vahid Moradinasab; mehran shirvani; shamsollah Ayoubi; mohammad reza babaei
Abstract
Introduction: Water shortage in arid and semiarid regions of the world is a cause of serious concerns. The severe water scarcity urges the reuse of treated wastewater effluent and marginal water as a resource for irrigation. Mobarake Steel Complex has been using treated industrial wastewater for drip-irrigation ...
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Introduction: Water shortage in arid and semiarid regions of the world is a cause of serious concerns. The severe water scarcity urges the reuse of treated wastewater effluent and marginal water as a resource for irrigation. Mobarake Steel Complex has been using treated industrial wastewater for drip-irrigation of trees in about 1350 ha of its green space. However, wastewater may contain some amounts of toxic heavy metals, which create problems. Excessive accumulation of heavy metals in agricultural soils through wastewater irrigation may not only result in soil contamination, but also affect food quality and safety. Improper irrigation management, however, can lead to the loss of soil quality through such processes as contamination and salination. Soil quality implies its capacity to sustain biological productivity, maintain environmental quality, and enhance plants, human and animal health. Soil quality assessment is a tool that helps managers to evaluate short-term soil problems and appropriate management strategies for maintaining soil quality in the long time. Mobarakeh Steel Complex has been using treated wastewater for irrigation of green space to combat water shortage and prevent environmental pollution. This study was performed to assess the impact of short- middle, and long-term wastewater irrigation on soil heavy metal concentration in green space of Mobarake Steel complex.
Materials and Methods: The impacts of wastewater irrigation on bioavailable and total heavy metal concentrations in the soils irrigated with treated wastewater for 2, 6 and 18 years as compared to those in soils irrigated with groundwater and un-irrigated soils. Soils were sampled from the wet bulb produced by under-tree sprinklers in three depths (0-20, 20-40 and 40-60 cm). Soil samples were air-dried, and crushed to pass through a 2-mm sieve. Plant-available metal concentrations were extracted from the soil with diethylenetriaminepentaacetic acid-CaCl2-triethanolamine (DTPA-TEA). To determine the total concentration of heavy metals, the soil samples were digested in 6 M HNO3. Concentrations of heavy metals in the extracts were determined by Atomic Absorption Spectroscopy. Finally, available metal micronutrient levels in the soil were compared with the critical deficiency ranges suggested for calcareous soils. Also, total concentrations of the metals in the soils were compared with the standards of the Iranian Environmental Protection Agency to assess possible contamination of soils with heavy metals in the studied area.
Results and discussion: The results of this study showed significant increases of plant-available Fe in the soils irrigated with wastewater for 6 and 18 years as compared to the unplanted control. Regardless of the type of irrigation water used, available Mn and Ni were significantly increased in all forested areas as compared to the unplanted soils. Available Zn fraction was significantly higher in the soils with history of 6 and 18 years of wastewater irrigation. Increase in available Cu concentration was statistically significant only in the soils irrigated with wastewater for 18 years. As the metal concentration in the wastewater used for irrigation was very low, it seems that the major source of metal accumulation in the soils is particulate fallout or emissions directly from the dump sites and metal plating operation. Furthermore, irrigation and forestation practices might have improved bioavailability of micronutrient metals in the soils of green space of Mobarakeh Steel complex through increasing organic matter content of the soils which enhances metal chelation reactions.
Total concentrations of the metals in the forested soils also increased as compared to those of the control. Total Fe, Mn, and Zn concentrations were notably higher in all soils of the green space area as compared to those in the unplanted control sites. Wind-driven particle transport from dumping site to nearby soils may be the main reason for metal build-up in the green space soils. Total concentration of Cu showed no significant difference among the soils of the treatments and the control. Although metal accumulation has been occurring in the soils of the Mobarakeh Steel complex green space, total concentrations in the soils were still considerably lower than the allowable levels recommended by the Iranian Environmental Protection Agency.
Conclusions: The results of this study revealed that metal accumulation has been occurring in the green space soils of the Mobarakeh Steel complex. Considering the short distance of the dumping and metal smelting sites with the green space and very low concentrations of metals in wastewater, in may be concluded that fall out of metallic particles on the soil surfaces from the dumping and smelting sites is the main route for metals accumulation in the soils of the green space areas.
Marzieh tavanaei; somayeh bakhtiari; mehran shirvani
Abstract
Introduction: Heavy metals contamination due to natural and anthropogenic sources is a global environmental concern. Lead (Pb) is one of the very toxic heavy metals. Industrial production processes and their emissions, mining operation, smelting, combustion sources and solid waste incinerators are the ...
