Benefits of ozone-activated carbon filtration in integrated treatment processes, including membrane systems

Amsterdam Water Supply introduced ozone-activated carbon filtration (biological activated carbon filtration) in the production plant Leiduin in 1995. This full-scale plant (capacity 70 million m³yr^-1)can be characterized as an integrated treatment process. Experience since 1995 has revealed that biological activated carbon filtration has several benefits in integrated treatment processes. It is a very effective barrier for organics in general and for pesticides and organic micropollutants in particular. Due to the preceding ozonation both adsorption and biodegradation take place, resulting in a very long lifetime of the carbon filters (2 years). The ozonation significantly increases the disinfection capacity of the plant. Together with the other process steps, the disinfection capacity is at such a high level that, in combination with the biological stability of the finished water and good engineering practice in the distribution system, no chlorination has to be applied to guarantee hygienic quality. The process stability of the final treatment step, slow sand filtration, is, importantly, increased by the introduction of ozone-activated carbon filtration. Running times of the slow sand filters are longer than 2-3 years, while before the introduction of ozone-activated carbon filtration they never exceeded 1 year. In integrated membrane processes--which may be used in the treatment plant Leiduin in the future and therefore are being tested on pilot plant scale--ozone-activated carbon filtration also offers many advantages. In a reverse osmosis pretreatment scheme, comprising ozone-activated carbon filtration and slow sand filtration, the reverse osmosis system was shown to have a running time of I year without any membrane cleaning, due to the excellent reverse osmosis feed water quality. The application of ozone-activated carbon filtration also enables the use of electrodialysis as an alternative for reverse osmosis in an integrated membrane system. It is concluded that ozone-activated carbon filtration is a versatile process, offering many benefits in integrated treatment systems.