**1. Introduction**

Natural organic matter (NOM) and arsenic present a major problem when found in drinking water. There have been many published scientific papers on the methods for their removal over the years [1-9]. Groundwater investigated in this chapter is one of the most arsenic and NOM contaminated water in Europe [10], and nevertheless population which inhabits these areas are using this groundwater as a drinking water without any treatment process.

Behavior of the strongly basic, macroporous ion-exchange resin Amberlite IRA 958-Cl [11] will be circumstantially explained in the book chapter. Effects of different specific flow rate (SFR) and determination of its optimum value as well as the effects of the empty-bed contact time (EBCT) values on the removal of NOM, arsenic, sulfate, electrical conductivity, bicarbonate, and chlorine from groundwater using strongly basic ion-exchange resin (SBIX) will be examined in this chapter. Determination of the resin's sorption characteristics is also part of the investigation. A new approach of pseudo equilibrium adsorption capacity will be presented.

Investigations of determination of optimum value of water flow rate and resin's sorption characteristics were conducted with native groundwater and native groundwater with addition of oxidizing agent. Sodium hypochorite was added to the raw water with the aim of oxidizing NOM and As(III) to As(V). The addition of sodium hypochlorite to water yields hypochloric acid, and the liberated atomic oxygen acts as an efficient disinfection agent and a very strong oxidant. Apart from oxidizing the present NOM and arsenic(III), the liberated nascent oxygen can also oxidize the present inorganic species such as nitrites, iron(II), and the like. This is important because of resin affinity for certain ions and their competition for resin binding sites which can affect NOM and arsenic ion-exchange and adsorption.

The intention was to find out whether the resin might be used beyond the range of operating conditions recommended by the manufacturer. Results will provide a better understand‐ ing of treatment of groundwater with similar physicochemical composition which is important when designing a water treatment plants for settlements in areas with such groundwater. Also, prolonging the resin working cycle can ultimately lead to water treatment plants cost reduction.

#### **1.1. Composition and characteristic of dissolved natural organic matter and arsenic**

Natural organic matter is frequently found dissolved in groundwater. In most cases, the presence of NOM gives these waters a characteristic yellow color. NOM consists usually of humic substances originated from the geological formations of the location of groundwater source [12]. Their molecules have a supramolecular structure, formed by condensation of smaller molecules resulting from the degradation of organic matter [13]. Humic matter has a very stable structure, a proof of this being the fact that they have been present in the Earth's crust for thousands of years [13, 14].

**Keywords:** Specific flow rate, resinsorption characteristics, arsenic, natural organic

Natural organic matter (NOM) and arsenic present a major problem when found in drinking water. There have been many published scientific papers on the methods for their removal over the years [1-9]. Groundwater investigated in this chapter is one of the most arsenic and NOM contaminated water in Europe [10], and nevertheless population which inhabits these

Behavior of the strongly basic, macroporous ion-exchange resin Amberlite IRA 958-Cl [11] will be circumstantially explained in the book chapter. Effects of different specific flow rate (SFR) and determination of its optimum value as well as the effects of the empty-bed contact time (EBCT) values on the removal of NOM, arsenic, sulfate, electrical conductivity, bicarbonate, and chlorine from groundwater using strongly basic ion-exchange resin (SBIX) will be examined in this chapter. Determination of the resin's sorption characteristics is also part of the investigation. A new approach of pseudo equilibrium adsorption capacity will

Investigations of determination of optimum value of water flow rate and resin's sorption characteristics were conducted with native groundwater and native groundwater with addition of oxidizing agent. Sodium hypochorite was added to the raw water with the aim of oxidizing NOM and As(III) to As(V). The addition of sodium hypochlorite to water yields hypochloric acid, and the liberated atomic oxygen acts as an efficient disinfection agent and a very strong oxidant. Apart from oxidizing the present NOM and arsenic(III), the liberated nascent oxygen can also oxidize the present inorganic species such as nitrites, iron(II), and the like. This is important because of resin affinity for certain ions and their competition for resin

The intention was to find out whether the resin might be used beyond the range of operating conditions recommended by the manufacturer. Results will provide a better understand‐ ing of treatment of groundwater with similar physicochemical composition which is important when designing a water treatment plants for settlements in areas with such groundwater. Also, prolonging the resin working cycle can ultimately lead to water

**1.1. Composition and characteristic of dissolved natural organic matter and arsenic**

Natural organic matter is frequently found dissolved in groundwater. In most cases, the presence of NOM gives these waters a characteristic yellow color. NOM consists usually of humic substances originated from the geological formations of the location of groundwater

binding sites which can affect NOM and arsenic ion-exchange and adsorption.

areas are using this groundwater as a drinking water without any treatment process.

matter

74 Ion Exchange - Studies and Applications

**1. Introduction**

be presented.

treatment plants cost reduction.

