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Subsurface movement of polychlorinated biphenyls
Published in Domy C. Adriano, Alex K. Iskandar, Ishwar P. Murarka, Contamination of Groundwaters, 2020
Thomas E. Hemminger, Benjamin J. Mason
Vaporization of the PCB isomers from pure chemical plated onto a surface generally is dependent upon the degree of chlorination. Haque and Kohnert (1976) reported half-lives for vaporization ranging from 5.2 m for 4-monochlorobiphenyl to 1.6 d for 2,2’,4,4’5,5’-hexachlorobiphenyl. Figure 9 shows the effect of chlorination on the rate of PCB volatilization from pure isomer and from a dry sand. The data for this figure were taken from Haque et al. (1974) and Haque and Kohnert (1976). Haque et al. (1974) note that the vapor loss from Woodburn soil was negligible when compared to planchets or dry sand samples. Girvin and Sklarew (1986) stated that ‘‘the mass transfer coefficient is three and one-half orders of magnitude less in soil than in air...”. (The mass transfer coefficient is a measure of transfer of a chemical from one phase to another.)
The Removal of Phenol and Phenolic Compounds from Wastewater Using Reverse Osmosis
Published in Iqbal M. Mujtaba, Thokozani Majozi, Mutiu Kolade Amosa, Water Management, 2018
Mudhar A. Al-Obaidi, Chakib Kara-Zaïtri, Iqbal M. Mujtaba
It is worth noting the mass transfer coefficient is basically affected by the solvent flux, flow rate, solute concentration, and both the solvent and solute properties [41]. The mass transfer coefficient also varies along the x-axis dimension. So, the impact of all these factors can be correlated in Equation 11.2 as follows: () Sh(x)=c1[Rep(x)Ref(x)Cm(x)Scp(x)Scf(x)]c2
Mass Transfer: Membrane Processes
Published in Shyam S. Sablani, M. Shafiur Rahman, Ashim K. Datta, Arun S. Mujumdar, Handbook of Food and Bioprocess Modeling Techniques, 2006
David Hughes, Taha Taha, Cui Zhanfeng
When used species such as dextran, the model is particularly useful for maximizing the hydrodynamic benefits of enhancement techniques such as gas sparging or spiral inserts. The steady-state flux in the UF of dextran, when operated under constant TMP, is controlled by concentration polarization. To improve performance in such a system, the mass-transfer coefficient must be increased. Conventionally, this is done by increasing the crossflow velocity in the module, which increases wall shear stress and therefore increases mass-transfer coefficient. However, this approach can be energy intensive because of the high pumping costs incurred. One method of increasing the mass-transfer coefficient without using high crossflow velocities is gas sparging. A gas, usually air, is injected into the feed stream just before the module and forms bubbles. As the bubbles move thorough the module, they cause high wall shear stresses that change rapidly in both magnitude and direction. This results in a higher overall wall shear, excellent mixing, and therefore an improved mass-transfer coefficient. However, the modelling of the wall shear stress in this process is challenging, requiring the use of computational fluid dynamics due to the unsteady nature of the flow. The Leveque mass-transfer equation is then used in conjunction with the osmotic-pressure model to predict the steady-state permeate flux. As an example, the predicted and experimental permeate fluxes are compared for the gas-sparged UF of 238 kDa dextran solutions.
Novel carbonized bone meal for defluoridation of groundwater: Batch and column study
Published in Journal of Environmental Science and Health, Part A, 2018
Somak Chatterjee, Sanjay Jha, Sirshendu De
Decrease in breakthrough and exhaustion time also occurs with inlet fluoride concentration (Fig. 8c). For example, the breakthrough and exhaustion time are 29 h (number of bed volume 246) and 57 h (number of bed volume 484), respectively, for fluoride concentration of 10 mg L−1; whereas they decrease to 8 h (number of bed volume 67) and 36 h (number of bed volume 305), respectively, for a fluoride concentration of 15 mg L−1. On the other hand, adsorbed amount of fluoride increases marginally for higher influent concentration. For example, the adsorbed fluoride amount by the column is 3.3 and 3.5 mg g−1 for influent concentration of 10 and 15 mg L−1, respectively. Higher transfer rate was observed at an increased concentration gradient, increasing the mass transfer coefficient.[43] Increase in mass transfer zone for higher fluoride concentration corroborates the observation (refer Table S2). Similar observations can be obtained from Yoon-Nelson model parameters, indicating decrease of τyn from 1,734 min to 965 min due to increase in fluoride concentration.