Taste and odour removal from an urban groundwater establishment – a case study

Abstract

A deep groundwater well was established in a village near Tel-Aviv, in order to supply drinking water for its 30,000 inhabitants. Although all water characteristics were within the range permitted by the Israeli regulations, operators received complaints about a funny taste and a rotten-egg odour in the water. This was attributed to the presence of 0.38 mgL -1 hydrogen sulfide. Removing the odour by the usual method of aeration was impossible because of the populated surroundings. Therefore it was decided to examine chemical oxidants for taste and odour removal. A treatment with 8 mgL -1 of chlorine successfully oxidized hydrogen sulfide but the complaints continued. This was attributed to the formation of elemental sulfur, which is converted into polysulfide that may hydrolyze to regenerate the odorous hydrogen sulfide. Treatment with 2 mgL -1 of chlorine dioxide successfully eliminates odour completely, but produces chlorite and chlorate which are above the permitted levels. A partial solution to this problem was found by a consequential treatment with 2 mgL -1 of ClO 2 for 10 min. followed by 1.5 mgL -1 of chlorine (30 min.). In this case the chlorite is reduced substantially to be within the permitted level. In addition, such treatment regenerates some of the chlorine dioxide thereby increasing its residual. The odorous H 2 S can also be eliminated with 3 mgL -1 of ozone. Advantages and disadvantages of the above treatments are discussed.