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A new ion exchange approach to the treatment of brackish waters
A NEW ION EXCHANGE TO THE TREATMENT
APPROACH
OF BRACKISH
WATERS*
In order to deve!op a system capable of treating brackish waters at an economical level, an effort has been made to combine the Aconex ZIQQZUSUS and the Desal process. The tint is an apparatus desipned fur continuous operation, and it posse%es (he aiiK%ntagesof high utifiwtion of the exchange CaQaCiIy and reduction of the required resin volume. The sxond is a prcxxss appIyin!: onlv weak elcctrotyte ion eschaye resins, which can he regenerated with high effrcicnq by using rctat~~cly cheap regcncrants, and ra~i\vor soft water cm be used for rinsing. The #ark has shown that such a system is possible, and the net result is P process for the continuous treatment of brackish water or concentrated solutions with a cosjt which WC consider competitive wirh those of other available processes.
In an effort to design ion eschange pracesses capable afec~nomically treating solutions of higher concentrations (above 500 pptn CaCO,), several systems have been dewIoped in the last few years., These systems can be classified in two groups. The first concerns chemicaf processes based on selected ion exchange resins, operating in conventional ion exchange equipment which can be regenerated with higher etficiency by using cheap regenerants. The rinsing and the regenerartt solutions can also be made with raw or soft water. The second group is composed of processes based on equipment designed for continuous operation, utilizing standard ion exchange resins and normal regenerants, but due to the specific design, a higher utilization of the exchange capacity and regcnerants is obtained, and the required resin volume is also decreased. The most promising of the first group we consider to be the Desal process, developed and patented by Rohm and Haas Company, which employs weak electrolyte ion exchange resins. This group of ion exchange resins has the advantage of high regeneration efficiency, high capacity, and can be rinsed with raw or soft water without appreciable exhaustion. According to this process, the bicarbonate form of a weak base resin converts the mineral acid salts of the water to corresponding bicarbonate saits, and a carboxylic resin, following in the system, removes the alkalinity, releasing * Paper presented at Ihe Second European Ssmtxxium on Fresh Water from the Sea, May 9-12, 1967, Athens, Greece. European Federation of Chemical Engineering.
40 Desalination,
S (1968) 40-48
IOX EXCHUGE
KN THE TREATMENT OF BRACMSN
WATERS
41
GO,
which can be absorbed in another column of the weak base exchanger or it can be recovered and rc-cycled by apptyins a degas&et. The chemica1 reactions which take place during the Desat process are the following: (R-NH)HCO, R-COOH (R---N)
-F NaCl
-I- NaHCO,
+ CO,
i- H,O
-
(R--NH)CI -6 NaHCU, (alkalization)
-_j
R-COONa
---+
(R-
+
NH)HCO,
Hz0 + CO, (deaikaiization) (carbonization)
Aftcl exhaustion, the anionic resin is resencrated with a base and the cationic with an acid. The flow sheet of the process is shown in Fig. 1. This process has been well described in the literature (I, 2, S,‘, and pilot plant studies hzlve proven its technical and economicai advzmtqes c-4, 5). An industrial &t&a&n is in operation in the U.S., and the reporrs indicatcl satisfactory performance, NoCi
-I
r
1
f
+
A
A
M
M
M
8 E R t
0 E R L
8
i
1
I
f
T
1
E
E
E
A
ALKALIZ~TION
4 NotiC03 -
L
IRA-68
IRC -84
IRA-68 +
E R
L
+
c
DEALKALlZATlON
CARBONli!AftON (CO2 RECCWERYt 4 . f-f20
Ii20 + co2 -
Fig. I. New dcionitation
flow she&,
fn the second group of processes based on improved equipment of continuous operation, the Aconcx process, developed in Italy by Servettaz-Bassevi on a license on a patent by Mrs. Brand& and Dr. AssaIini, appears to be more suitable to our purpose at the present time. The Aconex apparatus applies the “merry-go-round” concept in a new design, in which several columns (16-20) rotate at given time intervals Desafinntion,S <196fj)40-&
42
B. VASILIOU AND P. STURLA
Fig. 21
through exhaustion - back-washing - regeneration - rinsing cycles. The design of an Aconex unit is shown in Fig. 2. The parallef arrangement of the columns (6-S) under exhaustion gives the advantage of utilizing at a higher degree the exchange capacity of the exchange before regeneratkg, since in the last column a higher leakage can be tolerated due to the dilution factor of the effluent during the blending with the efhuent of the other parallel running c0hlm1l.s. The resin volume is decreased compared to conventional design also due to the fact that the resin is continually in operation and no stand-by time intervals occur
between regeneration and exhaustion. Furthermore, the resin quantity going to regeneration every time is smaller than the resin volume in work. In general, the advtitages of this system are claimed to be: 1. Continuous and automatic operation mechanicahy obtained, without employing pneumatic or electric automation. 2. Effluent of constant quality. 3. Amount of resin is reduced due to increased efficiency and continuous operation. Seveual industrial installations utilizing the Aconex design units have been operating for the last few years in Italy with successful results. ~esdirwziqn,
5 (1968) 40-48
ION EXCHANGE
IN THE TREAThfEhT
OF BRACKISH
WATERS
43
@ 1900 Fig.
