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Ammonia Removal from Municipal Water by Phillipsite
539 8. Drzaj, S. Hocevarand S. Pejovnik (Editors). Zcotitc: J 985 Elsevir Science Publishers B. V' .vmstcrdam Printed in Yugoslavia
©
AMMONIA REMOVAL FROM MUNICIPAL WATER BY PHILLIPSITE P. CIAMBELLI
1,
P. CORB0
1,
L. LIBERTI
2,
A. LOPEZ
2,
C. PORCELLI
l
lDipartimento di Chimica, Universita di Napoli, via Mezzocannone 4, 80134 Napoli (Italia). 2Istituto di Ricerca sulle Acque-CNR, via De Blasio 5, 70123 Bari (Italia)
ABSTRACT The performance of Italian phillipsite tuff has been investigatec, with the objective of checking the utilization in the RIMNUT process for ammonium removal from municipal wastewater. Basic ion exchange properties have been determined in small-scale column tests with synthetic effluents. Attrition resistance was evaluated by fluidized bed test. Operation of 35 exhaustion/regeneration cycles with real secondary effluent was performed in an automatic laboratory pilot plant. Comparison with the performance of commercial clinoptilolite has shown that Italian phillipsite is an effective alternative for the utilization in ammonium removal processes. INTRODUCTION In the recent years zeolites have attracted growing interest in the field of ion exchange separation processes. Different applications such as water treatment, detergency, radioactive waste storage have been reviewed by Sherman (ref.l). One of the most significant commercial applications of natural zeolites is the removal of ammonium from municipal wastewater. From the discovery of clinoptilolite selectivity for NH; by Ames in 1960 (ref.2) to the processes employed in the large installations operating in 1be Unit€rl States (ref.3) a significant progress has been achieved.
~ore
recently an Italian Patent (ref. 4) appeared clai-
ming for an original process for the treatment of municipal wastewater. It is based on anionic exchange on synthetic weak resin and cationic exchange on natural is recovered from the regenera4P04, tion eluates which can thus be reused. After laboratory experiments (ref.5) six 3/d) months'operation of a pilot plant (240 m built at Bari (Italy) has
clinoptilolite. A valuable fertilizer, MgNH
recently confirmed the feasibility of the process on a larger scale.
540
The potential superiority of phillipsite over clinoptilolite has been confirmed by experimental tests (ref.l). Utilization of Italian phillipsite, available in large deposits (ref.6), has been suggested in wastewater treatment (ref.7,8) and aquacultural systems (ref.g). The objective of this investigation was to check the performance of Italian phillipsite in the treatment of real secondary effluents as alternative to clinoptilolite in the RIMNUT process. EXPERIMENTAL tlateri a1 The material tested (PT 53526) was a phillipsite-rich tuff (60% content) from a quarry located in the Phlaegrean Fields area. Physico-chemical characterization and performance in ammonium exchange related to aquacultural systems was previously reported (ref.g). Clinoptilolite 1010A (Anaconda) was also tested. Ion exchange tests The NH: exchange capacity was determined by contacting phillipsite samples at 60°C with 1M NH
solution renewed five times over a two-week period. 4Cl In dynamic exchange tests, glass columns (1 cm diameter) were loaded with 109
of zeolite crushed and sized to different mesh fraction (25x35, 35x45, 45x60). The zeolite was washed with water immediately before the tests to remove the fines, treated with 60 BV of 2 wt% NaCl, and washed with water. The columns were operated downflow feeding at 10 to 30 BV/h flow rate. Cation concentration at the column outlet was determined by AAS. Ammonium ion concentration was measured by Orion specific electrode. Plexig1ass columns (5.6 cm diameter, 120 cm height) were used in an automatic laboratory plant, described elsewhere(ref.5), for consecutive exhaustion/regeneration cycles operation. Real effluents from the wastewater station of Bari West were employed. Attrition tests Attrition resistance was measured by the following procedure: 50 g of sample were fluidized by water in a plexiglass column (2.5 cm diameter) to bed expansion of 60%. Five consecutive cycles of 4 h at flow rate of 500 BV/h were carried out. At the end of each cycle weight loss and mesh size distribution aremeasured.
