Evaluation of a bark adsobent for removal of pharmaceuticals from wastewater

Abstract: During and after medical treatment, pharmaceutical compounds as well as their metabolites and conjugates are excreted from the users through urine and feces. The pharmaceuticals end up in wastewater treatment plants, which are not designed to deal with this kind of organic micro-pollutant. Eventually the pharmaceuticals end up in the environment where they can have adverse physiological and behavioral effects on aquatic life and could contribute to the spread of antibiotic resistance among microorganisms. Adsorption to activated carbon is an established method for removal of pharmaceuticals from wastewater. It is however quite expensive and it is of interest to identify cost-effective alternatives. One possible alternative is bark, which is a common by-product from forest industry and has a complex microstructure and high porosity compared to many other naturally occurring materials. In order to investigate the potential of using bark to remove pharmaceuticals from municipal wastewater four column filters were built, two with activated carbon and two with bark. They were used in an experiment conducted at Kungsängsverket, the largest wastewater treatment plant in Uppsala municipality. The objectives were to assess pharmaceutical concentrations in treated wastewater at Kungsängsverket and to compare the performance of bark and activated carbon filters under different loading rates. During this time the filters were run at different loading rates and two different types of bark was used. 24 common pharmaceuticals from different therapeutic groups were targeted. The pharmaceutical concentrations measured at Kungsängsverket were generally low, but mean concentrations of five pharmaceuticals (atenolol, metoprolol, furosemide, hydrochlorothizide and diclofenac) exceeded 250 ng/l. Out of these, four have been shown to have adverse effects on aquatic life and it would be preferable if they were not released into the recipient. Bark was not as good at removing pharmaceuticals from wastewater as activated carbon was, but decent removal rates were achieved for several compounds. The removal rates of either filter type did not seem to be significantly impacted by variations in loading rate or bark size. The concentrations of a few compounds increased after treatment with the bark filters and the reason for this is not clear. One possibility is interference from other organic substances in the wastewater or the bark, but determining the reason for this increase should be a priority for any further research on the subject. Another problem encountered during the project that is likely to pose a problem for future implementation is that the bark filters were very sensitive to clogging. Running the filters at full scale would require frequent back-washing which would be a disadvantage from both economical and practical reasons.