Question

Please provide me a correct and clear answer for these questions.

1. explain the growth curve of bacteria e coli?

2. Draw, label, explain function of each part in cstr bioreactor?

3. types of impeller with picture ?

Thanks in advance

Answer 1

1. E Coli is a bacterium and is mostly reproduced by binary fission, an asexual process, i.e., doubling in the number of bacterial cells.  The time required for a cell population to divide and double in number is called the generation time or the doubling time and it varies with organism and environment. The standard bacterial growth curve consists of various stages namely, lag phase, exponential phase, stationary phase and death phase. The exponential phase and death phase are the logarithmic incline and decline curve tracks. One can track the growth curve by considering the cell growth or estimation of cell number.

During the lag phase, the bacterial population increase in size but show no change in number as they prepare themselves for cell division. The length of the lag phase is determined by the characteristics of the bacterial species and by conditions in the media. The bacterial population then enters an active phase of growth called the logarithmic phase.

During the exponential phase, the bacteria divide exponentially, i.e., the mass of each cell increases rapidly followed by reproduction and the number of bacteria doubles during each generation time. The growth curve is linear during this phase and the cells are metabolically most active. The rate of reproduction and death equalizes as the amount of nutrients decrease. Then, the bacterial population enters into a plateau mode called as stationary phase.

During the stationary phase, the growth rate decreases to a point where it almost equals to the death rate as the nutrients get exhausted, hence the cell number remains the same. This phase follows untill the death phase occurs. In death phase, the viable cell population decreases exponentially as the amount of waste products increases. The death of cells in the population exceeds the formation of new cells. This continues until the population is diminished to a tiny fraction of the more resistant cells or the population might die out entirely.

Plz consider the picture of a typical bacerial growth curve.

				Time 2. The CSTR bioreactor is a stirred tank reactor with same components as CSTR. The main components include an inlet for reactants, a probe for temperature setting or thermostat, a probe for pH electrode and shaft for impeller. Sorry, I am unable to upload the images here. 3. Your request is not clear. Impellers types varies with application. Do u need impeller information for mixing operation or for a centrigugal pump. please mention your question clearly. For centrifugal pump, three basic types of impellers are open, semi-open and closed impellers. Open impellers have the vanes free on both sides and are structurally weak. They are typically used in small-diameter, inexpensive pumps and pumps handling suspended solids. In semi-open impellers, the vanes are free on one side and enclosed on the other and offer higher efficiencies than open impellers. They are used in medium-diameter pumps and with liquids containing small amounts of suspended solids. Whereas, in closed impellers the vanes are located between the two discs, all in a single casting. The centrifugal pumps with closed impeller are the most widely used pumps handling clear liquids. For mixing purpose, the most common impeller types are axial and radial flow impellers.