**3.2.2 Experiments in fixed bed column**

156 Technical Problems in Patients on Hemodialysis

Standard international and national norms regarding the quality of activated charcoal for water treatment bring specifications primarily concerning the minimal iodine adsorption limit (iodine number), 600 mg/g (ABNT - EB-2133, 1991 and AWWA – B600-05) and 900 mg/g (ASTM - D 4607-96), making no mention to the minimal limits of methylene blue adsorption. It is known that iodine is a small molecule of approximately 0.8 nm and being thus associated with micropore adsorption. Therefore, the iodine number cannot be the sole specification of quality standard adopted for an activated charcoal destined for water

In Marroco, the activated charcoals destined for water treatment have in their specifications the minimal limits established for the methylene blue adsorption capacity of 180.0mg/g (Baçaoui et al., 2001). Thus, if we consider this minimal limit as a specification for the activated charcoal sampled in both the Hemodialysis Centers, we would see that none of these charcoals could be used for water treatment, because they are specifically microporous

From results obtained in the characterization of the hemodialysis centers AC regarding the pore volume and methylene blue adsorption, it was possible to choose the best AC in each center and use it in the adsorption studies with the cyanobacteria toxin. The adsorption kinetics of the [D-Leucine1]MCYST-LR on the charcoals was studied, from which we could estimate the efficiency of the removal of this cyanobateria toxin by those adsorbents. Other two activated charcoals produced by Albuquerque et al. (2005) (AC-R-G and AC-R-H, originating from the sugarcane bagasse and coconut tree endocarp) were also studied

(a) (b)

Fig. 4. Adsorption kinetics of [D-Leucine1]MCYST-LR on the activated charcoals: (a) □ AC-B-

After 15 seconds of contact between the [D-Leu1]MCYST-LR and the charcoals, removal efficiencies of 7.40% (AC-R-G) and 26.47% (AC-R-H) were observed, compared to the very low results obtained by the AC-A-B and AC-B-F with removal efficiency of 1.96 and 2.26%, respectively. The adsorption kinetics evolved gradually with time until the adsorption balance was reached in around 30 minutes for the AC-R-G and AC-R-H, and of 60 minutes for the AC-A-B and AC-B-F (Figure 4). The removal efficiencies by these AC in the respective equilibrium times were of 62.31% (AC-R-G), 98.73% (AC-R-H), 4.3% (AC-B-F)

treatment, because it is a well-applied parameter for microporous charcoals.

regarding their removal efficiencies for [D-Leu1]MCYST-LR on water.

activated charcoals.

**3.2.1.1 Adsorption of [D-Leucine1]MCYST-LR** 

F, ■ AC-A-B, and (b) ○ AC-R-G and ∆ AC- CS – F.

In the dinamic adsorption dynamic of the [D-Leu1]MCYST-LR in a fixed bed of activated charcoal, the latter removed that toxin from a solution until the saturation of the bed, wherein the performance of this continuous adsorption process is affected, among other parameters, by the concentration of the entry solution (Gomes et al., 2001) and by operational conditionals such as particle size and fluid flow in the column (Inglezakis et al., 2002). According to Sag & Aktay (2001) and Barros et al. (2001), the solutions which are more concentrated saturate the bed faster, and small particles diminish the resistance to mass transfer. It is also known that an increase in the flow of the solution on the bed reduced its adsorption capacity, increasing the lenght of the mass transfer zone, because the phenomenon of mass transfer necessary for adsorption of [D-Leu1]MCYST-LR might not be able to continue in higher mass transfer rates, brought forth by an increase in the flow of the fluid (Watson, 1999). Besides, the bed flow can be deviated from the ideal because of the flow channeling due to insufficient material wettability. Those problems can reduce the adsorption process efficiency, because it is important that the column operates as close as possible to the flow/runoff conditions as the one observed for a tubular-type "plug flow" reactor. Hence, in order to correctely plan and operate the continuous adsorption process of that toxin in a AC fixed bed, as the one found in many water treatment stations of hemodialysis centers, it is necessary to study the kinetics and adsorption equilibrium for that toxin, besides knowing its adsorption dynamics in a fixed bed through the sizing of the breakthrough curves. The first step in a adsorption project for [D-Leu1]MCYST-LR in fixed bed column is the establishment of optimal conditions for preparing the process, that is, those that minimize the diffusional resistances both in the film and in the interior of adsorbent particles, thus favoring a greater interaction between the charcoals' active sites, accessible to adsorption, and the adsorbate.

