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The application of the foam fractionation process to the removal of viruses process to the removal of viruses
740
M.D. G t v . J D MclvEP, and M. J. LEWIS
PART II. THE PREDICTION OF THE RESIDUAL SURFACTANT CONCENTRATION Abstract Variations in the initial concentration of the surfactant. Arquad T50 ta blend of alkyl quaternary ammonium chloridesL and the gas to liquid flog ratio were assessed for their effect upon the residual surfactant level. This concentration was found to be dependent upon these variables as welt as upon the bubble diameter in the liquid phase as determined by the gas rate. An equation was derived which represented the removal of surfactant as a power function of il its initial concentration. lii) the gas to liquid flow rate ratio and (iii) the gas flow rate. The error of this equation established that this empirical approach accurately represented the removal of the surface-active agent. INTRODUCTION
In part l, a mathematical model was presented which predicted the removal of viruses during foam fractlonanon. This equation required that the residual surfactant concentration be k n o w n and therefore for prediction studies it should be derivable. Grieves a n d his co-workers (1965: 1968:19701 had found that the residual surfactant concentration could be determined from:
L- B
=
°)°(L)b(T)'(D)a
k(-/
111
where L is the initial surfactant concentration, B is the residual concentration in the treated water. G a n d F are the air and liquid feed rates, T is the temperature. D is the bubble diameter (dependent upon the pore size of the sparger) a n d k. a. b. c a n d d are constants. As these constants were dependent upon the type of surfactant a n d construction of the apparatus. our initial object was to determine their particular values for the equipment in use. MATERIALS AND METHODS The surfactant, its assay, the plant construction and operation were reported in part I. RESULTS AND DISCUSSION
Regression analysis of this data revealed that the relationship was as predicted by Grieves and Bhattacharyya (1965) a n d this could be represented by: L- B =klL¢' {2~ However. experiments to determine the effect of the G a s rate to Liquid feed rate ratio on the removal of surfactant, revealed this relationship to be different from that predicted by Grieves a n d Bhattachary.va [1965), in that surfactant removal was not solely related to this ratio IFig. l/. Examination of the liquid phase revealed a direct relationship between bubble size a n d air rate. This observation explains the discrepancy noted since Grieves and Bhattacharyya h a d concluded that bubble diameter did not alter significantly provided that the pore size of the sparger was a constant, However, these workers operated at air rates between 3000 a n d 4000 ml r a i n - ' and it is probable that bubble size did not vary over this limited range. It appeared, therefore, that the use of a wide range of air rates {2500-7500 ml rain - t ) necessitated that the size of the air bubbles be measured and included in any formula for the prediction o f surfactant removal. However. the diameter o f rapidly rising bubbles is not easily determined a n d a n empirical a p p r o a c h g E
During initial studies, the air rate to liquid feed rate ratio was kept constant while the effect of feed surfactant concentration was investigated. This demonstrated that the a m o u n t of surfactant removed was a function of its initial concentration (Table 1). Table I The relationship between the initial surfactant concentration and the amount of surfactant removed
log [L -8}
1&77C /
8 s
1 4.75( U3
2
3urfactant Concentration * ( ~ / ~ )
1.L760
1./.7/. 0
/
/
/
.# In£ti&l
l~-mov~d
30
Z9.86
20
T9.91
10
9.96
5
h'97
* G a s rate to Liquid held constant at 25.0.
feed rate
¢2
¢.6
~:8
2:0 -~o~)
Fig. I. The effect of the air rate (G) on the relationship the ratio of the flow rates (GF- t) and the coneentration of surfactant removed (L-B). Initial surfactant concentration 30mgl - t . air rates: + a. 7500mlmin-~: O -O 5000 ml rain - I : [] '7 2500 ml rain - t between
ratio
,I~
Logorithm of the Gos Rote to Liquid Feed Rote
Foam fractionation process to removal of viruses--H
Y
4
L-
95
z..90
Further regression analysis of the data, revealed that for our equipment:
I(}0
5.0
9"95
5-;0
4195
9"90
/
I
l,
9"95 10-00
30"0 29'8C
I
19.60
t
I
19,90 20:00
t
X
29"60 29-80 30"00
Fig. 2. Experimental and calculated surfactant concentrations removed from the bulk liquid. X is the calculated concentration [using Equation (4)] in m g l - t : y is the experimentally measured concentration in mgl- ~; + represents single points; © represents duplicate points; A represents triplicate points.
