**2. Materials and methods**

#### **2.1. Specificity of the investigated groundwater and geological survey of aquifer origin**

In the period of the Middle Miocene to the Quaternary, the space of the Central and South-Eastern Europe was covered by the Pannonian Sea, formed in the spacious depression between the Alpine, Carpathian, and Dinaridian mountain ranges, where very thick sediment series were deposited. The northern part of Serbia-Vojvodina is situated in the south-east part of this sedimentation zone on an area of 21,506 km2 . The basic mass of these sediments make the Mesozoic clastites and carbonates along with crystalline schists and granitoids of the Paleozoic The adsorption of arsenic ion on the surface of strongly basic ion exchanging resin may be

Since the affinity of the acrylic resin with quaternary ammonium groups is higher to doubly charged ions than to the singly charged ones, the efficiency of the ionic exchange is higher at

Removal of As(III) by ionic exchange is less effective, since at the pH < 9 it occurs in water in the form of the molecule H3AsO3 [20]. On the other hand, As(V) is present in the form of the

specific phenomenon of the occurrence of arsenous acid as an uncharged species that cannot be removed from water which allowed the development of procedures for distinguishing between arsenite and arsenate [33, 34]. Therefore, in order to remove arsenite from water, it has to be oxidized to arsenate. The regeneration of the ion-exchange resin proceeds according

*RH AsO Cl RCl H AsO* 2 4 2 4

Regeneration can be done with HCl and NaCl. The use of HCl yields arsenic acid, H3AsO4, which has no influence on the equilibrium of ion exchange and the regeneration is more efficient [32]. The strongly basic resin that has been pretreated by anions, e.g. chloride, is capable of removing a wide spectrum of anions from water, depending on their relative

2- 2- 2- - -- 2- 2- 3- - - CrO >> SeO >> SO >> HSO > NO > Br > HAsO >SeO >HSO >NO > Cl 4 4 4 43 4 3 32

**2.1. Specificity of the investigated groundwater and geological survey of aquifer origin**

In the period of the Middle Miocene to the Quaternary, the space of the Central and South-Eastern Europe was covered by the Pannonian Sea, formed in the spacious depression between the Alpine, Carpathian, and Dinaridian mountain ranges, where very thick sediment series were deposited. The northern part of Serbia-Vojvodina is situated in the south-east part of this

Mesozoic clastites and carbonates along with crystalline schists and granitoids of the Paleozoic


42 4 2 2 *R Cl HAsO R HAsO Cl* - - -+ ® - + (2)

2-, which makes the ionic exchange more probable. It is just the


. The basic mass of these sediments make the

*R Cl H AsO R H AsO Cl* 24 24

2

higher pH values, when doubly charged arsenate ions are dominant [32].

presented as follows:

78 Ion Exchange - Studies and Applications

anions H2AsO4


to the following reaction:

and HAsO4

affinities, shown by the following order [35]:

