EP0877922A1

EP0877922A1 - Method for monitoring biological activity in fluids

Info

Publication number: EP0877922A1
Application number: EP97903878A
Authority: EP
Inventors: Xin Yang; Jaw Fang Lee; Sergey K. Maneshin; Terrance J. Mah
Original assignee: Biochem Technology Inc
Current assignee: Biochem Technology Inc
Priority date: 1996-01-22
Filing date: 1997-01-22
Publication date: 1998-11-18
Also published as: CN1138855C; NZ331036A; CN1212053A; CA2243190C; CA2243190A1; WO1997026525A1; AU710378B2; KR100499830B1; MY129784A; NO983360L; BR9707013A; AR005521A1; JP2000504215A; RU2192474C2; AU1833697A; EP0877922A4; KR19990081969A; NO983360D0

Abstract

A method of monitoring a microbiological process in a fluid supply involving isolation of a fluid sample from a fluid supply, measuring the pH of the fluid sample at selected time intervals, then analyzing changes in pH, if any, to determine a pH variation rate for the sample. The dissolved oxygen in the sample is also measured at selected time intervals substantially synchronously with the pH measurements, and changes in dissolved oxygen, if any, are analyzed to determine a biological oxygen consumption rate for the sample.

Description

METHOD FOR MONITORING BIOLOGICAL ACTIVITY IN FLUIDS

FIELD OF THE INVENTION

The present invention relates to a method for monitoring metabolically significant transition points during the microbial metabolism of organic and inorganic substrates and controlling the microbiological process.

BACKGROUND OF THE INVENTION Microbial use of orgamc and inorganic substrates in metabolic processes can cause detectable changes in measurable parameters such as pH and oxygen utilization rates. If nitrification is a predominant reaction within a microbial culture, the production of hydrogen ions (H⁺) from the nitrification process would be expected to decrease markedly upon the exhaustion of readily usable ammonium (NH₄ ⁺) below some metabolically critical level. Consequently, the activity of hydrogen ions in solution, i.e, pH, would also be expected to change. Similarly, the oxygen utilization of a microbial culture would be expected to be higher in a condition in which exogenous organic substrates were readily available and plentiful than in a condition where these substrates were depleted below some metabolically significant level. In both examples, the measurable rate of change in pH, sometimes hereinafter referred to as "pH production rate" or "pHPR," and oxygen utilization, sometimes hereinafter referred to as

"biological oxygen consumption rate" or "BOCR," would be directly affected by the rate of substrate metabolism over time. Thus, assuming that changes in pH and oxygen consumption in a medium result from microbial metabolic activity alone, pHPR and BOCR could theoretically be used to signal metabolically significant transition points in a microbiological process. pHPR is defined as d(pH)/dt or -Δ(ρH)/Δt and BOCR is defined as d(DO)/dt or -Δ(DO)/Δt. A negative slope of pH and/or DO results in a positive pHPR and/or BOCR measurement.

SUMMARY OF THE INVENTION The method of the invention involves the isolation of a fluid sample from a fluid supply, such as wastewater in a purification process. pHPR is calculated from pH measurements taken from the fluid sample and analyzed to quickly determine when metabolically significant transition points occur. The analysis dictates what control steps are needed and when they should be implemented to maximize the efficiency of the process being monitored.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graphic representation describing the Michaelis-Menten theory of reaction kinetics. Fig. 2 is a graph depicting theoretical responses of oxygen utilization rate

(BOCR) and rate of change in pH (pHPR) of a mixed liquor sample as concentrations of ammonium (NH₄ ⁺) and organic carbonaceous material, collectively referred to as BOD (biochemical oxygen demand), change over time in a microbiological process. Fig. 3 is a graph depicting theoretical responses of oxygen utilization

(BOCR) and rate of change in pH (pHPR) of a mixed liquor sample as the concentrations of ammonium (NH₄ ⁺) and organic carbonaceous material, collectively referred to as BOD (biochemical oxygen demand), change over time in a microbiological process. Fig. 4 shows a schematic front elevational view of one embodiment of apparatus which may be used to separate and monitor a fluid sample from a fluid supply in a bioreactor tank in accordance with the invention.

Fig. 5 graphically illustrates the relationship between the rate of oxygen change between the cessation and onset of aeration and BOCR expressed as % change in oxygen saturation per minute.

Fig. 6 graphically illustrates the relationship between the pH change between the cessation and onset of aeration and pHPR expressed as change in pH per minute as ammonia concentration changes.

Fig. 7 graphically shows the relationship between pHPR expressed as change in pH per minute and ammonia concentration where COD is not a metabolically limiting factor.

