Electronic Foam Controller for FermentorsV. F. PFEIFER AND E. N. HEGER

Northern Utilization Research Branch,' Peoria, Illinois

Received for publication, August 23, 1956

Present industrial practice in submerged fermenta-tions of the aerobic type requires the dispersion oflarge quantities of air, and the dissipation of largeamounts of electrical energy in motor-driven agitators.Most fermentation media foam vigorously under theseconditions, and require the addition of some type ofantifoam agent or the use of special mechanical foam-breaking equipment to confine the foam to the fermen-tor. Equipment of this type has been described byEdwards (1946), Gordon and Veldhuis (1953), Humfeldet al. (1952) and Naucler (1948).

Several types of submerged pure-culture fermenta-tions of the aerobic type are carried out at this labora-tory, and the foaming problem has been encounteredin nearly every case. Liquid antifoam agents are used tocontrol foaming. These include soybean and lard oils,industrial oil-base antifoam agents, silicone suspensions,higher alcohols, and ethanol solutions of higher alco-hols such as octadecanol.A number of devices available on the market permit

the addition of antifoam agent from a reservoir whenfoam reaches a predetermined level in a tank. Some ofthese devices operate at high potentials and offer somedanger of electric shock. A recent paper by Echevarria(1955) described an electronic foam controller actuatedby two electrodes, and functioning in a manner suchthat the foam is maintained at or below the upperelectrode tip. Stefaniak et al. (1946) described a foamcontrol system in which a definite increment of anti-foam is added to a fermentor each time an insulatedelectrode is contacted by the foam. Hersh et al. (1938)described an electronic interface controller that m*-be used as a foam controller.

This paper describes an electronic foam controllerwhich operates at low electrode voltage, is simple andeasy to construct with components readily availablefrom radio and electric supply companies, and hasfeatures not obtainable in some marketed devices ofthis nature.

FOAM CONTROL SYSTEM

Figure 1 is a diagrammatic sketch of the foam-controlsystem used at this laboratory. Sterile antifoam agentis kept in the reservoir under slightly higher pressurethan that used in the fermentor. When foam rises and

1 One of the Branches of the Agricultural Research Service,U. S. Department of Agriculture.

Sterile

FIG. 1. Foam control system

contacts the insulated electrode, the relay of the elec-tronic antifoam controller is actuated, the solenoidvalve is energized in accordance with the cyclic pro-visions of the timer, and small increments of antifoamagent are added until the foam subsides below theprobe. If desired, the anti-foam agent may be sprayedinto the fermentor through some type of spray nozzle.

Figure 2 is a schematic diagram of the electronicfoam controller, and table 1 lists the materials requiredfor its construction. The controller includes a timerwhich allows cyclic energizing of the solenoid valve,so that reaction time is provided after each incrementaladdition of antifoam agent. Sensing is accomplishedin a simple grid bias circuit in which the grid of thecontrol tube becomes negative with respect to thecathode when foam touches the insulated probe, theplate current through the relay decreases abruptly,and the solenoid valve is actuated as permitted by thetimer.

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ELECTRONIC FOAM CONTROLLER FOR FERMENTORS

Sensing CircuitNo. I

Sensing CircuitNo. 2

t115 V.

S;

II5V. 60-.TOSupply

FIG. 2. Electronic foam c

Figure 3 is a photograph of a controller that containsonly one sensing circuit. The foam controller wasadapted from an interface controller developed at thislaboratory for use with a liquid-liquid extractionprocess. Operation of the foam control system is moredependable if the solenoid valve is spring-loaded.

OPERATION

Advantages accruing from the addition of minimumamounts of antifoam during an aerobic fermentationprocess are threefold. These are as follows: maintenanceof oxygen absorption rates close to those desired;elimination of the possibility of inhibiting the growthof the organisms or altering the normal metabolicpathways; simplification of the recovery of the fermen-tation product.