sedimentation zone on an area of 21,506 km2

**2. Materials and methods**

and Proterozoic eras. The town of Zrenjanin is located in the eastern part of the Vojvodina called the Middle Banat, and the specificity of the location stems primarily from the geological and hydrological characteristics of the terrain. The water-bearing formations in this region were formed in the final phase of the existence of the Pannonian Sea. On the territory of the town of Zrenjanin, in the geological profile to a depth of 400 m, there are several water-bearing strata, separated by strata layers of pure or sandy clay or clayey sands. The thickness of the water-bearing strata is from several meters to about 50 m, most often 10-20 m. The groundwater that can be used as drinking water occurs to a depth of about 400 m. In the upper part, to a depth of about 60 m, an unconfined aquifer (phreatic aquifer) is formed, whereas below it the aquifer is under the pressure (artesian aquifer). The groundwater of the artesian aquifer, to which belongs the investigated water, is by their chemical composition significantly different from the waters of the phreatic aquifer. The investigated water belongs to the type of bicar‐ bonate alkaline waters, with the bicarbonate share of about 85-90% equivalents. The total mineralization is most often lower compared to that of the phreatic water and is in the range 250-1500 mg/L. Content of sodium chloride increases generally with increase in the depth of the artesian aquifer. Local deviations are usually a consequence of tectonic disturbances. The ammonium content is usually below 2 mg/L, although there have been registered very high contents (up to 10 mg/L) at the locations south of Zrenjanin. The iron content often exceeds the maximum tolerable concentration (MTC); it is usually around 1 mg/L and decrease with depth. If compared to the contents in phreatic water, contents of total iron and manganese show a decrease. The artesian water is softer than phreatic water, and its hardness rarely exceeds the limit of 10° dH. Very soft waters (2-5° dH) have been found north of Zrenjanin. Artesian waters are often weakly alkaline, and their temperature is in the range of 15-20°C. In the Zranjanin region, these waters are of the very characteristic yellow color, have a specific taste, and in many settlements are used as drinking water. People that are accustomed to yellow water are reluctant to change their habit and this represents a problem. Namely, yellow color is due to the presence of undesirable organic (humic) matter. Content of this matter, expressed via the COD, determined by the permanganate method, is in the range of 20-150 mg/L, and in the extreme cases exceeds even 200 mg/L [36]. Up to now, water supply in the Middle Banat region has been based on the exploitation of artesian groundwater. Waters of this aquifer, in addition to marked humic matter load, contain significant amounts of ortho‐ phosphate, sodium, and arsenic. The measured arsenic contents are in the range from 0.040 to 0.380 mg/L, so that the Zrenjanin region is in this respect one of the most endangered regions in Europe. The size of the area of the arsenic occurrence suggests the supposition that it is of geological origin. However, there exists the possibility that it has been brought to Vojvodina by the Tisa River, whose water dissolves arsenic minerals of the Carpathian, where there are large deposits of arsenic ores [37]. In some Zrenjanin locations, many domestic and foreign corporations searched for practical groundwater treatment models, but without satisfactory results. A likely reason for this is the methodological research inadequacy for the actual problem. Pilot tests were conducted without a clear project assignment and a defined method of removal of many pollutants for the given case [38]. Groundwater from the Zrenjanin region as a resource outside the natural water cycle is of extremely complex chemical composition, which demands a complex technological treatment. Values of measured physicochemical parameters are given in Table 1.


**Table 1.** Selected physicochemical parameters of the investigated groundwater

### **2.2. Strongly basic macroporous ion-exchange resin**

To study the removal of dissolved NOM, arsenic bicarbonate, pH value, electrical conductivity, chlorine, and sulfate, an acrylic SBIX type Amberlite IRA 958-Cl, manufactured by Rohm and Haas Company, whose characteristics are given in Table 2 [11] was used. This type of resin has a rigid polymer porous network in which persist an intrinsic porous structure even after its drying. The resin large pores permit access to the interior exchange sites of the bead. They are also referred to as macroreticular or fixed-pore resins. Macroporous resins are manufac‐ tured by a process that leaves a network of pathways throughout the bead. This sponge-like structure allows the active portion of the bead to contain a high level of divinylbenzene crosslinked without affecting the exchange kinetics. Unfortunately, it also means that the resin has a lower capacity because the beads contain less exchange sites.



**Parameter MTC Groundwater**

pH 6.8-8.5 8.06 COD (mgO2/L) 2.0 7.73 TOC (mg/L) / 10.64 Electrical conductivity (μS/cm) 1000 820 Chloride (mg/L) 200 6.97 Bicarbonate (mg/L) / 645 Sulfate (mg/L) 250 25.6 Arsenic (mg/L) 0.01 0.2658

**Table 1.** Selected physicochemical parameters of the investigated groundwater

has a lower capacity because the beads contain less exchange sites.

**2.2. Strongly basic macroporous ion-exchange resin**

Co-Pt) 5 60

To study the removal of dissolved NOM, arsenic bicarbonate, pH value, electrical conductivity, chlorine, and sulfate, an acrylic SBIX type Amberlite IRA 958-Cl, manufactured by Rohm and Haas Company, whose characteristics are given in Table 2 [11] was used. This type of resin has a rigid polymer porous network in which persist an intrinsic porous structure even after its drying. The resin large pores permit access to the interior exchange sites of the bead. They are also referred to as macroreticular or fixed-pore resins. Macroporous resins are manufac‐ tured by a process that leaves a network of pathways throughout the bead. This sponge-like structure allows the active portion of the bead to contain a high level of divinylbenzene crosslinked without affecting the exchange kinetics. Unfortunately, it also means that the resin

