Chemostats are frequently used in the industrial manufacturing of ethanol. In this case, several chemostats are used in series, each maintained at decreasing sugar concentrations. The chemostat also serves as an experimental model of continuous cell cultures in the biotechnological industry. Technical concerns Foaming results in overflow with the volume of liquid not exactly constant. Some very fragile cells are ruptured during agitation and aeration. Cells may grow on the walls or adhere to other surfaces, which may be overcome by treating the glass walls of the vessel with a silane to render them hydrophobic. However, cells will be selected for attachment to the walls since those that do will not be removed from the system. Those bacteria that stick firmly to the walls forming a biofilm are difficult to study under chemostat conditions. Mixing may not truly be uniform, upsetting the "static" property of the chemostat. Dripping the media into the chamber actually results in small pulses of nutrients and thus oscillations in concentrations, again upsetting the "static" property of the chemostat. Bacteria travel upstream quite easily. They will reach the reservoir of sterile medium quickly unless the liquid path is interrupted by an air break in which the medium falls in drops through air. Continuous efforts to remedy each defect lead to variations on the basic chemostat quite regularly. Examples in the literature are numerous. Antifoaming agents are used to suppress foaming. Agitation and aeration can be done gently. Many approaches have been taken to reduce wall growth Various applications use paddles, bubbling, or other mechanisms for mixing Dripping can be made less drastic with smaller droplets and larger vessel volumes Many improvements target the threat of contamination Experimental design considerations Parameter choice and setup The steady state concentration of the limiting substrate in the chemostat is independent of the influx concentration. The influx concentration will affect the cell concentration and thus the steady state OD. Even though the limiting substrate concentration in the chemostat is usually very low, and is maintained by discrete highly concentrated influx pulses, in practice the temporal variation in the concentration within the chemostat is small (a few percent or less) and can thus be viewed as quasi-steady state. The time it takes for the cell density (OD) to converge to a steady-state value (overshoot/undershoot) will often be long (multiple chemostat turnovers), especially when the initial inoculum is large. But, the time can