Fig. 8 graphically shows the relationship between BOCR expressed as % change in oxygen saturation per minute and ammonia concentration where COD is not a metabolically limiting factor. Fig. 9 shows the response of pHPR expressed as change in pH per minute under various conditions of ammonia and COD availability.

Fig. 10 shows the relationships between pHPR expressed as change in pH per minute, BOCR expressed as % change in oxygen saturation per minute, ammonia concentration and COD under various conditions of ammonia and COD availability.

Fig. 11 is a graph of DO and pH change versus time under continouous aeration. Fig. 12 is a graph of pH, NH₃-N concentration and d(pH)/dt versus time.

Fig. 13 is a graph of DO and d(DO)/dt versus time.

DETAILED DESCRIPTION OF THE INVENTION

The mechanistic rate at which biochemical reactions proceed can be described in part by the Michaelis-Menten theory as illustrated in Fig. 1. This theory states that the rate of biochemical reaction is very low at very low substrate concentrations, but the rate increases as substrate concentration rises until a point is reached beyond which there are vanishingly small increases in the reaction rate no matter how much the substrate concentration rises. In other words, no matter how far the substrate concentration is raised beyond this point, the reaction rate will approach, but never reach a plateau. This plateau is the maximum reaction rate or V_ma.. It is a linear extrapolation corresponding to a substrate concentration equal to 2K_S. K_s is the substrate concentration at which the metabolic reaction rate is one-half the maximum reaction rate (V_max).

It, therefore, follows that from a metabolic perspective, 2K_S is a significant substrate concentration. Microbial metabolism of a substrate proceeds above 2K_S at a maximum and nearly constant rate. The metabolic reaction rate can become variable and limited by substrate availability below 2K_S.

Consequently, changes in certain measurable parameters directly affected by and/or related to the rate of microbial metabolism of particular inorganic and organic substrates can be expected to change as the concentration of the particular substrate changes. Specifically, at a substrate concentration equal to or greater than 2K_S, the dependent measurable parameter and/or the measured rate of change in this parameter over time would be expected to be relatively constant. As a substrate concentration decreases to below 2K_S, the dependent measurable parameter and/or the measured rate of change in this parameter over time would be expected to differ markedly from the values measured when the substrate concentration was equal to or higher than 2K_S.

For many biological reactions, it is desirable to determine the point at which certain substrates have been depleted below this metabolically significant 2K_S concentration. It is possible to detect changes in the pattern of metabolic behavior of a microbial culture by monitoring changes in certain dependent measurable parameters, as the concentrations of certain organic and inorganic substrates change.

For example, in many wastewater purification processes it is an object to reduce the concentrations of certain organic and inorganic substrates to very low levels. These substrates typically include those organic substrates collectively referred to and measured as BOD (biochemical oxygen demand) and/or COD (chemical oxygen demand) and inorganic ammonium (NH₄ ⁺) . Assuming that the nitrification reaction and the BOD/COD reduction reaction were the two most predominant reactions, it would be expected that characteristic changes would be seen in both the oxygen utilization rate (BOCR) and rate of change in pH (pHPR) as BOD and ammonia are depleted below their respective 2K_S values. A drawback of utilizing BOCR and pHPR as control parameters is that in a continuous wastewater purification process, the changes in pH and DO in the fluid medium are dependent on many factors such as concentration of nutrients (biodegradable carbonaceous, nitrogenous, phosphorous compounds and the like), concentration of biomass, alkalinity and the like. Those factors are constantly changing as wastewater passes through the treatment facility. Consequently, it is difficult to obtain the relationship between the measured parameters and the performance of wastewater purification due to the interference of too many unknown and ever changing factors. Unless these interfering factors can be either detected or maintained as constant during the pH and DO measurement, pHPR and BOCR measurement will not provide more valuable information on wastewater treatment performance.

Utilization of a biological activity detecting device such as that disclosed in U.S. Patent No. 5,466,604, incoφorated herein by reference, enables in situ isolation of wastewater samples from the main body of the wastewater under treatment. Of course, other apparatus may be used in accordance with this invention. Also, the term "in situ" is used herein to describe any real-time fluid sample isolation process, irrespective of whether the sample remains in the main body of the fluid, e.g. wastewater. In other words, apparatus may be used that ^" physically removes the sample(s) from the fluid main body so long as measurements may be made substantially in "real-time" and/or "on-line. "