2b,
The work carried out this year, combined the Desai process and the Aconex unit in order to develop a system suitable for the treatment of brackish waters and other concentrated solutions at a low cost. fn designing this system, an effort was made to Desahtarion, 5 (1968) 40-48
B. VASSILIOU AND P. STURLA
44
utilize the advantages of both systems, so that the end result would be a treatment cost lower than that given by each process employed separately. The constructed
pilot plant
consists of two Acones units. The
first unit is
charged
with Amberlite
IRA-68, which is a weak base anion resin, and the second with Amberlite IRC-84, a carboxyhc resin of improved kinetic and equilibrium tehavior. Since this is an experimental pilot plant. it is designed in such a way that it has flexibility with respect to the water quantity and quality to be treated. Therefore, the present pilot plant cannot be considered as the uhimate design. The basic design of the unit is the same as the one given in Fig. 2. The anionic unit consists of 20 containers, while the cationic unit has 15. The containers are made with reinforced PVC and glass fiber with dimensions of 25 cm diameter and cylindrical part height of 200 cm. Each container is charged with 40 liters of ion cxhange resin. The containers are provided with an interception valve applied on the inle: and outlet. in order to give the necessary flexibility to the system in employing them independently according to the salinity of the water. The flow-sheet of the integrntcd system, Fig. 3, shows the singe at which each container is operating. The rotary movement of the units is made through compressed air pistons. which disptnce each container through an angle equal to 360” divided by the number of containers. The time element between two movements is regulated by a timer adjusted according to the salt concentration of the treated water. in order to assess the economical advantages of the design, calculations were made comparing the results obtained in a recent pilot plant work applying the Desal process and those when the combination of the Aconex unit and the Dcsal process is applied.
The operating in Table I.
conditions
and the results obtained
using the Desal process are given
TABLE I l~~j%efstwater analysis
430
Hardness Sodium
as ppm C&IO3
740
”
1170
”
Aikalinity E.M.A.
202 as ppm C&O3 968 ” G
”
Flow rate
Exhaustion
Regeneration
12 l/l/hr 2 l/l/hr
Regeneration !ed
Amberlite LRC-84 Ambertite LRA-68
(lOOO~/literof resin NH3 (ioO%)/titer of resin
38 g HCI 23 g
IO g co2 Edmnge
/iiter of resin
capacity
Amberlite’lRC-84 Amberlite IRA-68
47 g CaCO3fliter 47 g CaCO3/Iitet (for total anions) 38 g CaCOJliter (for E.M.A.) Desafinat~on, 5 (f 968) 40-48
ION EXCHANGE
IN THE TREATMENT
OF BRACKISH
WATERS
45
Desalination, 5 (1968) 40-48
B. VASSlLlOU AND P. STURLA
46
Based on the above results a plant designed according to the Desal process having units containing 240 liter of resin each, will produce 2.88 m3jhr of water, and it will have a total capacity of 9.6 m3jcycle. Since the length of a cycle is 3.32 hr., two trains of columns are required to provide a continuous operation. With such a design the required resin volume is: Anionic
units:
2 x 2 s 240 =
960 liters of Amberlite
IRA-68
Cationic
units:
2x240=
480 Ii&-s of Amberlite
IRC-84
Total -- 14443liters By applying the combination of Desal process and Aconex apparatus and dctermining the optimum conditions of design with respect to the number of containers according to the data given in Tab’le I, the following number of containers was found: Anionic
: 18 containers
Cationic
: II
**
-
18 :r 40 =I
729 lite;s of Amberlite
IRA-68
-
I I Y 40 =
440 liters of Amberlite
IRC-84
Total = 1160 liters
The time element between two movements of the
various
containers
is 33 minutes. The operating are given in Table iI and Table III.