**Properties**

Functional groups Quaternary ammonium Physical form White opaque beads

Ionic form as shipped Chloride Total exchange capacity ≥ 0.8 eq/L (Cl-

Moisture holding capacity 66-72 % (Cl-

Specific gravity 1.05-1.08 (Cl-

Bulk density 655-730 g/L (Cl-

Effective size 470-570 μm Mean diameter 700-900 μm

Matrix Crosslinked acrylic macroreticular structure

form)

form)

form)

form)

Color, permanent (o

80 Ion Exchange - Studies and Applications

**Table 2.** Physicochemical characteristics of the Amberlite IRA 958-Cl macroporous resin and operating conditions recommended by the manufacturer

#### **2.3. Determination of optimal specific flow rate of strongly basic ion-exchange resin**

To study the influence of the different SFRs in the process of removal of NOM and arsenic from groundwater, a specially designed pilot plant system 1 was made (Figure 2). The pressure and the amount of water were ensured using the waterworks facilities of the Melenci settle‐ ment explained in Section 2.1. The mean operating water pressure and temperature were 3 bar and 18<sup>o</sup> C, respectively. The composite pressure vessels used for plant construction were Structural type Q-0844 and Q-0635, of total volume of 33.6 L and 14.4 L, respectively. The vessel was filled with 25 L and the later with 10 L of resin. The cross-section area of the tank Q-0844 was 0.034 m<sup>2</sup> , and the resin bed height was 0.735 m. The tank Q-0635 of the cross-section of 0.020 m<sup>2</sup> had the bed height of 0.5 m. The bigger tank was used for smaller SFRs, from 2 to 80 BV/h, and the smaller one for the SFRs ranging from 100 to 300 BV/h. The control valve (CV) was a Fleck 3150, injector type, with manual control. The pilot plant was equipped with four Franck Plastic flow meters (R), for the flow ranges of 50-500 L/h, 100-1000 L/h, 200-2000 L/h, and 600-6000 L/h, respectively. The plant was also equipped with a Prominent dosing pump (DP), with a Zenner pulse water meter (F) for dosing sodium hypochlorite, and with a vessel for its mixing with water (MT), to achieve a homogeneous solution with a constant chlorine concentration of 0.5 mg/L, determined by the colorimetric method [39] and a micro filter (M). Chlorinated water for the determination of the residual chlorine was sampled via the tap (S). The first part of the study was concerned with the investigation of the effect of different SFR and the determination of its optimum value, as well as of the EBCT value for the removal of NOM and arsenic from groundwater without addition of sodium hypochlorite as oxidizing agent. Sodium hypochorite was added to the raw water with the aim of oxidizing NOM and As(III) to As(V) in the second part of the study. Special attention was paid to those SFRs that were smaller than 6 BV/h and higher than 30 BV/h, in order to determine the ion-exchange capabilities and sorption possibilities of using the resin beyond the prescribed range of operating conditions in the treatment of the given groundwater. The first part of the series of measurements was carried out using the resin from the original package of 25 L. The resin was backwashed by standard procedure for 20 min, i.e. to the end of foam formation and appear‐ ance of an unpleasant odor. The other two experiments in the series of investigations using either chlorinated or non-chlorinated water were carried out on the resin regenerated accord‐ ing to the procedure described in Section 2.2.1. After the mentioned preparation of the resin, groundwater was passed through the bed in a down flow direction. The EBCT and SFR in these investigations were from 0.5 to 0.0033 h and from 2 to 300 BV/h, respectively. During the experiment, samples of both raw and treated water were taken regularly. Three series of samples of both chlorinated and non-chlorinated water were used to determine the following physicochemical parameters: pH, electrical conductivity, sulfates, bicarbonates, COD, TOC, and total arsenic. All the results represent mean values of three repetitions. Each series of measurements encompassed 30 samples of the effluent and one sample of groundwater. In the first part of the study, involving non-chlorinated groundwater, the overall contact time of water and resin at different SFR values was in average 38.5 h, whereas the average volume of the water passing through the bed was 17,187.50 L. This volume corresponded to 687.5 volumes of the resin in the bed. In the second part of the study, dealing with chlorinated water, the overall contact time of water and resin was in average 34.1 h, at different SFR values. The average volume of groundwater that passed through the bed was 16,650 L, which was equivalent to 666 volumes of the resin.

