**2.1 Characterization of activated charcoals**

For the characterization in liquid phase by means of use of methylene blue solution and in gaseous phase by N2, the charcoals were marked in mortar and pestle, grinded in a sieve with nominal opening mesh of 0.075mm. Whereas the ones used in the experiments in fixed bed column were grinded in sieves with nominal opening mesh of 0.50mm and 0.35mm, being the obtained material in this last sieve collected for the referred experiment. The charcoals were then dried in greenhouse at 150 ºC by 3 hours minimally, and then cooled in desiccators with silica gel until reached room temperature for its posterior use.

### **2.1.1 Adsorption in gaseous phase: Specific surface area and distribution of pores size**

As the analysis procedures, all the ACs were degasified in vacuum at 150 ºC for 24 h. A software in interface with a gas analyzer (model NOVA-1200, Quantachrome Corp.) was used in the measures of specific surface area and distribution of pores size. Equilibrium data obtained from the isothermal of adsorption /desorption of gaseous nitrogen at 196 ºC were used to determine the specific surface area by means of application of the method developed by Brunauer, Emmet and Teller (BET). The micropores area was obtained by the "t-plot" method. The total volume of the pores was determined converting in liquid volume the

Specifications of the Quality of Granulated Activated Charcoal

possible loss of adsorbent by reflux (Fig. 1).

Used in Water Systems Treatment in Hemodialysis Centers in Brazil 151

In order to evaluate the microcystin dynamics in experiments in fixed bed column, an acrylic column was used of 2.5 cm de di and height of up to 25 cm, adjusted by means of a piston. A distributor plate with five orifices of 1mm openings, made of stainless steel, was inserted in the base of this column. A net of 60 μm was used below the distributor and in the entrance of the piston through which the fluid that passed the column flowed, avoiding that

Fig. 1. The column scheme used in this work (a) *o*-ring, (b) distributor (perforated plate), (c)

The charcoal bed was continuously percolated by a solution having [D-Leu1]MCYST-LR of varied concentration, from which effluent samples were intermittently collected until the bed saturation. The toxin concentration in the liquid phase was determined by HPLC and the evaluation of the continuous process of adsorption was made by means of breakthrough curves sizing, which is the relation between the ration of the initial concentration by the

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)

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

net (60 μm), (d) screw, (e) rule, (f) piston. Source: Santos et al., 2002.

toxin concentration in the column effluent (C/C0) vs time (t).

**3.1 Textual characteristics of activated charcoals** 

observed for charcoals taken as reference (fig. 2).

**3. Results** 

(Everett, 1988).

**2.1.2.2 Experiments in fixed bed columns: Adsorption of [D-leucine1]MCYST-LR** 

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

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

#### **2.1.2.1 Batch experiments**

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

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

$$\mathbf{q} = \frac{\left(\mathbf{C}\_0 - \mathbf{C}\right)}{\mathbf{m}} \mathbf{V} \tag{1}$$

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

#### **2.1.2.2 Experiments in fixed bed columns: Adsorption of [D-leucine1]MCYST-LR**

In order to evaluate the microcystin dynamics in experiments in fixed bed column, an acrylic column was used of 2.5 cm de di and height of up to 25 cm, adjusted by means of a piston. A distributor plate with five orifices of 1mm openings, made of stainless steel, was inserted in the base of this column. A net of 60 μm was used below the distributor and in the entrance of the piston through which the fluid that passed the column flowed, avoiding that possible loss of adsorbent by reflux (Fig. 1).

Fig. 1. The column scheme used in this work (a) *o*-ring, (b) distributor (perforated plate), (c) net (60 μm), (d) screw, (e) rule, (f) piston. Source: Santos et al., 2002.

The charcoal bed was continuously percolated by a solution having [D-Leu1]MCYST-LR of varied concentration, from which effluent samples were intermittently collected until the bed saturation. The toxin concentration in the liquid phase was determined by HPLC and the evaluation of the continuous process of adsorption was made by means of breakthrough curves sizing, which is the relation between the ration of the initial concentration by the toxin concentration in the column effluent (C/C0) vs time (t).