I-ABLE ANIOSIC
conditions
II US-IT
Time Lntewal = 33 minutes Operating stage ---
No. of m&s
_P____
_-_____
Flow rate I/l!/w_ .__.-__
So~~~~ion
Vl?hZe of s&rim BY
___._._._-. . ..______--__________
Alkalitation
6
1’T
Raw water
Backwash
1
7
Soft water
3.5
Rezencration
1
2
4% NH3
0.56
39.5
First rinsing
1
4
Soft water
2.2
Second rinsing
1
12
Soft water
6.6
Find rinsing
I
4
Deionized
Carbonation
6
12
CO? water
CO2 make-up
I
4
co*
water
water
2.2 39.5 2.2
When comparing the Desal process with the Aconex and Desai modification, we showed that 20% less resin is required in the latter design. A further decrease in resin volume can be obtained because we can tolerate a higher leakage at the breakthrough point of the individual containers, which permits a higher utilization of the exchange capacity of the resins. This increase in exchange capacity is found to be Desalination,
5 (1968) 40-4”
ION EXCHANGE IN THE TREATMENT OF BRACKISH WATERS TABLE CA-KIOSK.
Time lntcnal
Opefatitfgstage -
_..-..._... ------..-.._
Deixlkrtlization
47
III USIT
= 33
minutes
Volume of Fiotc rate S&tioiz solution3 V t/l!hf. ..._._..__._. - .__.-_. . __._._ _. .- _.._. _______._.___ __.____... ___-___---._---12 39.5 6 M-HCO,
X0. of units
Back-ash
I
7
Soft water
3.5
Regeneration First rinsing
1 1
2
4% HCI Soft or raw water
I. 22
Second rinsing
1
12
Final rinsing
I
4
4
Soft or mw water
6.6
Deionized
2.2
water
20%. which means that the resin volume can be decreased by this magnitude without any decrease in the output of the plant. This inc:case in capacity is also impo~ant because higher utilization of the regenerant is obtained_ it is important especially for Amberlite IRA-68, for which higher requirements of ammonia were found in recent pilot plant studies than those anticipated. This may be due to the fact that the IRA-68 column, when ready for regenerin the Desal process, is still partially in the bicarbonate form and ammonia is consumed in needlessly removing bicarbonate which, in the present modified process, can be further utilized in the required bicarbonate-chloride exchange_ Finally, Table IV summarizes the results of the design applying to the Desal process and the combination of the Aconex apparatus and Desal process.
ation
TABLE IDS:
1140
ppm as CaCO3
IV
Q - 2.88 m-‘/fir. Lksai process
DesaI _____-_-_
.. . ..__.--.. No. of units
..-_.___-_-
___- -_-_--._-_.__.-.-
Resin volume (liters)
---
and Aconex unit _I_-.-_-.-
6 1440
Regencrant cost 8~1000 gal.
As a conclusion to our studies, it can be stated a new systew with the following advantages:
0.45
-_-_
2
1160 0.38
that the above
combination
gives
1. Fewer number of units. 2. Smaller volume of ion exchange resin. 3. Lower regenerant cost. 4. Constant effluent of treated water with conductivity
of 40-50 pS/cm. Desalination,5 (1968) 40-48
B. VASSILtOU
48
AND
P. STURLA
ACRSOWLEDGEMENT The
authors wish to thank the engineering firm of Servetau-Bascvi and Dr. Assalini and Mrs. Brandoli for providing the drawings of the Aconex units and fot their genera1 assistance on this project. The contribution of the Italian Nationtll Research Council (CNR) during the pilot plant studies is acknowledged with gratitude.
REFERENCES AND B. VASX.IOU, I&. fits. Clrcm. Process Des[en Dew!op., 13 (1964) 404-9. Enterprises B. VASSILIOU, Efluent anJ Wafer Treatment .\lumruI, 3rd Edition, Thunderbird Ltd , London (1966). R. KUNIN, hdusfrbl Wufcr Engineering, (July 1965). P. Snl~u. The International Water Confcrcncc of Engineer’s Society of Wcstem Pennsylvania, (scpt. 1964). P. STURL\, ProceedinKs First htertratiwol Symposium on Wbfer Desnlinarion, Washington D.C.. October 3-9, 1965, I (1967) 316. G. Ass~~_rsi, Acquo ItrdtrrrtriuIe, No. 44. (July-August 1966). Ci. .~~..8sr, Zndustria Saccarifera It&ma, No. I-2, (1965).
1. R. Kusrx 2.
3. 4. 5. 6. 7.
