BALWOIS 2010 – Ohrid, Republic of Macedonia -25, 29 May 2010

1. Formation of Disinfection By-products (DBPs) and Strategies to Reduce their Concentration in the Water Treatment Plants in Përlepnica and Velekince – Gjilan Abedin Azizi1, Kadri Berisha1, Selim Jusufi2, Shefqet Rashani1 1) Faculty of Mines and Metallurgy, Department of Technology – University of Prishtina 2) Faculty of Natural Sciences and Mathematics, Department of Chemistry – University of Prishtina BALWOIS 2010 – Ohrid, Republic of Macedonia -25, 29 May 2010

2. Introduction Chlorine is the most widely used disinfection agent in drinking water industry in the world. In Kosovo, practically, chlorine is the only reagent that is being used for disinfection purposes. Chlorine has many attractive features that contribute to its wide use in the drinking water industry: - Effectively inactivates a wide range of pathogens commonly found in water; - Leaves a residual in the water that is easily measured and controlled; - It is economical; and - Has an extensive track record of successful use in improving water treatment operations. There are, however, some concerns regarding chlorine usage that may impact its uses such as: -Chlorine reacts with many naturally occurring organic and inorganic compounds in water to produce undesirable DBPs; - Hazards associated with using chlorine, specifically chlorine gas, require special treatment and response programs; and - High chlorine doses can cause taste and odour problems. Disinfection By-product (DBP) Formation Considering the attractive properties of chlorine, operators at the treatment plants, were used to add as much chlorine as necessary to achieve desired aesthetic and microbial water quality. Soon it was discovered that chlorine, while reacting with natural organic matter (NOM) contained in water forms halogenated organic by-products, which were identified to represent health risk. In the table 1 are presented key data of some identified disinfection by-products, including potential health effects to humans.

3. Water Supply System of Gjilan The town of Gjilan receives major portion of its drinking water supply from the two treatment plants located at Përlepnica (North-East) and Velekince (South-East). Treatment steps are presented in the flow-diagrams presented below: Figure 1. Treatment scheme in WTP Përlepnica Figure 2. Treatment scheme in WTP Velekince

4. ` Strategies to control formation of disinfection by-products Halogenated organic by-products are formed when natural organic matter (NOM) reacts with free chlorine or free bromine. Free chlorine is added to the water as a primary or secondary disinfectant. Free bromine results from the oxidation of the bromide ion in source water (when adding the chlorine). Other important factors which have impact on formation of halogenated DBPs are: 1) concentration of natural organic matter in the source water, measured as total organic carbon (TOC); 2) oxidant/ disinfectant type and dosage rate; 3) contact time of water with the oxidant/ disinfectant; 4) bromide ion concentration; 5) pH value of water; and 6) temperature of water. 1 a) Concentration of TOC – Përlepnica: By using the coagulation, flocculation and filtration processes significant amount of TOC can be removed, as shown in the tables below: Table 1. TOC removal after coagulation and filtration (Përlepnica) Figure 3. DBP formation potential vs. TOC concentration (Përlepnica) Table 2 TOC removal TOC removal efficiency by different dosage rates of coagulant and coagulant aid

5. Strategies to control formation of disinfection by-products Results obtained from Përlepnica WTP shows that the TOC removal, under normal operation conditions is not sufficient, and that TOC concentration does not fall below 2 mg/l. There is no regulation specifying the TOC concentration level, but generally it is documented that concentrations above 2 mg/l represent unfavourable conditions and is defined as high risk potential for producing DBPs. In this context a JAR Test has been conducted to determine whether aluminium sulphate is sufficient to reduce the TOC concentration below 2 mg/l, and monitor what happens when coagulant aid (polyelectrolyte – polyacryl amide) is added. The results obtained from the JAR Test are compiled in the table 4. The JAR tests show that concentration of TOC is possible to reduce to acceptable levels either by increasing the aluminium sulphate dose or when aluminium sulphate is combined with polyelectrolyte. Addition of coagulant aid improves significantly not only TOC removal capacity; it improves also the quality of water exiting from pulsator unit in terms of turbidity. 1 b) Concentration of TOC in Velekince - Ground water exploited from Morava e Binçës aquifer and treated at the WTP Velekince is characterized with lower concentration of TOC, its concentration is quite constant and remains permanently below 0.9 mg/l. Results of TOC are summarized in the table 5. As such, TOC concentration levels do not represent yet any potential for producing DBPs. The dosage of aluminium sulphate does not reduce the concentration of TOC. Table 3. TOC removal after coagulation and filtration (Velekince) Figure 4. DBP formation potential vs. TOC concentration (Velekince)

