## 3 Results and Discussion
### PAH Concentration Detected in Darcill Sludge Landfill  
Figure 7 shows the concentrations of PAHs obtained from filtered, SPE-cleaned, microwaved or ultra-sonicated sludge samples at sampling points 7A and 14A of the Darcill sludge landfill used for sludge disposal by Darcill wastewater works. These two sampling points are the centre of the sludge landfill, which makes them likely to be more concentrated than the rest of the points. All the targeted PAHs were detected except for phenanthrene (Figure 7). Pyrene dominated with a total concentration of 34%, followed by fluoranthene and dibenz (ah) anthracene, both at 12%; their concentrations were all within the maximum allowable limits of 5.0 \(\times\) 10\({}^{4}\)\(\upmu\)g/kg. Since the sampling sites were also dominated by HMW-PAHs, similar pollution sources are expected as these two sampling sites are close to the New England dumpsite and Willowtown. The concentrations for microwave filtering and F + SPE cleaning ranged from 55.79 to 728.4 \(\upmu\)g/kg and 71.62 to 1656 \(\upmu\)g/kg, respectively, while for UE-filtered they ranged from 54.39 to 535.4 \(\upmu\)g/kg and UE F + SPE-cleaned 70.9 to 1443 \(\upmu\)g/kg. The SPE-cleaned samples in both sampling points gave higher concentrations compared to the filtered ones, with both extraction methods giving relatable concentrations. The high concentration levels of PAHs in the sludge landfill could be a result of the fact that Darcill is designed to biologically treat inorganic nutrients and trace metal to meet the discharge limits, and therefore whatever contaminant entered the treatment process, including PAHs, can still be detected after the treatment has taken place [35].  
Only a few studies have been carried out on PAHs in sediments, and even fewer in sludge matrices, especially in South Africa. The maximum concentration obtained from the sediment analysis of this study is higher (926 \(\upmu\)g/kg) than the concentrations obtained by [PERSON] et al. [7] at 42 \(\upmu\)g/kg, but lower than the ones obtained by [PERSON] et al. [36] at 69,070 \(\upmu\)g/kg in the same area of study (uMsunduzi river). However, pyrene was found at the highest average concentration in all three studies. The maximum concentration obtained in Kwa-Zulu Natal (69,070 \(\upmu\)g/kg) is higher than the ones obtained in other South African Provinces, such as Limpopo at 21,600 \(\upmu\)g/kg by [PERSON] et al. [37] and Eastern Cape at 22,310 \(\upmu\)g/kg by [PERSON] et al. [38]. The maximum concentration of PAHs observed in South African studies was higher than those obtained in other African countries, such as Nigeria by [PERSON] et al. at 6561 \(\upmu\)g/kg [39]. The maximum concentrations obtained in African countries were higher than those reported in overseas countries, such as Mexico by [PERSON] at 68 \(\upmu\)g/kg [40] or China by [PERSON] et al., at a maximum concentration of 5568 \(\upmu\)g/kg [41]. The PAHs obtained in the sludge analysis of this study showed lower concentrations than a study conducted in China (82,520 \(\upmu\)g/kg and 3264 \(\upmu\)g/kg) by [PERSON] et al. [42] and [PERSON] et al. [43], respectively, while in Italy, concentrations were found to be 2645 \(\upmu\)g/kg by [PERSON] et al. [44]. The high concentration of PAHs in South Africa and other parts of the world emphasizes the importance of monitoring the concentrations of PAHs in the environment.  
Figure 7: Concentrations of PAHs in Dravill sludge landfill.