RelatedArt A primary goal of fermentation research is high productivity (i. e. the amount of product formed per unit volume per unit time) and cost-effective production of desired products. (Lee,"High cell-density culture of Escherichia coli,"TIBTECH 14 : 98-105 (1996)). Each cubic meter of fermentor volume is capable of yielding a certain amount of desired product. In view of this fact, it is most efficient to use the greatest amount of fermentor volume during fermentation. Conversely, the use of only a portion of the fermentor volume during fermentation results in a production loss. Thus, the optimal goal during fermentation is to maintain the highest economically justifiable liquid volume within the fermentor (i. e., fermentor liquid volume) at all times. This is beneficial, since the optimum use of fermentor volume during fermentation results in the optimum amount of desired product.

Liquid volume within the fermentor, however, fluctuates during fermentation. The fill rate, the drop rate, foam production, desired product production and the way the fermentor is run all affect the fermentor liquid volume. Foam production poses a large problem. Foam is a mixture of air and liquid in which the liquid is present only in small quantities. Hence, foam is less dense than liquid. This is a disadvantage because of fermentor volume limitations. In addition, if the foam level within the fermentor is too high, foam is expelled from the fermentor via a fermentor vent. This leads to a loss of fermentor liquid which affects overall desired product production. This can also lead to contamination of the fermentor liquid. Furthermore, fermentation activity occurs in the liquid phase only. Thus, because of the small amounts of fermentor liquid within foam, fermentation activity is very low within foam. Therefore, to maximize the use of fermentor volume during fermentation, the level of foam during fermentation should be minimized.

In many fermentations, this problem is dealt with using defoamer. A defoamer is a substance that eliminates foam by increasing the liquid's surface tension. Thus, many fermentors simply dispense defoamer on top of the fermentor liquid when foam levels are too high. The user of defoamer, however, does not come without it's drawbacks. The use of too much defoamer can lead to costly purification of the desired product after fermentation. Also, the use of a defoamer can increase the surface tension of the fermentor liquid. This causes small bubbles within the fermentor liquid to collapse to larger bubbles. This, in turn, affects gas-to-liquid oxygen transfer, which is necessary for an efficient fermentation process. In addition, defoamer is expensive. Thus, the use of defoamer affects production cost. Accordingly, the use of defoamer should be minimized.

Therefore, given the foregoing, what is needed is a method for improving the efficiency of the fermentation process by maximizing fermentor liquid volume while minimizing the use of defoamer.

Summary of the Invention The present invention relates to a method for controlling the liquid volume within a fermentor using defoamer and defoamer usage information. The nature of this method allows for a more efficient production of desired products.

In the present invention, fermentor liquid volume is controlled by controlling the drop rate in proportion to the amount of defoamer used during a fermentation run. More specifically, the drop rate is proportional to the fill rate and a variable proportionality factor. The variable proportionality factor is affected by defoamer usage during a fermentation. Defoamer usage is proportional to the recent number of times the fermentor foam or fermentor liquid reached a high fermentor level, the amount of time the defoamer was dispensed during the current fermentation run and the last calculated value of the variable proportionality factor. The variable proportionality factor and the resulting drop rate are periodically updated during the fermentation run.

An advantage of the present invention is the maximum use of the fermentor volume. The present invention maximizes the fermentor liquid level during fermentation. This is beneficial because it maximizes the overall yield of the desired product.

Another advantage of the present invention is the decreased use of defoamer. Defoamer is costly, can reduce oxygen transfer within the fermentor and can lead to costly purification of the desired product. Thus, the decreased use of defoamer is beneficial because it leads to more efficient production of the desired product.

Another advantage of the present invention is the maximum use of fermentor liquid. The present invention maximizes the fermentor liquid level during fermentation while minimizing the amount of fermentor liquid expelled due to overflow. This is beneficial because of the cost associated with the fermentor liquid.

Further features and advantages of the invention as well as the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings.

BriefDescription of the Figures The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit of a reference number identifies the drawing in which the reference number first appears.

Fig. 1 is a block diagram illustrating the system architecture of a fermentor, in an embodiment of the present invention.

Fig. 2 is a flowchart depicting an embodiment of the operation and control flow of the fermentation process, in an embodiment of the present invention.

Fig. 3 is a flowchart depicting an embodiment ofthe operation and control flow of the defoamer dispensation process, in an embodiment of the present invention.

Fig. 4 is a flowchart depicting an embodiment of the operation and control flow of the fermentor liquid volume control process, in an embodiment of the present invention.

Fig. 5 is an example computer system and computer program product that can be used to implement the present invention.

Detailed Description of the Preferred Embodiments I. Overview The present invention relates to a method for controlling fermentor liquid volume using defoamer and defoamer usage information. The present invention allows for a more efficient production of desired products during fermentation while minimizing the use of defoamer, A. Definitions The following definitions are provided for illustrative purposes only.

Alternative definitions for the listed terms will be apparent to the persons skilled in the relevant art (s) based on the discussion contained herein, and fall within the scope and spirit of embodiments of the invention.

The term"fermentor feed"or"culture medium"refers to the materials that are used to feed, or otherwise enable the activity of, the organism within the fermentor. Dextrose is an example of a component of fermentor feed.

The term"fermentor medium"or"liquid medium"refers to the medium in which the organism within the fermentor resides. Fermentor medium is composed mostly of water and other components that enable the growth of the organism. Ammonia, urea, oxygen, carbon dioxide and defoamer are examples of fermentor medium components.

The term"fermentor liquid"or"broth"refers to the liquid that resides within the fermentor. Generally, fermentor liquid consists of fermentor feed, fermentor medium and the fermentor organism.

The term"fermentor volume"refers to the total volume of the fermentor tank. The fermentor tank is the portion of the fermentor that holds the fermentor liquid.

The term"fermentor liquid volume"refers to the volume of liquid within the fermentor. Since the fermentor liquid is located within the fermentor, fermentor liquid volume is always less than the fermentor volume.

The term"defoamer"refers to a substance used to eliminate foam. In a fermentor, defoamer is typically dispensed at the top of the fermentor and is applied to the top of the fermentor liquid to decrease foam.