Piccolo and Stevenson showed that humic acids exhibit affinity to metal ions from the soil, forming thus the complexes of different stability constants and other characteristics [15].

Humin of the investigated groundwater contains humic acids (HAs) and fulvic acids (FAs). Humins are macromolecular polymers whose structure and characteristics are determined by their origin and process of humification. Like HAs, FAs too, are naturally present in water, soil, and turf. They are formed by chemical and microbiological degradation of plant material (humification). There are opinions that FAs are formed after the constitution of HAs. The FAs are richer in oxygen and poorer in carbon than HAs. Like HAs, FAs contain a number of reactive functional groups including carboxylic, hydroxylic, phenolic, quinonic, and semiqui‐ nonic [16]. Molar masses of FAs are smaller than those of HAs. FAs contain more constitutive groups that are structurally similar to carbohydrates, originated from polysaccharides. In the determination of total carbon content (TOC) in groundwater, HAs and FAs make the source of total dissolved organic carbon (CT). Previous investigations showed that there exists labile (unstable) and non-labile components of NOM [17]. By taking advantage of the fact that labile NOM are sensitive to permanganate, it is possible to determine their fraction by standard method as the permanganate consumption (COD). The fraction of labile organic carbon is designated as CL, and the fraction of non-labile carbon (CNL) is calculated as the difference between the TOC and CL. Anderson and Schoenau showed that the FA fraction depends essentially on the content of CL, and that it is independent of CNL [18]. Labile components of organic matter consist of cell biopolymers such as carbohydrates, amino acids, peptides, amino sugars and fats. Contents of these components in FA fraction is smaller, and because of that it is biologically and chemically more resistant. The HA skeleton contains strongly condensed aromatic structures surrounded by the side chains of aliphatic components. The FA fractions are mainly composed of carbohydrates, microbiological metabolites, and "younger" materials that are not significantly related to the mineral fraction. This explains the strong correlation between CL and FA content, which is not observed for HAs. The strong correlation between CNL and HAs indicates that CNL consists of the fraction of organic carbon which is stabilized due to the chemical and physical associations with the mineral matrix. The groundwater that contains FAs has a characteristic yellow color.

Arsenic is a very toxic metalloid, occurring in nature in several oxidation states (-3, 0, 3, 5). In natural waters, it is present in its inorganic forms of oxyanions, primary and secondary arsenite, as well as in primary, secondary, and tertiary arsenate [19]. The water pH and redox potential influence dominantly the oxidation state of arsenic in natural waters. At the pH < 6.9 dominates H2AsO4 - , whereas at higher pH it is HAsO4 2-. In strongly acidic media, under oxidation conditions the molecular form H3AsO4 is dominant, whereas under alkaline conditions, it is AsO4 3-. Under reduction conditions, at the water pH < 9.2 dominates the amphoteric neutral molecular species H3AsO3 [20]. Arsenic is a constituent component of many ores and by the process of their dissolution reaches groundwater. Apart from natural arsenic, arsenic in groundwater may be due to anthropogenic activities. Namely, many insecticides and fungicides, wood-protecting agents, chemicals used in semiconductor production, and additives to various alloys and glasses contain arsenic compounds [21]. It is known that prolonged exposure of the human organism to small doses or short exposure to high doses of arsenic causes skin disease and serious disturbance of internal respiratory and digestive organs, blood circulation, and of the nervous system. Also, Ng et al. proved that arsenic is carcinogenic [22].

The EU Drinking Water Directive from 1998 recommended that the maximum tolerable concentration (MTC) of arsenic in drinking water should be 10 μg/L [23]. Three years later, in its revision of the corresponding standard, the US EPA adopted also the same MTC value of 10 μg/L [24]. Because of the geological and mineralogical origin of arsenic in groundwater, its removal is a technologically very complicated and demanding operation.
