Removal of emerging micropollutants from wastewater by nanofiltration and biofilm reactor (MicroStop)

Abstract Current wastewater treatment is not designed for the elimination of micropollutants (MP) and therefore these are released into the aquatic environment by means of the municipal wastewater. The MicroStop project investigates a combination of a fixed‐bed reactor (FBR) and a nanofiltration plant (NF) for the elimination of organic MP. NF acts as a barrier for MP while biological degradation of the pollutants is to be induced in the FBR. A simultaneous treatment of the retentate should be realized by its return to the FBR. The NF is to be supplied with energy by a large separation of organic matter in the primary clarification. The experiments showed that NF can eliminate more than 95% of the selected and detected MP on average, and therefore, this method represents a suitable barrier for these pollutants. The retentate of the NF was used to test the potential of the biological degradation in the FBR. The test results showed that a significant biological degradation of different MP took place in the FBR. The degradability of the substances could be verified by not detecting significant adsorption on sludge and fixed‐bed. For certain MP (sulfamethoxazole and carbamazepine) only little potential of biodegradation could be detected, which is confirmed by values from the literature. Apart from these two substances, the average degradation rate was 78%. The successful MP‐retention in connection with the biological degradation rates demonstrated the potential of the concept. Statement of Industrial Relevance It is undisputed that the conventional wastewater treatment has to be upgraded, since it is not able to eliminate residual MP. The following describes how the MicroStop ‐process is able to address MP where competitive processes such as activated carbon or ozonation fail to do so: The process is able to eliminate MP comprehensively and to retain microplastics, pathogenic germs and metabolites to a large extent before they reach the environment. The retentate, which normally occurs as residue of the NF, is directly treated in the FBR. The only residue of the MicroStop ‐process would be the excess sludge, which could easily be used for sludge treatment. The effluent of the process is of high quality. This could be used in other regions of the world for irrigating plants, for industrial processes or even as tap water. The potentially increased energy consumption (i.e., due to NF) is taken into account in our concept by the carbon extraction in the primary treatment. Novelty or Significance The combination of NF with biological degradation of MP in a FBR represents a process that has not yet been investigated in this form. In addition, the combination with an elevated carbon extraction in the primary treatment ( Powerstep ‐process) represents the idea of a complete redesign of conventional municipal wastewater treatment plants.