The term"fermentation run"refers to one complete cycle of a batch, semi- continuous or continuous fermentation. A fermentation run preferably begins when the fermentor is initially filled with starting materials and is inoculated with the proper organisms. A fermentation run preferably ends when the fermentor organisms are no longer active, or when the fermentor is emptied.

The term"probe"refers to a device located near the top of the fermentor to detect the liquid level or foam level within the fermentor. When the liquid level or foam level within the fermentor reaches the height of the probe and makes contact with the probe, the probe detects the liquid or foam.

The term"count"refers to an event that occurs when the probe detects liquid or foam within the fermentor. In other words, a count represents an instance when the liquid level or foam level within the fermentor reaches the height of the probe, makes contact with the probe and the event is registered.

The term"drop rate"refers to the rate at which liquid volume is flowing out of the fermentor. Drop rate is preferably measured in gallons per minute (gal/min). Liquid typically flows out of the fermentor via a fermentor output line.

The term"fill rate"refers to the rate at which fermentor liquid, added to the fermentor during the current fermentation run, is flowing into the fermentor. Fill rate is preferably measured in gallons per minute (gal/min). Liquid typically flows into the fermentor via a fermentor input line.

B. General Considerations The present invention is described in terms of the examples contained herein. This is for convenience only and is not intended to limit the application of the present invention. In fact, after reading the following description, it will be apparent to one skilled in the relevant art (s) how to implement the following invention in alternative embodiments.

II. Fermentor Architecture The choice of fermentor used in the method of the present invention will be apparent to one of ordinary skill in the art. Types of fermentors which can be used in the method of the present invention include common stirred-tank reactors (STR) with the usual instrumentation for feeding and process monitoring, STRs with various types of external or internal cell retention, dialysis-membrane reactors, cyclone reactors, gas-lift reactors and fluid bed reactors. STRs are well- known and the details are not provided here, but will be apparent to one of ordinary skill in the art. For example, because products often accumulate to inhibitory levels, the culture medium can be refreshed. While fresh culture medium is pumped into the STR and used broth flows out of the STR, cells can be held back in order to increase biomass and productivity. A membrane cell- recycle system with an external membrane filter connected to an STR can be used in the process of the present invention. An external cross-flow filtration system can also be employed to filter cells. Alternatively, internal cell retention can also be used. For example, an aerated STR can be used which contains a filter module consisting of vertical cylindrical filter rods for total cell retention. A membrane dialysis reactor which operates with total internal cell retention can also be employed.

A simple STR under semi-batch, continuous or semi-continuous fermentation can also be employed in the process of the present invention. Steel fermentors operating semi-continuous fermentations are also contemplated.

Fig. 1 shows a block diagram illustrating the system architecture 100 of a fermentor, in an embodiment of the present invention. System 100 includes a fermentor 102, fermentor input line 110, fermentor output line 112, defoamer probe 108, defoamer dispenser 109 and fermentor control 114. System 100 also includes fermentor liquid (i. e., broth) 104 and foam 106.

Fermentor 102 can be any fermentor commonly used in the art or any fermentor that one of ordinary skill in the art may use for batch, semi-batch, continuous or semi-continuous fermentation. An example of such a fermentor is the MFCS fermentor manufactured by Fermentation Engineering, Inc. of Ripon, California.

Fermentor input line 110 can be any valve, pipe or other orifice which is used to introduce a substance into fermentor 102. An example of a substance that can be introduced into fermentor 102 is dextrose, which is fermentor feed necessary for the fermentation process. Input line 110 can be either one such line or multiple lines for introducing multiple and/or various substances into fermentor 102. Likewise, output line 112 can be any valve, pipe or other orifice which is used to dismiss a substance from fermentor 102. An example of a substance that can be dismissed from fermentor 102 is broth 104, which can occur when the liquid level within fermentor 102 surpasses a threshold. Output line 112 can be either one such line or multiple lines for dismissing substances from fermentor 102. In an embodiment of the present invention, output line 112 and input line 110 are both controlled by fermentor control 114.

Defoamer probe 108 is a probe which detects the presence of liquid 104 or foam 106. When the level of liquid 104 or foam 106 within fermentor 102 reaches probe 108, a signal is sent to fermentor control 114. Probe 108 can be any probe which is capable of performing this task or any such probe that may be used by one of ordinary skill in the art to perform this task. Preferably, probe 108 is a conductance probe which constantly measures the conductance of the material in which it is immersed. When probe 108 is suddenly immersed in liquid 104 or foam 106 for a set time, the conductance measured by probe 108 suddenly changes and probe 108 sends a signal to fermentor control 114. After receiving the signal from probe 108, fermentor control 114 may then register the event as a count. This is described in greater detail below.

Defoamer dispenser 109 is similar to input line 110. Dispenser 109 dispenses defoamer into fermentor 102. Dispenser 109 is located near the top of fermentor 102 such that dispensed defoamer is sure to fall on foam 106, which rests on the top of liquid 104. This ensures that the defoamer will contact and interact with foam 106. In an embodiment of the present invention, dispenser 109 is controlled by fermentor control 114. Generally, defoamer is dispensed via dispenser 109 as a result of the registration of a count. This is described in greater detail below.

Fermentor control 114 is a computer system for controlling all aspects of fermentor 102. Fermentor control 114 controls input line 110, output line 112, probe 108 and dispenser 109. In addition, fermentor control 114 can control any other aspects of fermentor 102 that are typically conducive to centralized control.

Fermentor control 114 is described in greater detail below.

III. Fermentation Process A. Types The processes described in the present invention can use any fermentation method which facilitates the control processes of the present invention. In a batch fermentation process, fermentor medium, fermentor feed and fermentor organisms are typically introduced into the fermentation process at the beginning of fermentation run only. The fermentation is then allowed to run its course to yield the desired product batchwise.

In a continuous fermentation process, fermentor feed and/or fermentor medium is added to a fermentor continuously or periodically while withdrawing broth continuously or periodically to maximize the rate of desired product formation.

In a semi-continuous or semi-batch fermentation process, fermentor feed and/or fermentor medium is added to a fermentor continuously or periodically while withdrawing broth continuously or periodically to maximize the rate of desired product formation. However, the fermentation has a particular cycle time.

Preferably, the processes of the present invention utilize semi-continuous fermentation.