Desahztion.
5 (1968) 4-8
APPROACH
OF BRACKISH
WATERS*
In order to deve!op a system capable of treating brackish waters at an economical level, an effort has been made to combine the Aconex ZIQQZUSUS and the Desal process. The tint is an apparatus desipned fur continuous operation, and it posse%es (he aiiK%ntagesof high utifiwtion of the exchange CaQaCiIy and reduction of the required resin volume. The sxond is a prcxxss appIyin!: onlv weak elcctrotyte ion eschaye resins, which can he regenerated with high effrcicnq by using rctat~~cly cheap regcncrants, and ra~i\vor soft water cm be used for rinsing. The #ark has shown that such a system is possible, and the net result is P process for the continuous treatment of brackish water or concentrated solutions with a cosjt which WC consider competitive wirh those of other available processes.
In an effort to design ion eschange pracesses capable afec~nomically treating solutions of higher concentrations (above 500 pptn CaCO,), several systems have been dewIoped in the last few years., These systems can be classified in two groups. The first concerns chemicaf processes based on selected ion exchange resins, operating in conventional ion exchange equipment which can be regenerated with higher etficiency by using cheap regenerants. The rinsing and the regenerartt solutions can also be made with raw or soft water. The second group is composed of processes based on equipment designed for continuous operation, utilizing standard ion exchange resins and normal regenerants, but due to the specific design, a higher utilization of the exchange capacity and regcnerants is obtained, and the required resin volume is also decreased. The most promising of the first group we consider to be the Desal process, developed and patented by Rohm and Haas Company, which employs weak electrolyte ion exchange resins. This group of ion exchange resins has the advantage of high regeneration efficiency, high capacity, and can be rinsed with raw or soft water without appreciable exhaustion. According to this process, the bicarbonate form of a weak base resin converts the mineral acid salts of the water to corresponding bicarbonate saits, and a carboxylic resin, following in the system, removes the alkalinity, releasing * Paper presented at Ihe Second European Ssmtxxium on Fresh Water from the Sea, May 9-12, 1967, Athens, Greece. European Federation of Chemical Engineering.
40 Desalination,
S (1968) 40-48
IOX EXCHUGE
KN THE TREATMENT OF BRACMSN
WATERS
41
GO,
which can be absorbed in another column of the weak base exchanger or it can be recovered and rc-cycled by apptyins a degas&et. The chemica1 reactions which take place during the Desat process are the following: (R-NH)HCO, R-COOH (R---N)
-F NaCl
-I- NaHCO,
+ CO,
i- H,O
-
(R--NH)CI -6 NaHCU, (alkalization)
-_j
R-COONa
---+
(R-
+
NH)HCO,
Hz0 + CO, (deaikaiization) (carbonization)
Aftcl exhaustion, the anionic resin is resencrated with a base and the cationic with an acid. The flow sheet of the process is shown in Fig. 1. This process has been well described in the literature (I, 2, S,‘, and pilot plant studies hzlve proven its technical and economicai advzmtqes c-4, 5). An industrial &t&a&n is in operation in the U.S., and the reporrs indicatcl satisfactory performance, NoCi
-I
r
1
f
+
A
A
M
M
M
8 E R t
0 E R L
8
i
1
I
f
T
1
E
E
E
A
ALKALIZ~TION
4 NotiC03 -
L
IRA-68
IRC -84
IRA-68 +
E R
L
+
c
DEALKALlZATlON
CARBONli!AftON (CO2 RECCWERYt 4 . f-f20
Ii20 + co2 -
Fig. I. New dcionitation
flow she&,
fn the second group of processes based on improved equipment of continuous operation, the Aconcx process, developed in Italy by Servettaz-Bassevi on a license on a patent by Mrs. Brand& and Dr. AssaIini, appears to be more suitable to our purpose at the present time. The Aconex apparatus applies the “merry-go-round” concept in a new design, in which several columns (16-20) rotate at given time intervals Desafinntion,S <196fj)40-&
42
B. VASILIOU AND P. STURLA
Fig. 21
through exhaustion - back-washing - regeneration - rinsing cycles. The design of an Aconex unit is shown in Fig. 2. The parallef arrangement of the columns (6-S) under exhaustion gives the advantage of utilizing at a higher degree the exchange capacity of the exchange before regeneratkg, since in the last column a higher leakage can be tolerated due to the dilution factor of the effluent during the blending with the efhuent of the other parallel running c0hlm1l.s. The resin volume is decreased compared to conventional design also due to the fact that the resin is continually in operation and no stand-by time intervals occur
between regeneration and exhaustion. Furthermore, the resin quantity going to regeneration every time is smaller than the resin volume in work. In general, the advtitages of this system are claimed to be: 1. Continuous and automatic operation mechanicahy obtained, without employing pneumatic or electric automation. 2. Effluent of constant quality. 3. Amount of resin is reduced due to increased efficiency and continuous operation. Seveual industrial installations utilizing the Aconex design units have been operating for the last few years in Italy with successful results. ~esdirwziqn,
5 (1968) 40-48
ION EXCHANGE
IN THE TREAThfEhT
OF BRACKISH
WATERS
43
@ 1900 Fig.
