**3. Results**

150 Technical Problems in Patients on Hemodialysis

nitrogen aborted volume in the saturation point (P/P0 ~ 0.99). The micropores and primary micropores were calculated from the intercept point of the t-plot linear region after the saturation of the micropores and primary micropores respectively. The volume of the mesopores was calculated from the difference between the total volume of the pores and the volume of the micropores, also, the volume of the secondary micropores was calculated by the difference between the volume of the mesopores and the volume of the primary micropores. The distribution of the size of the pores in the micropore and mesopore regions in the ACs was obtained from the methods developed by Horvath-Kawazoe (HK) and

An isotherm study of adsorption equilibrium is important as to describe an interaction between adsorbate and adsorbents, and it is critical in the optimization of these materials for both studies in continuous or in batch process. Information regarding the distribution of the sizes of the AC pores were obtained from comparison of the adsorption characteristic for three different adsorbates: methylene blue and [D-Leucine1]microcystin-LR ([D-Leu1]MCYST-LR). The choice of these molecules is justified by their properties, forms and polarities, being the first commonly used for foretelling the capacity of the activated charcoal in adsorbing micropollutants in industrial effluents (Hsieh & Teng, 2000; Lussier et al., 1994), besides providing an estimate of the volumes in secondary micropores +

The trihydrate methylene blue (99.95%, Merck, EUA) analytical grade was used in the solution preparation as to determine the Methylene Blue Index (MBI). The adsorption experiments were made in accordance with the norm JIS (Japanese Industrial Standard), JIS-K 1474 (1991). The methylene blue concentrations in the liquid phase after the equilibrium were determined indirectly from molecular adsorption spectrophotometry (spectrophotometer GBC UV/VIS – 911 A) in the wave length of 665 nm. The experimental data were adjusted to the Freundlich's model, and the quantity of the methylene blue

> C C <sup>0</sup> q V m

For the foretelling of the capacity and removal de microcystine in water by activated charcoal, an aqueous extract of [D-Leu1]MCYST-LR of concentration around to 6000 g/L, prepared in drinkable water exempt of chloride, was used as adsorbate. This toxin has been already identified in growths in Lagoa dos Patos, Rio Grande do Sul, Brazil, (coordinates 31° 9'56.93"S 51°25'51.45"W) by Matthiensen et al. (2001) and in Lagoa de Jacarepaguá, Rio de Janeiro, Brasil (22°59'10.69"S 43°23'57.95"W) by Oliveira et al. (2004). The preparation of the respective extract, as in the quantification model of the referred toxin by High Performance Liquid Chromatography (HPLC) was fully discussed by Kuroda et al. (2005). The experimental data were adjusted to the Langmuir's model and the quantity of adsorbed

(1)

**]microcystin-**

Barrett-Joyner-Halenda (BJH), respectively (Webb & Orr, 1997).

**LR** 

**2.1.2.1 Batch experiments** 

**2.1.2 Adsorption in liquid phase: Methylene blue index and [D-Leucine<sup>1</sup>**

mesopores, as foretold in previous works by Albuquerque Junior et al. (2005).

adsorbed by the charcoals (q) was calculated according to the equation 1.

toxin by the activated charcoals was measured from the equation 1.

#### **3.1 Textual characteristics of activated charcoals**

The activated charcoals are formed by an interconnected net of pores, which according to IUPAC (International Union of Pure and Applied Chemistry) may be classified according to its diameters in different categories: macropores (di > 50 nm), mesopores (2 nm < di < 50 nm), primary micropores (di < 0,8 nm) and secondary micropores(0,8 nm < di < 2nm) (Everett, 1988).

The activated charcoal porosity may be estimated from the form of the isotherm of Nitrogen adsorption according to the Brunauer, Deming, Deming and Teller (BDDT) (Gregg & Sing, 1982) classification. Therefore, from that classification, it was observed that the AC-B-F, AC has presented an isotherm characteristic of the type I, typical of micropores material, with relatively small external surface area. Nevertheless, loops characteristic from hysteresis in partial pressures (P/P0) above 0,4 in other ACs, which indicate that these charcoals must present a small band of pores in the secondary micropore region and mesopores. Thus, these other charcoals have presented a combination between the isotherms I and II, the same observed for charcoals taken as reference (fig. 2).

Specifications of the Quality of Granulated Activated Charcoal

Centers A (HC Campinas) for the removal of contaminants.

REF. BET Micro Meso Primary

Table 2. Activated Charcoals textural properties.