In operation, the reservoir for antifoam agent andall connecting lines are sterilized with steam for about2 hr at 250 F, and the steam is replaced with sterileair during cooling. Sterile antifoam agent is transferredaseptically to the reservoir, and the pressure of sterileair is adjusted to several pounds above that in thefermentor. The electronic foam controller is actuated,and the timer is adjusted to allow introduction of anti-

controller, schematic diagram

TABLE 1. Components required for electric foam controller

T, = Power transformer, primary 115 v. 60 -, secondary480 v. at 55 ma., 5 v. at 2 a., 6.3 v. at 2 a.

Sl, S2, S3 = Toggle switches, SPST, 125 v. at 3 a.S4 = Automatic time switch for control of repeatingschedules, total cycle 30 sec, variable on-time between1 and 99 per cent of total time cycle.

F = Fuse, 250 v., 2 a.V, = Tube, type 80 or equal.V2OT3 = Tube, type 76 or equal.Ci = Dry electrolytic capacitator, 10 mfd., 450 v.Ri, R2, R4, R5 = Resistor, 20,000 0, 10 w.R3, R6 = Resistor, 5,000 Q, 5 w.R7, Rg = Potentiometer, 10 Meg., type A.PL1 = Pilot light, No. 44, 6.3 v.PL2, PL3, PL4 = Pilot lights, 115 v., 3 w.SOL1 = Antifoam agent solenoid valve, packless, 115 v. 60PCR,, PCR2 = Plate circuit relays, SPDT, 5000 Q.

foam during 2 sec out of each 30. The throttle valve isadjusted to control the dosage. The sensitivity of thecontroller is adjusted by variable resistor R7 so thatthe solenoid valve is energized if the electrode-groundresistance drops to about 100,000 ohms. This is accom-plished readily by shorting across the electrode to the

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6V. F. PFEIFER, AND E. N. HEGER

FIG. 4. Foam controller-2 sensing circuits

FIG. 3. Foam controller-1 sensing circuit

fermentor with the fingers, anid adjusting R7 so thatthe solenoid valve is then energized.

Switch S2 may be closed to add antifoam agent tothe fermentor when the probe is not covered, andswitch S3 may be closed to cut out the timer if this isdesired at any time.

J. C. Lewis at the Western Utilization ResearchBranch, USDA (1956, private communication), hasincorporated an electronic controller of this type intothe foam control system in a 50-L fermentor. In thisinstallation a small stainless-steel oxygen tank ij em-

ployed as an antifoam reservoir. Two valves next tothe tank with unions beyond permit the tank to beremoved for sterilization or weighing. The tank isvented to the fermentor head to permit gravity flow ofantifoam agent as required.

OTHER APPLICATIONS

The electronic controller may be used for other pur-poses, such as level control, or interface control inliquid-liquid systems. The instrument serves as a

simple and inexpensive level indicator when a multi-plicity of probes are used and a corresponding number ofsensing circuits are incorporated into the controller.A second sensing circuit is shown at the right in the

diagram of figure 2. Figure 4 is a photograph of a con-

troller containinig two sensinig circuits. One sensingcircuit detects and indicates foam and operates a sole-noid valve to allow the addition of antifoam agent. Thesecond circuit detects and indicates the presence offoam in the closed vent line, and serves as a safetywarning in case of any malfunction in the entire foamcontrol system.

DIscussIoNControllers of the type described in this paper have

been in operation at this laboratory for 6 years, andhave proved to be quite satisfactory. Some difficultieswere experienced with those fermentations that foameduncontrollably in the early part of the fermentationcycle. In these, foam rose to the top, left a residue onthe probe, and shorted it. In this case it was necessaryto wash the electrode. In pure-culture fermentations itwas necessary to provide a spray of sterile liquid toeliminate removal of the electrode from the fermentorfor washing.

In most fermentations the tank was left unattendedovernight, and the foam controller was successful inmaintaining the contents inside the tank, with a mini-mum consumption of antifoam agent.

ACKNOWLEDGMENTThe authors are indebted to W. H. Goss, formerly

of this laboratory, but now with Pillsbury Mills, Inc.,

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ANAEROBIC DIGESTION OF ALGAE

for development of the interface controller from whichthis foam control device was adapted.