was required. From Fig. 1 it was noted that the removal of surfactant was related to the air rate, and, since this factor also affected the bubble diameter, it appeared that the air rate could be used as an indication of bubble variation. Analysis of the data revealed that this was the case and that removal of Arquad T50 could be predicted by the equation: L-
B = k
(L)b(G)"
(4)
This equation was found to produce results that varied from the experimental assessment by only 0.16600. (Fig. 2). It was also determined that the error of equation (4) varied randomly within the temperature variations experienced (17-24=C) and. over this range, surfactant removal was independent of the temperature. CONCLUSIONS
4.
19.81 / ~ ÷
B = (t.009311)-1[ G I °°°-~'< ~.,F/ X (L)t°°°sv65(G) -0-00 I93
YI
20
/4,t
(3)
A model has been developed to predict the residual surfactant concentration from the operating parameters of foam fractionation equipment. It is believed that this model is more accurate than those previously presented because of the incorporation of a factor which is an indication of the alteration in the bubble size. The calculated values can also be used in conjunction with the formula previously presented in part I to determine the efficiency of such processes in removing viruses. It is interesting to note that the residual surfactant concentrations obtained were extremely low (0.01~3.25 mg 1-t) and that they could be reduced to undetectable levels by treatment with activated carbon. REFERENCES
Grieves R. B. & Bhattacharyya D. (1965) The foam separation process: a model for waste treatment applications. J. War. Pollut. Control Fed. 37, 980--989. Grieves R. B. (1968) Studies on the foam separation process. Brit. Chem. Engng 13, 77-82. Grieves R. B.. Ogbu I. U., Bhattacharyya D. & Gonger W. L. (1970) Foam fractionation rates. Sep. Sci. 5, 583-601.
M.D. G t v . J D MclvEP, and M. J. LEWIS
PART II. THE PREDICTION OF THE RESIDUAL SURFACTANT CONCENTRATION Abstract Variations in the initial concentration of the surfactant. Arquad T50 ta blend of alkyl quaternary ammonium chloridesL and the gas to liquid flog ratio were assessed for their effect upon the residual surfactant level. This concentration was found to be dependent upon these variables as welt as upon the bubble diameter in the liquid phase as determined by the gas rate. An equation was derived which represented the removal of surfactant as a power function of il its initial concentration. lii) the gas to liquid flow rate ratio and (iii) the gas flow rate. The error of this equation established that this empirical approach accurately represented the removal of the surface-active agent. INTRODUCTION
In part l, a mathematical model was presented which predicted the removal of viruses during foam fractlonanon. This equation required that the residual surfactant concentration be k n o w n and therefore for prediction studies it should be derivable. Grieves a n d his co-workers (1965: 1968:19701 had found that the residual surfactant concentration could be determined from:
L- B
=
°)°(L)b(T)'(D)a
k(-/
111
where L is the initial surfactant concentration, B is the residual concentration in the treated water. G a n d F are the air and liquid feed rates, T is the temperature. D is the bubble diameter (dependent upon the pore size of the sparger) a n d k. a. b. c a n d d are constants. As these constants were dependent upon the type of surfactant a n d construction of the apparatus. our initial object was to determine their particular values for the equipment in use. MATERIALS AND METHODS The surfactant, its assay, the plant construction and operation were reported in part I. RESULTS AND DISCUSSION