#### *2.3.1. Regeneration of SBIX*

The resin regeneration was carried out in three phases. In the first phase, by opening the control valve, the resin was counterwashed with raw water for 10 min. In the second phase, at a SFR of 4 BV/h, the regenerant (solution of NaCl (10%) and NaOH (2%)) from the regenerant vessel was injected with the aid of an injector inbuilt in the control valve. The overall contact time of the resin with the regenerant was 120 min in a regime encompassing successive repetition of 10-min passing the regenerant and 10-min of stopped flow. This regeneration method ensured a better dynamic equilibrium between the adsorbed and desorbed humic acid molecules, i.e. NOM and arsenic. In the beginning of the regeneration, the effluent was light yellow, and then became darker, and at the end of the first 10 min, it was of a typical brown color. The effluent began to regain a lighter color after about 80 min of regeneration, to become yellow at about the 100th min, and this color remained to the end of the regeneration. The third phase consisted of the fast rinsing of the resin with raw water, whereby the resin was dispersed in the whole working volume, and this was accompanied by the measurement of the electrical conductivity. When the effluent electrical conductivity dropped to that of the raw water, further washing was stopped. At the same time, the measured pH of the effluent became slightly alkaline, like the raw water. Measurements of the electrical conductivity and pH were necessary to check whether the resin had been freed of the regenerants. After the resin regeneration, the experi‐ ments were repeated both with chlorinated and non-chlorinated water, and it was subse‐ quently regenerated two times.

#### *2.3.2. Calculation of flow parameters*

capabilities and sorption possibilities of using the resin beyond the prescribed range of operating conditions in the treatment of the given groundwater. The first part of the series of measurements was carried out using the resin from the original package of 25 L. The resin was backwashed by standard procedure for 20 min, i.e. to the end of foam formation and appear‐ ance of an unpleasant odor. The other two experiments in the series of investigations using either chlorinated or non-chlorinated water were carried out on the resin regenerated accord‐ ing to the procedure described in Section 2.2.1. After the mentioned preparation of the resin, groundwater was passed through the bed in a down flow direction. The EBCT and SFR in these investigations were from 0.5 to 0.0033 h and from 2 to 300 BV/h, respectively. During the experiment, samples of both raw and treated water were taken regularly. Three series of samples of both chlorinated and non-chlorinated water were used to determine the following physicochemical parameters: pH, electrical conductivity, sulfates, bicarbonates, COD, TOC, and total arsenic. All the results represent mean values of three repetitions. Each series of measurements encompassed 30 samples of the effluent and one sample of groundwater. In the first part of the study, involving non-chlorinated groundwater, the overall contact time of water and resin at different SFR values was in average 38.5 h, whereas the average volume of the water passing through the bed was 17,187.50 L. This volume corresponded to 687.5 volumes of the resin in the bed. In the second part of the study, dealing with chlorinated water, the overall contact time of water and resin was in average 34.1 h, at different SFR values. The average volume of groundwater that passed through the bed was 16,650 L, which was

The resin regeneration was carried out in three phases. In the first phase, by opening the control valve, the resin was counterwashed with raw water for 10 min. In the second phase, at a SFR

equivalent to 666 volumes of the resin.

82 Ion Exchange - Studies and Applications

**Figure 2.** Scheme of pilot plant 1

*2.3.1. Regeneration of SBIX*

In order to study the removal process, it was necessary to calculate the flow parameters and the resins exposure time to the groundwater flowing through pilot plant 1. Specific flow rate was calculated using equation 4, where *Q* is the flow rate of chlorinated or non-chlorinated groundwater (L/h) and *VSBIX* is the volume of the resin bed (L). The SFR is expressed in the units of the bed volume per hour (BV/h), and it represents a universal quantity which can be applied to characterize any ion exchanger. Namely, when the results for the optimum SFR are obtained for a pilot plant system for concrete groundwater of distinct physicochemical characteristics, it is simple to design a unique ion-exchange water treatment system of any capacity. The empty bed contact time (EBCT) was expressed and calculated in the way shown in equation 5. The EBCT is used as a measure of the duration time of the contact between the resin granules and water flowing through the bed. The increase in the EBCT value presents increased time available for the adsorption of dissolved matter on the resin beads.