Theoretical responses of BOCR and pHPR to concentration changes in BOD and ammonia (NH₄ ⁺) are depicted in Figs. 2 and 3 and explained below. The Figures graphically represent responses from a single sample of mixed liquor (i.e. , wastewater) and microbes for biological nutrient removal (BNR) isolated from the main body of wastewater. The isolated sample is alternatively aerated and not aerated. Aeration begins and continues until a level of dissolved oxygen has been reached that is higher than the DO level in the main body of wastewater by a margin. Once this level is reached, the aeration stops and only begins once the level of dissolved oxygen within the sample reaches a level that is lower than the level of DO in the main body of wastewater by a margin. During the periods where aeration is not conducted, both BOCR and pHPR are evaluated and calculated as follows: BOCR = -(ΔDO)/(Δt) wherein ΔDO is equivalent to the change in saturation level of dissolved oxygen, expressed as percent saturation, measured over a time period Δt; and pHPR = -(ΔpH)/(Δt) wherein ΔpH is equivalent to the change observed in pH over a time period Δt. As shown in Period A of Figs. 2 and 3, when both the concentrations of

NH₄ ⁺ and BOD are above their respective 2K_S values, BOCR is constant and at its highest relative level, since BOD utilization proceeds at maximum rates and wins the competition over oxygen consuming reactions of nitrification. Thus pHPR is constant at a moderate level. This BOCR/pHPR pattern, as well as those described below, is expected assuming that 1) the nitrification and BOD utilizing reactions are the predominant reactions ongoing within the biological sample, 2) the production and activity of hydrogen ions are related to the rate of the nitrification reaction, and 3) the reactions are not limited by the availability of oxygen. Subsequently, continued metabolism depletes the available NH₄ ⁺ below its 2K_S value and, the rate of nitrification, hydrogen ion production falls from a maximum rate to a lower rate where ammonia concentration is a metabolically limiting factor. As shown in Period B of Fig. 2, pHPR drops significantly to a ^" comparatively low level and BOCR drops to a comparatively moderate level to reflect the decreased demand and use of oxygen caused by the significantly lower nitrification reaction rate. The transition from an ammonia concentration above the 2K_S value to below the 2K_S value is depicted in the transition between periods A and B in Fig. 2.

Period C of Figs. 2 and 3 shows that where the concentration of available NH₄ ⁺ is below its 2K_S value and upon depletion of BOD below its 2K_S value, pHPR increases very slightly to reflect the change in net metabolic behavior of the mixed biological population and BOCR drops to its lowest rate to reflect the very low oxygen utilization by BOD consuming and nitrification reactions. This transition is depicted between Periods B and C in Fig. 2.

Period D of Fig. 3 shows that where the concentration of BOD is below its 2K_S value, but the concentration of NH₄ ⁺ is above its 2K_S value, pHPR increases to its highest level reflecting a high rate of nitrification and BOCR drops to a moderate level reflecting a net decrease in total oxygen utilization caused by the decreased level of BOD consuming reactions. The highest pHPR is seen under this condition because the buffering effects of the BOD consuming reactions are absent. Normally, production of C0₂ in the BOD consuming reactions affords some pH buffering capacity to the sample via a carbonic acid system. Thus, in the absence of BOD consuming reactions and the resulting production of C0₂, the pHPR is much greater than in the other conditions.

It is possible to determine pertinent information about the biological sample based on the example provided above, by monitoring and comparing trends and/or levels of BOCR and pHPR because they represent key measurable, dependent parameters of microbial metabolic activity. Specifically, this example illustrates how a determination can be made as to whether 1) both nitrification and BOD removal are occurring simultaneously at maximum rates, 2) nitrification is occurring while BOD has been reduced to levels below its 2K_S value, 3) BOD removal reactions are ongoing while ammonia has been reduced below its 2K_S value, and 4) both ammonia and BOD have both been reduced below their respective 2K_S values.

Direct and continuous comparison of the measured parameters BOCR and pHPR leads to several conclusions about the condition of the wastewater. If a mixed liquor sample is continuously monitored and a large increase in pHPR occurs simultaneously with a decrease in BOCR, this indicates that BOD has been depleted below its respective 2K_S value while ammonia is still plentiful. If a mixed liquor sample is continuously monitored and BOCR decreases to a moderate level while pHPR decreases to a near zero level, it indicates that ammonia has been depleted below its respective 2K_S value while BOD is still plentiful. If a mixed liquor sample is continuously monitored and BOCR decreases to a low level while pHPR decreases to a low level, it indicates that both ammonia and BOD have been depleted below their respective 2K_S values. This condition is also indicated by a decrease in BOCR to a low level and slight increase in pHPR from a near zero level to a slightly higher, but low, level.

