Byproduct Formation of Chlorination and Chlorine Dioxide Oxidation in Drinking Water Treatment: Their Formation Mechanisms and Health Effects

Increasing water scarcity caused by population growth, climate change, pollution from natural and anthropogenic sources, etc. is likely to impact the occurrence of water-associated infectious diseases. Nowadays, access to clean and safe water is a growing concern worldwide. Therefore, disinfection of drinking water is a vital step in public treatment systems as it ensures the removal of various contaminants, including pathogenic microorganisms (protozoa, viruses, bacteria, and intestinal parasites) that give rise to waterborne diseases. Nevertheless, undesirable disinfection byproducts (DBPs) are formed during disinfection as a result of reactions between chemical disinfectants and natural organic matter (NOM), and/or anthropogenic contaminants, and/or bromide/iodide that are present in the raw water. The chemical complexity and heterogeneity of matters in the raw water makes the characterization and the mechanism of DBPs formation quite difficult and ambiguous regardless of the previous hundreds of studies on DBPs generation. As chlorination is still the most economic and most often used disinfection method, and beside chlorination, the application of chlorine dioxide is becoming more widespread, this paper investigates the possible DBPs generated using chlorine and chlorine dioxide with highlighting their adverse health effects. It overviews the reactions of those disinfectants with inorganic and organic compounds. It is important to note that in order to better understand the performance of disinfectants in water treatment, further investigations on the mechanisms of them with inorganic and organic compounds found in water are critically needed

Optimization of Breakpoint Chlorination Technologies for Drinking Water Treatment: a Hungarian Case Study

Ammonium ion is one of the major pollutants found in drinking water sources in Hungary, especially in deep aquifers. under oxidative conditions, ammonium can transform into nitrite ions in the water system, posing potential health risks. In Hungary mostly biological process or breakpoint chlorination are used to eliminate ammonium ion from raw water during the drinking water treatment process. When breakpoint chlorination is applied, harmful by-products are formed. Trihalomethanes concentrations have long been regulated in Hungary, therefore during the design and optimization of the breakpoint technologies trihalomethane concentrations have been considered. However, haloacetic acids (HAA5) and chlorate ion have been recently regulated in accordance with EU Directive 2020/2184. Chlorate is a by-product that appears in treated water when sodium hypochlorite is used in breakpoint chlorination.Experiments were carried out at four Hungarian case study areas to determine the optimal strategy for breakpoint chlorination: applying higher chlorine dosages with lower contact times, or lower chlorine dosages with higher contact times. The investigations concluded that the preferable dosing strategy is to use lower chlorine concentrations and longer contact times. This approach reduces chemical demand (cost-effective) and has a neutral effect on THMs formation. it can be concluded that when the raw water contains ammonium ion concentrations above 0.5 mg/l, the use of sodium hypochlorite may raise concerns due to elevated chlorate ion levels in the treated water, particularly during summer. Further research is required to expand the optimization strategy, considering not only ammonium and trihalomethane concentrations but also chlorate concentrations

Felszíni vízbázis ivóvíz tisztítási technológiája = Treatment technology of surface waters for drinking water supply

A hazai vízkivétel jelentős része felszín alatti vízbázisokból történik; a felszíni vízből származó ivóvíz aránya Magyarországon csupán néhány százalék. Jelen tanulmány áttekinti, hogy a felszíni vizekben jellemzően milyen szennyezőanyagok fordulnak elő, majd bemutatja azok eltávolítására szolgáló technológiákat. A felszíni vizekben található szilárd állapotú szennyezőanyagok közül először a nagyobb, majd lépésről-lépésre az egyre kisebb méretű részecskék eltávolítására kerül sor. A rácsot (gerebet) követően kerül sor a dobszűrésre, majd homokfogókra vezetik a vizet. Rendkívüli szennyezések alkalmával sor kerülhet por alakú aktívszén adagolására, majd a következő technológiai lépés általában a koagulációt és flokkulációt követően a derítés. Ezen technológiák alkalmazása során a kolloid és kvázi-kolloid részecskék vegyszeradagolás segítségével ülepíthető méretűvé alakulnak át, majd ezt követően a derítő műtárgyakban megtörténik eltávolításuk. A következő technológiai lépés a finom fázisszétválasztás, mely során homokszűrőkön vezetik át a derített vizet. A technológia-közi fertőtlenítési lépések (klórgázzal, nátrium-hypoklorittal vagy ózonnal megvalósított fertőtlenítés) során képződő melléktermékek eltávolítása miatt a felszíni-víz tisztítási technológiáknak része kell, hogy legyen a granulált aktív szén adszorpció is. Erre a technológiai lépésre a klórozott szerves melléktermékek, valamint az ózonizálás során fragmentálódott szervesanyagok eltávolítása céljából van szükség. A tanulmányban bemutatásra kerül egy minta-technológiai sor is. = The major part of drinking water comes from subsurface water sources in Hungary; the proportion of drinking water originating from surface water sources is only a few percent. The present study reviews the contaminants typically found in surface waters and then presents technologies for their removal. First the solid contaminants have to be removed, where the removal process starts with the bigger particles followed by the smaller ones: after screening, the water goes to drum filter followed by sand trap. In case of extreme pollutions, powdered activated carbon has to be added, followed by coagulation-flocculation and clarification process. During coagulation-flocculation, the colloidal and quasi-colloidal particles are converted to a settable size by chemical dosing and then removed in the clarification tank. The next technological step is the fine phase separation, where the clarified water is passed through sand filters. Due to the removal of by-products from inter-technological disinfection steps (disinfection with chlorine gas, sodium hypochlorite or ozone), surface-water treatment technologies must also include granular activated carbon adsorption. This technological step is required to remove chlorinated organic by-products as well as organic matter fragmented during ozonation. A sample technology line is also presented in the study