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Introduction: Heavy metals contamination due to natural and anthropogenic sources is a global environmental concern. Lead (Pb) is one of the very toxic heavy metals. Industrial production processes and their emissions, mining operation, smelting, combustion sources and solid waste incinerators are the primary sources of lead. This heavy metal has aberrant effects on the environment and living organisms. Hence, proper treatment of lead from soil and industrial wastewaters is very important. In order to remove toxic heavy metals from contaminated water systems, conventional methods such as chemical precipitation, coagulation, ion exchange, solvent extraction and filtration, evaporation and membrane methods are being used. These conventional methods generally have high costs and technical problems. Therefore, biosorption processes, in which microorganisms are used as sorbents, have been considered as economical and environmentally friendly options for removal of heavy metals from aqueous solution. Clay minerals are another group of sorbents used in removal of heavy metals from polluted environments. Furthermore, bacterial cells can be attached on clay mineral surfaces and form bacteria-mineral composites. These composites adsorb heavy metals and convert them into forms with low mobility and bioavailability. Pseudomonas putida is a unique microorganism with a high tendency to sorb and/or degrade certain environmental pollutants. Palygorskite and sepiolite are the fibrous clay minerals of arid and semiarid regions; their structures consist of ribbons and channels. These fibrous minerals have various applications in industry and the environment because of its large surface area and high adsorption capacity. The present study was conducted in order to determine the ability of Pseudomonas putida (P168), and its composites with palygorskite and sepiolite in lead sorption.
Materials and Methods: The bacterial strain used in the present study was Pseudomonas putida (P168) grown and maintained on Nutrient Broth (NB). The population of living and non-viable bacteria in suspension was determined by an optical microscope. The minerals used in this study were palygorskite from Florida (the Source Clay Minerals Repository, Purdue University, IN) and sepiolite from Yazd (Iran). The clay samples were ground and passed through 0.05 mm (mesh #270) sieve. The clays were then saturated with calcium chloride (0.5 M) and washed free of salts. Batch experiments were performed to measure Pb sorption by Pseudomonas putida. For this purpose, 10-ml aliquots of bacterial suspension (7.24×107 cells ml-1) were added to10 ml solutions containing Pb with concentration ranged from15-110 mg L-1. The mixtures were gently shaken at 30 ◦C for 24 h and centrifuged at 3000 rpm for 20 min. The concentration of Pb in the supernatants was finally measured by atomic absorption spectrometer. The percentage of sorbed Pb was determined by subtracting the amount of unabsorbed Pb from that initially added. Various hybrids of P. putida and clays were also exposed to solution of 0.5 mM Pb in 0.01 M KNO3 to determine the role of composites in sorption of Pb. Langmuir and Freundlich adsorption isotherms were chosen to describe the biosorption equilibrium data. GraphPad Prism 5.0 was used for determining the isothermal parameters using non-linear regression analysis. Data were analyzed with the Statistical Analysis System (SAS). Experimental design was factorial in form of complete randomized block.
Results and Discussion: Pseudomonas putida showed a considerable capacity to sorb Pb ions. Lead sorption isotherms were sufficiently fitted with the Langmuir and Freundlich models. The Pb sorption isotherms by P. putida were L-type showing a high affinity of P. putida for Pb ions. Lead sorption capacity (qmax) of P. putida was estimated to be 582.4 mg g-1 and its Langmuir constant (KL) was found to be 0.11 mg L-1. The experimental data of lead sorption (7.5-55.5 mg L-1 initial concentration) by P.putida (P168) demonstrated that about 31.5% to 78.4% of the intial concentration of Pb was taken up by these bacteria. Sorption of Pb decreased with the increase of bacteria in the bacteria-clay composites, which may be due to the occupation of adsorption sites on the clay surface by the bacteria. Composites of bacteria-sepiolite were more effective than bacteria-palygorskite in Pb sorption due to the larger channel dimensions, greater surface area, and more functional groups of sepiolite than palygorskite. LSD test showed that there were significant differences between the hybrid sorbents with different ratios and single bacterial cells in Pb sorption.
Conclusion: The results showed that P. putida and its composites with palygorskite and sepiolite clays exhibited a high potential for the removal of Pb from aqueous solutions.
Ahmadreza Sheikhhosseini; H. Shariatmadari; M. Shirvani
Abstract
Introduction: Pollution of soil and water environment by release of heavy metals is of great concerns of the last decades. Sorption of heavy metals by low cost materials is considered as an inexpensive and efficient method used for removal of heavy metals from soil-water systems. The presence of different ...
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Introduction: Pollution of soil and water environment by release of heavy metals is of great concerns of the last decades. Sorption of heavy metals by low cost materials is considered as an inexpensive and efficient method used for removal of heavy metals from soil-water systems. The presence of different ligands with various complexing abilities can change the sorption properties of heavy metals and their fate in the environment as well. In order to assess the effect of citrate and arginine as natural organic ligands in soil environment, in a batch study we investigated the effects of these ligands on equilibrium sorption of nickel to sepiolite and calcite minerals and also kinetics of Ni sorption by these minerals.
