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.

Removal of emerging micropollutants from nanofiltration retentate of municipal wastewater within biological fixed‐bed reactors under nitrifying and denitrifying conditions

“…This method covers a sum of 13 micropollutants, which are shown with their physical and chemical properties in Table 2. These micropollutants were selected in preceding studies based on their persistence, ecotoxicity, and poor elimination in municipal water resource recovery facilities (Büning et al, 2020). For substances not detected, the limit of quantification (LOQ) is considered.…”

“…Phase 1identical feed under pure aerobic conditions Within this experimental phase, the reactors were identically fed with Conc-1 in a rhythm of 500 mL in the first week, 500 mL in the second week, 1000 mL in the third week, and no additional feeding in the fourth week. Experimental data for micropollutant elimination were generated within 2-week experiments according to preceding research (Büning et al, 2020). The experimental phase was run over 140 days including a start-up phase of 4 weeks.…”

“…F I G U R E 1 -2 Flow chart of water resource recovery facility concept MicroStop (modified from Büning et al, 2020). by factor 10 was tackled.…”

“…Scope is the biodegradation of micropollutants while achieving sufficient nitrification and denitrification after increased carbon extraction within bioreactors. The downstream nanofiltration retains pollutants with > 80 to > 95% as well as wastewater substances (Acero et al, 2016; Büning et al, 2020; Ge et al, 2017), also leading to a higher phosphorus retention (Abegglen et al, 2012). The retentate is recycled back to induce thresholds for micropollutant degradation and achieve adaptation of microorganisms to the food supply.…”

“…Two known processes are ozonation and activated carbon adsorption, both of which were implemented on an industrial scale with the disadvantage of an additional post‐treatment step required for each (Abegglen et al, 2012). Therefore, the project MicroStop started in 2017 to investigate an alternative water resource recovery facility concept, which aims to eliminate micropollutants between nutrients and multi‐resistant germs by a biological treatment step (Büning et al, 2020). As a continuation of the project, this study further investigates the effect of different process conditions (with/without nitrogen removal, hydraulic retention time [HRT]) on the micropollutant elimination potential within biological fixed‐bed reactors.…”