541
RESULTS AND DISCUSSION Ammonium ion exchange capacity of PT 53526 is 2.7 meq/g, corresponding to 60% of total cation concentration in
pure phillipsite (ref.9).
Results of small.scale column-exchange tests with synthetic effluent are summarized in Fig. 1-4. The composition of feeding solution was: NH; 60 ppm, Na+ + 2+ 2+ 130 ppm, K 30 ppm, Mg 6 ppm, Ca 30 ppm. In Fig.l a typical ammonium breakthrough curve, obtained~fue conditions of 3 14 cm bed volume of 25x35 mesh size tuff, 30 BV/h flow rate, after activation with 60 BV of 5 wt% NaC1 (pH=7) fed at 30 BV/h, is shown. Ammonium exchange capacity at saturation was 15.2 mg NH;/9. Breakthrough of 25%, corresponding to NH; MAC value, required about 140 BV of solution. In comparison 120 BV were obtained for
1010 A c1inopti101ite. In the same Fig. 1 is shown that the effect of dou-
bling bed length or decreasing flow rate to 15 BV/h was not relevant to the performance of phillipsite. Ammonium uptake changed to 15 and 16 mg/g and breakthrough of 25% was 135 and 160, respectively.
lr-----~~===-=------___,
0.5
0+-_1'+lIliW---r----r---r--.........- - r - J 1 BY
Fig.l. Ammonium breakthrough curves from PT 5~526 with iYnthetic §ffluent.(C o= inlet NH,+ concentration; bed volume = .14 cm , .29 cm , .14 cm ; flow rate = .30 BV h, .30 BV/h, .15 BV/h). During activation calcium and potassium ions are exchanged~ Na+. In Fig. 2 2+ elution curves of Ca and K+ during activation with 2 wt% NaCl, calculated by integration of breakthrough curve, are shown. Activation by 60 BV results in par2+ tial exchange of Ca and K+, The effect of the extent of activation is shown in
542
u. u. 0.5
:)
Iell
Fig. 2. Elution curves of K+ and Ca 2+ during activation of PT 53526 with 30 BV/h of 2 wt% NaCl (pH = 7).
cr
II
E
0.3
0.1
60
20
BV
Fig. 3. Uptake curves of all cations, relating to the first exchange cycle and the second cycle after regeneration with 2 wt% NaCl are reported, indicating that phillipsite improves upon cycling. This improvement was
the performance of
0-
btained by increasing the time of regeneration to 350 BV. Calcium and potassium exchange was completed, resulting in increased ammonium exchange capacity in the second exhaustion cycle. Nevertheless a further smaller but constant improvement in the performance of phillipsite was observed upon two other cycles.
2 /
'"u,
;:) ~
/;.
/.
/.,...,--
----
------I N.+
//_------
....
o
E e
a:
l' O·~~;:::;;=::::;;:;:========--~j Cll
E
N
0.5
G
o
I
------100
300
~
.... CD
.
0"
500
BV
Fig.3. Uptake curves of cations for PT53526. (Solid lines: first exchange cycle; dashed lines: second exhaustion cycle after 350 BV of 2 wt% NaCl, pH = 7).
543
+. ~ Z
500
Fig.4+ Effect of regeneration flow rate on NH from PT 53526 ( • 15 BV/h, • 30 4 BV/h).
