Mass Flow Balances of Triclosan in Small Rural Wastewater Treatment Plants and the Impact of Biomass Parameters on the Removal

Three United Kingdom (UK) wastewater treatment plants (WWTP) – rotating biological contactor (RBC), trickling filter (TF) and oxidation ditch (OD) – were analyzed for their triclosan contents at different treatment stages. Furthermore, selected wastewater and biomass parameters were determined to draw correlations between the biological treatment, biomass make‐up and the removal efficiency of triclosan. Within this study, triclosan bound to the extracellular polymeric substances (EPS) of sludge flocs in the oxidation ditch seemed to have an adverse effect on the effluent quality, reducing the triclosan overall removal due to re‐balancing effects within the final clarifier. Within this study of the three examined WWTPs, temperature and pH of the bulk phase and as well the lipid content of the biomass seemed to have the most significant effects on the triclosan removal. The triclosan overall removal for each site was shown to be significantly high, ranging on average between 81 % (RBC) and 96 % (OD). The most efficient plant regarding the triclosan overall removal was found to be the oxidation ditch, which can be explained due to high hydraulic retention times. Primary settling points were found to have a significant impact on the triclosan overall loss rate, which was associated with the high fat content of primary sludge and the hydrophobic properties of triclosan. Besides the fat content of sludge or biomass, the pH and temperature showed a significant impact on triclosan loss rates as well.