Assessing the potential use of Water Treatment Sludge containing Activated Carbon for the removal of Emerging Pollutants

The presence of emerging pollutants (EP) in water bodies and its impacts on the environment and human health is of the utmost importance. Estrogens are a group of EP, that have a high prevalence in the environment and toxicity even at low concentrations, which leads to adverse impact in both wild and human life’s. This group include compounds such as estrone (E1), 17-estradiol (E2) and 17-ethinylestradiol (EE2). The discharge of wastewater into the environment is one of the main causes for the release of these compounds in the environment. Wastewater treatment plants are not designed to remove EP. Therefore, it is important to add complementary treatments to remove these compounds, especially with the increasing of the incentive of the reuse of treated wastewater, promoted by the United Nations (UN) Sustainable Development Goals. There are several additional treatments to accomplish EP removal. The adsorption process is one of the commonly used since it is simple to design and operate and does not generate toxic by-products. There are many kinds of adsorbent materials, however, the most used is activated carbon (AC). AC shows high removal capacity for the removal of E1, E2 and EE2. However, AC’s regeneration is an expensive process and result in a material with low adsorption capacity. As a result, efforts are being raised to find low-cost adsorbents. The use of water treatment sludges (WTSs) containing AC as an alternative adsorbent provides a new way of sustainable resources management, lining up with circular economy proposals and on another hand will contribute to the decarbonization of the water treatment industry. This work studied the potential of WTS containing AC for the removal of E1, E2 and EE2. For this purpose, WTS from two water treatment plants (WTP), St. Águeda WTS and Caldeirão WTS were characterised and tested as adsorbents. Both WTSs showed adsorption potential with efficiencies removal results above 50 %, without a significant decrease in their granulometry. For Caldeirão WTS final concentration for all the three EP were lower than the limit of quantification. As for St. Águeda WTS, the results for E1 and E2 removal were similar to Caldeirão WTS removal performance. However, for EE2 the removal efficiency was lower than the obtained with Caldeirão WTS. These results lead to a new approach in the management of this erstwhile reside and removal of EP.