B. Feed In an embodiment of the present invention, fermentor feed can be any "carbohydrate source,"i. e, any sugar or starch which is generally used as raw materials for fermentation. Preferred carbohydrate sources are those which a lysine-producing bacteria can assimilate. This includes monosaccharides and disaccharides, such as glucose (which is also referred to as dextrose), sucrose and hydrolyzed starch. Dextrose is a preferred form of carbohydrate source. Fermentor feed can also be carbon sources used in a fermentation. Such carbon sources include organic acids, lipids or alcohols, such as glycerol. Fermentor feed can also be nitrogen sources, oxygen and minerals used in a fermentation.

C. Medium There is no particular limitation to the fermentor medium used in the processes of the invention. In an embodiment of the present invention, any fermentor medium which is known to one of skill in the art can be used. For example, generally known fermentor media which contain organic and inorganic nutrient sources such as a carbon sources, nitrogen sources and other trace sources can be used in the processes of the present invention. Preferably, in an embodiment of the present invention, the fermentor organism is fed two sources of nitrogen: an ionized nitrogen source and an un-ionized nitrogen source. The un-ionized sources of nitrogen can be ammonia and urea. The ionized sources of nitrogen can be ammonium phosphate, ammonium acetate, ammonium sulfate and ammonium chloride. The preceding list is not meant to limit the present invention, as any ionized source of nitrogen which accomplishes the tasks of a fermentor medium in the processes of the present invention can be utilized.

D. Desired Products The process of the present invention can be used in the fermentation of a variety of organisms to produce primary and secondary metabolites, such as amino acids, vitamins, organic acids, emulsifiers and steroids. In an embodiment of the present invention organisms which produce amino acids, namely organisms which are capable of producing L-lysine or L-threonine, are used in the fermentation process.

In an embodiment of the present invention, the desired products produced by the process ofthe present invention can be isolated or purified by conventional means such as chromatography. For example, affinity or ion exchange chromatography, crystallization and other methods which will be readily apparent to one of ordinary skill in the art can be used to isolate or purify desired products.

E. Embodiment Fig. 2 shows a flowchart depicting an embodiment of the operation and control flow 200 of the fermentation process of the present invention. It should be noted that control flow 200 is an embodiment of a semi-continuous fermentation process. However, control flow 200 can also apply to semi-batch or continuous fermentation processes. Control flow 200 begins with step 202 and proceeds immediately to step 204.

In step 204, the starting materials are added to fermentor 102. Starting materials are those materials that are initially added to a fermentor to begin the fermentation process. Starting materials can consist of the fermentor organism, such as yeast, the fermentor feed, such as dextrose, and the fermentor medium.

Starting materials can be any fermentation starting materials that are commonly used in the art or any such materials that can perform the same function, as is readily determined by one of ordinary skill in the art.

In step 206, the fermentor liquid volume of fermentor 206 is controlled.

In an embodiment of the present invention, this portion of the process is accomplished by fermentor control 114. The manner in which the fermentor liquid volume of fermentor 206 is controlled is described in greater detail below.

In step 208, materials are added and dropped (i. e, introduced and dismissed) during fermentation. Generally, fermentor feed (for the fermentor organism) is added and the desired product is dropped.

In step 210, the desired product is removed from fermentor 102. Step 210 generally defines the end of the fermentation run. At this point, the broth is removed and the desired product is extracted form the broth. It should be noted that a continuous fermentation process does not have such an end point. Rather, a continuous fermentation process involves the periodic dropping of the desired product during the fermentation process. Thus, in the instance of a continuous fermentation process, step 210 entails the removal of a portion of the broth in order to extricate the desired product. Therefore, in the instance of a continuous fermentation process, control flows continuously from step 210 to step 206.

In step 212, control flow 212 ceases.

IV. Defoamer Usage Fig. 3 shows a flowchart depicting an embodiment of the operation and control flow 300 of the defoamer dispensation process of the present invention.

Control flow 300 begins with step 302 and proceeds immediately to step 304.

In step 304, it is determined whether the requisite time period has passed since the last time the defoamer was dispensed. Because defoaming characteristics of defoamer require some time to react with the foam, it is necessary to allow a time period to pass without responding to probe contact after defoamer is dispensed. This time period allows the defoamer time to react with the foam. After the time period has passed, additional defoamer may be dispensed if fermentor control 114 deems it necessary. In an embodiment of the present invention, the time period is from about one to about ten minutes. In another embodiment of the present invention, the time period is about five minutes. However, the time period may be any period that is deemed adequate to allow the foam to react with the defoamer. If the determination of step 304 is affirmative, controls flows to step 308. Otherwise, control flows to step 306.

If the fermentation process has just begun, i. e, it is time index zero, the determination of step 304 is affirmative. Likewise, the time index is less than the requisite time period, the determination of step 304 is affirmative.

If a time period was not allowed to pass after defoamer dispensation, excess defoamer may be dispensed onto the foam. That is, if control flow 300 allowed defoamer to be dispensed in reaction to a probe signal, regardless of the last time defoamer was dispensed, then additional defoamer may be dispensed without giving the previous defoamer time to react. As described above, this could lead to reduced oxygen transfer and costly purification techniques.

In step 306, a time increment passes before step 304 is executed again.

As described above, step 304 determines whether a time period has passed. This determination is executed once for each time increment defined by step 306, until the determination is affirmative. In an embodiment of the present invention, the time increment is one second. Alternatively, the time increment can be any time that is deemed adequate by one of ordinary skill in the art.

In step 308, it is determined whether foam has been detected by probe 108. In an embodiment of the present invention, step 308 entails probe 108 sending a signal to fermentor control 114, which, in turn, registers the event as a count. Alternatively, the event may be registered as a count by any device that is capable of receiving a signal from probe 108. If the determination of step 308 is affirmative, controls flows to step 312. Otherwise, control flows to step 310.

It should be noted that a count is only registered when probe 108 sends a signal to fermentor control 114 and the time period of step 304 has passed.

That is, a count can only be registered in step 308 when control of flow 300 is not currently in the loop between steps 304 and 306. This shows that a count is not registered every time probe 108 sends a signal to fermentor control 114. Rather a count is registered when probe 108 sends a signal to fermentor control 114 and the requisite time period has passed since the last time defoamer was dispensed.