$$SFR = \frac{Q}{V\_{SRIX}}\tag{4}$$

$$EBCT = \frac{V\_{SBX}}{Q} \tag{5}$$

#### **2.4. Strongly basic ion-exchange resin sorption characteristics determination**

The objective of this research was to experimentally examine the sorption efficiency of NOM and arsenic on Amberlite IRA 958-Cl resin. The aim was to compare experimentally obtained amounts of NOM and arsenic sorbed on the resin as indicators of the resin sorption capacity with the empirical sorption capacity based on the official data of the resin manufacturer. The investigations were conducted using native groundwater without (first part of investigation) and with addition of sodium hypochlorite (second part of investigation). For this purpose, a pilot plant 2 was designed and manufactured as shown in Figure 3. The main part of pilot plant 2 was the transparent container, manufactured by Atlas, filled with 1.4 L (970 g) of the resin Amberlite IRA 958-Cl. It was equipped with a flow meter (IHTM) for the flow range from 5 to 100 l/h, with a pump (Prominent) and pulse water meter (Zenner) for dosing sodium hypochlorite solution, and a vessel for mixing it with water, to obtain a homogeneous solution with a constant concentration of the residual chlorine. Samples of chlorinated water were taken from the tap. Concentration of the residual chlorine after the mixing vessel was measured by the colorimetric DPD method [39] and was kept constant as in the investigation of optimal flow parameters, at a level of 0.5 mg/L. The dosing system was not used in the first part of investigation, but only in the second one. In the first experiment in the series of measurements, both with native and chlorinated groundwater, a original packing of resin was used, which was backwashed with groundwater for 20 min, that is to the visually observed end of foaming and appearance of an unpleasant odor. The other two experiments in the series of investigation of chlorinated and non-chlorinated water were done using regenerated resin regenerated as described in Section 2.3.1. After the described resin preparation, the water was passed through it in a down flow direction. Samples of both the influent and effluent were taken regularly. Three series of samples of both chlorinated and non-chlorinated water were examined for the following parameters: COD, TOC, and total arsenic. All the measurement results are expressed as mean values of the determined parameters. The characteristics of the NOM and arsenic and of the resin applied as well as the chemical composition of groundwater and applied analytical methods and equipment for the determination of TOC, COD, and arsenic are identical to those described by the authors [40]. According to the resin manufacturer [11], the average sorption capacity of organic matter is 10-15 g of KMnO4/L resin. The capacity expressed as COD is between 2.5 and 3.75 g O2/L resin. The COD sorption capacity calculated per mass unit of SBIX, taking into account the filling density of 720 g/L, ranges from 3.47 to 5.21 mg O2/g resin.

#### *2.4.1. Mathematical expressions of volume and sorption parameters*

The efficiency of the removal of NOM and arsenic was followed by determination of COD, TOC, and arsenic concentrations in the effluent as a function of the overall water volume that passed through the SBIX bed, expressed as bed volume (BV). Bed volume is a dimensionless quantity that expresses the water volume as the number of the volume of resin bed (equation 6), where *Vout* is the effluent volume that passed through until the moment of sampling (L) and *VSBIX* is a constant, standing for the volume of SBIX, and it was 1.4 L in all series of experiments. The BV is a quantity that is not characteristic for only one concrete ion-exchange resin, but is universally applicable to any ion exchanger of any capacity, for the same treated water. The results obtained for BV can be used to calculate the SBIX volume, if one knows the volume of water and vice versa.

Effect of Extremely High Specific Flow Rates on the Ion-Exchange Resin Sorption Characteristics http://dx.doi.org/10.5772/60586 85

**Figure 3.** Scheme of pilot plant 2

amounts of NOM and arsenic sorbed on the resin as indicators of the resin sorption capacity with the empirical sorption capacity based on the official data of the resin manufacturer. The investigations were conducted using native groundwater without (first part of investigation) and with addition of sodium hypochlorite (second part of investigation). For this purpose, a pilot plant 2 was designed and manufactured as shown in Figure 3. The main part of pilot plant 2 was the transparent container, manufactured by Atlas, filled with 1.4 L (970 g) of the resin Amberlite IRA 958-Cl. It was equipped with a flow meter (IHTM) for the flow range from 5 to 100 l/h, with a pump (Prominent) and pulse water meter (Zenner) for dosing sodium hypochlorite solution, and a vessel for mixing it with water, to obtain a homogeneous solution with a constant concentration of the residual chlorine. Samples of chlorinated water were taken from the tap. Concentration of the residual chlorine after the mixing vessel was measured by the colorimetric DPD method [39] and was kept constant as in the investigation of optimal flow parameters, at a level of 0.5 mg/L. The dosing system was not used in the first part of investigation, but only in the second one. In the first experiment in the series of measurements, both with native and chlorinated groundwater, a original packing of resin was used, which was backwashed with groundwater for 20 min, that is to the visually observed end of foaming and appearance of an unpleasant odor. The other two experiments in the series of investigation of chlorinated and non-chlorinated water were done using regenerated resin regenerated as described in Section 2.3.1. After the described resin preparation, the water was passed through it in a down flow direction. Samples of both the influent and effluent were taken regularly. Three series of samples of both chlorinated and non-chlorinated water were examined for the following parameters: COD, TOC, and total arsenic. All the measurement results are expressed as mean values of the determined parameters. The characteristics of the NOM and arsenic and of the resin applied as well as the chemical composition of groundwater and applied analytical methods and equipment for the determination of TOC, COD, and arsenic are identical to those described by the authors [40]. According to the resin manufacturer [11], the average sorption capacity of organic matter is 10-15 g of KMnO4/L resin. The capacity expressed as COD is between 2.5 and 3.75 g O2/L resin. The COD sorption capacity calculated per mass unit of SBIX, taking into account the filling density of 720 g/L, ranges from 3.47 to 5.21 mg O2/g resin.

