Biological reactors

Where there are large volumes of contaminated water under a small site, it is sometimes most convenient to treat the contaminant in a biological reactor at the surface. Considerable research has gone into reactor optimization for different situations and a variety of stirred reactors, fluidized-bed reactors, and trickling filters have been developed. Such reactors are usually much more efficient than in situ treatments, although correspondingly more expensive. 

If more active treatment is required, such as pump-and-treat, it is possible that biological reactors will be a cost-effective replacement for activated carbon filters (63). 

Dunn, I. J., E. Heinzele, J. Ingham, and J. E. Prenosd, Biological Reactor Engineeiing—Fiinciples, Applications, and Modelling with PC Simulation, VCH, Weinheim, New York, 1992. 

Biological reactors play a valuable role in tlie conversion of substrates by microorganisms and mammalian cells into a wide range of products such as antibiotics, insulin, and polymers. Figures 11-12, 11-13, and 11-14 illustrate various types of biological reactor, and Figure 11-15 shows the physical characteristics of a typical coimuercial fermentation vessel. 

The size of most biological reactors is determined by pollution load, for example, kg BOD (biochemical oxygen demand) or COD (chemical oxygen demand) per kg MLVSS (mixed liquor volatile suspended solids) per day in the case of suspended growth type systems, and kg BOD or COD per m3 of media or reactor volume in the case of fixed-film type systems. 

X Microbial concentration (i.e., VSS) in the biological reactor, mass per unit volume (mg/L)... 

Macy, J. M., Lawson, S., and DeMoll-Decker, H., Bioremediation of Selenium Oxyanions in San Joaquin Drainage Water Using Thauera selenatis in a Biological Reactor System, Appl. Microbiol. Biotechnol., 40 588 (1993)... 

CNC A chemical/biological process for oxidizing cyanide ion in wastewater. The waste-water is mixed with a proprietary soluble reagent and passed through a biological reactor in which cyanide is oxidized to carbon dioxide and nitrogen. Developed and offered by Radian Corporation, Austin, TX. 

However, under dry-weather conditions that may occur around 95% of the time in many countries, chemical and biological sewer processes may exert pronounced effects on sewer performance and on the interaction between the sewer and subsequent treatment processes. Possibly, because researchers and operators interests have been devoted to wet-weather conditions, the biological and chemical performances of a sewer, i.e., the sewer as a chemical and biological reactor, have not been of great concern. It is, however, apparent that the sewer cannot be neglected as a chemical and biological process system. These processes may have impacts on the sewer itself, the treatment plant, the environment and the humans in direct or indirect contact with the sewer. 

Koch, C.M. and I. Zandi (1973), Use of pipelines as aerobic biological reactors. Journal Water Pollution Control Federation, 45, 2537-2548. 

The second main reason for wastewater quality monitoring is related to process control, particularly for treatment plants where analysers and sensors are generally used with physico-chemical or biological reactors, including settling tanks. This application is mainly encountered for important wastewater treatment plants, either urban (majority domestic) or industrial, where the storage capacities are rather small with regard to the flow to be treated. Obviously, on-line systems are preferable in this case, but the available instruments often limit the choice. 

Fermentation systems obey the same fundamental mass and energy balance relationships as do chemical reaction systems, but special difficulties arise in biological reactor modelling, owing to uncertainties in the kinetic rate expression and the reaction stoichiometry. In what follows, material balance equations are derived for the total mass, the mass of substrate and the cell mass for the case of the stirred tank bioreactor system (Dunn et ah, 2003). 

An overall treatment concept using the above unit operations is shown in Figure 9. This flow sketch presents some of the process considerations which may be required in industrial waste-water treatment design. The biological reactor is the key to... 

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