Endocrine disrupter removal from wastewater using membrane bioreactor and nanofiltration technology

Endocrine disrupting compounds can affect hormone systems in organisms. However, conventional wastewater treatment plants are not able to remove these substances sufficiently before disposing effluent into the environment. Membrane technology, which is proving to be an effective barrier to these substances, is the subject of this research. The removal techniques under investigation are membrane bioreactors and nanofiltration. Initial results using wastewater from a dumpsite leachate plant indicate removal of more than 90% of nonylphenol (NP) and bisphenol (BPA). The mass balance indicates the membrane bioreactor is the most important process step in removal while the granulated activated carbon treatment, applied downstream, is a further polishing stage. Eleven different nanofiltration membranes were tested in the laboratory set-up. The observed retentions for NP and BPA ranged between 70% and 100%. The contact angle is an indicator for the hydrophobicity of a membrane, whose influence on the permeability and retention of NP was evident. Regarding the retention of BPA no dependency on the contact angle was observed.

Fig. 4. Results of nanofiltration membrane screening. The results presented here show the general ability of membrane processes to contribute significantly to the removal of endocrine disrupting compounds in wastewater treatment. In mem- brane bioreactors with micro- or ultrafiltration membranes, the removal is attributed to the adsorption of EDCs on particulate matter, which is fully retained in the system. Hence, this kind of removal process might be limited to hydrophilic compounds, while more polar components might even undergo lower removal rates due to short hydraulic retention times, which are typical for membrane bioreactor systems. Due to their small pores, nanofiltration membranes can remove EDCs physically by molecular size exclusion. As NP represents one of the smallest endocrine disrupting substances in terms of molecular weight, a fairly high removal of all relevant components can be expected using nanofiltration membranes. Any decision on either membrane bioreactor or nanofiltration applications have to be made on the basis of particular boundary conditions and particularly with respect to overall process objectives. Nanofiltration should be regarded as an alternative option for final effluent treatment in comparison to ultrafiltration or other disinfection steps.