In this experiment, the previous studies of methylene blue adsorption in activated charcoal fixed bed have shown flows between approximately 8 and 12 mL/min and average particle size of 0.425 mm would be conditions that could reduce to minimum those mass transfer resistances without significant increase in charge loss on the bed, and thus be taken as a starting point for the planning of a continuous adsorption process for that toxin. Under these conditions, one should expect that the breakthrough curves come closer to a perfect degree, which is desirable (Mccabe et al., 2001). Thus, taking such conditions like particle size, flow and height of the bed, new experiments with solutions [D-Leu1]MCYST-LR were carried out aiming to evaluate the removal of this toxin from the treated water using fixed bed columns of AC-A-B charcoals and AC-B-F, besides the AC taken as standards AC-R-G and AC-R-H (Table 4).

Aiming to recover the solution initially containing [D-Leu1]MCYST-LR kept in contact in a continuous fashion with an activated charcoal bed initially free from it, the concentration of this toxin in the exit of the bed was monitored, in function of the time, producing curves as shown in Figure 5 denominated breakthrough curves.

Specifications of the Quality of Granulated Activated Charcoal

corresponding to 0.31 g/mg and 0.05 g/mg, respectively.

about 3.678g/mg and 5.314g/mg, respectively.

Table 5. Properties of the activated charcoal beds.

studies we have used an extract with four microcystins.

respectively.

Used in Water Systems Treatment in Hemodialysis Centers in Brazil 159

the bed, and the solute concentration in the effluent increases sensibly, the system is said to initiate rupture, so the solute concentration in the effluent increases rapidly when the adsorption zone (Zad) passes through the bed bottom and the solute concentration is

Based on the data obtained from the Breakthrough curves, it was possible to estimate the needed time for the C/C0 = 0.05 ratio to be reached in the exit of the column, which denominated breakthrough time (tb). Hence, for the AC fixed beds composed by the samples from the Recife (AC-B-F) and Campinas (AC-A-B) Hemodialysis Centers, this time was of 24 and 3 min. This results indicated that each charcoal bed composed by 8.12g (AC-B-F) and 8.26g (AC-A-B) of activated charcoal displayed an adsorbed mass of [D-Leu1]MCYST-LR of around 2541.9 g (24 min 0.0085 L/min = 0.204 L; 0.240 L 12460.6 g/L = 2541.9 g) and 424.8 g (3 min 0.01108 L/min = 0.03324 L; 0.03324 L 12779.6 g/L = 424.8 g),

With the continuous adsorption process until the exhaustion of each bed in 282 min (AC-B-F) and 310 min (AC-A-B), when the C/C0 = 1 ration was achieved in the column exit, it was possible to estimate the [D-Leu1]MCYST-LR mass adsorbed by the bed in those times. Under this conditions, each bed showed an adsorbed mass of [D-Leu1]MCYST-LR of 29,868.05 g (282 min 0.0085 L/min = 2.237 L; 2.237 L 12,460.6 g/L) (AC-B-F) and 43,895.37 g (310 min 0.01108 L/min = 3.435 L; 3.435 L 12,779.6 g/L) (AC-A-B), this corresponded to

Comparing the performance of the beds above with those composed by the activated charcoals AC-R-G and AC-B-F, adsorbed masses of [D-Leu1]MCYST-LR of 1,017.29 g (7.5 min 0.01005 L/min = 0.0754L; 0.0754L 13,496.4g/L) and 2,072.02 g (9 min 0.01202 L/min = 0.1082 L; 0.0754 L 19,153.5 g/L) were observed, which corresponds to 0.113 g/mg and 0.296 g/mg, respectively. These beds displayed an exhaustion time of 132 and 165 min. In those times, the beds presented adsorbed masses of 18,706.01 g (132 min 0.01005 L/min = 1.326 L; 1.326 L 13,496.4 g/L) and 37,987.13 g (165 min 0.01202 L/min = 1.9833 L; 1.9833 L 19,153.5 g/L), which corresponded to 2.07 and 5.43 g/mg,

REF. \*tb (min) te (min) tu (min) tt (min) AC-A-B 7.0 320 45.7 593.2 AC-B-F 24 282 153.5 615.6 AC-R-G 7.5 132 59.2 276.1 AC-R-H 9.0 165 56.6 384.9

Comparing the results obtained from the activated charcoals AC-R-G and AC-R-H with the Bernezeau (1994) data (50 μg microcystin-LR/12 mg Powdered Activated Charcoal - PAC), the sugarcane bagasse based-activated charcoal showed an adsorption capacity 1.3 times bigger than the PAC studied by the aforementioned researcher, remembering that in our

According to Zambon (2002), qualitative information regarding the resistance to mass transfer can be obtained from the form of breakthrough. If the mass transfer zone is narrow,

\*tb is the breakthrough time, te exhaustion time, tu utile time and tt stoichiometry time.

substantially equated to the concentration value in the initial solution (C0).