6. Strategies to control formation of disinfection by-products 2) Concentration of chlorine: Now it is known that all chemical disinfectants and oxidants used in water treatment form chemical by-products, out of them chlorine produces the most known DBPs. There are different alternative disinfection strategies which can be used to control DBPs. Chlorine concentration is the major factor that influences formation of BDPs. Therefore, optimizing the chlorine dosage can have big impact in the amount of DBPs produced. As shown in the figures 5 and 6, by increasing the disinfectant (chlorine) concentration, it increases the amount of DBPs produced too. Figure 5. TOC removal after coagulation and filtration (Përlepnica) Figure 6. DBP formation potential vs. TOC concentration (Velekince)

7. Strategies to control formation of disinfection by-products 3) Bromide ion concentration: Free chlorine oxidizes bromide ion to free bromine, which in contact with water produces hypobromous acid. Hypobromous acid, same as hypochlorous acid, forms brominated organic by-products. Therefore, removal of the bromide via enhanced coagulation can reduce the overall concentration of DBPs. Table 4. Composition of DBPs (Përlepnica) Table 5. Composition of DBPs (Velekinca) 4) Contact time: Reduction of free-chlorine contact time can reduce significantly the DBP formation. The contact time of free chlorine can be reduced by moving the chlorine addition to the end of the treatment chain. It has been confirmed that using chlorine as oxidation reagent increases the total concentration of DBPs, because the contact time is longer. Therefore, it is highly recommended to use an alternative reagent as oxidant (e.g. potassium permanganate), instead of chlorine.

8. Conclusions • Based on what was presented in this paper, the following conclusions can be drawn: • As it was clearly indicated and documented in this paper the concentration of DBPs is related to the concentration of TOC in source water. So one of the best strategies to avoid producing the DBPs is to choose the best working coagulant (alone or combined) and adjust properly the dose by doing the JAR Test. • - The situation is more critical in WTP Përlepnica (where the surface water is used). Concentration of TOC is exceeding the limit of 2 mg/l, which is defined as high potential to produce DBPs. • - JAR Testing has shown that the concentration of TOC can be lowered by increasing the dose of aluminium sulphate (alone) or combined with the polyelectrolyte (both are commonly used to address the raw water turbidity). Use of polyelectrolyte is especially recommended during cold temperatures, because it enhances significantly the coagulation and flocculation processes, and thus, reduces the concentration of TOC below 2 mg/l in treated water. • - The concentration of produced DBPs (TTHMs and THAAs) in WTP Përlepnica is below the maximum concentration levels (MCL), although relative high concentration of TOC is contained in raw and treated water. • - The situation is less critical in WTP Velekince, where the groundwater is exploited. Concentration of TOC is stable and it remains below the critical limit, its concentration is permanently below 1.2 mg/l in raw water and below 1 mg/l in treated water. At this level, it does not represent potential risk for producing the DBP. • - Analyses have shown that the amount of DBP produced in WTP Velekince is far below the MCL, so at the moment this is not of concern. • The amount of produced DBPs is strongly dependent on the type of oxidation/ disinfection reagent used. • 2) Reducing the dosage of chlorine leads to formation of fewer amounts of DBPs. This is possible to be controlled by operators in WTP Përlepnica. • The dosage of the chlorine is selected to be at the end of the treatment train, which reduces the contact time between chlorine and water. • - Usage of chlorine for oxidation (pre-chlorination) purpose shall be restricted; instead the potassium permanganate shall be utilized. • - Actually usage of any alternative disinfectants is not possible due to financial and operational purposes. • - Actual concentration of produced DBPs in both treatment plants is below the maximum concentration levels. However, considering the health effects these substances can cause, it is recommended to follow their concentration at least quarterly.

9. Thank you!