*2.4.1. Mathematical expressions of volume and sorption parameters*

water and vice versa.

84 Ion Exchange - Studies and Applications

The efficiency of the removal of NOM and arsenic was followed by determination of COD, TOC, and arsenic concentrations in the effluent as a function of the overall water volume that passed through the SBIX bed, expressed as bed volume (BV). Bed volume is a dimensionless quantity that expresses the water volume as the number of the volume of resin bed (equation 6), where *Vout* is the effluent volume that passed through until the moment of sampling (L) and *VSBIX* is a constant, standing for the volume of SBIX, and it was 1.4 L in all series of experiments. The BV is a quantity that is not characteristic for only one concrete ion-exchange resin, but is universally applicable to any ion exchanger of any capacity, for the same treated water. The results obtained for BV can be used to calculate the SBIX volume, if one knows the volume of

$$BV = \frac{V\_{out}}{V\_{SBIX}}\tag{6}$$

NOM and arsenic content in the total volume of investigated chlorinated or non-chlorinated water during the whole experiment are calculated in the following way:

$$\text{COD}\_{\text{total}} = V\_{\text{total}} \cdot \text{CODC}\_{\text{in}} \tag{7}$$

$$T\mathbf{OC}\_{\text{total}} = V\_{\text{total}} \cdot T\mathbf{OC}\mathbf{C}\_{\text{in}} \tag{8}$$

$$\mathbf{As}\_{\text{total}} = V\_{\text{total}} \cdot \mathbf{AsC}\_{\text{in}} \tag{9}$$

where *CODtotal* (mg O2) and *TOCtotal* (mg TOC) stand for the differently expressed total amounts of NOM; *Astotal* (mg) is the total amount of arsenic - the two quantities representing in fact the resin load; *Vtotal* (L) is the total volume of water treated in the experiment, whereas *CODCin* (mg O2/L) and *TOCCin* (mg O2/L) designate the NOM concentration in the influent, and *AsCin* (mg/ L) is the corresponding arsenic concentration.

The overall load of the resin with organic matter and arsenic is calculated as shown in equations 10, 11, and 12, where *CODload* (mgO2/g) and *TOCload* (mg TOC/g) represent the overall amounts of NOM; *Asload* (mg/g) the total amount of arsenic to which the resin was exposed in the experiment, and *m* represents the mass of the resin (g).

$$\text{COD}\_{\text{load}} = \frac{\text{COD}\_{\text{total}}}{m} \tag{10}$$

$$\text{TOC}\_{load} = \frac{\text{TOC}\_{\text{total}}}{m} \tag{11}$$

$$As\_{load} = \frac{As\_{total}}{m} \tag{12}$$

The amounts of NOM and arsenic that came in contact with the resin due to the volume of chlorinated or non-chlorinated water that passed through the bed in the real time of the experiment are calculated in the following way:

$$\text{COD}\_{\text{in}} = V\_{\text{out}} \cdot \text{CODC}\_{\text{in}} \tag{13}$$

$$T\mathbf{OC}\_{\rm in} = V\_{\rm out} \cdot T\mathbf{OC}\_{\rm in} \tag{14}$$

$$\mathbf{As}\_{\rm in} = V\_{\rm out} \cdot \mathbf{AsC}\_{\rm in} \tag{15}$$

where *CODin* (mg O2) and *TOCin* (mg TOC) stand for the amount of the NOM; *Asin* (mg As) is the amount of arsenic, and Vout (L) is the volume of water that passed to the moment of sampling.

