REMOVAL OF TASTE AND ODOUR FROM POTABLE WATER BY POWDERED ACTIVATED CARBON (PAC)

摘要

The paper presents experimental evidence that selection and addition of an appropriate type of powdered activated carbon can be very effective in removal of both geosmin and 2-MIB from surface waters intended for supplying potable water. The study refers to the water from the reservoir Plastiras which, after conventional treatment, supplies health safe potable water to the city of Karditsa, although during the autumn months noticeable odours and tastes have been repeatedly reported. The experimental evidence shows that addition of activated carbon (PAC) results in substantial removal of both geosmin and 2-MIB. However the adsorptive capacity of the carbon is about 5 times greater in the case of geosmin when compared to 2-MIB. Furthermore it was shown that the selection of an appropriate type of activated carbon is crucial for effective removal. Activated carbon with the characteristics corresponding to type WP-7 is about 3 times more efficient than type WP-5. This increased efficiency compensates for the higher price of the former carbon type. From a correlation of Threshold Odour Number (TON) and respective concentrations of geosmin, the threshold concentration for geosmin (the maximum concentration for no odour detection) was determined to be about 5 ng/l. From a similar correlation between TON and respective concentrations of 2-MIB, the threshold concentration for 2-MIB was estimated at about 15ng/l. It was found that a dose of 25 mg/l of PAC WP-5 is adequate for removal of odour caused by moderate concentrations of geosmin (35-40 ng/l), while a similar dose of PAC WP-7 can remove the odour caused by high geosmin concentrations to the order of 100 ng/l. Higher doses are needed for odour removal caused by 2-MIB. A dose of 50 mg/l PAC WP-5 can effectively remove odours due to moderate 2-MIB concentration (35-40 ng/l), while a similar dose of PAC WP-7 can effectively tackle the problem of odours caused by fairly high (70 ng/l) 2-MIB concentrations.