Determination of the solid–water distribution coefficient (Kd) for pharmaceuticals, estrogens and musk fragrances in digested sludge

This work determined the solid–water distribution coefficient (Kd) and the organic carbon normalized distribution coefficient (Koc) of several pharmaceuticals (carbamazepine, ibuprofen, naproxen, diclofenac, iopromide, sulfamethoxazole and roxithromycin), three estrogens (estrone, 17β-estradiol and 17α-ethinylestradiol) and two musk fragrances (HHCB and AHTN) in digested sludge. These sorption coefficients can be used to evaluate the fate of these substances during sludge treatment, thus avoiding the expensive and time-consuming analysis in the sludge phase. For determining the Kd and Koc values of the target compounds in digested sludge, their concentrations were measured in the aqueous and solid phase of the effluent of an anaerobic digestion pilot plant run at several operational conditions. The results obtained were compared with the values modelled by using simple Kow approaches. The resulting log Kd values ranged between 3.5 and 4.4 for the two musk fragrances (log Koc of 4.5–6.0), between 2.1 and 2.9 for estrogens (log Koc of 2.9–4.2) and between 0.8 and 1.9 for the remaining pharmaceuticals (log Koc of 1.8–3.5). These values are in the same range as those reported in the literature for primary and secondary sludge and no significant influence of the anaerobic digestion operational conditions was observed. For most compounds, the modelled Koc were close or within the lower range of the experimentally determined Koc. Major deviations of the modelled Koc values were found for iopromide, sulfamethoxazole and roxithromycin, which were 1–3 orders of magnitude lower than the measured values.