Used in Water Systems Treatment in Hemodialysis Centers in Brazil 153

The adsorption isotherms could also be analyzed from the hysteresis loop format according to the standard classification, which contains 4 types: H1–H4 (Girgis & Hendawy, 2002). The hysteresis loops appear in multilayer regions of isothermal of physiosorption, and are considered as being associated to capillary condensation. The hysteresis loop style found for the analyzed charcoals was of the H4 type, which was originated from the influence, even

The charcoal sample AC-A-D has presented an unusual behavior from the obtained isothermal data of N2 adsorption/desorption, as it has shown a very low Nitrogen adsorpted volume, around 0.27 cm3/g, when compared with those obtained by other sampled charcoals, which then Nitrogen adsorpted volumes were above 248 cm3/g (Figure 2d). By the adsorption behavior of that charcoal, it is assumed that the same is an activated charcoal and, thus, could not be used in the water treatment station in the Hemodialysis

The used ACs in the water treatment station of the Hemodialysis Center A have presented BET area (SBET) between 764.9 m2/g e 1,017.4 m2/g, whereas the ones used in the Hemodialysis Center B have presented SBET between 632.8 m2/g and 789.5 m2/g (Table 2).

\*Secondary

micropore (%) Mesopore (%) Total

Surface area ( m2/g) Pore Volume (cm3/g)

AC-A-A 764.9 756.2 8.7 0.16 (44.7) 0.21 (55.3) 0.01 (2.6) 0.38 AC-A-B 871.2 857.6 13.6 0.12 (31.9) 0.32 (68.1) 0.03 (6.4) 0.47 AC-A-C 1017.4 967.9 49.5 0.08 (31.9) 0.38 (69.1) 0.09 (16.4) 0.55 \*AC-A-D 4.6 4.5 0.015 - - - 0.003 AC-B-E 632.8 610.2 22.6 0.17 (55.9) 0.15 (44.1) 0.02 (5.9) 0.34 AC-B-F 789.5 772.0 17.5 0.14 (37.5) 0.30 (62.5) 0.04 (8.3) 0.48 AC-R-G 1079.5 1014.2 65.3 0.08 (50.0) 0.29 (50.0) 0.20 (34.5) 0.58 AC-R-H 1174.3 1097.3 77.3 0.10 (22.3) 0.35 (77.7) 0.39 (41.8) 0.76

A first observation of these results would imply in the choice of charcoals of any of the two centers, however, according to Quinlivan et al. (2005), the BET area (SBET) is a poor indicator of the adsorption capacity of activated charcoals, hence, the sampled charcoals quality cannot be assessed only by their BET (SBET) area data, so, other effectiveness parameters must be taken into consideration in order to choose a charcoal for a determined aim. Thus, beyond that parameter, the secondary micropores and mesopores volumetric fractions must also be considered in the choice of an activated charcoal for the use in water treatment, as these pores are significantly important in the adsorption of organic micropollutants like the microcystins by the activated charcoals according to Donati et al. (1994) and Pendleton et al. (2001). According to Donati et al. (1994), there is no correlation between the adsorption capacity of activated charcoals by microcystins and the BET area, the micropores volume and the number of Iodine. However, the mesopores presence in these adsorbents may favor the adsorption of the cyanobacterium toxin. Moreover, Pendleton et al. (2001), have shown that besides the mesopores volume, the adsorption capacity of that toxin, was also influenced by the

micropore (%)

\* The very low adsorption capacity has not allowed the calculation of these parameters.

small, of the existing secondary micropores and mesopores in these materials.

Fig. 2. Nitrogen adsorption/desorption Isothermes at -196oC. (a) AC-A-A, (b) AC-A-B, (c) AC-A-C, (d) AC-A-D, (e) AC-B-E, (f) AC-B-F, (g) AC-R-G and (h) AC-R-H

Fig. 2. Nitrogen adsorption/desorption Isothermes at -196oC. (a) AC-A-A, (b) AC-A-B, (c)

320

300

280

 (cm 2 Adsorbed volume N 3/g)

260

240

Adsorption

Desorption

170

160

220

200

(a) (b) (c) (d)

440

210

200

/g)

190

 (cm 2 Adsorbed volume N 3

180

400

350

/g)

300

 (cm 2 Adsorbed volume N 3

250

Adsorption

Desorption

420

/g)

400

 (cm 2 Adsorbed volume N 3

380

360

Adsorption

Desorption

340

Adsorption

Desorption

200

320

300

(e) (f) (g) (h)

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

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

P/P0

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

P/P0

P/P0

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

P/P0

150

AC-A-C, (d) AC-A-D, (e) AC-B-E, (f) AC-B-F, (g) AC-R-G and (h) AC-R-H

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

P/P0

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

P/P0

0,2

 0,4

 0,6

P/P0

 0,8

 1,0

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

P/P0

0,00

230

250

310

360

0,30

0,25

/g)

adsorption

0,20

 (cm 2 Adsorbed volume N 3

0,15

340

/g)