Materials and Methods: Minerals used in this study included sepiolite from Yazd (Iran) and pure calcite (Analytical grade, Merck, Germany). Sepiolite was purified, saturated with Ca using 0.5 M CaCl2, powdered in a mortar and sieved by non-metal 230 mesh standard wire sieve. For equilibrium sorption study, in a 50-mL polyethylene centrifuge tube,0.3 g sample of each mineral was suspended in 30 mL of a 0.01 M CaCl2 solution containing 0, 5, 10, 20, 40, 60, 80 and 100 mg L-1 Ni (NiCl2) and containing zero (as control) or 0.1mmol L-1 citrate or arginine ligands. The applied concentrationsfor each ligand can naturally occur in soils. Preparedtubes were shaken (180±2 rpm, 25±1oC) for 24 h using an orbital shaker and centrifuged (4000×g for 10 min) and the supernatants were analyzed for Ni concentration using an atomic absorption spectrophotometer (AAnalyst 200 Perkin-Elmer) at a wavelength of 232 nm and a detection limit of 0.05 mg L-1. The quantity of Ni retained by each mineral at equilibrium was calculated using equation qe = (Ci - Ce)V/W where qe was the amount of nickel retained by mineral surface at equilibrium. Ci and Ce were the initial and the equilibrium concentrations (mg L-1) of Ni, respectively, V was the volume (L) of the solution, and W was the mass (g) of the sorbent. The Langmuir, Freundlich and linear isotherm models were fitted to sorption data using Graphpad prism 5.0. For kinetic study,30 mL of 0.01 M CaCl2 solution, with or without 0.1 mM citrate or arginine, containing Ni at a concentration corresponding to the maximum sorption capacity of each mineral (estimated from sorption isotherms) were transferred into 50-ml polyethylene centrifuge tubes containing 0.3 g of sepiolite or calcite. The suspensions were shaken (180±2 rpm, 25 °C) continuously and after 0.5, 1.5, 3, 6, 12, 18 and 24 hours, corresponding tubes were centrifuged (4000×g for 10 min) and supernatants were analyzed for Ni concentration by atomic absorption spectrophotometer. Using Graphpad prism 5.0, kinetic data were fitted to Pseudo-first order, pseudo-second order and power function kinetic models.
Results: With or without ligands, the Langmuir model was the best description of Ni sorption to sepiolite while the linear model was the best fit of calcite data showing the physical nature of Ni sorption by this mineral. Kinetics of Ni sorption to sepiolite and calcite were best described by power function model. In the presence of citrate, both capacity and rate of sorption of Ni to sepiolite decreased. There was no considerable change in sorption of Ni to calcite. In the presence of arginine, however, sorption capacity of minerals for Ni increased. Arginine enhanced the rate of Ni sorption on all three minerals. Citrate showed opposing effects on Ni sorption kinetics depending on the studied minerals. Totally, citrate and arginine had opposite effects on sorption of Ni to sepiolite and calcite.
Conclusion: Organic ligands can change sorption characteristics of the minerals. It seems that citrate decreases sorption of Ni to sepiolite but its effect on Ni sorption to calcite is negligible, while arginine increases Ni sorption to both minerals. Our results suggested that presence of citrate and arginine in soil influence Ni sorption by soil minerals. As in warmer seasons of year,microbial activities due to optimum temperature and moisture result in production of citrate and argininewhich facilitate and suppress uptake of Ni by plants respectively. Production of citrate in soil may increase risk of Ni contamination of underground and surface water sources while arginine can decrease soil solution Ni and in turn the risk of water contamination.
H.R. Rafiei; M. Shirvani; T. Behzad
Abstract
The remediation of soils and water contaminated with heavy metals generate a great need to develop efficient adsorbents for these pollutants. This study reports the sorption of lead (Pb) by bentonite (Bent), and sepiolite (Sep), that were modified with cetyltrimethyl ammonium (CTMA+) organic cations. ...
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The remediation of soils and water contaminated with heavy metals generate a great need to develop efficient adsorbents for these pollutants. This study reports the sorption of lead (Pb) by bentonite (Bent), and sepiolite (Sep), that were modified with cetyltrimethyl ammonium (CTMA+) organic cations. The natural and surfactant modified clays (organo-clays) were characterized with some instrumental techniques including XRF, XRD, FTIR and SEM. Sorption studies were performed in a batch system, and the effects of various experimental parameters including contact time and initial Pb concentration were evaluated upon the Pb sorption onto sorbents. Maximum sorption of Pb was found to be, 83.26, 71.36, 56.25 and 37 mg g-1 for Sep, CTMA-Sep, Bent and CTMA-Bent adsorbents, respectively. The Pb sorption data were fitted to both the Langmuir and Freundlich models. The Freundlich model represented the sorption process better than the Langmuir model. Lead sorption rate was found to be considerably slower for organo-clays than that for unmodified clays. Sorption kinetics was evaluated by pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion models. The sorption processes of organo-clays followed intraparticle diffusion kinetics. The results showed that the cationic surfactant modified bentonite and sepiolite sorbed less Pb than the unmodified clays.
