Biological reactor conditions

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. 

It is not only the properties of the compound in question that influence its behaviour but also the environmental and operational conditions it is subjected to (temperature, pressure, pH, redox conditions), as well as the particular configurations of the (biological) reactors (in particular, their partitioning into compartments featuring different conditions mainly aerobic, anoxic and anaerobic), SRT and, to variable extents, HRT. Moreover, in chemical processes, reagent... 

They previously developed a consortium (i.e., a mixture) of microorganisms that could be immobilized in biological reactors and that was subsequently used to define process conditions for the treatment of an HE-contaminated waste stream. In this feasibility study performed jointly by LLNL and UCLA, experiments were conducted to define the tolerance of this denitrifying consortium to salinity and dilutions of base hydrolysate. 

Intermediate periodic operation lies between both extremes and covers systems in which the response time is of the same order as the imposed function cycle time so that resonance is possible. Here the state of the mechanism changes dynamically and is not directly related to the environmental conditions at the moment considered. Intermediate periodic operations encompass semibatch periodic operations, selectivity in periodically forced CSTRs, cycled reactors with heterogeneous catalysts, and non-steady-state biofilm reactors (e.g., Rittmann and McCarty, 1981). Lag, overshoot phenomena, and oscillations can typically occur. Biological reactor operation will basically fall into this latter class of operation, and balanced growth must be distinguished from steady-state growth (Barford et al., 1982). 

In this section, we discuss in detail how the selection of various experimental parameters affects each of these conditions. One of the first studies on EIS measurements in MXC applications by Strik et al. [29] covers some of these conditions very well, but we provide an expanded explanation here. While all these conditions are especially difficult to fulfill in a typical electrochemical cell, the conditions used in MXCs further exacerbate the problem. For example, it is known that polarization curves for microbial anodes exhibit nonlinear, Nernstian responses [30]. Thus, there are regions in the polarization curve where the system may not behave linearly even when small amplitudes are applied. The irreversibility of the enzymatic responses also leads to regions where finiteness is not met (Fig. 8.6). These cases would run also into difficulties in terms of the signal-to-noise ratio when small amplitudes are applied at potentials on the saturation region of the polarization curve. Similarly, as MXCs are biological reactors and can have changes in microbial responses due to small perturbations outside the conttol of researchers, conditions of both stability and causality are difficult to fulfill. 

Special reactors are required to conduct biochemical reactions for the transformation and production of chemical and biological substances involving the use of biocatalysts (enzymes, immobilised enzymes, microorganisms, plant and animal cells). These bioreactors have to be designed so that the enzymes or living organisms can be used under defined, optimal conditions. The bioreactors which are mainly used on laboratory scale and industrially are roller bottles, shake flasks, stirred tanks and bubble columns (see Table 1). 

The comparison of the results obtained from model particle systems with experience of biological systems shows a similar tendency on many points. Therefore it proved to be very advantageous for the basic investigations, especially for the comparison of different reactor types, to use suitable model particle systems with similar properties to those of biological material systems. This permitted the performance of test series under technically relevant operating conditions, similar to those prevailing in bioreactors, in a relatively short time. The results are more reproducible than in biological systems and therefore permit faster and more exact optimization of reactors. 

Chakrabarti, T. and Subrahmanyam, P.V.R., Biological hydrolysis of urea in a continuous flow stirred tank reactor under laboratory conditions—a bench scale study, Proc. 36th Industrial Waste Conference, Purdue University, pp. 477, 1981. 

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