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Design of Pump and Meat Systems
Published in Jimmy H.C. Wong, Chin Hong Lim, Greg L. Nolen, Design of Remediation Systems, 2020
Jimmy H.C. Wong, Chin Hong Lim, Greg L. Nolen
Air stripping is a mass transfer process that is effective in removing VOC. The air stripping process relies on the simple fact that volatile organic compounds (VOC) evaporate more readily than water. In a stripping tower, air and water are run countercurrent through randomly packed structure media. Contaminated water is introduced into the tower through a distributor located near the top of the tower, whereas air from a blower is forced upwards into the tower. The contaminated water trickles through the stack of packing that enhances air/water contact by breaking the water into thin films and exposing a large amount of liquid surface area to the upward flow of air. The VOC evaporate and are carried away by the upward flowing air to the atmosphere or vapor treatment units, such as activated carbon absorption units and thermal destruction units. The clean water that has been stripped of VOC drops to the sump of the tower and subsequently discharges into surface water bodies, sanitary sewers or reinjected into the subsurface. Figure 7.6 depicts a typical air stripping tower system.
Treatment Technologies
Published in Thomas K.G. Mohr, William H. DiGuiseppi, Janet K. Anderson, James W. Hatton, Jeremy Bishop, Barrie Selcoe, William B. Kappleman, Environmental Investigation and Remediation, 2020
William H. DiGuiseppi, James W. Hatton
Air stripping is a common method of removing volatile organic compounds (VOCs) from groundwater because the relationship between solubility and volatility is optimal in this group of contaminants. This method is typically conducted in a packed tower or a low-profile aeration system. Water is introduced to the top of the stripper and flows down through the system under gravity. Air is pumped into the bottom of the stripper under pressure and exits the top. This arrangement, called countercurrent flow, optimizes the exchange of contaminants from water to air. Air stripping is a nondestructive transfer of contaminants from the liquid phase to the vapor phase. The resulting gaseous phase contaminants often require treatment. Granular activated carbon (GAC) adsorption and thermal destruction are commonly used to treat contaminated air before it is discharged to the atmosphere. Although 1,4-dioxane is highly volatile when in pure form, its infinite solubility in water is generally considered to prevent efficient air-stripping removal from groundwater to concentrations suitable for discharge. Nevertheless, several studies have been performed to assess the ability of air stripping to remove 1,4-dioxane from groundwater.
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Published in J. Russell Boulding, Epa Environmental Engineering Sourcebook, 2019
Contaminated water with VOC or semi volatile concentrations greater than 0.01 percent generally cannot be treated by air stripping. Even at lower influent concentrations, air stripping may not be able to achieve cleanup levels required at certain sites. For example, a 99 percent removal of trichloroethene (TCE) from ground water containing 100 parts per million (ppm) would result in an effluent concentration of 1 ppm, well above drinking water standards. Without heating, only volatile organic contaminants with a dimensionless Henry’s law constant greater than 10‒2 are amenable to continuous flow air stripping in aqueous solutions [6; 5]. In certain cases, where a high removal efficiency is not required, compounds with lower Henry’s law constants may be air stripped. Ashworth et al. published the Henry’s law constants for 45 chemicals [10, p. 25]. Nirmalakhandan and Speece published a method for predicting Henry’s law constants when published constants are unavailable [11]. Air strippers operated in a batch mode may be effective for treating water containing either high contaminant concentrations or contaminants with lower Henry’s law constants. However, batch systems are normally limited to relatively low average flow rates.
The application of microalgae in removing organic micropollutants in wastewater
Published in Critical Reviews in Environmental Science and Technology, 2021
Hoang Tam Nguyen, Yeomin Yoon, Huu Hao Ngo, Am Jang
Volatilization can contribute to the removal of volatile and semi-volatile MPs in an open microalgae-based treatment system. The elimination of trace pollutants by volatilization during the microalgae-based process depends on Henry’s law constant of the analyzed trace pollutants, and becomes significant when this value is greater than 10−3 atm m3 mol−1 (Duchowicz et al., 2020). However, most MPs (e.g. pharmaceuticals) are large molecules with low Henry’s law constants (KH < 10−3 atm m3 mol−1) (e.g. diazepam 2.7 × 10−5, diclofenac 3.42 × 10−5, naproxen 2.52 × 10−5, ibuprofen 1.1 × 10−4, sulfamethoxazole 4.68 × 10−5, trimethoprim 1.76 × 10−4, erythromycin 3.96 × 10−5, roxithromycin 1.8 × 10−5, etc.) (Suárez et al., 2008). Thus, volatilization is usually considered negligible. This removal mechanism is also affected by the air stripping intensity and temperature in the system. In any case, volatilization might not be a desired outcome for wastewater treatment, since it converts pollutants only from a liquid phase into the atmosphere instead of degrading them into smaller molecules (Wang, Liu, et al., 2017).