Finally, the relevant issues regarding the methods and conditions for technical control and inspection of polyethylene sewer lines during construction and operation stages are provided.