It should also be noted that count data can then be used by fermentor control 114 in determining and controlling fermentor volume control. This is described in greater detail below.

In step 310, a time increment passes before step 308 is executed again.

As described above, step 308 determines whether foam has been detected. This determination is executed once for each time increment defined by step 310 until the determination is affirmative. In an embodiment of the present invention, the time increment is one second. The time increment can be any time that is deemed adequate by one of ordinary skill in the art.

In step 312, the defoamer is dispensed. In an embodiment of the present invention, the defoamer is dispensed via defoamer dispenser 109. However, the defoamer can be dispensed via any device that is capable of dispensing defoamer onto the foam within fermentor 102. In an embodiment of the present invention, the defoamer is dispensed via defoamer dispenser 109 for a time period, where the time period is from about one to about twenty seconds. In another embodiment of the present invention, the defoamer is dispensed via defoamer dispenser 109 for a time period, where the time period is about seven seconds. However, the defoamer can be dispensed for any period of time that is adequate to dispense an acceptable amount of defoamer onto the foam within fermentor 102.

After step 312, control flows directly back to step 304. As described above, flow 300 is a continuous process that continues throughout the entire fermentation run.

V. Volume Control The fermentor liquid volume is dependant on the fill rate and the drop rate. As materials enter and exit fermentor 102 via input lines 110 and output lines 112, the liquid volume of fermentor 102 fluctuates. It can also be seen that the fermentor liquid volume is proportional to the fill rate and inversely proportional to the drop rate. As the fill rate increases, fermentor liquid volume increases. Likewise, as the drop rate increases, fermentor liquid volume decreases. Thus, we see that, generally: changes in fermentor liquid volume = fill rate-drop rate + X (1) where X represents other independent aspects of the fermentation process that affect fermentor liquid volume. An example of such an independent aspect is evaporation.

As explained above, it is most efficient to have fermentor 102 at the highest liquid volume possible while using the minimal amount of defoamer.

Therefore, either the drop rate, the fill rate or both must be adjusted to achieve maximum fermentor liquid volume and, thus, maximum productivity.

The fill rate of fermentor 102 is a variable independent of the fermentor liquid volume control process. That is, the fill rate depends on other aspects of the fermentation process, such as fermentor medium requirements and dextrose concentration.

Since the fill rate is independent, the drop rate of fermentor 102, therefore, is the variable that must be adjusted by fermentor control 114 to meet maximum efficiency goals. Thus, considering equation (1), it can be seen that changes in fermentor liquid volume depends only on drop rate (variable X notwithstanding).

The question then turns to how the drop rate will be adjusted.

It is clear that the drop rate must be proportional to the fill rate. This can be gleamed from the fact that the drop rate must mirror the fill rate insofar as the drop rate must keep the fermentor from overflowing and from being underutilized. Likewise, the drop rate must not significantly change fermentor volume. Thus, the drop rate is defined by: drop rate = fill rate * A (2) where A is a variable proportionality factor representing other aspects of the fermentation process that affect fermentor liquid volume (A is explained in greater detail below). The proportionality of equation (2) indicates the following important relationships: 1) the drop rate increases as the fill rate increases and 2) the drop rate decreases as the fill rate decreases. Since the fill rate is independent, the question then turns to how A is defined.

A, as shown in equation (2), defines the relationship, or level of proportionality, between the drop rate and the fill rate. If A were equal to 1, for example, it could be seen that the drop rate would equal the fill rate and the fermentor liquid volume would generally not increase or decrease. As explained above, it is most efficient to have the highest fermentor liquid volume possible while using a minimal amount of defoamer. Thus, any determinations affecting the fermentor liquid volume should take defoamer usage into account. Therefore, in an embodiment of the present invention, A shall take defoamer usage into account. In an embodiment of the present invention, the following equation defines the manner in which A is calculated during fermentation, while taking defoamer usage into account.

Anew = Alast * [ (1-R) + (CH * 0.01 * (DM/4))] (3) where AneW is calculated periodically, Alast is the last value of AneW, R is a constant percentage decline of A for each calculation cycle, CH is the number of counts registered in the last hour and DM is the number of minutes defoamer has been dispensed during the fermentation run.

Equation (3) shows that each calculation of A (i. e., AneW) takes into account the last calculation of A (i. e., Alas ». This feature allows for smoother transitions between succeeding values of A, since the old value is taken into account when calculating the new value. A is calculated periodically, where the time period is any time period that is appropriate for the fermentation process. In an embodiment of the present invention, the time period is from about five to about thirty minutes. In another embodiment of the present invention, the time period is about fifteen minutes.

Upon initiation of liquid removal during the fermentation run, the initial determination of Anew is made. A prudent value of Alast may be used at this time.

In an embodiment of the present invention, upon the initial determination of AneW, the value 1.0 is used for Alastv The value 1.0 is significant because it indicates that the drop rate is equal to the fill rate (see equation (2)). This value is regarded as a"safe"value because it gives the general assurance that an overflow or an underutilization of fermentor volume will not occur. However, the initial value can be any value that is deemed adequate by one of ordinary skill in the art.

In an embodiment of the present invention, the range of A is from about 0.6 to about 2.0. In another embodiment of the present invention, the range of A is from about 0.6 to about 2.5, if DM is greater than or equal to nine (9) minutes. However, the range of A can be any range that is deemed adequate by one of ordinary skill in the art for any fermentation process.

In equation (3), R is a constant representing a percentage decline of A.

That is, R represents the percentage that A should decrease each time A is calculated, i. e., R is a reduction constant. It is desirable that A declines slightly upon each such calculation of A in order to guard against under-utilization of fermentor volume. Since the drop rate is proportional to A, a decrease of A over time translates into a decrease of the drop rate over time. This ensures maximum use of the fermentor volume. In an embodiment of the present invention, the value 0.03 is used for R. However, R can be any value that is deemed adequate by one of ordinary skill in the art.

Also in equation (3), CH represents the number of counts registered in the last hour. The registration of counts is described in greater detail above. As is explained above, the number of counts is recorded by fermentor controller 114.