Table 4. Experimental conditions and adsorption results in continuous regime

Fig. 5. Breakthrough curves of activated charcoals (C/C0 versus time): (a) AC-R-H, (b) AC-A- B, (c) AC-B- F, (d) AC-R-G.

Initially, the adsorbent layer located in the inferior part of the bed adsorbs the solution quickly and effectively thus reducing the concentration of that toxin in the exit of the column. The effluent on the top of the bed is practically free of solute. In this situation, the inferior layer of the bed is practically saturated and the adsorption occurs in an adsorption zone (Zad) that is relativelly narrow and the concentration changes rapidly. Continuing with the solution flow, the Adsorption Zone flow (Zad) moves in an ascendant way like a wave, at an ordinarily much slower rate than the linear fluid velocity through the bed. In a certain time, practically half of the bed is saturated with the solute, but the concentration in the effluent is still substantially zero. When the adsorption zone (Zad) has reached the top of

0,0

0,0 0,2 0,4 0,6 0,8 1,0 1,2

(c) (d) Fig. 5. Breakthrough curves of activated charcoals (C/C0 versus time): (a) AC-R-H, (b) AC-

Initially, the adsorbent layer located in the inferior part of the bed adsorbs the solution quickly and effectively thus reducing the concentration of that toxin in the exit of the column. The effluent on the top of the bed is practically free of solute. In this situation, the inferior layer of the bed is practically saturated and the adsorption occurs in an adsorption zone (Zad) that is relativelly narrow and the concentration changes rapidly. Continuing with the solution flow, the Adsorption Zone flow (Zad) moves in an ascendant way like a wave, at an ordinarily much slower rate than the linear fluid velocity through the bed. In a certain time, practically half of the bed is saturated with the solute, but the concentration in the effluent is still substantially zero. When the adsorption zone (Zad) has reached the top of

C/C0

(a) (b)

0,2

0,4

0,6

C/C0

0,8

1,0

1,2

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 Time (min)

0 20 40 60 80 100 120 140 160 180 Time (min)

REF. C0 (g/L) Flow (mL/min) Hbed (cm) mZ (g) AC-A-B 12,779.6 11.1 2.4 8.3 AC-B-F 12,460.6 8.5 2.3 8.1 AC-R-G 13,496.4 10.5 2.4 9.2 AC-R-H 19,153.5 12.2 2.3 7.0

Table 4. Experimental conditions and adsorption results in continuous regime

0 20 40 60 80 100 120 140 160 180 200 220 240 Time (min)

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 Time (min)

0,0

0,0 0,2 0,4 0,6 0,8 1,0 1,2

A- B, (c) AC-B- F, (d) AC-R-G.

C/C0

0,2

0,4

0,6

C/C0

0,8

1,0

1,2

the bed, and the solute concentration in the effluent increases sensibly, the system is said to initiate rupture, so the solute concentration in the effluent increases rapidly when the adsorption zone (Zad) passes through the bed bottom and the solute concentration is substantially equated to the concentration value in the initial solution (C0).

Based on the data obtained from the Breakthrough curves, it was possible to estimate the needed time for the C/C0 = 0.05 ratio to be reached in the exit of the column, which denominated breakthrough time (tb). Hence, for the AC fixed beds composed by the samples from the Recife (AC-B-F) and Campinas (AC-A-B) Hemodialysis Centers, this time was of 24 and 3 min. This results indicated that each charcoal bed composed by 8.12g (AC-B-F) and 8.26g (AC-A-B) of activated charcoal displayed an adsorbed mass of [D-Leu1]MCYST-LR of around 2541.9 g (24 min 0.0085 L/min = 0.204 L; 0.240 L 12460.6 g/L = 2541.9 g) and 424.8 g (3 min 0.01108 L/min = 0.03324 L; 0.03324 L 12779.6 g/L = 424.8 g), corresponding to 0.31 g/mg and 0.05 g/mg, respectively.

