Currently, 15% of the total Hungarian population is affected by either the elevated arsenic or ammonium concentration of drinking water, and 8% is affected by both compounds. The break-point chlorination is a well-kno...Currently, 15% of the total Hungarian population is affected by either the elevated arsenic or ammonium concentration of drinking water, and 8% is affected by both compounds. The break-point chlorination is a well-known method for ammonium removal, however, during the ammonium-removal process carcinogenic and mutagenic by-products （e.g., THM （trihalogenmethane） and AOX （absorbable organically bound halogens）） may be formed. In order to remove these harmful organic by-products, activated carbon adsorption has to be applied in the technology. The break-point chlorine dose is capable of oxidizing the As3＋ to As5＋. The oxidized form of arsenic can be easily converted to solid phase by adding coagulant （Fe（Ⅲ） or AI（Ⅲ） salt） to the water, and the formed iron/aluminium flocs can be removed by simple rapid sand filtration. Laboratory experiments were performed with raw water from two Hungarian settlements, where the water originated from a deep confined aquifer. In the studied settlements, six wells were in operation, and the supplied drinking water contained ammonium above the maximum allowable concentration, and the arsenic content was around the 10 μg/L standard value. It was found that higher chlorine dose （- 10 Cl2：NH4-N） was needed to achieve the breakpoint than the theoretical value （7.6）. The amount of by-products was also measured during the experiments. The AOX concentrations were significantly higher （21.6 μg/L to 143μg/L） in all cases than the THM concentrations （9-18 μg/L）. The needed coagulant doses were also studied in order to achieve the required arsenic concentrations. Fe（Ⅲ） coagulant was applied in all cases, and it was found that 1-1.5 mg/L Fe（Ⅲ） dose was sufficient to achieve 2-5 μg/L arsenic concentration in the treated water. Based on the results, it can be stated that the breakpoint chlorination combined with Fe（Ⅲ） coagulation is a potential technology to achieve the required ammonium and arsenic concentration at the studied settlements. However, activated carbon has to be installed in order to remove the harmful AOX compounds.展开更多
文摘Currently, 15% of the total Hungarian population is affected by either the elevated arsenic or ammonium concentration of drinking water, and 8% is affected by both compounds. The break-point chlorination is a well-known method for ammonium removal, however, during the ammonium-removal process carcinogenic and mutagenic by-products （e.g., THM （trihalogenmethane） and AOX （absorbable organically bound halogens）） may be formed. In order to remove these harmful organic by-products, activated carbon adsorption has to be applied in the technology. The break-point chlorine dose is capable of oxidizing the As3＋ to As5＋. The oxidized form of arsenic can be easily converted to solid phase by adding coagulant （Fe（Ⅲ） or AI（Ⅲ） salt） to the water, and the formed iron/aluminium flocs can be removed by simple rapid sand filtration. Laboratory experiments were performed with raw water from two Hungarian settlements, where the water originated from a deep confined aquifer. In the studied settlements, six wells were in operation, and the supplied drinking water contained ammonium above the maximum allowable concentration, and the arsenic content was around the 10 μg/L standard value. It was found that higher chlorine dose （- 10 Cl2：NH4-N） was needed to achieve the breakpoint than the theoretical value （7.6）. The amount of by-products was also measured during the experiments. The AOX concentrations were significantly higher （21.6 μg/L to 143μg/L） in all cases than the THM concentrations （9-18 μg/L）. The needed coagulant doses were also studied in order to achieve the required arsenic concentrations. Fe（Ⅲ） coagulant was applied in all cases, and it was found that 1-1.5 mg/L Fe（Ⅲ） dose was sufficient to achieve 2-5 μg/L arsenic concentration in the treated water. Based on the results, it can be stated that the breakpoint chlorination combined with Fe（Ⅲ） coagulation is a potential technology to achieve the required ammonium and arsenic concentration at the studied settlements. However, activated carbon has to be installed in order to remove the harmful AOX compounds.
