Ozone combined with ceramic membranes for water treatment: Impact on HO[rad] radical formation and mitigation of bromate

Abstract

The beneficial effect of combining ozone with ceramic membrane filtration (CMF) to enhance membrane flux performances during water treatment (e.g., wastewater and drinking water) could be related to the formation of hydroxyl (HO) radicals from the interaction of ozone with ceramic membrane. To explore this effect, para-chlorobenzoic acid was used to probe HO radical activity during a combined ozone/CMF process using a 0.1 μm pore size membrane supplied by Metawater, Japan. Tests were then extended to explore the impact on bromate formation downstream CMF, a well-known undesirable by-product from ozone use in water treatment. Ozone reduction by the membrane and its module appeared to be more associated with physical degassing, but a noticeable formation of HO radicals was observed during the interaction of ozone with the ceramic membrane. CMF treatment of ozonated potable water containing bromide showed a reduced bromate formation of 50% when the water was recirculated to the filtration module containing the ceramic membrane, compared to the experiment performed with an empty module. Single pass experiments showed bromate mitigation of around 10%. The mitigation of bromate formation was attributed to reduced overall ozone exposure by deagassing effect, but also potentially from suppression of the oxidation of Br− and HOBr/BrO− to BrO3− due to the catalytic degradation of ozone via a HO radical pathway.