Endocrine flocculation, osmosis followed by activated sludge and ultrafiltration

Endocrine disrupting compounds (EDCs) are a challenge forwater and wastewater treatment because they exist at very low concentrations inthe presence of substances at much higher concentrations competing foradsorption sites.Many separation processes such as precipitation, flocculation, and coagulation have been used forthe removal of EDCs from different water 3,5.

EDCs may also be removed by bio-degradationprocesses 35, but numerous investigationsshowed significant variability between the treatment processes 36.Conventional biological processes such as constructed wetlands,bio-filtration, and activated sludge have shown limited removal of EDCs 3,5.Conventional WWTPs have been typically designed to remove the organic carbonload and nutrients (N and P) but no attention was given to the specific removalof EDCs xvi. Whereas, advanced treatment processes such as ferrate 4 free radicaloxidation, photolysis, granular activated carbon, photocatalysis, ozonation,separation, Fenton oxidation, chlorination, and membrane separation have shownmore satisfying results 3,5,7,8. Advanced oxidation processes (AOPs), such asozonation and non-thermal plasma, have also been studied and proven to achievegood removal of EDCs in wastewater 30,32–34.However, the effects of oxidation products are still not fully understood,which may delay the wide utilisation of such methods.

In addition, some hybridsystems such as membrane bioreactor (MBR) followed by ultra- filtration/nano-filtration/reverseflocculation, osmosis followed by activated sludge and ultrafiltration can alsoremove EDCs efficiently from water and wastewater 3,9. Membrane techniques,specifically reverse osmosis (RO) and nano-filtration (NF), have attractedgreat attention for EDCs removal in wastewater treatment 37–39, while microfiltration (MF) andultrafiltration (UF) had limited performance due to their large pore sizes 40. Chemical fouling and bio-fouling remain themajor drawbacks of membrane application in wastewater though.

Some researchershave studied the adsorption of EDCs by activated carbon (AC) and found that ACis effective in removing EDCs in the lab as well as pilot and full-scale plants29. However, operational conditions shouldbe strictly controlled and large amount of AC is required in full-scale plants,making this method expensive 31. Finally, giventhe significant research carried out and knowledge gained so far on the fate ofEDCs in the treatment process and their effects on humans and the environment,additional treatment modules to the existing WWTPs have been proposed andinvestigated in the recent decade. These include physical, biological andchemical advanced oxidation methods 29,30.