With the continuous adsorption process until the exhaustion of each bed in 282 min (AC-B-F) and 310 min (AC-A-B), when the C/C0 = 1 ration was achieved in the column exit, it was possible to estimate the [D-Leu1]MCYST-LR mass adsorbed by the bed in those times. Under this conditions, each bed showed an adsorbed mass of [D-Leu1]MCYST-LR of 29,868.05 g (282 min 0.0085 L/min = 2.237 L; 2.237 L 12,460.6 g/L) (AC-B-F) and 43,895.37 g (310 min 0.01108 L/min = 3.435 L; 3.435 L 12,779.6 g/L) (AC-A-B), this corresponded to about 3.678g/mg and 5.314g/mg, respectively.

Comparing the performance of the beds above with those composed by the activated charcoals AC-R-G and AC-B-F, adsorbed masses of [D-Leu1]MCYST-LR of 1,017.29 g (7.5 min 0.01005 L/min = 0.0754L; 0.0754L 13,496.4g/L) and 2,072.02 g (9 min 0.01202 L/min = 0.1082 L; 0.0754 L 19,153.5 g/L) were observed, which corresponds to 0.113 g/mg and 0.296 g/mg, respectively. These beds displayed an exhaustion time of 132 and 165 min. In those times, the beds presented adsorbed masses of 18,706.01 g (132 min 0.01005 L/min = 1.326 L; 1.326 L 13,496.4 g/L) and 37,987.13 g (165 min 0.01202 L/min = 1.9833 L; 1.9833 L 19,153.5 g/L), which corresponded to 2.07 and 5.43 g/mg, respectively.


\*tb is the breakthrough time, te exhaustion time, tu utile time and tt stoichiometry time.

Table 5. Properties of the activated charcoal beds.

Comparing the results obtained from the activated charcoals AC-R-G and AC-R-H with the Bernezeau (1994) data (50 μg microcystin-LR/12 mg Powdered Activated Charcoal - PAC), the sugarcane bagasse based-activated charcoal showed an adsorption capacity 1.3 times bigger than the PAC studied by the aforementioned researcher, remembering that in our studies we have used an extract with four microcystins.

According to Zambon (2002), qualitative information regarding the resistance to mass transfer can be obtained from the form of breakthrough. If the mass transfer zone is narrow,

Specifications of the Quality of Granulated Activated Charcoal

capacity of the respective beds.

RJ, Brazil, p. 401-410.

432, ISSN 0008-6223.

2001, v. 1, p. 84-98.

February, 2011.

3, pp.343-350, ISSN 0008-6223.

**5. Acknowledgment** 

**6. References** 

Used in Water Systems Treatment in Hemodialysis Centers in Brazil 161

bagasse based-activated charcoals it was observed a 2.07 and 5.43 g/mg adsorption

The authors acknowledge the financial support (02-11529-8) received from the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and fellowship from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for development this work.

Albuquerque Junior, EC.; Mendez, M.O.; Coutinho, A.R. & Franco, T.T. (2005). Production

American Society for Testing and Materials. ASTM, D 4607-96; Standard Test Method for Determination of Iodine Number of Activated Carbon. PA, EUA, 1999. 2p. American Water Works Assosiation Standards, Denver, CO. AWWA B600-05; Powdered

Arvanitidou, M.; Spaia, S.; Tsoubaris, P.; Katsinas, C.; Askepidis, N.; Pagidis, P.; Kanetidis,

Associação Brasileira de Normas Técnicas. Rio de Janeiro. EB 2133; Carvão ativado

Baçaoui, A.; Yaacoubi, A.; Dahbi, A.; Bennouna, C.; Phan Tan Luu, R.; Maldonado-Hodar, F.

Barros, M.A.S.D.; Arroyo, P. A. Métodos de remoção de cromo de águas residuais - troca

Barton, S. S. (1987). The adsorption of methylene blue by active carbon. *Carbon*, Vol.25, No.

Buchanan, M.; Stevens, B.; Marshal, A.; Plomley, R.; d'Apice, A. & Kincaid-Smith, P. (1982).

Brazilian Society of Nephrology. Available from: <http://www.sbn.org.br>. Accessed in

Campinas, M. & Rosa, M.J. (2010a). The ionic strength effect on microcystin and natural

Campinas, M. & Rosa, M.J. (2010b). Removal of microcystins by PAC/UF. *Separation and* 

*Purification Technology*, Vol. 71, No. 1, p. 114-120, ISSN 1383-5866.

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*Science*, Vol.299, No.2, pp. 520-529, ISSN 0021-9797.

*Dialysis & transplantation*, Vol.29, No.9, pp.519-525, ISSN 0090-2934.

