**8. References**

368 Mass Transfer - Advanced Aspects

The *L b k a* and *L s k a* of conventional aeration testings are shown in Table 8 (i.e., *L b k a* = 7.5 hr-1 and *L s k a* = 0.9 hr-1). That is, in a water tank with a water loading of 80 L, aeration depth of 53 cm, and surface area of 1510 cm2, while aerating at an air flow rate of 6 L/min, oxygen transfer amount through water surface has a share of roughly 11% of the overall oxygen

The oxygen transfer of liquid film aeration involves oxygen transfers through gas bubbles, water surface and liquid film. Because the experimental conditions such as aeration depth, aeration amount and gas bubble diameter are identical between the conventional aeration and liquid film aeration, it is reasonable to consider that gas bubble based oxygen transfer capabilities are same in both cases. For the water surface based oxygen transfer ability, liquid film aeration apparatus only occupies a water surface area of 12.56 cm2 out of the total surface area of 1510 cm2, taking up roughly 0.83% of the whole water surface area. Hence, the coverage area from the liquid film apparatus is completely negligible. However, because the disturbance effect of the liquid film apparatus on the water surface can not be estimated (either positive or negative action), in this discussion, water surface based oxygen transfer capacity is hard to be regarded as same in both cases. Accordingly, the liquid film based oxygen transfer capacity can not be accurately quantified. For the liquid-film aeration experiment, the oxygen transfers through the water surface and liquid film are thus

Based upon the reason above, the *L b k a* and *L s k a* of a liquid-film aeration system are derived as 7.5 and 2.1 hr-1, respectively. Namely, the oxygen transfer amount via water surface

As shown in Table 8, water surface based oxygen transfer efficiency by means of liquid film aeration apparatus is enhanced to 2.3 times in relation to that by the conventional aeration

*kLa* (hr-1) Conventional aeration system Liquid-film aeration system

*L t k a* 8.4 9.6 *L b k a* 7.5 7.5 *L s k a* 0.9 2.1

Table 8. Comparative results for *kLa* between the conventional aeration and liquid-film

Through a series of experiments, it is proven that the oxygen transfer rate of liquid-film aeration system is higher than that of conventional aeration system. Furthermore, the former can transiently produce the water with a high DO concentration. Obviously, this efficient aeration process is considered as a less energy-intensive alternative to current aeration

transfer quantity.

summed up as an overall entity.

*kLat*: total volumetric mass transfer coefficient.

*kLab*: volumetric mass transfer coefficient for bubble surface. *kLas*: volumetric mass transfer coefficient for water surface.

setup.

aeration systems.

**7. Summary** 

methods.

accounts for 22% of overall oxygen transfer capacity.


**16** 

Karl J. Ottmar

*United States* 

**Microcontaminant Sorption and** 

**Modeled as a Two-Phase System** 

It has only been within the past 15 years that concern about the presence of pharmaceutical compounds and other emerging contaminants in water and wastewater has garnered the attention of the scientific community. Although earlier research can be documented, it was not until the publication of the overarching analysis by Daughton and Ternes (1999) that scientific investigations began to take off, as evidenced by being cited over 900 times (As of March 2011). One of the key contributions of their research was to highlight the ubiquitous nature of those compounds in the environment and to highlight that their potential impact on human and environmental health was unknown. This work helped to spur one of the largest studies conducted, to date, the 1999 National Reconnaissance conducted by the U.S. Geological Survey (USGS 2003, Kolpin et al. 2003). As part of that study, investigators sampled 139 streams in 30 states and tested for 149 emerging compounds of interest to include hormones, steroids, prescription pharmaceuticals, insecticides, and pesticides. Perhaps the key finding from that survey was that every compound that was tested for was found to be present in the environment. Subsequent studies (Richardson and Ternes 2005, Daughton 2009, Bartelt-Hunt et al. 2009) have reinforced the need for continued research, both in regards to occurrence in surface water systems, as well as wastewater treatment

As the research on the origination of these microcontaminants has progressed, it has become more apparent that wastewater treatment plants play a critical role (Lietz and Meyer 2004, Glassmeyer et al. 2005, Vanderford and Snyder 2006, Yu et al. 2006). These facilities are located at the nexus connecting the anthropogenic with the ecological and, as such, have become a focal point for environmental research, especially in regards to the fate, transport, and occurrence of emerging contaminants. A closer examination of the wastewater treatment process reveals two key fundamental processes: sorption and biodegradation (Joss et al. 2006, Ottmar et al. 2010a). These two processes are intrinsically linked as, in almost all instances, the rate of biodegradation will be related to the concentration of compound present in the aqueous phase, which, itself, is linked to the concentration in the solid phase by the process of sorption. It is this linkage that provides the motivation behind the development of a two-phase model that will account for both of

**1. Introduction** 

plants.

these processes.

**Biodegradation in Wastewater** 

*Ottmar Environmental Science and Engineering* 

