Figure 1.
This liquid feeder has only one pair of syringe-pumps mounted Approximate scale 1 to 5.5
I
WALTER BORZANI and MARINA L. R. VAIRO Department of Chemistry, Escola PolitCcnica, University of
SGo Paulo, SGo
Paulo, Brazil
Liquid Feeder for Constant Low Rates This simple equipment is useful for studying the kinetics of continuous laboratory-scale fermentations
LABoRATow-scale experiments on continuous processes can be used for two important purposes: to study the kinetics of the proctss, and to observe the effect of several factors on process efficiency. Both purposes have great theoretical and economical significance, and justify the improvement of apparatus to permit a more efficient control of the experimentdl conditions. Many types of fermentors have been described for studying laboratory-scale fermentations (7, 3-5, 7). I n this particular case one of the major experimental problems is the continuous feeding of the fermentation flask with fresh sterile mash at constant low rates. Some devices were proposed to ensure constant feed (2,8>,but usually, in these
experiments, intermittent feed of nutrient medium and withdrawal of broth have been employed (6); however, this procedure does not correspond exactly to the continuous fermentation conditions. The study of the kinetics of continuous fermentations was carried out in flasks containing about 2 liters of fermenting medium. A liquid feeder was designed to permit experiments with controlled cycle times from 2 to 285 hours (feeding rates from 1000 to 7 ml. per hour, respectively). The pump described here can handle different liquids such as water, concentrated aqueous solutions, oils, and preparations containing suspended solids. Table I shows the calibration results
obtained with some assayed rates. When preparations containing suspended solids are used, the constant rate is attained after a suitable pumping time; if suspended solids are present in very high concentrations, it is necessary to clarify the liquid because the feeder is designed for very low rates and the suspended solids will settle in the connection tubes. The apparatus shown in Figure 1 has only one pair of syringe-pumps mounted. Figure 2 shows a syringe-pump system. The pistons of the syringe-pumps are operated by means of eccentric disks as shown in Figure 3. For working under sterile conditions, the entire syringe-pump system, except for the piston, and the connection tubes are sterilized by autoclaving; VOL. 51, NO. 1
JANUARY 1959
71
n
GLASS /VALVE
BAND -STEEL
Figure 2. system
LAMIN
This shows the syringe-pump Scale 1 to 2
7 Table I. Calibration of Liquid Feeder with Various Solutions a t Assayed Rates Av. Feeding Rate, Ml./Hr. % Std. Dev. With Water 8.35 24.2 123 241
997
Figure 3. disks
Scale 1 to 1
0.7 0.3 0.4 0.5 1.3
the piston is sterilized separately by autoclaving. .4fter sterilization, the syringepump system is easily mounted. hTo special lubrication is necessary on the syringes; the water condensed during sterilization and the feeding liquid are sufficient for lubrication needs. The operation times for as long as 30 hours were tested without troubles.
With 40% Sucrose Solution 6.88 22.3 115 2 13 706
2.5 1.1 0.9 0.3 1.5
With Molasses Mash" 7.24 21.6 118 231 886
1.5 1.7 1.2 0.6 0.8
Table II.
With Lubricating Oilb 3.08 18.9 32.5 60.2
Details of pumping system show that pistons are operated b y eccentric
Back pressure, Cm. of Hg
2.4
0.9 1.3 1.8
0 2 4 6 8
Mash contains about 18% reducing sugars and 1.3 grams per liter of suspended dry solids. Viscosity = 26' Engler at 28' C.
TO THE FERMENTOR
Effect of Back Pressure on Pumping Rate
Feeding Rate, M1. per Hour Test 1 Test 2 24.0 19.5 13.7 7.1 3.2
118 110 105 98 91
GLASS TUBE
"\ PISTON
SYRINGE FLEXIBLE RUBBER TUBE Figure 4. rate
72
Pressure-equalizing device can minimize back pressure on the pumping
INDUSTRIAL AND ENGINEERING CHEMISTRY
Table I1 shows the effect of back pressure on the pumping rate. This effect can be minimized, even with back pressure of 38 cm. of mercury by using the pressure equalization device illustrated in Figure 4. Acknowledgment
The authors wish to express h e i r appreciation to Francisco Branelli, Carlos J. de Resende, Gentil hlendes. Horacio S. de Oliveira, Helio P. Engelberg, Jost Genova, Boris Schneiderman? and the Instituto de Pesquizas Tecnol6gicas for their assistance in the construction of this apparatus. Literature Cited (1) Bartholomew, \$'. H., Karow, E. O., Sfat, M. R., IKD. F.NG. CHEM. 42, 1827-30 (1950). (2) Dale, R. F., Amsz, J., Jr., Shu, P., Peppler, H. J., Rudert, F. J., .4ppl. Microbiol. 1, 6 8 4 (1953). (3) Dworschack, R. G., Lasoda, A . A , , Jackson, R. W., Zbid., 2, 130-7 (1954). (4) Friedland, W. C., Peterson, M. H., Sylvester, J. C., IND.ENG. CIIEM.48, 2180-2 11956). (5) Fuld, G. J.; Dunn, C. G., -4ppl. Microhid. 6, 15-23 (1958). (6) Kroll, C. L., Formanek, S., Covert, .4. S., Cutter, L. A , , West, J . h4., Brown, Lv. E., I N D . ENG. ClIEM. 48, 2190-3
(1956). (7) Lakata, G. D., Afipl. Microbiol. 2, 2-4 (1954). ( 8 , Nelson, H. .4., Maxon, W. D., Elferdink. T. H.. IND.ENG. CHEM.48. 21 83-9'(1956). '
RECEIVED for review October 9, 1957 ACCEPrED July 16, 1958 Work supported in part by grants in aid from the Brazilian National Research Council.