Regression analysis of this data revealed that the relationship was as predicted by Grieves and Bhattacharyya (1965) a n d this could be represented by: L- B =klL¢' {2~ However. experiments to determine the effect of the G a s rate to Liquid feed rate ratio on the removal of surfactant, revealed this relationship to be different from that predicted by Grieves a n d Bhattachary.va [1965), in that surfactant removal was not solely related to this ratio IFig. l/. Examination of the liquid phase revealed a direct relationship between bubble size a n d air rate. This observation explains the discrepancy noted since Grieves and Bhattacharyya h a d concluded that bubble diameter did not alter significantly provided that the pore size of the sparger was a constant, However, these workers operated at air rates between 3000 a n d 4000 ml r a i n - ' and it is probable that bubble size did not vary over this limited range. It appeared, therefore, that the use of a wide range of air rates {2500-7500 ml rain - t ) necessitated that the size of the air bubbles be measured and included in any formula for the prediction o f surfactant removal. However. the diameter o f rapidly rising bubbles is not easily determined a n d a n empirical a p p r o a c h g E
During initial studies, the air rate to liquid feed rate ratio was kept constant while the effect of feed surfactant concentration was investigated. This demonstrated that the a m o u n t of surfactant removed was a function of its initial concentration (Table 1). Table I The relationship between the initial surfactant concentration and the amount of surfactant removed
log [L -8}
1&77C /
8 s
1 4.75( U3
2
3urfactant Concentration * ( ~ / ~ )
1.L760
1./.7/. 0
/
/
/
.# In£ti&l
l~-mov~d
30
Z9.86
20
T9.91
10
9.96
5
h'97
* G a s rate to Liquid held constant at 25.0.
feed rate
¢2
¢.6
~:8
2:0 -~o~)
Fig. I. The effect of the air rate (G) on the relationship the ratio of the flow rates (GF- t) and the coneentration of surfactant removed (L-B). Initial surfactant concentration 30mgl - t . air rates: + a. 7500mlmin-~: O -O 5000 ml rain - I : [] '7 2500 ml rain - t between
ratio
,I~
Logorithm of the Gos Rote to Liquid Feed Rote
Foam fractionation process to removal of viruses--H
Y
4
L-
95
z..90
Further regression analysis of the data, revealed that for our equipment:
I(}0
5.0
9"95
5-;0
4195
9"90
/
I
l,
9"95 10-00
30"0 29'8C
I
19.60
t
I
19,90 20:00
t
X
29"60 29-80 30"00
Fig. 2. Experimental and calculated surfactant concentrations removed from the bulk liquid. X is the calculated concentration [using Equation (4)] in m g l - t : y is the experimentally measured concentration in mgl- ~; + represents single points; © represents duplicate points; A represents triplicate points.
was required. From Fig. 1 it was noted that the removal of surfactant was related to the air rate, and, since this factor also affected the bubble diameter, it appeared that the air rate could be used as an indication of bubble variation. Analysis of the data revealed that this was the case and that removal of Arquad T50 could be predicted by the equation: L-
B = k
(L)b(G)"
(4)
This equation was found to produce results that varied from the experimental assessment by only 0.16600. (Fig. 2). It was also determined that the error of equation (4) varied randomly within the temperature variations experienced (17-24=C) and. over this range, surfactant removal was independent of the temperature. CONCLUSIONS
4.
19.81 / ~ ÷
B = (t.009311)-1[ G I °°°-~'< ~.,F/ X (L)t°°°sv65(G) -0-00 I93
YI
20
/4,t
(3)
A model has been developed to predict the residual surfactant concentration from the operating parameters of foam fractionation equipment. It is believed that this model is more accurate than those previously presented because of the incorporation of a factor which is an indication of the alteration in the bubble size. The calculated values can also be used in conjunction with the formula previously presented in part I to determine the efficiency of such processes in removing viruses. It is interesting to note that the residual surfactant concentrations obtained were extremely low (0.01~3.25 mg 1-t) and that they could be reduced to undetectable levels by treatment with activated carbon. REFERENCES
Grieves R. B. & Bhattacharyya D. (1965) The foam separation process: a model for waste treatment applications. J. War. Pollut. Control Fed. 37, 980--989. Grieves R. B. (1968) Studies on the foam separation process. Brit. Chem. Engng 13, 77-82. Grieves R. B.. Ogbu I. U., Bhattacharyya D. & Gonger W. L. (1970) Foam fractionation rates. Sep. Sci. 5, 583-601.