320

 (cm 2 Adsorbed volume N 3

300

300

290

/g)

280

 (cm 2 Adsorbed volume N 3

270

240

/g)

 (cm 2 Adsorbed volume N 3

230

220

adsorption

260

Adsorption

280

Adsorption

Desorption

0,10

0,05

260

240

Desorption

250

240

desorption

210

The adsorption isotherms could also be analyzed from the hysteresis loop format according to the standard classification, which contains 4 types: H1–H4 (Girgis & Hendawy, 2002). The hysteresis loops appear in multilayer regions of isothermal of physiosorption, and are considered as being associated to capillary condensation. The hysteresis loop style found for the analyzed charcoals was of the H4 type, which was originated from the influence, even small, of the existing secondary micropores and mesopores in these materials.

The charcoal sample AC-A-D has presented an unusual behavior from the obtained isothermal data of N2 adsorption/desorption, as it has shown a very low Nitrogen adsorpted volume, around 0.27 cm3/g, when compared with those obtained by other sampled charcoals, which then Nitrogen adsorpted volumes were above 248 cm3/g (Figure 2d). By the adsorption behavior of that charcoal, it is assumed that the same is an activated charcoal and, thus, could not be used in the water treatment station in the Hemodialysis Centers A (HC Campinas) for the removal of contaminants.

The used ACs in the water treatment station of the Hemodialysis Center A have presented BET area (SBET) between 764.9 m2/g e 1,017.4 m2/g, whereas the ones used in the Hemodialysis Center B have presented SBET between 632.8 m2/g and 789.5 m2/g (Table 2).


\* The very low adsorption capacity has not allowed the calculation of these parameters.

Table 2. Activated Charcoals textural properties.

A first observation of these results would imply in the choice of charcoals of any of the two centers, however, according to Quinlivan et al. (2005), the BET area (SBET) is a poor indicator of the adsorption capacity of activated charcoals, hence, the sampled charcoals quality cannot be assessed only by their BET (SBET) area data, so, other effectiveness parameters must be taken into consideration in order to choose a charcoal for a determined aim. Thus, beyond that parameter, the secondary micropores and mesopores volumetric fractions must also be considered in the choice of an activated charcoal for the use in water treatment, as these pores are significantly important in the adsorption of organic micropollutants like the microcystins by the activated charcoals according to Donati et al. (1994) and Pendleton et al. (2001). According to Donati et al. (1994), there is no correlation between the adsorption capacity of activated charcoals by microcystins and the BET area, the micropores volume and the number of Iodine. However, the mesopores presence in these adsorbents may favor the adsorption of the cyanobacterium toxin. Moreover, Pendleton et al. (2001), have shown that besides the mesopores volume, the adsorption capacity of that toxin, was also influenced by the

Specifications of the Quality of Granulated Activated Charcoal

with an internal diameter close to 2-3 nm.

**3.2 Adsorption on liquid phase 3.2.1 Batch experiments** 

from adsorption data in gaseous phase.

Reference

impossible to calculate the MBI.

Table 3. Freundlich's model adsorption parameters.

charcoals' Methylene Blue Index (MBI), are displayed on Table 3.

Freundlich's model parameters

AC-A-A 9.2 0.13 0.91 7.6 AC-A-B 40.7 0.07 0.98 36.6 AC-A-C 43.4 0.02 0.95 42.1 \* AC-A-D - - - - AC-A-E 35.4 0.1 0.97 32.5 AC-A-F 85.6 0.05 0.99 79.2 AC-A-G 104.5 0.08 0.94 92.6 AC-A-H 271.4 0.16 0.99 217.5 \*This charcoal has a very low adsorption capacity (close to zero) for methylene blue, which makes it

Used in Water Systems Treatment in Hemodialysis Centers in Brazil 155

be taken as referential of the latter. Thus, taken the approximate dimensions of the MCYST-LR it is presumed that the [D-Leu1]MCYST-LR is adsorbed in the activated charcoal pores

The distribution of the pores size (Figure 3) estimated from the HK/BJK has allowed to observe that the sampled charcoals have a pores average diameter between 2.5-4 nm, which would make these charcoals potential adsorbents for their use in the removal of the water microcystin, but the low volume of the pores observed in this 2.5-4 nm band is smaller than 0.07 cm3/g, which makes these charcoals adsorbents of low adsorption capacity for such aim.