Activated Carbon. Denver, CO, EUA, 2005. 24p.

pulverizado: especificação. Rio de Janeiro, 1991. 54p.

and characterization of physically activated carbon from Brazilian agricultural and industrial residues. In: *Proceedings of III Brazilian Congress of Carbon*. Rio de Janeiro,

D.; Pazarloglou, M.; Bersos, G.; Digenis, P.; Katsouyannopoulos, V. & Vayonas, G. (1999). Chemical Quality of Hemodialysis Water in Greece: A Multicenter Study.

J.; Rivera-Utrilla, J. & Moreno-Castilla, C. (2001). Optimization of conditions for the preparation of activated carbons olive-waste cakes. Carbon, Vol.39, No. 3, pp.425-

iônica. IN: Maria Angélica Simòes D. De Barros; Pedro Augusto Arroyo; Eduardo Falabella Sousa-Aguiar; Pedro Avila García. (Org.). Problemas Ambientais com soluções analíticas. Vol. I. O Cromo no processamento de peles. Madri: CYTED,

Aluminium associated bone disease: clinic-pathologic correlations. *American Journal* 

organic matter surrogate adsorption onto PAC. *Journal of Colloid and Interface* 

the breakthrough curve will be more inclined, whereas if the zone is wider, the curve will be more elongated. From Figure 6, it is possible to see that such zones differed from charcoal to charcoal according to the operational parameters established in each experiment such as initial concentration, flow and bed height. Hence, in the case of the Breakthrough curves obtained for the AC-R-G, AC-A-B and AC-R-H beds, a narrower S-shaped curved indicating a narrower mass transfer zone and, therefore, with mass transfer resistance to be considered. Nonetheless, the breakthrough curve obtained from the bed packaged with charcoal AC-B-F (Hemodialysis Center B) displayed a more elongated S-shaped curved, as seen on Figure 5, indicating a broader mass transfer zone and, therefore, little resistance to mass transfer. The supposition of the adsorption zone provides the basis for a method for a much simpler project, which makes it possible to scale up the experiments from a small laboratory scale. However, besides the Mass Transfer Zone (MTZ) concept, the estimative of parameters such as average residence time and dimensionless variance can help in the design of an adsorption column (activated charcoal filter).

### **4. Conclusion**

Granulated Activated charcoals are largely used in adsorption continuous processes in fixed bed for the water treatment in Hemodialysis Centers. The quality of the water used in these centers is intrinsically associated with the quality of these charcoals. As in Brazil, there are no norms, and neither, entities which control the quality of these adsorbents; it is each day more important to find the correct parameters indicators of quality. Activated charcoals used in two water treatment stations in hemodialysis centers were sampled as to assess their qualities. The Specific Surface Area (SBET) of the charcoal sampled in the water treatment stations in the two centers have presented values between 600 and 1000 m2/g approximately. SBET values around 800 m2/g are usually taken as reference value, for those who acquire such adsorbents, mainly those destined to the water treatment. From that principle, it is verified that the sampled charcoals of both Hemodialysis Centers are in accordance with this parameter, however, it was also observed, that the same charcoals have mesopores volume of (0.01-0.09 cm3/g), which are significantly below from those specified in the literature (0.40 cm3/g), thus, the charcoals from both centers must be rejected for such aim or used with caution. The blue methylene adsorption was proposed as adsorption capacity measure of activated charcoals, as this molecule has been used as to estimate the charcoal mesopores volume. It was observed that the activated charcoals which have presented higher mesopores+ secondary micropores volume have more adsorption capacity to that molecule, and, hence, may be taken as a model to estimate the referred pores region, which is important for the charcoals used in the water treatment.

Regarding the first estimate of the adsorption capacity in batch of the activated charcoal in both hemodialysis centers for the cyanobacterium toxin [D-Leu1]MCYST-LR, low removal efficiencies for that toxin were observed (close to 4%), compared with the activated charcoal from sugarcane bagasse (close 99%). The behavior in the adsorption of the sampled charcoals in the hemodialysis centers is associated with its low mesopores volumes, smaller than 0.04 cm3/g, contrary to the sugarcane bagasse based-activated charcoal whose mesopores volume is around 0.40 cm3/g.

Preliminary studies regarding the dynamic adsorption of the [D-Leu1]MCYST-LR in fixed beds of the activated charcoals in the Hemodialysis Centers have shown low adsorption capacity between 3.67 and 5.31 g/mg. Regarding the coconut shell and the sugarcane bagasse based-activated charcoals it was observed a 2.07 and 5.43 g/mg adsorption capacity of the respective beds.
