Yield of Bromate from Ozonated Wastewater and the Potential for Biological Reduction of Bromate in Wastewater in Sweden

Sammanfattning: The impact that anthropogenic micropollutants have on the environment is increasingly gaining attention. As a result of this, Sweden, among other countries, is looking towards implementing advanced treatment for micropollutant and pharmaceutical product removal from wastewater prior to discharge into the environment. The leading method to achieve this is ozonation, which unfortunately also creates a host of undesirable by-products, one of which being the formation of bromate from bromide-containing wastewaters. Bromate has been identified as a carcinogenic compound with additional ecotoxicological impacts. A survey of wastewater treatment plants in southern Sweden showed that a number of plants, particularly those situated on the coastline, received levels of bromide high enough to potentially cause bromate levels above the environmental discharge recommended limit of 50 μg/L, if ozonated. Ozonation of wastewater from southern Sweden demonstrated that yields of bromate are in line with previous literature values, with a conversion of approximately 7% at applied ozone doses capable of the recommended 80% removal of micropollutants. A novel and cost-effective method for removal of bromate is therefore required if ozonation is to be considered viable at wastewater plants with incoming bromide present in their wastewater. Biological reduction of bromate has been identified as a promising technology, due to the possibility of utilizing existing wastewater treatment infrastructure and technology to achieve bromate removal. Experimental work concluded that biological reduction of bromate is possible at rates that are implementable on a large scale. The rate of reduction is influenced by the concentration of nitrate present, with the rate of bromate removal rapidly increasing once denitrification was complete. Complete removal of bromate was achieved using carriers from both methanol and ethanol adapted post-denitrification units, and using wastewater from different sources. Near stoichiometric quantities of bromide were produced, although the rate of bromide formation was an order of magnitude lower than that of bromate reduction. These findings demonstrate that biological reduction of bromate is a feasible possibility for wastewaters containing bromide, where ozonation is desirable for micropollutant removal.