2b,
The work carried out this year, combined the Desai process and the Aconex unit in order to develop a system suitable for the treatment of brackish waters and other concentrated solutions at a low cost. fn designing this system, an effort was made to Desahtarion, 5 (1968) 40-48
B. VASSILIOU AND P. STURLA
44
utilize the advantages of both systems, so that the end result would be a treatment cost lower than that given by each process employed separately. The constructed
pilot plant
consists of two Acones units. The
first unit is
charged
with Amberlite
IRA-68, which is a weak base anion resin, and the second with Amberlite IRC-84, a carboxyhc resin of improved kinetic and equilibrium tehavior. Since this is an experimental pilot plant. it is designed in such a way that it has flexibility with respect to the water quantity and quality to be treated. Therefore, the present pilot plant cannot be considered as the uhimate design. The basic design of the unit is the same as the one given in Fig. 2. The anionic unit consists of 20 containers, while the cationic unit has 15. The containers are made with reinforced PVC and glass fiber with dimensions of 25 cm diameter and cylindrical part height of 200 cm. Each container is charged with 40 liters of ion cxhange resin. The containers are provided with an interception valve applied on the inle: and outlet. in order to give the necessary flexibility to the system in employing them independently according to the salinity of the water. The flow-sheet of the integrntcd system, Fig. 3, shows the singe at which each container is operating. The rotary movement of the units is made through compressed air pistons. which disptnce each container through an angle equal to 360” divided by the number of containers. The time element between two movements is regulated by a timer adjusted according to the salt concentration of the treated water. in order to assess the economical advantages of the design, calculations were made comparing the results obtained in a recent pilot plant work applying the Desal process and those when the combination of the Aconex unit and the Dcsal process is applied.
The operating in Table I.
conditions
and the results obtained
using the Desal process are given
TABLE I l~~j%efstwater analysis
430
Hardness Sodium
as ppm C&IO3
740
”
1170
”
Aikalinity E.M.A.
202 as ppm C&O3 968 ” G
”
Flow rate
Exhaustion
Regeneration
12 l/l/hr 2 l/l/hr
Regeneration !ed
Amberlite LRC-84 Ambertite LRA-68
(lOOO~/literof resin NH3 (ioO%)/titer of resin
38 g HCI 23 g
IO g co2 Edmnge
/iiter of resin
capacity
Amberlite’lRC-84 Amberlite IRA-68
47 g CaCO3fliter 47 g CaCO3/Iitet (for total anions) 38 g CaCOJliter (for E.M.A.) Desafinat~on, 5 (f 968) 40-48
ION EXCHANGE
IN THE TREATMENT
OF BRACKISH
WATERS
45
Desalination, 5 (1968) 40-48
B. VASSlLlOU AND P. STURLA
46
Based on the above results a plant designed according to the Desal process having units containing 240 liter of resin each, will produce 2.88 m3jhr of water, and it will have a total capacity of 9.6 m3jcycle. Since the length of a cycle is 3.32 hr., two trains of columns are required to provide a continuous operation. With such a design the required resin volume is: Anionic
units:
2 x 2 s 240 =
960 liters of Amberlite
IRA-68
Cationic
units:
2x240=
480 Ii&-s of Amberlite
IRC-84
Total -- 14443liters By applying the combination of Desal process and Aconex apparatus and dctermining the optimum conditions of design with respect to the number of containers according to the data given in Tab’le I, the following number of containers was found: Anionic
: 18 containers
Cationic
: II
**
-
18 :r 40 =I
729 lite;s of Amberlite
IRA-68
-
I I Y 40 =
440 liters of Amberlite
IRC-84
Total = 1160 liters
The time element between two movements of the
various
containers
is 33 minutes. The operating are given in Table iI and Table III.