E
~ ~
300
100
10
30
50
BV
The effect of mesh size on phillipsite performance was also considered. Column tests for different fractionsin the range of commercial interest were carried out. Ammonium breakthrough for 20x35, 35x45, 45x60 mesh size showed only small difference in kinetics of exchange and comparable 25% breakthrough time. Comparable results were obtained for ammonium elution during regeneration with 60 BV of 2 wt% NaCl (pH = 7) at 15 and 30 BV/h, respectively (Fig. 4.). Regeneration by 5 wt% NaCl was found to be After checking
inconvenient in respect of 2 wt%.
basic ion exchange properties of phillipsite PT 53526, its
physical strength was measured. In fact the good combination of attrition resistance and ion exchange capacity and selectivity is the goal to be attained in a commercial zeolite application. Results of attrition tests carried out as indicated before are collected in Table 1. Comparison with performance of 1010 A clinoptilolite sample showed that PT 53526 exhibits a very good attrition resistance. It seems to be suitable for practical utilization. Before concluding that phillipsite is a real alternative to clinoptilolite we have taken
into account the effect of "scaling-up" the investigation. An auto-
matic laboratory pilot plant was employed to compare the performance of PT 53526 and 1010 A clinoptilolite in the treatment of real effluent. In Table 2 the average composition of the secondary effluent taken from the biological treatment plant of Bari West is reported. Operating conditions are presented
in Table 3.
544
Table Weight loss and mesh size distribution upon attrition testa. PHILLIPSITE PT 53526 1st cycle 2nd cycle 3rd cycle 4th cycle 5th cycle Weight loss (%) Mesh size distribution (wt%) 25x35 35x45 45x60 60
2.2
1.1
0.4
0.0
0.0
95.6 3.8 0.4 0.2
94.5 4.6 0.4 0.5
94.7 4.7 0.4 0.2
93.6 5.3 0.4 0.7
93.6 5.3 0.5 0.6
CLI NOPTI LOL ITE 1010 A Weight loss (%) Mesh size distribution (wU) 25x35 35x45 45x60 60
3.7
1.3
0.7
0.2
0.0
96.4 3.0 0.2 0.4
96.4 3.2 0.2 0.2
96.3 3.3 0.2 0.2
96.3 2.8 0.2 0.7
96.3 2.8 0.2 0.7
aInitial mesh size distribution was 99.5 wt%. Every other 80 BV of treated effluent, the tuff was regenerated with 20 BV of neutral 3.5 wt% NaCl. Thirty-five cycles were performed without interruption. The results of this investigation are reported in Fig. 5 (A-B} for PT 53526 and clinoptilolite 1010 A, respectively. Percentage of ammonium removal higher than 95% was obtained, corresponding to NH; effluent concentration well below MAC values for both sea and lake discharge. Moreover ammonium ion exchange capacity during exhaustion and regeneration was comparable, showing almost complete release of ammonium from phillipsite by NaCl regeneration. Finally after 35 cycles of operation no losses of phillipsite were noticed. Comparison with clinoptilolite performance indicates that phillipsite can be considered as effective alternative in ammonium removal from wastewater. ACKNO\~LEDGMENTS
This work was financially supported by "Programma Finalizzato Chimica Fine e Secondaria" of Research National Council (CNR) of Italy.
545
TABLE 2 Average composition of Bari West secondary effluent (concentration in mg/l). Species
Concentration
Chlorides
as Cl
161
Bicarbonates
as CaC0 ) 3 as S042- ) as P )
415
as NO; as NO; as NH+ ) 4 as K+ )
105
130
Magnesium
as Na+ ) as Ca 2+ 2+ as Mg
BOD
as 02
32
as 02
107
Sulphates Phosphates Nitrates Nitrites Ammonium Potassium Sodium Calcium
COD
5
pH
55 12.5
°
55 15 70 15
7.4
TABLE 3 Operative conditions of laboratory pilot plant. Material Bed volume Bed height
Phillipsite PT 53526 600 cm3 120 cm
Exhaustion Flow direction Time Flow rate
Downwards 6 hand 40 min 12 BV/h
Regeneration Flow direction Time Flow rate
Upwards at 25% bed height expansion 1 hand 20 min 15 BV/h
Backwashing
After each exhaustion cycle
546
, ~c
e ~
50
+:I:.. Z
0
+:::E:. 80
z
....
