Metal -ozone catalytic systems for water treatment
Water utilities in the U.S. and Europe are investigating a wide range of treatment process improvements to meet more stringent water quality regulations (e.g., the U.S. D/DBP Rule). A relatively new process that has shown promise is catalytic ozonation, the use of a metal catalyst in conjunction with ozone.
Laboratory-scale experiments were performed using a stirred batch and semi-continuous ozonation apparatus to study the catalytic ozonation process.
Initial experiments were designed to evaluate dissolved metal ion assisted ozonation of oxalic acid at pH 6.
The catalytic properties of dissolved cobalt (II) were subsequently studied in more detail. The results suggested that the first step in the catalytic ozonation reaction pathway is the formation of a cobalt (II) oxalate complex. Cobalt (II) oxalate is then oxidized by ozone.
Further experiments showed that the rate of cobalt (II) assisted ozonation of oxalic acid increased with decreasing pH over the pH range of 5.3 to 6.7.
The dissolved cobalt (II) studies provided the basis for understanding the catalytic properties of cobalt (II) oxide. It is anticipated that solid phase catalysts have more practical applications than dissolved catalysts in water treatment.
The catalytic reactivity of two model di-carboxylic acids, oxalate and malonate, were compared in a series of laboratory experiments. In-situ attenuated total reflectance infrared spectroscopy indicated that oxalate formed an inner sphere complex and malonate formed an outer sphere complex with cobalt (II) oxide.
Catalytic ozonation was evaluated for removal of pCBA, a non-adsorbing model micropollutant that does not react directly with molecular ozone. Cobalt (II) oxide and a mixed metal oxide (copper and zinc oxide with a calcium aluminate binder) either did not change the removal or they inhibited the removal of pCBA in deionized water compared to ozone alone.
Alumina supported ruthenium also accelerated the removal of pCBA from a natural water, but it may follow a different catalytic reaction pathway. (Abstract shortened by UMI.)