**1. Introduction**

370 Mass Transfer - Advanced Aspects

[12] Polprasert, C. and Raghunandana, H. S., Wastewater treatment in a deep aeration tank.

[13] Gnirss, R. and Peter-Frölich, A., Biological treatment of municipal wastewater with

[14] Asselin, C., Comeau, Y. and Ton-That, Q. A., Alpha correction factors for static aerators

[15] Gillot, S. and Héduit, A., Effect of air flow rate on oxygen transfer in an oxidation ditch

[16] Omatsu, R., Energy-saving efficiency of fine bubble diffuser in actual operation.

[17] Gillot, S., Capela-Marsal, S., Roustan, M. and Héduit, A., Predicting oxygen transfer of

[18] ASCE, Standard for the measurement of oxygen transfer in clean water, 2nd ed. ASCE,

[19] Sewerage Facilities Planning and Design Manual (Volume 2), Japan Sewage Works

deep tanks and flotation for secondary clarification. *Water Sci. Technol.*, 34, p.257-

and fine bubble diffusers used in municipal facultative aerated lagoons. *Water Sci.* 

equipped with fine bubble diffusers and slow speed mixers. *Water Res.*, 34, p.1756-

fine bubble diffused aeration systems-model issued from dimensional analysis.

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1762, 2000.

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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 plants.

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 these processes.

Microcontaminant Sorption and Biodegradation in Wastewater Modeled as a Two-Phase System 373

Having defined it as a two-phase system, the initial focus will be on the differential volume indicated by the ΔZ (and multiplied by A) in Figure 3. This differential volume is shown

For this volume, a mass balance on the target compound in both phases is performed. First,

(Change) = (Flow in with aqueous phase) – (Flow out with aqueous phase) + (flux from

.. . . *in out sorb* \_ *flux bio*

=− + − (1)

0 =− +− *QC QC V j V r Z ZZ* +Δ *aq sl aq bio* (2)

*mm m m*

Because the differential volume is extremely small, it is assumed to be at steady state, and so

as a word formulation and then as the mathematical representation of that phase:

**2.1.1 Compound mass in the aqueous phase in the differential volume** 

aqueous phase to solid phase) – (biodegradation in aqueous phase)

*dm*

*dt*

Fig. 2. Schematic of a plug flow reactor (PFR)

more clearly in the following figure.

Fig. 3. Close-up of the differential volume

the overall change is mass is zero.