Table I summarizes these patterns and illustrates how comparison of the relative values and patterns of the measured parameters of BOCR and pHPR yields the pertinent information described above in conjunction with Figs. 2 and 3.

TABLE I

Fig. 4 shows an example of a preferred apparatus used to isolate a wastewater sample. The apparatus 11, immersed in wastewater batch 2 (only a portion of which is depicted), includes a detection chamber 8 having a movable cover 32. Movable cover 32 is pushed in the direction of arrow "A" by inner shaft 56 driven by an Acme shaft 57 connected to motor 53. At the open position, rotation of propeller 48 forces an exchange of wastewater between the inside and outside of detection chamber 8 and detection chamber 8 is filled with a fresh sample of wastewater. After a given period of time, e.g. 30 seconds, motor 53 is programmed to reverse its rotation direction, movable cover 32 is pulled in the direction of arrow "B" until detection chamber 8 is fully closed and sealed. The movable cover 32 and propeller 48 are driven by the same reversible low RPM motor 53 which coaxially connects inner shaft 56 and outer shaft 55. The coaxial assembly is shielded by stainless steel pipe 54. The DO concentration is detected by DO probe 10 after filling detection chamber 8 with a fresh sample of wastewater and, if DO is less than the oxygen concentration in the main body of wastewater by a given margin, air and/or oxygen is pumped into detection chamber 8 through aeration tube 13 until that DO concentration is attained. A DO concentration at a level that is higher or lower than the oxygen concentration in the main body of wastewater by a given margin will ensure that the aerobic metabolic reactions inside detection chamber 8 is the same or close to the nutrient removal process in the main body of wastewater. Similarly, pH probe 12 detects changes in pH. Additionally, propeller 48 may be periodically or constantly rotated to maintain the sample in well-mixed and suspended condition.

Aeration in the apparatus 11 is interrupted for the measurement interval after the maximum DO concentration is attained. During this period, residual DO concentration and pH, both unaffected by aeration of the wastewater batch at large, are monitored through the probes. The pH and residual DO signals from the respective probes 12 and 10 are sent to controllers which convert changes in DO over time to BOCR and changes in pH over time to pHPR by numerical differentiation according to the equations (6) and (7) described above.

In most wastewater treatment plants, concentrations of BOD and ammonium in the final effluent are below the 2K_S values of BOD and NH₄ ⁺ . When the concentration of BOD and NH₄ ⁺ in the detection chamber decrease to below 2K_S values, the aerobic metabolic reactions for nutrients removal is considered complete with significant changes in BOCR and pHPR values. The completion of aerobic metabolic reactions for nutrients removal can be detected through BOCR and pHPR analysis according to the criteria listed in TABLE I. For other biological processes the concentrations of substrates in the medium is usually considerably higher than 2K_S values to maintain maximum rate of microbial growth and production of target substance. Thus, the detection of completion of metabolic reactions will signal the requirement of nutrient and substrate addition, or the time to stop the biological process, or the time to harvest the target substance produced during the process.

Information about the aerobic metabolic reactions for nutrients removal, such as the nitrification completion time (NT), denitrification time (DNT), etc. can be used for adjusting and controlling the wastewater purification process and other aerobic metabolic processes. For example, the measured NT can be compared with the average hydraulic retention time of wastewater in aeration basins in a wastewater treatment plant. If NT is significantly shorter than HRT, the aerobic nutrient removal is finished in a section in the middle of the aeration basin. The rest of the aeration basins after this section where nutrients removal is finished is, in fact, in an idle condition and does not contribute to the wastewater purification process. In this case, the plant can take proper actions to: (1) remove certain sections of aeration basins from service to save operation costs, and/or (2) accept more volume of wastewater and effectively increase the treatment capacity of the plant, and/or (3) reduce the amount of air supplied to the aeration basins to reduce the rate of aerobic metabolic reactions so that NT will closely match HRT in the aeration basins and reduce the power consumption from air blowers.

EXAMPLE 1 A mixed liquor sample recovered from the aerobic basin of an advanced biological wastewater treatment plant located in Oaks, Pennsylvania, was isolated in a vessel equipped with devices to measure sample pH and dissolved oxygen saturation levels, as well as devices to aerate and maintain the sample in a well mixed condition. The data from the devices measuring sample pH and dissolved oxygen saturation levels was recorded and analyzed by a computer to calculate

BOCR and pHPR. The sample was exposed to fixed, alternating periods of aerated and non-aerated conditions. Aeration began and continued until a level of dissolved oxygen was reached that was compatible with that in the main body of the wastewater plus a margin when the sample was isolated. Once this level was reached, aeration was stopped and only began once the level of dissolved oxygen within the sample fell to the level lower by a margin than the DO of the main body of the wastewater when the sample was isolated. Concentrations of NH₄ ⁺ and soluble carbonaceous organic substrates were measured and reported as COD. Linear correlation existed between COD and BOD. Therefore, COD analysis was used to represent BOD concentration. During the periods of non- aeration, examples of which are marked with arrows on Figs. 5 and 6, both BOCR and pHPR was evaluated and calculated by numerical differentiation as described above.

