Introduction

The inclusion of living systems into chemical processes creates the area of biochemical processes. As such, the life sciences must be combined with chemistry, physics, and the engineering sciences to deal with these processes.

The nature of the living systems means that the processes must be operated within narrow limits so that these systems can function optimally. Further, system stability can be affected adversely by the complexity of the biochemistry. This requires the practicing engineer to be aware of the behavior of the living systems used in biochemical processing.

Microorganisims; characteristics; uses

Biochemical processing enhances the use of microorganisms, which are a large and varied group. Members of the group include algae, bacteria, fungi (molds and yeasts), protozoa, and viruses. The principal microorganisms involved in biochemical processing are bacteria, molds, and yeasts.

Table 9-1 summarizes these latter members by structure and size.

Bacteria reproduce asexually while yeasts and molds can reproduce either asexually or sexually. Temperature ranges for optimum microorganism growth lead to a classification: psychrophiles (below 20 C); mesophiles (20 to 45 C); thermophiles (45 to 60 C). Other important parameters are pH ranges and relation to the presence of oxygen (i.e., aerobic, in which free oxygen is required; anaerobic, requiring the absence of oxygen). Table 9-2 summarized such data for bacteria, yeasts, and molds.