2. Parameters characterizing a bioreactor

The presence of the living microorganisms inside the bioreactor makes it more complicated than the  conventional  chemical  reactor.  As  already  indicated,  it  is extremely important to gather the knowledge about the state of the bioreactor prior to  design  and  implementation of  any  control system for the reactor. The complete state of the  biochemical  reactor  can  be   assessed    by    knowing    the   following   parameters:   physical   parameters,  chemical (extracellular) parameters,    biochemical (intracellular),    and    biological    parameters.³   The   following subsections will list the various parameters in each category. The common methods for the determination of these parameters are discussed in section 9.2.

2.1 Physical parameters

The  following  are  the  important  physical  parameters  for  the operation of a bioreactor: agitation power,  agitation speed,  broth volume,  color,  expanded broth volume (density), foaming, gas flow rate, gas humidity, heat generation rate, heat  transfer  rate,  liquid  feed rate, liquid level,  mass,  osmotic pressure, pressure, shear rate, tip speed, temperature, turnover time, and viscosity.³ Many of these parameters have important implications in the control of bioreactors.

2.2 Chemical Parameters

The following list  gives  the  different  parameters  that  define  the  chemical  environment inside  the  reactor:  amino  acids, carbon dioxide (gas), cation level, conductivity, inhibitor, intermediate(s),   ionic strength,    malliard    reaction   products,   nitrogen (free and total), nutrient composition, oxygen, pH, phosphorous, precursor, product, redox and substrate.³

2.3 Biochemical (intracellular) parameters

Biochemical parameters are the intracellular  parameters  that  indicate the metabolic state of  the   cell   at   any   given   time   during   the   cell  growth.  These  include  amino  acids, ATP/ADP/AMP,    carbohydrates,    cell     mass    composition,     enzymes,    intermediates, NAD/NADH, nucleic acids, total protein, and vitamins.³

2.4 Biological parameters

Biological parameters characterize the bioreactor in terms of what is happening inside the reactor    at    the    cellular   level.   The   list   includes   age/age   distribution,  aggregation, contamination,  degeneration,  doubling time,  genetic  instability,   morphology,   mutation, size/size distribution, total cell count and viable cell count.³