Contents of NOM and arsenic in the instantaneous sample, i.e. in the effluent after the flow of a given volume of chlorinated or non-chlorinated water, are calculated as follows:

$$\text{COD}\_{out} = V\_{out} \cdot \text{CODC}\_{out} \tag{16}$$

$$\text{TOC}\_{out} = V\_{out} \cdot \text{TOC}\_{out} \tag{17}$$

$$\mathbf{As}\_{out} = \mathbf{V}\_{out} \cdot \mathbf{AsC}\_{out} \tag{18}$$

where *CODout* (mg O2) and *TOCout* (mg TOC) are the differently expressed amounts of NOM; *Asout* (mg As) is the amount of arsenic that was not sorbed onto the resin and is found in the effluent from the pilot unit, whereas *CODCout* (mgO2/L) and *TOCCou*<sup>t</sup> (mg TOC/L) are the concentrations of NOM in the effluent determined by the two different methods. Finally, *AsCout* (mg/L) represents the arsenic concentration in the effluent.

The amounts of NOM and arsenic that in a given time instant of sampling, after collecting the effluent volume *Vout* (L), were sorbed onto the SBIX are calculated in the following way:

$$\text{COD}\_{\text{ads}} = \text{COD}\_{\text{in}} - \text{COD}\_{\text{out}} \tag{19}$$

$$\text{TOC}\_{\text{ads}} = \text{TOC}\_{iu} - \text{TOC}\_{out} \tag{20}$$

$$\mathbf{As}\_{\rm ads} = \mathbf{As}\_{\rm in} - \mathbf{As}\_{\rm out} \tag{21}$$

where *CODads* (mg O2) and *TOCads* (mg TOC) are the adsorbed amounts of dissolved organic matter, and *Asads* (mg) the amount of arsenic adsorbed.

The sorption efficiency can be presented by the following expressions:

*total*

*total*

*total*

The amounts of NOM and arsenic that came in contact with the resin due to the volume of chlorinated or non-chlorinated water that passed through the bed in the real time of the

where *CODin* (mg O2) and *TOCin* (mg TOC) stand for the amount of the NOM; *Asin* (mg As) is the amount of arsenic, and Vout (L) is the volume of water that passed to the moment of

Contents of NOM and arsenic in the instantaneous sample, i.e. in the effluent after the flow of

where *CODout* (mg O2) and *TOCout* (mg TOC) are the differently expressed amounts of NOM; *Asout* (mg As) is the amount of arsenic that was not sorbed onto the resin and is found in the effluent from the pilot unit, whereas *CODCout* (mgO2/L) and *TOCCou*<sup>t</sup> (mg TOC/L) are the concentrations of NOM in the effluent determined by the two different methods. Finally, *AsCout*

(mg/L) represents the arsenic concentration in the effluent.

a given volume of chlorinated or non-chlorinated water, are calculated as follows:

*<sup>m</sup>* <sup>=</sup> (10)

*<sup>m</sup>* <sup>=</sup> (11)

*<sup>m</sup>* <sup>=</sup> (12)

*COD V CODC in out in* = × (13)

*in out in TOC V TOCC* = × (14)

*As V AsC in out in* = × (15)

*COD V CODC out out out* = × (16)

*out out out TOC V TOCC* = × (17)

*As V AsC out out out* = × (18)

*load COD COD*

*load TOC TOC*

> *load As As*

experiment are calculated in the following way:

86 Ion Exchange - Studies and Applications

sampling.

$$E\_{\rm COD} = \frac{\left(\text{CODC}\_{\rm in} - \text{CODC}\_{\rm out}\right)}{\text{CODC}\_{\rm in}} \cdot 100 \text{(\%)}\tag{22}$$

$$E\_{\rm TOC} = \frac{\left(TOCC\_{\rm in} - TOCC\_{\rm out}\right)}{TOCC\_{\rm in}} \cdot 100\left(\%\right) \tag{23}$$

$$E\_{As} = \frac{\left(A\text{sC}\_{in} - A\text{sC}\_{out}\right)}{A\text{sC}\_{in}} \cdot 100 \left(\%\right) \tag{24}$$

where *ECOD* and *ETOC* are the efficiencies of sorption of NOM, and *EAs* is the efficiency of arsenic sorption, all expressed as the corresponding percentages.

