Determination of sorption of seventy-five pharmaceuticals in sewage sludge

Sorption of 75 active pharmaceutical ingredients (APIs) to three different types of sludge (primary sludge, secondary sludge with short and long sludge age respectively) were investigated. To obtain the sorption isotherms batch studies with the APIs mixture were performed in four nominal concentrations to water containing 1 g of sludge. The range of APIs concentrations was between ng L−1 to μg L−1 which are found in the wastewater effluents. Isotherms were obtained for approximately 45 of the APIs, providing distribution coefficients for linear (Kd), Freundlich (Kf) and Langmuir (KL) isotherms. Kd, Kf and KL ranging between 7.1 × 104 and 3.8 × 107, 1.1 × 10−2 and 6.1 × 104 and 9.2 × 10−3 and 1.1 L kg−1, respectively. The obtained coefficients were applied to estimate the fraction of APIs in the water phase (see Abstract Graphic). For 37 of the 75 APIs, the predicted presence in the liquid phase was estimated to >80%. 24 APIs were estimated to be present in the liquid phase between 20 and 80%, and 14 APIs were found to have <20% presence in the liquid phase, i.e. high affinity towards sludge. Furthermore, the effect of pH at values 6, 7 and 8 was evaluated using one way ANOVA-test. A significant difference in Kds due to pH changes were found for 6 of the APIs (variation 10–20%).

Graphical abstractEstimated fraction, i.e. the fraction of the total APIs load into the activated sludge tank which is not lost either by degradation or stripping, of the API in the water phase based on experimentally determined sorption isotherms obtained by using primary and secondary sludge. For further information see Supplementary data Figure S1.Figure optionsDownload full-size imageDownload high-quality image (149 K)Download as PowerPoint slideHighlights► Sorption isotherms were experimentally obtained for roughly 45 of active pharmaceutical ingredients (APIs). ► By sorption to sludge the removal of 31 APIs were estimated to be <20% in the WWTP. ► By sorption to sludge the removal of 15 APIs were estimated to be >80% in the WWTP. ► For 13 of the API the sorption to sludge was stronger than 1.2 × 106 L kg−1 ► For 10 of the API the sorption to sludge was less than 100 L kg−1.