CH can be updated immediately upon the registration of a count (see step 308 above) or can be updated periodically. In an embodiment of the present invention, CH is updated periodically, where the period is from about five to about every thirty minutes. In another embodiment of the present invention, CH is updated every fifteen minutes. Alternatively, CH can be updated any time period that is deemed adequate by one of ordinary skill in the art.

Also in equation (3), DM represents the total number of minutes during which defoamer has been released during the current fermentation run. DM is directly related to the number of counts registered during the current fermentation run. As explained above, defoamer is dispensed for a specified period of time (7 seconds in an embodiment of the present invention), each time it is dispensed.

Thus, in order to calculate DM, the following equation is used: DM = (TC * time period)/60 (4) where TC is the total number of counts registered during the current fermentation run and time period is the period of time (in seconds) for which defoamer is dispensed. It is seen that the product of TC and time period is divided by sixty (60) to render a result in the unit of minutes. In an embodiment of the present invention, DM is updated periodically, where the period is from about five to about thirty minutes. In another embodiment of the present invention, DM is updated every fifteen minutes. Alternatively, DM can be updated any time period that is deemed adequate by one of ordinary skill in the art.

In an example use of equation (3), let us assume that a current fermentation has registered five counts in the last hour (CH = 5) and that the total minutes of defoamer received during the current fermentation run is eight (DM = 8). We will also assume that R is equal to 0.03. This renders: Anew = Alast * [ (1-0. 03) + (5 * 0.01 * (8/4))] Anew =Alast * [ (0. 97) + (0.1)] Anew = Alast * 1. 07 Therefore, the new value of A will be 7% higher than the previous value of A.

As a result, referring to equation (2), the drop rate will increase by 7% over its calculated value fifteen minutes ago.

Fig. 4 shows a flowchart depicting an embodiment of the operation and control flow 400 of the fermentor volume control process of the present invention. Control flow 400 applies to fermentation processes, such as some semi-batch, continuous and semi-continuous fermentation processes that allow fermentor volume control. Control flow 400 begins with step 402 and proceeds immediately to step 404.

In step 404, AneW is set to an initial value. In an embodiment of the present invention, the initial value is 1.0. The value 1.0 is significant because it indicates that the drop rate is equal to the fill rate. This is described in greater detail above. The initial value, however, can be any value that is deemed adequate by one of ordinary skill in the art.

In step 406, a time period is allowed to pass. This time period allows for fermentation events to occur before volume control is performed. In an embodiment of the present invention, the time period is from about five to about thirty minutes. In another embodiment of the present invention, the time period can be fifteen minutes. However, this time period can be any time period that is adequate to allow fermentation events to occur.

In step 408, Alast is set to AneW. This feature allows previous values of A to be taken into account when calculating new values of A. This is described in greater detail below.

In step 410, the variables for equation (3) are evaluated. These variables are CH (counts per hour) and DM (defoamer minutes). As described above, CH is determined by fermentor control 114 during fermentation as counts occur. This is described in greater detail above. DM is determined from count information using equation (4).

In step 412, AneW is calculated using equation (3).

In step 414, the value of A calculated in step 412 is used in equation (2) to calculate the drop rate. In this step, the fill rate is also evaluated (note that the fill rate is independent of the drop rate and of A) and used in the calculation of the drop rate. Subsequently, the drop rate of the fermentor is adjusted according to the calculation of the drop rate. Control then flows back to step 406, where the process is reiterated through the fermentation run.

VI. Fermentor Control The functions performed by fermentor controller 114 are preferably implemented in software. Alternatively, the same may be implemented using hardware or a combination of hardware and software.

In an embodiment of the present invention, fermentor controller 114 comprises a computer system which may be connected to a network. An example of such a computer system 500 is shown in FIG. 5. The computer system 500 represents any single or multi-processor computer. Single-threaded and multi- threaded computers can be used. Unified or distributed memory systems can be used.

The computer system 500 includes one or more processors, such as processor 504. One or more processors 504 can execute software implementing the operations described in flow 300 and flow 400. Each processor 504 is connected to a communication bus 502 (e. g., cross-bar or network). Various software embodiments are described in terms of this exemplary computer system.

After reading this description, it will become apparent to a person skilled in the relevant art how to implement the invention using other computer systems and/or computer architectures.

Computer system 500 also includes a main memory 506, preferably random access memory (RAM), and can also include a secondary memory 508.

The secondary memory 508 can include, for example, a hard disk drive 510 and/or a removable storage drive 512, representing a floppy disk drive, a magnetic tape drive, an optical disk drive, etc. The removable storage drive 512 reads from and/or writes to a removable storage unit 514 in a well known manner. Removable storage unit 514 represents a floppy disk, magnetic tape, optical disk, etc., which is read by and written to by removable storage drive 512.

As will be appreciated, the removable storage unit 514 includes a computer usable storage medium having stored therein computer software and/or data.

In alternative embodiments, secondary memory 508 can include other means for allowing computer programs or other instructions to be loaded into computer system 500. Such means can include, for example, a removable storage unit 522 and an interface 520. Examples can include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM, or PROM) and associated socket, and other removable storage units 522 and interfaces 520 which allow software and data to be transferred from the removable storage unit 522 to computer system 500.

Computer system 500 can also include a communications interface 524.

Communications interface 524 allows software and data to be transferred between computer system 500 and external devices via communications path 526.

Examples of communications interface 520 can include a modem, a network interface (such as Ethernet card), a communications port, etc. Software and data transferred via communications interface 524 are in the form of signals which can be electronic, electromagnetic, optical or other signals capable of being received by communications interface 524, via communications path 526. Note that communications interface 524 provides a means by which computer system 500 can interface to a network such as the Internet.

The present invention can be implemented using software running (that is, executing) in an environment similar to that described above with respect to FIG. 5. In this document, the term"computer program products used to generally refer to removable storage unit 514, a hard disk installed in hard disk drive 510, or a carrier wave carrying software over a communication path 526 (wireless link or cable) to communication interface 524. A computer useable medium can include magnetic media, optical media, or other recordable media, or media that transmits a carrier wave. These computer program products are means for providing software to computer system 500.

Computer programs (also called computer control logic) are stored in main memory 506 and/or secondary memory 508. Computer programs can also be received via communications interface 524. Such computer programs, when executed, enable the computer system 500 to perform the features of the present invention as discussed herein. In particular, the computer programs, when executed, enable the processor 504 to perform the features of the present invention. Accordingly, such computer programs represent controllers of the computer system 500.