E
20
o .
\--
Q
. ~
ZL .
.
100
200
v·
A
+" X
c
~:
. ··
+Z'
1.
· 0
n° of
B
1
~':"'-==-==-':"'-=-T-= o, ,
10
10
X
I
30
300
'00
'0
30
eve! ••
Fig. 5. Cyclic performance of the column. (A) Phillipsite PT 53526, (B) Clinoptilolite 1010 A. (a, percentage NH; removal; b, NH; concentration in the fe~d; c, effluent concentration; d, 'NH; exchange capacity during exhaustion; e, NH ex- + 4 change capacity during regeneration; 1, NH~ MAC value for sea discharge; 2, rlH 4 MAC value for lake discharge). REFERENCES 1 2 3 4 5 6 7 8 9
J. D. Sherman, AIChE Symp. Ser., 74, No 179 (1978) 98-116. L. L. Ames, Amer. Mineral., 45 (1960) 689-700. J. D. Sherman, NATO ASI Ser., Ser. E,80 (1984) 151-92. L. Liberti, G. Boari and R. Passino, Ital. Pat. No 47912-A/81, 27 Feb. 1981. L. Liberti, G. Boari, D. Petruzzelli and R. Passino, Water Res., 15 (1981) 337-42. R. Sersale, in L. B. Sand and F.A. Mumpton (Eds.), Natural Zeolites: Occurrence Properties, Use, Pergamon Press, New York, 1978, pp. 285-302. P. Ciambelli, P. Corbo, L. Liberti, N. Limoni, A. Lopez and C. Porcelli, Bull. Soc. Natural. Napol., in press. C. Colella, R. Aiello and A. Nastro, in W.G. Pond and F.A. Mumpton (Eds.), Zeo Agriculture. Use of Natural Zeolites in Aquaculture and Agriculture, Westview Press, Boulder, 1984, pp. 239-44. P. Ciambelli, P. Corbo, F. Lumare and C. Porcelli, Ibid., pp.245-52.
©
AMMONIA REMOVAL FROM MUNICIPAL WATER BY PHILLIPSITE P. CIAMBELLI
1,
P. CORB0
1,
L. LIBERTI
2,
A. LOPEZ
2,
C. PORCELLI
l
lDipartimento di Chimica, Universita di Napoli, via Mezzocannone 4, 80134 Napoli (Italia). 2Istituto di Ricerca sulle Acque-CNR, via De Blasio 5, 70123 Bari (Italia)
ABSTRACT The performance of Italian phillipsite tuff has been investigatec, with the objective of checking the utilization in the RIMNUT process for ammonium removal from municipal wastewater. Basic ion exchange properties have been determined in small-scale column tests with synthetic effluents. Attrition resistance was evaluated by fluidized bed test. Operation of 35 exhaustion/regeneration cycles with real secondary effluent was performed in an automatic laboratory pilot plant. Comparison with the performance of commercial clinoptilolite has shown that Italian phillipsite is an effective alternative for the utilization in ammonium removal processes. INTRODUCTION In the recent years zeolites have attracted growing interest in the field of ion exchange separation processes. Different applications such as water treatment, detergency, radioactive waste storage have been reviewed by Sherman (ref.l). One of the most significant commercial applications of natural zeolites is the removal of ammonium from municipal wastewater. From the discovery of clinoptilolite selectivity for NH; by Ames in 1960 (ref.2) to the processes employed in the large installations operating in 1be Unit€rl States (ref.3) a significant progress has been achieved.
~ore
recently an Italian Patent (ref. 4) appeared clai-
ming for an original process for the treatment of municipal wastewater. It is based on anionic exchange on synthetic weak resin and cationic exchange on natural is recovered from the regenera4P04, tion eluates which can thus be reused. After laboratory experiments (ref.5) six 3/d) months'operation of a pilot plant (240 m built at Bari (Italy) has
clinoptilolite. A valuable fertilizer, MgNH
recently confirmed the feasibility of the process on a larger scale.
