Removal of Trichloroethylene from water by adsorption on to multiwall carbon nanotubes

Groundwater recourses may be contaminated with trichloroethylene [TCE] which is used in electronic, electric, dry cleaning and other similar industries and often treated by air stripping, which TCE in its vapor form is stripped from groundwater by air and is emitted into the atmosphere without any additional treatments. Carbon nanotubes are expected to play an important role in sensing, pollution treatment and separation techniques. In this study adsorption of trichloroethylene on multiwall carbon nanotubes has been investigated. The effect of contact time, pH, initial concentration of trichloroethylene and temperature on its adsorption were investigated. Adsorption isotherms and related constants were also determined. Results showed that contact times to reach equilibrium changed from 30 min [for 150 microg/L initial concentration] to 10 min [for 600 microg/L concentrations] at 25 [degree sign]C; the equilibrium times in 40[degree sign] C were 40 min and 15 min, respectively. Multi-wall carbon nanotubes showed to act as a good adsorbent for TCE in a wide range of pH=[3-9]. For pH>9, adsorption decreased due to ionization of oxygen-containing groups. Adsorption test results revealed that TCE adsorption on the studied adsorbents could be better described by Freundlich isotherm

[Determination the level of dust and free silica in air of Khaf iron stone quarries]

Silica is an inorganic material that found in the nature in various forms. The hazards of crystal of silica or ?-quartz [free silica] is greater than other forms. Exposure to dust that contains free silica result to pulmonary injury and result to silicosis and death finally. The present research was conducted in order to evaluate the level of workers exposure to free silica in air of Khaf Iron stone quarries. The exposure level to total and respiratory dust measured based on personal and environmental sampling methods and concentration of dust determined based on gravimetric method. For determination of amounts of free silica, dust samples analyses based on X-ray diffraction [XRD] method, and results compared with standard levels. The maximum amount of total dust and free silica measured in stone breaking station [800 +/- 155mg/m3 and 26.11 +/- 6.7 mg/m3] and minimum of them measured in official and safeguarding station [8.28 +/- 2.2 mg/m3 and 0.012 +/- 0.0019 mg/m3]. The maximum amount of respiratory dust and free silica measured in red mound digging number 1 [66.14 +/- 13.45 mg/m3 and 1.48 +/- 0.39 mg/m3] and minimum of them measured in air hammer machine station [5.26 +/- 2.62 mg/m3 and 0.01 +/- 0.005 mg/m3]. Amount of total dust only in official and safeguarding station was lower than standard levels of Iran. Amount of respiratory dust in all stations was greater than Iran standard levels. Furthermore the level of respiratory free silica only in airy hammer machine station was lower than standard level of Iran. Regarding to this amounts it is so essential to that with applying different methods generation and emission of dust protected

Evaluation of hollow fiber membrane bioreactor efficiency for municipal wastewater treatment

The membrane bioreactor technology has been proven to be a single step process in efficient treatment of wastewater, either directly or after pretreatment by reverse osmosis. In this study, a pilot scale experiment was studied to treat a synthetic municipal wastewater sample. The aerobic reactor with a submerged membrane used in this work was continuously aerated for organic matter oxidation, nitrification and phosphorous uptake as well as for fouling control. The mixed liquor was recycled from the aerated zone to the anoxic zone for denitrification. The membrane had a nominal pore size of 0.1 micro m and a filtration area of 4.0 m2. The performance of submerged membrane bioreactor was examined in order to determine the removal efficiency of organic compounds and nitrogen in different solid retention times [10, 20, 30, and 40 days] under a continuous inflow of the synthetic municipal wastewater. Results indicated that the submerged membrane bioreactor could efficiently remove the pollutants. Average removal rates of chemical oxygen demand, total Kejeldahl nitrogen removal, total nitrogen and phosphorous reached to as high as 99.3%, 98.1%, 85.5%, and 52%, respectively. Furthermore, concentrations of nitrate and nitrite in the last stage were well reduced and reached to 5.3 and 0.047 mg/L, respectively