Fig. 5 shows dissolved oxygen saturation and BOCR during a period of the test where the measured COD concentration was consistently greater than 150 mg COD/L, which was well above the 2K_S value for COD, but where the ammonia concentration varied from a concentration above the 2K_S value to a concentration below the 2K_S value. Fig. 5 reveals the relationship between the raw dissolved oxygen data, that is the rate of oxygen change between the cessation and onset of aeration as indicated, and BOCR. Fig. 5 also illustrates the transition in the level of BOCR from a high to a moderate level during the metabolically significant transition when ammonia concentration dropped below its 2K_S value. BOCR is expressed as % change in oxygen saturation per minute.

Fig. 6 shows the sample pH and pHPR for the same period as depicted in Fig. 5. During this period the measured COD concentration was consistently greater than 150 mg COD/L, which was well above the 2K_S value for COD, but the ammonia concentration varied from above its 2K_S value to below the 2K_S value. Fig. 6 illustrates the relationship between the raw pH data, i.e, the pH change between the cessation and onset of aeration as indicated, and pHPR. Fig. 6 also illustrates the transition in pHPR from a moderate to a near zero level during the metabolically significant transition when the ammonia concentration dropped below its 2K_S value. pHPR is expressed as change in pH per minute. Fig. 7 shows the changes in measured ammonia levels and calculated pHPR for the same period as depicted in Fig. 6. Fig. 7 illustrates the transition in pHPR from a moderate to a near zero level during the ammonia concentration transition from about 2K_S to below 2K_S. pHPR is expressed as change in pH per " minute.

Fig. 8 shows the changes in measured ammonia levels and calculated

BOCR for the same period as depicted in Fig. 5. Fig. 8 illustrates the transition in BOCR from a high to a moderate level during the ammonia concentration transition from above 2K_S to below 2K_S. BOCR is expressed as % change in oxygen saturation per minute.

Fig. 9 graphically depicts the consistency of the response of pHPR to ammonia concentrations. This was accomplished by the addition of an ammonia solution to the mixed liquor sample at points where the ammonia contained within the sample was depleted, i.e., at T= 120 and T= 170 minutes. From the period between T=0 and T= 195 minutes, COD concentration was well above its 2K_S value. After T= 195 minutes, COD concentration dropped below its 2K_S value. At about T =90 minutes, a significant transition can be observed in pHPR as ammoma concentration is depleted below its 2K_S value. Subsequent additions of ammonia were made at T= 120 and T= 170 minutes when pHPR was at a near zero level. Fig. 9 shows that pHPR jumped from the near zero level immediately before each subsequent addition to a comparably moderate level like that observed between T=0 and T=90 minutes. After the subsequent ammonia additions, pHPR returned to a near zero or low level upon depletion of ammonia below its 2K_S value. COD was plentiful and ammonia depletion resulted in a pHPR decrease to a near zero level in the case of the first ammonia addition at T= 120 minutes. Ammonia depletion occurred at a time when COD concentration was also just depleted to below its 2K_S value in the second case of ammonia addition at T= 170 minutes. Consequently, the pHPR decreases to a low, but not zero, level as shown in Period C of Figs. 2 and 3.

Fig. 10 provides a more complete picture of the data shown in Fig. 9 and includes calculated pHPR, calculated BOCR, ammonia and COD concentrations. Fig. 10 best illustrates the transitions in pHPR and BOCR between the different relative levels as significant metabolic events occur.

It is possible to quickly and accurately ascertain the moment when the concentration of organic substrates and/or inorganic substrates fall below their respective 2K_S levels as evidenced by this Example, by monitoring relative levels of BOCR and pHPR, in accordance with the invention. Detecting the depletion of a particular substrate below its respective and metabolically significant 2K_S concentration value frequently signals a significant change in the condition of a microbial population or its environment, or a change in the metabolic pattern and/or behavior of a sample containing active microbes.

Various control steps may then be taken in response depending on the particular process. For example, the depletion of a particular substrate in a microbial population might signal a change in metabolism whereby the production of a desirable secondary metabolite may ensue, thus indicating that the process should proceed to a separation, collection and/or purification phase.