540
The potential superiority of phillipsite over clinoptilolite has been confirmed by experimental tests (ref.l). Utilization of Italian phillipsite, available in large deposits (ref.6), has been suggested in wastewater treatment (ref.7,8) and aquacultural systems (ref.g). The objective of this investigation was to check the performance of Italian phillipsite in the treatment of real secondary effluents as alternative to clinoptilolite in the RIMNUT process. EXPERIMENTAL tlateri a1 The material tested (PT 53526) was a phillipsite-rich tuff (60% content) from a quarry located in the Phlaegrean Fields area. Physico-chemical characterization and performance in ammonium exchange related to aquacultural systems was previously reported (ref.g). Clinoptilolite 1010A (Anaconda) was also tested. Ion exchange tests The NH: exchange capacity was determined by contacting phillipsite samples at 60°C with 1M NH
solution renewed five times over a two-week period. 4Cl In dynamic exchange tests, glass columns (1 cm diameter) were loaded with 109
of zeolite crushed and sized to different mesh fraction (25x35, 35x45, 45x60). The zeolite was washed with water immediately before the tests to remove the fines, treated with 60 BV of 2 wt% NaCl, and washed with water. The columns were operated downflow feeding at 10 to 30 BV/h flow rate. Cation concentration at the column outlet was determined by AAS. Ammonium ion concentration was measured by Orion specific electrode. Plexig1ass columns (5.6 cm diameter, 120 cm height) were used in an automatic laboratory plant, described elsewhere(ref.5), for consecutive exhaustion/regeneration cycles operation. Real effluents from the wastewater station of Bari West were employed. Attrition tests Attrition resistance was measured by the following procedure: 50 g of sample were fluidized by water in a plexiglass column (2.5 cm diameter) to bed expansion of 60%. Five consecutive cycles of 4 h at flow rate of 500 BV/h were carried out. At the end of each cycle weight loss and mesh size distribution aremeasured.
541
RESULTS AND DISCUSSION Ammonium ion exchange capacity of PT 53526 is 2.7 meq/g, corresponding to 60% of total cation concentration in
pure phillipsite (ref.9).
Results of small.scale column-exchange tests with synthetic effluent are summarized in Fig. 1-4. The composition of feeding solution was: NH; 60 ppm, Na+ + 2+ 2+ 130 ppm, K 30 ppm, Mg 6 ppm, Ca 30 ppm. In Fig.l a typical ammonium breakthrough curve, obtained~fue conditions of 3 14 cm bed volume of 25x35 mesh size tuff, 30 BV/h flow rate, after activation with 60 BV of 5 wt% NaC1 (pH=7) fed at 30 BV/h, is shown. Ammonium exchange capacity at saturation was 15.2 mg NH;/9. Breakthrough of 25%, corresponding to NH; MAC value, required about 140 BV of solution. In comparison 120 BV were obtained for
1010 A c1inopti101ite. In the same Fig. 1 is shown that the effect of dou-
bling bed length or decreasing flow rate to 15 BV/h was not relevant to the performance of phillipsite. Ammonium uptake changed to 15 and 16 mg/g and breakthrough of 25% was 135 and 160, respectively.
lr-----~~===-=------___,
0.5
0+-_1'+lIliW---r----r---r--.........- - r - J 1 BY
Fig.l. Ammonium breakthrough curves from PT 5~526 with iYnthetic §ffluent.(C o= inlet NH,+ concentration; bed volume = .14 cm , .29 cm , .14 cm ; flow rate = .30 BV h, .30 BV/h, .15 BV/h). During activation calcium and potassium ions are exchanged~ Na+. In Fig. 2 2+ elution curves of Ca and K+ during activation with 2 wt% NaCl, calculated by integration of breakthrough curve, are shown. Activation by 60 BV results in par2+ tial exchange of Ca and K+, The effect of the extent of activation is shown in
542
u. u. 0.5
:)
Iell
Fig. 2. Elution curves of K+ and Ca 2+ during activation of PT 53526 with 30 BV/h of 2 wt% NaCl (pH = 7).
