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

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.Micropollutants have gained attention and concern in recent years over the impact that they have on the natural environment when they are released within our wastewater. Micropollutants are pollutants from human activities that accumulate in small concentrations, but which have a disproportionately large impact on the environment. Of particular concern are pharmaceutical residues, which originate from the increased use of a wide variety of pharmaceutical drugs, and are injected into the water cycle through sewage and domestic wastewater. The increased levels of micropollutants leads to decreased river health, and also contributes to the increasing levels of antibiotic-resistant bacteria in existence. One of the leading technologies to remove micropollutants is ozonation, which breaks down molecules, including micropollutants and pharmaceutical residues, through its strong oxidizing action. However, the downside of this catch-all approach is the production of undesirable by-products, which may be worse for the natural environment than the micropollutants which the ozone is aimed at. One such by-product of concern is bromate, which is formed when bromide is exposed to ozone. Bromate has been shown to be carcinogenic and have toxic impacts on the aquatic environment and the natural fauna living in natural water bodies. As such, bromide is one of the compounds which, if present, rules out ozonation as an option for micropollutant removal. Bromide originates from the sea and is carried inland as sea spray and aerosols. A survey of southern Sweden’s wastewater plants showed that bromide was present in all wastewater streams tested, generally within an acceptable range, but that plants closest to the coast had higher concentrations than those inland. Particular individual plants had higher concentrations of bromide than would be naturally occurring, indicating that contamination from nearby industries are likely to be contributing bromide. Recent research at Lund University has shown that bromate can be removed from wastewater using microorganisms found in existing wastewater treatment processes. Plastic carriers taken from existing operational units at wastewater treatment plants were observed to be able to efficiently reduce bromate back to bromide, once nitrate was no longer available as a primary source of energy. This finding means that it is likely that existing infrastructure at wastewater treatment plants could therefore be used to control bromate concentrations by simply extending the time that the water remains within the plant. The results observed in laboratory test work indicated that 100% removal of bromate was achieved, using wastewaters from a variety of treatment plants, and using bacteria acclimatised to both methanol and ethanol denitrification systems. This finding means that bromide in incoming wastewater might not have to be a deterrent to wastewater treatment plants looking to implement ozonation