Similarly, in biological processes where it is the object to maintain a particular step-feeding protocol of substrate to a microbial population, the capability to detect the depletion of this substrate below its 2K_S concentration and/or when substrate addition increase the substrate concentration above 2K_S can be used to indicate that increased or decreased feeding of substrate is desirable.

Example 1 involved aerobic biological wastewater purification, where it is often the object to reduce through biological mechanisms particular inorganic and organic substrates such as the reduction of soluble ammonia and carbonaceous organics. Thus, various control steps may be taken in response to the depletion of one or more of these substrates below its 2K_S concentration, as a concentration of 2K_S is often below the low concentration level targeted for many substrates. For example, if both organic and inorganic (ammonia) substrates are found to be below their respective 2K_S concentration values, the flow rate through the wastewater treatment process can be increased, thereby increasing the capacity of the treatment facility. If both organic and ammonia substrates are found to be above their respective 2K_S concentration values, the flow rate through the wastewater treatment process can be decreased. When ammonia substrate is below 2K_S but organic substrate is above 2K_S, aeration of the batch can be decreased due to the reduced desire for nitrification. Finally, if the organic substrate is below 2K_S but ammonia substrate is above 2K_S, aeration can be increased to create a more favorable condition for nitrification. EXAMPLE 2

In Example 2, a mixed liquor sample was isolated in the same manner as described in Example 1. Continuous aeration to the mixed liquor sample was maintained throughout the period in which the sample was kept in isolation. The aeration rate was selected so that the dissolved oxygen concentration level in the sample was higher than the critical value required for biological carbonaceous nutrient and ammonia removal. The oxygen concentration and pH changes were monitored by a dissolved oxygen probe and a pH probe as shown in Fig. 11.

Then, a small volume of mixed liquor was periodically withdrawn from the isolated sample and the ammonia concentration analyzed. Fig. 12 shows the changes in pH and ammonia concentrations during the entire aeration period in which the sample was isolated. The end of nitrification (ammonia concentration was lower than detection level, i.e. 0.1 ppm) was accompanied by a slow increase in the pH value. A derivative of pH against time, d(pH)/dt was plotted and is shown in

Fig. 12. When the ammonia concentration approached zero, the value of d(pH)/dt passed the second zero point. The characterization of d(pH)/dt as being at the second zero point can also be referred to as the point where d(pH)/dt changes from a negative value to zero. The time corresponding to this point is defined as the nitrification completion time of the mixed liquor or NT. In

Example 2 and as shown in Fig. 12, NT is measured at about 75 minutes. The d(pH)/dt measurement in Example 2 is different from that in Example 1. In Example 1, the d(pH)/dt was measured during the non-aeration period, while in Example 2, d(pH)/dt was measured with continuous aeration. Due to continuous strip off of C0₂ from the mixed liquor, it is possible to see a pH decrease in the pH measurement. Thus, pHPR is sometimes negative.

Fig. 13 shows the dissolved oxygen profile and its derivative, d(DO)/dt for the same sample. As ammoma was consumed, the value of the first derivative of DO, d(DO)/dt, started to increase significantly. The value of nitrification time (NT) measured from DO was also at about 75 minutes.

One practical application of NT measurement in the control of biological nitrification process will now be described here. In a bioreactor or a series of bioreactors where the biological nitrification process is taking place, one sampling device is installed at the very beginning of the bioreactor or the front of the first bioreactor in the series. The measured NT indicates that at current biomass concentration and ammonia loading, it will take time NT to complete the nitrification. The hydraulic retention time (HRT) of the mixed liquor in the bioreactor or the series of bioreactors is calculated by considering the flow rate and flow pattern of the mixed liquor and the geometry of the bioreactor or the series of bioreactors. NT is then compared with the hydraulic retention time of the mixed liquor. A proper nitrification process will have comparable values of NT and HRT in daily operations. When NT is considerably smaller than HRT, nitrification is finished in the bioreactor or the series of bioreactors earlier than the given HRT, which means the process has extra nitrification capacity. In the case where other contaminants are removed before ammoma is fully nitrified, NT detection signals the end of the wastewater treatment process. This indicates that the process can treat more wastewater with the given tankage volume under the same operation conditions or the process can reduce the volume of tankage in the operation and realize some saving in operation costs.

On the other hand, if NT is longer than HRT, the concentration of ammonia will be higher than zero but not necessarily higher than the discharge permit. To ensure the quality of the plant discharge, the aeration rate to the bioreactor (s) and/or mixed liquor concentrations is increased. When the condition that NT is longer than HRT for a prolonged period, this tends to indicate that the process is overloaded regarding ammonia removal and the treatment facility will likely have to be expanded to treat the given volume of wastewater.