cr
II
E
0.3
0.1
60
20
BV
Fig. 3. Uptake curves of all cations, relating to the first exchange cycle and the second cycle after regeneration with 2 wt% NaCl are reported, indicating that phillipsite improves upon cycling. This improvement was
the performance of
0-
btained by increasing the time of regeneration to 350 BV. Calcium and potassium exchange was completed, resulting in increased ammonium exchange capacity in the second exhaustion cycle. Nevertheless a further smaller but constant improvement in the performance of phillipsite was observed upon two other cycles.
2 /
'"u,
;:) ~
/;.
/.
/.,...,--
----
------I N.+
//_------
....
o
E e
a:
l' O·~~;:::;;=::::;;:;:========--~j Cll
E
N
0.5
G
o
I
------100
300
~
.... CD
.
0"
500
BV
Fig.3. Uptake curves of cations for PT53526. (Solid lines: first exchange cycle; dashed lines: second exhaustion cycle after 350 BV of 2 wt% NaCl, pH = 7).
543
+. ~ Z
500
Fig.4+ Effect of regeneration flow rate on NH from PT 53526 ( • 15 BV/h, • 30 4 BV/h).
E
~ ~
300
100
10
30
50
BV
The effect of mesh size on phillipsite performance was also considered. Column tests for different fractionsin the range of commercial interest were carried out. Ammonium breakthrough for 20x35, 35x45, 45x60 mesh size showed only small difference in kinetics of exchange and comparable 25% breakthrough time. Comparable results were obtained for ammonium elution during regeneration with 60 BV of 2 wt% NaCl (pH = 7) at 15 and 30 BV/h, respectively (Fig. 4.). Regeneration by 5 wt% NaCl was found to be After checking
inconvenient in respect of 2 wt%.
basic ion exchange properties of phillipsite PT 53526, its
physical strength was measured. In fact the good combination of attrition resistance and ion exchange capacity and selectivity is the goal to be attained in a commercial zeolite application. Results of attrition tests carried out as indicated before are collected in Table 1. Comparison with performance of 1010 A clinoptilolite sample showed that PT 53526 exhibits a very good attrition resistance. It seems to be suitable for practical utilization. Before concluding that phillipsite is a real alternative to clinoptilolite we have taken
into account the effect of "scaling-up" the investigation. An auto-
matic laboratory pilot plant was employed to compare the performance of PT 53526 and 1010 A clinoptilolite in the treatment of real effluent. In Table 2 the average composition of the secondary effluent taken from the biological treatment plant of Bari West is reported. Operating conditions are presented
in Table 3.
544
Table Weight loss and mesh size distribution upon attrition testa. PHILLIPSITE PT 53526 1st cycle 2nd cycle 3rd cycle 4th cycle 5th cycle Weight loss (%) Mesh size distribution (wt%) 25x35 35x45 45x60 60
2.2
1.1
0.4
0.0
0.0
95.6 3.8 0.4 0.2
94.5 4.6 0.4 0.5
94.7 4.7 0.4 0.2
93.6 5.3 0.4 0.7
93.6 5.3 0.5 0.6
CLI NOPTI LOL ITE 1010 A Weight loss (%) Mesh size distribution (wU) 25x35 35x45 45x60 60
3.7
1.3
0.7
0.2
0.0
96.4 3.0 0.2 0.4
96.4 3.2 0.2 0.2
96.3 3.3 0.2 0.2
96.3 2.8 0.2 0.7
96.3 2.8 0.2 0.7
aInitial mesh size distribution was 99.5 wt%. Every other 80 BV of treated effluent, the tuff was regenerated with 20 BV of neutral 3.5 wt% NaCl. Thirty-five cycles were performed without interruption. The results of this investigation are reported in Fig. 5 (A-B} for PT 53526 and clinoptilolite 1010 A, respectively. Percentage of ammonium removal higher than 95% was obtained, corresponding to NH; effluent concentration well below MAC values for both sea and lake discharge. Moreover ammonium ion exchange capacity during exhaustion and regeneration was comparable, showing almost complete release of ammonium from phillipsite by NaCl regeneration. Finally after 35 cycles of operation no losses of phillipsite were noticed. Comparison with clinoptilolite performance indicates that phillipsite can be considered as effective alternative in ammonium removal from wastewater. ACKNO\~LEDGMENTS
This work was financially supported by "Programma Finalizzato Chimica Fine e Secondaria" of Research National Council (CNR) of Italy.