In an embodiment where the invention is implemented using software, the software can be stored in a computer program product and loaded into computer system 500 using removable storage drive 512, hard drive 510, or communications interface 524. Alternatively, the computer program product can be downloaded to computer system 500 over communications path 524. The control logic (software), when executed by the one or more processors 504, causes the processor (s) 504 to perform the functions of the invention as described herein.

In an embodiment where the invention is implemented using software, a commercially available software package such as D/3 DCS available from GSES Systems, Inc. of Columbia, Maryland may be used. As described above, the computer program product representing this software package can be loaded into computer system 500 using removable storage drive 512, hard drive 510, or communications interface 524. D/3 DCS can also access a further, secondary, computer program product to perform the functions of the invention as described herein. The secondary computer program product consists of a text file written in an interpreted computer language named Sequence and Batch Language (SABL). SABL is a computer language with syntax similar to the BASIC computer language. As the D/3 DCS software package executes, it reads instructions within a SABL file to determine how to perform the functions of the invention as described herein. The source code below is an example of a SABL file used to control dextrose feed in a fermentor: FEED CREATED FROM MFPH-1. COM ; 3-NOV-2000 08: 19 : 26. 17 MAIN FER 31 DEXTROSE FLOW SPIKE CONTROL ; MF31PH-1.SEQ PHIF3 IFGB : CAL VCVL: 3 = MINUMUM SHOT TIME IN SECONDS PHIF3 PHIF31FGB : CAL VDVL: 3 = MAXIMUM SHOT TIME IN SECONDS PHIF33FGB : CAL-VAVL: 3 = TARGET DEXTROSE ASSAY FOR FTIR CONTROL BOB CONTROL PHIF33FGB : CAL-VBVL: 3 = MF33RAT INCREMENT UP OR DOWN BOB CONTROL PHIF3 PHIF31FGB : CAL-VBVL : 2 = RATIO-> MF31RAT2 (varries based on MF 31TIME1, 2) PHIF3 PHIF31FGB : CAL VCVL: 2 = NECESSARY PH SPIKE----0. 08 ; PHIF31FGB : CAL-VDVL : 2 = MINIMUM TIME BETWEEN SHOTS---1800 SEC, ST8 PHIF3 PHIF31FGB : CAL-VEVL: 2 = BIAS-> MF31BIA--2 SMALL MAIN 3 BIG MAIN PHIF31FGB : CAL VFVL: 2 = INCREMENT DURING SHOT----16GPM SMALL MAIN 21GPM ; BIG MAIN ST7 MEASURES THE TIME DURING SHOT THAT THE DEXTROSE IS AT INCREASED RATE MF3 MF31TIME1 MEASURES THE TIME BETWEEN SPIKES MF3 1TIME2 SAVES THE ELAPSED TIME BETWEEN PH SPIKES FOR LATER USE IN ; CALCULATING THE RATIO MT05 DELAY PH SETPT ON FILL UNIT MF31 LET IN24=9999 LET IN25=9999 LET IN26=9999 LOOP: ON ERROR GOSUB FAULT WAIT 3 IF (MF31DSEQ : DEV STAT=1) THEN BEGIN TIMEROFF ST08 TIMERCLR ST08 TIMEROFF ST07 TIMERCLR ST07 LET FL19=0 LET FL20=0 LET FL21=0 LET FL22=0 LET FL23=0 LET FL24=0 LET FL25=0 LET FL26=0 LET FL27=0 LET FL28=0 LET FL29=0 LET FG24=0 LET IN24=9999 LET IN25=9999 LET IN26=9999 GOTO LOOP END IF (MF31DSEQ: DEV STAT=2) THEN GOTO FIE 1 IF (MF31DSEQ : DEV STAT=4) THEN GOTO SPK1 IF (MF31DSEQ : DEV STAT=8) THEN GOTO SPK2 IF (MF31DSEQ: DEV STAT=16) THEN GOTO SP-K3 GOTO LOOP DEXTROSE INITIAL FILL PART FILI : WAIT 1 LET MF31RAT2 : CAL VBVL : 2=0. 2; set the nonadjustable variable B to 0.25 at ; start of run LET MF31RAT2 : CAL VBVL: 3=0.15; set the nonadjustable variable B to 0.15 ; at start of run LET MF31RAT2 : CB-OTLO : 3=0.2; set the lo ratio clamp at 0.2 LET MF31RAT2 : CAL VAVL: 1=0.3; set the operator adjustable variable A to ; 0.35 at start of run LET MF31RAT2: CB-OTLO: 5=0. 1; set the lo ratio clamp at 0.2 LET MF31RAT2 : CB-OTHI : 3=0. 55 ; set the hi ratio clamp at 0.55 LET MF31PAT2 : CB-OTHT: 5=0. 55 ; set the hi ratio clamp at 0.55 LET PHIF31FGB : CB OTHI : 2=24. 