Water bioreactor design

The treatment of PAH-contaminated soil in a reactor environment is basically limited to the use of soil slurry reactors. Conversely, many different bioreactor designs exist for the treatment of water contaminated with PAHs. As reviewed by Grady (1989) and Grady Lim (1980), these include fixed film reactors, plug flow reactors, and a variety of gas-phase systems, to name a few. Given the depth and magnitude of such a topic, for the purposes of this review discussions will be limited to a generic overview of reactor applications for PAH bioremediation. 

Figure 5 Bioreactor design for treatment of arsenic-contaminated water. (From Ref. 59.)...

These issues, positive and negative, are reflected in the available correlations. These correlations are both highly useful and also limited. Some are useful because the inputs are easily measured and adjusted as needed however, correlations are mostly empirical or semi-empirical, which means that they are not widely applicable but, rather, are bioreactor design dependent at best. Hence, geometric similarity is very important. Furthermore, most studies are performed in air-water systems while most industrial processes use much more complicated and time-variant liquids. In other words, the airhft bioreactor correlations have similar problems as those for stirred-tank bioreactors and bubble columns and are due to the fact that they share the problem source bubble-bubble interactions. Bubble-bubble interactions are highly variable and lead to hydrodynamics which, in turn, are difficult to quantify and predict. Hence, the result has been that the airlift bioreactor correlations and models are either system dependent or not adequately constrained. 

Design and development of an electro spray bioreactor was reported and its suitability for biodesulfurization applications was demonstrated [261], Mixing oil with water in large bioreactors requires significant energy input for classical impeller-based reactors. The electro spray bioreactor (ESB) was developed from an emulsion phase contactor... 

The system design is based on two upflow anaerobic bioreactors (ABRs) followed by three horizontal sub-surface flow (HSSF) wetlands cells. The water flows by gravity through the cells. Once treated, the water is stored in a holding pond and subsequently used for irrigation of a tree farm. 

The design characteristics outlined in Table XXV allow this reactor to treat various kinds of waste water biologically in extremely short periods. For example, a waste water of initial BOD, = 850 mg/1 had its value reduced to 30 mg/1 during a mean residence time of 17 min. Compared with a conventional concrete basin, the volume of the reciprocating bioreactor required for purification of a given flow rate can be reduced to approximately 1/30 or 1/60. 

Drews A and Kraume M. Process improvement by application of membrane bioreactors. Chem Eng Res Design. 2005 83(A3) 276-284. Cornel P, Wagner M, and Krause S. Investigation of oxygen transfer rates in full scale membrane bioreactors. Water Sci Technol. 2003 47(11) 313-319. 

An example of integration of part of the downstream processing in the actual bioreactor is two-liquid-phase biocatalysis (see above), in which the organic-solvent phase is used as extractant for the product. The liquid-impelled loop reactor (Fig. 7.3) is specifically designed for this purpose. It is based on the well-known air-lift principle, but instead of air, a water-immiscible, heavier or lighter organic solvent is injected. 

When designing a bioreactor for lipolysis for preparative scale or larger, the use of immobilized lipases is essential to facilitate reusability and recovery of the biocatalyst from the reaction medium. The major issue to decide is the relative amounts of water and TAG, and the means of contacting the two poorly miscible liquids. The most common approach, to employ rapid stirring, resulting in either water-in-oil or oil-in-water... 

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