SUMMARYThis paper describes the construction and operation

of an electronic foam controller suitable for use withfermentation vessels. Details are given of a completefoam control system making use of the electronic con-troller for the control of fermentations of the aerobictype in which large quantities of air are dispersed, andlarge amounts of electric energy are dissipated.The electronic foam controller operates at low elec-

trode voltage, and is simple and easy to construct.Components are readily available. The controller isactuated when foam in the fermentor touches an in-sulated electrode, and small increments of antifoamagent are then admitted as permitted by a timer.The controller may be used for other purposes, such

as level control, or interface control in liquid-liquid

systems. By incorporating several sensing and acti-vating circuits into the controller, it may be used toperform several functions simultaneously.

REFERENCESECHEVARRIA, J. 1955 Foam control improves fermenta-

tions. Chem. Eng., 62, No. 4, 212.EDWARDS, M. L. 1946 Foam reducer. U. S. Patent 2,401,469,

June 4.GORDON, W. 0. AND VELDHUIS, M. K. 1953 Controlling foam

in submerged and aerated propagation of microorganisms.U. S. Patent 2,635,070, April 14.

HERSH, R. E., FRY, E. M., AND FENSKE, M. R. 1938 Liquid-level control apparatus. Ind. Eng. Chem., 30, 363-364.

HUMFELD, H., AESCHLIMANN, E., AND HOFFMAN, J. R. 1952Fermentor with rotating foam-breaking vanes. U. S.Patent 2,610,155, Sept. 9.

NAUCLER, J. 0. 1948 Defrothing apparatus. U. S. Patent2,446,717, August 10.

STEFANIAK, J. J., GAILEY, F. B., BROWN, C. S., AND JOHNSON,M. J. 1946 Pilot-plant equipment for submerged produc-tion of penicillin. Ind. Eng. Chem., 38, 666-671.

Anaerobic Digestion of Algae

C. G. GOLUEKE, W. J. OSWALD AND H. B. GOTAAS

Sanitary Engineering Research Laboratory, Department of Engineering, University of California, Berkeley, California

Received for publication September 4, 1956

Stabilization lagoons, in which secondary treatmentof waste waters is accomplished through the combinedactivities of bacteria and algae, are being used exten-sively, especially as a substitute for more complexand expensive methods. In the lagoons, bacteria pri-marily decompose the organic constituents of thewastes, making them available to the algae. The algae,by way of photosynthesis, release oxygen which, inturn, is used by the bacteria to oxidize the wastes.Whenever photosynthesis is utilized for oxygenationin waste treatment, ultimate disposal of the algal cellmaterial, produced simultaneously with oxygen, may

require further processing.In low-rate deep lagoons in which the approximate

treatment rate is less than 30 lb of 5-day BOD peracre ft per day (Caldwell, 1946; Van Huvelin andSvore, 1954), the disposal problem is either minor or

nonexistent, since algae are in concentrations rarelyexceeding 20 mg per L. Many of the algae in theselagoons are consumed by planktonic phagotrophs suchas Daphnia or Cyclops, or slowly settle and become partof the complex at the lagoon bottom. Much of thissettled material is consumed by Chironomas larvae,which flourish in rich organic sediments when a smallamount of oxygen is available (Kellen, 1956). In sec-

tions of the pond bottom where anaerobiosis exists,digestion occurs and algal carbon is converted intoorganic acids, carbon dioxide, and methane. A largefraction of the-suspended algae is entrai-ned in pondcurrents and is discharged into the receiving streams,where the algae serve as food for aquatic organisms.Because of their low settling velocities, unicellularalgae ordinarily do not settle in streams, and hence donot immediately become part of stream-bottom de-posits. Natural processes thus solve the problem ofalgal disposal in low-rate ponds, excess carbon, nitrogen,and energy being dispersed into the atmosphere andwaters.

In high-rate shallow lagoons, sewage may be appliedat several times the rate used in low-rate lagoons, andphotosynthesis is practically the sole source of oxygenfor aerobic biologic decomposition of wastes. Algalconcentrations frequently reach 400 mg per L. Becauseof the high concentrations of algae characteristic ofthis process, suitable provision must be made for theultimate disposal of the algal crop. If permitted tosettle, the algae become a part of the bottom depositsand ultimately die. The algal debris then undergoesfermentation, and substances toxic to algae, such asH2S, are produced. In addition, rising gas resulting

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