Knowing the adsorption equilibrium represents the first step in investigating the possibilities for using an adsorbent in a determined separation process. Besides, additional information regarding the distribution of the sizes of the activated charcoal pores can be obtained by comparing the adsorption characteristics of adsorbate by taking those obtained

Methylene blue (MB) has been widely used as an adsorbate to estimate the adsorption capacity of CA from continuous in fixed bed or batch experiments (Kumar & Sivanesan, 2006; Macedo et al., 2006; Zhang et al., 2006). Studies on MB adsorption equilibrium in activated charcoal can provide important information about the selectivity of these adsorbents regarding this molecule, given that the MB is accessible to the charcoal pores with an inner diameter greater than 1.5 nm, being important for the characterization of the secondary micropores (0.8 <di <2.0 nm) and mesopores (2 nm < di < 50 nm) mainly, besides being a model compost used for predicting the adsorption of organic contaminants found in industrial effluents such as textile dye and microcystines (Barton, 1987; Baçaoui et al., 2001). According to the JIS norm (1994), the Methylene Blue Index is operationally defined as the adsorbed amount of that molecule when its residual concentration in liquid phase after equilibrium is of 0.24 mg/L. This adsorption capacity was obtained from an equilibrium isotherm where the experimental data were adjusted to Freundlich's adsorption model. The correlation coefficients for linear regression from the adjustment of the experimental data to the respective linearized model along with its empirical parameters, K and 1/n, besides the

> Methylene Blue Index K (L/mg) 1/n r2 MBI (mg/g)

volumetric fraction correspondent to the secondary micropores. In these charcoals, the secondary micropores and mesopores volumetric fractions have exceeded 37% e 28%, respectively, favoring the adsorption of microcystin in 200.0 g/mg.

The activated charcoals of the water treatment in the hemodialysis Center (A and B) have presented secondary micropores and mesopores volumetric portions of 0.15 to 0.38 cm3/g (44.1 to 69.1%) and of 0.01 to 0.09 cm3/g (2.6 to 16.4%), respectively. These charcoals have presented secondary micropores portions higher than those found by Pendleton et al. (2001), however, they have also presented very low mesopores volumetric fractions, around 8% in average, which characterizes microporous charcoals. Nevertheless, those commercial activated charcoals obtained as reference by the authors, have presented secondary micropores volumetric fractions and mesopores of 59.2 to 63.6% and of 34.5 to 41.8%, respectively, which can be characterized as a good indicator for the AC for the treatment water use.

A visualization of the pores size distribution can be obtained from the distribution function calculated by the HK and BJH (Figure 3) methods. The (A), (B) and (C) charcoals have shown a distribution function HK/BJH, with dW/dLo of 0.04; 0.07 and 0.06 cm3/nm/g consisting of pores average diameters of 3.81, 3.80 and 3.28 nm, respectively. Due to the low adsorption capacity of the D charcoal, it was not possible to obtain its distribution of the pores sizes. For the E charcoal, the distribution function dW/dLo has presented two peaks with 0.02 and 0.01 cm3/nm/g a 2.53 and 4.15 nm in pores average diameter; while the AC-B-F has presented dW/dLo ≈ 0.06 cm3/nm/g to an average pore diameter of 2.7 nm. In contrast with these results, the standards AC-R-G and AC-R-H have shown a distribution function a little higher: (AC-R-G) dW/dLo ≈ 0.3 cm3/nm/g with 1.61 nm of pore average diameter, and AC-R-H has presented two peaks with dW/dLo ≈ 0.17 and 0.08 cm3/nm/g with pore average diameter of approximately 1.71 and 3.00 nm, respectively.

Fig. 3. Function distribution HK/BJH: (■) AC-A-A; (□) AC-A-B; (∆) AC-A-C; () AC-B-E; () AC-B-F; (Ө) AC-R-G; (О) AC-R-H.

According to Lanaras et al. (1991) the MCYST-LR when dissolved in water, has a solvated volume of 2.63 nm, length of 1.9nm, height of 1.5nm, thickness of 1.1nm, and solvated area of 1.8 nm2. The [D-Leu1]MCYST-LR has an amino acid residue, D-Leucine, which has replaced the amino acid residue, D-Alanine, of MCYST-LR, that confers the [D-Leu1]MCYST-LR more hydrophobicity than the MCYST-LR. But, these differences between their chemical structures are not so significant regarding their heights, solvated volume and transversal section area, enabling that approximate dimensions of the first MCYST-LR might be taken as referential of the latter. Thus, taken the approximate dimensions of the MCYST-LR it is presumed that the [D-Leu1]MCYST-LR is adsorbed in the activated charcoal pores with an internal diameter close to 2-3 nm.

The distribution of the pores size (Figure 3) estimated from the HK/BJK has allowed to observe that the sampled charcoals have a pores average diameter between 2.5-4 nm, which would make these charcoals potential adsorbents for their use in the removal of the water microcystin, but the low volume of the pores observed in this 2.5-4 nm band is smaller than 0.07 cm3/g, which makes these charcoals adsorbents of low adsorption capacity for such aim.