0; set the hi dextrose flow setpoint clamp at ; 24.0 gpm LET MF3 lBIA : AI-INVL : O = 0; set bias equal to zero LET PHIF31FGB : CAL VCVL: 2 = 0.08; spike criteria LET PHIF31FGB : CAL-VDVL : 2 = 1800 ; min time betw shots SEC, ST8 IF (FG24=0) THEN BEGIN PUTMANL F31DEXTOT ; put dextrose flow totalizer in manual WAIT 7 PUTAUTO F31DEXTOT ; put dex flow tot in auto (resets tot) END OPEN SVF31DX1 ; open DX1 binary valve WAIT 3 OPEN SVF31DX2 ; open DX2 binary valve PUTAUTO FCF31DEX ; put dex flow controller in auto PUTAUTO PHIF31FM WAIT 5 LET PHIF3 IFM : PID-SPVL: 1=7.0; not quite final pH setpt adjustment TIMERON MT05 ; final ph delay IF (FG24=0) THEN TIMERCLR MT05 ; final pH delay LET FCF31DEX : PID-SPVL: 1=3.5; set dex flow setpt BIG main FTL2: WAIT 5 IF (MF31DSEQ: DEV STAT! =2) THEN GOTO L05P IF MT05 > 15 THEN BEGIN LET PHIF3 IFM : PID-SPVL: 1=7.2 TIMEROFF MT05 TIMERCLR MT05 END LET FG24=1 IF (F31DEXTOT : AI-MEAS: O < FL04) THEN; fill till totalizer exceeds fill ; setpt GOTO FIL2 LET FG24=0 CLOSE SVF31 DX2' ; c) ose DX2 binary valve PUTMANL FCF31DEX ; put dex flow controller in manual WAIT 5 PUTOUT FCF31DEX, 0.0; close dex flow controller valve LET FCF31CWJ: AI-INHIB: 0=0 ; make sure following alarms are not LET PHIF31FM: AI INHTB : 0-0 ; inhibited LET FCF31DEX: AI INHIB : 0-0 LET FCF31AS: AI-INHIB : 0=0 LET MF31BIA : AT-TNVL: O = 3; set bias to 3 BIG main PRINT 1,"MF% i INITIAL DEX FILL GALS. = % f &num &num &num &num &num ", TNI1, F31DEXTOT : AT-MEAS: O ; prints out fill gallons LET MF31DSEQ : DEVCMD=4 SPKIA : WAIT 3 IF (MF31DSEQ: DEV STAT! =4) THEN GOTO LOOP LET FG24=0 LET FL08=PHIF31FM : AI-MEAS: O ; comparing ph indication LET FL09@PHIF31FM : PID-SPVL: 1 ; with the setpt LET FL10=FL08-FL09 ;let FL10 be the deviation from setpt IF FLIO< (PHIF31FGB : CAL-VCVL: 2) THEN; wait until ph is spiking GOTO SPK1 PUTMANL FCF31DEX ; put dex flow controller in manual PUTOUT FCF31DEX, 10.0; set output at 10% OPEN SVF31DX2 ; open DX2 binary valve PUTAUTO FCF31DEX ; put dex flow controller in auto WAIT 3 CLOSCASC FCF31DEX; close cascade on dex flow controller LET MF3 IBIA : AI INVL : O = 3 ; set bias to 3 LET MF31BIA: AI-INVL: O PHIF31FGB : CAL-VEVL : 2 + PHIF31FGB: CAL-V FVL : 2 TIMERCLR ST07 TIMERON ST07 PRINT 1,"MF% i FIRST SPIKE", IN11 ; prints out when first spike occurred SPK1 : WAIT 3 IF (MF31DSEQ : DEV STAT! =4) THEN GOTO L03P IF (ST07 < 900) THEN ; 15 minute minimum GOTO SPKIA IF (ST07 < 1800) & (PHIF31FM : CB OTVL : 2 < 25.0) THEN ; after ; 40 min or 25% out on NH3 valve the shot will be done GOTO SPKIA LET MF31BIA : AI INVL: O = 3; set bias back to 3 TIMEROFF ST07 TIMERCLR ST07 PUTAUTO MF31TIMEI ; put spike timer in auto WAIT 3 LET MF31TIME1 : INTTOT : I = 0; zero out spike timer LET MF31TIME1 : INTETIM : 1 = 0 LET MF31DSEQ : DEV CMD=8 TIMERCLR ST08; zeros out minimum time between shots timer TIMERON ST08 SFK2: WAIT 3 IF (MF31DSEQ : DEV STAT ! =8) THEN GOTO L06P LET FG24=0 LET FL08=PHIF31FM : AI-MEAS : O ; comparing ph indication LET FL09=PHIF31FM : PID-SPVL : I ; with the setpt LET FL10=FL08-FLO9 ; let FLIO be the deviation from setpt TIMERON ST08 IF ST08>32000 THEN; resets ST8 in case of error LET ST08=PHIF31FGB : CAL VDVL: 2 IF (ST07=0) & (ST08<1799) THEN GOTO SPK2 IF FL10< (PHIF31FGB : CAL-VCVL: 2) & (AND (FCF31DEX : PID-SPVS: 1,64) =64) THEN ; wait until ph is spiking GOTO SPK2 LET MF31BIA : AI INVL: O = 3; set bias back to 3 LET MF31BIA : AI-INVL: O = PHIF31FGB : CAL-VEVL: 2 + PHIF31FGB : CAL-VFVL: 2 TIMERCLR ST07 TIMERON ST07 PRINT 1,"MF% i SECOND SPIKE", INl l ; prints out when second spike; occurred SPK2A: WAIT 3 IF (MF31DSEQ : DEV STAT! =8) THEN GOTO LOOP IF (ST07 < 900) THEN; 15 minute minimum GOTO SPK2A IF (ST07 < 1800) & (PHIF31FM : CB OTVL: 2 < 25. 0) THEN; after 40 min or 25% ; out on NH3 valve the shot will be done GOTO SPK2A TIMEROFF ST07 TIMERCLR ST07 LET MF31BIA : AI INVL : O = 3; set bias back to 3 WAIT 5 LET MF31TIME2 : AI-INVL: O = MF31TIME1 : CB-OTVL: 1 ; save elapsed time ; between spikes WAIT 5 LET MF31TIME1: TNT TOT: 1 =0; zero out spike timer LET MF31TIME1 : INT ETIM: 10 WAIT 3 LET MF31DSEQ : DEV-CMD=16 GOTO SPK3 SPK3: WAIT 1 TIMERCLR ST08 TTMERON ST08 TTMEROFF ST07 TIMERCLR ST07 PUTAUTO MF31TIME1 IF (IN07=1) THEN BEGIN PUTAUTO FCF31DEX WAIT 3 CLOSCASC FCF31DEX END LOOP2: ON ERROR GOSUB FAULT IF (MF31DSEQ : DEV STAT ! =16) THEN GOTO L06P LET FG24@0 WAIT 3 IF ST08>32000 THEN ; resets ST8 in case of error BEGIN LET ST08=PHIF31FGB : CAL-VDVL : 2 TIMERON ST08 END LET FL08=PHIF31FM : AI MEAS: O ; compares ph indication LET E'L09=PHIF31FM : PI-5-SPVL : 1 ; with the setpt LET FL10=FL08-FLO9 ; let FL10 be the deviation from setpt ; starts testing for a spike IF (ST07=0) & (ST08>PHIF31FGB : CAL VDVL: 2) THEN; checks to see that main is ; not in the middle of a shot and minimum time requirement has been met IF FL10> (PHIF31FGB : CAL VCVL:2) & (AND (FCF31DEX : PID SPVS: 1,64) 