I-ABLE ANIOSIC
conditions
II US-IT
Time Lntewal = 33 minutes Operating stage ---
No. of m&s
_P____
_-_____
Flow rate I/l!/w_ .__.-__
So~~~~ion
Vl?hZe of s&rim BY
___._._._-. . ..______--__________
Alkalitation
6
1’T
Raw water
Backwash
1
7
Soft water
3.5
Rezencration
1
2
4% NH3
0.56
39.5
First rinsing
1
4
Soft water
2.2
Second rinsing
1
12
Soft water
6.6
Find rinsing
I
4
Deionized
Carbonation
6
12
CO? water
CO2 make-up
I
4
co*
water
water
2.2 39.5 2.2
When comparing the Desal process with the Aconex and Desai modification, we showed that 20% less resin is required in the latter design. A further decrease in resin volume can be obtained because we can tolerate a higher leakage at the breakthrough point of the individual containers, which permits a higher utilization of the exchange capacity of the resins. This increase in exchange capacity is found to be Desalination,
5 (1968) 40-4”
ION EXCHANGE IN THE TREATMENT OF BRACKISH WATERS TABLE CA-KIOSK.
Time lntcnal
Opefatitfgstage -
_..-..._... ------..-.._
Deixlkrtlization
47
III USIT
= 33
minutes
Volume of Fiotc rate S&tioiz solution3 V t/l!hf. ..._._..__._. - .__.-_. . __._._ _. .- _.._. _______._.___ __.____... ___-___---._---12 39.5 6 M-HCO,
X0. of units
Back-ash
I
7
Soft water
3.5
Regeneration First rinsing
1 1
2
4% HCI Soft or raw water
I. 22
Second rinsing
1
12
Final rinsing
I
4
4
Soft or mw water
6.6
Deionized
2.2
water
20%. which means that the resin volume can be decreased by this magnitude without any decrease in the output of the plant. This inc:case in capacity is also impo~ant because higher utilization of the regenerant is obtained_ it is important especially for Amberlite IRA-68, for which higher requirements of ammonia were found in recent pilot plant studies than those anticipated. This may be due to the fact that the IRA-68 column, when ready for regenerin the Desal process, is still partially in the bicarbonate form and ammonia is consumed in needlessly removing bicarbonate which, in the present modified process, can be further utilized in the required bicarbonate-chloride exchange_ Finally, Table IV summarizes the results of the design applying to the Desal process and the combination of the Aconex apparatus and Desal process.
ation
TABLE IDS:
1140
ppm as CaCO3
IV
Q - 2.88 m-‘/fir. Lksai process
DesaI _____-_-_
.. . ..__.--.. No. of units
..-_.___-_-
___- -_-_--._-_.__.-.-
Resin volume (liters)
---
and Aconex unit _I_-.-_-.-
6 1440
Regencrant cost 8~1000 gal.
As a conclusion to our studies, it can be stated a new systew with the following advantages:
0.45
-_-_
2
1160 0.38
that the above
combination
gives
1. Fewer number of units. 2. Smaller volume of ion exchange resin. 3. Lower regenerant cost. 4. Constant effluent of treated water with conductivity
of 40-50 pS/cm. Desalination,5 (1968) 40-48
B. VASSILtOU
48
AND
P. STURLA
ACRSOWLEDGEMENT The
authors wish to thank the engineering firm of Servetau-Bascvi and Dr. Assalini and Mrs. Brandoli for providing the drawings of the Aconex units and fot their genera1 assistance on this project. The contribution of the Italian Nationtll Research Council (CNR) during the pilot plant studies is acknowledged with gratitude.
REFERENCES AND B. VASX.IOU, I&. fits. Clrcm. Process Des[en Dew!op., 13 (1964) 404-9. Enterprises B. VASSILIOU, Efluent anJ Wafer Treatment .\lumruI, 3rd Edition, Thunderbird Ltd , London (1966). R. KUNIN, hdusfrbl Wufcr Engineering, (July 1965). P. Snl~u. The International Water Confcrcncc of Engineer’s Society of Wcstem Pennsylvania, (scpt. 1964). P. STURL\, ProceedinKs First htertratiwol Symposium on Wbfer Desnlinarion, Washington D.C.. October 3-9, 1965, I (1967) 316. G. Ass~~_rsi, Acquo ItrdtrrrtriuIe, No. 44. (July-August 1966). Ci. .~~..8sr, Zndustria Saccarifera It&ma, No. I-2, (1965).
1. R. Kusrx 2.
3. 4. 5. 6. 7.
Desahztion.
5 (1968) 4-8