## 3 Results and Discussion
### Pharmaceuticals Extracted from Sludge
Corresponding relative comparison between the methods for ciprofloxacin, citalopram, metoprolol and venlafaxine showed 5.1, 4.1, 1.5 and 1.2 times higher for the four compounds, respectively. In a previous investigation we showed that the matrix content of organic matter measured as total organic carbon content in sediments and sludge dictated drug sorption together with the presence of charged sites [PERSON] (2010). All of these top five compounds carry a positive charge at pH 7 (Table 2), and one of the explanations to these large amounts is probably the electrostatic interaction by the compounds positively charged groups and the negatively charged surfaces of the sludge matrix. Another part of the explanation is likely due to the existence of plural aromatic structures. Ketoconazole, which is by far the most abundant API found in the investigated sewage sludge samples contains three aromatic rings, citalopram, the second most abundant API contains two aromatic rings. Figure 4: Concentrations in \(\upmu\)g/kg of 23 APIs in lyophilized sewage sludge from Kristianstad STP determined using the _Espresso method_ (light blue) and the _PHWE method_ (dark blue). The APIs are listed in descending order of concentration (_PHWE method_) together with the charge and the number of aromatic ring structures of the compound in question. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c} \hline \hline
**Substance** & **pkA** & \begin{tabular}{c} **Change** \\ **(pH \(\%\))** \\ \end{tabular}  & \begin{tabular}{c} **Log D** \\ **(pH \(\%\))** \\ \end{tabular}  & \begin{tabular}{c} **log** \\ **(\(\%\))** \\ \end{tabular}  & \begin{tabular}{c} **Eyseco** \\ **(\(\%\))** \\ \end{tabular}  & \begin{tabular}{c} **PSD** \\ **(\(\%\))** \\ \end{tabular}  & \ \begin{tabular}{c} **Water** \\ **(\(\%\))** \\ \end{tabular}  &
\begin{tabular}{c} **Water** \\ **Label** \\ **Onlet** \\ **Onlet** \\ **Onlet** \\ **  
From Table 2 it can be seen that of the 23 compounds analysed, 20 showed a concentration in sludge exceeding 1 ug/kg sludge. These are all shown visually in descending order of concentration in Figure 4, and reveals that 18 of these compounds are all in favour of the _PHWE method_. Figure 4 also shows the clear pattern of positively charged molecules being at the highest concentrations range in the sludge as discussed above, followed by neutrals, and some additional positively and negatively charged compounds. The reason for finding some of the positively charged compounds on the far-right side could likely be attributed to two circumstances. The most obvious is that some of these compounds simply do not occur at high enough concentrations in the incoming water to reach high concentrations in the sludge despite a high degree of affinity to this negatively charged matrix. This is further discussed in the next section presenting APIs in the incoming wastewater. The other option is, as already touched upon, is that there are other chemical interactions at play. One of these is the aromatic ring structure. As mentioned, the two top compounds, ketoconazole and citalopram, have three and two aromatic rings. To reveal any possible relation to aromaticity, Figure 4 also presents the number of aromatic rings present on each of the 20 APIs. From this it becomes evident that those neutral compounds that reach fairly high concentrations in most cases have 2 aromatic rings, the one exception being paracetamol. Yet, finding paracetamol at such high concentrations in sludge might not come as too much of a surprise considering the large amounts of this compound being sold over the counter in Sweden, and being found in enormous concentrations in incoming water (see below). Additionally, on the very far right end there are 4 positively charged APIs. Three of these have no aromatic ring structure at all. In conclusion, there are strong indications that both the number of aromatic rings and the presence of a positive charge are important for the sorption processes of APIs to sewage sludge.