#### **2.5. Calculation of equilibrium adsorption capacity of SBIX toward NOM**

Effects of NOM adsorption by measuring of effluent NOM concentrations (C) in mg/L, during the experiments were shown in the dependence of cumulative time (*Στ*) in hours, i.e. number of effluent's bed volumes (BV). Shapes of these curves are the primary overview of adsorption process kinetics toward starting, breakpoint, and pseudo-equilibrium stages. The big challenge and most important scope of this work was pathway to calculation of mass of the adsorbent (*m*) in g, in the mass transfer zone (MTZ) [1, 1x] corresponding to each experimental sampling, i.e. measuring point. Elucidation of the *m* values was significant operation for reaching the final target, which represents the determination of Amberlite IRA-958 pseudo-adsorption capacity toward NOM. It was supposed that the mass of exhausted resin is proportional to effluent NOM concentrations in the moment of sampling time. Based on the obtained percent equation data, all masses of the resin corresponding to effluent NOM concentrations were calculated using the mathematical expression (25).

$$m = \frac{\text{C}}{\text{C}\_0} \cdot M \tag{25}$$

Adsorbed amount of NOM (α) in mg O2, at each sampling point was calculated as shown:

$$\mathfrak{a} = \left(\mathbb{C}\_0 - \mathbb{C}\right) \cdot V \tag{26}$$

where V is the volume of the effluent between two samplings (L).

Regarding the fact that samples have been taken randomly, calculation of the adsorption process rate as represented in equation 27 was an essential step:

$$\text{VADS} = \alpha / \tau \tag{27}$$

where *VADS* (mg/h) is adsorption rate and τ (h) is time between two sampling points.

Obtaining *VADS* data was a real contribution to equalize the adsorption process during the contact time of the complete experiment. Adsorption capacity of Amberlite IRA-958 in the time of experiment duration - specific adsorption capacity (*ADC*) in mg/gh - was calculated using equation 28:

$$\text{ADC} = \text{VADS} / \,\text{m} \tag{28}$$

The mutual relation of *ADC* values at measured *C* values was described as exponential regression plot. General equation form of the curve was represented (equation 29).

$$ADC = \beta \cdot e^{-\delta \cdot C} \tag{29}$$

*β* (L g-1 h-1) and *δ* are empiric adsorption coefficients obtained from the experimental data and calculated from the plot ln *ADC* vs. *C* (equation 30) as intercept and slope, respectively.

$$
\ln{ADC} = \ln{\beta} - \delta \cdot \mathbf{C} \tag{30}
$$

The total *ADC* (*ADCa*) in mg/gh, during the experiment, was calculated by integration of the surface above the curve using the following equation 31:

Effect of Extremely High Specific Flow Rates on the Ion-Exchange Resin Sorption Characteristics http://dx.doi.org/10.5772/60586 89

$$ADC\_{\mathfrak{a}} = \left[ \left( \mathbf{C}\_{\text{max}} - \mathbf{C}\_{\text{min}} \right) \cdot ADC\_{\text{max}} \right] - \int\_{\mathbf{C}\_{\text{min}}}^{\mathbf{C}\_{\text{max}}} \mathcal{J} \cdot e^{-\mathcal{J} \cdot \mathbf{C}} d\mathbf{C} \tag{31}$$

where *Cmax* and *Cmin* are the highest and lowest measured values of *C*, and *ADCmax* is the maximal value of *ADC*.

Value of adsorption capacity of the resin (*Qpe*) in mg O2 of NOM per gram of the resin at pseudo equilibrium was calculated as a function of overall experiment time (*Στmax*) in h, using following equation 32:

$$Q\_{pe} = ADC\_a \cdot \Sigma \tau\_{\text{max}} \tag{32}$$

Investigated adsorption process is flow and time dependent. There is no equilibrium at every sampling point, but only the adsorption capacity could be recorded in the appointed time. Dynamic adsorption kinetics is different to batch experiments adsorption kinetics [41-46]. The difference is that time of adsorption in batch processes is infinitely and equilibrium could be detected with differences depending of time and temperature. In dynamic fixed bed adsorp‐ tion, process time is defined and finite when sampling. During the adsorption and sampling as well, lasting irreversible adsorption is a consequence of constant addition of adsorbate which is dominant with regard to reversible equilibrium.