545
TABLE 2 Average composition of Bari West secondary effluent (concentration in mg/l). Species
Concentration
Chlorides
as Cl
161
Bicarbonates
as CaC0 ) 3 as S042- ) as P )
415
as NO; as NO; as NH+ ) 4 as K+ )
105
130
Magnesium
as Na+ ) as Ca 2+ 2+ as Mg
BOD
as 02
32
as 02
107
Sulphates Phosphates Nitrates Nitrites Ammonium Potassium Sodium Calcium
COD
5
pH
55 12.5
°
55 15 70 15
7.4
TABLE 3 Operative conditions of laboratory pilot plant. Material Bed volume Bed height
Phillipsite PT 53526 600 cm3 120 cm
Exhaustion Flow direction Time Flow rate
Downwards 6 hand 40 min 12 BV/h
Regeneration Flow direction Time Flow rate
Upwards at 25% bed height expansion 1 hand 20 min 15 BV/h
Backwashing
After each exhaustion cycle
546
, ~c
e ~
50
+:I:.. Z
0
+:::E:. 80
z
....
E
20
o .
\--
Q
. ~
ZL .
.
100
200
v·
A
+" X
c
~:
. ··
+Z'
1.
· 0
n° of
B
1
~':"'-==-==-':"'-=-T-= o, ,
10
10
X
I
30
300
'00
'0
30
eve! ••
Fig. 5. Cyclic performance of the column. (A) Phillipsite PT 53526, (B) Clinoptilolite 1010 A. (a, percentage NH; removal; b, NH; concentration in the fe~d; c, effluent concentration; d, 'NH; exchange capacity during exhaustion; e, NH ex- + 4 change capacity during regeneration; 1, NH~ MAC value for sea discharge; 2, rlH 4 MAC value for lake discharge). REFERENCES 1 2 3 4 5 6 7 8 9
J. D. Sherman, AIChE Symp. Ser., 74, No 179 (1978) 98-116. L. L. Ames, Amer. Mineral., 45 (1960) 689-700. J. D. Sherman, NATO ASI Ser., Ser. E,80 (1984) 151-92. L. Liberti, G. Boari and R. Passino, Ital. Pat. No 47912-A/81, 27 Feb. 1981. L. Liberti, G. Boari, D. Petruzzelli and R. Passino, Water Res., 15 (1981) 337-42. R. Sersale, in L. B. Sand and F.A. Mumpton (Eds.), Natural Zeolites: Occurrence Properties, Use, Pergamon Press, New York, 1978, pp. 285-302. P. Ciambelli, P. Corbo, L. Liberti, N. Limoni, A. Lopez and C. Porcelli, Bull. Soc. Natural. Napol., in press. C. Colella, R. Aiello and A. Nastro, in W.G. Pond and F.A. Mumpton (Eds.), Zeo Agriculture. Use of Natural Zeolites in Aquaculture and Agriculture, Westview Press, Boulder, 1984, pp. 239-44. P. Ciambelli, P. Corbo, F. Lumare and C. Porcelli, Ibid., pp.245-52.