In general, by comparing NT and HRT, information such as the nitrification capacity of the process, the required aeration rate to the bioreactor or the series of bioreactors, and the quality of the effluent from the bioreactor, can be determined and sent to the plant operator for adjustment of the nitrification process. The invention may be applied to any kind of microbial process including, but not limited to, wastewater purification (municipal, industrial and the like), pharmaceutical/biotechnology production, brewing, fermentation or any other process involving pure or mixed populations of microorganisms.

Claims

" What Is Claimed Is:

1. A method of monitoring a microbiological process in a fluid supply having a microbial population comprising: a) isolating a fluid sample from said fluid supply; b) measuring the pH of said fluid sample at selected time intervals; c) analyzing changes in pH, if any, to determine a pH variation rate for said sample; d) measuring amounts of dissolved oxygen in said fluid sample at selected time intervals substantially synchronously with said measuring of pH; and e) analyzing changes in dissolved oxygen, if any, to determine a biological oxygen consumption rate for said sample.

2. The method defined in claim 1 wherein analyzing changes in pH to determine said pH variation rate is performed according to the following formula: pHPR = (dpH)/(dt) wherein pHPR is said pH variation rate, dpH is a change in pH and dt is a change in time and dpH and dt both approach zero.

3. The method defined in claim 1 wherein said measuring of pH and dissolved oxygen is substantially continuous.

4. The method defined in claim 1 wherein analyzing changes in DO to determine said biological oxygen consumption rate is performed according to the following formula:

BOCR = (dDO)/(dt) wherein BOCR is said biological consumption rate, dDO is a change in dissolved oxygen and dt is a change in time and dDO and dt both approach zero.

5. The method defined in claim 1 further comprising repeating steps b) through e) at selected time intervals and comparing newly determined pH variation rate(s) and biological oxygen consumption rate(s) with previously determined pH variation rate(s) and biological oxygen consumption rate(s).

6. The method defined in claim 5 wherein comparing said newly determined pH variation rate(s) and biological oxygen consumption rate(s) with previously determined pH variation rate(s) and biological oxygen consumption rate(s) determines whether levels of organic and inorganic compounds in said fluid supply are greater or less than their respective 2K_S concentrations.

7. The method defined in claim 1, further comprising the step of performing a control step in response to changes in said pH variation rate(s) and/or said biological oxygen control rate(s), if any.

8. The method according to claim 7, wherein said fluid supply is aerated and has a fluid supply process flow, and wherein said control step is at least one treatment selected from the group consisting of increasing aeration of said fluid supply, decreasing aeration of said fluid supply, increasing said fluid supply process flow and decreasing said fluid supply process flow.

9. The method according to claim 7, wherein a feeding protocol of substrate additions is maintained for said microbial population, and wherein said control step comprises varying said substrate additions.

10. The method according to claim 7, wherein said microbiological process produces a desirable metabolite, and wherein said control step is at least one step selected from the group consisting of separation of said metabolite from said fluid supply, collection of said metabolite and purification of said metabolite.

11. The method defined in claim 1 wherein said step of isolating said fluid sample is performed in situ.

12. The method according to claim 1, wherein before said steps of measuring the pH and amounts of dissolved oxygen the fluid sample contains a desired dissolved oxygen content.

13. The method according to claim 1, wherein said fluid sample is isolated in a fluid sample chamber, said fluid sample chamber including an aerator capable of supplying air and/or oxygen in said fluid sample and a sample agitator.

14. The method according to claim 13, further comprising aerating said fluid sample with said aerator during the entire duration said sample is isolated in said sample container and dissolved oxygen and pH in said sample are continuously measured while said sample is continuously agitated.

15. The method of claim 13, further comprising the steps of aerating said fluid sample with said aerator until said fluid sample contains a desired level of saturation of dissolved oxygen before the steps of measuring the pH and amounts of dissolved oxygen of said fluid sample, and periodically or continuously agitating said sample with said agitator during the steps of measuring the pH and amounts of dissolved oxygen of said fluid sample.

16. The method defined in claim 1 applied to a microbiological process selected from the group consisting of wastewater purification, pharmaceutical production and brewing.

17. A method of monitoring a microbiological process in a fluid supply having a microbial population comprising: a) isolating a fluid sample from said fluid supply; b) measuring the pH of said fluid sample at selected time intervals; c) analyzing changes in pH, if any, to determine a pH production rate for said sample; d) determining when said pH production rate 1) changes from a negative value to zero and/or 2) changes to zero for a second time; and e) displaying results from said determination.

