Removal and fate of emerging contaminants combining biological, flocculation and membrane treatments

An experimental study combining biological treatment with flocculation (F) and ultrafiltration (UF) membrane technology was conducted, separately and in combination, seeking to increase insight into the capability of such treatment processes to remove emerging contaminants (ECs). The occurrence and removal efficiencies of 17 ECs are reported for wastewater from Mexico City. Results showed that activated sludge (AS) is the predominant process for removing acidic pharmaceutical compounds, and the use of a cationic flocculant increases the biodegradability of these compounds as well as that of 4-nonylphenol. The UF process alone showed greater removal of phenolic compounds than AS. However, the contribution of flocculation to EC removal by the UF unit was fairly limited. In general, the F + AS + UF processes yielded better results than their separate use, leading to the highest removal rates of 15 of the 17 compounds. In the case of some phenolic compounds and the phthalic acid esters, a competitive sorption process between the membrane and the sludge steps seemed to take place. Bis-2-ethylhexylphthalate (DEHP) was found to be significantly sorbed onto sludge. The F + AS + UF process operated as a membrane bioreactor (MBR) using 16 gL⁻¹ of suspended solids in the mixed liquor (MLSS) yielded the highest removal efficiencies for the ECs tested.