64) THEN ; checks to see if deviation above setpt exceeds ; limit allowed and that the dextrose flow controller is in auto cascade BEGIN LET FG06=1 PRINT 1,"DEX PULSE PH% 5.2f PH DEV% 5.2fl 1, FL08, FL10 ; records shot in alarm file LET MF31BIA: AI-INVL: O = 3; sets bias bac // WAIT 5 LET MF31BTA: AI-INVL : O = PHIF31FGB: CAL-VEVL:2 + PHIF31FGB : CAL-VFVL : 2 ; increases bias during shot TIMERON ST07; starts measuring the time during the shot TIMERCLR ST07 <BR> <BR> <BR> LET IN26 @ IN25<BR> <BR> <BR> <BR> LET IN25 = IN24 LET IN24 = MF31TIME1 : CB OTVL: 1 LET MF31TIME2 : AI-INVL: O = MF31TIME1 : CB-OTVL: I ; saves the elapsed time between spikes into MF31TIME2 IF ( (IN24+IN23+IN26) < 240) THEN BEGIN LET PHIF31FGB : CAL-VDVL: 3 = 5700; maximum shot time PRINT 1,"3 SPIKES IN 4 HOURS" END IF ( (IN24+IN25+IN26) < 300 & (TN24+IN25+IN26) > 240) THEN BEGIN LET PHIF31FGB : CAL-VDVL: 3 4800; maximum shot time PRINT 1,"3 SPIKES IN 4 TO 5 HOURS" END IF ( (IN24+IN25+IN26) > 300) THEN BEGIN LET PHIF31FGB : CAL-VDVL: 3 3900; maximum shot time END WAIT 5 LET MF31TIME1 : INTTOT : 1 = 0 ; zeros out spike timer LET MF31TIME1 : INTETIM : I = 0 IF (SVF31AS2: DEV_STAT=2 S V F 3 1 A S 2 : D E V _ S T A T = 8 ) & (SVF31D X2: DEV_STAT=1) THEN BEGIN PRINT 1,"SPIKE PROGRAM REOPENNED SVF31DX2" TURNON SVF31DX2 END END IF ( INTIME : CB-OTVL: 1 > 30. 0) & (MF31TIME : CB-OTVL: 1 < 30. 2)) THEN LET MF31RAT2 : CAL VAVL: 1=0.30 ; set the operator adjustable variable A to 0.35 at start of run IF (MF3ITIME : CB OTVL: 1 < 24.0) THEN BEGIN LET MF31RAT2 : CB-OTHI : 3=0.55; set the hi ratio clamp at 0.55 LET MF31RAT2: CB-OTHI : 5=0. 55; set the hi ratio clamp at 0.55 END ELSE BEGIN LET MF31RAT2 : CB-OTHI : 3=0. 75; set the hi ratio clamp at 0.75 LET MF31RAT2 : CB-OTHI: 5=0. 75; set the hi ratio clamp at 0.75 END LET PHIF31FGB : CAL VCVL : 3 = 1500 ; minimum shot time LET PHIF31FGB : CAL VDVL : 3 =3900 ; maximum shot time LET PHIF31FGB : CAL-VDVL: 2 = 1500; minimum time between shots IF (ST07 > PHIF31FGB : CAL VCVL: 3) THEN IF ( ( (ST07 > PHI3 FOB : CTkL-VDVL: 3) 1 (PHIF31FM : CB-OTVL: 2 > 40.0)) & (FG06=1)) THEN BEGIN LET FG06=0 TIMERCLR ST08; zeros out minimum time between shots timer TIMERON ST08 LET MF31BIA: AI-INVL : 0 = 3; sets bias back to 3 IF MF31BIA: AI INVL: O < 0.0 THEN ; prevents bias from becoming a negative number LET MF31BIA : AI-INVL: O = 0.0 TIMEROFF ST07 ; stops shot timer from counting TIMERCLR ST07; zeros out shot timer END ; for alarm on graphics, if have a ph spike before 30 minutes minimum time after ; last shot will alarm on graphics indicating problem IF (ST07=0) & (ST08<1799) THEN IF FL10> (PHIF31FGB : CAL-VCVL : 2) & (AND (FCF31DEX : PID-SPVS: 1,64) =64 ) THEN TURNON MF31DXALM ELSE TURNOFF MF31DXALM .*********************************************************** ********** LYSINE PH PROBE ONE-POINTING AMM VALVE CLAMP SEQUENCE * LETFL19=FL20 LET FLl9=FL20 LET FL20=FL21 LET FL21=FL22 LET FL22=FL23 LET FL23=FL24 LET FL24=FL25 LET FL25=FL26 LET FL26=FL27 LET FL27=FL28 LET FL28=FL29 LETFL29=FLO8 IF ( (FL19-FL08) >0.2) & (AND (PHIF31FM : CB-FLG: 1,64) =64) & (FG13=0) THEN BEGIN LET FG13=1 LET PHIF3 IFM : CB OTHI : 1=60 PRINT 1,"PHIF31 FM PID OUTPUT CLAMPED AT 60 PERCENT" END IF ( (FL09-FL08) <0.2) & (FG13=1) THEN BEGIN LET FG13=0 LETPHIF31FM : CB OTHI : 1=100 PRINT l,"PHIF31FM PID OUTPUT HI BACK TO 100 PERCENT" END END ; * LYSINE PH PROBE ONE-POINTING AMM VALVE CLAMP SEQUENCE * ;*********************************************************** ********* GOTO LOOP2 FAULT: UINOO=ERRNUMQ UIN01=ERRLINO WAIT 10 PRINT 1,"FAULT EPP, % i line % i", UINOO, UIN01 ERSCLR GOTO LOOP END In another embodiment, the invention is implemented primarily in firmware and/or hardware using, for example, hardware components such as application specific integrated circuits (ASICs). Implementation of a hardware state machine so as to perform the functions described herein will be apparent to persons skilled in the relevant art (s).

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. The various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without the use of inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

VII. Conclusion While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art (s) that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.