جستجوی مقالات مرتبط با کلیدواژه « sand filter » در نشریات گروه « مهندسی آب »

Organic pollutants soluble in water such as chlorine compounds, biphenyls and aldrins caused by dyes, detergents, herbicides and toxins cannot be removed in conventional purification processes such as filtration. Carbon nanotubes have a high ability to separate organic pollutants, but its slurry application is not desirable due to the need to remove them at the end of purification. In the present study, upgraded carbon nanotubes attached to particles of sand filters (CNTsand) were synthesized and used to remove organic pollutants. The capacity and efficiency of these nanotubes and the variables affecting it including pH, temperature, contact time and concentration were investigated. Also, reaction kinetics and adsorption isotherms were analyzed. The results showed that CNTsand has a high capacity to remove organic compounds. The data processing showed the pseudo-second order kinetic model for the elimination reaction and the Langmuir isotherm was the most consistent. The reaction enthalpy change equal to ΔH=11.02 kJ/mol and the free energy change from ΔG=-7.32 to -9.20 kJ/mol both indicate an endothermic and thermodynamically spontaneous reaction. Therefore, the adequacy and efficiency of the upgraded nanotube coating on sand grains in removing organic pollutants was confirmed.

Granular media including rapid gravity sand filters are used in water and wastewater treatments. When sand filters are clogged due to deposits of particles and particul-bound pollutants, it will lead to head loss and under this situation it is necessary to perform filter backwashing. Prediction of sand filter head loss is the major focus of this study. To meet the primary ojective of this study, a single-layer rapid gravity filter with sandy media was tested with inflow water containing different concentrations of lead (Pb). The amount of deposited sediments and the resulting head loss were simulated in the filter media by combination of Karman-Cozeny, Rose and Gregory equations under different discharges. The maximum time to reach the various amounts of head loss was obtained when the inflow lead concentration was lowest (25 ppm) and the surface filter leading was the highest (6.22 m3/m2/hr). The highest lead removal efficiency (92%) was obtained when the input lead concentration was 25 ppm and filter surface loading was 3.11m3/m2/hr. Comparing the specific head loss under different operating condition it has been shown that the time difference is less under lower head losses of 5 and 7 centimeters. In addition, the slopes of filtration discharge under similar operating condition showed to be steeper verifying a higher filtration performance when the concentration of input lead and filter surface loading was lower.

The aim of this study was to investigate the application of micro-filtration and ultra-filtration membrane systems in order to improve the physical and microbial quality and the reuse of backwash water from the sand filter units in water treatment plants. The backwash water from filters makes up for 3 to 5 percent of the total water treated, which is disposed in most WTPs. However, the treatment and reuse of the backwash water is more admissible from technical and economic viewpoints, especially in view of the present water scarcity. For the purposes of this study, use was made of membrane modules of micro- and ultra-filters on a pilot scale. The micro-filter employed consisted of a polypropylene membrane module with a porosity of 1 micron in size and a fiberglass module with a porosity of 5 microns. The ultra-filter was made of PVC hollow fiber with a molecular weight of 100,000 Dalton. In order to feed the two pilots, backwash water from a sand filter was collected from one of the WTPs in Tehran. After samples were taken from the backwash water, the physical and microbial removal efficiency was periodically evaluated based on the standard method and the micro-filtration, ultra-filtration, and combined MF/UF processes were compared with respect to their performance. The results indicate that the combined MF/UF process is able to decrease turbidity, MPN, COD, TSS, and Fe with efficiency values of 99.9, 100, 61.5, 99.9 and 98.8 percent, respectively. Overall, the findings confirmed the technical capabilities of this method for the recovery and reuse of the effluent produced in the backwashing mechanism of sand filters in WTPs.