18. The method defined in claim 17 wherein analyzing changes in pH to determine said pH production rate is performed according to the following formula: pHPR = (dpH)/(dt) wherein pHPR is said pH production rate, dpH is a change in pH and dt is a change in time and dpH and dt approach zero.

19. The method defined in claim 17 wherein said measuring of pH is substantially continuous.

20. The method defined in claim 17 further comprising: f) measuring amounts of dissolved oxygen in said fluid sample at selected time intervals substantially synchronously with said measuring of pH; and g) analyzing changes in dissolved oxygen, if any, to determine a biological oxygen consumption rate for said sample.

21. The method defined in claim 19 wherein analyzing changes in dissolved oxygen to determine said biological oxygen consumption rate is performed according to the following formula:

BOCR = (dDO)/(dt) wherein BOCR is said biological consumption rate, dDO is a change in dissolved oxygen and dt is a change in time and dDO and dt approach zero.

22. The method defined in claim 17 further comprising repeating steps a) through e) at selected time intervals and comparing newly determined pH production rate(s) with previously determined pH production rate(s).

23. The method defined in claim 20 further comprising repeating steps a) through g) at selected time intervals and comparing newly determined pH production rate(s) and biological oxygen consumption rate(s) with previously determined pH production rate(s) and biological oxygen consumption rate(s).

24. The method defined in claim 17, further comprising the step of performing a control step in response to changes in said pH production rate(s).

25. The method according to claim 24, wherein said fluid supply is aerated and has a fluid supply process flow, and wherein said control step is at least one treatment selected from the group consisting of increasing aeration of said fluid supply, decreasing aeration of said fluid supply, increasing said fluid supply process flow and decreasing said fluid supply process flow.

26. The method according to claim 24, wherein said control step comprises determining a nitrification time as elapsed time between sample isolation and pH production rate changing from said negative value to zero and/or changing to zero for a second time, measuring hydraulic retention time in said fluid supply and comparing said nitrification time to said hydraulic retention time.

27. The method according to claim 26, wherein said control step further comprises increasing the rate of fluid input to the fluid supply or reducing the rate of aeration to the fluid supply when said nitrification time is less than said hydraulic retention time or increasing the rate of aeration of the fluid supply when said nitrification time is greater than said hydraulic retention time.

28. The method defined in claim 17 wherein said step of isolating said fluid sample is performed in situ.

29. The method according to claim 17, wherein before said steps of measuring the pH and amounts of dissolved oxygen the fluid sample contains a dissolved oxygen content of from zero to 100% of saturation.

30. The method according to claim 17, wherein said fluid sample is isolated in a fluid sample chamber, said fluid sample chamber including an aerator capable of supplying air and/or oxygen to said fluid sample and a sample agitator.

31. The method of claim 30 further comprising the steps of aerating said fluid sample with said aerator until said fluid sample contains dissolved oxygen at a level that is higher than the DO level in the sample when it is isolated, by a margin, before the steps of measuring the pH of said fluid sample, and periodically agitating said sample with said agitator during the steps of measuring the pH of said fluid sample.

32. The method defined in claim 17 wherein said microbiological process is selected from the group consisting of wastewater purification, pharmaceutical or biotechnological production, brewing and fermentation.

33. The method according to claim 32, further comprising aerating said fluid sample with said aerator during the entire duration while said sample is isolated in said sample container and dissolved oxygen and pH in said sample are continuously measured while said sample is continuously agitated.

34. The method defined in claim 17 further comprising substantially continuously aerating said fluid sample.

35. A method of monitoring and controlling a microbiological process in a fluid supply having a microbial population comprising: a) isolating a fluid sample from said fluid supply; b) measuring the pH of said fluid sample at selected time intervals; c) analyzing changes in pH, if any, to determine a pH production rate for said sample; d) determining when said pH production rate 1) changes from a negative value to zero and/or 2) changes to zero for a second time; and e) performing a controlling step in response to changes in said pH production rate(s), said controlling step comprising: f) determining a nitrification time as elapsed time between sample isolation and pH production rate changing from a negative value to zero and/or changing to zero for a second time; g) measuring hydraulic retention time in said fluid supply and comparing said nitrification time to said hydraulic retention time; and h) increasing the rate of fluid input to the fluid supply or reducing the rate of aeration of the fluid supply when said nitrification time is less than said hydraulic retention time or increasing the rate of aeration of the fluid supply when said nitrification time is greater than said hydraulic retention time.